全文获取类型
收费全文 | 230459篇 |
免费 | 24087篇 |
国内免费 | 17330篇 |
专业分类
化学 | 128861篇 |
晶体学 | 2368篇 |
力学 | 15801篇 |
综合类 | 1125篇 |
数学 | 50477篇 |
物理学 | 73244篇 |
出版年
2024年 | 497篇 |
2023年 | 2943篇 |
2022年 | 5203篇 |
2021年 | 5639篇 |
2020年 | 5911篇 |
2019年 | 5656篇 |
2018年 | 14413篇 |
2017年 | 13834篇 |
2016年 | 12526篇 |
2015年 | 7925篇 |
2014年 | 9076篇 |
2013年 | 11794篇 |
2012年 | 17190篇 |
2011年 | 23697篇 |
2010年 | 14935篇 |
2009年 | 14916篇 |
2008年 | 16063篇 |
2007年 | 17148篇 |
2006年 | 8670篇 |
2005年 | 8372篇 |
2004年 | 7106篇 |
2003年 | 6346篇 |
2002年 | 5037篇 |
2001年 | 3749篇 |
2000年 | 3438篇 |
1999年 | 3547篇 |
1998年 | 3075篇 |
1997年 | 2704篇 |
1996年 | 2812篇 |
1995年 | 2427篇 |
1994年 | 2201篇 |
1993年 | 1859篇 |
1992年 | 1639篇 |
1991年 | 1430篇 |
1990年 | 1184篇 |
1989年 | 995篇 |
1988年 | 765篇 |
1987年 | 715篇 |
1986年 | 657篇 |
1985年 | 587篇 |
1984年 | 418篇 |
1983年 | 355篇 |
1982年 | 299篇 |
1981年 | 225篇 |
1980年 | 182篇 |
1979年 | 118篇 |
1978年 | 112篇 |
1976年 | 87篇 |
1975年 | 95篇 |
1973年 | 99篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
X Y Liu C J Li 《Science in China. Series B, Chemistry, life sciences & earth sciences》1989,32(10):1215-1223
To further evaluate the causality between endogenous pyrogen (EP)-induced fever and cyclic adenosine-3',5'-monophosphate (cyclic AMP) level, the effects of sodium salicylate (SS) on the febrile response and increased levels of cyclic AMP in both cerebrospinal fluid (c.s.f.) and plasma during EP-induced fever in rabbits were observed. The results suggest that cyclic AMP is probably involved in the central mediation of EP-induced fever and that increased concentration of cyclic AMP in c.s.f. associated with EP-induced fever is not the result of temperature elevation but appears to be caused by the increased synthesis in the central nervous system. In addition it is confirmed that blood is impossibly a contributory source of increased cyclic AMP in c.s.f. during EP fever, and that SS may act subsequent to the increase in cyclic AMP. 相似文献
42.
Q. B. Li 《Optics and Lasers in Engineering》1989,11(2)
The smoothing spline function has been used for differentiation of photomechanical data in experimental stress analysis. However, since the available software packages use the algorithm with the so-called natural boundary conditions which are not necessarily suitable in many circumstances, errors tend to occur in both the first and second derivatives. In this paper we have modified the algorithm so that the user can have more freedom in selecting boundary conditions which suit the problem best and therefore, as a result, improve the accuracy of the analysis. Two examples are given to show the improvement achievable using the new scheme. 相似文献
43.
Singlet-Triplet Transition in Quantum Dots Confined by Triangular and Bowl-Like Potentials: the Effect of Electric Fields 下载免费PDF全文
We theoretically investigate the energy spectra of two-electron two-dimensional (2e 2D) quantum dots (QDs) confined by triangular potentials and bowl-like potentials in a magnetic field by exact diagonalization in the framework of effective mass theory. An in-plane electric field is found to contribute to the singlet-triplet transition of the ground state of the 2e 2D QDs confined by triangular or bowl-like potentials in a perpendicular magnetic field. The stronger the in-plane electric field, the smaller the magnetic field for the total spin of the ground states in the dot systems to change from S = 0 to S = 1. However, the influence of an in-plane electric field on the singlettriplet transition of the ground state of two electrons in a triangular QD modulated by a perpendicular magnetic field is quite small because the triangular potential just deviates from the harmonic potential well slightly. We find that the strength of the perpendicular magnetic field needed for the spin singlet-triplet transition of the ground state of the QD confined by a bowl-like potential is reduced drastically by applying an in-plane electric field. 相似文献
44.
The semi‐iterative method (SIM) is applied to the hyper‐power (HP) iteration, and necessary and sufficient conditions are given for the convergence of the semi‐iterative–hyper‐power (SIM–HP) iteration. The root convergence rate is computed for both the HP and SIM–HP methods, and the quotient convergence rate is given for the HP iteration. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
45.
46.
Nonlocal vertex algebras generated by formal vertex operators 总被引:2,自引:0,他引:2
Haisheng Li 《Selecta Mathematica, New Series》2005,11(3-4):349-397
This is the first paper in a series to study vertex algebra-like objects arising from infinite-dimensional quantum groups
(quantum affine algebras and Yangians). In this paper we lay the foundations for this study. For any vector space W, we study what we call quasi compatible subsets of Hom (W,W((x))) and we prove that any maximal quasi compatible subspace has a natural nonlocal (namely noncommutative) vertex algebra
structure with W as a natural faithful quasi module in a certain sense, and that any quasi compatible subset generates a nonlocal vertex algebra
with W as a quasi module. In particular, taking W to be a highest weight module for a quantum affine algebra we obtain a nonlocal vertex algebra with W as a quasi module. We also formulate and study a notion of quantum vertex algebra and we give general constructions of nonlocal
vertex algebras, quantum vertex algebras and their modules. 相似文献
47.
In this paper we obtain a number of Maharam-type slice integral representations, with respect to scalar measures, for positive
projections in Dedekind complete vector lattices and f-algebras.
AMS Classification: 47B65, 46A40, 06F25 相似文献
48.
Compact, time‐harmonic, acoustic sources produce waves that decay too slowly to be square‐integrable on a line away from the sources. We introduce an inner product, arising directly from Green's second theorem, to form a Hilbert space of these waves and present examples of its computation.1 © 2005 Wiley Periodicals, Inc. 相似文献
49.
M. Lashkarizadeh Bami 《Semigroup Forum》2004,69(2):219-229
In the present paper it is shown that if S1 and S2 are two
Clifford topological semigroups satisfying certain conditions
and T is an isometric isomorphism of LUC(S1*) onto LUC(S2*), then T
maps S1 topologically isomorphically onto S2. Furthermore, T
maps M
l
n(S1) (M(S1), respectively) isometrically
isomorphically onto M
l
n(S2) (M(S2), respectively). Indeed,
we have obtained a generalization of a well-known result of
Ghahramani, Lau and Losert for locally compact groups to a more
general setting of Clifford topological semigroups. 相似文献
50.
Andrew Barton 《The Journal of the Operational Research Society》1987,38(10):965-974
This paper describes some work carried out in the Scientific Research and Development Branch (SRDB) of the Home Office, intended to contribute to an overall aim of building up internal expertise in the field of expert systems. This was done by carrying out a number of pilot and demonstrator projects, two of which are described in some detail. The plan, which proved successful, was to build as far as possible on the relevant skills already possessed by an OR group in the branch. The lessons learned from these are summarized in the hope that they will be of use to other groups who wish to become involved in this important area. 相似文献