全文获取类型
收费全文 | 550724篇 |
免费 | 12711篇 |
国内免费 | 7761篇 |
专业分类
化学 | 272386篇 |
晶体学 | 7809篇 |
力学 | 28885篇 |
综合类 | 387篇 |
数学 | 95301篇 |
物理学 | 166428篇 |
出版年
2022年 | 3912篇 |
2021年 | 4695篇 |
2020年 | 5160篇 |
2019年 | 5334篇 |
2018年 | 20897篇 |
2017年 | 21357篇 |
2016年 | 16676篇 |
2015年 | 7987篇 |
2014年 | 9630篇 |
2013年 | 19764篇 |
2012年 | 23057篇 |
2011年 | 36842篇 |
2010年 | 23641篇 |
2009年 | 23724篇 |
2008年 | 30568篇 |
2007年 | 34504篇 |
2006年 | 16262篇 |
2005年 | 20599篇 |
2004年 | 16614篇 |
2003年 | 15500篇 |
2002年 | 12778篇 |
2001年 | 12067篇 |
2000年 | 9541篇 |
1999年 | 7267篇 |
1998年 | 6169篇 |
1997年 | 5941篇 |
1996年 | 5949篇 |
1995年 | 5312篇 |
1994年 | 5202篇 |
1993年 | 4933篇 |
1992年 | 5273篇 |
1991年 | 5263篇 |
1990年 | 4984篇 |
1989年 | 4772篇 |
1988年 | 4650篇 |
1987年 | 4564篇 |
1986年 | 4450篇 |
1985年 | 5749篇 |
1984年 | 5830篇 |
1983年 | 5032篇 |
1982年 | 5323篇 |
1981年 | 4938篇 |
1980年 | 4715篇 |
1979年 | 5008篇 |
1978年 | 5218篇 |
1977年 | 5113篇 |
1976年 | 5211篇 |
1975年 | 4860篇 |
1974年 | 4915篇 |
1973年 | 5157篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
191.
192.
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
193.
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
194.
The Iyengar Type Inequalities with Exact Estimations and the Chebyshev Central Algorithms of Integrals 总被引:3,自引:0,他引:3
Xing Hua WANG Shi Jun YANG 《数学学报(英文版)》2005,21(6):1361-1376
In this paper, both low order and high order extensions of the Iyengar type inequality are obtained. Such extensions are the best possible in the same sense as that of the Iyengar inequality. hzrthermore, the Chebyshev central algorithms of integrals for some function classes and some related problems are also considered and investigated. 相似文献
195.
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
196.
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
197.
198.
199.
Stress-Strain State in the Zone of Load Transfer in a Composite Specimen under Uniaxial Tension 总被引:2,自引:2,他引:0
Kulakov V. L. Tarnopol'skii Yu. M. Arnautov A. K. Rytter J. 《Mechanics of Composite Materials》2004,40(2):91-100
The stress-strain state in the zone of load transfer in a uniaxially stretched specimen made of a unidirectional epoxy carbon-fiber-reinforced plastic (CFRP) is investigated. A parametric analysis of the influence of geometric and mechanical characteristics of the specimen on its stress-strain state is performed by means of finite-element modeling. The parameters allowing us to significantly reduce the dangerous concentration of transverse and tangential stresses are revealed. The mechanical tensile characteristics of a high-strength pultruded unidirectional CFRP are determined experimentally, and the size effect of its strength is estimated. 相似文献
200.
M. Lashkarizadeh Bami 《Semigroup Forum》2004,69(2):219-229
In the present paper it is shown that if S1 and S2 are two
Clifford topological semigroups satisfying certain conditions
and T is an isometric isomorphism of LUC(S1*) onto LUC(S2*), then T
maps S1 topologically isomorphically onto S2. Furthermore, T
maps M
l
n(S1) (M(S1), respectively) isometrically
isomorphically onto M
l
n(S2) (M(S2), respectively). Indeed,
we have obtained a generalization of a well-known result of
Ghahramani, Lau and Losert for locally compact groups to a more
general setting of Clifford topological semigroups. 相似文献