全文获取类型
收费全文 | 52658篇 |
免费 | 10536篇 |
国内免费 | 3839篇 |
专业分类
化学 | 52752篇 |
晶体学 | 543篇 |
力学 | 1174篇 |
综合类 | 258篇 |
数学 | 3755篇 |
物理学 | 8551篇 |
出版年
2024年 | 47篇 |
2023年 | 304篇 |
2022年 | 544篇 |
2021年 | 715篇 |
2020年 | 1809篇 |
2019年 | 3112篇 |
2018年 | 1530篇 |
2017年 | 1181篇 |
2016年 | 4088篇 |
2015年 | 4277篇 |
2014年 | 4265篇 |
2013年 | 5209篇 |
2012年 | 4320篇 |
2011年 | 3651篇 |
2010年 | 3837篇 |
2009年 | 3787篇 |
2008年 | 3473篇 |
2007年 | 2737篇 |
2006年 | 2449篇 |
2005年 | 2543篇 |
2004年 | 2133篇 |
2003年 | 1957篇 |
2002年 | 2641篇 |
2001年 | 1832篇 |
2000年 | 1708篇 |
1999年 | 703篇 |
1998年 | 266篇 |
1997年 | 259篇 |
1996年 | 238篇 |
1995年 | 181篇 |
1994年 | 161篇 |
1993年 | 158篇 |
1992年 | 118篇 |
1991年 | 91篇 |
1990年 | 83篇 |
1989年 | 84篇 |
1988年 | 52篇 |
1987年 | 53篇 |
1986年 | 55篇 |
1985年 | 49篇 |
1984年 | 28篇 |
1983年 | 25篇 |
1982年 | 23篇 |
1981年 | 34篇 |
1980年 | 20篇 |
1979年 | 20篇 |
1977年 | 22篇 |
1976年 | 21篇 |
1974年 | 23篇 |
1973年 | 17篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
2.
3.
5‐Amino‐4‐methyl‐2‐phenyl‐6‐substitutedfuro[2,3‐d]pyrimidines ( 2a‐c ) were reacted with 2,5‐dimethoxytetrahydrfuran to afford the pyrrolyl derivatives 3a‐c . Compound 3a was chosen as intermediate for the synthesis of poly fused heterocycles incorporated furopyrimidines moiety 4–11 . Some of the synthesized compounds were screened for their antibacterial and antifungal activities. 相似文献
4.
5.
甲基紫掺杂聚乙烯醇薄膜材料在两束相干光照射下生成相位光栅.当改变一束相干光光程,通过监测相位光栅的一级衍射信号强度的变化,可以检测相位光栅的生长和擦除过程.在此实验基础上,讨论了甲基紫掺杂聚乙烯醇薄膜材料多重全息存储的原理与结果. 相似文献
6.
This paper proposes two constructive heuristics for the well-known single-level uncapacitated dynamic lot-sizing problem. The proposed heuristics, called net least period cost (nLPC) and nLPC(i), are developed by modifying the average period cost concept from Silver and Meal's heuristic, commonly known as least period cost (LPC). An improved tie-breaking stopping rule and a locally optimal decision rule are proposed in the second heuristic to enhance performance. We test the effectiveness of the proposed heuristics by using 20 benchmarking test problems frequently used in the literature. Furthermore, we perform a large-scale simulation study involving three factors, 50 experimental conditions, and 100?000 randomly generated problems to evaluate the proposed heuristics against LPC and six other well-known constructive heuristics in the literature. The simulation results show that both nLPC and nLPC(i) produce average holding and setup costs lower than or equal to those of LPC in every one of the 50 experimental conditions. The proposed heuristics also outperform each of the six other heuristics evaluated in all experimental conditions, without an increase in computational requirements. Lastly, considering that both nLPC and nLPC(i) are fairly simple for practitioners to understand and that lot-sizing heuristics have been commonly used in practice, there should be a very good chance for practical applications of the proposed heuristics. 相似文献
7.
Wen Zhang Hui Huang Yu Ding Margherita Gavagnin Ernesto Mollo Guido Cimino Yue‐Wei Guo 《Helvetica chimica acta》2006,89(4):813-820
Three new polyoxygenated steroids, muricesteroid ( 1 ), and menellsteroids A ( 2 ) and B ( 3 ), were isolated from two species of the South China Sea gorgonian Muricella flexuosa and Menella verrucosa Brundin , respectively. The structures of these new compounds were elucidated on the basis of extensive spectroscopic analysis, chemical methods and comparison with known related compounds. 相似文献
8.
It is proved that the variety of relevant disjunction lattices has the finite embeddability property. It follows that Avron's relevance logic RMI min has a strong form of the finite model property, so it has a solvable deducibility problem. This strengthens Avron's result that RMI min is decidable. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
9.
The fuzzification of convex sets in median algebras is considered, and some of their properties are investigated. A characterization of finite valued fuzzy convex set is given. 相似文献
10.
On Dirichlet Characters of Polynomials 总被引:1,自引:0,他引:1
The main purpose of this paper is to use the properties of Gaussiansums and the analytic method to study the problem of calculatingone kind of character sums modulo q, and to give an interestingidentity. 2000 Mathematics Subject Classification 11L10, 11L40. 相似文献