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   83187篇
  免费   465篇
  国内免费   389篇
化学   27093篇
晶体学   818篇
力学   6905篇
综合类   1篇
数学   32718篇
物理学   16506篇
  2021年   60篇
  2020年   72篇
  2019年   67篇
  2018年   10495篇
  2017年   10315篇
  2016年   6173篇
  2015年   966篇
  2014年   430篇
  2013年   557篇
  2012年   4019篇
  2011年   10751篇
  2010年   5788篇
  2009年   6185篇
  2008年   6856篇
  2007年   8987篇
  2006年   492篇
  2005年   1547篇
  2004年   1719篇
  2003年   2118篇
  2002年   1154篇
  2001年   360篇
  2000年   376篇
  1999年   226篇
  1998年   242篇
  1997年   207篇
  1996年   280篇
  1995年   170篇
  1994年   131篇
  1993年   158篇
  1992年   101篇
  1991年   108篇
  1990年   88篇
  1989年   104篇
  1988年   108篇
  1987年   100篇
  1986年   102篇
  1985年   114篇
  1984年   117篇
  1983年   83篇
  1982年   105篇
  1981年   88篇
  1980年   111篇
  1979年   106篇
  1978年   106篇
  1977年   79篇
  1976年   71篇
  1975年   59篇
  1974年   49篇
  1973年   64篇
  1914年   46篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
51.
Sodium trichloro­methane­sulfonate monohydrate, Na+·CCl3SO3·H2O, crystallizes in P21/a with all the atoms located in general positions. The trichloro­methane­sulfonate (trichlate) anion consists of pyramidal SO3 and CCl3 groups connected via an S—C bond in a staggered conformation with approximate C3v symmetry. The water mol­ecule is hydrogen bonded to the sulfonate O atoms, with one water H atom forming weak bifurcated O—H⋯O hydrogen bonds to two different trichlate ions. Two water O atoms and three O atoms from different SO3 groups form a square‐pyramidal arrangement around the sodium ion.  相似文献   
52.
In this paper we obtain a number of Maharam-type slice integral representations, with respect to scalar measures, for positive projections in Dedekind complete vector lattices and f-algebras. AMS Classification: 47B65, 46A40, 06F25  相似文献   
53.
We calculate the leptonic constant for the pseudoscalar ground state of the B c meson in the framework of a QCD-motivated potential model taking into account the two-loop anomalous dimension for the heavy quark current in nonrelativistic QCD as matched with full QCD.  相似文献   
54.
We define analytic functions within Clifford Algebras CL, and study their trigonometric properties. We write the addition formulas when their arguments, A and B in CL, commute, this generalizes ordinary trigonometry. We examine in particular the case A2 = 1.   相似文献   
55.
In the present paper it is shown that if S1 and S2 are two Clifford topological semigroups satisfying certain conditions and T is an isometric isomorphism of LUC(S1*) onto LUC(S2*), then T maps S1 topologically isomorphically onto S2. Furthermore, T maps M l n(S1) (M(S1), respectively) isometrically isomorphically onto M l n(S2) (M(S2), respectively). Indeed, we have obtained a generalization of a well-known result of Ghahramani, Lau and Losert for locally compact groups to a more general setting of Clifford topological semigroups.  相似文献   
56.
This paper describes some work carried out in the Scientific Research and Development Branch (SRDB) of the Home Office, intended to contribute to an overall aim of building up internal expertise in the field of expert systems. This was done by carrying out a number of pilot and demonstrator projects, two of which are described in some detail. The plan, which proved successful, was to build as far as possible on the relevant skills already possessed by an OR group in the branch. The lessons learned from these are summarized in the hope that they will be of use to other groups who wish to become involved in this important area.  相似文献   
57.
58.
59.
What strategy should a football (soccer, in American parlance) club adopt when deciding whether to sack its manager? This paper introduces a simple model assuming that a club's objective is to maximize the number of league points that it scores per season. The club's strategy consists of three choices: the length of the honeymoon period during which it will not consider sacking a new manager, the level of the performance trapdoor below which the manager get the sack, and the weight that it will give to more recent games compared to earlier ones. Some data from the last six seasons of the English Premiership are used to calibrate the model. At this early stage of the research, the best strategy appears to have only a short honeymoon period of eight games (much less than the actual shortest period of 12 games), to set the trapdoor at 0.74 points per game, and to put 47% of the weight on the last five games. A club adopting this strategy would obtain on average 56.8 points per season, compared to a Premiership average of 51.8 points.  相似文献   
60.
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