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   18979篇
  免费   1610篇
  国内免费   1184篇
化学   10085篇
晶体学   113篇
力学   72篇
综合类   54篇
数学   9591篇
物理学   1858篇
  2024年   31篇
  2023年   307篇
  2022年   246篇
  2021年   254篇
  2020年   491篇
  2019年   595篇
  2018年   587篇
  2017年   382篇
  2016年   551篇
  2015年   664篇
  2014年   990篇
  2013年   1604篇
  2012年   900篇
  2011年   1235篇
  2010年   1091篇
  2009年   1272篇
  2008年   1352篇
  2007年   1342篇
  2006年   1056篇
  2005年   761篇
  2004年   708篇
  2003年   673篇
  2002年   561篇
  2001年   385篇
  2000年   408篇
  1999年   429篇
  1998年   381篇
  1997年   247篇
  1996年   297篇
  1995年   328篇
  1994年   284篇
  1993年   209篇
  1992年   184篇
  1991年   82篇
  1990年   82篇
  1989年   74篇
  1988年   70篇
  1987年   48篇
  1986年   44篇
  1985年   75篇
  1984年   78篇
  1983年   27篇
  1982年   80篇
  1981年   58篇
  1980年   41篇
  1979年   39篇
  1978年   42篇
  1977年   30篇
  1976年   33篇
  1975年   22篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
The qualitative behavior of buckled states of two different models of elastic beams is studied. It is assumed that random imperfections affect the governing nonlinear equations. It is shown that near the first critical value of the buckling load the stochastic bifurcation is described asymptotically by an algebraic equation whose coeffficients are Gaussian random variables. The corresponding asymptotic expansion for the displacement is to lowest order a Gaussian stochastic process.Work supported by NSF Grant No. DCR81-14726.Work supported by NSF Grant No. DMS87-01895.  相似文献   
102.
In this paper we study the Calabi diastasis function of Hermitian symmetric spaces. This allows us to prove that if a complete Hermitian locally symmetric space (M,g) admits a Kähler immersion into a globally symmetric space (S,G) then it is globally symmetric and the immersion is injective. Moreover, if (S,G) is symmetric of a specified type (Euclidean, noncompact, compact), then (M,g) is of the same type. We also give a characterization of Hermitian globally symmetric spaces in terms of their diastasis function. Finally, we apply our analysis to study the balanced metrics, introduced by Donaldson, in the case of locally Hermitian symmetric spaces.  相似文献   
103.
本文对二种新合成的2,3-二羟基萘二钼和四钼多酸有机衍生物[n-Bu)4N]2[Mo2O5(OC10H6O)2](Ⅰ)和[n-Bu)4N]2[Mo4O10(OC10H6O)2(OCH3)2](Ⅱ)进行了红外光谱与核磁共振波谱研究,发现[Mo2O5]^2 中钼氧多桥键的红外振动频率较[Mo4O10(OCH3)2]^2 中钼氧多桥键的红外振动频率红移,而在配合物Ⅱ中2,3-二羟基中芳环的^1H化学位移较配合物Ⅰ中向低场移动。同时还发现含二钼配位中心[Mo2O5]^2 的[Mo2O5(OC10H6O)2]^2-与含四钼配位中心[Mo4O10(OCH3)2]^2 的[Mo4O10(OC10H6O)2(OCH3)2]^2-生成条件的差异仅仅只在反应体系的pH值的微小变化,说明钼多酸有机衍生物阴离子是对体系酸碱度极为敏感的物质。  相似文献   
104.
Common fixed-point results are established for a new class of noncommuting selfmaps. We apply them to obtain several invariant approximation results which unify, extend, and complement well-known results.  相似文献   
105.
Higher spin extensions of the non-Abelian gauge symmetries for the classical WZNW model are considered. Both linear and nonlinear realizations of the extended affine Kac-Moody algebra are obtained. It is a characteristic property of the WZNW model that it admits a higher spin linear realization of the extended affine Kac-Moody algebra which is equivalent to the corresponding higher spin nonlinear realization of the same algebra. However, in both cases, the higher spin Noether currents do not span an invariant space with respect to their generating transformations. Here, the current space is extended to an invariant space which allows us to gauge the symmetry.Supported by Bulgarian Foundation on Fundamental Research under contract Ph-318/93-95.  相似文献   
106.
Multiderivations of Coxeter arrangements   总被引:3,自引:0,他引:3  
Let V be an ℓ-dimensional Euclidean space. Let GO(V) be a finite irreducible orthogonal reflection group. Let ? be the corresponding Coxeter arrangement. Let S be the algebra of polynomial functions on V. For H∈? choose α H V * such that H=ker(α H ). For each nonnegative integer m, define the derivation module D (m) (?)={θ∈Der S |θ(α H )∈Sα m H }. The module is known to be a free S-module of rank ℓ by K. Saito (1975) for m=1 and L. Solomon-H. Terao (1998) for m=2. The main result of this paper is that this is the case for all m. Moreover we explicitly construct a basis for D (m) (?). Their degrees are all equal to mh/2 (when m is even) or are equal to ((m−1)h/2)+m i (1≤i≤ℓ) (when m is odd). Here m 1≤···≤m are the exponents of G and h=m +1 is the Coxeter number. The construction heavily uses the primitive derivation D which plays a central role in the theory of flat generators by K. Saito (or equivalently the Frobenius manifold structure for the orbit space of G). Some new results concerning the primitive derivation D are obtained in the course of proof of the main result. Oblatum 27-XI-2001 & 4-XII-2001?Published online: 18 February 2002  相似文献   
107.
A series of noncyclic neutral ionophores has been synthesized by the reaction of oligoethylene glycol dihalides with 8-quinolinol. Complexation properties for alkali metal picrates were evaluated from solvent extraction and bulk liquid membrane transport experiments. Complexation profiles of the newly synthesized ionophores with a hexyl chain were similar to those of their homologues without the hexyl chain in the extraction experiments. Among them, the pentaethylene glycol derivatives showed the highest extraction efficiency and selectivity towards potassium ion. From the1H NMR spectra (400 MHz), the change in chemical shifts of the aromatic protons upon the addition of alkali metal thiocyanates suggested the existence of a stabilization effect which is caused by intramolecular stacking conformations between the quinoline rings during complexation. Aryl stacking interactions depend on the size of the cations and on the chain length of the oligoethylene glycol. The relationship between transport ability towards alkali metal cations and lipophilicity of these ionophores is also discussed.  相似文献   
108.
Summary We show that each holomorphic Wiener function has a skeleton which is intrinsic from several viewpoints. In particular, we study the topological aspects of the skeletons by using the local Taylor expansion for holomorphic Wiener functions.Supported in part by the Grant-in-Aid for Science Research 03740120 Min. Education  相似文献   
109.
Here we prove that every compact differential manifold has a smooth algebraic model defined over Q. In dimension 2 we find an algebraic model (may be singular) defined over Q and birational over Q to the projective plane.  相似文献   
110.
We find a new class of Fuchsian equations, with algebro-geometric solutions associated to a hyperelliptic curve. A method for calculating its arithmetic genus and branching points is suggested. Numerous examples are given.  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