全文获取类型
收费全文 | 333268篇 |
免费 | 2916篇 |
国内免费 | 942篇 |
专业分类
化学 | 173368篇 |
晶体学 | 5017篇 |
力学 | 15146篇 |
综合类 | 10篇 |
数学 | 36725篇 |
物理学 | 106860篇 |
出版年
2021年 | 2485篇 |
2020年 | 2748篇 |
2019年 | 2999篇 |
2018年 | 3925篇 |
2017年 | 3823篇 |
2016年 | 5816篇 |
2015年 | 3616篇 |
2014年 | 5674篇 |
2013年 | 14592篇 |
2012年 | 11326篇 |
2011年 | 13880篇 |
2010年 | 9565篇 |
2009年 | 9472篇 |
2008年 | 12598篇 |
2007年 | 12791篇 |
2006年 | 12162篇 |
2005年 | 11013篇 |
2004年 | 10010篇 |
2003年 | 8849篇 |
2002年 | 8723篇 |
2001年 | 9925篇 |
2000年 | 7643篇 |
1999年 | 5889篇 |
1998年 | 4936篇 |
1997年 | 4896篇 |
1996年 | 4490篇 |
1995年 | 4236篇 |
1994年 | 4056篇 |
1993年 | 3811篇 |
1992年 | 4356篇 |
1991年 | 4447篇 |
1990年 | 4208篇 |
1989年 | 4021篇 |
1988年 | 4006篇 |
1987年 | 3941篇 |
1986年 | 3702篇 |
1985年 | 4877篇 |
1984年 | 5183篇 |
1983年 | 4273篇 |
1982年 | 4585篇 |
1981年 | 4416篇 |
1980年 | 4245篇 |
1979年 | 4473篇 |
1978年 | 4729篇 |
1977年 | 4567篇 |
1976年 | 4667篇 |
1975年 | 4380篇 |
1974年 | 4410篇 |
1973年 | 4530篇 |
1972年 | 2960篇 |
排序方式: 共有10000条查询结果,搜索用时 11 毫秒
121.
122.
Al.Th. Kermanidis D.G. Stamatelos G.N. Labeas Sp.G. Pantelakis 《Theoretical and Applied Fracture Mechanics》2006,45(2):148-158
The synergetic effect of corrosion and corrosion induced hydrogen embrittlement damage processes which occur at local scale has been found to result in a dramatic macroscopic tensile ductility loss of the 2024 aluminum alloy. In the present work, the tensile behaviour of corroded 2024 T351 specimens has been estimated on the basis of FE analysis by taking into account the local material properties in the damaged areas. A parametric study is involved to account for the effect of thickness in the results. Calculated tensile properties obtained with the analysis agree well with experimental data. 相似文献
123.
D. N. Karimov E. A. Krivandina Z. I. Zhmurova B. P. Sobolev V. A. Bezhanov S. P. Chernov G. M. Shapochkin 《Crystallography Reports》2006,51(6):1009-1015
Crystalline materials that are transparent in the vacuum UV spectral region and currently used have been reviewed. Transmission of crystals of solid solutions with the fluorite structure Ca1?x R xF2+x (R = Sc, Y, La, Yb, Lu) in the UV and vacuum UV spectral regions has been investigated. It is shown that application of different methods of purification of fluorides from some impurities can significantly improve the optical quality of fluoride multicomponent crystals in the short-wavelength spectral region. 相似文献
124.
M. F. Bobrov G. V. Popova V. G. Tsirelson 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2006,80(4):584-590
The restricted Hartree-Fock method was used to determine the cycle size effects on the geometric parameters of several inorganic templates, cyclophosphazenes PnNnX2n (X = H, F, Cl; n = 2, 3, 4). A topological analysis of local electronic properties at the electron density critical points of bonds allowed us to quantitatively characterize the chemical bond in cyclophosphazenes and its dependence on the cycle size and substituents at phosphorus. The calculated distributions of the electron density Laplacian and electron pair localization functions revealed the special features of the electronic structure of the nitrogen and phosphorus atoms. These results explain the nature of noncovalent interactions between the P atoms of one cyclophosphazene molecule and the N atoms of the other. 相似文献
125.
126.
Analysis of amlodipine in human plasma by gas chromatography 总被引:3,自引:0,他引:3
127.
In this paper the performances of inhomogeneous dielectric slabs as solar light collectors for both illumination and solar energy applications are analysed. 相似文献
128.
Calculations are performed, using a basis of two-center functions described previously, for excited states of the following three-and four-electron compounds: H2
–, He2
+, He2, Li2
+2. High efficiency is demonstrated for the frozen ionic core approximation and the nonorthogonal orbital method in such calculations. For four-electron systems the practical feasibility of the frozen hybrid core approximation is demonstrated.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 53–56, August, 1987. 相似文献
129.
We present here a methodology for searching a robust pore size distribution (PSD) for adsorbent materials. The method is based on a combination of individual adsorption isotherms, obtained from Grand Canonical Monte Carlo simulations, a regularization procedure to invert the adsorption integral equation (Tikhonov regularization solved by singular value decomposition), and the needed experimental adsorption isotherm. The selection of several parameters from the available choices to start the procedure are discussed here: the size of the kernel (number of individual pores and number of experimental adsorption points to be included), the fulfillment of the Discrete Picard condition, and the L-curve criteria, all leading to find a reliable and robust PSD. The procedure is applied to plugged hexagonal templated silicas (PHTS), synthesized, and characterized in our laboratory. 相似文献
130.
Molecular electroactive monolayers have been produced from vinylferrocene (VFC) via light-assisted surface anchoring to H-terminated n- and p-Si(1 0 0) wafers prepared via wet chemistry, in a controlled atmosphere. The resulting Si-C bound hybrids have been characterized by means of XPS and AFM. Their performance as semiconductor functionalized electrodes and their surface composition have been followed by combining electrochemical and XPS measurements on the same samples, before and after use in an electrochemical cell. White-light photoactivated anchoring at short (1 h) exposure times has resulted in a mild route, with a very limited impact on the initial quality of the silicon substrate. In fact, the functionalized Si surface results negligibly oxidized, and the C/Fe atomic ratio is close to the value expected for the pure molecular species. The VFC/Si hybrids can be described as (η5-C5H5)Fe2+(η5-C5H4)-CH2-CH2-Si species, on the basis of XPS results. Electrochemical methods have been applied in order to investigate the role played by a robust, covalent Si-C anchoring mode towards substrate-molecule electronic communication, a crucial issue for a perspective development of molecular electronics devices. The response found from cyclic voltammograms for p-Si(1 0 0) functionalized electrodes, run in the dark and under illumination, has shown that the electron transfer is not limited by the number of charge carriers, confirming the occurrence of electron transfer via the Si valence band. The hybrids have shown a noticeable electrochemical stability and reversibility under cyclic voltammetry (cv), and the trend in peak current intensity vs. the scan rate was linear. The molecule-Si bond is preserved even after thousands of voltammetric cycles, although the surface coverage, evaluated from cv and XPS, decreases in the same sequence. An increasingly larger surface concentration of Fe3+ at the expenses of Fe2+ redox centers has been found at increasing number of cv’s, experimentally associated with the growth of silicon oxide. Surface SiO− groups from deprotonated silanol termination, induced by the electrochemical treatments, are proposed as the associated counterions for the Fe3+ species. They could be responsible for the observed decrease in the electron transfer rate constant with electrode ageing. 相似文献