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   24316篇
  免费   3762篇
  国内免费   2629篇
化学   16932篇
晶体学   296篇
力学   1439篇
综合类   239篇
数学   2659篇
物理学   9142篇
  2024年   78篇
  2023年   504篇
  2022年   818篇
  2021年   877篇
  2020年   984篇
  2019年   904篇
  2018年   752篇
  2017年   726篇
  2016年   1100篇
  2015年   1036篇
  2014年   1292篇
  2013年   1672篇
  2012年   2074篇
  2011年   2077篇
  2010年   1424篇
  2009年   1366篇
  2008年   1529篇
  2007年   1403篇
  2006年   1342篇
  2005年   1085篇
  2004年   869篇
  2003年   720篇
  2002年   623篇
  2001年   519篇
  2000年   513篇
  1999年   590篇
  1998年   487篇
  1997年   428篇
  1996年   436篇
  1995年   387篇
  1994年   357篇
  1993年   325篇
  1992年   269篇
  1991年   229篇
  1990年   235篇
  1989年   159篇
  1988年   119篇
  1987年   84篇
  1986年   97篇
  1985年   65篇
  1984年   37篇
  1983年   39篇
  1982年   37篇
  1981年   21篇
  1980年   8篇
  1979年   6篇
  1976年   1篇
  1957年   4篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Annals of the Institute of Statistical Mathematics - The research is about a systematic investigation on the following issues. First, we construct different outcome regression-based estimators for...  相似文献   
92.
93.
94.
95.
96.
The anharmonic potential felt by a single-species ions confined in a rf quadrupole trap which results from a non-ideal trap configuration and the charge distribution of the ion cloud is studied. The rf resonance-absorption spectra are explained by a Duffing oscillator and a representation of the line-shape parameter is derived. For > 0.77, the electric signals will exhibit hysteresis. The relation with the anharmonic potential is discussed.  相似文献   
97.
98.
99.
Summary In this paper it is proved that, for any positive integern 2, 3 (mod 4),n 7, there exists an incomplete idempotent Schröder quasigroup with one hole of size two IISQ(n, 2) except forn = 10. It is also proved that for any positive integern 0, 1 (mod 4), there exists an idempotent Schröder quasigroup ISQ(n) except forn = 5 and 9. These results completely determine the spectrum of ISQ(n) and provide an application to the packing of a class of edge-coloured block designs.Research supported by NSERC grant A-5320.Research supported by NSFC grant 19231060-2.  相似文献   
100.
This article employs new data envelopment analysis/assurance region (DEA/AR) methods to evaluate the efficiency of the 35 textile factories of the Nanjing Textiles Corporation (NTC), Nanjing, China. The returns to scale (RTS) of these factories were studied without assuming that the optimal DEA solutions were unique. All DMUs are identified with pointsE (Extreme Efficient),E (Efficient but not an extreme point) andF (Frontier but not efficient). We then further identify the nonfrontier DMUs with pointsNE, NE andNF according to whether they are projected onto a point inE, E, orF en route to evaluating their performances. All of the inefficient factories were in classNF and had unique optimal primal-dual solution pairs. Consequently, the solution pairs satisfy the strong complementary slackness condition (SCSC). Application of cone-ratio (CR) ARs reduced significantly the number of factories in classE, and showed that some AR-efficient factories were more flexible in adopting the mixture of central planning and market economies that China currently is trying to use. Also, linked-cone (LC) ARs were applied to measure maximum and minimum profit ratios. The SCSC multiplier space approach was utilized to analyze the sensitivity of the efficiency results to potential errors in the data with and without ARs. The results in this article suggest that collective units had a better performance than state-owned units in the two consecutive years analyzed.This paper was written while the author was at the School of Economics and Management, Southeast University, Nanjing 210018, P.R. China.  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