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   945篇
  免费   14篇
化学   459篇
晶体学   1篇
力学   37篇
数学   307篇
物理学   155篇
  2023年   3篇
  2022年   17篇
  2021年   8篇
  2020年   13篇
  2019年   7篇
  2018年   10篇
  2017年   7篇
  2016年   18篇
  2015年   9篇
  2014年   7篇
  2013年   33篇
  2012年   24篇
  2011年   614篇
  2010年   21篇
  2009年   9篇
  2008年   16篇
  2007年   3篇
  2006年   8篇
  2005年   9篇
  2004年   5篇
  2003年   9篇
  2002年   7篇
  2001年   3篇
  2000年   6篇
  1999年   2篇
  1998年   4篇
  1997年   2篇
  1996年   8篇
  1995年   3篇
  1993年   6篇
  1992年   2篇
  1990年   4篇
  1989年   3篇
  1988年   3篇
  1987年   6篇
  1985年   6篇
  1984年   6篇
  1983年   4篇
  1982年   3篇
  1979年   2篇
  1978年   2篇
  1977年   3篇
  1976年   2篇
  1974年   4篇
  1972年   2篇
  1964年   1篇
  1962年   2篇
  1958年   2篇
  1956年   1篇
  1950年   1篇
排序方式: 共有959条查询结果,搜索用时 15 毫秒
1.
2.
Paramagnetic pyrroline and 1,2,3,6-tetrahydropyridine derivatives of BODIPY and their diamagnetic analogs have been synthesized and characterized as novel redox double sensor and cation sensitive reagents.  相似文献   
3.
By reacting poly(methacryloyl chloride) (PMKC) with allyl amine, a multiallyl monomer in PMKC matrix has been obtained. Free-radical polymerization of multiallyl monomer in diluted solutions at a concentration of 12 g/L multiallyl monomer occurs partly along ordered allyl units in the matrix and results in ladder-type branched polymers. The polymers obtained are soluble in alcohols, DMF, DMSO and have unreacted allyl double bonds. The structures of multiallyl monomer and homopolymer have been found on the basis of elemental analysis, IR and 1H-NMR spectra and an examination of the products of hydrolysis. The effect of the reaction of degradative chain transfer on the structure of the polymer obtained has been discussed.  相似文献   
4.
Cyclodextrin polymer was compared to other well known disintegrants concerning the swelling properties /water uptake, moisture uptake, hydration capacity, sedimentation volume in water/. Its high disintegrating effect was proved in directly compressed tablets as well as in tablets made by wet granulation. A remarkable improvement in tablet properties was observed. Not only the disintegration of tablets and the dissolution of the drug was accelerated but also the hardness increased when CDP was used as disintegrant.  相似文献   
5.
An initiation system of the anionic polymerization, intended for the syntheses of homopolymers and block copolymers with narrow molar mass distribution, was tested with styrene and isoprene. The actual initiating species, viz., the oligomeric α-methylstyryl anion, originates by the reaction of n-butyllithium with α-methylstyrene in a benzene/diethyl ether 1:1 (v:v) solvent mixture at room temperature. The homopolymers and two-block copolymers of styrene and isoprene, prepared by using this system, were characterized by light scattering, membrance osmometry, GPC, and 1H NMR spectroscopy. By using the suggested initiation system, it is possible to synthesize well-defined homopolymers and block copolymers with low polydispersity (as judged by the shape of the GPC peaks and by the values of the polydispersity index), especially in a molar mass region between 4 × 104 and 1.5 × 105 g/mol. Above the upper limit of this interval, an appropriate decrease of the diethyl ether/benzene volume ratio is recommended, though the polymerization time must then be prolonged.  相似文献   
6.
JPC – Journal of Planar Chromatography – Modern TLC - The chemical composition of the oils of four thyme (Lamiaceae) chemotypes (Thymus vulgaris L., Thymus serpyllum L., Thymus x...  相似文献   
7.
Circular dichroism (CD) and visible spectra of inclusion compounds between Methyl Orange (MO) analogues and -, -, -cyclodextrin (cdx), 2,6-dimethyl-and 2,3,6-trimethyl--cdx, water soluble -, -, -cdx polymer products were investigated. In the CD-spectroscopic investigation, the complex with -cdx epichlorohydrin condensate showed a large amplitude and splitting of the induced * band. Fractions of glyceryl ether of less than 2000 and polymer of more than 10000 dalton molecular mass were separated. Complexes of above two fractions and MO showed the same splitting spectral pattern. Job's plots from visible spectra showed the formation of the 11 complex and CD-data suggested the co-existence of the 21 MO-cdx complex. This splitting pattern showed the reversal of the signs when -cdx-ethyleneglycol-bis(epoxypropyl) ether was used and disappeared when larger host molecules and azo dyes were used. The splitting was explained by exciton interaction.  相似文献   
8.
The complex forming ability of a water-soluble -cyclodextrin epichlorohydrin, polymer (CDPS) and its different molecular weight fractions was studied and compared with the complexing properties of -cyclodextrin (CD) and dimethyl-CD (DM-CD). CDPS was separated into two main fractions. CDPS and its fractions formed well soluble inclusion compounds with the studied drugs. The low molecular weight fraction formed rather stable complexes with small guest molecules, the high molecular weight fraction was found to be more efficient in binding larger substrates. Structural studies of furosemide-CD complexes were attempted by NMR spectroscopy.Presented at the Fourth International Symposium on Inclusion Phenomena and the Third International Symposium on Cyclodextrins, Lancaster, U.K., 20–25 July 1986.  相似文献   
9.
Various disinfecting drugs (ethacridine lactate, methylene blue, gentian violet, brilliant green, fuchsin acid, cetylpyridinium chloride) were incorporated into CD bead polymers substituted with carboxymetbyl groups and a retarded release rate was measured. These polymers were successfully used as sustained release wound powders as well as in chewing gum formulations.  相似文献   
10.
Bioavailability and toxic effect of contaminants are the main limitations during soil bioremediation. Cyclodextrins may influence bioavailability of the contaminants during biodegradation and also toxicity of the pollutant on soil microbes and plants since their ability to form inclusion complei with organic compounds. The effect of cyclodextrins on bioremediation and on toxic effect of hydrocarbons was investigated by testing the activity of hydrocarbon degrading microflora and of plant growth. The effect of cyclodextrins could be demonstrated in both cases: biodegradation of hydrocarbons could be enhanced and toxic effect of hydrocarbons on plants and soil microbes could be decreased by adding cyclodextrins.  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