全文获取类型
收费全文 | 53730篇 |
免费 | 11180篇 |
国内免费 | 4355篇 |
专业分类
化学 | 53684篇 |
晶体学 | 575篇 |
力学 | 1516篇 |
综合类 | 226篇 |
数学 | 3770篇 |
物理学 | 9494篇 |
出版年
2024年 | 73篇 |
2023年 | 404篇 |
2022年 | 715篇 |
2021年 | 894篇 |
2020年 | 2022篇 |
2019年 | 3287篇 |
2018年 | 1693篇 |
2017年 | 1336篇 |
2016年 | 4227篇 |
2015年 | 4365篇 |
2014年 | 4435篇 |
2013年 | 5389篇 |
2012年 | 4535篇 |
2011年 | 3772篇 |
2010年 | 3892篇 |
2009年 | 3904篇 |
2008年 | 3523篇 |
2007年 | 2783篇 |
2006年 | 2392篇 |
2005年 | 2434篇 |
2004年 | 2086篇 |
2003年 | 1913篇 |
2002年 | 2680篇 |
2001年 | 1902篇 |
2000年 | 1650篇 |
1999年 | 760篇 |
1998年 | 339篇 |
1997年 | 281篇 |
1996年 | 254篇 |
1995年 | 221篇 |
1994年 | 196篇 |
1993年 | 153篇 |
1992年 | 131篇 |
1991年 | 120篇 |
1990年 | 94篇 |
1989年 | 71篇 |
1988年 | 48篇 |
1987年 | 46篇 |
1986年 | 53篇 |
1985年 | 39篇 |
1984年 | 25篇 |
1983年 | 23篇 |
1982年 | 18篇 |
1981年 | 20篇 |
1980年 | 9篇 |
1975年 | 7篇 |
1974年 | 6篇 |
1973年 | 6篇 |
1957年 | 7篇 |
1936年 | 7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.
X. Dong 《Discrete and Computational Geometry》2002,27(1):85-97
We prove that the homotopy types of two naturally defined simplicial complexes are related in the following way: one is homotopy
equivalent to a multiple suspension of the canonical Alexander dual of the other. These simplicial complexes arise in free
resolutions of semigroup rings and modules. The relation between their homotopy types was conjectured by Reiner, and was suggested
by a homological consequence of a result due independently to Danilov and Stanley on canonical modules of normal semigroup
rings. Our proof is purely topological, and gives an alternative proof of their result. We also prove a generalization of
a result of Hochster saying that these rings are Cohen—Macaulay, and indicate a new proof of Ehrhart's reciprocity law for
rational polytopes.
Received October 3, 2000, and in revised form April 2, 2001, and May 10, 2001. Online publication November 7, 2001. 相似文献
5.
复合体系方法测量液体力学谱 总被引:2,自引:0,他引:2
本文介绍了采用复合体系,测量得到凝聚态物质从固态到液态连续变化力学谱的一种新的实验方法。以簧振动为例,给出了解析的计算公式,以及应用条件。通过进一步综合分析,得到具有更广应用范围的近似公式,可以近似应用于其他不同的振动模式,如低频扭摆。应用新的测量方法,给出了典型小分子玻璃材料甘油和碳酸丙稀从玻璃态到液态的力学谱,观察到甘油和碳酸丙稀玻璃化转变、碳酸丙稀的再结晶、熔化和挥发的过程;测量得到挥发过程中水的质量随时间精确变化的曲线。最后,本文给出了新方法的一些应用展望。 相似文献
6.
A convenient route was developed to synthesize S-oxo-[(methylthio)-methyl]cysteinols on a large scale from cheap l-serine as the starting material. The structures of diastereoisomers were determined by NMR, CD spectra, and X-ray diffraction analysis. All four diastereoisomers were examined for their ability to inhibit certain bacteria from growing. 相似文献
7.
8.
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
9.
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
10.
A (w,r) cover‐free family is a family of subsets of a finite set such that no intersection of w members of the family is covered by a union of r others. A (w,r) superimposed code is the incidence matrix of such a family. Such a family also arises in cryptography as the concept of key distribution pattern. In the present paper, we give some new results on superimposed codes. First we construct superimposed codes from super‐simple designs which give us results better than superimposed codes constructed by other known methods. Next we prove the uniqueness of the (1,2) superimposed code of size 9 × 12, the (2,2) superimposed code of size 14 × 8, and the (2,3) superimposed code of size 30 × 10. Finally, we improve numerical values of upper bounds for the asymptotic rate of some (w,r) superimposed codes. © 2004 Wiley Periodicals, Inc. 相似文献