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   30879篇
  免费   4137篇
  国内免费   3115篇
化学   14954篇
晶体学   538篇
力学   1444篇
综合类   441篇
数学   9951篇
物理学   10803篇
  2024年   39篇
  2023年   249篇
  2022年   518篇
  2021年   574篇
  2020年   766篇
  2019年   820篇
  2018年   799篇
  2017年   970篇
  2016年   1197篇
  2015年   1080篇
  2014年   1347篇
  2013年   2858篇
  2012年   1622篇
  2011年   1834篇
  2010年   1598篇
  2009年   1862篇
  2008年   1971篇
  2007年   2031篇
  2006年   1814篇
  2005年   1645篇
  2004年   1483篇
  2003年   1429篇
  2002年   1432篇
  2001年   1041篇
  2000年   1112篇
  1999年   945篇
  1998年   844篇
  1997年   674篇
  1996年   559篇
  1995年   489篇
  1994年   403篇
  1993年   318篇
  1992年   278篇
  1991年   216篇
  1990年   186篇
  1989年   132篇
  1988年   149篇
  1987年   118篇
  1986年   110篇
  1985年   115篇
  1984年   110篇
  1983年   48篇
  1982年   81篇
  1981年   44篇
  1980年   50篇
  1979年   56篇
  1978年   24篇
  1977年   18篇
  1976年   13篇
  1973年   19篇
排序方式: 共有10000条查询结果,搜索用时 375 毫秒
991.
本文用浊度滴定(UV-Vis)、透射电镜(TEM)和激光光散射(QELS)等方法对Al3+离子与卵磷脂(EYPC)囊泡之间的相互作用及其这种相互作用对溶液中磷脂微结构的影响进行了研究。结果表明,一定量的Al3+离子使EYPC多层囊泡转变为线团状聚集体;Al3+与牛磺胆酸钠(TC)的协同作用可以破坏EYPC的多层囊泡结构,促进相转变,形成混合胶束。  相似文献   
992.
Small angle X-ray scattering (SAXS) is measured for the lamellar phase in aqueous systems of 1-o-β-3,7-dimethyoctyl-D-glucopyranoside (β-Glc(Ger)), which has recently been prepared by us, 1-o-β-decyl-D-glucopyranoside (β-GlcC10), and 1-o-β-octyl-D-glucopyranoside (β-GlcC8). The repeat distance d obtained from the position of the diffraction peak does not follow the swelling law d = 2δhc/hc, where δhc and hc are the thickness and the volume fraction of the hydrophobic layer, respectively. This may result from the fact that δhc increases and, equivalently, the surface area per surfactant molecule (as) decreases with increasing concentration. So we calculate δhc and as from the observed d value at each concentration using the above swelling law. The half-thickness δhc increases in the order β-GlcC8 < β-Glc(Ger) < β-GlcC10 at a fixed concentration. On the other hand, the data on as for β-GlcC10 and β-GlcC8 lie on the same line and the data for β-Glc(Ger) lies above this line. These results suggest that the cross-sectional area of the geranyl chain is larger than that of the glucose headgroup. Existence of water filled defects in bilayer sheets is also discussed based on the SAXS pattern and the concentration dependence of d.  相似文献   
993.
β-Cyclodextrin-polyurethane (β-CDPU) polymer was synthesized by the reaction of β-cyclodextrin with hexamethylene diisocyanate in dry dimethylformamide and used as a sorbent for the solid phase extraction (SPE) of carcinogenic aromatic amines from water. The polymers were characterized by Fourier transform infrared spectroscopy, thermogravimetric analysis, differential scanning calorimetry and particle size analysis. The separation and quantification was performed by Liquid chromatography with RP-C18 column and diode array detection using standard arylamines for quantification. When compared with commercially available sorbents, β-CDPU gave better recovery for the aromatic amines. From the variation of pH of the extractant from 4.0 to 8.5 recovery was highest at pH 8.5. The breakthrough volume has been ascertained to be 100 ml for 200 mg of the resin. The new SPE material offers better recovery and estimation of banned arylamines.  相似文献   
994.
Reversed phase high performance liquid chromatography (RPLC) is currently the method of choice for the analysis of basic compounds. However, with traditional silica materials, secondary interactions between the analyte and residual silanols produce peak tailing which can negatively affect resolution, sensitivity, and reproducibility. In order to reduce these secondary interactions, which comprise ion exchange, hydrogen bonding, and London forces interactions, chromatographic analyses can be carried out at low or high pH values where silanol groups and basic compounds are mostly uncharged. The chromatographic behaviour of a particular bidentate stationary phase, Zorbax Extend C18, was studied with a set of basic and neutral compounds. Thanks to a higher chemical stability than traditional silica based supports, analyses were carried out with a high pH mobile phase, which represents a good alternative to the acidic mobile phases generally used to reduce ion exchange interactions. The performance of this bidentate stationary phase was also compared with that of other supports and it was proved that it is advantageous to work with high pH mobile phases when analyzing basic compounds.  相似文献   
995.
The surface pressure-molecular area curve of the mixed monolayer of 16-(9-anthroyloxy) palmitic acid (16AP) and fatty acid (palmitic or stearic acids) showed various kink points which indicated the phase transitions of the monolayer. On the basis of the surface phase rule, the phase diagrams of the mixed monolayer were elucidated. The bifunctional molecule, 16AP, takes two orientations in a monolayer state, that is, horizontal and vertical ones. Horizontally oriented 16AP and vertically oriented fatty acid form a mixed monolayer but this exhibits deviation from the ideal mixing, which was interpreted in terms of the surface regular solution theory. On the other hand, the 16AP molecule in the vertical state was found to be immiscible with the fatty acid molecule in a monolayer de spite both molecules being vertical to the surface and parallel to each other. This was caused by the participation of the 9-anthroyloxy moiety of 16AP in the interaction of 16AP and fatty acid in the hydrophobic region of the monolayer.  相似文献   
996.
A non ionic surfactant with a rigid rod-like hydrophobic group has been synthesized. Owing to the molecular geometry of the surfactant only lamellar micelles are formed in aqueous solution.This system exhibits a lyotropic nematic phase (N L), which for the first time has been found for a binary non ionic surfactant/water system.Herrn Professor Dr. H.-G. Kilian mit herzlichen Glückwünschen zum 60. Geburtstag gewidmet.  相似文献   
997.
魏芸  樊立民 《分析化学》1997,25(9):1043-1047
介绍了不同孔径的硅胶聚合物键合相的合成,比较了其对蛋白质的分离特性。结果表明,大孔径的硅胶聚合物键合相比表面积小,易于获得生物大了分子的快速分离。  相似文献   
998.
Summary A correlation between the retention polarity and the Kováts' coefficient has been found for a number of commercial stationary phases used in gas chromatography. The correlation has been used to predict the polarity of a few mixed stationary phase columns prepared as binary mixtures of OV-101 with OV-25, DC-550 or Carbowax 20M, and also mixtures of OV-225 with SP-2340. A linear relationship was found between polarity and mixture composition. The temperature dependence of the Kováts' coefficient was investigated and found to increase linearly with temperature, the rate of increase depending on the polarity of the stationary phase, with greater increases for more polar stationary phases.  相似文献   
999.
Let X be an abstract set and L a lattice of subsets of X. To each lattice regular measure µ, we associate two induced measures and on suitable lattices of the Wallman space IR(L) and another measure µ on the spaceIR(L). We will investigate the reflection of smoothness properties of p onto , and µ; and try to set some new criterion for repleteness and measure repleteness.  相似文献   
1000.
We give a necessary and sufficient condition for the uniformly non-l n (1) property of Musielak-Orlicz sequence spacesl Φ generated by a sequence Φ=(ϕn:n⩾l) of finite Orlicz functions such that for eachn∈ℕ. As a result, forn 0⩾2, there exist spacesl Φ which are only uniformly non-l n (1) fornn 0. Moreover we obtain a characterization of uniformly non-l n (1) and reflexive Orlicz sequence spaces over a wide class of purely atomic measures and of uniformly non-l n (1) Nakano sequence spaces. This extends a result of Luxemburg in [19]. Submitted in memory of Professor W. Orlicz  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