全文获取类型
收费全文 | 1644篇 |
免费 | 110篇 |
国内免费 | 259篇 |
专业分类
化学 | 21篇 |
力学 | 41篇 |
综合类 | 52篇 |
数学 | 1826篇 |
物理学 | 73篇 |
出版年
2023年 | 20篇 |
2022年 | 18篇 |
2021年 | 18篇 |
2020年 | 56篇 |
2019年 | 44篇 |
2018年 | 51篇 |
2017年 | 63篇 |
2016年 | 54篇 |
2015年 | 29篇 |
2014年 | 52篇 |
2013年 | 149篇 |
2012年 | 67篇 |
2011年 | 76篇 |
2010年 | 78篇 |
2009年 | 97篇 |
2008年 | 114篇 |
2007年 | 127篇 |
2006年 | 109篇 |
2005年 | 109篇 |
2004年 | 57篇 |
2003年 | 109篇 |
2002年 | 73篇 |
2001年 | 58篇 |
2000年 | 75篇 |
1999年 | 62篇 |
1998年 | 36篇 |
1997年 | 54篇 |
1996年 | 38篇 |
1995年 | 25篇 |
1994年 | 12篇 |
1993年 | 11篇 |
1992年 | 11篇 |
1991年 | 9篇 |
1990年 | 4篇 |
1989年 | 5篇 |
1988年 | 4篇 |
1986年 | 3篇 |
1985年 | 4篇 |
1984年 | 4篇 |
1983年 | 5篇 |
1982年 | 5篇 |
1981年 | 4篇 |
1980年 | 2篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1977年 | 5篇 |
1974年 | 1篇 |
1973年 | 1篇 |
排序方式: 共有2013条查询结果,搜索用时 15 毫秒
1.
A *-ring R is called a nil *-clean ring if every element of R is a sum of a projection and a nilpotent.Nil *-clean rings are the *-version of nil-clean rings introduced by Diesl.This paper is about the nil *-clean property of rings with emphasis on matrix rings.We show that a *-ring R is nil *-clean if and only if J(R) is nil and R/J(R) is nil*-clean.For a 2-primal *-ring R,with the induced involution given by (aij)* =(a*ij)T,the nil *-clean property of Mn(R) is completely reduced to that of Mn(Z2).Consequently,Mn(R) is not a nil *-clean ring for n =3,4,and M2(R) is a nil *-clean ring if and only if J(R) is nil,R/J(R) is a Boolean ring and a*-a ∈ J(R) for all a ∈ R. 相似文献
2.
研究了广义半交换环的幂零结构,定义了一类新的环类,即幂零$\alpha$-半交换环.说明了$\alpha$-半交换环与半交换环, $\alpha$-半交换环和$\alpha$-刚性环等环密切相关,通过构造反例说明了幂零$\alpha$-半交换环未必是$\alpha$-半交换环.研究了幂零$\alpha$-半交换环的各种性质,推广和统一了与环的半交换性质有关的若干结论. 相似文献
3.
《Arabian Journal of Chemistry》2022,15(4):103712
Although recent decades have witnessed the synthesis of 1,3,4-thiadiazoles via phosphorus POCl3-promoted cyclization reaction, simultaneous access to 2-amino-1,3,4-thiadiazole and 2-amino-1,3,4-oxadiazole analogs remains unexpected and elusive. Herein, a detailed regiocontrolled synthesis of 2-amino-1,3,4-thiadiazoles in good to high yields with good regioselectivities from readily available thiosemicarbazides using POCl3 was disclosed. Meantime, to establish a comprehensive structure–activity relationship, 2-amino-1,3,4-oxadiazole derivatives as single regioisomers were prepared via EDCI·HCl-triggered cyclization of the thiosemicarbazide intermediates. The in vitro anti-influenza assays proved that the selected compounds with the pyrazine/pyridine ring exhibited certain inhibitory activities against influenza A virus strains A/HK/68 (H3N2) and A/PR/8/34 (H1N1) in MDCK cells. Among them, N-(adamantan-1-yl)-5-(5-(azepan-1-yl)pyrazin-2-yl)-1,3,4-thiadiazol-2-amine (4j) was the most active compound, and exhibited favorable activity with EC50 values of 3.5 μM and 7.5 μM, respectively. In addition, the molecular docking results explained the reason why compound 4j had dual inhibitory activity and revealed the reasonable binding mode of this compound with the M2-S31N and M2-WT ion channels. This compound had the potential to be further developed as an anti-influenza drug. 相似文献
4.
5.
6.
We describe degenerations of four-dimensional binary Lie algebras, and five- and six-dimensional nilpotent Malcev algebras over ?. In particular, we describe all irreducible components of these varieties. 相似文献
7.
G. Peruginelli 《代数通讯》2018,46(11):4724-4738
We classify the maximal subrings of the ring of n×n matrices over a finite field, and show that these subrings may be divided into three types. We also describe all of the maximal subrings of a finite semisimple ring, and categorize them into two classes. As an application of these results, we calculate the covering number of a finite semisimple ring. 相似文献
8.
9.
10.
Fausto De Mari 《代数通讯》2018,46(4):1709-1715
In this paper (generalized) soluble groups for which the set of all non-modular subgroups satisfies some weak chain condition are described. Groups satisfying weak chain conditions on non-permutable subgroups are also considered. 相似文献