全文获取类型
收费全文 | 26991篇 |
免费 | 1682篇 |
国内免费 | 751篇 |
专业分类
财政金融 | 1584篇 |
工业经济 | 958篇 |
计划管理 | 3937篇 |
经济学 | 3371篇 |
综合类 | 2821篇 |
运输经济 | 266篇 |
旅游经济 | 214篇 |
贸易经济 | 2616篇 |
农业经济 | 1289篇 |
经济概况 | 2026篇 |
水利工程 | 10339篇 |
邮电经济 | 3篇 |
出版年
2023年 | 199篇 |
2022年 | 614篇 |
2021年 | 1030篇 |
2020年 | 596篇 |
2019年 | 462篇 |
2018年 | 553篇 |
2017年 | 749篇 |
2016年 | 610篇 |
2015年 | 999篇 |
2014年 | 1289篇 |
2013年 | 1905篇 |
2012年 | 1957篇 |
2011年 | 1951篇 |
2010年 | 1833篇 |
2009年 | 1813篇 |
2008年 | 1814篇 |
2007年 | 1772篇 |
2006年 | 1621篇 |
2005年 | 1361篇 |
2004年 | 725篇 |
2003年 | 459篇 |
2002年 | 428篇 |
2001年 | 440篇 |
2000年 | 380篇 |
1999年 | 165篇 |
1998年 | 149篇 |
1997年 | 125篇 |
1996年 | 119篇 |
1995年 | 135篇 |
1994年 | 95篇 |
1993年 | 123篇 |
1992年 | 126篇 |
1991年 | 123篇 |
1990年 | 112篇 |
1989年 | 145篇 |
1988年 | 116篇 |
1987年 | 119篇 |
1986年 | 113篇 |
1985年 | 108篇 |
1984年 | 122篇 |
1983年 | 106篇 |
1982年 | 100篇 |
1981年 | 111篇 |
1980年 | 118篇 |
1979年 | 109篇 |
1978年 | 98篇 |
1977年 | 89篇 |
1976年 | 95篇 |
1973年 | 82篇 |
1972年 | 88篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
102.
103.
水闸安全运行,会受到水工金属结构安全性状影响.京密引水渠安河泄洪闸已投入运行54年.为保障水闸运行安全,需对其金属结构进行全面的安全检测.文章采用多种检测手段对安河泄洪闸金属结构开展现场检测,对结构病害进行梳理,对金属结构的安全状态进行综合评价,为水闸安全运行提供技术支撑. 相似文献
104.
杨芙荣 《中国水能及电气化》2021,(9):52-57
为了解决传统软土地基变形沉降模拟分析方法存在的模拟误差大、应用效果不佳的问题,在水利施工环境下,利用有限元的概念实现软土地基变形沉降模拟分析方法的优化设计.分析软土地基变形沉降机理和受力情况,并根据分析结果,通过设置边界条件和材料参数,构建有限元分析模型.在该模型下确定软土地基变形沉降影响因素,从瞬时、固结和次固结三个方面,得出变形沉降的计算结果.最终通过确定影响因素和模型参数的具体取值,实现软土地基变形沉降的有限元模拟.通过与传统模拟分析方法的对比,发现设计分析方法得出的模拟结果误差降低了0.089mm,且将其应用到水利施工中能够有效地控制施工质量,在应用效果方面更加具有优势. 相似文献
105.
杨益英 《中国水能及电气化》2021,(10):14-20
在盾构机体积大、质量大、工期紧张及施工场地狭小的情况下,盾构机吊装作业过程中如何充分利用有限作业空间,在确保吊机安全性、稳定性的前提下,顺利完成吊装作业是施工的重难点.文章结合西安地铁八号线工程盾构机吊装实际,从编制安全合理的吊装方案及流程入手,通过理论计算验证汽车吊稳定性、吊耳承载力,对盾构机的吊装方案进行论证分析.实践证明,所选盾构机吊装方案安全性和可操作性强. 相似文献
106.
杨亮亮 《水资源开发与管理》2021,(3):6-13
为克服能量方程逐段试算方法在河道水面线计算上存在的不足与局限,本文以黄河干流白银市水川段为例,采用二维水动力数值计算模型,对4种洪水频率工况下黄河干流白银市段的水面线高程进行计算,并将二维数值计算结果与能量方程计算结果进行复核和评价。经计算可知两种计算方法在计算结果上存在偏差,能量方程在河道水面线计算上是一种近似成果,而二维数值计算能够更加真实反映河道的实际情况,因此在水面线计算时推荐二维数值计算方法。 相似文献
107.
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. |
108.
In search of the meaning of entrepreneurship 总被引:9,自引:0,他引:9
This paper is an attempt to build a bridge between the popular and the academic usage of the terms entrepreneur and entrepreneurship, and to identify the raw materials needed to construct an interpretive framework capable of illuminating the nature of entrepreneurship and its role in economic theory. We review briefly the contributions made to this topic by Cantillon, Schumpeter, Schultz and Kirzner. We advance a synthetic definition of the entrepreneur as someone who specializes in taking responsibility for and making judgemental decisions that affect the location, the form, and the use of goods, resources, or institutions. We then conclude with some observations on the basic choice confronting economics regarding the place of entrepreneurship in economic analysis. 相似文献
109.
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.). |
110.
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. |