全文获取类型
收费全文 | 1389篇 |
免费 | 26篇 |
国内免费 | 5篇 |
专业分类
化学 | 973篇 |
晶体学 | 11篇 |
力学 | 16篇 |
数学 | 55篇 |
物理学 | 365篇 |
出版年
2023年 | 7篇 |
2022年 | 10篇 |
2021年 | 15篇 |
2020年 | 11篇 |
2019年 | 22篇 |
2017年 | 11篇 |
2016年 | 15篇 |
2015年 | 12篇 |
2014年 | 22篇 |
2013年 | 88篇 |
2012年 | 40篇 |
2011年 | 52篇 |
2010年 | 27篇 |
2009年 | 40篇 |
2008年 | 67篇 |
2007年 | 63篇 |
2006年 | 57篇 |
2005年 | 50篇 |
2004年 | 47篇 |
2003年 | 65篇 |
2002年 | 51篇 |
2001年 | 32篇 |
2000年 | 46篇 |
1999年 | 32篇 |
1998年 | 21篇 |
1997年 | 21篇 |
1996年 | 17篇 |
1995年 | 10篇 |
1994年 | 22篇 |
1993年 | 15篇 |
1992年 | 41篇 |
1991年 | 20篇 |
1990年 | 20篇 |
1989年 | 22篇 |
1988年 | 26篇 |
1987年 | 26篇 |
1986年 | 18篇 |
1985年 | 29篇 |
1984年 | 23篇 |
1983年 | 13篇 |
1982年 | 13篇 |
1981年 | 19篇 |
1980年 | 14篇 |
1979年 | 28篇 |
1978年 | 22篇 |
1977年 | 13篇 |
1976年 | 11篇 |
1975年 | 12篇 |
1974年 | 13篇 |
1973年 | 20篇 |
排序方式: 共有1420条查询结果,搜索用时 15 毫秒
21.
Abstract— A new method of using hydroxylamine as the reagent was developed to determine the concentrations of chlorophylls a and b in plant extracts accurately and sensitively. The method is based on the principle that hydroxylamine reacts in a short time with the aldehyde group of chlorophyll b in 95 per cent methanol at pH 5.8 to afford a derivative having a red band similar in position to the red band of chlorophyll a , while the spectrum of chlorophyll a is unaffected by the treatment with hydroxylamine. The method includes the measurements of absorbanlce for the mixture of a plant extract with hydroxylamine and for the reagent blank at a single wavelength, 666 mμ, and the concentrations of chlorophylls a and b are calculated from the absorbance value for the reagent blank and the increment of absorbance due to the reaction. By measuring this increment directly by difference photometry, one can determine a low concentration of chlorophyll b relative to chlorophyll a . The contents of chlorophylls in matured and etiolated leaves were determined by the method, and the errors included in this method were shown to be smaller than those in a commonly used technique including the measurements at two different wavelengths. 相似文献
22.
23.
24.
T Takamura T Kato E Arakawa S Ogawa Y Suzumura T Kato 《Chemical & pharmaceutical bulletin》1989,37(10):2828-2831
Several analogues substituted with fatty acid at the 2'-, 3'-, or 5'-position of the ribose moiety of N6,N6-dimethyladenosine were synthesized and tested for antitumor activity against cultured cells of L1210 leukemia and/or Ehrlich ascites. The cytotoxicity and increase of life span obtained with congeners in the N6,N6-dimethyladenosine 3'- or 5'-substituted series were comparable to in vitro or several times better in vivo than those of the mother compound. 相似文献
25.
26.
27.
28.
(Styrene-p-chlorostyrene) triblock copolymers of the ABA and BAB types (A—polystyrene; B—poly-p-chlorostyrene) were prepared by anionic polymerization and their conformational behaviours in solutions were studied from measurements of the dipole moments. Two solvents, toluene and cumene, were used for the study; toluene is a good solvent for both polystyrene and poly-p-chlorostyrene whereas cumene is a selective solvent, good for polystyrene but poor for poly-p-chlorostyrene. It was found that the dipole moments of the block copolymers measured in toluene are the same for the ABA and BAB copolymers; in cumene however the dipole moment of the BAB copolymer is smaller than that of the ABA copolymer. The results give an additional support to our previous conclusion that the conformation of the block copolymers in a good solvent such as toluene could be approximated with a pseudo-random coil form; in a selective solvent, however, some anomalies take place in the conformation of the block copolymers, as deduced from intrinsic viscosity, osmotic pressure and light scattering measurements. 相似文献
29.
Toshio Ogawa Masakazu Sakai Wataru Ishitobi 《Journal of polymer science. Part A, Polymer chemistry》1986,24(1):109-118
Molecular weight distribution of Nylon 12 was determined with hexafluoroisopropanol/toluene mixture as eluent by gel permeation chromatography. Calibration curve for Nylon 12 was easily obtained from that of polystyrene because the method of universal calibration was applicable among these polymers. The molecular weight distributions of Nylon 12 were always broader than expected by the theory of polymerization, i.e., most probable distribution. This result was not caused by broadening effect in gel permeation chromatography, but by polymerization itself. 相似文献
30.
M Ogawa H Matsuda H Eto T Asaoka T Kuraishi A Iwasa T Nakashima K Yamaguchi 《Chemical & pharmaceutical bulletin》1991,39(9):2301-2307
A series of vinylimidazoles containing a hetero atom such as sulfur or oxygen at a beta-position of the vinyl group was prepared and the antifungal activities were tested. It was found that sulfur-substituted derivatives such as (E)-1-[2-(methylthio)-1-[2-(pentyloxy)phenyl]ethenyl]-1H-imidazole (5a-5) and (E)-1-[1-[2-(hexyloxy)phenyl]-2-(methylthio)ethenyl]-1H-imidazole (5a-6) showed excellent antifungal activities against dermatophytes and yeast cells. The stereochemistry of the hydrochloride salt of 5a-5 was determined by X-ray crystallography. The structure-activity relationships were discussed. 相似文献