全文获取类型
收费全文 | 268147篇 |
免费 | 3442篇 |
国内免费 | 1093篇 |
专业分类
化学 | 147348篇 |
晶体学 | 3805篇 |
力学 | 10504篇 |
综合类 | 3篇 |
数学 | 32281篇 |
物理学 | 78741篇 |
出版年
2020年 | 2065篇 |
2019年 | 2313篇 |
2018年 | 2725篇 |
2017年 | 2670篇 |
2016年 | 4373篇 |
2015年 | 3145篇 |
2014年 | 4502篇 |
2013年 | 12445篇 |
2012年 | 9333篇 |
2011年 | 11497篇 |
2010年 | 7450篇 |
2009年 | 7220篇 |
2008年 | 10275篇 |
2007年 | 10432篇 |
2006年 | 9726篇 |
2005年 | 9043篇 |
2004年 | 8168篇 |
2003年 | 7179篇 |
2002年 | 7074篇 |
2001年 | 7617篇 |
2000年 | 5744篇 |
1999年 | 4588篇 |
1998年 | 3907篇 |
1997年 | 3964篇 |
1996年 | 3657篇 |
1995年 | 3456篇 |
1994年 | 3309篇 |
1993年 | 3321篇 |
1992年 | 3598篇 |
1991年 | 3613篇 |
1990年 | 3406篇 |
1989年 | 3355篇 |
1988年 | 3401篇 |
1987年 | 3228篇 |
1986年 | 3147篇 |
1985年 | 4324篇 |
1984年 | 4484篇 |
1983年 | 3702篇 |
1982年 | 4075篇 |
1981年 | 3941篇 |
1980年 | 3833篇 |
1979年 | 3800篇 |
1978年 | 4068篇 |
1977年 | 3868篇 |
1976年 | 4025篇 |
1975年 | 3567篇 |
1974年 | 3703篇 |
1973年 | 3984篇 |
1972年 | 2431篇 |
1971年 | 1880篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
811.
812.
R. Resel M. Oehzelt O. Lengyel T.U. Schülli G. Hlawacek C. Teichert G. Koller 《Surface science》2006,600(19):4645-4649
A para-sexiphenyl monolayer of near up-right standing molecules (nominal thickness of 30 Å) is investigated in-situ by X-ray diffraction using synchrotron radiation and ex-situ by atomic force microscopy. A terrace like morphology is observed, the step height between the terraces is approximately one molecular length. The monolayer terraces, larger than 20 μm in size, are extended along the [0 0 1] direction of the TiO2(1 1 0) substrate i.e. along the Ti-O rows of the reconstructed substrate surface. The structure of the monolayer and its epitaxial relationship to the substrate is determined by grazing incidence X-ray diffraction. Extremely sharp diffraction peaks reveal high crystalline order within the monolayer, which was found to have the bulk structure of sexiphenyl. The monolayer terraces are epitaxially oriented with the (0 0 1) plane parallel to the substrate surface (out-of-plane order). Four epitaxial relationships are observed. This in-plane alignment is determined by the arrangement of the terminal phenyl rings of the sexiphenyl molecules parallel to the oxygen rows of the substrate. 相似文献
813.
We construct division algebras with involution containing a Baer ordering with noninvariant order ring. This gives a negative
answer to a question of Holland, whether the order ring is always invariant under inner automorphisms. Furthermore, we give
examples of any index. Previously, the only known examples of division algebras containing Baer orderings were of index 2
n
or of indexp forp a prime of the form 4m + 3.
Supported in part by the National Science Foundation. 相似文献
814.
Summary We report on neutron emission in palladium and titanium electrolitically charged with deuterium. The detection of neutrons
is observed after thermal treatment of the electrode. In the hypothesis that neutrons came from cold fusion processes, we
estimate a fusion rate as high as 1.3·10−21 fusions/deuteron pair/second. 相似文献
815.
We consider equations of motion for some massiveN=1 supermultiplets of fields, using superfields and their superderivatives. The formalism is based on the superprojectors. 相似文献
816.
A comparison of results of indirect and direct electrochemical fluorosulfation of nonsaturated fluorocarbons shows that the main or the only product in potentiostatic conditions is vicinal fluorosulfates. Owing to a high rate of the electrochemical step, which exceeds the rate of desorption of intermediate radicals from the electrode surface into solution, it is possible to improve the process selectivity by increasing the contribution of the ionic reaction route. 相似文献
817.
S. Park T. U. Kampen T. Kachel P. Bressler W. Braun D. R. T. Zahn 《Applied Surface Science》2002,190(1-4):376-381
The interaction of Ag and In with a thin film of 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) was studied by near-edge X-ray absorption fine structure (NEXAFS). Upon Ag deposition on a PTCDA film of 20 nm thickness the relative intensities and lineshapes, as well as the angular dependence of the spectra remains unchanged, illustrating the formation of a chemically unreactive Ag/PTCDA interface. On the other hand, the adsorption of 0.3 nm In strongly decreases the intensity of the π* resonances in C and O K-edge NEXAFS spectra. This is attributed to a strong charge transfer between In and PTCDA, leading to a redistribution of the charge in the molecule. However, the absence of a strong shift or new features and negligible dependence of peak intensities corresponding to π* resonances on the In thickness indicate that the interaction between In and PTCDA is not accompanied by a covalent bond formation. 相似文献
818.
4(3H)-Quinazolinones have been synthesized in high to excellent yields through the one-pot condensation of anthranilic acid, trimethyl orthoformate and primary amines in the presence of 5 mol % of Bi(TFA)3 immobilized on [nbp]FeCl4 as a room temperature ionic liquid. 相似文献
819.
This paper proposes an extension of the expansions of analytic functions in the An polynomials defined by Adomian [1] to consider piecewise-differentiable functions. 相似文献
820.
S. D. Borkute U. H. Nagvekar S. A. Balakrishnan R. S. Mani 《Journal of Radioanalytical and Nuclear Chemistry》1987,119(4):297-302
A novel method to eliminate T3 from gross sera/plasma based on prior treatment with 8-anilino-1-naphthalene sulphonic acid has been standardized. This method is rapid with a minimum loss of protein and uses only small quantities of charcoal. The treated sera have been tested for acceptance in the RIA system for routine assays. 相似文献