全文获取类型
收费全文 | 37626篇 |
免费 | 1928篇 |
国内免费 | 1908篇 |
专业分类
化学 | 24477篇 |
晶体学 | 167篇 |
力学 | 634篇 |
综合类 | 616篇 |
数学 | 6725篇 |
物理学 | 8843篇 |
出版年
2023年 | 291篇 |
2022年 | 1644篇 |
2021年 | 1392篇 |
2020年 | 691篇 |
2019年 | 812篇 |
2018年 | 566篇 |
2017年 | 598篇 |
2016年 | 797篇 |
2015年 | 895篇 |
2014年 | 1099篇 |
2013年 | 2052篇 |
2012年 | 1497篇 |
2011年 | 1602篇 |
2010年 | 1514篇 |
2009年 | 1913篇 |
2008年 | 2048篇 |
2007年 | 2220篇 |
2006年 | 1636篇 |
2005年 | 1053篇 |
2004年 | 1022篇 |
2003年 | 1052篇 |
2002年 | 3505篇 |
2001年 | 1206篇 |
2000年 | 758篇 |
1999年 | 618篇 |
1998年 | 627篇 |
1997年 | 454篇 |
1996年 | 534篇 |
1995年 | 465篇 |
1994年 | 465篇 |
1993年 | 509篇 |
1992年 | 503篇 |
1991年 | 338篇 |
1990年 | 301篇 |
1989年 | 264篇 |
1988年 | 279篇 |
1987年 | 192篇 |
1986年 | 208篇 |
1985年 | 316篇 |
1984年 | 232篇 |
1983年 | 156篇 |
1982年 | 289篇 |
1981年 | 470篇 |
1980年 | 426篇 |
1979年 | 474篇 |
1978年 | 376篇 |
1977年 | 284篇 |
1976年 | 242篇 |
1974年 | 111篇 |
1973年 | 187篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Jan P. Boroński 《Topology and its Applications》2007,154(18):3156-3166
A set (or a collection of sets) contained in the Euclidean space Rm is symmetric if it is invariant under the antipodal map. Given a symmetric unicoherent polyhedron X (like an n-dimensional cube or a sphere) and an odd real function f defined on vertices of a certain symmetric triangulation of X, we algorithmically construct a connected symmetric separator of X by choosing a subcollection of the triangulation. Each element of the subcollection contains the vertices v and u such that f(v)f(u)?0. 相似文献
102.
Michael Holcomb 《Topology and its Applications》2007,154(1):124-143
One can form a polygonal linkage by identifying initial and terminal points of two free linkages. Likewise, one can form a multipolygonal linkage by identifying initial and terminal points of three free linkages. The geometric and topological properties of moduli spaces of multipolygonal linkages in the plane are studied. These spaces are compact algebraic varieties. Some conditions under which these spaces are smooth manifolds, cross products or disjoint unions of moduli spaces of polygonal linkages, or connected, are determined. Dimensions in smooth manifold cases and some Euler characteristics are computed. A classification of generic multiquadrilateral linkages is also made. 相似文献
103.
We investigate separability questions for the mapping class group of a surface. While this group is not subgroup separable in general, we prove a large family of interesting subgroups are separable. This includes many classically studied subgroups such as solvable subgroups, Heegaard and Handlebody groups, geometric subgroups, and all the terms in the Johnson filtration. 相似文献
104.
New criteria are provided for determining whether an integral representation of a stable process is minimal. These criteria are based on various nonminimal sets and their projections, and have several advantages over and shed light on already available criteria. In particular, they naturally lead from a nonminimal representation to the one which is minimal. Several known examples are considered to illustrate the main results. The general approach is also adapted to show that the so-called mixed moving averages have a minimal integral representation of the mixed moving average type. 相似文献
105.
106.
E. García-Matres N. Stüßer M. Hofmann M. Reehuis 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,32(1):35-42
The magnetic structures of Mn1-xFexWO4 with x
= 0.0, 0.16, 0.21, 0.225, 0.232, 0.24, 0.27, 0.29, and 1.0 were refined from neutron powder diffraction data. The magnetic phase
diagram could be completed in the coexistence range of different magnetic structures up to x
= 0.29. For the magnetic state at 1.5 K a commensurate antiferromagnetic structure with a propagation vector
= (±1/4, 1/2, 1/2) was found for x
⩽ 0.22 while the magnetic spins order with
= (1/2, 0, 0) for x
≥ 0.22. In the latter phase, additionally, weak magnetic reflections indexed to an incommensurate ordering with
= (- 0.214, 1/2, 0.457) occur in the diffraction pattern up to x
= 0.29 indicating the occurence of a reentrant phase. For 0.12 ⩽
x
⩽ 0.29 the low temperature phases are separated from a magnetic high temperature phase showing only magnetic reflections indexed
to a spin arrangement with
= (1/2, 0, 0). The magnetic phase diagram is discussed qualitatively considering random superexchange between the statistically distributed
Mn2+- and Fe2+-ions in the coexistence range 0.12 ⩽
x
⩽ 0.29 of different magnetic structures related to those of pure MnWO4 and FeWO4.
Received 9 October 2002 Published online 14 March 2003 相似文献
107.
Photoinduced optical and second-order non-linear optical effects in the interfaces separating In2O3–SiON (O/N ratio equals 1) films doped with A1, Sn and glass substrates were investigated using the photoinduced optical second harmonic generation. The photoinduced effective second-order optical susceptibility deff (at λ=1.76 μm) shows a good correlation with the linear optical susceptibility, particularly with the shift of the absorption edge. The maximal response of the photoinduced optical response signal was observed for the pump–probe delaying time of 34 ps. The performed experimental measurements indicate that the observed effects are mainly caused by the interface potential gradients on the border glass–In2O3–SiON film and by additional polarization due to insertion of the Al and Sn atoms. The observed phenomenon may be proposed as a sensitive tool for investigation of thin semiconducting interfacial layers and simultaneously such films may be used as materials for non-linear optical devices. 相似文献
108.
Xuyuan GuScott Cowell Jinfa YingXuejun Tang Victor J. Hruby 《Tetrahedron letters》2003,44(31):5863-5866
(2S,3S)- and (2R,3R)-2-amino-3-phenyl-5-hexenoic acids have been synthesized in large scale by using Ni(II)-complexes as a template. The amino acids were used in the synthesis of [4,3,0]-bicyclic β-turn mimetics by a convergent methodology. The unique advantage of this strategy is the convenience of introducing side chain groups with predetermined chiralities on both the five- and six-membered heterocyclic rings. 相似文献
109.
Summary. We consider the spline collocation method for a class of parabolic pseudodifferential operators. We show optimal order convergence
results in a large scale of anisotropic Sobolev spaces. The results cover the classical boundary integral equations for the
heat equation in the general case where the spatial domain has a smooth boundary in the plane. Our proof is based on a localization
technique for which we use our recent results proved for parabolic pseudodifferential operators. For the localization we need
also some special spline approximation results in anisotropic Sobolev spaces.
Received May 17, 2001 / Revised version received February 19, 2002 / Published online April 17, 2002 相似文献
110.