全文获取类型
收费全文 | 222775篇 |
免费 | 6464篇 |
国内免费 | 4816篇 |
专业分类
化学 | 102350篇 |
晶体学 | 2940篇 |
力学 | 13563篇 |
综合类 | 332篇 |
数学 | 41099篇 |
物理学 | 73771篇 |
出版年
2023年 | 896篇 |
2022年 | 2135篇 |
2021年 | 2647篇 |
2020年 | 3003篇 |
2019年 | 3365篇 |
2018年 | 12073篇 |
2017年 | 12562篇 |
2016年 | 8809篇 |
2015年 | 4136篇 |
2014年 | 4979篇 |
2013年 | 7224篇 |
2012年 | 11232篇 |
2011年 | 19406篇 |
2010年 | 12758篇 |
2009年 | 12748篇 |
2008年 | 16555篇 |
2007年 | 19502篇 |
2006年 | 5883篇 |
2005年 | 10790篇 |
2004年 | 7026篇 |
2003年 | 6655篇 |
2002年 | 4917篇 |
2001年 | 3164篇 |
2000年 | 2976篇 |
1999年 | 2084篇 |
1998年 | 2055篇 |
1997年 | 1846篇 |
1996年 | 1730篇 |
1995年 | 1362篇 |
1994年 | 1383篇 |
1993年 | 1282篇 |
1992年 | 1231篇 |
1991年 | 1286篇 |
1990年 | 1272篇 |
1989年 | 1172篇 |
1988年 | 1065篇 |
1987年 | 1063篇 |
1986年 | 1016篇 |
1985年 | 1088篇 |
1984年 | 1092篇 |
1983年 | 965篇 |
1982年 | 959篇 |
1981年 | 854篇 |
1979年 | 958篇 |
1978年 | 983篇 |
1977年 | 885篇 |
1976年 | 1037篇 |
1975年 | 897篇 |
1974年 | 934篇 |
1973年 | 973篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
993.
We have observed three-dimensional sponge-like structures as well as strips of connecting pits on the surface of the LR 115 detector after etching, which can be confused with the small tracks formed after short etching time. We have employed an atomic force microscope (AFM) to study these “damages” as well as genuine alpha tracks for short etching time. It was found that while the track and damage openings could be similar in size and shape, the depths for the damages were consistently smaller. Therefore, the depth of the pits will serve as a clear criterion to differentiate between tracks and other damages. The ability to discriminate between genuine tracks from other damages is most important for etching for short time intervals. 相似文献
994.
E. Yu. Daniyarova I. V. Kazatchkov V. N. Remeslennikov 《Journal of Mathematical Sciences》2005,131(6):6015-6022
This article is the fourth part of the series of papers whose aim is the construction of algebraic geometry over metabelian
Lie algebras.
__________
Translated from Sovremennaya Matematika i Ee Prilozheniya (Contemporary Mathematics and Its Applications), Vol. 14, Algebra,
2004. 相似文献
995.
996.
Tm3+/Yb3+-codoped germanate-niobic (GN) and germanium-bismuth (GB) glasses have been synthesized by conventional melting and quenching method. Intense blue and weak red emissions centered at 477 and 650 nm, corresponding to the transitions 1G4→3H6 and 1G4→3H4, respectively, were observed at room temperature. The possible up-conversion mechanisms are discussed and estimated. GN glass showed a weaker up-conversion emission than GB glass, which is inconsistent with the prediction from the difference of maximum phonon energy between GN and GB glasses. In this paper, Raman spectroscopy was employed to investigate the origin of the difference in up-conversion luminescence in the two glasses. Compared with phonon side-band spectroscopy, Raman spectroscopy extracts more information including both phonon energy and phonon density. For the first time, our results reveal that, besides the maximum phonon energy, the phonon density of host glasses is also an important factor in determining the up-conversion efficiency. 相似文献
997.
998.
The load-carrying capacity of circular plates made of a fiber-reinforced composite and loaded with axisymmetric transverse forces under axisymmetric boundary conditions is investigated. The plates can be freely supported or clamped along their contour. To the known yield condition used, in the plane of main bending moments, there correspond irregular hexagons, which depend on the mechanical properties of composite constituents and some characteristic geometrical parameters. It is shown that, depending on the ratio of ultimate radial and circumferential bending moments, in the plastic state, the circular plates (the central part of the clamped plates) take the form of a cone or a frustum of cone. For each of the cases, the limit load is found, which is a function of the above-mentioned mechanical parameters. The statically allowable fields of bending moments and the corresponding allowable fields of deflection rates are determined. The solutions found are exact. Special cases for the freely supported plates are analyzed, and the results obtained are presented in the form of graphs.__________Translated from Mekhanika Kompozitnykh Materialov, Vol. 41, No. 2, pp. 177–192, March–April, 2005. 相似文献
999.
S. S. Yarovoi S. F. Solodovnikov Z. A. Solodovnikova Yu. V. Mironov V. E. Fedorov 《Journal of Structural Chemistry》2006,47(1):97-101
A cluster complex of the composition [Th(DMSO)8Cl][Re6Se7Cl7] has been obtained by interaction of ThCl4 solution in DMSO with a water solution of K3[Re6Se7Cl7] and KCl. The compound crystallizes in the rhombic space group Pbcm with unit cell parameters a = 12.262(2) Å, b = 19.653(6) Å, c = 23.603(6) Å, V = 5688(2) Å3, Z = 4, d calc = 3.282 g/cm3. The structure is built from centrosymmetric cluster anions [Re6Se7Cl7]3? and complex cations [Th(DMSO)8Cl]3+ possessing mirror-plane symmetry, half of the DMSO ligands being doubly disordered. 相似文献
1000.
The spatial structure of a luminous cloud near a hydrogen pellet sublimated in a tokamak plasma is investigated experimentally. The luminous cloud has the form of a constant-intensity plateau extended along the magnetic field and is surrounded by an exponentially fading halo. The cross size of the plateau is determined by the boundary of the ionization region of atoms leaving the pellet surface. The plateau length is approximately determined by the balance between the pressures in the luminous cloud and the bulk plasma. Taking into account the structure described is important for the correct interpretation of the signals from alpha-particle diagnostics by charge-exchange neutral fluxes, because these signals depend on the characteristic dimensions of the cloud. 相似文献