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   326622篇
  免费   2021篇
  国内免费   826篇
化学   148181篇
晶体学   5304篇
力学   17325篇
综合类   1篇
数学   49274篇
物理学   109384篇
  2020年   1809篇
  2019年   2054篇
  2018年   10976篇
  2017年   11724篇
  2016年   7720篇
  2015年   3215篇
  2014年   4100篇
  2013年   10258篇
  2012年   11692篇
  2011年   21256篇
  2010年   13498篇
  2009年   13506篇
  2008年   18715篇
  2007年   22081篇
  2006年   8501篇
  2005年   13871篇
  2004年   10119篇
  2003年   9394篇
  2002年   7450篇
  2001年   7269篇
  2000年   5684篇
  1999年   4295篇
  1998年   3623篇
  1997年   3514篇
  1996年   3481篇
  1995年   3130篇
  1994年   3066篇
  1993年   3142篇
  1992年   3245篇
  1991年   3421篇
  1990年   3164篇
  1989年   3108篇
  1988年   3166篇
  1987年   3050篇
  1986年   2883篇
  1985年   3916篇
  1984年   4123篇
  1983年   3301篇
  1982年   3508篇
  1981年   3440篇
  1980年   3325篇
  1979年   3451篇
  1978年   3540篇
  1977年   3391篇
  1976年   3517篇
  1975年   3199篇
  1974年   3205篇
  1973年   3286篇
  1972年   2277篇
  1971年   1871篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 55, No. 3, pp. 478–484, September, 1991.  相似文献   
72.
A fast-frequency modulated (FM) diode laser has been optically narrowed using the technique of resonant optical feedback, to provide linewidths in each FM mode of ≈ 200 kHz peak-to-peak. With a drive frequency of 50 MHz and modulation index of 0.2, the FM laser has been used for the first time to obtain Doppler-free FM spectra of the Rb D1 line at 795 nm. The potential use of this system for laser frequency stabilisation is discussed.  相似文献   
73.
Translated from Itogi Nauki i Tekhniki, Seriya Matematicheskii Analiz, Vol. 27, pp. 3–146, 1989.  相似文献   
74.
Summary Considered here are model equations for weakly nonlinear and dispersive long waves, which feature general forms of dispersion and pure power nonlinearity. Two variants of such equations are introduced, one of Korteweg-de Vries type and one of regularized long-wave type. It is proven that solutions of the pure initial-value problem for these two types of model equations are the same, to within the order of accuracy attributable to either, on the long time scale during which nonlinear and dispersive effects may accumulate to make an order-one relative difference to the wave profiles.This research was supported in part by the National Science Foundation. A considerable portion of the project was completed while the first author was resident at the Institute for Mathematics and Its Applications, University of Minnesota.  相似文献   
75.
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   
76.
77.
78.
Some well-known theorems on typical properties of real-valued continuous functions defined on [0, 1] are improved using the notion of porosity.  相似文献   
79.
80.
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   
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