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   29417篇
  免费   2798篇
  国内免费   2447篇
化学   5670篇
晶体学   68篇
力学   2358篇
综合类   555篇
数学   17913篇
物理学   8098篇
  2024年   46篇
  2023年   339篇
  2022年   618篇
  2021年   688篇
  2020年   797篇
  2019年   750篇
  2018年   778篇
  2017年   939篇
  2016年   973篇
  2015年   797篇
  2014年   1516篇
  2013年   2431篇
  2012年   1583篇
  2011年   1757篇
  2010年   1528篇
  2009年   1998篇
  2008年   2001篇
  2007年   1930篇
  2006年   1676篇
  2005年   1609篇
  2004年   1304篇
  2003年   1115篇
  2002年   942篇
  2001年   822篇
  2000年   789篇
  1999年   701篇
  1998年   627篇
  1997年   597篇
  1996年   462篇
  1995年   358篇
  1994年   298篇
  1993年   232篇
  1992年   197篇
  1991年   149篇
  1990年   153篇
  1989年   113篇
  1988年   103篇
  1987年   94篇
  1986年   81篇
  1985年   119篇
  1984年   112篇
  1983年   65篇
  1982年   86篇
  1981年   80篇
  1980年   55篇
  1979年   48篇
  1978年   41篇
  1977年   34篇
  1976年   36篇
  1973年   26篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
A finite support product of ω1 clones of Jensen's minimal Π21 singleton forcing is used to define a model in which any non-empty analytically definable set of reals contains an analytically definable real (the full basis theorem), but there is no analytically definable wellordering of the reals.  相似文献   
2.
3.
The development of synthetic routes which lead to five new diisocyanide monomers with one or two phenolic groups is described. Their polymerization behavior is studied with Pd‐ and Ni‐based initiators, as well as under microwave irradiation. The polymerizability is mainly dominated by steric effects as is concluded from experiments using different protecting groups. Chiroptical properties of these new polymers are studied by CD‐spectroscopy. After deprotection, helically chiral poly(quinoxalin‐2,3‐diyl)s are obtained which display a Brønsted function attached to a stereolabile biaryl axis whose configuration should be influenced by the chiral polymer backbone. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1320–1329  相似文献   
4.
The mechanism of lithium insertion that occurs in an iron oxyfluoride sample with a hexagonal–tungsten–bronze (HTB)-type structure was investigated by the pair distribution function. This study reveals that upon lithiation, the HTB framework collapses to yield disordered rutile and rock salt phases followed by a conversion reaction of the fluoride phase toward lithium fluoride and nanometer-sized metallic iron. The occurrence of anionic vacancies in the pristine framework was shown to strongly impact the electrochemical activity, that is, the reversible capacity scales with the content of anionic vacancies. Similar to FeOF-type electrodes, upon de-lithiation, a disordered rutile phase forms, showing that the anionic chemistry dictates the atomic arrangement of the re-oxidized phase. Finally, it was shown that the nanoscaling and structural rearrangement induced by the conversion reaction allow the in situ formation of new electrode materials with enhanced electrochemical properties.  相似文献   
5.
In this paper, the deformation of the Heisenberg algebra, consistent with both the generalized uncertainty principle and doubly special relativity, has been analyzed. It has been observed that, though this algebra can give rise to fractional derivative terms in the corresponding quantum mechanical Hamiltonian, a formal meaning can be given to them by using the theory of harmonic extensions of function. Depending on this argument, the expression of the propagator of the path integral corresponding to the deformed Heisenberg algebra, has been obtained. In particular, the consistent expression of the one dimensional free particle propagator has been evaluated explicitly. With this propagator in hand, it has been shown that, even in free particle case, normal generalized uncertainty principle and doubly special relativity show very much different result.  相似文献   
6.
本文利用统计计量学方法对山西省农民家庭消费水平和消费结构的变化及原因进行了实证分析。建立了山西省农民人均消费的消费函数和山西省农民总消费支出与食品、衣着、住房、日用品、燃料及文化生活服务支出的关系模型,并通过模型分析解释了农民的消费结构,也为决策者提供一些有效的参考资料。  相似文献   
7.
In this paper a new state called odd-excited binomial state (OEBS) is introduced. It interpolates between the odd number state and the odd-excited coherent state. We discuss some statistical properties, such as the Glauber second-order correlation function and squeezing phenomenon (normal and amplitude-squared squeezing) for this state. The quasiprobability distribution functions (Husimi Q-function and Wigner W-function) are also examined.  相似文献   
8.
Balaganskii  V. S. 《Mathematical Notes》2002,72(5-6):752-756
Necessary conditions for the Gâteaux differentiability of the distance function to a set are considered. A series of characterizing results is obtained.  相似文献   
9.
The problem is to determine nonsensitiveness regions for threshold ellipsoids within a regular mixed linear model.  相似文献   
10.
The non-proteinogenic amino acid 3-hydroxy-4-methylproline (HMP) is an active constituent of some potent antimicrobials including echinocandins, nostopeptins, pneumocandins, sporiofungin and mulundocandins. A synthesis has been achieved in 10 steps with 29% overall yield; the Evans’ aldol reaction using Crimmins’ modified method was pivotal to the success of the strategy.  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