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   260206篇
  免费   19419篇
  国内免费   755篇
化学   165416篇
晶体学   3095篇
力学   11488篇
综合类   6篇
数学   27912篇
物理学   72463篇
  2023年   4296篇
  2021年   4158篇
  2020年   6369篇
  2019年   4392篇
  2018年   5010篇
  2017年   3320篇
  2016年   9320篇
  2015年   7772篇
  2014年   8610篇
  2013年   14742篇
  2012年   11053篇
  2011年   10781篇
  2010年   9790篇
  2009年   9475篇
  2008年   9792篇
  2007年   9745篇
  2006年   8768篇
  2005年   7858篇
  2004年   7249篇
  2003年   6333篇
  2002年   6158篇
  2001年   6678篇
  2000年   5179篇
  1999年   4029篇
  1998年   3261篇
  1997年   3346篇
  1996年   3111篇
  1995年   2950篇
  1994年   2729篇
  1993年   2756篇
  1992年   2974篇
  1991年   2841篇
  1990年   2704篇
  1989年   2519篇
  1988年   2616篇
  1987年   2614篇
  1986年   2416篇
  1985年   3186篇
  1984年   3510篇
  1983年   2854篇
  1982年   3071篇
  1981年   3081篇
  1980年   2934篇
  1979年   3028篇
  1978年   3160篇
  1977年   3245篇
  1976年   3343篇
  1975年   3207篇
  1974年   3210篇
  1973年   3150篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
Siberian Mathematical Journal - Suppose that $ n $ is an integer, $ n\geq 3 $ . We prove that a periodic group saturated with a set of the finite simple groups $ O_{2n+1}(q) $ , where $ q $ is...  相似文献   
22.
We prove a well-posedness result for two pseudo-parabolic problems, which can be seen as two models for the same electrical conduction phenomenon in heterogeneous media, neglecting the magnetic field. One of the problems is the concentration limit of the other one, when the thickness of the dielectric inclusions goes to zero. The concentrated problem involves a transmission condition through interfaces, which is mediated by a suitable Laplace-Beltrami type equation.  相似文献   
23.
Kobayashi  M.  Zhang  Y.  Ishikawa  H.  Sun  J.  Oddershede  J.  Juul Jensen  D.  Miura  H. 《Experimental Mechanics》2021,61(5):817-828
Experimental Mechanics - The internal strain distribution developing during plastic deformation is important for understanding the mechanical properties of polycrystalline materials. Such...  相似文献   
24.
Russian Physics Journal - The specific features of the sorption activity of silver nanoparticles (AgNPs) on biodegradable polymers of natural (collagen) and artificial (polyamide 6.6) origin have...  相似文献   
25.
26.
Doklady Physics - This work is devoted to analysis and generalization of the kinetic criteria of vitrification using the model of delocalized atoms. The generalized criterion of a...  相似文献   
27.
Pentafluorosulfanyl (SF5)-containing compounds and corresponding analogs are a highly valuable class of fluorine-containing building blocks owing to their unique properties. The reason for that is the set of peculiar and tremendously beneficial characteristics they can impart on molecules once introduced onto them. Despite this, their application in distinct scientific fields remains modest, given the extremely harsh reaction conditions needed to access such compounds. The recent synthetic approaches via S−F, and C−SF5 bond formation as well as the use of SF5-containing building blocks embody a “stairway-to-heaven” loophole in the synthesis of otherwise-inaccessible chemical scaffolds only a few years ago. Herein, we report and evaluate the properties of the SF5 group and analogs, by summarizing synthetic methodologies available to access them as well as following applications in material science and medicinal chemistry since 2015.  相似文献   
28.
Ferrarini  A.  Finotello  A.  Salsano  G.  Auricchio  F.  Palombo  D.  Spinella  G.  Pane  B.  Conti  M. 《Acta Mechanica Sinica》2021,37(7):1192-1192
Acta Mechanica Sinica - A Correction to this paper has been published: https://doi.org/10.1007/s10409-021-01066-2  相似文献   
29.
Journal of Experimental and Theoretical Physics - The studies of the topological properties of systems have recently been extended due to a new concept of higher-order topological insulators and...  相似文献   
30.
BPh3 catalyzes the N-methylation of secondary amines and the C-methylenation (methylene-bridge formation between aromatic rings) of N,N-dimethylanilines or 1-methylindoles in the presence of CO2 and PhSiH3; these reactions proceed at 30–40 °C under solvent-free conditions. In contrast, B(C6F5)3 shows little or no activity. 11B NMR spectra suggested the generation of [HBPh3]. The detailed mechanism of the BPh3-catalyzed N-methylation of N-methylaniline ( 1 ) with CO2 and PhSiH3 was studied by using DFT calculations. BPh3 promotes the conversion of two substrates (N-methylaniline and CO2) into a zwitterionic carbamate to give three-component species [Ph(Me)(H)N+CO2⋅⋅⋅BPh3]. The carbamate and BPh3 act as the nucleophile and Lewis acid, respectively, for the activation of PhSiH3 to generate [HBPh3], which is used to produce key CO2-derived species, such as silyl formate and bis(silyl)acetal, essential for the N-methylation of 1 . DFT calculations also suggested other mechanisms involving water for the generation of [HBPh3] species.  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