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   88624篇
  免费   1281篇
  国内免费   951篇
化学   31180篇
晶体学   898篇
力学   7171篇
综合类   70篇
数学   33448篇
物理学   18089篇
  2023年   148篇
  2022年   203篇
  2021年   327篇
  2020年   352篇
  2019年   378篇
  2018年   10684篇
  2017年   10462篇
  2016年   6454篇
  2015年   1260篇
  2014年   810篇
  2013年   1104篇
  2012年   4520篇
  2011年   11258篇
  2010年   6141篇
  2009年   6485篇
  2008年   7165篇
  2007年   9216篇
  2006年   733篇
  2005年   1724篇
  2004年   1860篇
  2003年   2285篇
  2002年   1321篇
  2001年   525篇
  2000年   494篇
  1999年   329篇
  1998年   316篇
  1997年   248篇
  1996年   306篇
  1995年   209篇
  1994年   217篇
  1993年   194篇
  1992年   165篇
  1991年   167篇
  1990年   141篇
  1989年   125篇
  1988年   122篇
  1987年   114篇
  1986年   115篇
  1985年   128篇
  1984年   116篇
  1983年   78篇
  1982年   111篇
  1981年   103篇
  1980年   115篇
  1979年   104篇
  1978年   98篇
  1977年   74篇
  1976年   67篇
  1975年   56篇
  1973年   66篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
We give the form of the output function in Ginsburg’s machine in which the input and output dictionaries are abelian groups and the transition function is of a special form.  相似文献   
22.
23.
Inorganic planar ring-shape molecules with 4n + 2 π electrons are always the focus of experimental synthesis and theoretical research due to their potential aromaticity and stability. In this work, the whole series of five-membered heterocycle monoanions X nY5-n (X, Y = group 15 elements; n = 1-4) were thoroughly investigated by means of density functional theory calculations. They all have large formation energies and HOMO-LUMO gap energies, suggesting the potential thermodynamic and kinetic stability. Their aromaticities are comparable to that of typical aromatic hydrocarbons. Their thermal stabilities were firmly established by the ab initio molecular dynamics simulations. As most of them are predicted for the first time, their various spectra were simulated for experimental characterization. Furthermore, we demonstrate that these five-membered cyclic anions can be employed as η5-ligand to construct novel all-inorganic metallocenes, which may serve as the building blocks of low-dimensional nanomaterials.  相似文献   
24.
Mixed-graft block copolymers (mGBCPs) consist of two or more types of polymeric side chains grafted on a linear backbone in a random, alternating, or pseudo-alternating sequence. They can phase-separate with the backbone serving as the interface of the blocks, and the side chains dominate their self-assembly behavior. mGBCPs are an accessible polymer architecture for exploring the idea of encoding polymer properties through the macromolecular architecture, as there are two distinct structural components that can be tuned: the backbone and the side chains. In this Concept article, the current literature on the synthesis of mGBCPs is reviewed, and the advantages and disadvantages of each synthetic method are noted. The self-assembly of mGBCPs is also discussed where possible. Finally, directions for future research on mGBCP synthesis and self-assembly are suggested.  相似文献   
25.
26.
27.
28.
29.
The structure, chemical composition, and magnetic properties of electrochemically deposited nanocrystalline Co-Ni-Fe films were investigated using a number of techniques. A high saturation magnetic induction up to B s = 21 kG was attained. An enhancement of the saturation magnetization compared to the ideal anticipated one was revealed, which correlated with the nonlinear behavior of the structural phase composition and lattice parameters with the change of the composition. The text was submitted by the authors in English.  相似文献   
30.
The asymptotics of the necessary sample size is considered in testing close hypotheses when the error probabilities vanish. Proceedings of the XVII Seminar on Stability Problems for Stochastic Models, Kazan, Russia, 1995, Part III.  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