全文获取类型
收费全文 | 19100篇 |
免费 | 1598篇 |
国内免费 | 1593篇 |
专业分类
化学 | 2402篇 |
晶体学 | 58篇 |
力学 | 1264篇 |
综合类 | 490篇 |
数学 | 13444篇 |
物理学 | 4633篇 |
出版年
2023年 | 166篇 |
2022年 | 284篇 |
2021年 | 303篇 |
2020年 | 365篇 |
2019年 | 396篇 |
2018年 | 383篇 |
2017年 | 483篇 |
2016年 | 508篇 |
2015年 | 408篇 |
2014年 | 788篇 |
2013年 | 1270篇 |
2012年 | 783篇 |
2011年 | 1088篇 |
2010年 | 1056篇 |
2009年 | 1334篇 |
2008年 | 1385篇 |
2007年 | 1387篇 |
2006年 | 1259篇 |
2005年 | 1044篇 |
2004年 | 855篇 |
2003年 | 873篇 |
2002年 | 738篇 |
2001年 | 656篇 |
2000年 | 555篇 |
1999年 | 555篇 |
1998年 | 496篇 |
1997年 | 438篇 |
1996年 | 349篇 |
1995年 | 254篇 |
1994年 | 206篇 |
1993年 | 180篇 |
1992年 | 179篇 |
1991年 | 135篇 |
1990年 | 107篇 |
1989年 | 104篇 |
1988年 | 91篇 |
1987年 | 70篇 |
1986年 | 52篇 |
1985年 | 93篇 |
1984年 | 75篇 |
1983年 | 48篇 |
1982年 | 78篇 |
1981年 | 67篇 |
1980年 | 51篇 |
1979年 | 77篇 |
1978年 | 51篇 |
1977年 | 44篇 |
1976年 | 32篇 |
1974年 | 24篇 |
1973年 | 23篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
Takashi Shioya 《Geometriae Dedicata》2004,103(1):1-32
We study the behavior of maximal geodesics in a finitely connected complete two-dimensional Riemannian manifold M admitting curvature at infinity. In the case where M is homeomorphic to 2 the Cohn–Vossen theorem states that the total curvature of M, say c(M), is 2. We already studied the case c(M)<2 in our previous paper. So we study the behavior of geodesics in M with total curvature 2 in this paper. Next we consider the case where M has nonempty boundary. In order to know the behavior of distant geodesics in M with boundary, it is useful to investigate the 'visual image' of the boundary of M. The latter half of this paper will be spent to study the asymptotic behavior of the visual image of a subset of M with located point tending to infinity. 相似文献
992.
Rollin S. Armour Jr. 《Foundations of Physics》2004,34(5):815-842
Requiring covariance of Maxwell's equations without a priori imposing charge invariance allows for both spin-1 and spin-1/2 transformations of the complete Maxwell field and current. The spin-1/2 case yields new transformation rules, with new invariants, for all traditional Maxwell field and source quantities. The accompanying spin-1/2 representations of the Lorentz group employ the Minkowski metric, and consequently the primary spin-1/2 Maxwell invariants are also spin-1 invariants; for example,
2–A
2, E
2–B
2+2i
EB–(0
+A)2. The associated Maxwell Lagrangian density is also the same for both spin-1 and spin-1/2 fields. However, in the spin-1/2 case, standard field and source quantities are complex and both charge and gauge invariance are lost. Requiring the potentials to satisfy the Klein–Gordon equation equates the Maxwell and field-potential equations with two Dirac equations of the Klein–Gordon mass, and thus one complex Klein–Gordon Maxwell field describes either two real vector fields or two Dirac fields, all of the same mass. 相似文献
993.
S. A. Mikhnov 《Journal of Applied Spectroscopy》2004,71(5):757-759
It has been found that the phase shift min in the synchronous detection block that ensures the minimum amplitude of the EPR lines of ruby, diphenylpicrylhydrazyl, and MnSO4·5H2O, depends on the amplitude of the modulationH
m of a stationary magnetic field. The dependence of min on H
m is explained by the inertial nature of the recovery of the stationary states of paramagnetic centers on a change in the magnetic field strength. 相似文献
994.
A. L. Vlasyuk G. D. Gamalevich A. V. Ignatenko E. P. Serebryakov M. I. Struchkova 《Russian Chemical Bulletin》2004,53(3):693-702
Acetylation of (±)-1-phenylnon-2-yn-1-ol, (±)-1-phenylhept-1-yn-3-ol, and (±)-1-phenylundec-4-yn-3-ol ((±)-5) in the presence of lipase from Candida cylindracea (CCL) proceeds slowly to give products with ee 20%. The acetates of these alcohols are hydrolyzed in the presence of porcine pancreatic lipase (PPL) equally unsatisfactorily. The (6-arene)tricarbonylchromium complex of alcohol (±)-5 is acetylated in the presence of CCL up to 22% conversion to give (R)-acetate whose oxidative decomplexation followed by saponification results in alcohol (R)-(–)-5 with ee 95%. The configuration of alcohols (–)-5 and (+)-5 was determined by NMR spectroscopy of their esters with (R)- and (S)-Mosher"s acids. 相似文献
995.
996.
997.
I set forth and discuss I.I. Rabis views on the nature of science and society, focusing specifically on Rabis views on science and government, science and education, and science and religion. I also explore the influence of Rabi and C.P. Snow on each other. In the 1960s, Rabi set forth his mature and boldest positions, advocating science as the center of education and science as the replacement for religion. His positions culminate in science as the universal culture. I highlight Rabi not only as a scientist and public servant, but also as a public intellectual actively engaged with and connected to major issues of his time.Michael A. Day is Professor of Physics at Lebanon Valley College. He holds doctorates in both physics and philosophy. 相似文献
998.
L. V. Baev V. N. Solodovnikov 《Journal of Applied Mechanics and Technical Physics》2004,45(6):860-870
The problem of spherically symmetric, gravitational compression of an isotropic hyperelastic layered sphere which modeling the region of the Earth below the Mohorovii boundary is solved. The known mechanical characteristics of the Earth in the compressed state are used to find its characteristics in the unstrained state obtained by adiabatic or isothermal stress relief. The stress state differs significantly from the state of purely hydrostatic compression. The minimum bulk compression and maximum radial tension occur not on the boundary of the sphere but in depth at certain distances from the boundary. 相似文献
999.
Ákos Császár 《Journal of Mathematical Analysis and Applications》2004,297(2):490-494
The paper presents a formula for the γ-interior of a set under special conditions for , more general than those in the previous paper [Acta Math. Hungar. 80 (1998) 89-93]. There are also some applications. 相似文献
1000.
在C~n中有界凸Reinhardt域上讨论了一类介于凸映射类与星形映射类之间的“完全准凸映射类”.特别地,在C~n中的多圆柱上给出了完全准凸映射的分解定理,得到了多圆柱上判别凸映射的一个改进的充分条件. 相似文献