全文获取类型
收费全文 | 4819篇 |
免费 | 163篇 |
国内免费 | 11篇 |
专业分类
化学 | 3843篇 |
晶体学 | 118篇 |
力学 | 179篇 |
数学 | 194篇 |
物理学 | 659篇 |
出版年
2023年 | 33篇 |
2022年 | 52篇 |
2021年 | 74篇 |
2020年 | 97篇 |
2019年 | 118篇 |
2018年 | 114篇 |
2017年 | 94篇 |
2016年 | 168篇 |
2015年 | 124篇 |
2014年 | 211篇 |
2013年 | 505篇 |
2012年 | 349篇 |
2011年 | 309篇 |
2010年 | 176篇 |
2009年 | 167篇 |
2008年 | 270篇 |
2007年 | 255篇 |
2006年 | 199篇 |
2005年 | 190篇 |
2004年 | 177篇 |
2003年 | 156篇 |
2002年 | 129篇 |
2001年 | 46篇 |
2000年 | 48篇 |
1999年 | 37篇 |
1998年 | 24篇 |
1997年 | 26篇 |
1996年 | 44篇 |
1995年 | 34篇 |
1994年 | 33篇 |
1993年 | 35篇 |
1992年 | 32篇 |
1991年 | 28篇 |
1990年 | 43篇 |
1989年 | 39篇 |
1988年 | 30篇 |
1987年 | 38篇 |
1986年 | 34篇 |
1985年 | 46篇 |
1984年 | 47篇 |
1983年 | 36篇 |
1982年 | 26篇 |
1981年 | 34篇 |
1980年 | 31篇 |
1979年 | 23篇 |
1978年 | 23篇 |
1977年 | 26篇 |
1976年 | 29篇 |
1975年 | 26篇 |
1974年 | 12篇 |
排序方式: 共有4993条查询结果,搜索用时 62 毫秒
81.
J.S. Yadav B.V. Subba Reddy A.K. Basak A.V. Narsaiah A. Prabhakar B. Jagadeesh 《Tetrahedron letters》2005,46(4):639-641
Baylis-Hillman acetates undergo SN2′ allylic substitution with indoles in the presence of 20 mol % of indium tribromide under mild conditions to afford a new class of substituted indoles in high yields with (E)-stereoselectivity. The stereochemistry of the products was assigned by various NMR experiments. 相似文献
82.
Bose G Nguyen VT Ullah E Lahiri S Görls H Langer P 《The Journal of organic chemistry》2004,69(26):9128-9134
The Lewis acid mediated domino "[3+3]-cyclization-homo-Michael" reaction of 1,3-bissilyl enol ethers with 1,1-diacylcyclopropanes allows an efficient one-pot synthesis of functionalized salicylates containing a halogenated side chain. A great variety of substitution patterns could be realized by variation of the starting materials and of the Lewis acid. The mechanism of the domino process was studied. 相似文献
83.
Muralidhar P Kumar MM Krishna N Rao CB Rao DV 《Chemical & pharmaceutical bulletin》2005,53(2):168-171
Chemical investigation of a soft coral species of the genus Lobophytum has resulted in the isolation of three new sphingolipids--(2S,3S,4R)-2-nonadecanoylamino-octadecane-1,3,4-triol (1), (2S,3R,4E,8E)-[(2'R)-2'-hydroxyheptadecanoylamino]-4,8-octadecadiene-1,3-diol (2), 1-O-(beta-D-glucopyranosyl)-(2S,3R,4E,8E)-2-[(2'R)-2'-hydroxynonadecanoylamino]-9-methyl-4,8-octadecadiene-1,3-diol (3) and a sterol--(24S)-ergost-5-en-3beta,7beta-diol (4) along with the known sphingolipid--(2S,3R,4E,8E)-2-hexadecanoylamino-4,8-octadecadien-1,3-diol (5) which showed cytotoxicity against human peripheral blood mononuclear cells (PBMC). 相似文献
84.
Deva Prasad Raju B Lakshmana Rao J Narasimhulu KV Gopal NO Sunandana CS 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2005,61(9):2195-2198
EPR and optical absorption spectra of Cr3+ ions doped in KZnClSO4 x 3H2O single crystals have been studied at room temperature. The EPR spectrum exhibits a group of three fine structure transitions characteristic of Cr3+ ions. From the observed EPR spectra, the spin-Hamiltonian parameters have been determined. The optical absorption spectrum exhibits two broad bands characteristic of Cr3+ ions in an octahedral symmetry. From the observed band positions, the crystal field parameters have been evaluated. 相似文献
85.
A highly efficient and stereoselective synthesis of (2R,3R,4R)-HMP is disclosed employing the sulfinyl group as an internal nucleophile to functionalize an olefin in the key step of the reaction sequence. The proline ring is elaborated by a (4C+N) cyclization. 相似文献
86.
Spin configuration of Gd13 clusters 总被引:1,自引:0,他引:1
87.
Andhe V. Narender Reddy Charles Y. Fiakpui David P. Czajkowski Paul Spevak Jadwiga Kaleta Ronald G. Micetich Samarendra N. Maiti 《Chemistry of Heterocyclic Compounds》1998,34(11):1289-1295
A new series of 2-spiro(2,2-diphenylcyclopropane) cephalosporin sulfones was synthesizes as potent human leukocyte elastase inhibitors.SynPhar Laboratories Inc., #2 Taiho Alberta Centre, 4290-91A Street, Edmonton, Canada T6R 5V2. Published in Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1517–1523, November, 1998. 相似文献
88.
Oludotun A. Phillips Eduardo L. Setti Andhe V. N. Reddy Ronald G. Micetich Chieko Kunugita Akio Hyodo Samarendra N. Maiti 《Chemistry of Heterocyclic Compounds》1998,34(11):1319-1323
Two monobactam derivatives, potassium 4-methyl-(3E)-[(thien-2-yl)methylene]-2-azetidinone-1-sulfonate and its (3Z)-isomer, were prepared and evaluated for their -lactamase inhibitory activities. These compounds were devoid of -lactamase inhibitory activity.SynPhar Laboratories Inc., #2, 4290-91A Street, Edmonton, Alberta T6E 5V2, Canada. Tokushima Research Institute, Taiho Pharmaceutical Co., Ltd., 224-2 Ebisuno Hiraishi, Kawauchi-cho, Tokushima 771-01, Japan. Published in Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1548–1552, November, 1998. 相似文献
89.
Application of sodium metaperiodate for the determination of ribavirin in pharmaceutical formulations 总被引:1,自引:0,他引:1
Three simple and sensitive visible spectrophotometric methods (A-C) have been described for the assay of ribavirin either in pure form or in pharmaceutical formulations. They are based on the oxidation of ribavirin with excess sodium metaperiodate and estimating either the products formed (dialdehyde with MBTH, method A; iodate with metol-sulphanilamide, in the presence of Mo(VI) and iodide, method B) or the amount of periodate consumed (celestine blue in the presence of telurium (IV), method C). All of the variables have been optimized and the reaction mechanisms presented. The concentration measurements are reproducible within a R.S.D. of 1.0%. Recoveries are 99.2-101.2%. 相似文献
90.
K. Premchand B. Seetharami Reddy B. Mallikarjuna Rao K. Parthasaradhi M. V. R. Murti K. S. Rao 《Il Nuovo Cimento D》1993,15(1):73-76
Summary An attempt is made to study theK
α
L
1 satellite multiplet structure of chlorine atoms in different compounds by photon excitation. A comparison of the averageK
α
L
1 group energy shift from the diagram line with those based on Dirac-Fock evaluations with different number ofM-shell electrons shows a reasonable agreement. The
intensity ratios are found to be higher than those studied in Mg compounds in general. 相似文献