全文获取类型
收费全文 | 8479篇 |
免费 | 241篇 |
专业分类
财政金融 | 1327篇 |
工业经济 | 612篇 |
计划管理 | 1156篇 |
经济学 | 1451篇 |
综合类 | 72篇 |
运输经济 | 37篇 |
旅游经济 | 103篇 |
贸易经济 | 1138篇 |
农业经济 | 357篇 |
经济概况 | 768篇 |
水利工程 | 1695篇 |
信息产业经济 | 1篇 |
邮电经济 | 3篇 |
出版年
2021年 | 66篇 |
2020年 | 105篇 |
2019年 | 144篇 |
2018年 | 206篇 |
2017年 | 185篇 |
2016年 | 215篇 |
2015年 | 113篇 |
2014年 | 198篇 |
2013年 | 762篇 |
2012年 | 316篇 |
2011年 | 334篇 |
2010年 | 224篇 |
2009年 | 250篇 |
2008年 | 273篇 |
2007年 | 292篇 |
2006年 | 326篇 |
2005年 | 285篇 |
2004年 | 292篇 |
2003年 | 171篇 |
2002年 | 146篇 |
2001年 | 176篇 |
2000年 | 166篇 |
1999年 | 152篇 |
1998年 | 135篇 |
1997年 | 133篇 |
1996年 | 132篇 |
1995年 | 135篇 |
1994年 | 111篇 |
1993年 | 123篇 |
1992年 | 136篇 |
1991年 | 120篇 |
1990年 | 116篇 |
1989年 | 113篇 |
1988年 | 119篇 |
1987年 | 99篇 |
1986年 | 114篇 |
1985年 | 123篇 |
1984年 | 121篇 |
1983年 | 108篇 |
1982年 | 123篇 |
1981年 | 109篇 |
1980年 | 122篇 |
1979年 | 92篇 |
1978年 | 116篇 |
1977年 | 84篇 |
1976年 | 86篇 |
1975年 | 69篇 |
1974年 | 60篇 |
1973年 | 55篇 |
1972年 | 53篇 |
排序方式: 共有8720条查询结果,搜索用时 15 毫秒
51.
NOMENCLATUREc radialclearanceh filmthickness h dimensionlessfilmthickness (h/c)L/D ratiooflengthtodiameterp film pressuree eccentri 相似文献
52.
The Dynamics of Alliance Conditions in the Alliance Development Process 总被引:10,自引:0,他引:10
One of the key issues in understanding the developmental processes of strategic alliances is how the alliance conditions change over the different stages of alliance development. A related question concerns the nature of the co-evolutionary dynamics of alliances in terms of their constituent partner firms. In this article we propose an integrated process model of alliances that is based on alliance conditions, allianc developmental stages, and an alliance system comprising co-evolutionary elements. We suggest that alliance conditions, or the key characteristics of an alliance at any given moment, link the alliance environment (firm characteristics) and the alliance development process. We also explore how specific patterns of alliance conditions have differential impacts on the interactive elements of the alliance co-evolutionary system. 相似文献
53.
54.
The use of transferable discharge permits as a water pollution control policy is rapidly increasing in the United States. Drawing on evidence from existing water quality trading programs, this paper provides a taxonomy of the forms that such markets take. Four main structures are identified: exchanges, bilateral negotiations, clearinghouses, and sole-source offsets. Each of these structures has its own strengths and weaknesses; none is optimal for all scenarios. Since market structure is largely determined by a program's rules, policy makers should be aware of the differences between these structures and the conditions under which each comes to be. 相似文献
55.
The major steps of sewerage rehabilitation include inspection of sewerage, assessment of structural conditions, computation of structural condition grades, and determination of rehabilitation methods and materials. Conventionally, sewerage rehabilitation planning relies on experts with professional background that is tedious and time-consuming. This paper proposes an automation model of planning optimal sewerage rehabilitation strategies for the sewer system by integrating image process, clustering technology, optimization, and visualization display. Firstly, image processing techniques, such as wavelet transformation and co-occurrence features extraction, were employed to extract various characteristics of structural failures from CCTV inspection images. Secondly, a classification neural network was established to automatically interpret the structural conditions by comparing the extracted features with the typical failures in a databank. Then, to achieve optimal rehabilitation efficiency, a genetic algorithm was used to determine appropriate rehabilitation methods and substitution materials for the pipe sections with a risk of mal-function and even collapse. Finally, the result from the automation model can be visualized in a geographic information system in which essential information of the sewer system and sewerage rehabilitation plans are graphically displayed. For demonstration, the automation model of optimal sewerage rehabilitation planning was applied to a sewer system in east Taichung, Chinese Taiwan. 相似文献
56.
E. V. Chernyshev E. N. Veprov V. A. Petrov S. L. Bogdanov T. Yu. Levina T. I. Petrova V. I. Kashinskii A. A. Zonov A. E. Verkhovskii 《Power Technology and Engineering (formerly Hydrotechnical Construction)》2006,40(1):34-37
Results of a study of tube specimens cut from hot-water boilers show that film-forming octadecyl amine (ODA) used in the process
of preservation removes deposition from the surface of the metal. An ODA film is preserved on the surface after repeated washing
of the latter with hot water. The concentration of chlorides at the surface of the metal after treatment with ODA is lower
than before the treatment.
__________
Translated from élektricheskie Stantsii, No. 11, November 2005, pp. 15–18. 相似文献
57.
Since the natural estrogens 17 beta-estradiol (E2) and estron (E1), and the synthetic estrogen 17 alpha-ethynyl estradiol (EE2) have strong endocrine disrupting effects and the tendency to persist in effluent from wastewater treatment plants, effective measures are needed to remove them from wastewater. In this research, to gain an understanding of the characteristics of estrogen decomposition by ozonation, experiments were conducted using effluent from an actual wastewater treatment plant. In this experiment, estrogen was added to effluent at a concentration of 200 ng/l and 20 ng/l before the ozonation experiments. The results showed 90% or more of estrogen concentration and estrogenic activity of E2, El and EE2 to be removed at an ozone dose of 1 mg/l. At an ozone dose of 3 mg/l, the estrogen concentration and estrogenic activity of E2, El and EE2 in the treated water fell below the detection limit. The removal rate was not influenced by the kind of estrogen. No generation of byproducts with estrogenic activity was observed. The authors conclude that estrogen in secondary treated wastewater can be almost entirely removed at the practical ozone dose rate applied for the purpose of disinfection, which is up to about 5 mg/l. 相似文献
58.
A common approach to the evaluation of the standard of living is based on a function of real income. In the United States this often takes the form of CPI-deflated mean household income. Material well-being is more appropriately evaluated using a consumption-based index. Using data from the Consumer Expenditure Surveys we find that real mean income provides an inaccurate representation of the level and trend of the standard of living relative to real per equivalent total expenditure in the postwar United States. The differences between real income and real total expenditure per household equivalent member are found at all levels of aggregation. 相似文献
59.
Chief Executives from New Zealand's largest companies were surveyed to distinguish divesting and nondivesting companies, and to identify the relative importance of the factors and motives which led to the divestment of 208 business units in the period 1985 through 1990. The divesting companies were considerably larger and faster growing than nondivestors. The typical divestment was motivated by the need to convert unattractive assets into liquid form which could then be held to strengthen the balance sheet, or reinvested in either the core business or new areas. 相似文献
60.
The underidentification of linear models with measurement error does not necessarily extend to panel data models, as has been shown by GAiliches and Hausman (1986). We discuss and extend some of their results for a simple case and address particular issues concerning identification and asymptotic variances. 相似文献