全文获取类型
收费全文 | 60808篇 |
免费 | 859篇 |
国内免费 | 296篇 |
专业分类
化学 | 28383篇 |
晶体学 | 1050篇 |
力学 | 3251篇 |
综合类 | 8篇 |
数学 | 4834篇 |
物理学 | 24437篇 |
出版年
2022年 | 552篇 |
2021年 | 517篇 |
2020年 | 471篇 |
2019年 | 463篇 |
2018年 | 614篇 |
2017年 | 546篇 |
2016年 | 961篇 |
2015年 | 662篇 |
2014年 | 1035篇 |
2013年 | 2577篇 |
2012年 | 2398篇 |
2011年 | 3098篇 |
2010年 | 2201篇 |
2009年 | 2244篇 |
2008年 | 2831篇 |
2007年 | 2659篇 |
2006年 | 2511篇 |
2005年 | 2234篇 |
2004年 | 2034篇 |
2003年 | 1798篇 |
2002年 | 1700篇 |
2001年 | 3047篇 |
2000年 | 2187篇 |
1999年 | 1592篇 |
1998年 | 1100篇 |
1997年 | 1084篇 |
1996年 | 906篇 |
1995年 | 802篇 |
1994年 | 729篇 |
1993年 | 642篇 |
1992年 | 982篇 |
1991年 | 967篇 |
1990年 | 875篇 |
1989年 | 769篇 |
1988年 | 754篇 |
1987年 | 824篇 |
1986年 | 675篇 |
1985年 | 899篇 |
1984年 | 845篇 |
1983年 | 588篇 |
1982年 | 584篇 |
1981年 | 547篇 |
1980年 | 517篇 |
1979年 | 638篇 |
1978年 | 686篇 |
1977年 | 681篇 |
1976年 | 593篇 |
1975年 | 505篇 |
1974年 | 547篇 |
1973年 | 471篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
X-ray diffraction patterns of nanocrystalline Fe-Cu-Nb-Si-B (FINEMET) alloys reveal that bcc α-Fe/α-FeSi crystallites with
the average grain size of 20(5) nm are dispersed in amorphous matrix. Enhanced electron—electron interaction (EEI) and quantum
interference (QI) effects as well as electron-magnon (and/or electron-spin fluctuation) scattering turn out to be the main
mechanisms that govern the temperature dependence of resistivity. Of all the inelastic scattering processes, inelastic electron-phonon
scattering is the most effective mechanism to destroy phase coherence of electron wave functions. The diffusion constant,
density of states at the Fermi level and the inelastic scattering time have been estimated, for the first time, for the alloys
in question
Article presented at the International Symposium on Advances in Superconductivity and Magnetism: Materials, Mechanisms and
Devices, ASMM2D-2001, 25–28 September 2001, Mangalore, India. 相似文献
62.
A series of low density polyethylene systems has been studied with respect to structural evolution and short-term dielectric breakdown behaviour. All materials were based upon a single polymer, that is commonly used in high voltage applications, but with different additives. In all three of these systems, multiple melting transitions were observed, as a result of molecular fractionation effects during crystallization. In the virgin polymer, a space-filling banded spherulitic morphology was found to develop at low temperatures (102 °C and below) whereas, at higher temperatures, only a few isolated axialites were observed. Inclusion of the antioxidant resulted in greatly increased nucleation densities, such that, at low temperatures, no evidence of spherulitic organisation remained. At higher temperatures, sheaf-like lamellar aggregates developed, which were much smaller and much more numerous than in the case of the virgin polymer. Further addition of dicumyl peroxide (DCP) resulted in the rapid formation of a crosslinked network at 200 °C. Some crosslinking also occurred at 150 °C, but over a much longer timescale. Where extensive crosslinking occurred prior to crystallization, the resulting gel inhibited structural development, such that only a few small, isolated sheaves were able to form at 102 °C. In view of the principal application area of this material, the breakdown strength of each of the above systems was then measured and the whole data set was analysed statistically. When structural factors were considered alongside the statistics, no clear trends emerged to indicate that either the compositional or morphological variations were reflected in the short-term electrical failure processes. 相似文献
63.
The crystal structure, magnetic and magnetotransport properties of the variation of B′-site transition metal in Sr2FeMO6 (M=Mo, W) with double perovskites structure have been investigated systematically. Measurements of magnetization vs. temperature at H=5 T show that Sr2FeMoO6 is a ferromagnet and Sr2FeWO6 is an antiferromagnet with TN∼35 K. Additionally, the large magnetoresistance ratio (MR) of ∼22% (H=3 T) at room temperature (RT) was observed in the Sr2FeWO6 compound. However, the Sr2FeMoO6 compound did not show any significant MR even at high fields and RT (MR∼1%; H=3 T and 300 K). The implications of these findings are supported by band structure calculations to explain the interaction between the 4d(Mo) and 5d(W) orbitals of transition metal ions and oxygen ions. 相似文献
64.
X Y Liu C J Li 《Science in China. Series B, Chemistry, life sciences & earth sciences》1989,32(10):1215-1223
To further evaluate the causality between endogenous pyrogen (EP)-induced fever and cyclic adenosine-3',5'-monophosphate (cyclic AMP) level, the effects of sodium salicylate (SS) on the febrile response and increased levels of cyclic AMP in both cerebrospinal fluid (c.s.f.) and plasma during EP-induced fever in rabbits were observed. The results suggest that cyclic AMP is probably involved in the central mediation of EP-induced fever and that increased concentration of cyclic AMP in c.s.f. associated with EP-induced fever is not the result of temperature elevation but appears to be caused by the increased synthesis in the central nervous system. In addition it is confirmed that blood is impossibly a contributory source of increased cyclic AMP in c.s.f. during EP fever, and that SS may act subsequent to the increase in cyclic AMP. 相似文献
65.
Comprehensive studies of X-ray diffraction, oxygen content, superconductivity and Mössbauer effect have been made on FexCu1−xBa2YCu2O7+y superconductors (0.00≤x≤0.70) synthesized by ambient (AM) and high pressure (HP). Results indicate that all the HP-samples have tetragonal structure, smaller lattice parameter c and unit-cell volume than the AM-samples. The studies of oxygen content, and Mössbauer spectroscopy indicate that the HP-samples have higher oxygen content, carrier concentration and average valence of Fe than the AM-samples. Moreover, for the HP-samples more Fe atoms located in CuOx chains have fivefold-oxygen coordination. These are important reasons for the enhancement of Tc in the HP-samples. 相似文献
66.
67.
Y.B. Melnichenko G.D. Wignall D.R. Cole H. Frielinghaus L.A. Bulavin 《Journal of Molecular Liquids》2005,120(1-3):7-9
Small angle neutron scattering (SANS) is a well-established technique for investigating the behavior of confined binary liquid solutions, as it can probe the correlation length and susceptibility in pores on length scales 1 – 100 nm. We applied SANS to explore the influence of confinement on critical behavior of an individual fluid carbon dioxide (CO2) in a highly porous aerogel. The results demonstrate that quenched disorder induced by aerogel significantly depresses density fluctuations. Despite the negligible volume occupied by aerogel (< 4%), the macroscopic phase separation of confined CO2 into coexisting liquid and gaseous phases is suppressed and below the critical temperature of the bulk fluid frozen methastable microdomains are formed. Experimental data show that critical adsorption is as important as the effect of confinement in defining the behavior of confined fluids. 相似文献
68.
Applied Magnetic Resonance - We examined by electron spin resonance (ESR) spectroscopy the thermal decay of radicals as induced by γ-irradiation on pepper. Upon irradiation, the satellite... 相似文献
69.
Selective reflection of a laser wave from a resonance gas is considered for arbitrary intensity, polarization, and angle of incidence on the interface. Variations of the reflection spectra nonlinear in the wave amplitude are studied taking into account the nonlinear increment of the optical phase upon reflection. The result of this increment is a quadrature component of the reflected wave shifted by a quarter period, which may be observed using the homodyning technique (optical mixing). The regularities studied are of interest both for spectroscopy and for nonlinear transformations in the quantum statistics of reflected light. 相似文献
70.