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   20093篇
  免费   2030篇
  国内免费   1864篇
化学   1721篇
晶体学   26篇
力学   1115篇
综合类   326篇
数学   17379篇
物理学   3420篇
  2024年   40篇
  2023年   229篇
  2022年   268篇
  2021年   389篇
  2020年   605篇
  2019年   656篇
  2018年   603篇
  2017年   657篇
  2016年   690篇
  2015年   493篇
  2014年   977篇
  2013年   1740篇
  2012年   938篇
  2011年   1109篇
  2010年   991篇
  2009年   1325篇
  2008年   1263篇
  2007年   1367篇
  2006年   1201篇
  2005年   1039篇
  2004年   929篇
  2003年   930篇
  2002年   874篇
  2001年   625篇
  2000年   660篇
  1999年   617篇
  1998年   509篇
  1997年   479篇
  1996年   317篇
  1995年   201篇
  1994年   182篇
  1993年   108篇
  1992年   127篇
  1991年   74篇
  1990年   67篇
  1989年   58篇
  1988年   52篇
  1987年   34篇
  1986年   41篇
  1985年   65篇
  1984年   81篇
  1983年   40篇
  1982年   63篇
  1981年   52篇
  1980年   57篇
  1979年   50篇
  1978年   27篇
  1977年   31篇
  1976年   27篇
  1936年   7篇
排序方式: 共有10000条查询结果,搜索用时 12 毫秒
91.
The relation between generalized operators and operator-valued distributions is discussed so that these two viewpoints can be used alternatively to explain quantum fields.  相似文献   
92.
Using non-linear connection of Finsler manifold M, the existence of local coordinates which is normalized at a point x is proved, and the Laplace operator A on 1-form of M is defined by non-linear connection and its curvature tensor. After proving the maximum principle theorem of Hopf-Bochner on M, the Bochner type vanishing theorem of Killing vectors and harmonic 1-form are obtained.  相似文献   
93.
OSCILLATION RESULTS FOR A SECOND ORDER NEUTRAL DELAY DIFFERENTIAL EQUATIONS   总被引:1,自引:0,他引:1  
Some new oscillation criteria are established for a second order neutral delay differential equations. These results improve oscillation results of Y.V. Rogo-vchenko for the retarded delay differential equations. The relevance of our theorems is illustrated with two carefully selected examples.  相似文献   
94.
This paper uses the method of linear approximation for impulsive systems and gets a theorem which guarantees a fishery modei to be asymptotically stable at its equilibrium point and gives the ecological explanation.  相似文献   
95.
In this paper, we present some counterexamples which show that there is no theory on the spectrum of homogeneous compact operators which parallels the Riesz-Schauder theory on the spectrum of linear compact operators. These counterexamples also illustrate that it is impossible to study in a unified setting the Fucik spectrum of the Laplacian: -△w = au+ - bu- inΩand u = 0 on (?)Ω, as well as the spectrum of the p-Laplacian: -div(|(?)u| p-2(?)u) = λ|u|p-2u and u = 0 on (?)Ω.  相似文献   
96.
The theory of monotone semiflows has been widely applied to functional differential equations (FDEs). The studies on the theory and applications of monotone semiflows for FDEs are very important and interesting. A brief des-cription of our recent works are as follows.By using general monotone semiflow theory, several results of positively invariant sets, monotone solutions and contracting rectangles of retarded functional differential equations(RFDEs) with infinite delay are gained under the assumption of quasimonotonicity; sufficient conditions for the existence, un-iqueness and global attractivity of periodic solutions are also established by combining the theory of monotone semiflows for neutral functional differential equations(NFDEs) and Krasnoselskii's fixed point theorem.  相似文献   
97.
In this paper, we establish some differential identities and obtain some Sturm comparison theorems for the second order nonlinear differential equation by using them.and generalize some classicial Sturm comparison theorems.  相似文献   
98.
Sufficient conditions are established for the asymptotic behavior of solutionsof nonlinear delay differential equations x′(t)+sum from i=1 to m(pi(t)x(t-т_i))=F(t,x_t),t≥0where 0<т_1<т_2<…<т_m≤r,pi∈C([0,∞)),i=1,2,…,m,F∈C([0,∞)×C_0,R).C_0=C([-r,0],R)equipped with the sup norm ||·|| forsome r>0. A new result is established, some known results are improved.  相似文献   
99.
By means of an abstract continuation theory for κ-set contraction and continuation theorem of coincidence degree principle, some criteria are established for the existence of positive periodic solutions of following neutral functional differential equation dN/dt=N(t)[α(t)-β(t)N(t)-∑j=1^n bj(t)N(t-σj(t))-∑i=1^mci(t)N‘(t-γi(t)0].  相似文献   
100.
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