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   18499篇
  免费   682篇
  国内免费   338篇
化学   12374篇
晶体学   117篇
力学   466篇
综合类   30篇
数学   2306篇
物理学   4226篇
  2022年   212篇
  2021年   348篇
  2020年   310篇
  2019年   293篇
  2018年   228篇
  2017年   193篇
  2016年   498篇
  2015年   469篇
  2014年   519篇
  2013年   1005篇
  2012年   949篇
  2011年   1079篇
  2010年   719篇
  2009年   661篇
  2008年   944篇
  2007年   952篇
  2006年   812篇
  2005年   756篇
  2004年   759篇
  2003年   716篇
  2002年   733篇
  2001年   467篇
  2000年   426篇
  1999年   333篇
  1998年   241篇
  1997年   224篇
  1996年   245篇
  1995年   256篇
  1994年   244篇
  1993年   181篇
  1992年   170篇
  1991年   181篇
  1990年   197篇
  1989年   163篇
  1988年   142篇
  1987年   144篇
  1986年   134篇
  1985年   235篇
  1984年   249篇
  1983年   174篇
  1982年   195篇
  1981年   164篇
  1980年   161篇
  1979年   146篇
  1978年   122篇
  1977年   175篇
  1976年   149篇
  1975年   124篇
  1974年   117篇
  1973年   118篇
排序方式: 共有10000条查询结果,搜索用时 296 毫秒
51.
Summary We study the integration theory for general integral metrics when restricted to upper integrals q, finding improvements in the relation between the classes of the q-integrable and the ql-integrable functions. We give new results and notions which lead to the desirable characterizations of q-integrable functions as ql-integrable f with q(|f|) < ∞, and of ql-integrable functions via the integrability of their upper truncations, under natural conditions which are fulfilled in most finitely additive integration theories.  相似文献   
52.
53.
Modulated DSC for gas hydrates analysis   总被引:1,自引:0,他引:1  
Modulated DSC has been applied to the study of methane, ethane and propane hydrates at different hydrate and ice concentrations. The reversing component of the TMDSC curves, makes it possible to characterize such hydrates. Methane and ethane hydrates show the melting-decomposition peak at a temperatures higher than the ice contained in the sample, while propane hydrate melts and decomposes at lower temperature than the ice present in the sample. The hydrate peaks tend to disappear if the hydrate is stored at atmospheric pressure. Guest size and cavity occupation fix the heat of dissociation and stability of the hydrates, as confirmed by parallel tests on tetrahydrofurane hydrates.  相似文献   
54.
In [3] it was shown that a (real) signed measure on a cyclic coarse-grained quantum logic can be extended, as a signed measure, over the entire power algebra. Later ([9]) this result was re-proved (and further improved on) and, moreover, the non-negative measures were shown to allow for extensions as non-negative measures. In both cases the proof technique used was the technique of linear algebra. In this paper we further generalize the results cited by extending group-valued measures on cyclic coarse-grained quantum logics (or non-negative group-valued measures for lattice-ordered groups). Obviously, the proof technique is entirely different from that of the preceding papers. In addition, we provide a new combinatorial argument for describing all atoms of cyclic coarse-grained quantum logics.  相似文献   
55.
激光准直仪的设计性物理实验   总被引:2,自引:1,他引:1  
黄水平  胡德敬 《物理实验》2004,24(5):31-33,36
介绍了激光准直仪的结构、工作原理及其在设计性物理实验中的应用  相似文献   
56.
A subgroupH of a groupG is said to bepermutable ifHX=XH for every subgroupX ofG. In this paper the structure of groups in which every subgroup either is abelian or permutable is investigated. This work was done while the last author was visiting the University of Napoli Federico II. He thanks the “Dipartimento di Matematica e Applicazioni” for its financial support.  相似文献   
57.
The review outlines the various different azaheterocycles available from 5-spirocyclopropane isoxazolidines. These compounds can be regarded as versatile direct precursors of tetrahydro-, dihydropyridone and azetidinone derivatives. The current scope and limitations, and the selectivity aspects of the different processes are discussed therein.  相似文献   
58.
Initial concentration of enantioenriched or enantiopure catalysts proved to be an important factor for the achievement of a more pronounced amplification of ee's in the Ti(IV)/BINOL-catalyzed aldol reaction of an O-silyldienolate.  相似文献   
59.
60.
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