首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   1360篇
  免费   16篇
  国内免费   7篇
化学   1139篇
晶体学   15篇
力学   11篇
数学   51篇
物理学   167篇
  2020年   5篇
  2019年   12篇
  2018年   9篇
  2017年   5篇
  2016年   16篇
  2015年   10篇
  2014年   18篇
  2013年   63篇
  2012年   56篇
  2011年   59篇
  2010年   32篇
  2009年   43篇
  2008年   59篇
  2007年   72篇
  2006年   68篇
  2005年   60篇
  2004年   64篇
  2003年   72篇
  2002年   81篇
  2001年   15篇
  2000年   14篇
  1999年   23篇
  1998年   19篇
  1997年   14篇
  1996年   14篇
  1995年   16篇
  1994年   14篇
  1993年   13篇
  1992年   13篇
  1991年   23篇
  1990年   11篇
  1989年   12篇
  1988年   10篇
  1987年   6篇
  1986年   9篇
  1985年   26篇
  1984年   36篇
  1983年   21篇
  1982年   23篇
  1981年   20篇
  1980年   30篇
  1979年   28篇
  1978年   24篇
  1977年   20篇
  1976年   27篇
  1975年   17篇
  1974年   20篇
  1973年   15篇
  1972年   14篇
  1967年   4篇
排序方式: 共有1383条查询结果,搜索用时 15 毫秒
11.
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   
12.
Applied Biochemistry and Biotechnology - A marine photosynthetic bacterium,Rhodopseudomonas sp. strain W-1S, accumulated polyhydroxybutyrate (PHB) to 56% of the dry cell weight under microaerobic...  相似文献   
13.
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   
14.
15.
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   
16.
17.
Effect of titanium dioxide on photostability of solid-state mequitazine   总被引:1,自引:0,他引:1  
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   
18.
[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   
19.
Vanadiuin(V) com: with an acidic hydroxy group attached to the metal form the crorrresponding.; with alcohols. These esters show a characteristic absorption at 445–480 that alcoholic hydroxy groups can be determined photometrically. The formation constant of the n-butanol esters of vanadium maltolate and 2-methyl-.S-hydroxyquinolinate Were determined in benzene or benzenechloroform (1:1). Simple methods are determined for the determination of alcohol in the concentration range 10-1–10-4M.  相似文献   
20.
Treatment of alkyl allyl carbonates derived from various alcohols with a palladium catalyst in MeCN affords ketones and aldehydes in high yields. This new method of oxidation of alcohols can be applied to various alcohols except simple primary alcohols.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号