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   9643篇
  免费   240篇
  国内免费   191篇
化学   1340篇
晶体学   70篇
力学   55篇
综合类   21篇
数学   7562篇
物理学   1026篇
  2023年   35篇
  2022年   44篇
  2021年   52篇
  2020年   75篇
  2019年   220篇
  2018年   197篇
  2017年   112篇
  2016年   103篇
  2015年   129篇
  2014年   277篇
  2013年   445篇
  2012年   334篇
  2011年   613篇
  2010年   478篇
  2009年   615篇
  2008年   650篇
  2007年   718篇
  2006年   549篇
  2005年   346篇
  2004年   274篇
  2003年   296篇
  2002年   259篇
  2001年   199篇
  2000年   201篇
  1999年   251篇
  1998年   245篇
  1997年   217篇
  1996年   210篇
  1995年   274篇
  1994年   217篇
  1993年   217篇
  1992年   178篇
  1991年   101篇
  1990年   101篇
  1989年   123篇
  1988年   65篇
  1987年   55篇
  1986年   63篇
  1985年   87篇
  1984年   80篇
  1983年   61篇
  1982年   71篇
  1981年   50篇
  1980年   40篇
  1979年   43篇
  1978年   43篇
  1977年   25篇
  1976年   20篇
  1975年   4篇
  1974年   4篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
We use the machinery of categorified Jones-Wenzl projectors to construct a categorification of a type A Reshetikhin-Turaev invariant of oriented framed tangles where each strand is labelled by an arbitrary finite-dimensional representation. As a special case, we obtain a categorification of the coloured Jones polynomial of links.  相似文献   
2.
3.
Ocotillol, pseudo-ginsenoside RT5 (RT5), and pseudo-ginsenoside F11 (PF11) are ocotillol-type saponins that have the same aglycone structure but with different numbers of glucose at the C-6 position. In this study, the metabolites of ocotillol, RT5, and PF11 in rat plasma, stomach, intestine, urine, and feces after oral administration were investigated by ultra-performance liquid chromatography coupled with time-of-flight mass spectrometry. The results showed that RT5 was easily biotransformed into metabolites in vivo, whereas PF11 and RT5 were difficult to be biotransformed. Hydrogenation, dehydrogenation, dehydration, deglycosylation, deoxygenation, hydration, phosphorylation, deoxidation, glucuronidation, and reactions combining amino acid were speculated to be involved in the biotransformation of ocotillol, RT5, and PF11. Based on the structural analysis of metabolites, it was deduced that hydrogenation, dehydration, deoxidation, and reactions combining amino acid occurred on the aglycone structure, whereas deglycosylation, hydration, and phosphorylation occurred on the glycosyl chain. Further, metabolites in plasma, urine, feces, and tissues were different: First, glucuronidation products were found in urine, stomach, intestine, and feces, but not in plasma. Second, the ocotillol prototype was not identified in urine samples. Third, the RT5 prototype was found in stomach, intestine, feces, and urine, but not in plasma.  相似文献   
4.
5.
6.
Let M be a closed spin manifold and let N be a closed manifold. For maps and Riemannian metrics g on M and h on N, we consider the Dirac operator of the twisted Dirac bundle . To this Dirac operator one can associate an index in . If M is 2‐dimensional, one gets a lower bound for the dimension of the kernel of out of this index. We investigate the question whether this lower bound is obtained for generic tupels .  相似文献   
7.
We provide a bound on a distance between finitely supported elements and general elements of the unit sphere of ?2(N1). We use this bound to estimate the Wasserstein-2 distance between random variables represented by linear combinations of independent random variables. Our results are expressed in terms of a discrepancy measure related to Nourdin–Peccati’s Malliavin–Stein method. The main application is towards the computation of quantitative rates of convergence to elements of the second Wiener chaos. In particular, we explicit these rates for non-central asymptotic of sequences of quadratic forms and the behavior of the generalized Rosenblatt process at extreme critical exponent.  相似文献   
8.
This work presents sufficient conditions for the existence of homoclinic solutions for second order coupled discontinuous systems of differential equations on the real line without the usual growth condition in the literature.The arguments apply the fixed point theory, Green's functions technique, L1-Carathéodory functions, lower and upper solutions and Schauder's fixed point theorem.  相似文献   
9.
10.
利用高温固相法成功制备了Er~(3+)单掺、Er~(3+)/Yb~(3+)共掺杂Ca_(12)Al_(14)O_(32)F_2上转换发光样品。在980 nm激光激发下,Er~(3+)单掺和Er~(3+)/Yb~(3+)共掺杂样品均呈现出较强的绿光(528,549 nm)和较弱的红光(655 nm)发射,分别归因于Er~(3+)离子的~2H_(11/2),~4S_(3/2)→~4I_(15/2)和~4F_(9/2)→~4I_(15/2)能级跃迁。随着Er离子浓度的增加,单掺杂样品上转换发光强度先增大后减小,最佳掺杂浓度为0.8%。共掺杂Yb~(3+)后,Er~(3+)的发光强度明显增大。还原气氛下合成的样品上转换发光强度增大约两倍,可能和笼中阴离子基团变化有关。发光强度和激发光功率的关系表明所得上转换发射为双光子吸收过程,借助Er~(3+)-Yb~(3+)体系能级结构详细讨论了上转换发射的跃迁机制。  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