全文获取类型
收费全文 | 3932篇 |
免费 | 124篇 |
国内免费 | 10篇 |
专业分类
化学 | 3156篇 |
晶体学 | 99篇 |
力学 | 174篇 |
数学 | 113篇 |
物理学 | 524篇 |
出版年
2023年 | 25篇 |
2022年 | 49篇 |
2021年 | 55篇 |
2020年 | 72篇 |
2019年 | 93篇 |
2018年 | 97篇 |
2017年 | 76篇 |
2016年 | 127篇 |
2015年 | 90篇 |
2014年 | 170篇 |
2013年 | 429篇 |
2012年 | 263篇 |
2011年 | 234篇 |
2010年 | 146篇 |
2009年 | 138篇 |
2008年 | 223篇 |
2007年 | 216篇 |
2006年 | 160篇 |
2005年 | 161篇 |
2004年 | 153篇 |
2003年 | 132篇 |
2002年 | 132篇 |
2001年 | 47篇 |
2000年 | 43篇 |
1999年 | 35篇 |
1998年 | 21篇 |
1997年 | 24篇 |
1996年 | 42篇 |
1995年 | 25篇 |
1994年 | 32篇 |
1993年 | 30篇 |
1992年 | 29篇 |
1991年 | 25篇 |
1990年 | 38篇 |
1989年 | 30篇 |
1988年 | 26篇 |
1987年 | 29篇 |
1986年 | 28篇 |
1985年 | 37篇 |
1984年 | 40篇 |
1983年 | 29篇 |
1982年 | 26篇 |
1981年 | 24篇 |
1980年 | 24篇 |
1979年 | 19篇 |
1978年 | 13篇 |
1977年 | 21篇 |
1976年 | 16篇 |
1975年 | 18篇 |
1974年 | 9篇 |
排序方式: 共有4066条查询结果,搜索用时 31 毫秒
111.
A. R. Reddy 《manuscripta mathematica》1977,20(1):95-97
In this note we obtain error bounds to x2n+1–x2n on [–1, 1] by polynomials of degree at most (2n–1). The result proved here improves and extends some of the known results of Zolotarev and Bernstein. The proof presented here is different (and simple) from the one adopted by Zolotarev and Bernstein. 相似文献
112.
A simple stereocontrolled synthesis of salinosporamide A 总被引:1,自引:0,他引:1
A simple and effective stereocontrolled synthesis of salinosporamide A has been developed. This process, the first synthesis of salinosporamide A, is capable of providing the compound in substantial quantities for further biological studies. Salinosporamide A was of special interest as a synthetic target because of its potent in vitro cytotoxic activity against many tumor cell lines (IC(50) values of 10 nM or less). 相似文献
113.
Ciprofloxacin-protected gold nanoparticles 总被引:3,自引:0,他引:3
Tom RT Suryanarayanan V Reddy PG Baskaran S Pradeep T 《Langmuir : the ACS journal of surfaces and colloids》2004,20(5):1909-1914
The antibacterial drug ciprofloxacin (cfH) has been used to protect gold nanoparticles of two different mean diameters, 4 and 20 nm. The protection is complete with about 65 and 585 cfH molecules covering 4 and 15 nm particles, respectively. The nature of binding has been investigated by several analytical techniques. The nitrogen atom of the NH moiety of piperazine group binds on the gold surface, as revealed by voltammetric and spectroscopic studies. The cfH-adsorbed particles are stable in the dry state as well as at room temperature, and as a result, redispersion is possible. The rate of release of the drug molecule from the nanoparticles is more in the basic medium than in pure water, and the kinetics depend on the size of the particle; faster desorption is seen in smaller particles. The bound cfH is fluorescent, and this property could be used in biological investigations. This study shows that metal nanoparticles could be useful carriers for cfH and fluoroquinolone molecules. Most of the bound molecules could be released over an extended period of time. 相似文献
114.
Isobaric vapor–liquid equilibrium data at 95.96 kPa for the three binary systems of 2,2,4-trimethylpentane with methyl tert-butyl ether, di-isopropyl ether and dimethoxymethane are determined. A Swietoslawski type ebulliometer is used for the measurements. The experimental T–x data are used to estimate Wilson parameters and the parameters, in turn, are used to calculate vapor phase compositions and activity coefficients. All the systems studied here do not exhibit azeotropes and behave like non-ideal solutions. 相似文献
115.
[reaction: see text] Optically pure allylic amines have been synthesized from alpha,beta-unsaturated aldehydes via allylboration with (-)-B-allyldiisopinocampheylborane, followed by Overman rearrangement. By incorporating crotyl and alkoxyallylboration, functionalization at delta-position was readily accomplished. By applying this methodology, the synthesis of several chiral alpha-amino acids has been achieved. 相似文献
116.
A novel methodology for the regio- and stereoselective synthesis of amino alcohol derivatives from allylalcohols/ethers via intramolecular nucleophilic participation by the sulfilimine moiety is disclosed. The sulfilimine moiety is stereospecifically transformed to a sulfinyl moiety with an inverted configuration. The reaction is general and affords highly functionalised products. 相似文献
117.
Kumar MR Prabhakar S Kumar MK Reddy TJ Vairamani M 《Rapid communications in mass spectrometry : RCM》2004,18(10):1109-1115
The negative ion electrospray ionization (ESI) mass spectra of a series of dicarboxylic acids, a pair of isomeric (cis/trans) dicarboxylic acids and two pairs of isomeric (positional) substituted benzoic acids, including a pair of hydroxybenzoic acids, were recorded in the presence of halide ions (F(-), Cl(-), Br(-) and I(-)). The ESI mass spectra contained [M--H](-) and [M+X](-) ions, and formation of these ions is found to be characteristic of both the analyte and the halide ion used. The analytes showed a greater tendency to form adduct ions with Cl(-) under ESI conditions compared with the other halide ions used. The isomeric compounds yielded distinct spectra by which the isomers could be easily distinguished. The collision-induced dissociation mass spectra of [M+X](-) ions reflected the gas-phase basicities of both the halide ion and [M--H](-) ion of the analyte. However, the relative ordering of gas-phase basicities of all analyte [M--H](-) and halide ions could not account for the dominance of chloride ion adducts in ESI mass spectra of the analytes mixed with equimolar quantities of the four halides. 相似文献
118.
A stereoselective synthesis of the pentaketide lactone (3R,4S,5S,9S)-3,5,9-trihydroxy-4-methylundecanoic acid δ-lactone has been achieved. 相似文献
119.
S. M. Malathy Sony M. Kuppayee M. N. Ponnuswamy D. Bhasker Reddy V. Padmavathi Hoong‐Kun Fun 《Acta Crystallographica. Section C, Structural Chemistry》2002,58(11):o678-o680
Due to steric repulsions, the cyclohexane ring in the title compound, C23H24N2O5·H2O, shows some bond‐length abnormalities and adopts a chair conformation. The pyrimidine and cyclohexane rings are approximately perpendicular to each other, and the phenyl rings are equatorial. C—H?π and N—H?O intermolecular interactions, as well as C—H?O inter‐ and intramolecular interactions, occur between the molecules. In addition to van der Waals interactions, the water molecule interacts with the pyrimidinetrione ring to stabilize the structure. 相似文献
120.
J.S. Yadav B.V. Subba Reddy P. Vishnumurthy Ch. Janardhana Chary 《Tetrahedron letters》2007,48(33):5915-5918
Lithium tetrafluoroborate is found to be an efficient catalyst for allylation and cyanation of aldehydes with allyltrimethylsilane and trimethylsilyl cyanide in the presence of acetic anhydride at room temperature to produce homoallylic acetates and α-cyano acetates in excellent yields. A solution of 10 mol % of LiBF4 in acetonitrile provides a convenient reaction medium to carry out allylation and cyanation reactions under very mild and neutral conditions. 相似文献