全文获取类型
收费全文 | 2376篇 |
免费 | 37篇 |
国内免费 | 16篇 |
专业分类
化学 | 1393篇 |
晶体学 | 15篇 |
力学 | 40篇 |
数学 | 516篇 |
物理学 | 465篇 |
出版年
2021年 | 23篇 |
2020年 | 28篇 |
2019年 | 18篇 |
2018年 | 19篇 |
2017年 | 19篇 |
2016年 | 40篇 |
2015年 | 31篇 |
2014年 | 39篇 |
2013年 | 105篇 |
2012年 | 82篇 |
2011年 | 90篇 |
2010年 | 57篇 |
2009年 | 47篇 |
2008年 | 88篇 |
2007年 | 98篇 |
2006年 | 106篇 |
2005年 | 95篇 |
2004年 | 94篇 |
2003年 | 73篇 |
2002年 | 58篇 |
2001年 | 37篇 |
2000年 | 28篇 |
1998年 | 20篇 |
1997年 | 22篇 |
1996年 | 44篇 |
1995年 | 32篇 |
1994年 | 24篇 |
1993年 | 26篇 |
1992年 | 32篇 |
1991年 | 23篇 |
1990年 | 20篇 |
1989年 | 22篇 |
1988年 | 18篇 |
1987年 | 20篇 |
1986年 | 22篇 |
1985年 | 32篇 |
1984年 | 34篇 |
1983年 | 17篇 |
1982年 | 39篇 |
1981年 | 30篇 |
1980年 | 43篇 |
1979年 | 39篇 |
1978年 | 32篇 |
1977年 | 42篇 |
1976年 | 48篇 |
1975年 | 44篇 |
1974年 | 36篇 |
1973年 | 27篇 |
1972年 | 19篇 |
1971年 | 21篇 |
排序方式: 共有2429条查询结果,搜索用时 15 毫秒
121.
Saidbakhrom Saidjalolov Dr. Zainab Edoo Dr. Matthieu Fonvielle Louis Mayer Dr. Laura Iannazzo Dr. Michel Arthur Prof. Dr. Mélanie Etheve-Quelquejeu Dr. Emmanuelle Braud 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(10):3542-3551
The carbapenem class of β-lactams has been optimized against Gram-negative bacteria producing extended-spectrum β-lactamases by introducing substituents at position C2. Carbapenems are currently investigated for the treatment of tuberculosis as these drugs are potent covalent inhibitors of l,d -transpeptidases involved in mycobacterial cell wall assembly. The optimization of carbapenems for inactivation of these unusual targets is sought herein by exploiting the nucleophilicity of the C8 hydroxyl group to introduce chemical diversity. As β-lactams are structure analogs of peptidoglycan precursors, the substituents were chosen to increase similarity between the drug and the substrate. Fourteen peptido-carbapenems were efficiently synthesized. They were more effective than the reference drug, meropenem, owing to the positive impact of a phenethylthio substituent introduced at position C2 but the peptidomimetics added at position C8 did not further improve the activity. Thus, position C8 can be modified to modulate the pharmacokinetic properties of highly efficient carbapenems. 相似文献
122.
123.
124.
Grigor’ev Arthur A. Kayukov Yakov S. Nikiforova Anastasiya L. Karpov Sergey V. Shchegravina Ekaterina S. Kayukova Olga V. Tafeenko Victor A. 《Chemistry of Heterocyclic Compounds》2019,55(2):167-171
Chemistry of Heterocyclic Compounds - 4-Acyl-2-amino-6-chloropyridine-3,5-dicarbonitriles underwent heterocyclization in the presence of ammonia in aqueous dioxane medium, involving the... 相似文献
125.
A tunable microwave-assisted protocol for the synthesis of two biologically relevant families of heterocycles has been designed. Via a simple switch of reaction conditions, the same starting materials can be engaged in either an improved synthesis of the dihydrotriazine scaffold or a novel, first-in-class MCR to render the challenging 5-aminoimidazole nucleus in a single step. An additional first-in-class MCR is also reported utilizing guanidines to afford 2,5-aminoimidazoles. 相似文献
126.
Arthur R. Tulyabaev Airat R. Tuktarov Leonard M. Khalilov 《Magnetic resonance in chemistry : MRC》2014,52(1-2):3-9
Using gauge‐invariant atomic orbital PBE/3ζ quantum chemistry approach, 13C NMR chemical shifts and diastereotopic splittings of sp2 fullerenyl carbons of a number of sulfur homofullerenes and methanofullerenes have been predicted and discussed. An anisochrony of fullerene carbons is caused by a chiral center of attached moieties. Clearly distinguishable diastereotopic pairs (from 8 to 11) of fullerenyl carbons of homofullerenes were observed. Unambiguous assignments of 13C NMR chemical shifts were performed, and diastereotopic splittings of methanofullerenes were observed for α, β and γ to a functionalization site. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
127.
128.
Arthur J. Banister 《Phosphorus, sulfur, and silicon and the related elements》2013,188(2):147-157
Abstract Recent studies of delocalized inorganic species containing a sulfur-nitrogen chain or ring are reviewed, and some general principles of structure and synthesis of cyclic thiazenes are discussed. Linear correlations between sulfur-nitrogen bond distance and (i) SNS bond angle and (ii) stretching wavelength are of value in deducing structural data for unstrained species. 相似文献
129.
130.
Prof. Dr. Christian Brückner Dr. Nivedita Chaudhri Dustin E. Nevonen Dr. Sayantan Bhattacharya Arthur Graf Elizabeth Kaesmann Dr. Ruoshi Li Dr. Matthew J. Guberman-Pfeffer Prof. Dr. Tomoyasu Mani Dr. Arunpatcha Nimthong-Roldán Dr. Matthias Zeller Dr. Adrien A. P. Chauvet Prof. Dr. Victor Nemykin 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(65):16189-16203