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   408111篇
  免费   3058篇
  国内免费   954篇
化学   189749篇
晶体学   6450篇
力学   21391篇
综合类   7篇
数学   59855篇
物理学   134671篇
  2021年   3132篇
  2020年   3332篇
  2019年   3764篇
  2018年   11918篇
  2017年   12618篇
  2016年   10500篇
  2015年   4818篇
  2014年   7122篇
  2013年   16003篇
  2012年   15764篇
  2011年   24769篇
  2010年   16809篇
  2009年   16792篇
  2008年   21812篇
  2007年   24596篇
  2006年   12305篇
  2005年   15892篇
  2004年   12517篇
  2003年   11452篇
  2002年   9859篇
  2001年   10518篇
  2000年   7932篇
  1999年   5998篇
  1998年   5002篇
  1997年   4823篇
  1996年   4645篇
  1995年   3958篇
  1994年   3904篇
  1993年   3777篇
  1992年   4160篇
  1991年   4375篇
  1990年   4168篇
  1989年   4083篇
  1988年   3862篇
  1987年   3994篇
  1986年   3756篇
  1985年   4713篇
  1984年   4777篇
  1983年   3975篇
  1982年   4055篇
  1981年   3781篇
  1980年   3734篇
  1979年   4015篇
  1978年   4016篇
  1977年   3931篇
  1976年   3940篇
  1975年   3722篇
  1974年   3663篇
  1973年   3723篇
  1972年   2638篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
Nonperturbative nolocal structure of QCD vacuum is well described by instanton model. Specific helicity and flavor structure of zero modes of quarks, in instanton field allows simultaneously to explain some important features of low-and high-energy hadron phenomemology. The basic characteristics of hadron spectrum, partonic sum rules, heavyquark potential etc within the instanton liquid model are briefly discussed.  相似文献   
22.
23.
The simple relation between representations of the covering groups of SL2 and GL2 makes it possible to fuse and extend the recent metaplectic results of Shimura, Waldspurger, Flicker, and ourselves. By giving a new (purely local andL-function theoretic) treatment of the Waldspurger-Shintani correspondence, we also simplify some of Waldspurger’s original results.  相似文献   
24.
25.
26.
This paper presents an alternative to the beta continuous probability distribution for risk analysis. Particular attention has been given to two major applications of distributions, namely project management risk and critical path analysis (PERT). In conjunction with the beta, the triangular and normal distributions are frequently employed in order to give sufficient robustness to risk analysis. The beta distribution, as used in PERT, has a major theoretical implementation flaw. The new distribution was developed to give a possible alternative method of assessing risk. It is shown that the requirement to estimate the most pessimistic variate may be replaced by the probability to exceed the mode. Proposals for other simplifications in risk analysis are discussed. Practical means to validate the most appropriate distributions for risk analysis are outlined, and a cost-data case study is included.  相似文献   
27.
We consider the growth of a spherical crystal in a supersaturatedsolution. In the first part, existence and uniqueness resultsfor radially symmetric growth are obtained, provided that thesupersaturation is not too large; conversely, when the far-fieldsupersaturation exceeds a critical value, it is shown that theradially symmetric solution ceases to exist in finite time.In the second part, we examine the linear stability of a radiallysymmetric similarity solution (in which the radius grows ast?) to shape perturbations. The results are compared with previousquasi-static analyses, and, in particular, the critical radiusat which the crystal becomes unstable is found to be largerfor small supersaturations, but smaller for large supersaturations,than those predicted by the quasi-static analysis  相似文献   
28.
29.
A convenient method is proposed for the synthesis of all the individual methyl ethers of methyl 2-acetamido-2-deoxy-α-D-glucopyranoside based on the partial methylation of 2-acetamido-2-deoxy-α-D-glucopyranoside with dimethyl sulfate in an alkaline medium followed by preparative liquid column chromatography on silica gel of the resulting mixture of methyl ethers.  相似文献   
30.
A masked lithium homoenolate, generated by tellurium/lithium exchange, was reacted with epoxides. The lithium compound was also converted into other organometallics such as Grignard, and cuprates and the reactivity of those organometallics with epoxides was evaluated. The same building block was employed in the synthesis of (+/−)-frontalin.  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