全文获取类型
| 收费全文 | 16685篇 |
| 免费 | 442篇 |
| 国内免费 | 19篇 |
专业分类
| 财政金融 | 2417篇 |
| 工业经济 | 1068篇 |
| 计划管理 | 2320篇 |
| 经济学 | 2959篇 |
| 综合类 | 308篇 |
| 运输经济 | 93篇 |
| 旅游经济 | 290篇 |
| 贸易经济 | 2551篇 |
| 农业经济 | 745篇 |
| 经济概况 | 1468篇 |
| 水利工程 | 2903篇 |
| 邮电经济 | 24篇 |
出版年
| 2021年 | 134篇 |
| 2020年 | 200篇 |
| 2019年 | 291篇 |
| 2018年 | 396篇 |
| 2017年 | 398篇 |
| 2016年 | 384篇 |
| 2015年 | 252篇 |
| 2014年 | 408篇 |
| 2013年 | 1447篇 |
| 2012年 | 536篇 |
| 2011年 | 547篇 |
| 2010年 | 451篇 |
| 2009年 | 483篇 |
| 2008年 | 567篇 |
| 2007年 | 595篇 |
| 2006年 | 501篇 |
| 2005年 | 475篇 |
| 2004年 | 434篇 |
| 2003年 | 339篇 |
| 2002年 | 311篇 |
| 2001年 | 301篇 |
| 2000年 | 297篇 |
| 1999年 | 268篇 |
| 1998年 | 288篇 |
| 1997年 | 288篇 |
| 1996年 | 291篇 |
| 1995年 | 269篇 |
| 1994年 | 251篇 |
| 1993年 | 282篇 |
| 1992年 | 274篇 |
| 1991年 | 254篇 |
| 1990年 | 238篇 |
| 1989年 | 212篇 |
| 1988年 | 178篇 |
| 1987年 | 204篇 |
| 1986年 | 198篇 |
| 1985年 | 289篇 |
| 1984年 | 302篇 |
| 1983年 | 297篇 |
| 1982年 | 260篇 |
| 1981年 | 278篇 |
| 1980年 | 245篇 |
| 1979年 | 255篇 |
| 1978年 | 196篇 |
| 1977年 | 190篇 |
| 1976年 | 172篇 |
| 1975年 | 133篇 |
| 1974年 | 130篇 |
| 1973年 | 119篇 |
| 1972年 | 92篇 |
排序方式： 共有10000条查询结果，搜索用时 15 毫秒
91.
Kuzmenko A. P. Saburov S. V. Korolenko L. A. Shutko V. P. 《Power Technology and Engineering (formerly Hydrotechnical Construction)》2021,55(4):487-493
Power Technology and Engineering - The results of processing annual data of the automated seismometric monitoring system (ASMS) of the Zeya HPP are presented. They are compared with the results of... 相似文献
92.
Method of calculating the technological parameters when designing hydraulic-fill dams of silty soils
E. L. Vvedenskii 《Power Technology and Engineering (formerly Hydrotechnical Construction)》1990,24(6):354-362
| 1. | Investigations showed that when constructing dams of fine-grained silty soils by hydraulic filling, it is expedient to use the technology of layerwise placement of soil with consolidation of each layer. |
| 2. | Dependences are given for calculating the thickness of the layers and period of consolidation of the soil on the basis of investigations of the dynamics of the hydrophysical properties of these soils in relation to technological factors. |
| 3. | Dependences are also proposed for predicting the density of the hydraulic-filled soil during construction, as well as the distribution of soil in the profile of the structure. |
| 4. | A method is proposed for calculating the technological parameters, in particular, the rate of construction of hydraulic-fill structures, calculating the size and number of the hydraulic-fill plots referred to one dredge, and prediction of the seepage discharge into the foundation of the dams during their hydraulic filling. |
| 5. | The proposed calculation methods make possible a more substantiated approach to the design of hydraulic-fill structures of fine-grained silty soils and technology of their construction. |
93.
L. A. Sirenko A. I. Denisova M. N. Pakhmova 《Power Technology and Engineering (formerly Hydrotechnical Construction)》1990,24(6):384-388
| 1. | The upper and lower pools of hydrostation reservoirs do not significantly differ with respect to the main water quality indices, number and biomass of algae, their qualitative composition, degree of viability of cells, and photosynthetic activity. |
| 2. | The noted variations and scatter of the indices are mainly a consequence of a certain heterogeneity of water masses in the surface and bottom horizons of reservoirs. The proportion of dead phytoplankton under the effect of operation of the units at hydrostations do not have a significant effect on its development, since restoration of the stock of phytoplankton occurs rather rapidly in the lower pool. |
94.
V. A. Ashikhmen V. G. Buchatskii N. V. Dmitriev L. I. Malyshev 《Power Technology and Engineering (formerly Hydrotechnical Construction)》1989,23(1):47-53
| 1. | The side curtains as necessary cutoff elements of the al-Qadisiyah hydro development were made in an optimal design variant, on time, and with a high quality. A considerable technical and economic effect was obtained by eliminating excessive volumes of works specified by the original design as a result of a combined analysis of the data of engineering surveys, investigations of experimental grouting works, and optimization of the grouting technology. |
| 2. | The index of unit cement absorption in the control holes used as the criterion of sufficiency of grouting on the side curtains should be used everywhere where the purpose of grouting works is to detect and eliminate large cavities and fissures. |
| 3. | Grouting works on elimination of karst cavities and large fissures, being in essence infill grouting, require the development of an industrial technology of the works with the use of considerable volumes of grouts (concretes) and use of a large number of machines and mechanisms (concrete plants, mixers, concrete pumps, etc.). |
95.
L. N. Rasskazov Kh. S. Sherimbetov 《Power Technology and Engineering (formerly Hydrotechnical Construction)》1989,23(5):262-268
| 1. | A study of the strength and deformation properties of asphaltic concrete is necessary for analyzing the stress-strain state of dams with asphaltic concrete diaphragms. The properties of asphaltic concrete substantially depend not only on composition but also on temperature. The results obtained make possible an evaluation of the main deformation and strength properties of asphaltic concrete, diaphragms, and facings of dams in relation to composition and temperature at early design stages. |
| 2. | To obtain generalized indices of properties in relation to composition and temperature of asphaltic concrete, all experiments were conducted on the basis of the mathematical theory of design of experiments. Each experiment had threefold replication. |
| 3. | The experiments showed that the angle of internal friction for 7% bitumen in excess of 100% of the mineral part is practically independent of temperature. The strength of the material increases due to cohesion, which with a drop of temperature from 200 to 10 increases about fivefold. |
| 4. | Investigation of the deformation properties of asphaltic concrete showed that the modulus of volume changeE 0 for=0.1 MPa varies by 4–7 times depending on the temperature. |
96.
M. A. Reznikov L. P. Kachalina 《Power Technology and Engineering (formerly Hydrotechnical Construction)》1988,22(8):476-480
| 1. | When ventilating complex underground hydraulic systems during their construction it is necessary to take into account the natural draft. |
| 2. | The method presented for calculating the natural draft pressure drop of single tunnels (formulas 1–6) reflects the specific characteristics of hydrotechnical construction in mountainous areas and for the first time takes into account the direction of movement of the ventilation flow. |
| 3. | For the particular conditions of constructing the Rogun hydrostation the values of the lapse rates were established, which can be used in calculations to take into account the natural draft when designing the ventilation of underground workings. |
| 4. | For calculating the natural draft pressure drop of a complex network of underground workings, an algorithm was developed which makes it possible to calculate by a standard program on a computer the air distribution in the underground complex being constructed in relation to a number of technological and natural factors. |
| 5. | On the basis of analyzing the results of different variants of the air distribution, the selection of the types and arrangement of the ejector fans (including in the future) was optimized, making it possible to increase the quality of ventilation and safety of underground operations, as well as to obtain a substantial technical-economic effect. |
97.
L. N. Shapiro V. A. Sharapov 《Power Technology and Engineering (formerly Hydrotechnical Construction)》1988,22(10):613-615
| 1. | During operation of large multipurpose reservoirs their unsatisfactory sanitary and engineering state, ineffective use of their water and biological resources, and unfavorable ecological conditions were revealed, which requires their immediate improvement. |
| 2. | There are real ways of improving these sanitary state and use of the water and biological resources of reservoirs, which were established when drawing up the schemes. |
| 3. | A thorough elaboration of ecological problems of the examined reservoirs aimed at an improvement of the ecological conditions on each reservoir and on the territories adjacent to them is required. |
| 4. | To solve the stated problem it is necessary to implement a number of coordinated measures. For this purpose, a scientifically founded approach based on a prediction of the results of their accomplishment is required. The interrelatedness and interdetermination of these measures with respect to increasing the effectiveness of using water, land, and biological resources should be based on scientific approaches of aquatorial regionalization and planning of reservoirs. Such an approach, unfortunately, is absent in many schemes. |
| 5. | The investments and expenditures being provided for the indicated purposes should be aimed at achieving priority goals on improving the sanitary state of reservoirs, water quality, and effective use of their resources. The investments provided for in the schemes should be based on real sources of financing and should be coordinated with the plan of the concerned organizations, which are the title holders of the objects planned for construction. |
98.
L. I. Dvorkin V. L. Shestakov V. G. Ganchikov V. N. Marchuk 《Power Technology and Engineering (formerly Hydrotechnical Construction)》1988,22(11):652-655
| 1. | For a porosity of about 5% the quality indices of APC are at the level of the requirements of the existing specifications P20-85:K F0.85,R 20>3 MPa,R 50>1.2 MPa,K th>2.5–3. |
| 2. | The experiments on the impermeability of APC showed that material with a porosity of 4–5% withstands a water pressure of 0.2–0.3 MPa without its infiltration through the specimens. |
| 3. | The results obtained give grounds to revise the traditional requirements imposed on the residual porosity — not more than 3% — of APC-base structural members. Compaction of asphaltic and asphaltic polymer-impregnated concrete mixes to a residual porosity of 4–5% will make it possible to reduce expenditures on compaction. In this case, variants of compacting mixes to various residual porosities are possible in combination with surface treatment of the material with sealing compositions (for example, with a bitumen-polymer binder) which must be substantiated by technical and economic calculations for the particular conditions of conducting works on constructing watertight facings of hydraulic structures. |
99.
A method capable of estimating the hydrograph from a prescribed storm for a practical mild slope upstream catchment is proposed. This method makes use of two new characteristic parameters, andS, in conjunction with the kinematic wave equation to compute lateral inflows of the main stream of the catchment. The depth profile of overland flow at any instant within the catchment and hydrograph at any location can be easily found. Lag times for individual lateral inflows are then considered and are linearly combined to obtain the hydrograph at the outlet of the catchment or depth profile of the main stream at any instant. The validity of the excess rainfall-surface runoff linear relationship in this study has also been verified with Tatsunokuchiyama catchment, and it shows good results for this computed runoff. 相似文献
100.
An aging population with nearly unlimited access to high-priced doctors and technology is pushing medical costs skyward. Managed care is the best way to bring them down. 相似文献