全文获取类型
收费全文 | 6824篇 |
免费 | 140篇 |
国内免费 | 294篇 |
专业分类
化学 | 3019篇 |
晶体学 | 19篇 |
力学 | 31篇 |
综合类 | 8篇 |
数学 | 2984篇 |
物理学 | 1197篇 |
出版年
2024年 | 8篇 |
2023年 | 37篇 |
2022年 | 54篇 |
2021年 | 52篇 |
2020年 | 70篇 |
2019年 | 141篇 |
2018年 | 84篇 |
2017年 | 65篇 |
2016年 | 62篇 |
2015年 | 76篇 |
2014年 | 176篇 |
2013年 | 757篇 |
2012年 | 449篇 |
2011年 | 672篇 |
2010年 | 621篇 |
2009年 | 701篇 |
2008年 | 651篇 |
2007年 | 534篇 |
2006年 | 442篇 |
2005年 | 249篇 |
2004年 | 186篇 |
2003年 | 189篇 |
2002年 | 106篇 |
2001年 | 76篇 |
2000年 | 63篇 |
1999年 | 59篇 |
1998年 | 61篇 |
1997年 | 75篇 |
1996年 | 83篇 |
1995年 | 66篇 |
1994年 | 69篇 |
1993年 | 48篇 |
1992年 | 42篇 |
1991年 | 38篇 |
1990年 | 23篇 |
1989年 | 11篇 |
1988年 | 15篇 |
1987年 | 12篇 |
1986年 | 11篇 |
1985年 | 24篇 |
1984年 | 13篇 |
1983年 | 12篇 |
1982年 | 13篇 |
1981年 | 11篇 |
1980年 | 6篇 |
1979年 | 11篇 |
1978年 | 11篇 |
1977年 | 5篇 |
1976年 | 5篇 |
1975年 | 5篇 |
排序方式: 共有7258条查询结果,搜索用时 109 毫秒
1.
《Mendeleev Communications》2022,32(1):126-128
3-Aryl-5-methylidene-2-thiohydantoins were constructed in one-pot reaction of aryl isothiocyanates and 3-morpholino- alanine in alkaline medium with the subsequent treatment with boiling hydrochloric acid. 相似文献
2.
Joshua Maglione 《Journal of Pure and Applied Algebra》2021,225(3):106528
Like the lower central series of a nilpotent group, filters generalize the connection between nilpotent groups and graded Lie rings. However, unlike the case with the lower central series, the associated graded Lie ring may share few features with the original group: e.g. the associated Lie ring can be trivial or arbitrarily large. We determine properties of filters such that every isomorphism between groups is induced by an isomorphism between graded Lie rings. 相似文献
3.
4.
Let T and S be invertible measure preserving transformations of a probability measure space (X, ℬ, μ). We prove that if the group generated by T and S is nilpotent, then exists in L
2-norm for any u, v∈L
∞(X, ℬ, μ). We also show that for A∈ℬ with μ(A)>0 one has . By the way of contrast, we bring examples showing that if measure preserving transformations T, S generate a solvable group, then (i) the above limits do not have to exist; (ii) the double recurrence property fails, that
is, for some A∈ℬ, μ(A)>0, one may have μ(A∩T
-n
A∩S
-
n
A)=0 for all n∈ℕ. Finally, we show that when T and S generate a nilpotent group of class ≤c, in L
2(X) for all u, v∈L
∞(X) if and only if T×S is ergodic on X×X and the group generated by T
-1
S, T
-2
S
2,..., T
-c
S
c
acts ergodically on X.
Oblatum 19-V-2000 & 5-VII-2001?Published online: 12 October 2001 相似文献
5.
Michel Hébert 《Archive for Mathematical Logic》1991,31(2):133-143
Summary We give a syntactic characterization of (finitary) theories whose categories of models are closed under the formation of connected limits (respectively the formation of pullbacks and substructures) in the category of all structures. They are also those theories whose consistent extensions by new atomic facts admit in each component an initial structure (respectively an initial term structure), and also thoseT for whichM(T) is locally finitely multi-presentable in a canonical way. We also show that these two properties of theories are nonuniform. 相似文献
6.
Using Brown's construction (J. Algebra 15 (1970) 103) of an exact 6-term sequence for a fibration of groupoids we show how an exact 9-term sequence can be associated to a fibration of bigroupoids. Applications to topology and algebra are given. 相似文献
7.
F. Balibrea 《Topology and its Applications》2006,153(12):2092-2095
Recently, Forti, Paganoni and Smítal constructed an example of a triangular map of the unite square, F(x,y)=(f(x),g(x,y)), possessing periodic orbits of all periods and such that no infinite ω-limit set of F contains a periodic point. In this note we show that the above quoted map F has a homoclinic orbit. As a consequence, we answer in the negative the problem presented by A.N. Sharkovsky in the eighties whether, for a triangular map of the square, existence of a homoclinic orbit implies the existence of an infinite ω-limit set containing a periodic point. It is well known that, for a continuous map of the interval, the answer is positive. 相似文献
8.
Kazem Ghanbari 《Positivity》2006,10(4):721-729
We denote the spectrum of an square matrix A by σ(A), and that of the matrix obtained by deleting the first i rows and columns of A by σi(A). It is known that a symmetric pentadiagonal oscillatory (SPO) matrix may be constructed from σ, σ1 and σ2. The pairs σ, σ1 and σ1, σ2 must interlace; the construction is not unique; and the conditions on the data which ensure that A is oscillatory are extremely complicated. Given one SPO matrix A, the paper shows that operations may be applied to A to construct a family of such matrices with σ and σ1 in common. Moreover, given one totally positive (TP) matrix A, we construct a family of TP matrices with σ, σ1 and σ2 in common. 相似文献
9.
10.
We construct cellular homotopy theories for categories of simplicial presheaves on small Grothendieck sites and discuss applications to the motivic homotopy category of Morel and Voevodsky. 相似文献