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   44157篇
  免费   609篇
  国内免费   605篇
化学   19854篇
晶体学   377篇
力学   1828篇
综合类   45篇
数学   10986篇
物理学   12281篇
  2022年   193篇
  2021年   225篇
  2020年   224篇
  2019年   234篇
  2018年   1385篇
  2017年   1614篇
  2016年   1073篇
  2015年   864篇
  2014年   861篇
  2013年   1533篇
  2012年   3757篇
  2011年   3052篇
  2010年   2364篇
  2009年   2068篇
  2008年   1282篇
  2007年   1357篇
  2006年   1189篇
  2005年   5002篇
  2004年   4489篇
  2003年   2913篇
  2002年   1122篇
  2001年   770篇
  2000年   522篇
  1999年   489篇
  1998年   346篇
  1997年   277篇
  1996年   273篇
  1995年   281篇
  1994年   274篇
  1993年   205篇
  1992年   335篇
  1991年   330篇
  1990年   330篇
  1989年   260篇
  1988年   238篇
  1987年   193篇
  1986年   166篇
  1985年   258篇
  1984年   274篇
  1983年   189篇
  1982年   204篇
  1981年   164篇
  1980年   165篇
  1979年   171篇
  1978年   145篇
  1977年   182篇
  1976年   223篇
  1975年   156篇
  1974年   156篇
  1973年   168篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
81.
In the paper we indicate an error made in the proof of the main result of the paper [M.A. Darwish, On quadratic integral equation of fractional orders, J. Math. Anal. Appl. 311 (2005) 112-119]. Moreover, we provide correct proof of a slightly modified version of the mentioned result. The main tool used in our proof is the technique associated with the Hausdorff measure of noncompactness.  相似文献   
82.
In this paper we deal with nonlinear second-order boundary value problems with impulses. The impulsive functions depend implicitly on the different considered variables and the boundary value conditions are nonlinear. In both cases functional dependence on the solution is allowed. The existence results follow from the existence of a pair of well-ordered lower and upper solutions.  相似文献   
83.
文章讨论无界区域上GBBM方程的Cauchy问题,对方程的解进行了先验估计,并证明了在H1弱拓扑中整体吸引子的存在性.  相似文献   
84.
85.
A Fubini theorem     
Let I0 be the σ-ideal of subsets of a Polish group generated by Borel sets which have perfectly many pairwise disjoint translates. We prove that a Fubini-type theorem holds between I0 and the σ-ideals of Haar measure zero sets and of meager sets. We use this result to give a simple proof of a generalization of a theorem of Balcerzak-Ros?anowski-Shelah stating that I0 on N2 strongly violates the countable chain condition.  相似文献   
86.
87.
Brouwer and Wilbrink [3] showed the nonexistence of regular near octagons whose parameters s, t2, t3 and t satisfy s ≥ 2, t2 ≥ 2 and t3t2(t2+1). Later an arithmetical error was discovered in the proof. Because of this error, the existence problem was still open for the near octagons corresponding with certain values of s, t2 and t3. In the present paper, we will also show the nonexistence of these remaining regular near octagons. MSC2000 05B25, 05E30, 51E12 Postdoctoral Fellow of the Research Foundation - Flanders  相似文献   
88.
The ion-beam-assisted etching of silicon in Cl2 environment is considered. The theoretically calculated dependences of silicon etching rate on the flux of Cl2 molecules at different ion current densities are compared with experimentally measured. The composition of the adsorbed layer is determined. It is found that SiCl2 molecules prevail in the adsorbed layer. The reciprocal of relative concentration of SiCl2 molecules in the adsorbed layer linearly depends on the ion-to-neutral flux ratio.  相似文献   
89.
In this paper, we study the dynamical behavior for a 4-dimensional reversible system near its heteroclinic loop connecting a saddle-focus and a saddle. The existence of infinitely many reversible 1-homoclinic orbits to the saddle and 2-homoclinic orbits to the saddle-focus is shown. And it is also proved that, corresponding to each 1-homoclinic (resp. 2-homoclinic) orbit F, there is a spiral segment such that the associated orbits starting from the segment are all reversible 1-periodic (resp. 2-periodic) and accumulate onto F. Moreover, each 2-homoclinic orbit may be also accumulated by a sequence of reversible 4-homoclinic orbits.  相似文献   
90.
Summary Analysis of thirteen medicinal plants of various biological activities commonly used in South-western Nigeria was carried out using PIXE technique. Nine of these plants are anti-cancer while four are antimicrobial. PIXE measurements were carried out using collimated proton beams delivered by the 2. 5 MV AN 2000 Van de Graaff accelerator at the Istituto Nazionale di Fisica Nucleare (INFN), (LNL) Legnaro, (Padova), Italy. The results showed the presence of twenty three different elements in the plants and none of them contains any toxic heavy metals. Only Chenopodium ambrosioides showed detectable levels of selenium which is considered important in cancer prevention.  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