全文获取类型
收费全文 | 1326292篇 |
免费 | 29679篇 |
国内免费 | 7727篇 |
专业分类
化学 | 659775篇 |
晶体学 | 20317篇 |
力学 | 74464篇 |
综合类 | 108篇 |
数学 | 241422篇 |
物理学 | 367612篇 |
出版年
2021年 | 13480篇 |
2020年 | 15940篇 |
2019年 | 16051篇 |
2018年 | 12600篇 |
2016年 | 27851篇 |
2015年 | 20822篇 |
2014年 | 30462篇 |
2013年 | 74509篇 |
2012年 | 37170篇 |
2011年 | 33690篇 |
2010年 | 36849篇 |
2009年 | 39329篇 |
2008年 | 33266篇 |
2007年 | 28928篇 |
2006年 | 34977篇 |
2005年 | 27749篇 |
2004年 | 28965篇 |
2003年 | 27473篇 |
2002年 | 28640篇 |
2001年 | 27199篇 |
2000年 | 24120篇 |
1999年 | 22161篇 |
1998年 | 20910篇 |
1997年 | 20967篇 |
1996年 | 21084篇 |
1995年 | 19169篇 |
1994年 | 18619篇 |
1993年 | 18171篇 |
1992年 | 17962篇 |
1991年 | 18301篇 |
1990年 | 17439篇 |
1989年 | 17532篇 |
1988年 | 17086篇 |
1987年 | 17101篇 |
1986年 | 15992篇 |
1985年 | 22442篇 |
1984年 | 23756篇 |
1983年 | 19931篇 |
1982年 | 21651篇 |
1981年 | 20888篇 |
1980年 | 20252篇 |
1979年 | 20365篇 |
1978年 | 21706篇 |
1977年 | 21279篇 |
1976年 | 21004篇 |
1975年 | 19675篇 |
1974年 | 19335篇 |
1973年 | 19782篇 |
1972年 | 14291篇 |
1967年 | 12543篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
951.
952.
Summary A system for capillary electrophoresis combined with enzymatic assay has been evaluated for the two enzymes glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase. Instrumentation included a post-column reactor coupled to the separation capillary by a liquid junction. A technique for generating a substrate solution flow into the reactor by utilizing two high voltage supplies is proposed. This method offers a high degree of freedom in optimizing the separation and enzymatic reaction conditions individually. Possibilities for improving the enzymatic assay sensitivity were also examined. 相似文献
953.
M. Hanson 《Chromatographia》1994,39(7-8):431-437
Summary Pressure/temperature variation in SFC was shown to influence selectivity towards steroids. Major changes were observed for polar column packings compared to non-polar packings and variation of the amount of modifier showed that this is valid over the whole investigated range. The effect is underlined by a fall in resolution in the low density range (low pressure/high temperature) for polar stationary phases and appears to be significantly larger than for non-polar phases. Major selectivity shifts induced by variation of the physical properties of the mobile phase are considered to be due to the greater effect of polar modifiers on the nature of polar stationary phases than on non-polar phases. 相似文献
954.
Summary Experiments and simulations prove that correlation chromatography can greatly reduce the disadvantage of a non-linear response of the chromatographic column. A factor that has been accepted as being an important source of error in correlation or multiplex chromatography, has been shown not to be. Separations affected, improve dramatically when correlation chromatography is used, and a substantial amount of correlation noise only arises when there is a large difference in separation between a conventional chromatogram and a correlogram.A model has been developed for simulating these nonlinearities. It is shown that, especially for correlation chromatography, the simulation results match the practical measurements very well. 相似文献
955.
956.
Separation of 23 dansylated amino acids by micellar electrokinetic chromatography at low temperature
Summary The baseline separation of 23 dansylated amino acids (including 3 didansylated species) is reported. Lowering of the analysis
temperature and fine control of the surfactant concentration were essential in obtaining this result. Calibration graphs with
good linearity were obtained. 相似文献
957.
The coordination chemistry of beryllium with particular emphasis on chelates under physiological or near physiological conditions is surveyed. Hard donors such as oxygen are emphasized; equilibrium data and formation constants are reported as an indication of the strength of the complex. 相似文献
958.
J. Escudi C. Couret H. Ranaivonjatovo J. Satge 《Coordination chemistry reviews》1994,130(1-2):427-480
During the last 10 years, several compounds of the type Ge=X (X = C, Ge, N, P, S) have been isolated as monomers. The stabilization of such derivatives, which are generally highly polymerizable, was achieved by using very bulky groups both on the germanium atom and on the heteroelement X. Conjugation (particularly in a few germenes and germaimines) and intramolecular or intermolecular coordination with oxygen or nitrogen, also contributes, in some cases, to the stabilization. The X-ray analyses of such compounds show a significant bond shortening of the double bond (8–10%) relative to the corresponding single bond and a planar or nearly planar germanium. These doubly bonded germanium derivatives are usually thermally stable but must be handled in an inert atmosphere because of their high sensitivity to oxygen and moisture; they are extremely reactive, much more than the corresponding carbon analogues. Nearly quantitative additions on the double bond have been observed with electrophiles and nucleophiles, and various types of cycloadditions also occur. Except in one case, a germylene behavior has not been observed, proving that such compounds retain their structural integrity in solution. 相似文献
959.
The copolymerization of methyl methacrylate and methacrylic acid in isopropyl alcohol is studied by kinetic, dynamic laser scattering and 13C-NMR methods. Correlations are established between the dependence of the copolymerization rate, the apparent average molecular weight, the diffusion coefficients and the configurational triad composition on the monomer feed. These correlations and the fact that both copolymerization constants are smaller than unity (rMMA = 0.63 ± 0.03; rMA = 0.25 ± 0.05) are in good agreement with the assumption that a comonomer complex takes part in the propagation reaction. A new Markov chain method for the estimation of the configurational triad mole fraction which accounts for the complex participation in a macromolecule formation is developed. Qualitative criteria for evidence the participation of the comonomer complex in copolymerization are proposed using experimental and terminal model calculated mole fractions of the compositional triads and diads. 相似文献
960.
Twelve series of linear oligomers of four different degrees of polymerization (xn = 8.77−41.55), having a common perfluorinated random copolymeric chain as molecular body and two equal foreign end units of one of the types listed in Table 1, have been synthesized by derivatization of base samples of one of them having a diolic---CH2OH functionality. The glass transition temperature Tg of all the series was measured and thus examined as a function of xn. A clear end unit effect is observed, dominantly determined in every series by chemical nature and structure of the end units, quantitatively expressed at any xn by different positive or negative Tg deviations from the common asymptotic Tg∞ value. The results are also discussed in terms of copolymer end effect and of relation between Tg and end copolymeric composition. 相似文献