全文获取类型
收费全文 | 386715篇 |
免费 | 3476篇 |
国内免费 | 1026篇 |
专业分类
化学 | 194815篇 |
晶体学 | 6182篇 |
力学 | 18331篇 |
综合类 | 8篇 |
数学 | 45428篇 |
物理学 | 126453篇 |
出版年
2021年 | 3678篇 |
2020年 | 3912篇 |
2019年 | 4466篇 |
2018年 | 6215篇 |
2017年 | 6484篇 |
2016年 | 8736篇 |
2015年 | 4836篇 |
2014年 | 8199篇 |
2013年 | 18267篇 |
2012年 | 14400篇 |
2011年 | 17107篇 |
2010年 | 12828篇 |
2009年 | 12831篇 |
2008年 | 15388篇 |
2007年 | 15223篇 |
2006年 | 14090篇 |
2005年 | 12234篇 |
2004年 | 11411篇 |
2003年 | 10198篇 |
2002年 | 10226篇 |
2001年 | 12002篇 |
2000年 | 8862篇 |
1999年 | 6920篇 |
1998年 | 5817篇 |
1997年 | 5613篇 |
1996年 | 5154篇 |
1995年 | 4496篇 |
1994年 | 4444篇 |
1993年 | 4340篇 |
1992年 | 4743篇 |
1991年 | 5016篇 |
1990年 | 4742篇 |
1989年 | 4689篇 |
1988年 | 4378篇 |
1987年 | 4470篇 |
1986年 | 4237篇 |
1985年 | 5275篇 |
1984年 | 5435篇 |
1983年 | 4507篇 |
1982年 | 4645篇 |
1981年 | 4286篇 |
1980年 | 4200篇 |
1979年 | 4476篇 |
1978年 | 4624篇 |
1977年 | 4628篇 |
1976年 | 4489篇 |
1975年 | 4286篇 |
1974年 | 4247篇 |
1973年 | 4257篇 |
1972年 | 3069篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
A. Peláiz-Barranco O. García-Zaldívar F. Calderón-Piñar 《Solid State Communications》2005,133(8):515-519
The Ac behaviour of PLZT 6/80/20 ferroelectric ceramics was analyzed around and above the phase transition. Two relaxation processes are identified, showing that the so-called ‘universal relaxation law’ holds for the ceramics. A critical point in the values of the Ac conductivity, around the temperature corresponding to the maximum of the dielectric losses, is observed below the transition temperature due to the relaxor behaviour. The frequency dependence of the Ac conductivity at various temperatures and the hysteresis loops show classical relaxor behaviour with a diffuse phase transition. 相似文献
142.
143.
Morey Timothy E. Varshney Manoj Flint Jason A. Seubert Christoph N. Smith W. Brit Bjoraker David G. Shah Dinesh O. Dennis Donn M. 《Journal of nanoparticle research》2004,6(2):159-170
Background: Although microemulsion-based nanoparticles (MEs) may be useful for drug delivery or scavenging, these benefits must be balanced against potential nanotoxicological effects in biological tissue (bio-nano interface). We investigated the actions of assembled MEs and their individual components at the bio-nano interface of thrombosis and hemolysis in human blood.
Methods: Oil-in-water MEs were synthesized using ethylbutyrate, sodium caprylate, and pluronic F-68 (ME4) or F-127 (ME6) in 0.9% NaClw/v. The effects of MEs or components on thrombosis were determined using thrombo-elastography, platelet contractile force, clot elastic modulus, and platelet counting. For hemolysis, ME or components were incubated with erythrocytes, centrifuged, and washed for measurement of free hemoglobin by spectroscopy.
Results and conclusions: The mean particle diameters (polydispersity index) for ME6 and ME4 were 23.6 ± 2.5 nm (0.362) and 14.0 ± 1.0 nm (0.008), respectively. MEs (0, 0.03, 0.3, 3 mM) markedly reduced the thromboelastograph maximal amplitude in a concentration-dependent manner (49.0 ± 4.2, 39.0 ± 5.6, 15.0 ± 8.7, 3.8 ± 1.3 mm, respectively), an effect highly correlated (r2 = 0.94) with similar changes caused by pluronic surfactants (48.7 ± 10.9, 30.7 ± 15.8, 20.0 ± 11.3, 2.0 ± 0.5) alone. Neither oil nor sodium caprylate alone affected the thromboelastograph. The clot contractile force was reduced by ME (27.3 ± 11.1–6.7 ± 3.4 kdynes/cm2, P = 0.02, n = 5) whereas the platelet population not affected (175 ± 28–182 ± 23 106/ml, P = 0.12, n = 6). This data suggests that MEs reduced platelet activity due to associated pluronic surfactants, but caused minimal changes in protein function necessary for coagulation. Although pharmacological concentrations of sodium caprylate caused hemolysis (EC50 = 213 mM), MEs and pluronic surfactants did not disrupt erythrocytes. Knowledge of nanoparticle activity and potential associated nanotoxicity at this bio-nano interface enables rational ME design for in vivo applications. 相似文献
144.
V. S. Berezinsky 《Physics of Atomic Nuclei》2003,66(3):423-434
About 400 years have passed since the great discoveries by Galileo, Kepler, and Newton, but astronomy still remains an important source of discoveries in physics. They start with puzzles, with phenomena difficult to explain, and phenomena which in fact need new physics for explanation. Do such puzzles exist now? There are at least three candidates: absence of absorption of TeV gamma radiation in extragalactic space (violation of Lorentz invariance?), absence of GZK cutoff in the spectrum of ultrahigh-energy cosmic rays (new particle physics?), tremendous energy (up to 1054 erg) released in gamma ray bursts on a time scale of a second (collapsing stars or sources of a new type?). Do these puzzles really exist? A critical review of these phenomena is given. 相似文献
145.
146.
147.
In this paper, we obtain a nonlinear Poisson structure and two first integrals in the problem of the plane motion of a circular cylinder and n point vortices in an ideal fluid. This problem is a priori not Hamiltonian; specifically, in the case n= 1 (i.e., in the problem of the interaction of a cylinder with a vortex) it is integrable. 相似文献
148.
We present all-atom molecular dynamics simulations ofn-hexane on the basal plane of graphite at monolayer and multilayer coverages. In keeping with experimental data, we find the
presence of ordered adsorbed layers both at single monolayer coverage and when the adsorbed layer coexists with excess liquid
adsorbate. Using a simulation method that does not impose any particular periodicity on the adsorbed layer, we quantitatively
compare our results to the results of neutron diffraction experiments and find a structural transition from a uniaxially incommensurate
lattice to a fully commensurate structure on increasing the coverage from a monolayer to a multilayer. The zig-zag backbone
planes of all the alkane molecules lie parallel to the graphite surface at the multilayer coverage, while a few molecules
are observed to attain the perpendicular orientation at monolayer coverage.
Dedicated to Professor C N R Rao on his 70th birthday 相似文献
149.
Yu. A. Kumzerov L. S. Parfen’eva I. A. Smirnov H. Misiorek J. Mucha A. Jezowski 《Physics of the Solid State》2003,45(1):57-60
The thermal conductivity of crystalline chrysotile asbestos made up of hollow tubular Mg3Si2O5(OH)4 filaments is measured in the range 5–300 K. The paper discusses the possibility of using this material in studies of the thermal conductivity of thin filaments of metals and semiconductors incorporated into the channels of crystalline chrysotile asbestos tubes. 相似文献
150.
We provide a rigorous derivation of an asymptotic formula for perturbations in the eigenvalues caused by the presence of a finite number of inhomogeneities of small diameter with conductivity different from the background conductivity. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献