全文获取类型
收费全文 | 3110篇 |
免费 | 72篇 |
国内免费 | 18篇 |
专业分类
化学 | 2383篇 |
晶体学 | 27篇 |
力学 | 71篇 |
数学 | 306篇 |
物理学 | 413篇 |
出版年
2023年 | 14篇 |
2022年 | 18篇 |
2021年 | 23篇 |
2020年 | 45篇 |
2019年 | 31篇 |
2018年 | 25篇 |
2017年 | 21篇 |
2016年 | 55篇 |
2015年 | 54篇 |
2014年 | 64篇 |
2013年 | 128篇 |
2012年 | 165篇 |
2011年 | 239篇 |
2010年 | 88篇 |
2009年 | 90篇 |
2008年 | 152篇 |
2007年 | 203篇 |
2006年 | 225篇 |
2005年 | 206篇 |
2004年 | 152篇 |
2003年 | 112篇 |
2002年 | 149篇 |
2001年 | 51篇 |
2000年 | 41篇 |
1999年 | 37篇 |
1998年 | 47篇 |
1997年 | 34篇 |
1996年 | 46篇 |
1995年 | 38篇 |
1994年 | 32篇 |
1993年 | 31篇 |
1992年 | 29篇 |
1991年 | 27篇 |
1990年 | 23篇 |
1989年 | 20篇 |
1988年 | 20篇 |
1987年 | 28篇 |
1985年 | 33篇 |
1984年 | 31篇 |
1983年 | 27篇 |
1982年 | 38篇 |
1981年 | 30篇 |
1980年 | 35篇 |
1979年 | 27篇 |
1978年 | 22篇 |
1977年 | 26篇 |
1976年 | 18篇 |
1975年 | 18篇 |
1974年 | 20篇 |
1973年 | 20篇 |
排序方式: 共有3200条查询结果,搜索用时 15 毫秒
91.
Burford N Eelman MD Mahony DE Morash M 《Chemical communications (Cambridge, England)》2003,(1):146-147
Solutions containing BiCl3, bismuth subsalicylate or Bi(NO3)3 with L-cysteine, DL-homocysteine, D-methionine or glutathione have been examined by electrospray mass spectrometry. Prominent peaks are assigned to bismuth complexes of these biomolecules and provide insight towards understanding the bioactivity of bismuth compounds. 相似文献
92.
Dobson N McDowell DG French DJ Brown LJ Mellor JM Brown T 《Chemical communications (Cambridge, England)》2003,(11):1234-1235
An FMOC-protected 2'-hydroxyethyl uridine phosphoramidite has been used to synthesise fluorescein-labelled HyBeacon probes and "FAM-ROX" dual-labelled fluorogenic oligonucleotides. 相似文献
93.
An unprecedented combination of photochromism and electrochromism is observed for two 1,2-bis(dithienyl)cyclopentene derivatives; the ring-opening reactions are photochemically driven while the ring-closing reactions can be triggered by electrochemical oxidation. 相似文献
94.
Oluwole S. Aremu Parvesh Singh Moganavelli Singh Chunderika Mocktar Neil A. Koorbanally 《Journal of heterocyclic chemistry》2019,56(11):3008-3016
Chloro, fluoro, and nitro derivatives of 7‐amino‐5‐aryl‐6‐cyano‐5H‐pyrano pyrimidin‐2,4‐diones were produced by reacting malononitrile, barbituric acid, and aromatic aldehydes together with a DABCO catalyst in an aqueous one‐pot reaction. This is the first report of these compounds being synthesized with DABCO as a catalyst, which produced the compounds in yields in excess of 90%. The 2,4‐difluoro derivative ( 11 ) was novel. The structures of the synthesized compounds were elucidated by means of 1H, 13C, and 2D NMR spectroscopy. Compound 2 (2‐Cl derivative) had MBC values of <200μM against both Staphylococcus aureus and MRSA, and the 2‐nitro derivative 5 had an MBC of 191μM against the Gram–ve Escherichia coli. The synthesized compounds were also tested for their anticancer activity against a HeLa cell line, where all the compounds showed better activity (IC50 values between 129μM and 340μM) than 5‐fluorouracil, a commonly known anticancer drug. 相似文献
95.
Alexander Tuan-Huy Duong Bryan J. Simmons Mohammad Parvez Alam Jesus Campagna Neil K. Garg Varghese John 《Tetrahedron letters》2019,60(3):322-326
This study describes our development of a microfluidic reaction scheme for the synthesis of fused indoline ring systems found in several bioactive compounds. We have utilized a continuous-flow microfluidic reactor for the reaction of hydrazines with latent aldehydes through the interrupted Fischer indolization reaction to form fused indoline and azaindoline products. We have identified optimal conditions and evaluated the scope of this microfluidic reaction using various hydrazine and latent aldehyde surrogates. This green chemistry approach can be of general utility to rapidly produce indoline scaffolds and intermediates in a continuous manner. 相似文献
96.
97.
Badham NF Mendelson WL Allen A Diederich AM Eggleston DS Filan JJ Freyer AJ Killmer LB Kowalski CJ Liu L Novack VJ Vogt FG Webb KS Yang J 《The Journal of organic chemistry》2002,67(15):5440-5443
A convenient two-step homologation of both aliphatic and aromatic ketones to the corresponding carboxylic acid has been developed. First ketones were converted to epoxynitriles with the Darzens reaction. Second, a Lewis acid mediated rearrangement of these epoxynitriles with lithium bromide was achieved to give homologated secondary alkanoic acids (as well as aryl-alkanoic) in good yields. The mechanism and the scope of the rearrangement reaction were investigated. This strategy constitutes a two-step homologation of ketones to secondary carboxylic acids. 相似文献
98.
Chemical reactions occurring at the mineral–water interface are controlled by an interfacial layer, nanometers thick, whose properties may deviate from those of the respective bulk mineral and water phases. The molecular-scale structure of this interfacial layer, however, is poorly constrained, and correlations between macroscopic phenomena and molecular-scale processes remain speculative. The application of high-resolution X-ray scattering techniques has begun to provide substantial new insights into the molecular-scale structure of the mineral–water interface. In this review, we describe the characteristics of synchrotron-based X-ray scattering techniques that make them uniquely powerful probes of mineral–water interfacial structures and discuss the new insights that have been derived from their application. In particular, we focus on efforts to understand the structure and distribution of interfacial water as well as their dependence on substrate properties for major mineral classes including oxides, carbonates, sulfates, phosphates, silicates, halides and chromates. We compare these X-ray scattering results with those from other structural and spectroscopic techniques and integrate these to provide a conceptual framework upon which to base an understanding of the systematic variation of mineral–water interfacial structures. 相似文献
99.
Zinc bromide-catalyzed heterolysis reactions of glycol ether radicals were studied by laser flash photolysis methods, which gave the binding constants and catalytic rate constants for fragmentation. The Lewis acid-catalyzed heterolysis reactions mimic a putative reaction pathway in diol dehydratase-catalyzed reactions and are potentially useful polar processes for incorporation into conventional radical chain reaction sequences. [reaction: see text] 相似文献
100.
It has been suggested from QSAR data (P. D. Edwards, D. J. Wolanin, D.A. Andisik and M. W. Davis, J. Med. Chem., 1995, 38, 76) that the inhibition of elastase by peptidyl alpha-ketoheterocyclic inhibitors can occur in two ways, the less potent inhibitors forming a non-bonded Michaelis complex and the more potent set a covalently bonded enzyme-substrate intermediate. We report QM/MM studies of both binding and reactivity that confirm these findings, showing that the activity of the least potent set of inhibitors correlates with the calculated binding energy, and that of the more potent set correlates with the stability of the intermediate. These calculations show that QM/MM methods can be successfully employed to understand complicated structure-activity relationships and might be employed in the design and assessment of new inhibitors. 相似文献