全文获取类型
收费全文 | 657802篇 |
免费 | 5634篇 |
国内免费 | 2179篇 |
专业分类
化学 | 313343篇 |
晶体学 | 9441篇 |
力学 | 33996篇 |
综合类 | 18篇 |
数学 | 109392篇 |
物理学 | 199425篇 |
出版年
2021年 | 4579篇 |
2020年 | 4858篇 |
2019年 | 5498篇 |
2018年 | 20865篇 |
2017年 | 21140篇 |
2016年 | 17858篇 |
2015年 | 7682篇 |
2014年 | 10520篇 |
2013年 | 25382篇 |
2012年 | 24639篇 |
2011年 | 38942篇 |
2010年 | 25377篇 |
2009年 | 25611篇 |
2008年 | 32653篇 |
2007年 | 36494篇 |
2006年 | 19356篇 |
2005年 | 23108篇 |
2004年 | 19674篇 |
2003年 | 18029篇 |
2002年 | 15550篇 |
2001年 | 16121篇 |
2000年 | 12433篇 |
1999年 | 9462篇 |
1998年 | 7956篇 |
1997年 | 7839篇 |
1996年 | 7581篇 |
1995年 | 6713篇 |
1994年 | 6507篇 |
1993年 | 6542篇 |
1992年 | 7020篇 |
1991年 | 7150篇 |
1990年 | 6824篇 |
1989年 | 6704篇 |
1988年 | 6522篇 |
1987年 | 6554篇 |
1986年 | 6233篇 |
1985年 | 8119篇 |
1984年 | 8290篇 |
1983年 | 6858篇 |
1982年 | 7244篇 |
1981年 | 6895篇 |
1980年 | 6768篇 |
1979年 | 7002篇 |
1978年 | 7278篇 |
1977年 | 6996篇 |
1976年 | 7174篇 |
1975年 | 6581篇 |
1974年 | 6663篇 |
1973年 | 6942篇 |
1972年 | 4659篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
G. S. Bisnovatyi-Kogan 《Physics of Particles and Nuclei》2006,37(5):647-676
It is now commonly accepted that cosmic γ-ray bursts (GRBs) are of cosmological origin. This conclusion is based on the statistical analysis of GRBs and the measurements of line redshifts in GRB optical afterglows, i.e., in the so-called long GRBs. In this review, the models of radiation and models of GRB sources are considered. In most of these models, if not in all of them, the isotropic radiation cannot provide the energy release necessary for the appearance of a cosmological GRB. No correlation is noted between the redshift, the GRB-spectrum shape, and the total detected energy. The comparison between data obtained in the Soviet experiment KONUS and the American experiment BATSE shows that they substantially differ in statistical properties and the detection of hard x-ray lines. The investigation of hard gamma (0.1–10 GeV) afterglows, the measurement of prompt optical spectra during the GRB detection, and the further investigation of hard x-ray lines is of obvious importance for gaining insight into the GRB origin. Observations of two bright optical GRB afterglows point to the fact that an initially bright optical flare is directly related to the GRB itself, and the subsequent weak and much more continuous optical radiation is of a different nature. The results of observations of optical GRB afterglows are discussed. They point to the fact that the GRBs originate in distant galaxies with a high matter density, where intense star formation takes place. The interaction of the cosmological GRB radiation with a dense surrounding molecular cloud results in the appearance of long-duration (up to 10 years) weak optical afterglows associated with the heating and reradiation of gas. Results of 2D numerical simulation of the heating and reradiation of gas in various variants of the relative disposition of GRB and molecular clouds are presented. In conclusion, the possible relation between the so-called short GRBs and recurrent sources of soft γ rays in our Galaxy, the so-called “soft gamma repeaters,” is discussed. 相似文献
992.
G. S. Patrin V. V. Beletskiĭ D. A. Velikanov O. A. Bayukov V. V. Vershinin O. V. Zakieva T. N. Isaeva 《Physics of the Solid State》2006,48(4):700-704
The results of experimental and theoretical studies of the low-temperature properties of FeSi crystals are presented. The specific features of the magnetic susceptibility are shown to be related to the superparamagnetic behavior of impurity clusters. The thermomagnetic hysteresis phenomena observed are explained using the model of exchange-coupled clusters. 相似文献
993.
The proton magnetic resonance spectra of water molecules diffusing over regular sites in natrolite are numerically simulated. Experimental data and the results of simulation are found to be in good agreement in a wide temperature interval including the transition range, where the magnetic resonance spectrum is a superposition of a wide unaveraged spectrum and a spectrum averaged by the motion of molecules. The simulation uses generators of pseudorandom-number Markovian sequences. For a binary Markovian process, it is shown, in particular, that the time within which a physical quantity remains constant is described by an exponentially distributed random number. 相似文献
994.
Within the framework of fractal analysis and percolation theory, an alternative model of reinforcement of filled polymers
is offered. Practically, this model can be used only to describe the reinforcement of nanocomposites, because, according to
the treatment considered, a pronounced reinforcement can be reached only at ratios of filler particle diameter to the statistical
segment length of about 10 and less. A theoretical calculation showed a good qualitative and quantitative agreement with experiments.
The type of reinforcement mechanism of composites is determined by the type of the space (fractal or Euclidean) in which the
structure of the polymeric matrix is formed.
__________
Translated from Mekhanika Kompozitnykh Materialov, Vol. 42, No. 6, pp. 797–802, November–Decem ber, 2006. 相似文献
995.
High temperature GaN layers have been grown on Si (1 1 1) substrate by metalorganic vapor phase epitaxy (MOVPE). AlN was used as a buffer layer and studied as a function of thickness and growth temperature. The growth was monitored by in situ laser reflectometry. High resolution X-ray diffraction (HRXRD) revealed that optimized monocrystalline GaN was obtained for a 40 nm AlN grown at 1080 °C. This is in good agreement with the results of morphological study by scanning electron microscopy (SEM) and also confirmed by atomic force microscopy (AFM) observations. The best morphology of AlN with columnar structure and lower rms surface roughness is greatly advantageous to the coalescence of the GaN epilayer. Symmetric and asymmetric GaN reflections were combined for twist and stress measurements in monocrystalline GaN. It was found that mosaicity and biaxial tensile stress are still high in 1.7 μm GaN. Curvature radius measurement was also done and correlated to the cracks observations over the GaN surface. 相似文献
996.
997.
998.
A theory that predicts the effect of the counterion size on the swelling and collapse of a weakly charged polyelectrolyte gel was developed. In addition to excluded-volume interactions between monomer units of the gel, the theory involves the counterion-monomer unit and counterion-counterion interactions in terms of the virial approximation. The character of interactions between different units in the system varies from repulsion to attraction depending on the type of solvent, counterion, and dielectric permittivity of the solvent. For solvents with a low permittivity, the effect of condensation of counterions resulting in the formation of ion pairs is taken into account. 相似文献
999.
B. D. Kabulov K. A. Akhundzhanov F. U. Yunusov O. A. Shpigun S. S. Negmatov 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2007,81(3):354-356
The hydrolytic polycondensation of tetraethoxysilane in the presence of various polymers (polyacrylonitrile, polycaproamide, and chitosan) as templates was performed with the use of the sol-gel technology to obtain nanohybrid composite polymer-silica sorbents-nanofractals. 相似文献
1000.
E. Baggio Saitovitch F. J. Litterst I. Souza Azevedo R. B. Scorzelli 《Hyperfine Interactions》1989,50(1-4):529-535
The Mössbauer spectra of YBa2(Cu1?x Fe x )3O7 at room temperature show several doublets attributed to Fe in Cu(1) sites with different oxygen configurations. Here we present a systematic study performed at 4.2 K forx=0.005, 0.01, 0.03, 0.05, 0.10, 0.15. To obtain information about the magnetic ordered state two samples, withx=0.005 andx=0.15, have been studied at 4.2 K underB ext=5 T. The Mössbauer spectra indicate that the iron moments are polarized forx=0.005, while in the ordered state (x=0.15) they have an antiferromagnetic or spin-glass-like arrangement with high anisotropy. 相似文献