全文获取类型
收费全文 | 338462篇 |
免费 | 1995篇 |
国内免费 | 550篇 |
专业分类
化学 | 157225篇 |
晶体学 | 4648篇 |
力学 | 19208篇 |
综合类 | 11篇 |
数学 | 50911篇 |
物理学 | 109004篇 |
出版年
2021年 | 2545篇 |
2020年 | 2676篇 |
2019年 | 3276篇 |
2018年 | 11513篇 |
2017年 | 12107篇 |
2016年 | 9520篇 |
2015年 | 3687篇 |
2014年 | 5613篇 |
2013年 | 11153篇 |
2012年 | 12498篇 |
2011年 | 20595篇 |
2010年 | 13941篇 |
2009年 | 14319篇 |
2008年 | 18496篇 |
2007年 | 21321篇 |
2006年 | 8919篇 |
2005年 | 12725篇 |
2004年 | 9881篇 |
2003年 | 9602篇 |
2002年 | 7951篇 |
2001年 | 7416篇 |
2000年 | 5697篇 |
1999年 | 4153篇 |
1998年 | 3646篇 |
1997年 | 3591篇 |
1996年 | 3431篇 |
1995年 | 2962篇 |
1994年 | 3024篇 |
1993年 | 2951篇 |
1992年 | 3251篇 |
1991年 | 3373篇 |
1990年 | 3199篇 |
1989年 | 3321篇 |
1988年 | 3185篇 |
1987年 | 3143篇 |
1986年 | 2991篇 |
1985年 | 3732篇 |
1984年 | 3919篇 |
1983年 | 3276篇 |
1982年 | 3291篇 |
1981年 | 3173篇 |
1980年 | 2940篇 |
1979年 | 3363篇 |
1978年 | 3484篇 |
1977年 | 3585篇 |
1976年 | 3516篇 |
1975年 | 3259篇 |
1974年 | 3241篇 |
1973年 | 3369篇 |
1972年 | 2527篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
A. D. Zorina L. V. Balykina O. V. Nazarova A. A. Rebezov 《Russian Journal of Applied Chemistry》2006,79(4):654-659
Polymeric derivatives of dammarane triterpenoids with both labile and strong (covalent) polymer-triterpenoid bonds were prepared from N-vinylpyrrolidone copolymers. 相似文献
992.
993.
We fabricated high-quality InAlN/GaN heterostructures by metal–organic vapor phase epitaxy (MOVPE). X-ray diffraction measurements revealed that InAlN/GaN heterostructures grown under optimal conditions have flat surfaces and abrupt heterointerfaces. Electron mobility from 1200 to 2000 cm2/V s was obtained at room temperature. To our knowledge, this mobility is the highest ever reported for InAlN/GaN heterostructures. We also investigated the relationship between the Al composition and sheet electron density (Ns) for the first time. Ns increased from 1.0×1012 to 2.7×1013 cm−2 when the Al composition increased from 0.78 to 0.89. 相似文献
994.
G.J. Babonas A. Reza I. Simkiene M. Baran U.O. Karlsson 《Applied Surface Science》2006,252(15):5391-5394
Optical properties of Fe-doped silica films on Si were investigated by ellipsometric technique in the region 1-5 eV. Samples were produced by sol-gel method. Precursors were prepared by mixing tetraethoxysilane (TEOS) solution in ethanol and water with aqueous solution of Fe-chloride or Fe-acetate. The coating solution was deposited on Si substrates by spin on technique. The size of Fe-containing nanometric-sized particles depended on technology and varied from 20 to 100 nm. Optical response of complex hybrid samples SiO2:Fe/Si was interpreted in a multi-layer model. In the inverse problem, the Maxwell equations were solved by transfer matrix technique. Dielectric function of Fe-doped silica layers was calculated in the model of effective media. Analysis of optical data has shown that various Fe-oxides formed. Experimental data for films obtained from precursors with Fe-acetate and annealed in hydrogen were well described by the model calculations taking into account a small contribution 1-5% of metal Fe imbedded in silica. The Fe/Fe-O contribution to optical response increased for samples grown from FeCl3-precursor. Ellipsometric data for Fe-doped silica films on Si were interpreted taking into account the structural AFM studies as well as the results of magnetic measurements. 相似文献
995.
N. Raju T. Špaček J. Ježek I. M. Caminiti F. Leinisch K. Hideg P. Ježek W. E. Trommer 《Applied magnetic resonance》2006,30(3-4):373-383
Electron paramagnetic resonance (EPR) spectroscopy of spin-labeled fatty acids was used to investigate their interaction withEscherichia coli-expressed human mitochondrial uncoupling protein UCP2 refolded from inclusion bodies in nonaethylene glycol monododecyl ether (C12E9) micelles. 5-DOXYL-stearic acid and 4-PROXYL-palmitic acid bound to UCP2 exhibited additional clearly separated h+1I, h?1I “immobile” peaks in the low- and high-field region, respectively, separated by 42 and 44 Gauss, and extensively reduced h+1M, h?1M “mobile” peaks, separated by about 30 G, whereas with 7-DOXYL-stearic acid the I and M peaks were smoothed together into one wide peak. Competition of 4-PROXYL-palmitic acid with added palmitic acid, arachidonic acid, and all-cis-8,11,14-eicosatrienoic acid and of 7-DOXYL-stearic acid with arachidonic acid was indicated by the disappearance of the h+1I, h?1I “immobile” peaks, whereas redistribution in micelles without protein was indicated by the rising of the h+1M, h?1M “mobile” peaks. In conclusion, a competition of palmitic, arachidonic, and eicosatrienoic acid within a putative fatty acid binding site was observed for mitochondrial uncoupling protein UCP2. This finding together with the observation of EPR spectra of highly immobilized probes exclusively in the presence of the recombinant UCP2 suggest the existence of a fatty acid binding site on UCP2 which is a prerequisite of the fatty acid cycling mechanism as previously postulated for UCP1. 相似文献
996.
Consider the problem of rolling a dynamically asymmetric balanced ball (the Chaplygin ball) over a sphere. Suppose that the
contact point has zero velocity and the projection of the angular velocity to the normal vector of the sphere equals zero.
This model of rolling differs from the classical one. It can be realized, in some approximation, if the ball is rubber coated
and the sphere is absolutely rough. Recently, J. Koiller and K. Ehlers pointed out the measure and the Hamiltonian structure
for this problem. Using this structure we construct an isomorphism between this problem and the problem of the motion of a
point on a sphere in some potential field. The integrable cases are found.
相似文献
997.
A. L. Ivanovskii 《Theoretical and Experimental Chemistry》2007,43(1):1-27
The present state of research on the production and modeling of nanostructures based on titanium carbide-a typical representative
of an extensive class of carbides of d-and f-metals-is reviewed. Methods for the synthesis of various Ti-C nanostructures
(molecular clusters, nanocrystallites, nanospheres, nanofibers, nanowires) are examined, and their morphology, atomic structure,
and known physicochemical characteristics are described. Theoretical models of the atomic structure and properties of new
types of nanostructures in the titanium-carbon system (endo-and exohedral titanofullerenes, “hybrid” structures based on carbon
nanotubes, the so-called peapods, nanocables, and a number of others) and the prospects for their application as components
of nanoceramics, hydrogen accumulators, materials for spintronics, etc. are discussed.
__________
Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 43, No. 1, pp. 1–23, January–February, 2007. 相似文献
998.
O. Yu. Dashkova 《Algebra and Logic》2007,46(5):297-302
We are concerned with infinite-dimensional locally soluble linear groups of infinite central dimension that are not soluble
A3-groups and all of whose proper subgroups, which are not soluble A3-groups, have finite central dimension. The structure of groups in this class is described. The case of infinite-dimensional
locally nilpotent linear groups satisfying the specified conditions is treated separately. A similar problem is solved for
infinite-dimensional locally soluble linear groups of infinite fundamental dimension that are not soluble A3-groups and all of whose proper subgroups, which are not soluble A3-groups, have finite fundamental dimension.
__________
Translated from Algebra i Logika, Vol. 46, No. 5, pp. 548–559, September–October, 2007. 相似文献
999.
We investigate the existence and stability of solutions for higher-order two-point boundary value problems in case the differential
operator is not necessarily positive definite, i.e. with superlinear nonlinearities. We write an abstract realization of the
Dirichlet problem and provide abstract existence and stability results which are further applied to concrete problems. 相似文献
1000.
We study problems of interpolation of positive linear operators in couples of ordered Banach spaces. From this viewpoint, we study couples of noncommutative spaces L 1, L ∞ associated with weights and traces on von Neumann algebras. 相似文献