首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   548251篇
  免费   4635篇
  国内免费   1362篇
化学   269722篇
晶体学   8765篇
力学   26943篇
综合类   16篇
数学   74582篇
物理学   174220篇
  2021年   4116篇
  2020年   4537篇
  2019年   5099篇
  2018年   12689篇
  2017年   13326篇
  2016年   12604篇
  2015年   6320篇
  2014年   9533篇
  2013年   22541篇
  2012年   20037篇
  2011年   29362篇
  2010年   20077篇
  2009年   20087篇
  2008年   25890篇
  2007年   28304篇
  2006年   17020篇
  2005年   19649篇
  2004年   16152篇
  2003年   14769篇
  2002年   13189篇
  2001年   14545篇
  2000年   11108篇
  1999年   8426篇
  1998年   6969篇
  1997年   6783篇
  1996年   6538篇
  1995年   5797篇
  1994年   5635篇
  1993年   5353篇
  1992年   6255篇
  1991年   6370篇
  1990年   6119篇
  1989年   6112篇
  1988年   5874篇
  1987年   5985篇
  1986年   5637篇
  1985年   7203篇
  1984年   7274篇
  1983年   5939篇
  1982年   6125篇
  1981年   5941篇
  1980年   5654篇
  1979年   6205篇
  1978年   6259篇
  1977年   6271篇
  1976年   6144篇
  1975年   5708篇
  1974年   5585篇
  1973年   5648篇
  1972年   3965篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
141.
Cognitive style refers to differences that can be perceived in individuals due to differing cognitive structures. There has been a large amount of research on how cognitive style affects managerial decision-making, particularly in the context of management information systems, but little or no attempt to relate these findings to operational research. This paper reviews the findings of cognitive-style research from the perspective of operational research, and draws a number of useful inferences concerning the matching of OR aids to managers, the presentation of information and recommendations, the use and acceptance of OR, and the structure of OR groups. Further, it is argued that cognitive-style findings help to give a justification to the move towards ‘soft’ approaches to analysis.  相似文献   
142.
143.
Partially supported by the general research fund at the University of Kansas  相似文献   
144.
Selected experiences in the control of contamination and the threat it poses to the quality of analytical date are discussed in the context of the whole analytical process from collection of marine environmental samples, through handling and radiochemical separation, to the final interpretation of results. Examples include a demonstration of the contamination introduced during sediment core sectioning, contamination of sea water by a ship's pumping system, and the effect of filtration on the apparent partitioning of radionuclides between solid and liquid phases of sea water.  相似文献   
145.
146.
The objective of this research is to evaluate a new methodology, data envelopment analysis (DEA), as a tool for measuring and evaluating the operational efficiency of US Air Force organizations. This study involves the application of DEA to locate possible inefficiencies in the performance of US Air Force real-property maintenance activities. Dynamic behaviour, as exhibited via window analyses, is reviewed along with static counterparts. The testing was done in close coordination with Air Force officials, who reviewed the results for accuracy, validity and relevance. We conclude that this type of efficiency analysis does have value for the Air Force, where it can serve as a guide to auditors, budget programmers, managers and others in measuring, evaluating and enhancing operational efficiency.  相似文献   
147.
148.
149.
150.
Various methods for describing the distribution of water in the H2O-tributyl phosphate (TBP) system were considered. An equation for describing the deviations from the Henry law was proposed. A three-parameter equation for calculating the distribution of water in H2O-TBP-solvent systems was derived. It is based on the additive solubility model and allows for the dependence of the activity coefficients on the TBP concentration. Based on the published data, the parameters of the equation for a number of systems were calculated.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号