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   137876篇
  免费   31743篇
  国内免费   23282篇
化学   91058篇
晶体学   1659篇
力学   9050篇
综合类   505篇
数学   16513篇
物理学   74116篇
  2024年   633篇
  2023年   1973篇
  2022年   2946篇
  2021年   3123篇
  2020年   3474篇
  2019年   3830篇
  2018年   3469篇
  2017年   3895篇
  2016年   5045篇
  2015年   5192篇
  2014年   5806篇
  2013年   8507篇
  2012年   9634篇
  2011年   11373篇
  2010年   12812篇
  2009年   12859篇
  2008年   7112篇
  2007年   6285篇
  2006年   5745篇
  2005年   5445篇
  2004年   5733篇
  2003年   4639篇
  2002年   4276篇
  2001年   4361篇
  2000年   3359篇
  1999年   3830篇
  1998年   3242篇
  1997年   2924篇
  1996年   3229篇
  1995年   3583篇
  1994年   3543篇
  1993年   3514篇
  1992年   3018篇
  1991年   2618篇
  1990年   2242篇
  1989年   2211篇
  1988年   2089篇
  1987年   1349篇
  1986年   1412篇
  1985年   1029篇
  1984年   1064篇
  1983年   459篇
  1982年   972篇
  1981年   793篇
  1980年   798篇
  1979年   546篇
  1978年   539篇
  1977年   646篇
  1976年   1051篇
  1972年   537篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
111.
112.
The crystal structures of two potential tumor imaging agents and therapeutic agents -copper(Ⅱ) complexes with salicylidene-tyrosinato Schiff base and nitrogen-donor chelating Lewis base, [Cu(sal-tyr)(bipy)] 1 and [Cu(sal-tyr)(phen)]2CH3OH 2 are presented. Our work is helpful to get deep understanding of novel 64Cu tumor imaging agents and therapeutic agents.  相似文献   
113.
In this paper, a model of a linear multilevel programming problem with dominated objective functions (LMPPD(l)) is proposed, where multiple reactions of the lower levels do not lead to any uncertainty in the upper-level decision making. Under the assumption that the constrained set is nonempty and bounded, a necessary optimality condition is obtained. Two types of geometric properties of the solution sets are studied. It is demonstrated that the feasible set of LMPPD(l) is neither necessarily composed of faces of the constrained set nor necessarily connected. These properties are different from the existing theoretical results for linear multilevel programming problems.  相似文献   
114.
The notion of Kuratowski convergence is applied to describe a kind of convergence in the context of holomorphic functions. We associate it to a convenient topology, explore its relation with the compact-open topology, thus providing a new set theoretic point of view of this classic topology, and present it in the framework of set-valued mappings.  相似文献   
115.
We consider a spinning charge coupled to the Maxwell field. Through the appropriate symmetry in the initial conditions the charge remains at rest. We establish that any time-dependent finite energy solution converges to a sum of a soliton wave and an outgoing free wave. The convergence holds in global energy norm. Under a small constant external magnetic field the soliton manifold is stable in local energy seminorms and the evolution of the angular velocity is guided by an effective finite-dimensional dynamics. The proof uses a non-autonomous integral inequality method.  相似文献   
116.
117.
New heuristics for over-constrained flight to gate assignments   总被引:1,自引:0,他引:1  
We consider the over-constrained Airport Gate Assignment Problem where the number of flights exceed the number of gates available, and where the objectives are to minimize the number of ungated flights and the total walking distances. The problem is formulated as a binary quadratic programming problem. We design a greedy algorithm and use a Tabu Search meta-heuristic to solve the problem. The greedy algorithm minimizes ungated flights while we devise a new neighbourhood search technique, the Interval Exchange Move, which allows us flexibility in seeking good solutions, especially when flight schedules are dense in time. Experiments conducted give good results.  相似文献   
118.
We give a Gray code and constant average time generating algorithm for derangements, i.e., permutations with no fixed points. In our Gray code, each derangement is transformed into its successor either via one or two transpositions or a rotation of three elements. We generalize these results to permutations with number of fixed points bounded between two constants.  相似文献   
119.
We prove here that the surface of the regular icosahedron can be triangulated with 8 non-obtuse and with 12 acute triangles. We also show these numbers to be smallest possible.  相似文献   
120.
The extensive study of metric spaces and their embeddings has so far focused on embeddings that preserve pairwise distances. A very intriguing concept introduced by Feige allows us to quantify the extent to which larger structures are preserved by a given embedding. We investigate this concept, focusing on several major graph families such as paths, trees, cubes, and expanders. We find some similarities to the regular (pairwise) distortion, as well as some striking differences.  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