全文获取类型
收费全文 | 57383篇 |
免费 | 3812篇 |
国内免费 | 2039篇 |
专业分类
化学 | 30399篇 |
晶体学 | 536篇 |
力学 | 2669篇 |
综合类 | 80篇 |
数学 | 12762篇 |
物理学 | 16788篇 |
出版年
2023年 | 474篇 |
2022年 | 681篇 |
2021年 | 921篇 |
2020年 | 979篇 |
2019年 | 1009篇 |
2018年 | 2055篇 |
2017年 | 2152篇 |
2016年 | 2058篇 |
2015年 | 1655篇 |
2014年 | 1839篇 |
2013年 | 2650篇 |
2012年 | 5374篇 |
2011年 | 4653篇 |
2010年 | 3374篇 |
2009年 | 2987篇 |
2008年 | 2323篇 |
2007年 | 2264篇 |
2006年 | 2073篇 |
2005年 | 5692篇 |
2004年 | 4892篇 |
2003年 | 3044篇 |
2002年 | 1255篇 |
2001年 | 784篇 |
2000年 | 514篇 |
1999年 | 660篇 |
1998年 | 491篇 |
1997年 | 475篇 |
1996年 | 451篇 |
1995年 | 383篇 |
1994年 | 343篇 |
1993年 | 341篇 |
1992年 | 391篇 |
1991年 | 394篇 |
1990年 | 341篇 |
1989年 | 277篇 |
1988年 | 241篇 |
1987年 | 183篇 |
1986年 | 179篇 |
1985年 | 197篇 |
1984年 | 191篇 |
1983年 | 135篇 |
1982年 | 121篇 |
1981年 | 114篇 |
1980年 | 107篇 |
1979年 | 104篇 |
1978年 | 105篇 |
1976年 | 135篇 |
1975年 | 102篇 |
1974年 | 106篇 |
1973年 | 100篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
111.
It can be conjectured that the colored Jones function of a knot can be computed in terms of counting paths on the graph of
a planar projection of a knot. On the combinatorial level, the colored Jones function can be replaced by its weight system.
We give two curious formulas for the weight system of a colored Jones function: one in terms of the permanent of a matrix
associated to a chord diagram, and another in terms of counting paths of intersecting chords.
Electronic supplementary material to this article is available at and is accessible to authorized users.
* S. G. was partially supported by an NSF and by an Israel-US BSF grant.
† M. L. was partly supported by GAUK 158 grant and by the Project LN00A056 of the Czech Ministry of Education. 相似文献
112.
We study a class of shape optimization problems for semi-linear elliptic equations with Dirichlet boundary conditions in smooth
domains in ℝ2. A part of the boundary of the domain is variable as the graph of a smooth function. The problem is equivalently reformulated
on a fixed domain. Continuity of the solution to the state equation with respect to domain variations is shown. This is used
to obtain differentiability in the general case, and moreover a useful formula for the gradient of the cost functional in
the case where the principal part of the differential operator is the Laplacian.
Online publication 23 January 2004. 相似文献
113.
In this paper, by means of the method of upper and lower solutions and monotone iterative technique, the existence of maximal and minimal solutions of the boundary value problems for first order impulsive delay differential equations is established. 相似文献
114.
Il Bong Jung Alan Lambert Jan Stochel 《Proceedings of the American Mathematical Society》2004,132(8):2291-2302
The concept of backward extension for subnormal weighted shifts is generalized to arbitrary subnormal operators. Several differences and similarities in these contexts are explored, with emphasis on the structure of the underlying measures.
115.
116.
We perform three tests on our proposal to implement diffeomorphism invariance in the non-abelian D0-brane DBI action as a base-point independence constraint between matrix Riemann normal coordinate systems. First, we show that T-duality along an isometry correctly interchanges the potential and kinetic terms in the action. Second, we show that the method to impose base-point independence using an auxiliary dN2-dimensional nonlinear sigma model also works for metrics which are curved along the brane, provided a physical gauge choice is made at the end. Third, we show that without alteration this method is applicable to higher order in velocities. Testing specifically to order 4, we elucidate the range of validity of the symmetrized trace approximation to the non-abelian DBI action. 相似文献
117.
118.
Abnormalities in the cochlear function usually cause broadening of the auditory filters which reduces the speech intelligibility. An attempt to apply a spectral enhancement algorithm has been undertaken to improve the identification of Polish vowels by subjects with cochlear-based hearing-impairment. The identification scores of natural (unprocessed) vowels and spectrally enhanced (processed) vowels has been measured for hearing-impaired subjects. It has been found that spectral enhancement improves vowel scores by about 10% for those subjects, however, a wide variation in individual performance among subjects has been observed. The overall vowels identification scores obtained were 85% for natural vowels and 96% for spectrally enhanced vowels. 相似文献
119.
Hamid R. Memarian Mohammad Bagheri Dietrich D?pp 《Monatshefte für Chemie / Chemical Monthly》2004,42(3):833-838
In continuation of previous work some novel 3,5-diacetyl-1,4-dihydropyridine derivatives were synthesized and their photochemical behavior was studied under oxygen and argon atmosphere. Oxidation of the dihydropyridine ring and formation of pyridine derivatives was the result of the reaction. The presence of oxygen affects not only on the rate of oxidation, but also the formation of some unidentified by-products was observed on irradiation under this atmosphere. 相似文献
120.