全文获取类型
收费全文 | 6604篇 |
免费 | 327篇 |
国内免费 | 31篇 |
专业分类
化学 | 5178篇 |
晶体学 | 23篇 |
力学 | 133篇 |
数学 | 650篇 |
物理学 | 978篇 |
出版年
2023年 | 62篇 |
2022年 | 95篇 |
2021年 | 114篇 |
2020年 | 139篇 |
2019年 | 162篇 |
2018年 | 127篇 |
2017年 | 109篇 |
2016年 | 251篇 |
2015年 | 192篇 |
2014年 | 199篇 |
2013年 | 326篇 |
2012年 | 538篇 |
2011年 | 615篇 |
2010年 | 285篇 |
2009年 | 217篇 |
2008年 | 465篇 |
2007年 | 466篇 |
2006年 | 473篇 |
2005年 | 437篇 |
2004年 | 324篇 |
2003年 | 270篇 |
2002年 | 229篇 |
2001年 | 86篇 |
2000年 | 39篇 |
1999年 | 33篇 |
1998年 | 41篇 |
1997年 | 35篇 |
1996年 | 35篇 |
1995年 | 30篇 |
1994年 | 25篇 |
1993年 | 31篇 |
1992年 | 36篇 |
1991年 | 29篇 |
1990年 | 17篇 |
1989年 | 15篇 |
1988年 | 24篇 |
1987年 | 22篇 |
1986年 | 17篇 |
1985年 | 35篇 |
1984年 | 28篇 |
1983年 | 19篇 |
1982年 | 25篇 |
1981年 | 25篇 |
1980年 | 13篇 |
1979年 | 23篇 |
1978年 | 15篇 |
1977年 | 25篇 |
1976年 | 18篇 |
1975年 | 19篇 |
1973年 | 12篇 |
排序方式: 共有6962条查询结果,搜索用时 15 毫秒
91.
Darensbourg DJ Maynard EL Holtcamp MW Klausmeyer KK Reibenspies JH 《Inorganic chemistry》1996,35(9):2682-2684
92.
93.
Conformations of cyclopropyl methyl ketone have been studied using ab initio methods in an effort to quantify the effects of conjugative overlap between the cyclopropane ring and an adjacent ketone carbonyl. Results were comparable with previous experimental and theoretical studies. Cyclopropyl methyl ketone exhibits a global energy minimum in the s-cis conformer and a local energy minimum near the s-trans conformer. The potential energy curve obtained was used to derive torsion parameters which were employed in molecular mechanics studies of the conformations of the set of bicyclo[m.1.0]alkan-2-ones having larger ring sizes from five- to 16-membered. Similar conformations for the cyclopropyl ketone substructure are observed for all the medium and large ring systems examined. Possible synthetic ramifications of local conformational anchoring by this functional group array are discussed. 相似文献
94.
5-Methyl-4-phenyl-2-styryipyridine has been oxidized to 5-methyl-4-phenylpyridinie-2-carboxylic acid. The decarboxylation of this acid has given 3-methyl-4-phenylpyrldine. To prove the structure of -(5-methyl-4-phenyl-2-pyridyl)acetophenone, it has been converted into 2, 5-dimethyl-4-phenylpyridine. The reaction of benzyl chloride with the lithium derivative of 2, 5-dimethyl-4-phenylpyridine has been studied. 3,7-Dimethyl-2-azafluorene has been obtained from 2,5-dimethyl-4-p-tolylpyridine. 相似文献
95.
Carrillo-Marquez T Caggiano L Jackson RF Grabowska U Rae A Tozer MJ 《Organic & biomolecular chemistry》2005,3(22):4117-4123
Two distinct routes to beta-cycloalkylalanine derivatives have been developed. The first route employs the reaction of the iodoalanine-derived zinc-copper reagent 2 with cycloalk-1-en-3-yl phosphates, and the second uses the palladium-catalysed coupling of the iodoalanine-derived zinc reagent 1 with cycloalkenyl triflates; in each case, catalytic hydrogenation of the unsaturated product leads to the protected beta-cycloalkylalanine. The latter route allows access to a range of cycloalkyl derivatives, with ring sizes of 5-8. beta-(1-Methyl-1-cyclohexyl)alanine may be prepared using reaction of the zinc-copper reagent 2 with 3-methyl-2-cyclohexenyl chloride, followed by hydrogenation. The corresponding cyclopentyl derivative may be prepared by reaction of the same zinc-copper reagent 2 with diethyl geranylphosphate, followed by ring-closing metathesis and hydrogenation. 相似文献
96.
A response equation for conductivity detection in ion chromatography has been derived. This equation is applicable to non-suppressed ion chromatography using both fully ionised and partially ionised eluents. A prime assumption of this equation is that when partially ionised eluents are used (such as benzoic acid), both the ionised and neutral components of the eluent species contribute to the detector response of anionic analytes. Experimental evidence is provided to support this assumption in that pH changes accompanying the elution of an analyte have been measured. These pH changes are proportional to the concentration of analyte injected onto the column, in accordance with predictions from the response equation. Furthermore, it is shown that protonated eluents (such as benzoic acid) give more sensitive detection than equivalent ionised eluents (such as potassium benzoate) and the signal enhancement achieved using a protonated eluent species is in accordance with theory. 相似文献
97.
The reactions of benzocyclic ketones and α-ketoacids as carbonyl components in the Biginelli reaction were investigated. These unusual Biginelli substrates furnished novel drug-like dihydropyrimidinone scaffolds suitable for further elaboration. 相似文献
98.
The mode of action of the secondary metabolite chlorofusin, which antagonises the interaction between p53 and MDM2, involves direct binding to the N-terminal domain of MDM2. 相似文献
99.
Smith BD Soellner MB Raines RT 《Langmuir : the ACS journal of surfaces and colloids》2005,21(1):187-190
Intact RNA and DNA are of central importance to biochemical research and biotechnology. The preservation of these nucleic acids requires the absence of nuclease activity. Here, radical-mediated polymerization of vinylsulfonate on resin and glass surfaces is shown to produce a high-density poly(vinylsulfonate) coating that sequesters ribonucleases from aqueous solutions quickly and completely. The adsorptive efficacy of this coating exceeds that of other known coatings by > or =10(7)-fold. Surfaces coated with poly(vinylsulfonate) could be used to maintain the integrity of ribonucleic acids in a variety of contexts. 相似文献
100.