全文获取类型
收费全文 | 12729篇 |
免费 | 558篇 |
国内免费 | 2058篇 |
专业分类
化学 | 10130篇 |
晶体学 | 186篇 |
力学 | 151篇 |
综合类 | 90篇 |
数学 | 2988篇 |
物理学 | 1800篇 |
出版年
2024年 | 11篇 |
2023年 | 122篇 |
2022年 | 313篇 |
2021年 | 249篇 |
2020年 | 246篇 |
2019年 | 287篇 |
2018年 | 264篇 |
2017年 | 296篇 |
2016年 | 309篇 |
2015年 | 262篇 |
2014年 | 348篇 |
2013年 | 901篇 |
2012年 | 638篇 |
2011年 | 823篇 |
2010年 | 721篇 |
2009年 | 938篇 |
2008年 | 918篇 |
2007年 | 908篇 |
2006年 | 840篇 |
2005年 | 714篇 |
2004年 | 698篇 |
2003年 | 555篇 |
2002年 | 489篇 |
2001年 | 360篇 |
2000年 | 392篇 |
1999年 | 300篇 |
1998年 | 268篇 |
1997年 | 270篇 |
1996年 | 253篇 |
1995年 | 265篇 |
1994年 | 238篇 |
1993年 | 208篇 |
1992年 | 183篇 |
1991年 | 126篇 |
1990年 | 91篇 |
1989年 | 95篇 |
1988年 | 60篇 |
1987年 | 37篇 |
1986年 | 45篇 |
1985年 | 48篇 |
1984年 | 36篇 |
1983年 | 29篇 |
1982年 | 31篇 |
1981年 | 43篇 |
1980年 | 22篇 |
1979年 | 23篇 |
1978年 | 19篇 |
1977年 | 9篇 |
1976年 | 15篇 |
1974年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
We give three formulas expressing the Smale invariant of an immersion f of a (4k−1)-sphere into (4k+1)-space. The terms of the formulas are geometric characteristics of any generic smooth map g of any oriented 4k-dimensional manifold, where g restricted to the boundary is an immersion regularly homotopic to f in (6k−1)-space.The formulas imply that if f and g are two non-regularly homotopic immersions of a (4k−1)-sphere into (4k+1)-space then they are also non-regularly homotopic as immersions into (6k−1)-space. Moreover, any generic homotopy in (6k−1)-space connecting f to g must have at least ak(2k−1)! cusps, where ak=2 if k is odd and ak=1 if k is even. 相似文献
72.
The dynamic external hashing proposed in this paper allocates records according to the spiral storage technique. Separators derived from the signature technique are used for distinguishing primary from overflow records and for subdividing overflow chains into segments allocated into the primary file. Single access retrieval is obtained by means of a main memory index with an entry per bucket and containing separators and pointers. While this method uses a larger index than other recent proposals, it is much more convenient regarding load factor and insertion cost. Furthermore, file expansion is directed by various control parameters, thus allowing the user to choose the most suitable policy for his application. 相似文献
73.
74.
Hiroshi Sawai 《Topology and its Applications》2007,154(18):3125-3134
The purpose in this paper is to prove that there exists a lattice on certain solvable Lie groups and to construct a symplectic solvmanifold with the Hard Lefschetz property, and a locally conformal Kähler solvmanifold. We see that minimal models for these solvmanifolds are formal. 相似文献
75.
The hyperspaces of strongly countable dimensional compacta of positive dimension and of strongly countable dimensional continua of dimension greater than 1 in the Hilbert cube are homeomorphic to the Hurewicz set of all nonempty countable closed subsets of the unit interval [0,1]. These facts hold true, in particular, for covering dimension dim and cohomological dimension dimG, where G is any Abelian group. 相似文献
76.
We show that a theorem of Shchepin and Repovš concerning the smoothness of compacta follows from the theory of semicontinuous relations. 相似文献
77.
Summary An analysis of five different datasets of inhibitors of serotonin uptake has yielded quantitative structure/ activity relationships (QSARs) which delineate the role of steric and hydrophobic properties essential for inhibition by phenylethylamine-type analogues. 相似文献
78.
以MCl2和配体L(L=1,10-菲罗啉-5,6-二酮)为原料,合成了标题配合物MLCl2,M=NiⅡ,CuⅡ,ZnⅡ,并经元素分析、热谱、IR和摩尔电导表征.三者均为四配位的电中性配合物,热稳定性高于500K,易溶于DMF、DMSO和吡啶,可溶于乙腈和水.它们在DMF中于350nm和315nm附近显示出强的M-L荷移跃迁 相似文献
79.
Yuichiro Fujiwara 《组合设计杂志》2006,14(3):237-250
In this paper, we present three constructions for anti‐mitre Steiner triple systems and a construction for 5‐sparse ones. The first construction for anti‐mitre STSs settles two of the four unsettled admissible residue classes modulo 18 and the second construction covers such a class modulo 36. The third construction generates many infinite classes of anti‐mitre STSs in the remaining possible orders. As a consequence of these three constructions we can construct anti‐mitre systems for at least 13/14 of the admissible orders. For 5‐sparse STS(υ), we give a construction for υ ≡ 1, 19 (mod 54) and υ ≠ 109. © 2005 Wiley Periodicals, Inc. J Combin Designs 14: 237–250, 2006 相似文献
80.
A.A. George Michael 《Topology and its Applications》2006,153(14):2591-2612
Edmonds showed that two free orientation preserving smooth actions φ1 and φ2 of a finite Abelian group G on a closed connected oriented smooth surface M are equivalent by an equivariant orientation preserving diffeomorphism iff they have the same bordism class [M,φ1]=[M,φ2] in the oriented bordism group Ω2(G) of the group G. In this paper, we compute the bordism class [M,φ] for any such action of G on M and we determine for a given M, the bordism classes in Ω2(G) that are representable by such actions of G on M. This will enable us to obtain a formula for the number of inequivalent such actions of G on M. We also determine the “weak” equivalence classes of such actions of G on M when all the p-Sylow subgroups of G are homocyclic (i.e. of the form n(Z/pαZ)). 相似文献