全文获取类型
收费全文 | 58593篇 |
免费 | 3762篇 |
国内免费 | 7989篇 |
专业分类
化学 | 48291篇 |
晶体学 | 474篇 |
力学 | 1206篇 |
综合类 | 786篇 |
数学 | 6831篇 |
物理学 | 12756篇 |
出版年
2023年 | 694篇 |
2022年 | 883篇 |
2021年 | 1961篇 |
2020年 | 1460篇 |
2019年 | 1560篇 |
2018年 | 1286篇 |
2017年 | 1423篇 |
2016年 | 1632篇 |
2015年 | 1651篇 |
2014年 | 2090篇 |
2013年 | 3759篇 |
2012年 | 2792篇 |
2011年 | 2977篇 |
2010年 | 2658篇 |
2009年 | 3209篇 |
2008年 | 3414篇 |
2007年 | 3782篇 |
2006年 | 3130篇 |
2005年 | 2315篇 |
2004年 | 2304篇 |
2003年 | 2140篇 |
2002年 | 4392篇 |
2001年 | 2028篇 |
2000年 | 1604篇 |
1999年 | 1365篇 |
1998年 | 1349篇 |
1997年 | 1187篇 |
1996年 | 1110篇 |
1995年 | 1050篇 |
1994年 | 966篇 |
1993年 | 957篇 |
1992年 | 865篇 |
1991年 | 594篇 |
1990年 | 488篇 |
1989年 | 410篇 |
1988年 | 391篇 |
1987年 | 290篇 |
1986年 | 270篇 |
1985年 | 364篇 |
1984年 | 284篇 |
1983年 | 167篇 |
1982年 | 315篇 |
1981年 | 481篇 |
1980年 | 439篇 |
1979年 | 473篇 |
1978年 | 377篇 |
1977年 | 283篇 |
1976年 | 243篇 |
1974年 | 78篇 |
1973年 | 152篇 |
排序方式: 共有10000条查询结果,搜索用时 109 毫秒
121.
Phenomena accompanying electrochemical doping of solid fullerene films with potassium were studied by sputter ion depth profiling
(XPS and SIMS). The potassium distribution was determined, and artifacts associated with possible damage of the layer composition
caused by ion impact were investigated and discussed. To compare the charge transfer while reductive doping is taking place
at fullerene/solution interface with doping from gas phase, model layers were prepared and doped by potassium under UHV conditions.
It was found that sputtering by Ar+ primary ions yields both accurate information on the alkaline metal distribution and on its concentration. Sputtering by
O+ ions led to an enrichment of potassium, apparently due to the reactivity of oxygen with the fullerene matrix. It is shown
that the reductive doping starts at the fullerene/solution interface. The concentration of potassium in the doped films was
found to be lower than expected from the charge transferred during the electrochemical reduction. Other phase transformations
such as hydrogenation are discussed.
Received March 4, 2002; accepted July 26, 2002 相似文献
122.
Jérôme Le NôtreAna Acosta Martinez Pierre H DixneufChristian Bruneau 《Tetrahedron》2003,59(47):9425-9432
Enyne rearrangement of silylated modified terpenoids has been used as the key step for the synthesis of new terpenes and terpenoids. The catalytic system generated in situ from [RuCl2(p-cymene]2, 1,3-bis(mesityl)imidazolinium chloride and cesium carbonate is able to perform the transformation of silylated 1,7-enynes into cyclic siloxanes. Selective cleavage of the silicon-carbon and silicon-oxygen bonds by simple reactions has been performed to afford new terpenes and terpenoids by formal addition of a C5 unit. 相似文献
123.
Aldehydes undergo smooth conjugate addition to α,β-unsaturated ketones in the presence of 5-(2-hydroxyethyl)-1,3-thiazolium halides and DBU adsorbed onto the surface of basic alumina under microwave irradiation and solvent-free conditions to afford 1,4-diketones in enhanced yields and reduced reaction times compared to conventional methods. 相似文献
124.
两相同部件温贮备可修的人机系统解的性质分析 总被引:5,自引:1,他引:4
郭卫华 《数学的实践与认识》2003,33(7):88-95
本文首先用强连续算子半群理论证明了两相同部件温贮备可修的人机系统动态非负解的存在唯一性 ,然后证明了 0是系统主算子的本征值 ,并得到 0本征值对应的本征向量是正的 ,从而系统存在稳态正解 . 相似文献
125.
A fully quantum mechanical approach to the calculation and normalization of the Franck–Condon factors for diatomic species is described. The treatment is based on the fundamental demand of completeness of the energy eigenfunctions, which results in the rigorous sum rule for the Franck–Condon overlap integrals. The importance of this general rule has been discussed and thoroughly illustrated in the case of diatomic xenon molecules. Exactly solvable reference potentials for this system have been constructed and a complete basis of the actual energy eigenstates (including both bound and scattering states) has been created. Several direct spectroscopic applications to xenon excimers are presented, and their good agreement with relevant experimental data demonstrated. In particular, a kinetic model is proposed to explain the observed oscillatory structures in the fluorescence spectra of Xe2* [Chem. Phys. Lett. 117 (1985) 301] related to their classical left turning points. The same model gives a uniform explanation to the well-known first and second emission continua of rare gases. 相似文献
126.
J. T. Hoeft M. Polcik D. I. Sayago M. Kittel R. Terborg R. L. Toomes J. Robinson D. P. Woodruff M. Pascal G. Nisbet C. L. A. Lamont 《Surface science》2003,540(2-3):441-456
The local adsorption geometry of CO adsorbed in different states on Ni(1 0 0) and on Ni(1 0 0) precovered with atomic hydrogen has been determined by C 1s (and O 1s) scanned-energy mode photoelectron diffraction, using the photoelectron binding energy changes to characterise the different states. The results confirm previous spectroscopic assignments of local atop and bridge sites both with and without coadsorbed hydrogen. The measured Ni–C bondlengths for the Ni(1 0 0)/CO states show an increase of 0.16 ± 0.04 Å in going from atop to bridge sites, while comparison with similar results for Ni(1 1 1)/CO for threefold coordinated adsorption sites show a further lengthening of the bond by 0.05 ± 0.04 Å. These changes in the Ni–CO chemisorption bondlength with bond order (for approximately constant adsorption energy) are consistent with the standard Pauling rules. However, comparison of CO adsorbed in the atop geometry with and without coadsorbed hydrogen shows that the coadsorption increases the Ni–C bondlength by only 0.06 ± 0.04 Å, despite the decrease in adsorption energy of a factor of 2 or more. This result is also reproduced by density functional theory slab calculations. The results of both the experiments and the density functional theory calculations show that CO adsorption onto the Ni(1 0 0)/H surface is accompanied by significant structural modification; the low desorption energy may then be attributed to the energy cost of this restructuring rather than weak local bonding. 相似文献
127.
François Ledrappier Mark Pollicott 《Bulletin of the Brazilian Mathematical Society》2005,36(2):143-176
In this paper we study the ergodic properties of the linear action of lattices Γ of SL(2,ℚp) on ℚp × ℚp and distribution results for orbits of Γ. Following Serre, one can define a “geodesic flow” for an associated tree (actually
associated to GL(2,ℚp)). The approach we use is based on an extension of this approach to “frame flows” which are a natural compact group extension
of the geodesic flow. 相似文献
128.
The content of residual monomers is one of the most important characteristics of polymer dispersions. As a result of the similar physicochemical parameters of ethyl acrylate and methyl methacrylate, it is very difficult to determine the residual monomers in acrylate dispersions obtained by emulsion polymerization of both monomers. Gas chromatography with capillary columns, however, permits separation of these monomers and their quantitative determination in acrylate dispersions. 相似文献
129.
130.