全文获取类型
收费全文 | 6607篇 |
免费 | 740篇 |
国内免费 | 625篇 |
专业分类
化学 | 3893篇 |
晶体学 | 37篇 |
力学 | 299篇 |
综合类 | 83篇 |
数学 | 2362篇 |
物理学 | 1298篇 |
出版年
2024年 | 2篇 |
2023年 | 48篇 |
2022年 | 69篇 |
2021年 | 102篇 |
2020年 | 181篇 |
2019年 | 180篇 |
2018年 | 176篇 |
2017年 | 238篇 |
2016年 | 212篇 |
2015年 | 215篇 |
2014年 | 302篇 |
2013年 | 983篇 |
2012年 | 303篇 |
2011年 | 328篇 |
2010年 | 283篇 |
2009年 | 330篇 |
2008年 | 367篇 |
2007年 | 379篇 |
2006年 | 358篇 |
2005年 | 302篇 |
2004年 | 285篇 |
2003年 | 261篇 |
2002年 | 864篇 |
2001年 | 184篇 |
2000年 | 186篇 |
1999年 | 126篇 |
1998年 | 147篇 |
1997年 | 81篇 |
1996年 | 89篇 |
1995年 | 90篇 |
1994年 | 63篇 |
1993年 | 42篇 |
1992年 | 35篇 |
1991年 | 21篇 |
1990年 | 23篇 |
1989年 | 18篇 |
1988年 | 21篇 |
1987年 | 16篇 |
1986年 | 7篇 |
1985年 | 8篇 |
1984年 | 10篇 |
1983年 | 2篇 |
1982年 | 5篇 |
1981年 | 6篇 |
1980年 | 4篇 |
1979年 | 7篇 |
1978年 | 3篇 |
1973年 | 3篇 |
1968年 | 1篇 |
1936年 | 1篇 |
排序方式: 共有7972条查询结果,搜索用时 31 毫秒
991.
992.
This note is concerned with generalizations of commutativity. We introduce identity-symmetric and right near-commutative, and study basic structures of rings with such ring properties. It is shown that if R is an identity-symmetric ring, then the set of all nilpotent elements forms a commutative subring of R. Moreover, identity-symmetric regular rings are proved to be commutative. The near-commutativity is shown to be not left-right symmetric, and we study some conditions under which the near-commutativity is left-right symmetric. We also examine the near-commutativity of skew-trivial extensions, which has a role in this note. 相似文献
993.
S. K. Tiwari 《代数通讯》2013,41(12):5356-5372
994.
Frank Loose 《代数通讯》2013,41(7):2395-2416
Abstract A ring R is called left P-injective if for every a ∈ R, aR = r(l(a)) where l( ? ) and r( ? ) denote left and right annihilators respectively. The ring R is called left GP-injective if for any 0 ≠ a ∈ R, there exists n > 0 such that a n ≠ 0 and a n R = r(l(a n )). As a response to an open question on GP -injective rings, an example of a left GP-injective ring which is not left P-injective is given. It is also proved here that a ring R is left FP -injective if and only if every matrix ring 𝕄 n (R) is left GP-injective. 相似文献
995.
We call a ring R a right SA-ring if for any ideals I and J of R there is an ideal K of R such that r(I) + r(J) = r(K). This class of rings is exactly the class of rings for which the lattice of right annihilator ideals is a sublattice of the lattice of ideals. The class of right SA-rings includes all quasi-Baer (hence all Baer) rings and all right IN-rings (hence all right selfinjective rings). This class is closed under direct products, full and upper triangular matrix rings, certain polynomial rings, and two-sided rings of quotients. The right SA-ring property is a Morita invariant. For a semiprime ring R, it is shown that R is a right SA-ring if and only if R is a quasi-Baer ring if and only if r(I) + r(J) = r(I ∩ J) for all ideals I and J of R if and only if Spec(R) is extremally disconnected. Examples are provided to illustrate and delimit our results. 相似文献
996.
In this article we construct free groups and subgroups of finite index in the unit group of the integral group ring of a finite non-Abelian group G for which every nonlinear irreducible complex representation is of degree 2 and with commutator subgroup G′ a central elementary Abelian 2-group. 相似文献
997.
998.
In this paper, we provide equivalent conditions for the two-sided reverse order law for the group inverse (ab)# = b # a # and (ba)# = a # b #, in semigroups and rings. Moreover, we prove that, under finiteness conditions, these conditions are also equivalent with the one-sided reverse order law (ab)# = b # a #. 相似文献
999.
Charles Lanski 《代数通讯》2013,41(1):139-152
It is known that for a nonzero derivation d of a prime ring R, if a nonzero ideal I of R satisfies the Engel-type identity [[…[[d(x k 0 ), x k 1 ], x k 2 ],…], x k n ], then R is commutative. Here we extend this result to a skew derivation of R for a Lie ideal I, which has an immediate corollary that replaces d by an automorphism of R. A related result in two variables is obtained for d a (θ, ?)-derivation. 相似文献
1000.