全文获取类型
收费全文 | 430926篇 |
免费 | 4152篇 |
国内免费 | 1429篇 |
专业分类
化学 | 235939篇 |
晶体学 | 6482篇 |
力学 | 17902篇 |
综合类 | 10篇 |
数学 | 48352篇 |
物理学 | 127822篇 |
出版年
2021年 | 2946篇 |
2020年 | 3495篇 |
2019年 | 3516篇 |
2018年 | 3455篇 |
2017年 | 3398篇 |
2016年 | 6178篇 |
2015年 | 4513篇 |
2014年 | 6351篇 |
2013年 | 18784篇 |
2012年 | 14410篇 |
2011年 | 17710篇 |
2010年 | 11505篇 |
2009年 | 11556篇 |
2008年 | 16576篇 |
2007年 | 16625篇 |
2006年 | 16131篇 |
2005年 | 14745篇 |
2004年 | 13275篇 |
2003年 | 11915篇 |
2002年 | 11695篇 |
2001年 | 13986篇 |
2000年 | 10587篇 |
1999年 | 8361篇 |
1998年 | 6424篇 |
1997年 | 6369篇 |
1996年 | 6330篇 |
1995年 | 5795篇 |
1994年 | 5539篇 |
1993年 | 5279篇 |
1992年 | 6141篇 |
1991年 | 6080篇 |
1990年 | 5733篇 |
1989年 | 5513篇 |
1988年 | 5734篇 |
1987年 | 5456篇 |
1986年 | 5162篇 |
1985年 | 7177篇 |
1984年 | 7279篇 |
1983年 | 5926篇 |
1982年 | 6260篇 |
1981年 | 6151篇 |
1980年 | 5902篇 |
1979年 | 6291篇 |
1978年 | 6365篇 |
1977年 | 6319篇 |
1976年 | 6209篇 |
1975年 | 6008篇 |
1974年 | 5854篇 |
1973年 | 6033篇 |
1972年 | 3642篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
871.
Optical properties of thiopyrimidine nucleosides 总被引:1,自引:0,他引:1
872.
Condensation of α-halocarbonyl compounds and 2-mercaptobenzimidazole gives thiazolo-[3,2-a]benzimidazoles. This condensation occurred at the mercapto group of the benzimidazole followed by cyclization to form the thiazole ring. This was confirmed by the examination of the mass spectra of 2- and 3-methylthiazolo[3,2-a]benzimidazoles, 2- and 3-phenylthiazolo[3,2-a]-benzimidazoles, and their derivatives. 相似文献
873.
874.
Crystals of 1,6-8, 13-bis-oxido-[14]-annulene are monoclinic, a = 9,29, b = 9,74, c = 11,46 Å, β = 90,0°, space group P 21/c, with 4 molecules in the unit cell. The structure has been solved by direct methods and refined by full-matrix least-squares analysis of three-dimensional intensity data. The cis-configuration of the two oxygen bridges is confirmed, and the observed molecular parameters are in full accord with the aromatic properties of the molecule. 相似文献
875.
876.
A. V. Kashevskii M. A. Mamalyga T. L. Petrova A. Yu. Safronov V. N. Kizhnyaev 《Russian Journal of Applied Chemistry》2007,80(2):316-321
Copolymers of 1-vinyl-1,2,4-triazole and 5-vinyltetrazole with 1,1,5-trihydrooctafluoropentyl methacrylate and 1,1,7-trihydrododecafluoroheptyl methacrylate were prepared under the conditions of radical initiation. These copolymers were used for modification of the surface of a glassy carbon electrode, and the effect of the modification on the electrochemical behavior of the electrode in anodic oxidation of dopamine and NO was studied. The possibility of enhancing the selectivity of the electrochemical sensor for monitoring NO in biological media was demonstrated. 相似文献
877.
The conjugate of mitomycin C (MMC) with linear (1----3)-beta-D-glucan from Alcaligenes faecalis var. myxogenes IFO 13140 was synthesized and its antitumor activities investigated. The conjugate (MMC-carboxymethylated linear (1----3)-beta-D-glucan (CMPS)) was obtained by treatment of CMPS with MMC in the presence of 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide. In vitro cytotoxicity of MMC-CMPS against L1210 leukemia cells was similar to that of MMC. In i.p.-i.p. system in vivo against P388 leukemia in mice, the maximum increase of MMC-CMPS conjugate in life span (ILSmax) was higher than that of MMC but the therapeutic index was reduced. However, the antitumor activity of MMC-CMPS conjugate against subcutaneously implanted sarcoma 180 solid tumor in mice by i.p. administration was similar to that of MMC at a dose of 1.5 mg eq MMC/kg/d x 7 and the reduction of the number of leukocytes caused by MMC was suppressed by attaching MMC to CMPS. In addition, on assay using serum of sarcoma 180 solid tumor-bearing mice with injection of MMC-CMPS conjugate, a drastic loss of tumor cells and an increase in polymorphonuclear leukocytes (PMN) were observed. This result suggested that MMC-CMPS conjugate induced tumor-regressing factor similar to CMPS. 相似文献
878.
A combined solid-phase microextraction-GC-MS analytical technique was used to monitor the formation of metabolites in the biodegradation of biphenyl, which were originally obtained from the solar photodechlorination of Aroclor 1254 by Pseudomonas pseudoalcaligenes KF707 and Burkholderia sp LB400. In both cases, the following metabolites were detected: 2-hydroxybiphenyl (2-OH-BP), 2,3-dihydroxybiphenyl (2,3-di-OH-BP), and benzoic acid, which was detected as its benzoate derivative 1-methylethylbenzoate. A time course study for the formation and disappearance of these metabolites was used to construct a degradation pathway, which in both cases, involved the formation of 2-OH-BP and 2,3-di-OH-BP. 相似文献
879.
Devyatkina T. I. Gun'ko Yu. L. Mikhalenko M. G. 《Russian Journal of Applied Chemistry》2001,74(7):1122-1125
The influence exerted by addition of -hydroxynaphthoic acid and combined additive Hg + Pb + -hydroxynaphthoic acid on the corrosion and self-discharge of a porous zinc electrode in alkali solution was studied. 相似文献
880.