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   433536篇
  免费   2201篇
  国内免费   847篇
化学   180065篇
晶体学   5843篇
力学   27674篇
综合类   4篇
数学   90076篇
物理学   132922篇
  2021年   3351篇
  2020年   3735篇
  2019年   4555篇
  2018年   19974篇
  2017年   20110篇
  2016年   15681篇
  2015年   5068篇
  2014年   7657篇
  2013年   13191篇
  2012年   16593篇
  2011年   28757篇
  2010年   19281篇
  2009年   19871篇
  2008年   24082篇
  2007年   27842篇
  2006年   10970篇
  2005年   13926篇
  2004年   11914篇
  2003年   12074篇
  2002年   10329篇
  2001年   8180篇
  2000年   6743篇
  1999年   4823篇
  1998年   4587篇
  1997年   4415篇
  1996年   4180篇
  1995年   3630篇
  1994年   3615篇
  1993年   3625篇
  1992年   3569篇
  1991年   3990篇
  1990年   3966篇
  1989年   3969篇
  1988年   3735篇
  1987年   3814篇
  1986年   3497篇
  1985年   4050篇
  1984年   4288篇
  1983年   3663篇
  1982年   3874篇
  1981年   3540篇
  1980年   3303篇
  1979年   3800篇
  1978年   3879篇
  1977年   3949篇
  1976年   4059篇
  1975年   3768篇
  1974年   3620篇
  1973年   3826篇
  1972年   3243篇
排序方式: 共有10000条查询结果,搜索用时 10 毫秒
1.

The problem of the minimax testing of the Poisson process intensity \({\mathbf{s}}\) is considered. For a given intensity \({\mathbf{p}}\) and a set \(\mathcal{Q}\), the minimax testing of the simple hypothesis \(H_{0}: {\mathbf{s}} = {\mathbf{p}}\) against the composite alternative \(H_{1}: {\mathbf{s}} = {\mathbf{q}},\,{\mathbf{q}} \in \mathcal{Q}\) is investigated. The case, when the 1-st kind error probability \(\alpha \) is fixed and we are interested in the minimal possible 2-nd kind error probability \(\beta ({\mathbf{p}},\mathcal{Q})\), is considered. What is the maximal set \(\mathcal{Q}\), which can be replaced by an intensity \({\mathbf{q}} \in \mathcal{Q}\) without any loss of testing performance? In the asymptotic case (\(T\rightarrow \infty \)) that maximal set \(\mathcal{Q}\) is described.

  相似文献   
2.
3.
4.
5.
6.
7.
The structure, chemical composition, and magnetic properties of electrochemically deposited nanocrystalline Co-Ni-Fe films were investigated using a number of techniques. A high saturation magnetic induction up to B s = 21 kG was attained. An enhancement of the saturation magnetization compared to the ideal anticipated one was revealed, which correlated with the nonlinear behavior of the structural phase composition and lattice parameters with the change of the composition. The text was submitted by the authors in English.  相似文献   
8.
Methods for phase stabilization of ammonium nitrate were sought for in order to considerably expand the application area of this oxidizing agent in various-purpose self-combustible formulations, including that in a new generation of gas-generating formulations for automobile air bags. New methods for stabilization of ammonium nitrate were studied and, in particular, a search was made for organic compounds that can stabilize ammonium nitrate even at their low content. The mechanism of phase state stabilization of ammonium nitrate by compounds of this kind was examined.  相似文献   
9.
Kinetic, sorption and selectivity properties of commercial adsorbents are improved by adding petroleum residues (tar asphaltene concentrates) 13% of whole mass. Obtained adsorbents can be used for selective extraction of nobel metals from multicomponent polymetallic solutions of heavy metals and fro sewages purification for removing arsenic.  相似文献   
10.
The ethylene polymerization reaction of a neutral nickel catalyst was studied by DFT calculations at the Becke3LYP/6-31G(d) level of theory. As in related cases a β-agostic bond stabilizes the nickel alkyl ground states. Transition states for the insertion of the olefin show a distinct α-agostic interaction, which has not been observed for late metal polymerization catalysts before. An ethylene-alkyl complex was identified as the resting state of the reaction. The overall barrier height of the reaction amounts to 17.54 kcal/mol, which slightly increases to 17.60 kcal/mol for the polymerization of deuterated ethylene. Therefore, a small positive kinetic isotope effect (kH/kD = 1.09) can be calculated, which is caused by the α-agostic interaction in the transition state. A comparison to other late metal based polymerization systems reveals that the ethylene coordination step of highly active catalysts is significantly lower in energy compared to catalysts which are only moderately active.  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