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   272554篇
  免费   4271篇
  国内免费   1847篇
化学   146135篇
晶体学   3067篇
力学   12459篇
综合类   86篇
数学   30380篇
物理学   86545篇
  2020年   2534篇
  2019年   2701篇
  2018年   3449篇
  2017年   3398篇
  2016年   4966篇
  2015年   3082篇
  2014年   4797篇
  2013年   11414篇
  2012年   8992篇
  2011年   10846篇
  2010年   7704篇
  2009年   7494篇
  2008年   9995篇
  2007年   10109篇
  2006年   9407篇
  2005年   8534篇
  2004年   7714篇
  2003年   6931篇
  2002年   6371篇
  2001年   7280篇
  2000年   5558篇
  1999年   4264篇
  1998年   3777篇
  1997年   3776篇
  1996年   3506篇
  1995年   3409篇
  1994年   3525篇
  1993年   3199篇
  1992年   3655篇
  1991年   3641篇
  1990年   3585篇
  1989年   3428篇
  1988年   3505篇
  1987年   3435篇
  1986年   3222篇
  1985年   4309篇
  1984年   4587篇
  1983年   3810篇
  1982年   3946篇
  1981年   3859篇
  1980年   3833篇
  1979年   3809篇
  1978年   4136篇
  1977年   4059篇
  1976年   4127篇
  1975年   3796篇
  1974年   3861篇
  1973年   4004篇
  1972年   2822篇
  1971年   2349篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Doklady Mathematics - New properties of convex infinitely differentiable functions related to extremal problems are established. It is shown that, in a neighborhood of the solution, even if the...  相似文献   
2.
JETP Letters - The effect of static mechanical strain on the splitting of spin sublevels of color centers based on spin 3/2 silicon vacancies in silicon carbide at room temperature has been shown....  相似文献   
3.
Crystallography Reports - The orientation of grains and the special boundaries formed by them in multicrystalline silicon has been studied by electron backscattered diffraction. It is found that...  相似文献   
4.
Doklady Physics - The dependence of Raman spectra of the molecules containing polyene chains on the conjugation length, structure of side and end groups, and isomer type is analyzed theoretically.  相似文献   
5.
JETP Letters - Photonically controlled metastructures containing resonant conducting dipole and chiral elements with CdS and CdSe in gaps have been proposed, implemented, and studied in a waveguide...  相似文献   
6.
Zhang  Lei  Liu  Maoxing  Xie  Boli 《Nonlinear dynamics》2021,103(2):2097-2107
Nonlinear Dynamics - At present, the main measures for disease control are vaccination, quarantine and treatment. Taking the three measures into consideration, time-varying optimal control problems...  相似文献   
7.
8.
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   
9.
Integrated information theory (IIT) provides a mathematical framework to characterize the cause-effect structure of a physical system and its amount of integrated information (Φ). An accompanying Python software package (“PyPhi”) was recently introduced to implement this framework for the causal analysis of discrete dynamical systems of binary elements. Here, we present an update to PyPhi that extends its applicability to systems constituted of discrete, but multi-valued elements. This allows us to analyze and compare general causal properties of random networks made up of binary, ternary, quaternary, and mixed nodes. Moreover, we apply the developed tools for causal analysis to a simple non-binary regulatory network model (p53-Mdm2) and discuss commonly used binarization methods in light of their capacity to preserve the causal structure of the original system with multi-valued elements.  相似文献   
10.
A formal computation proving a new operator identity from known ones is, in principle, restricted by domains and codomains of linear operators involved, since not any two operators can be added or composed. Algebraically, identities can be modelled by noncommutative polynomials and such a formal computation proves that the polynomial corresponding to the new identity lies in the ideal generated by the polynomials corresponding to the known identities. In order to prove an operator identity, however, just proving membership of the polynomial in the ideal is not enough, since the ring of noncommutative polynomials ignores domains and codomains. We show that it suffices to additionally verify compatibility of this polynomial and of the generators of the ideal with the labelled quiver that encodes which polynomials can be realized as linear operators. Then, for every consistent representation of such a quiver in a linear category, there exists a computation in the category that proves the corresponding instance of the identity. Moreover, by assigning the same label to several edges of the quiver, the algebraic framework developed allows to model different versions of an operator by the same indeterminate in the noncommutative polynomials.  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