全文获取类型
收费全文 | 400818篇 |
免费 | 2913篇 |
国内免费 | 1265篇 |
专业分类
化学 | 181858篇 |
晶体学 | 5490篇 |
力学 | 21671篇 |
综合类 | 7篇 |
数学 | 76975篇 |
物理学 | 118995篇 |
出版年
2020年 | 1930篇 |
2019年 | 2227篇 |
2018年 | 18978篇 |
2017年 | 19473篇 |
2016年 | 12578篇 |
2015年 | 4259篇 |
2014年 | 4497篇 |
2013年 | 11947篇 |
2012年 | 15238篇 |
2011年 | 29879篇 |
2010年 | 17851篇 |
2009年 | 18218篇 |
2008年 | 24280篇 |
2007年 | 29192篇 |
2006年 | 9015篇 |
2005年 | 15745篇 |
2004年 | 11756篇 |
2003年 | 11226篇 |
2002年 | 8460篇 |
2001年 | 7655篇 |
2000年 | 5975篇 |
1999年 | 4427篇 |
1998年 | 3796篇 |
1997年 | 3749篇 |
1996年 | 3633篇 |
1995年 | 3355篇 |
1994年 | 3136篇 |
1993年 | 3199篇 |
1992年 | 3449篇 |
1991年 | 3478篇 |
1990年 | 3271篇 |
1989年 | 3236篇 |
1988年 | 3307篇 |
1987年 | 3164篇 |
1986年 | 3059篇 |
1985年 | 4120篇 |
1984年 | 4293篇 |
1983年 | 3534篇 |
1982年 | 3880篇 |
1981年 | 3772篇 |
1980年 | 3649篇 |
1979年 | 3696篇 |
1978年 | 3926篇 |
1977年 | 3655篇 |
1976年 | 3886篇 |
1975年 | 3457篇 |
1974年 | 3569篇 |
1973年 | 3918篇 |
1972年 | 2382篇 |
1971年 | 1817篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
J. S. Chiou J. W. Barlow D. R. Paul 《Journal of Polymer Science.Polymer Physics》1987,25(7):1459-1471
The miscibility of bisphenol-A polycarbonate (PC) with poly(methyl methacrylate) (PMMA) has been reexamined using differential scanning calorimetry (DSC) and optical indications for phase separation on heating, i.e., lower critical solution temperature (LCST) behavior. Various methods have been used to prepare the blends including methylene chloride (CH2Cl2) and tetrahydrofuran (THF) solution casting, melt mixing, and precipitation of PC and PMMA simultaneously from THF solution by using the nonsolvents methanol and heptane. It is shown that the resulting phase behavior for PC/PMMA blends is strongly affected by the blend preparation method. However, these blends are miscible over the whole blend composition range (unambiguous single composition-dependent Tg's and LCST behavior) when prepared by precipitation from solution using heptane as the nonsolvent. To the contrary, solution-cast and melt-mixed PC/PMMA blends were all phase separated, which may be attributed to the “solvent” effect and LCST behavior, respectively, not discovered in previous reports. Methanol precipitation does not lead to fully mixed blends, which demonstrates the importance of the choice of nonsolvent when using the precipitation method. 相似文献
92.
93.
Using elementary graded automorphisms of polytopal algebras (essentially the coordinate rings of projective toric varieties)
polyhedral versions of the group of elementary matrices and the Steinberg and Milnor groups are defined. They coincide with
the usual K-theoretic groups in the special case when the polytope is a unit simplex and can be thought of as compact/polytopal substitutes
for the tame automorphism groups of polynomial algebras. Relative to the classical case, many new aspects have to be taken
into account. We describe these groups explicitly when the underlying polytope is 2-dimensional. Already this low-dimensional
case provides interesting classes of groups.
Received: 13 December 2001 / Revised version: 24 June 2002
The second author was supported by the Deutsche Forschungsgemeinschaft, INTAS grant 99-00817 and TMR grant ERB FMRX CT-97-0107
Mathematics Subject Classification (2000): 14L27, 14M25, 19C09, 52B20 相似文献
94.
王巨平 《中国科学A辑(英文版)》2002,45(7):827-835
This paper verifies the singularity conjecture for Jacobi forms with higher degree in some typical cases, and gives constructions
for the Jacobi cusp forms whose Fourier coefficients can be expressed by some kind of Rankin-typeL-series. 相似文献
95.
A.R. DegheidyM.T. Attia M. Sallah 《Journal of Quantitative Spectroscopy & Radiative Transfer》2002,74(3):285-297
The time-independent radiative transfer problem in a scattering and absorbing planar random medium with general boundary conditions and internal energy source is considered. The medium is assumed to consist of two randomly mixed immiscible fluids, with the mixing statistics described as a two-state homogeneous Markov process. The problem is solved in terms of the solution of the corresponding free-source problem with simple boundary conditions which is solved using Pomraning-Eddington approximation in the deterministic case. A formalism, developed to treat radiative transfer in statistical mixtures, is used to obtain the ensemble-averaged solution. The average partial heat fluxes are calculated in terms of the albedoes of the source-free problem. Results are obtained for isotropic and anisotropic scattering for specular and diffused reflecting boundaries. 相似文献
96.
The method described in this paper allows an investigator to determine the intrinsic stress of a polymer layer in a way that
does not result in damage to devices or test structures. The method requires that a small area of the polymer be released
from the substrate to form a diaphragm. The diaphragm is stimulated with acoustic white noise and the diaphragm movement is
monitored with a laser vibrometer. The first few resonance frequencies of the diaphragm are obtained using a laser vibrometer
and then those frequencies are used to calculate the membrane intrinsic bi-axial tension. 相似文献
97.
It is explicitly shown that if phase transition occurs at the core of a newborn neutron star with moderately strong magnetic
field strength, which populates only the electron’s Landau levels, then in the β -equilibrium condition, the quark core is
energetically much more unstable than the neutron matter of identical physical condition. 相似文献
98.
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
99.
Mutual–temporal coherence of the supercontinuum (SC) generation has been experimentally investigated using a diffraction grating based interferometer. A broadband SC generation was produced in a pyrex glass plate with a 1.6-μm coherence length at 550-nm center wavelength. The degree of mutual coherence of 0.34 was measured for a wavefront shift for zero and first diffraction orders of half of the beam diameter. A design of SC source with the capability of manipulating the amplitudes and phases of optical frequency components within the SC pulse is presented for coherence applications. 相似文献
100.