全文获取类型
收费全文 | 2384篇 |
免费 | 34篇 |
国内免费 | 11篇 |
专业分类
化学 | 1664篇 |
晶体学 | 32篇 |
力学 | 32篇 |
综合类 | 1篇 |
数学 | 68篇 |
物理学 | 632篇 |
出版年
2020年 | 18篇 |
2019年 | 22篇 |
2018年 | 13篇 |
2017年 | 12篇 |
2016年 | 28篇 |
2015年 | 21篇 |
2014年 | 28篇 |
2013年 | 104篇 |
2012年 | 90篇 |
2011年 | 116篇 |
2010年 | 78篇 |
2009年 | 71篇 |
2008年 | 129篇 |
2007年 | 143篇 |
2006年 | 144篇 |
2005年 | 123篇 |
2004年 | 115篇 |
2003年 | 112篇 |
2002年 | 117篇 |
2001年 | 41篇 |
2000年 | 39篇 |
1999年 | 35篇 |
1998年 | 22篇 |
1997年 | 31篇 |
1996年 | 22篇 |
1995年 | 28篇 |
1994年 | 35篇 |
1993年 | 33篇 |
1992年 | 39篇 |
1991年 | 24篇 |
1990年 | 28篇 |
1989年 | 29篇 |
1988年 | 25篇 |
1987年 | 16篇 |
1986年 | 23篇 |
1985年 | 45篇 |
1984年 | 48篇 |
1983年 | 30篇 |
1982年 | 26篇 |
1981年 | 30篇 |
1980年 | 35篇 |
1979年 | 34篇 |
1978年 | 30篇 |
1977年 | 26篇 |
1976年 | 29篇 |
1975年 | 17篇 |
1974年 | 23篇 |
1973年 | 16篇 |
1972年 | 14篇 |
1969年 | 11篇 |
排序方式: 共有2429条查询结果,搜索用时 15 毫秒
21.
Takuji Hirose Kumiko Naito Megumi Nakahara Hiroaki Shitara Yoshio Aoki Hiroyuki Nohira Bruce W. Baldwin 《Journal of inclusion phenomena and macrocyclic chemistry》2002,43(1-2):87-93
Two Kemp's acid diamides were synthesized and applied to chiral amine recognition using 1H NMR analysis. One derivative based on 1-(1-naphthyl)ethylamine had good chiral recognition of six amines and was useful to determine the optical purity for three amines, i.e., methylbenzylamine, 1-(1-naphthyl)ethylamine and 1- henylpropylamine,however, the cyclohexylethylamine derivative showed little discrimination for the amines studied. Together with the results for alkylamines, it was shown that aromatic structure was important for aromatic shielding anisotropy and –– interactions between host and guest. The structure of the 1-(1-naphthyl)ethylamine derivative in solution was also considered based on 1H NMR data and computer simulation. 相似文献
22.
Suzuki Masayasu Watamabe Nobuyuki Tamiya Eiichi Kataoka Tetsuro Tokunaga Tohru Karube Isao 《Applied biochemistry and biotechnology》1987,15(3):191-200
A novel tumor-detection system consisting of complementmediated cytolytic reaction and an image processing system was developed
for the simple and rapid determination of tumor cells.
The present system consists of a CCD image sensor, image memory board, personal computer, and microscope.
When monoclonal antibody 3C4, which is specific to the guinea pig hepatoma L-10, was added to cell suspension, only L-10 cytolysis
occurred. Cytolysis caused a decrease in brightness of the cells observed by phase-contrast microscopy. The phase contrast
image of the cells before cytolysis was converted to a digitalized signal and stored in computer memory. After cytolysis,
a brightness threshold above that of lysed cells was subtracted from the digitalized signal and compared to the signal stored
before reaction.
L-10 cells in mixed cell suspension were determined specifically by the system. Measurement time was only 2 sec and overall
time, including reaction time, was approximately 30 min. Since this method does not require a cell washing process, automation
of the whole system is possible. 相似文献
23.
T. Takeuchi Y. Nakano A. Aoki S. Ohmori T. Tsukatani 《Journal of Radioanalytical and Nuclear Chemistry》1987,112(1):259-272
Human hair collected from the mercury, arsenic and cadmium polluted areas has been analysed by instrumental neutron activation method. The concentrations of 27 elements were compared with those of normal Japanese. Correlation coefficients of logarithmic concentrations between the elements were calculated and their significance levels were determined. Factor contribution and factor loadings of the elements were calculated for each factor by making use of principal component analysis. The factor score of each sample was also calculated for each factor to examine the effects of the contamination by heavy metals on individuals. 相似文献
24.
Y. Adachi K. Aoki 《Colloids and surfaces. A, Physicochemical and engineering aspects》2003,230(1-3):37-44
Standardized mixing procedure was applied to the analysis of flocculation of polystyrene latex (PSL) particles with polyelectrolytes. After confirming the initial enhancement of flocculation rate in the very beginning followed by abrupt stop with excess dosage, attention was shifted to the system of moderate dosage. In the former, effects of ionic strength were further analyzed to find the consistency with adsorption isotherm. In the latter, flocculation started slowly in the beginning, sometime slower than salt-induced rapid coagulation, however, the rate gradually increases in the middle stage. Often, the increased rate exceeds that of salt-induced rapid coagulation. This behavior emerged more clearly in the case of lower ionic strength. This is the indication that the rate of relaxation of polymer on the colloidal surface is a function of surface coverage and ionic strength. The ultimate degree of flocculation is usually higher than that observed for excess dosage. The size distribution of flocs was also examined, however, no clear difference between different experimental conditions was confirmed for the same degree of flocculation. 相似文献
25.
Rearrangement of Tertiary Allyl Alcohols Induced by Bromination: The Effect of a Fluorine Substituent on the Rate and the Outcome of the Reaction The allyl alcohol bearing a methyl and a t-butyl group at the hydroxylated position was found to undergo a rearrangement when treated with bromine (or N-bromosuccinimide) in an aqueous medium and to afford a product mixture containing two regioisomeric ketones and one oxirane. Introduction of an additional methyl group or a fluorine atom at the non-terminal olefinic center led to a more selective discrimination between potential migratory groups. As the result of an exclusive t-butyl shift only one product, a ketone, was formed in both cases. Whereas the reaction rate was only slightly affected by the additional methyl group, it was substantially decreased by the fluorine atom. 相似文献
26.
27.
Oxidation of substituted thioanisoles by chemically generated singlet oxygen was investigated in polar aqueous media. The formation of the superoxide ion was observed during sulphoxidation of 4-hydroxythioanisole (4) in phosphate buffer at pH 7.5. Control experiments indicated that the superoxide ion was formed by a direct reaction between singlet oxygen and 4. The kinetics of the trapping reaction by diphenylsulphoxide indicated the involvement of a single intermediate. The overall rate constants of the reaction of thioanisoles with singlet oxygen in methanol-water (1:1) are one order of magnitude larger than those in benzene. On the basis of these results, a mechanism involving a charge-transfer complex has been proposed for the reaction of electron-rich thioanisoles with singlet oxygen, whereby the charge-transfer complex would produce persulphoxide directly or dissociate to the cation radical and superoxide ion in polar aqueous media. 相似文献
28.
29.
Kakinoki K Yamane K Yamamoto M Teraoka R Sugimoto I Matsuda Y 《Chemical & pharmaceutical bulletin》2005,53(9):1092-1096
TiO(2) has been widely used in pharmaceutical products, and it also has been used as a photocatalyst. In this study, the influence of photocatalytic activity on the stability of solid-state mequitazine, an H(1)-blocker, was investigated. The photo-degradation of mequitazine with TiO(2) occurred under irradiation with both light sources. The degree of degradation of mequitazine with anatase was higher than that of rutile. The degradation was significantly enhanced with increasing relative humidity. The relationship between the apparent degradation rate constant and water vapor pressure could be clearly described by a simple power law. The major photo-degradation products of mequitazine, resulting from photocatalytic activity of TiO(2), were mequitazine-S-oxide and mequitazine-sulphone. A remarkable degradation of mequitadine occurred with addition of TiO(2), and its photocatalytic activity was controlled by water vapor pressure. The photo-degradation of mequitazine with TiO(2) is a different process from mequitazine without TiO(2), because mequitazine-S-oxide and mequitazine-sulphone are not formed with normal photo-degradation of mequitazine. 相似文献
30.
[structure: see text] New fluorescent compounds (1), lariat ethers having plural pyrenylmethyl groups on the sidearms, were prepared, and their complexation behavior with alkaline earth metal cations was examined by fluorescence spectrometry. The pyrene excimer emission decreased accompanied with an increase in the monomer emission upon complexation with the metal ion. This finding is ascribed to the cooperative participation of one of the two sidearms in the complexation of the crown ring with the metal ion. 相似文献