全文获取类型
收费全文 | 11870篇 |
免费 | 1315篇 |
国内免费 | 420篇 |
专业分类
化学 | 5197篇 |
晶体学 | 27篇 |
力学 | 1117篇 |
综合类 | 34篇 |
数学 | 5249篇 |
物理学 | 1981篇 |
出版年
2023年 | 150篇 |
2022年 | 147篇 |
2021年 | 220篇 |
2020年 | 406篇 |
2019年 | 303篇 |
2018年 | 271篇 |
2017年 | 251篇 |
2016年 | 459篇 |
2015年 | 468篇 |
2014年 | 600篇 |
2013年 | 981篇 |
2012年 | 660篇 |
2011年 | 702篇 |
2010年 | 490篇 |
2009年 | 764篇 |
2008年 | 699篇 |
2007年 | 752篇 |
2006年 | 625篇 |
2005年 | 487篇 |
2004年 | 452篇 |
2003年 | 430篇 |
2002年 | 358篇 |
2001年 | 364篇 |
2000年 | 331篇 |
1999年 | 271篇 |
1998年 | 283篇 |
1997年 | 225篇 |
1996年 | 231篇 |
1995年 | 162篇 |
1994年 | 123篇 |
1993年 | 121篇 |
1992年 | 81篇 |
1991年 | 77篇 |
1990年 | 60篇 |
1989年 | 55篇 |
1988年 | 55篇 |
1987年 | 42篇 |
1986年 | 52篇 |
1985年 | 38篇 |
1984年 | 48篇 |
1983年 | 17篇 |
1982年 | 29篇 |
1981年 | 29篇 |
1980年 | 20篇 |
1979年 | 25篇 |
1978年 | 41篇 |
1977年 | 42篇 |
1976年 | 41篇 |
1975年 | 15篇 |
1974年 | 15篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
Corresponding-states group-contribution methods (CSGC-ST1 and CSGC-ST2) have been applied to four binary liquid mixtures (propyl acetate + o-xylene, propyl acetate + m-xylene, propyl acetate + p-xylene and propyl acetate + ethyl benzene); two ternary (benzene + cyclohexane + toluene and n-hexane + cyclohexane + benzene) and two quaternary liquid mixtures (pentane + hexane + cyclohexane + benzene and pentane + hexane + benzene + toluene) at 298.15 K. In this work, the CSGC-ST2 method is modified and extended to multicomponent liquid mixtures. The excess magnitudes of surface tension were also calculated and graphs were plotted using Redlich–Kister method. 相似文献
993.
994.
Dapeng Zhao Dr. Wei Gao Dr. Ying Mu Prof. Ling Ye 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(14):4394-4401
A series of new titanium(IV) complexes with o‐metalated arylimine and/or cis‐9,10‐dihydrophenanthrenediamide ligands, [o‐C6H4(CH?NR)TiCl3] (R=2,6‐iPr2C6H3 ( 3 a ), 2,6‐Me2C6H3 ( 3 b ), tBu ( 3 c )), [cis‐9,10‐PhenH2(NR)2TiCl2] (PhenH2=9,10‐dihydrophenanthrene; R=2,6‐iPr2C6H3 ( 4 a ), 2,6‐Me2C6H3 ( 4 b ), tBu ( 4 c )), [{cis‐9,10‐PhenH2(NR)2}{o‐C6H4(HC?NR)}TiCl] (R=2,6‐iPr2C6H3 ( 5 a ), 2,6‐Me2C6H3 ( 5 b ), tBu ( 5 c )), have been synthesised from the reactions of TiCl4 with o‐C6H4(CH?NR)Li (R=2,6‐iPr2C6H3, 2,6‐Me2C6H3, tBu). Complexes 4 and 5 were formed unexpectedly from the reactions of TiCl4 with two or three equivalents of the corresponding o‐C6H4(CH?NR)Li followed by sequential intramolecular C? C bond‐forming reductive elimination and oxidative coupling reactions. Attempts to isolate the intermediates, [{o‐C6H4(CH?NR)}2TiCl2] ( 2 ), were unsuccessful. All complexes were characterised by 1H and 13C NMR spectroscopy, and the molecular structures of 3 a , 4 a – c , 5 a , and 5 c were determined by X‐ray crystallography. 相似文献
995.
Jan Bornholdt Dr. Jakob Felding Dr. Rasmus P. Clausen Dr. Jesper L. Kristensen 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(41):12474-12480
The pyrimidine‐2‐sulfonyl (pymisyl) group is introduced as a new protecting group that can be used to activate aziridines towards ring opening. It is readily introduced and removed under mild conditions. Regioselective ring opening of pymisyl‐protected 2‐methyl‐aziridine with organocuprates gives the corresponding sulfonamides in high yields, and the pymisyl group can subsequently be removed upon treatment with a thiolate. The versatility of this new nitrogen protecting group is illustrated with a new synthesis of Selegiline, a monoamine oxidase‐B inhibitor marketed for the treatment of Parkinson’s disease. 相似文献
996.
Stereocontrolled synthesis of 5-epi- and 5,7a-di-epi-hyacinthacine C1 (7 and 8), two potential glycosidase inhibitors are described using α,β-unsaturated ketone 9 as homochiral starting material. The key step in the synthesis is the highly diastereoselective dihydroxylation reaction of 9, that allows the obtention of a single bis-hydroxylated ketone (10). Further derivatization into two epimeric mesylate esters followed by internal cyclization form the pyrrolizidinic compounds 7 and 8. This type of compounds can be useful in glycobiology due to their ability to inhibit carbohydrate-processing enzymes. 相似文献
997.
Herein we report the first total synthesis of alkaloid caulophyllumine B in 14 steps by an iterative olefin cross-metathesis strategy from l-glutamic acid. 相似文献
998.
999.
1000.