全文获取类型
收费全文 | 15808篇 |
免费 | 544篇 |
国内免费 | 8篇 |
专业分类
化学 | 8856篇 |
晶体学 | 51篇 |
力学 | 312篇 |
数学 | 2178篇 |
物理学 | 4963篇 |
出版年
2023年 | 117篇 |
2021年 | 132篇 |
2020年 | 190篇 |
2019年 | 132篇 |
2018年 | 171篇 |
2017年 | 186篇 |
2016年 | 398篇 |
2015年 | 383篇 |
2014年 | 362篇 |
2013年 | 723篇 |
2012年 | 680篇 |
2011年 | 877篇 |
2010年 | 374篇 |
2009年 | 334篇 |
2008年 | 784篇 |
2007年 | 754篇 |
2006年 | 732篇 |
2005年 | 640篇 |
2004年 | 509篇 |
2003年 | 465篇 |
2002年 | 418篇 |
2001年 | 362篇 |
2000年 | 285篇 |
1999年 | 234篇 |
1998年 | 195篇 |
1997年 | 212篇 |
1996年 | 225篇 |
1995年 | 204篇 |
1994年 | 184篇 |
1993年 | 209篇 |
1992年 | 210篇 |
1991年 | 162篇 |
1990年 | 145篇 |
1989年 | 136篇 |
1988年 | 125篇 |
1987年 | 140篇 |
1986年 | 153篇 |
1985年 | 162篇 |
1984年 | 208篇 |
1983年 | 183篇 |
1982年 | 188篇 |
1981年 | 196篇 |
1980年 | 174篇 |
1979年 | 157篇 |
1978年 | 175篇 |
1977年 | 169篇 |
1976年 | 147篇 |
1975年 | 137篇 |
1974年 | 127篇 |
1973年 | 124篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
The trisilanol 1,3,5‐(HOi‐Bu2Si)3C6H3 ( 7 ), prepared in three steps from 1,3,5‐tribromobenzene via the intermediates 1,3,5‐(Hi‐Bu2Si)3C6H3 ( 8 ) and 1,3,5‐(Cli‐Bu2Si)3C6H3 ( 9 ) forms an equimolar complex with trans‐bis(4‐pyridyl)ethylene (bpe), 7 ·bpe, whose structure was investigated by X‐ray crystallography. The hydrogen‐bonded network features a number of SiO? H(H)Si and SiO? H hydrogen bridges. Evidence was found for cooperative strengthening within the sequential hydrogen bonds. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
32.
33.
Simple and convenient methods for determining surface chemical composition of lignocellulosic materials are described. The
methods are based on vapor phase fluorine surface derivatization with either trifluoro acetic anhydride (TFAA), tri-fluoro
ethanol (TFE) or pentafluorophenyl hydrazine (PFPH) and subsequent Electron Spectroscopy for Chemical Analysis (ESCA). Model
cellulosic surfaces with well defined functionalities were used to optimize the derivatization reaction conditions. Detection
and accessibility of surface hydroxyl functional groups were investigated in cotton and regenerated cellulose as models. Carboxymethyl
cellulose (CMC) was used as a model surface for detection and quantification of carboxylic acid groups. Theoretical conversion
curves for derivatization reactions were calculated and used to evaluate the extent of the reactions on the model surfaces.
It was found that the conversion was higher for the regenerated cellulose and CMC than for cotton. The protocols developed
using the model surfaces were applied to a case study on wood fibers with different degrees of complexity, namely dissolving
and chemithermomechanical (CTMP) pulp. Untreated and oxygen-plasma modified pulps were compared with respect to the surface
composition of functional groups. According to the derivatization reactions, functionalities containing oxygen were significantly
increased on the plasma-treated samples. The effect of the treatment was found to be dependent on the type of pulp. Fluorine
derivatization is shown to be an unambiguous method for clear assessment of the chemical functionalities of cellulosic surfaces. 相似文献
34.
Ph. Hägler B. Pire L. Szymanowski O.V. Teryaev 《The European Physical Journal C - Particles and Fields》2002,24(2):261-270
We study Pomeron-Odderon interference effects giving rise to charge and single-spin asymmetries in diffractive electroproduction
of a pair. We calculate these asymmetries, originating from both longitudinal and transverse polarizations of the virtual photon,
in the framework of QCD and in the Born approximation, in a kinematical domain accessible to HERA experiments. We predict
a sizable charge asymmetry with a characteristic dependence on the invariant mass of the pair, which makes this observable very important for establishing the magnitude of the Odderon exchange in hard processes.
The single-spin asymmetry turns out to be rather small. We briefly discuss future improvements of our calculations and their
possible effects on the results.
Received: 18 July 2002 / Published online: 25 October 2002 相似文献
35.
Joachim Käschel 《Proceedings Mathematical Sciences》1992,102(2):155-158
In Venkaiah [1] an algorithm for solving linear optimization problems based on the idea of the projective algorithm of Karmarkar,
is proposed. The essential simplification in the new algorithm is the use of a fixed projection operator. In this way the
algorithm requires onlyO(n
2
) operations to obtain a sufficient exact solution. In this note it is shown that in some special cases the algorithm of Venkaiah
yields a feasible solution that is far from the optimal one. 相似文献
36.
37.
Michael Grätzel 《Journal of Sol-Gel Science and Technology》1994,2(1-3):673-677
Transparent nanocrystalline films of oxide semiconductors such as TiO2 and Fe2O3 have been prepared on a conducting glass support employing a sol-gel procedure. The films are composed of nanometer-sized particles sintered together to allow for percolative charge carrier transport. The internal surface of these films is very high, roughness factors of the order of 1000 being readily obtained. Electric polarization was applied for forward and reverse biasing of the films and the resulting optical changes have been analyzed to derive their flat band potential. Band gap excitation of such nanocrystalline semiconductors produces electron-hole pairs which migrate through the film to be collected as electric current. Steady state photolysis and time resolved laser techniques have been applied to scrutinize the mechanism of light induced charge separation within the nanostructure. When derivatized with a suitable chromophore, TiO2 films give extraordinary efficiencies for the conversion of incident photons into electric current, exceeding 90% for certain transition metal complexes within the wavelength range of their absorption band. The underlying physical principles of these astonishing findings will be discussed. Exploiting this discovery, we have developed a new type of photovoltaic device whose overall light to electric energy conversion yield is 10% under simulated AM 1.5 solar radiation. 相似文献
38.
Erkki Mäkinen 《BIT Numerical Mathematics》1987,27(3):330-339
The splay tree is a self-adjusting binary search tree which has a good amortized performance. This paper studies some properties of top-down splay trees. Different ways to charge for the primitive operations of top-down splaying are discussed. We also give some empirical results concerning the behaviour of different top-down restructuring algorithms.This work was supported by the Academy of Finland. 相似文献
39.
P. Schwab A. Kochemasov R. Kullmer D. Bäuerle 《Applied Physics A: Materials Science & Processing》1992,54(2):166-169
Pulsed-laser deposition of YBa2Cu3O7 in N2O permits lowering of the substrate temperature with respect to deposition in O2 atmosphere. Additional photodissociation of N2O near the substrate surface deteriorates the superconducting properties of deposited films.On leave from: Institute of Applied Physics of the Academy of Sciences of the USSR, SU-603600 Nishni Nowgorod, USSR 相似文献
40.
In this paper we present photoionization cross sections of the Cu and Al dimers and tetramers. The local spin density method is applied to calculate the electronic structure and the ground state potential. The cross sections are calculated using the continuum multiple scattering method, and a basic analysis of the photoionization process is given within the independent particle picture. 相似文献