全文获取类型
收费全文 | 62633篇 |
免费 | 1060篇 |
国内免费 | 532篇 |
专业分类
化学 | 33903篇 |
晶体学 | 489篇 |
力学 | 2165篇 |
综合类 | 12篇 |
数学 | 14522篇 |
物理学 | 13134篇 |
出版年
2022年 | 327篇 |
2021年 | 474篇 |
2020年 | 568篇 |
2019年 | 521篇 |
2018年 | 1563篇 |
2017年 | 1817篇 |
2016年 | 1565篇 |
2015年 | 1309篇 |
2014年 | 1305篇 |
2013年 | 2420篇 |
2012年 | 4998篇 |
2011年 | 4695篇 |
2010年 | 2984篇 |
2009年 | 2582篇 |
2008年 | 2640篇 |
2007年 | 2707篇 |
2006年 | 2649篇 |
2005年 | 6273篇 |
2004年 | 5499篇 |
2003年 | 3703篇 |
2002年 | 1812篇 |
2001年 | 715篇 |
2000年 | 514篇 |
1999年 | 563篇 |
1998年 | 466篇 |
1997年 | 444篇 |
1996年 | 566篇 |
1995年 | 417篇 |
1994年 | 363篇 |
1993年 | 312篇 |
1992年 | 454篇 |
1991年 | 402篇 |
1990年 | 350篇 |
1989年 | 314篇 |
1988年 | 337篇 |
1987年 | 265篇 |
1986年 | 232篇 |
1985年 | 403篇 |
1984年 | 386篇 |
1983年 | 281篇 |
1982年 | 345篇 |
1981年 | 354篇 |
1980年 | 319篇 |
1979年 | 315篇 |
1978年 | 290篇 |
1977年 | 251篇 |
1976年 | 286篇 |
1975年 | 253篇 |
1974年 | 256篇 |
1973年 | 260篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
Asymptotics in the random assignment problem 总被引:1,自引:0,他引:1
David Aldous 《Probability Theory and Related Fields》1992,93(4):507-534
Summary We show that, in the usual probabilistic model for the random assignment problem, the optimal cost tends to a limit constant in probability and in expectation. The method involves construction of an infinite limit structure, in terms of which the limit constant is defined. But we cannot improve on the known numerical bounds for the limit.Research supported by NSF Grant MCS90-01710 相似文献
82.
F. Cannata J. P. Dedonder L. Le?niak 《Zeitschrift für Physik A Hadrons and Nuclei》1992,343(4):451-460
We investigate the origin of the attraction in theK¯K channel around the threshold by introducing an additional channel to theππ andK¯K channels in a separable potential formalism assuming, in general, no direct interaction in theK¯K channel. To reproduce the features of the data, we find that the threshold of the additional channel is much above thef 0(975) meson position. We show that this three-channel problem can be reduced to an effective two-channel problem where thef 0(975) behaves as if it were aK¯K molecule bound by the coupling to the exotic channel. This picture is also supported by the fact that a single pole only, in the complexK¯K momentum plane, is associated to thef 0(975) meson. Various physical observables, like the decay branching ratio and theK¯K scattering length, are then discussed in an effective two-channel framework. 相似文献
83.
Eschweiler-Clarke methylations of both acyclic and cyclic polyamines can lead to methylation products of fragments of the original polyamine; thus 1,5,9,13-tetra-azatridecane yields 1,1,3,3-tetramethylpropanediamine exclusively and 1,5,9-triazacyclododecane gives 45% 1,5,9-trimethyl-1,5,9-triazacyclodecane and 45% 2,6,10-trimethyl-2,6,10-triazaundecane. 相似文献
84.
Dorota G?azowska Janusz Matkowski 《Journal of Mathematical Analysis and Applications》2007,331(2):1187-1199
The invariance of the geometric mean G with respect to the Lagrangian mean-type mapping (Lf,Lg), i.e. the equation G○(Lf,Lg)=G, is considered. We show that the functions f and g must be of high class regularity. This fact allows to reduce the problem to a differential equation and determine the second derivatives of the generators f and g. 相似文献
85.
In the paper we indicate an error made in the proof of the main result of the paper [M.A. Darwish, On quadratic integral equation of fractional orders, J. Math. Anal. Appl. 311 (2005) 112-119]. Moreover, we provide correct proof of a slightly modified version of the mentioned result. The main tool used in our proof is the technique associated with the Hausdorff measure of noncompactness. 相似文献
86.
87.
In this paper we deal with nonlinear second-order boundary value problems with impulses. The impulsive functions depend implicitly on the different considered variables and the boundary value conditions are nonlinear. In both cases functional dependence on the solution is allowed. The existence results follow from the existence of a pair of well-ordered lower and upper solutions. 相似文献
88.
François Loiseau Jean-Mary Simone David Carcache Pavel Bobal Reinhard Neier 《Monatshefte für Chemie / Chemical Monthly》2007,138(2):121-129
Summary. Free radical couplings from furan, as cheap starting material, were studied in view of developing a rapid strategy en route to the synthesis of derivatives of nonactin. The chain containing the alcohol function was introduced in one or two steps
in 86% yield. For the introduction of the second chain with the ester function two different coupling methods were tested.
Starting from the advanced intermediates obtained nonactin derivatives can be prepared by catalytic hydrogenation of the furan
ring. 相似文献
89.
David Worthington 《The Journal of the Operational Research Society》1991,42(10):833-843
This paper describes work carried out with hospital consultants in Lancaster District Health Authority to develop and use computerized waiting list management models. The ‘what if?’ models produced have been found to be a very useful tool in the constructive debate about problems faced by consultants and managers, and of the options available to them. 相似文献
90.