全文获取类型
收费全文 | 3565篇 |
免费 | 282篇 |
国内免费 | 454篇 |
专业分类
化学 | 2450篇 |
晶体学 | 24篇 |
力学 | 159篇 |
综合类 | 42篇 |
数学 | 1291篇 |
物理学 | 335篇 |
出版年
2024年 | 1篇 |
2023年 | 78篇 |
2022年 | 90篇 |
2021年 | 140篇 |
2020年 | 168篇 |
2019年 | 145篇 |
2018年 | 95篇 |
2017年 | 126篇 |
2016年 | 151篇 |
2015年 | 91篇 |
2014年 | 159篇 |
2013年 | 245篇 |
2012年 | 142篇 |
2011年 | 164篇 |
2010年 | 141篇 |
2009年 | 202篇 |
2008年 | 199篇 |
2007年 | 221篇 |
2006年 | 222篇 |
2005年 | 185篇 |
2004年 | 181篇 |
2003年 | 209篇 |
2002年 | 156篇 |
2001年 | 127篇 |
2000年 | 93篇 |
1999年 | 109篇 |
1998年 | 71篇 |
1997年 | 73篇 |
1996年 | 52篇 |
1995年 | 64篇 |
1994年 | 43篇 |
1993年 | 28篇 |
1992年 | 29篇 |
1991年 | 23篇 |
1990年 | 21篇 |
1989年 | 7篇 |
1988年 | 8篇 |
1987年 | 6篇 |
1986年 | 6篇 |
1985年 | 7篇 |
1984年 | 5篇 |
1983年 | 3篇 |
1982年 | 4篇 |
1981年 | 1篇 |
1979年 | 5篇 |
1977年 | 1篇 |
1972年 | 3篇 |
1971年 | 1篇 |
排序方式: 共有4301条查询结果,搜索用时 15 毫秒
1.
2.
3.
4.
Andrey V. Lunchev Dr. Samuel A. Morris Dr. Rakesh Ganguly Prof. Andrew C. Grimsdale 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(7):1819-1823
A route to the synthesis of novel 5,7-diazapentacenes and some preliminary studies on their properties is reported. A single crystal X-ray diffraction study of the dihexyl derivative showed it had formed a dimer during the analysis. The materials possess lower lying frontier orbitals than pentacene and may have potential applications in organic electronic devices. This synthetic method may be applicable to the synthesis of other azaacenes. 相似文献
5.
6.
7.
Let be an abelian group. A finite multiset A over G is said to give a λ-fold factorization of G if there exists a multiset B over G such that each element of G occurs λ times in the multiset . In this article, restricting G to a cyclic group, we will provide sufficient conditions on a given multiset A under which the exact value or an upper bound of the minimum multiplicity λ of a factorization of G can be given by introducing a concept of ‘lcm-closure’. Furthermore, a couple of properties on a given factor A will be shown when A has a prime or prime power order (cardinality). A relation to multifold factorizations of the set of integers will be also glanced at a general perspective. 相似文献
8.
《大分子反应工程》2018,12(1)
A model is used to simulate batch copolymerization of caprolactam with hexamethylene diamine (HMD) and adipic acid (ADA) to produce nylon 6/6,6. Four different recipes are considered: a recipe containing caprolactam and an aqueous solution of HMD and ADA, a recipe containing caprolactam and dry HMD/ADA salt, and two recipes with a portion of the caprolactam replaced by nylon 6 cyclic dimer (CD). Consuming CD would be advantageous because CD is an undesirable side product from nylon 6 production. Simulation results lead to three important findings: (i) operation using dry salt rather than aqueous salt solution leads to higher degree of polymerization, (ii) substantial quantities of CD can be consumed to produce nylon 6/6,6 copolymer, and (iii) including water in the recipe is beneficial for achieving improved consumption of CD. The results of this study will be helpful in designing experiments aimed at improving industrial nylon 6/6,6 copolymerization processes. 相似文献
9.
We provide a theoretical study of Algebraic Geometry codes constructed from abelian surfaces defined over finite fields. We give a general bound on their minimum distance and we investigate how this estimation can be sharpened under the assumption that the abelian surface does not contain low genus curves. This approach naturally leads us to consider Weil restrictions of elliptic curves and abelian surfaces which do not admit a principal polarization. 相似文献
10.