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   10189篇
  免费   429篇
  国内免费   87篇
化学   6988篇
晶体学   91篇
力学   266篇
综合类   1篇
数学   1738篇
物理学   1621篇
  2023年   77篇
  2022年   56篇
  2021年   187篇
  2020年   209篇
  2019年   250篇
  2018年   158篇
  2017年   159篇
  2016年   384篇
  2015年   288篇
  2014年   321篇
  2013年   604篇
  2012年   607篇
  2011年   653篇
  2010年   453篇
  2009年   404篇
  2008年   586篇
  2007年   632篇
  2006年   494篇
  2005年   547篇
  2004年   440篇
  2003年   350篇
  2002年   336篇
  2001年   162篇
  2000年   144篇
  1999年   96篇
  1998年   99篇
  1997年   88篇
  1996年   99篇
  1995年   89篇
  1994年   80篇
  1993年   95篇
  1992年   74篇
  1991年   76篇
  1990年   69篇
  1989年   64篇
  1988年   48篇
  1987年   54篇
  1986年   64篇
  1985年   102篇
  1984年   99篇
  1983年   77篇
  1982年   66篇
  1981年   70篇
  1980年   62篇
  1979年   64篇
  1978年   67篇
  1977年   41篇
  1976年   40篇
  1975年   50篇
  1974年   53篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
The crystals of the title compound, [Mg(C32H16N8)(H2O)]·2C3H9N, are built up from MgPc(H2O) [Pc is phthalo­cyaninate(2−)] and n‐propyl­amine mol­ecules that inter­act via O—H⋯N hydrogen bonds. The MgPc(H2O) mol­ecule is non‐planar. The central Mg atom is coordinated by the four equatorial isoindole N atoms of the Pc ring system and by the O atom of an axial water mol­ecule. The Mg atom is displaced by 0.509 (1) Å from the N4 plane towards the water O atom. MgPc(H2O)·2(n‐propyl­amine) mol­ecules related by the inversion centre are linked by N—H⋯O hydrogen bonds to form a dimeric aggregate.  相似文献   
72.
Modelling financial and insurance time series with Lévy processes or with exponential Lévy processes is a relevant actual practice and an active area of research. It allows qualitatively and quantitatively good adaptation to the empirical statistical properties of asset returns. Due to model incompleteness it is a problem of considerable interest to determine the dependence of option prices in these models on the choice of pricing measures and to establish nontrivial price bounds. In this paper we review and extend ordering results of stochastic and convex type for this class of models. We also extend the ordering results to processes with independent increments (PII) and present several examples and applications as to α-stable processes, NIG-processes, GH-distributions, and others. Criteria are given for the Lévy measures which imply corresponding comparison results for European type options in (exponential) Lévy models.  相似文献   
73.
74.
75.
Let be a bounded, connected linearly convex set in with boundary. We show that the maximal ideal (both in ) and ) consisting of all functions vanishing at is generated by the coordinate functions . Received: 2 July 2001; in final form: 26 September 2001 / Published online: 28 February 2002  相似文献   
76.
77.
A multivalued version of Sharkovskiĭ’s theorem is formulated for M-maps on linear continua and, more generally, for triangular M-maps on a Cartesian product of linear continua. This improves the main result of [AP1] in the sense that our multivalued analogue holds with at most two exceptions. A further specification requires some additional restrictions. For instance, 3- orbits of m-maps imply the existence of k-orbits for all k ? \mathbbNk \in {\mathbb{N}} , except possibly for k ?k \in {4, 6}. It is also shown that, on every connected linearly ordered topological space, an M-map with orbits of all periods can always be constructed. This demonstrates that Baldwin’s classification of linear continua in terms of admissible periods [Ba] is useless for multivalued maps.  相似文献   
78.
We present a construction which shows that some special continua do not have the nonwandering-eventually-periodic property. The construction applies e.g. to the topologist's sin curve and to the harmonic fan.  相似文献   
79.
We investigate traces of functions, belonging to a class of functions with dominating mixed smoothness in ℝ3, with respect to planes in oblique position. In comparison with the classical theory for isotropic spaces a few new phenomenona occur. We shall present two different approaches. One is based on the use of the Fourier transform and restricted to p = 2. The other one is applicable in the general case of Besov-Lizorkin-Triebel spaces and based on atomic decompositions.  相似文献   
80.
The stoichiometric reactions of trimethylaluminum with 2,6‐(MeOCH2)2C6H3OH (LH) revealed compounds L3Al ( 1 ) and L2AlMe ( 2 ). On the other hand reaction of 1 equiv. of LH with trimethylaluminum did not lead to the formation of complex LAlMe2 ( 3 ), rather 2 together with Me3Al were observed as a result of a disproportionation of 3 . Compounds 1 and 2 were characterized by elemental analysis, 1H and 13C NMR spectroscopy and in the case of 1 by X‐ray diffraction. Derivative 2 underwent transmetalation with Ph3SnOH, giving LSnPh3 ( 4 ) as the result of a migration of ligand L from the aluminum to the tin atom. The identity of 4 was established by elemental analysis, 1H, 13C and 119Sn NMR spectroscopy and 1H, 119Sn HMBC experiments. The system 2 and B(C6F5)3 in a 1:1 molar ratio was shown to be active in the polymerization of propylene oxide and ε‐caprolactone. Copyright © 2007 John Wiley & Sons, Ltd.  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