全文获取类型
收费全文 | 3563篇 |
免费 | 64篇 |
国内免费 | 5篇 |
专业分类
化学 | 2101篇 |
晶体学 | 17篇 |
力学 | 77篇 |
综合类 | 1篇 |
数学 | 460篇 |
物理学 | 976篇 |
出版年
2021年 | 53篇 |
2020年 | 53篇 |
2019年 | 42篇 |
2018年 | 54篇 |
2017年 | 67篇 |
2016年 | 85篇 |
2015年 | 72篇 |
2014年 | 90篇 |
2013年 | 176篇 |
2012年 | 150篇 |
2011年 | 206篇 |
2010年 | 113篇 |
2009年 | 92篇 |
2008年 | 201篇 |
2007年 | 184篇 |
2006年 | 168篇 |
2005年 | 126篇 |
2004年 | 125篇 |
2003年 | 95篇 |
2002年 | 98篇 |
2001年 | 50篇 |
2000年 | 59篇 |
1999年 | 38篇 |
1998年 | 29篇 |
1997年 | 28篇 |
1996年 | 27篇 |
1995年 | 45篇 |
1994年 | 35篇 |
1993年 | 38篇 |
1992年 | 32篇 |
1991年 | 25篇 |
1989年 | 35篇 |
1988年 | 30篇 |
1987年 | 35篇 |
1986年 | 37篇 |
1985年 | 45篇 |
1984年 | 35篇 |
1983年 | 40篇 |
1982年 | 40篇 |
1981年 | 29篇 |
1980年 | 32篇 |
1979年 | 26篇 |
1978年 | 44篇 |
1977年 | 29篇 |
1976年 | 39篇 |
1975年 | 33篇 |
1974年 | 28篇 |
1972年 | 25篇 |
1968年 | 29篇 |
1966年 | 30篇 |
排序方式: 共有3632条查询结果,搜索用时 15 毫秒
61.
The gas phase basicities of a series of carbofunctional derivatives H3M(CH2)nX (M = C, Si, Ge; X = NH2, OH, F; n = 1–3) were investigated by the semiempirical CNDO/2 method. The calculations indicate that the electronic effects of silyl- and germyl-substituents differ greatly from the effect of simple alkyls. Moreover, in contrast to simple carbon derivatives, the overall nature of the electronic effects of siliyl- and germyl-substituents is crucially influenced by the molecular conformation. 相似文献
62.
Paths of length two and three appear to dominate variations in isomers of alkanes when various physical and chemical molecular properties are compared. The regularities previously observed for octanes have been fully examined for the set of 35 nonane isomers C9H20. Such examinations are facilitated by construction of appropriate grid graphs with paths of length two and three, respectively, representing molecules and connecting such points along the grid axes. By ordering structures in the two-dimensional coordinate plane, various trends and regular changes in the relative magnitudes for the selected thermodynamic properties have been traced to molecular connectivity and topology. 相似文献
63.
Glatz Z Marini MV Wimmerová M Damborský J Nagata Y 《Journal of chromatography. A》2000,895(1-2):219-225
A new sensitive method has been developed for the determination of haloalkane dehalogenase activity. The enzymatic reactions were carried out directly in thermostatted autosampler vials and the formation of product - bromide or chloride ions - was monitored by sequential capillary zone electrophoresis runs. The determinations were performed in a 75 microm fused-silica capillary using 5 mM chromate, 0.5 mM tetradecyltrimethylammonium bromide (pH 8.4) as a background electrolyte, separation voltage 15 kV (negative polarity) and indirect detection at sample wavelength 315 nm, reference wavelength 375 nm for brominated and chlorinated substrates, respectively 0.1 M beta-alanine-HCl (pH 3.50) as a background electrolyte, separation voltage 18 kV (negative polarity) and direct detection at 200 nm for brominated substrates. The temperature of capillary was in both cases 25 degrees C. The method is rapid, can be automated, and requires only small amount of enzyme preparation and substrate. 相似文献
64.
65.
Pavel Novotný 《Geometriae Dedicata》1994,50(1):53-55
This paper deals with the following kind of approximation of a convex bodyQ in Euclidean space E
n
by simplices: which is the smallest positive numberh
S(Q) such thatS
1 Q S
2 for a simplexS
1 and its homothetic copyS
2 of ratioh
S(Q). It is shown that ifS
0 is a simplex of maximal volume contained inQ, then a homothetic copy ofS
0 of ratio 13/3 containsQ. 相似文献
66.
67.
68.
69.
P. PŘikryl F. Vodák O. Kapičková J. Drchalová R. černý 《Czechoslovak Journal of Physics》1993,43(1):63-71
The influence of the microgravity environment on solidification processes is discussed. A simple model of the solidification of a binary-alloy is presented with the chemical diffusion influenced by the gravitational field. Using the results of Mullins and Sekerka, we employ the linear theory of hydrodynamic stability to investigate the interfacial instability driving the pattern-forming processes in solidification. As a result, we estimate the characteristic size of the elements of the emerging pattern. We show that, in spite of good agreement of our result with the size of cellulae observed in experiments, the model cannot explain the changes in the patterns occurring in space environment. In conclusion we shortly discuss the possibility of adding realism to our simple model by including the effect of convection. 相似文献
70.
Milan Randi 《International journal of quantum chemistry》1983,23(5):1707-1722
Many regularities in properties among structurally related compounds are known but a systematic approach to investigate all such cases is rare. A plan is outlined for a systematic study of structural regularities that is based on use of selected graph invariants as prime auxiliary quantities. In this paper carbon-13 chemical shifts in alkanes are examined. Since NMR spectra of paraffins are well understood, the example provides a useful illustration of the approach, introduces basic concepts, and illustrates the kind of the results that the graph-theoretical scheme generates. Differences and similarities between graph-theoretical viewing of the problem of structural regularities and customary direct use of additivities are discussed in some detail. 相似文献