全文获取类型
收费全文 | 238180篇 |
免费 | 1249篇 |
国内免费 | 365篇 |
专业分类
化学 | 120096篇 |
晶体学 | 3525篇 |
力学 | 12104篇 |
综合类 | 7篇 |
数学 | 27812篇 |
物理学 | 76250篇 |
出版年
2020年 | 2488篇 |
2019年 | 3013篇 |
2018年 | 4413篇 |
2017年 | 4589篇 |
2016年 | 5557篇 |
2015年 | 2591篇 |
2014年 | 4765篇 |
2013年 | 9464篇 |
2012年 | 7674篇 |
2011年 | 8995篇 |
2010年 | 7404篇 |
2009年 | 7566篇 |
2008年 | 8594篇 |
2007年 | 8455篇 |
2006年 | 7711篇 |
2005年 | 6783篇 |
2004年 | 6483篇 |
2003年 | 5919篇 |
2002年 | 6149篇 |
2001年 | 6720篇 |
2000年 | 4969篇 |
1999年 | 3819篇 |
1998年 | 3482篇 |
1997年 | 3266篇 |
1996年 | 2963篇 |
1995年 | 2699篇 |
1994年 | 2626篇 |
1993年 | 2681篇 |
1992年 | 2780篇 |
1991年 | 3103篇 |
1990年 | 2995篇 |
1989年 | 3073篇 |
1988年 | 2874篇 |
1987年 | 2846篇 |
1986年 | 2685篇 |
1985年 | 3324篇 |
1984年 | 3415篇 |
1983年 | 2931篇 |
1982年 | 3018篇 |
1981年 | 2871篇 |
1980年 | 2638篇 |
1979年 | 2983篇 |
1978年 | 3241篇 |
1977年 | 3360篇 |
1976年 | 3350篇 |
1975年 | 3136篇 |
1974年 | 3098篇 |
1973年 | 3236篇 |
1972年 | 2584篇 |
1971年 | 2372篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
931.
Condensation of 4-chlorosulfonyl- and 4-fluorosulfonyl-benzoyl chlorides with p-dimethylamino--aminoacetophenone followed by cyclodehydration of the resulting amides leads to the formation of 4-(5-dimethylaminophenyl-2-oxazolyl)benzenesulfonyl halides, and the corresponding sulfonic ester, sulfomorpholide, sulfonamide, and sodium salt are synthesized from them. The spectral and luminescence properties of the compounds synthesized have been studied in toluene, ethanol, and DMF. The ability of the sulfonyl group to transmit the electronic effects of the substituents on it to the overall molecular -electron system of 2,5-diaryloxazole has been demonstrated. Salvation fluorochromia has been detected in polar solvents. In some of the compounds studied the Stokes shift exceeds 200 nm.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 234–237, February, 1993. 相似文献
932.
Conditions for the formation of rare earth element (Y, La–Lu) 3-methylglutarates were studied and their quantitative composition
and solubilities in water at 293 K were determined (10–2 mol dm–3). The IR spectra of the prepared complexes with general formula Ln2(C6H8O4)3
nH2O (n=3–8) were recorded and their thermal decomposition in the air were investigated. During heating the hydrated 3-methylglutarates
are dehydrated in one step and next anhydrous complexes decompose to oxides Ln2O3 with intermediate formation Ln2O2CO3 (Y, La, Nd–Gd) or directly to the oxides, Ln2O3, CeO2, Pr6O11 and Tb4O7 (Ce, Pr, Tb–Lu).
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
933.
Studies have been made of the slow dynamic processes which occur with the silicon cyclopentadienyls C5H5Si(CH3)Cl2, such as prototropic rearrangement and dimerisation. The product formed through spontaneous dimerisation has been found to consist almost entirely of the dimer of the main vinylic isomer of C5H5Si(CH3)Cl2. The dimeric structure has been proved by means of PMR spectra (100 MHz). From kinetic studies values of the rate constants at temperatures of 20,44,55, and 65° have been obtained and an approximate plot of log kvs. (1/T)x103, has enabled the thermodynamic characteristics of the prototropic rearrangement and of the dimerisation to be calculated. The ability of cyclopentadienyl systems to undergo hydrogen migration is discussed and the reactivity of fluxional systems is shown to be governed by the rate of metallotropic rearrangement. 相似文献
934.
The coulometric electrolytic principle is utilized for the measurement of moisture sorbed on sintered thorium dioxide. Moisture is removed from the sample by heating and is swept by dry argon gas through a hygrometer. The resulting hygrometer output is converted into frequency pulses and counted cumulatively. The instrument is calibrated by use of standard hydrated chemicals. The number of counts/mu;g of water obtained from standards compares favourably with the theoretical number of counts/mu;g calculated from performance specifications of the components employed. The error is <5% for 1-350mu;g of water. A high sensitivity and low operating blank recommends application of this method to materials other than thorium dioxide, having very low moisture contents. 相似文献
935.
936.
The Böckelheide reaction was accomplished with a number of imidazo[4,5-b]pyrazine N-oxides, and the N-oxidation of the resulting acetoxy(hydroxy)methyl derivatives of imidazo[4,5-b]pyrazine and 6-bromo-1-methylimidazo[4,5-b]pyrazine was studied. The hydrolytic cleavage of 6-bromo-1-methylimidazo[4,5-b]pyrazine and its 4-N-oxide was studied.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 690–693, May, 1975. 相似文献
937.
2-Pyridylethylation of benzazothiones-2 which are potential mercapto compounds (benzothiazolethione-2, benzoxazolethione-2, 1-methylbenzoimidazolethione-2, benzoimidazolethione-2, 5, 6-dimethylbenzoimidazolethione-2), is described, as well as preparation of 5, 6-dimethylbenzoimidazolethione-2 by direct oxidation of 5, 6-dimethylbenzoimidazole. 相似文献
938.
The Gelcode color-based silver staining system, an improved formulation based on the original publication by Sammons et al. (Electrophoresis 1981, 2, 141-147) has been adapted to automated rapid staining in the PhastSystem Development Unit. The use of elevated temperatures in the fixation, washing, staining, and stabilization steps of the protocol reduces the total time of the process from 18 h to 1 h. The limit of detection, which is at least tenfold more sensitive than the silver staining protocol recommended for the PhastSystem, corresponds to 0.05-0.1 ng of protein per band. The method is applicable to both one- and two-dimensional polyacrylamide gels. 相似文献
939.
940.