全文获取类型
收费全文 | 7549篇 |
免费 | 772篇 |
国内免费 | 550篇 |
专业分类
化学 | 1393篇 |
晶体学 | 32篇 |
力学 | 742篇 |
综合类 | 138篇 |
数学 | 5220篇 |
物理学 | 1346篇 |
出版年
2024年 | 14篇 |
2023年 | 99篇 |
2022年 | 113篇 |
2021年 | 131篇 |
2020年 | 197篇 |
2019年 | 196篇 |
2018年 | 224篇 |
2017年 | 239篇 |
2016年 | 266篇 |
2015年 | 214篇 |
2014年 | 320篇 |
2013年 | 683篇 |
2012年 | 375篇 |
2011年 | 377篇 |
2010年 | 303篇 |
2009年 | 415篇 |
2008年 | 466篇 |
2007年 | 469篇 |
2006年 | 406篇 |
2005年 | 369篇 |
2004年 | 342篇 |
2003年 | 299篇 |
2002年 | 277篇 |
2001年 | 250篇 |
2000年 | 242篇 |
1999年 | 206篇 |
1998年 | 169篇 |
1997年 | 163篇 |
1996年 | 159篇 |
1995年 | 93篇 |
1994年 | 96篇 |
1993年 | 66篇 |
1992年 | 73篇 |
1991年 | 62篇 |
1990年 | 46篇 |
1989年 | 40篇 |
1988年 | 38篇 |
1987年 | 42篇 |
1986年 | 36篇 |
1985年 | 34篇 |
1984年 | 36篇 |
1983年 | 26篇 |
1982年 | 25篇 |
1981年 | 26篇 |
1980年 | 27篇 |
1979年 | 30篇 |
1978年 | 25篇 |
1977年 | 20篇 |
1976年 | 23篇 |
1974年 | 9篇 |
排序方式: 共有8871条查询结果,搜索用时 15 毫秒
31.
The Mannich-type reaction of imines with (1-methoxy-2-methylpropenyloxy)trimethylsilane and aza-Diels-Alder reaction of imines with Danishefsky's diene can be carried out in scCO2 in the presence of lithium heptadecafluorooctanesulfonate which offer a way to synthesize β-amino carbonyl compounds and nitrogen-containing six-membered ring compounds under environmentally benign conditions. 相似文献
32.
Jack Harrowfield Dominique Matt 《Journal of inclusion phenomena and macrocyclic chemistry》2004,50(3-4):133-150
The problems involved in identifying and quantifying labile interactions considered to influence complex compound structures are highlighted through the assessment of four different families of metal complexes for which extensive crystallographic data are available. Modification of the charge distribution within a ligand molecule as a result of coordination is one factor with a number of ramifications. A detailed analysis of evidence for both intra- and inter-molecular attractions in dimethylsulfoxide complexes of metal perchlorates is used to provide a basis for the consideration of weak interactions between complex ions involving forces including phenyl-group attractions, hydrogen bonding and cavity inclusion. 相似文献
33.
T′相R2CuO4稀土铜氧化合物由于尺度效应而产生弱铁磁性行为已经被人们关注,报导了通过高温高氧压(6GPa,1000℃)合成稀土T′相R2CuO4(R=Nd,Sm,Eu,Gd,Tb,Dy,Ho,Er和Tm)化合物的结构和磁学性能。磁化率曲线显示,在低温下所有的高压增氧R2CuO4样品都出现新的低温弱铁磁性反常行为,转变温度在28K附近。新的低温弱铁磁性行为是由于CuO2面上微量氧空穴的掺入,使处于反铁磁有序CuO2面形成局域化的铁磁性团簇造成。实验证明新发现的低温弱铁磁性行为与尺度效应产生弱铁磁性行为属于完全不同的物理机制。结果还预示T′相R2CuO4稀土铜氧化合物很难通过空穴掺杂而实现超导。 相似文献
34.
We introduce extensions of the Mangasarian-Fromovitz and Abadie constraint qualifications to nonsmooth optimization problems with feasibility given by means of lower-level sets. We do not assume directional differentiability, but only upper semicontinuity of the defining functions. By deriving and reviewing primal first-order optimality conditions for nonsmooth problems, we motivate the formulations of the constraint qualifications. Then, we study their interrelation, and we show how they are related to the Slater condition for nonsmooth convex problems, to nonsmooth reverse-convex problems, to the stability of parametric feasible set mappings, and to alternative theorems for the derivation of dual first-order optimality conditions.In the literature on general semi-infinite programming problems, a number of formally different extensions of the Mangasarian-Fromovitz constraint qualification have been introduced recently under different structural assumptions. We show that all these extensions are unified by the constraint qualification presented here. 相似文献
35.
For vector quasivariational inequalities involving multifunctions in topological vector spaces, an existence result is obtained without a monotonicity assumption and with a convergence assumption weaker than semicontinuity. A new type of quasivariational inequality is proposed. Applications to quasicomplementarity problems and traffic network equilibria are considered. In particular, definitions of weak and strong Wardrop equilibria are introduced for the case of multivalued cost functions. 相似文献
36.
Patrick Guidotti 《Mathematische Nachrichten》2004,272(1):32-45
We consider elliptic and parabolic problems in unbounded domains. We give general existence and regularity results in Besov spaces and semi‐explicit representation formulas via operator‐valued fundamental solutions which turn out to be a powerful tool to derive a series of qualitative results about the solutions. We give a sample of possible applications including asymptotic behavior in the large, singular perturbations, exact boundary conditions on artificial boundaries and validity of maximum principles. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
37.
Sergue A. Nazarov Maria Specovius‐Neugebauer 《Mathematical Methods in the Applied Sciences》2004,27(13):1507-1544
The approximation of solutions to boundary value problems on unbounded domains by those on bounded domains is one of the main applications for artificial boundary conditions. Based on asymptotic analysis, here a new method is presented to construct local artificial boundary conditions for a very general class of elliptic problems where the main asymptotic term is not known explicitly. Existence and uniqueness of approximating solutions are proved together with asymptotically precise error estimates. One class of important examples includes boundary value problems for anisotropic elasticity and piezoelectricity. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
38.
A. Azizi 《Czechoslovak Mathematical Journal》2003,53(3):529-534
In this paper we characterize weak multiplication modules. 相似文献
39.
G.N. Gatica 《Applied Mathematics Letters》1997,10(6):29-35
We study the solvability and Galerkin approximation of an exterior hyperelastic interface problem arising in plane elasticity. The weak formulation is obtained from an appropriate combination of a mixed finite element approach with a Dirichlet-to-Neumann method. The derivation of our results is based on some tools from nonlinear functional analysis and the Babuska-Brezzi theory for variational problems with constraints. 相似文献
40.
OU型Markov过程的不变测度及弱对偶性 总被引:1,自引:1,他引:0
本文研究OU型Markov过程的不变测度、参考测度和弱对偶半群的存在性问题,并得出了不变测度的唯一性。 相似文献