全文获取类型
收费全文 | 7734篇 |
免费 | 320篇 |
国内免费 | 34篇 |
专业分类
化学 | 6313篇 |
晶体学 | 54篇 |
力学 | 99篇 |
数学 | 926篇 |
物理学 | 696篇 |
出版年
2024年 | 6篇 |
2023年 | 79篇 |
2022年 | 290篇 |
2021年 | 430篇 |
2020年 | 236篇 |
2019年 | 236篇 |
2018年 | 198篇 |
2017年 | 164篇 |
2016年 | 316篇 |
2015年 | 230篇 |
2014年 | 318篇 |
2013年 | 488篇 |
2012年 | 533篇 |
2011年 | 581篇 |
2010年 | 392篇 |
2009年 | 298篇 |
2008年 | 481篇 |
2007年 | 455篇 |
2006年 | 421篇 |
2005年 | 323篇 |
2004年 | 279篇 |
2003年 | 204篇 |
2002年 | 183篇 |
2001年 | 98篇 |
2000年 | 67篇 |
1999年 | 48篇 |
1998年 | 55篇 |
1997年 | 43篇 |
1996年 | 55篇 |
1995年 | 39篇 |
1994年 | 34篇 |
1993年 | 38篇 |
1992年 | 32篇 |
1991年 | 33篇 |
1990年 | 25篇 |
1989年 | 32篇 |
1988年 | 21篇 |
1987年 | 22篇 |
1986年 | 28篇 |
1985年 | 45篇 |
1984年 | 24篇 |
1983年 | 17篇 |
1982年 | 29篇 |
1981年 | 21篇 |
1980年 | 22篇 |
1979年 | 12篇 |
1978年 | 6篇 |
1977年 | 9篇 |
1976年 | 9篇 |
1932年 | 5篇 |
排序方式: 共有8088条查询结果,搜索用时 62 毫秒
951.
Atmospheric electricity measurements made during the last decade at Poona using balloon-borne sondes are briefly reviewed. The vertical distribution of potential gradient in the free atmosphere follows theoretical values only during the monsoon months, when the air is comparatively free from dust. During the summer months, the potential gradient is constant above the exchange layer and this is associated with the presence of the deep, dense dust layer that lies over the region and extends to over 10 km. into the atmosphere. The increase with height of the potential gradient above the 10 km. level during winter is shown to be closely related to the presence of the subtropical jet stream, which presumably transports electric charges to the upper levels over Poona. 相似文献
952.
A systematic study of the dependence of the collective quantities (energies and matrix elements of the E2, M1 and E0 moments) on the form of approximations to the potential energy V and the inertia tensor B is performed. Various approximations used up to now are tested. Macroscopic-microscopic values for V and cranking results for B are taken as a reference. The collective quantities are calculated by solving the Schrödinger equation corresponding to the collective Bohr hamiltonian. The contribution of all nucleons is explicitly taken into account; no renormalization factors are used. Spherical, transitional and deformed even-even nuclei are considered. The quality of various approximations for V and B used in the boson-expansion method is discussed. Large effects of the microstructure of the inertia tensor B are obtained and commented on. 相似文献
953.
Summary The combined application of thermogravimetry reactiongas chromatography and gel-permeation chromatography permits to follow the heat degradation of polyurethane polymers in inert gas, air and water-saturated environment. The examinations give information on the rate of thermal degradation, the individual volatile degradation components, the critical points of the polymer chains and on the change of their molecular-weight distribution. Gas chromatographic examinations also permit the identification of the chain-extending components of different types of polyurethanes. 相似文献
954.
3-O-Methyl-6-deoxy-D -allose (V) and its methyl β-D -pyranoside (IV) have been synthesized and obtained in a crystalline state, although in low yield, starting from methyl 6-deoxy-β-D -allopyranoside (I) via the 2,4-di-O-benzoyl derivative II. 相似文献
955.
Anna Salvadori 《Rendiconti del Circolo Matematico di Palermo》1980,29(2):277-290
We introduce two new sufficient conditions for the existence of Burkill-Cesari integral: the «quasi additivity by refinement» and the «almost quasi additivity by refinement», that are intermediate between the well-known concepts of quasi additivity; moreover we study the behavior of these concepts in relation to subsets. 相似文献
956.
The Herrlich's problem from [8] whether there are nontrivial classes of topological spaces that are both almost reflective or injective and almost coreflective or projective, is investigated in a more general setting using cone and cocone modifications of the classes used in the problem. We look also at the problem for uniform spaces. Typical results: There is no nontrivial multiprojective and orthogonal class of topological spaces; There is a reflective class of uniform spaces that is almost coreflective in Unif.Work on this paper was initiated while the first author was a C.N.R. visitor of the University of L'Aquila. Partial financial assistence by Charles University Grant 349/1994 is also acknowledged. 相似文献
957.
Anna B. Druzhko † David J. Vanderah Baldwin Robertson Howard H. Weetall 《Photochemistry and photobiology》1996,64(5):867-869
Abstract— The photoinduced changes of absorbance as well as proton release and uptake have been observed for an azulenic analog of wild-type bacteriorhodopsin. The release and uptake of protons have been measured using a highly sensitive electrochemical technique. Bacteriorhodopsin membrane patches on a tin-oxide electrode produce a transient photocurrent that is negative for proton release and positive for proton uptake. For azulenic bacteriorhodopsin the photocurrent is approximately 20% of the transient observed with native bacteriorhodopsin. The existence of the photoinduced absorbance changes and the transient photocurrent are important results for gaining further insight into the photoinduced function of bacteriorhodopsin. 相似文献
958.
This paper shows that market equilibrium problems of production may generally be modelled as equilibrium flow problems in networks and that their equilibrium conditions can be visualized as a variational inequality. This connection would allow us to transplant directly elements of the well-developed theory of equilibrium flow in networks to the theory of market equilibrium. 相似文献
959.
960.
Let G be a free group with r generators, 1 < r < ∞. All the eigenfunctions of an operator on G which plays the same role of the Laplace Beltrami operator on semisimple Lie groups are characterized. Furthermore, an analytic family of representations πz of G on functions on the boundary Ω is considered, defined by , where p(x, ω) is the Poisson kernel relative to the action of G on Ω. It is proved that, for 0 < s = Re z < 1, πz is uniformly bounded on an appropriate Hilbert space . Finally the uniform boundedness of other special representations of G, obtained by considering the free group either as a subgroup of the group of all isometries of a tree or as a subgroup of GL(2, Qp) is proved. 相似文献