全文获取类型
收费全文 | 403024篇 |
免费 | 20031篇 |
国内免费 | 11136篇 |
专业分类
化学 | 206450篇 |
晶体学 | 5808篇 |
力学 | 23423篇 |
综合类 | 534篇 |
数学 | 67323篇 |
物理学 | 130653篇 |
出版年
2022年 | 4006篇 |
2021年 | 5176篇 |
2020年 | 5933篇 |
2019年 | 6053篇 |
2018年 | 15295篇 |
2017年 | 14836篇 |
2016年 | 14275篇 |
2015年 | 7790篇 |
2014年 | 9948篇 |
2013年 | 17775篇 |
2012年 | 19944篇 |
2011年 | 28351篇 |
2010年 | 18016篇 |
2009年 | 18124篇 |
2008年 | 21048篇 |
2007年 | 22525篇 |
2006年 | 13728篇 |
2005年 | 13092篇 |
2004年 | 11541篇 |
2003年 | 10488篇 |
2002年 | 9308篇 |
2001年 | 9146篇 |
2000年 | 7316篇 |
1999年 | 6372篇 |
1998年 | 5525篇 |
1997年 | 5268篇 |
1996年 | 5343篇 |
1995年 | 4600篇 |
1994年 | 4454篇 |
1993年 | 4251篇 |
1992年 | 4236篇 |
1991年 | 4359篇 |
1990年 | 3898篇 |
1989年 | 3627篇 |
1988年 | 3570篇 |
1987年 | 3380篇 |
1986年 | 3221篇 |
1985年 | 4158篇 |
1984年 | 4281篇 |
1983年 | 3378篇 |
1982年 | 3583篇 |
1981年 | 3478篇 |
1980年 | 3344篇 |
1979年 | 3415篇 |
1978年 | 3483篇 |
1977年 | 3396篇 |
1976年 | 3493篇 |
1975年 | 3184篇 |
1974年 | 3201篇 |
1973年 | 3247篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
991.
P. C. Morais A. C. Oliveira V. K. Garg M. L. Silva E. F. C. Alcântara F. Q. Soares D. Rabelo 《Hyperfine Interactions》2007,177(1-3):51-56
We have used time-differential perturbed angular correlation (PAC) spectroscopy with 181Ta-probes to study the electric field gradient at Zr-sites in synthetic zircon and hafnon between room temperature and 1,200°C. PAC spectra are similar to those obtained from naturally occurring zircons. In particular, a change in slope of the quadrupole coupling vs. temperature is observed in the synthetic zircon at the same temperature as seen in natural zircons from the Mud Tank carbonatite (Australia). The synthetic hafnon data also shows this feature but at somewhat higher temperature. Low-temperature PAC spectra of both synthetic zircon and hafnon have a clearly reduced anisotropy. We believe that the cause for this is a electronic defect, possibly created during the β-decay of the probe parent nucleus. 相似文献
992.
Vasily L. Morgunov 《Pramana》2007,69(6):1097-1100
A new calorimeter energy calibration method was developed for the proposed ILC detectors. The method uses the center-of-mass
energy of the accelerator as the reference. It has been shown that using the energy conservation law it is possible to make
ECAL and HCAL cross calibration to reach a good energy resolution for the simple calorimeter energy sum.
相似文献
993.
994.
Wang Dunhui Huang Songling Han Zhida Su Zhenghua Wang Yi Du Youwei 《Solid State Communications》2004,131(2):97-99
A series of Gd(1−x)Bx alloys have been prepared by arc melting method. After introducing small quantity of B atom in Gd, the Curie temperature of these alloys increase while the magnetic entropy changes are almost same as that of Gd. The refrigerant capacities of these alloys are also greater than that of Gd. These results suggest that Gd(1−x)Bx alloys may be utilized as refrigerant in household magnetic refrigeration. 相似文献
995.
Yong Nam Choi Shin Ae Kim Sung Kyu Kim Sung Baek Kim Chang-Hee Lee Pavel Mikula 《Pramana》2004,63(1):175-181
In a conventional diffractometer having single monochromator, only one position, parallel position, is used for the diffraction
experiment (i.e. detection) because the resolution property of the other one, anti-parallel position, is very poor. However,
a bent perfect crystal (BPC) monochromator at monochromatic focusing condition can provide a quite flat and equal resolution
property at both parallel and anti-parallel positions and thus one can have a chance to use both sides for the diffraction
experiment. From the data of the FWHM and the Δd/d measured on three diffraction geometries (symmetric, asymmetric compression and asymmetric expansion), we can conclude that
the simultaneous diffraction measurement in both parallel and anti-parallel positions can be achieved. 相似文献
996.
Mathematical models with stage structures are proposed to describe the process of awareness, evaluation and decision-making. First, a system of ordinary differential equations is presented that incorporates the awareness stage and the decision-making stage. If the adoption rate is bilinear and imitations are dominant, we find a threshold above which innovation diffusion is successful. Further, if the adoption rate has a higher nonlinearity, it is shown that there exist bistable equilibria and a region such that an innovation diffusion is successful inside and is unsuccessful outside. Secondly, a model with a time delay is proposed that includes an evaluation stage of a product. It is proved that the system exhibits stability switches. The bifurcation direction of equilibria is also discussed. 相似文献
997.
M. N. Vidyakin Yu. N. Lazareva Yu. P. Yampolskii A. Yu. Alentiev D. Yu. Likhachev A. L. Rusanov O. V. Kozlova 《Polymer Science Series A》2006,48(6):596-600
The correlation between chemical structure and gas transport properties is considered for a new class of membrane materials based on structurally similar polyphenylquinoxalines that are characterized by different numbers of flexible-O-ether bonds in the repeating unit and different chain rigidities. Permeability, diffusion, and solubility coefficients have been estimated for the gases H2, He, O2, N2, CO, CO2, and CH4; separation factors for various gas pairs have been determined. For the materials with a similar level of cohesive energy density, which characterizes interchain interactions, permeability decreases with a decrease in chain rigidity, whereas selectivity of gas separation increases. 相似文献
998.
E. D. Mishina N. É. Sherstyuk V. O. Val’dner A. V. Mishina K. A. Vorotilov V. A. Vasil’ev A. S. Sigov M. P. De Santo E. Cazzanelli R. Barberi Th. Rasing 《Physics of the Solid State》2006,48(6):1210-1213
Ferroelectric composite two-dimensional ferroelectric/aluminum oxide nanostructures were studied. A porous aluminum oxide matrix was used as a template into which a ferroelectric precursor was introduced, followed by annealing. The prepared nanostructures were studied using optical second harmonic generation and micro-Raman scattering. 相似文献
999.
Currents in high-resistivity semiconductors arising due to the rectification of space-charge waves are theoretically studied. Attention is primarily focused on the situation where the effective trap concentration is low. It is shown that, in this case, the dispersion law of trap-recharging waves changes from the inverse proportionality to a linear law and the drift waves no longer exist. In crystals with bipolar conduction, there are two modes of trap-recharging waves with a linear dispersion law. The dc and ac currents are found for the first time as functions of the trap concentration, the mobility and lifetime of carriers, the wavenumber of space-charge waves, and the applied electric field. 相似文献
1000.
A novel type of corner reflector for the reflection of surface plasmon polariton (SPP) is proposed. The reflector consists
of two layers of compensatory media whose permittivity and permeability take opposite signs to that of the corresponding layer
of the SP waveguide. By rigorously solving Maxwell's equations, the reflected SPP is proved to exist. The transverse wave
vector of the reflected SPP is always antiparallel to that of the incident SPP and no phase retardation is introduced. 相似文献