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   238479篇
  免费   22288篇
  国内免费   24017篇
化学   109278篇
晶体学   3501篇
力学   14251篇
综合类   3110篇
数学   64528篇
物理学   90116篇
  2023年   2139篇
  2022年   5067篇
  2021年   5057篇
  2020年   4955篇
  2019年   5153篇
  2018年   4537篇
  2017年   5231篇
  2016年   5652篇
  2015年   5064篇
  2014年   7863篇
  2013年   14103篇
  2012年   9357篇
  2011年   10961篇
  2010年   10113篇
  2009年   16533篇
  2008年   17903篇
  2007年   16698篇
  2006年   14937篇
  2005年   11822篇
  2004年   11154篇
  2003年   10528篇
  2002年   12581篇
  2001年   8509篇
  2000年   7931篇
  1999年   7143篇
  1998年   6204篇
  1997年   5064篇
  1996年   4531篇
  1995年   4690篇
  1994年   4318篇
  1993年   3514篇
  1992年   2941篇
  1991年   2322篇
  1990年   1850篇
  1989年   1603篇
  1988年   1550篇
  1987年   1112篇
  1986年   844篇
  1985年   1715篇
  1984年   1252篇
  1983年   835篇
  1982年   1217篇
  1981年   1358篇
  1980年   1163篇
  1979年   1045篇
  1978年   903篇
  1977年   765篇
  1976年   727篇
  1974年   480篇
  1973年   636篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
151.
   Abstract. We propose a general approach to deal with nonlinear, nonconvex variational problems based on a reformulation of the problem resulting in an optimization problem with linear cost functional and convex constraints. As a first step we explicitly explore these ideas to some one-dimensional variational problems and obtain specific conclusions of an analytical and numerical nature.  相似文献   
152.
The purpose of this paper is to investigate the problem of approximating fixed points of non-Lipschitizian asymptotically pseudocontractive mappings in an arbitrary real Banach space by the modified Ishikawa iterative sequences with errors.  相似文献   
153.
In this paper, we give the following dominated theorem: Let φ(g) ∈ L1(G//K),φε(t)=ε> 0, and the least radical decreasing dominatedfunction φ(t) = sup |φ(y)| ∈L1(G//K). If shtφ(t) is monotonically decreasingon (0, ∞), then for any f∈L1loc(G//K) , the following inequality holds:sup |φε * f(x)| ≤ Cmf(x),where mf(x) is the Hardy-Littlewood maximal function of f, and C = ||φ||1.An application of this dominated theorem is also given.  相似文献   
154.
基于稠密气体分子运动论和颗粒动理学,建立可压稠密气固两相流动模型。采用梯度模拟来考虑气相可压缩性对气相湍流的影响。模拟计算表明气固两相射流速度沿轴向和径向减小,颗粒浓度下降。气固两相射流具有高的颗粒温度,呈现强烈的气固两相湍流流动特性。  相似文献   
155.
New radiative lifetime measurements based on time-resolved laser-induced fluorescence techniques are reported for 18 even-parity levels belonging to the 4f5d26p and 4f 25d 2 configurations of Ce I and 6 even-parity levels belonging to the 5d26s, 4f5d6p, and 4f6s6p configurations of Ce II. Free neutral and singly ionized cerium atoms were produced by laser ablation. The Ce I and Ce II levels range in energy from 26 545 to 29 102 cm-1, and 42 573 to 48 152 cm-1, respectively. Received 25 September 2002 Published online 4 March 2003  相似文献   
156.
For time-periodic dissipative and irreducible type-K competitive Kolmogorov systems, it is proved that there is a canonically defined countable family F of unordered, disjoint invariant sets with the property that, for every persistent trajectory whose ω-limit set is not a cycle, there exists a unique trajectory in some element of F such that these two trajectories are asymptotic and the corresponding points in these two trajectories are K-related.  相似文献   
157.
2-Formyl glycals undergo rapid condensation with arylhydrazines under solvent-free conditions to give the corresponding optically pure 4-substituted pyrazoles in good yields with high selectivity. The stereochemistry of the products was assigned by various NMR experiments.  相似文献   
158.
Reaction of acetylene dicarboxaldehyde monoacetal with substituted Meldrum’s acid leads good yields in 2-pyranones-4-carboxaldehydes substituted in position 3.  相似文献   
159.
The fusion evaporation reaction 122Sn(14N, 4n)132La was used to populate the high-spin states of 132La at the beam energy of 60 MeV. A new band consisting of mostly E2 transitions has been discovered. This band has the interesting links to the ground state 2- and the isomeric state 6-. A new transition of energy 351 keV connecting the low-spin states of the positive-parity band based on the πh 11/2 ⊗ νh 11/2 particle configuration, has been found. This has played a very important role in resolving the existing ambiguities and inconsistencies in the spin assignment of the band head. Received: 12 August 2002 / Accepted: 18 March 2003 / Published online: 7 May 2003  相似文献   
160.
For an arbitrary bounded closed set E in the complex plane with complement Ω of finite connectivity, we study the degree of convergence of the lemniscates in Ω.  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