全文获取类型
收费全文 | 55470篇 |
免费 | 12842篇 |
国内免费 | 4854篇 |
专业分类
化学 | 55889篇 |
晶体学 | 594篇 |
力学 | 1721篇 |
综合类 | 340篇 |
数学 | 4704篇 |
物理学 | 9918篇 |
出版年
2024年 | 53篇 |
2023年 | 467篇 |
2022年 | 643篇 |
2021年 | 869篇 |
2020年 | 2078篇 |
2019年 | 3321篇 |
2018年 | 1744篇 |
2017年 | 1304篇 |
2016年 | 4301篇 |
2015年 | 4421篇 |
2014年 | 4612篇 |
2013年 | 5450篇 |
2012年 | 4726篇 |
2011年 | 4043篇 |
2010年 | 4248篇 |
2009年 | 4027篇 |
2008年 | 3692篇 |
2007年 | 3038篇 |
2006年 | 2619篇 |
2005年 | 2663篇 |
2004年 | 2273篇 |
2003年 | 2003篇 |
2002年 | 2820篇 |
2001年 | 2078篇 |
2000年 | 1836篇 |
1999年 | 861篇 |
1998年 | 435篇 |
1997年 | 356篇 |
1996年 | 370篇 |
1995年 | 315篇 |
1994年 | 263篇 |
1993年 | 225篇 |
1992年 | 179篇 |
1991年 | 178篇 |
1990年 | 126篇 |
1989年 | 120篇 |
1988年 | 87篇 |
1987年 | 61篇 |
1986年 | 47篇 |
1985年 | 55篇 |
1984年 | 46篇 |
1983年 | 29篇 |
1982年 | 22篇 |
1981年 | 16篇 |
1980年 | 15篇 |
1979年 | 5篇 |
1978年 | 3篇 |
1977年 | 4篇 |
1975年 | 3篇 |
1957年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
171.
172.
Let f be a smooth map between unit spheres of possibly different dimensions. We prove the global existence and convergence of the mean curvature flow of the graph of f under various conditions. A corollary is that any area‐decreasing map between unit spheres (of possibly different dimensions) is isotopic to a constant map. © 2004 Wiley Periodicals, Inc. 相似文献
173.
Jensen and Toft 8 conjectured that every 2‐edge‐connected graph without a K5‐minor has a nowhere zero 4‐flow. Walton and Welsh 19 proved that if a coloopless regular matroid M does not have a minor in {M(K3,3), M*(K5)}, then M admits a nowhere zero 4‐flow. In this note, we prove that if a coloopless regular matroid M does not have a minor in {M(K5), M*(K5)}, then M admits a nowhere zero 4‐flow. Our result implies the Jensen and Toft conjecture. © 2005 Wiley Periodicals, Inc. J Graph Theory 相似文献
174.
175.
176.
A simple model has been developed to describe the Zeeman patterns of far-infrared laser magnetic resonance spectra of the monobromomethyl radical CH2Br observed at 447.3 and 671.1μm. A satisfactory agreement between the experimental spectra of the radical and their simulation with this simple model has been achieved. This approach can be used to gain further information about the structure and the spectrum of this interesting radical. 相似文献
177.
178.
To incorporate an acceptor type polythiophene segment onto a supramolecular block copolymer for potential light harvesting applications, effective synthetic routes for the end‐functionalized and acceptor‐substituted polythiophenes are critical. The Ullmann coupling reaction can be utilized to obtain electron‐deficient polythiophenes and to attach terminal thiophene units that carry functional groups. In this article, the reactions involving a 2,5‐dibromothiophene monomer containing an electron‐withdrawing fluorinated ester and 5‐bromo‐2‐thiophenecarboxaldehyde (the end‐capper) were studied in detail. It was found that the Ullmann coupling reaction of the dibromide is very fast (completed in a few minutes) and the terminal bromine group does not survive long under the reaction condition. These findings lead to the development of an effective procedure for aldehyde end‐capping of electron‐deficient polythiophenes. Polymers with molecular weights around 4000 Da are routinely obtained. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 41–47, 2007 相似文献
179.
Jing Zhang Dan Shan Shaolin Mu 《Journal of polymer science. Part A, Polymer chemistry》2007,45(23):5573-5582
A copolymer, poly(aniline‐co‐o‐aminophenol), was prepared chemically by using ammonium peroxydisulfate as an oxidant. The monomer concentration ratio of o‐aminophenol to aniline strongly influences the copolymerization rate and properties of the copolymer. The optimum composition of a mixture for the chemical copolymerization consisted of 0.3 M aniline, 0.021 M o‐aminophenol, 0.42 M ammonium peroxydisulfate, and 2 M H2SO4. The result of cyclic voltammograms in a potential region of ?0.20 to 0.80 V (vs.SCE) indicates that the electrochemical activity of the copolymer prepared under the optimum condition is similar to that of polyaniline in more acid solutions. However, the copolymer still holds the good electrochemical activity until pH 11.0. Therefore, the pH dependence of the electrochemical property of the copolymer is improved, compared with poly(aniline‐co‐o‐aminophenol) prepared electrochemically, and is much better than that of polyaniline. The spectra of IR and 1H NMR confirm that o‐aminophenol units are included in the copolymer chain, which play a key role in extending the usable pH region of the copolymer. The visible spectra of the copolymers show that a high concentration ratio of o‐aminophenol to aniline in a mixture inhibits the chain growth. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5573–5582, 2007 相似文献