全文获取类型
收费全文 | 85614篇 |
免费 | 2042篇 |
国内免费 | 170篇 |
专业分类
化学 | 49702篇 |
晶体学 | 912篇 |
力学 | 3201篇 |
综合类 | 2篇 |
数学 | 11192篇 |
物理学 | 22817篇 |
出版年
2022年 | 606篇 |
2021年 | 855篇 |
2020年 | 992篇 |
2019年 | 964篇 |
2018年 | 1514篇 |
2017年 | 1257篇 |
2016年 | 2225篇 |
2015年 | 1817篇 |
2014年 | 2138篇 |
2013年 | 4475篇 |
2012年 | 4885篇 |
2011年 | 5314篇 |
2010年 | 3406篇 |
2009年 | 3035篇 |
2008年 | 4505篇 |
2007年 | 4502篇 |
2006年 | 4042篇 |
2005年 | 3751篇 |
2004年 | 3340篇 |
2003年 | 2764篇 |
2002年 | 2491篇 |
2001年 | 2240篇 |
2000年 | 1717篇 |
1999年 | 1340篇 |
1998年 | 1010篇 |
1997年 | 948篇 |
1996年 | 980篇 |
1995年 | 769篇 |
1994年 | 791篇 |
1993年 | 744篇 |
1992年 | 839篇 |
1991年 | 796篇 |
1990年 | 769篇 |
1989年 | 713篇 |
1988年 | 689篇 |
1987年 | 674篇 |
1986年 | 588篇 |
1985年 | 815篇 |
1984年 | 810篇 |
1983年 | 574篇 |
1982年 | 716篇 |
1981年 | 688篇 |
1980年 | 595篇 |
1979年 | 669篇 |
1978年 | 631篇 |
1977年 | 598篇 |
1976年 | 651篇 |
1975年 | 580篇 |
1974年 | 569篇 |
1973年 | 575篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
The 57Fe Mössbauer effect study at 5.0 K and in an external magnetic field of 9.0 T on a high-quality stable decagonal quasicrystal Al65Co15Cu19.9Fe0.1 is presented. It is shown that the iron atoms are located in two distinct classes of sites. The values of the principal component of the electric field gradient tensor and the asymmetry parameter at these sites are, respectively, ?1.90(10)?×?1021 V/m2, 0.97(15) and ?3.95(12)?×?1021 V/m2, 0.00(17). 相似文献
102.
In this investigation, the crystalline structure of a nanometric CoSi2 layer, formed in heat treated Co/WxTa(1−x)/Si(1 0 0) systems, has been studied by XRD analysis. Careful measurements of the diffraction intensities revealed that temporary formation of a metastable diamond cubic structure of CoSi2 phase, rather than its usual CaF2 structure, was occurred. It has been shown that formation of this metastable structure depends on the kind of the applied interlayer in addition to the annealing temperature. Among the studied systems with x = 0, 0.25, 0.5, 0.75 and 1, the second and the last systems resulted in growing a (1 0 0) single-texture CoSi2 layer with the preferred usual CaF2 structure, a strained lattice parameter, and the best thermal stability (900-1000 °C). 相似文献
103.
A. Veiga N. Martínez P. Mendoza Zélis G. A. Pasquevich F. H. Sánchez 《Hyperfine Interactions》2006,167(1-3):905-909
A prototype of a programmable constant-velocity scaler is presented. This instrument allows the acquisition of partial Mössbauer spectra in selected energy regions using standard drivers and transducers. It can be fully operated by a remote application, thus data acquisition can be automated. The instrument consists of a programmable counter and a constant-velocity reference. The reference waveform generator is amplitude modulated with 13-bit resolution, and is programmable in a wide range of frequencies and waveforms in order to optimize the performance of the transducer. The counter is compatible with most standard SCA, and is configured as a rate-meter that provides counts per selectable time slice at the programmed velocity. As a demonstration of the instrument applications, a partial Mössbauer spectrum of a natural iron foil was taken. Only positive energies were studied in 512 channels, accumulating 20 s per channel. A line width of 0.20 mm/s was achieved, performing with an efficiency of 80%. 相似文献
104.
X.P. Hu X. Wang Z. Yan H.X. Li J.L. He S.N. Zhu 《Applied physics. B, Lasers and optics》2007,86(2):265-268
High power red light was generated from a periodically-poled stoichiometric LiTaO3 (PPSLT) by single-pass frequency doubling of a diode-side-pumped, Q-switched Nd:YAG laser at 1319 nm. An average power of
2.4 W of the 660 nm red light was obtained at the fundamental power of ∼5.4 W with the conversion efficiency up to 44.4% and
with low fluctuation down to 2%. The high efficiency and stability at the red output indicate that it is a practical method
to construct a reliable compact red laser.
PACS 42.70.Mp; 42.79.Nv; 42.55.Xi 相似文献
105.
Nanometer scale Al/AlN multilayers have been prepared by dc magnetron sputtering technique with a columnar target. A set of Al/AlN multilayers with the Al layer thickness of 2.9 nm and the AlN layer thickness variation from 1.13 to 6.81 nm were determined. Low angle X-ray diffraction (LAXRD) was used to analyze the layered structure of multilayers. The phase structure of the coatings was investigated with grazing angle XRD (GAXRD). Mechanical properties of these multilayers were thoroughly studied using a nanoindentation and ball-on-disk micro-tribometer. It was found that the multilayer hardness and reduced modulus showed no strong dependence on the AlN layer thickness. Al2.9 nm/AlN1.13 nm multilayer had more excellent tribological properties than single layers and other proportion multilayers with a lowest friction coefficient of 0.15. And the tribological properties of all the multilayers are superior to the AlN single layer. 相似文献
106.
A. Z. Dubničková S. Dubnička R. Baldini-Ferroli 《Czechoslovak Journal of Physics》1991,41(11):1075-1081
It is shown that all global analyses of nucleon electromagnetic form factor data predict the electron-positron annihilation into neutron-antineutron cross section (for which there are no data till now) to be in a finite energy region substantially larger than the electron-positron annihilation into the proton-antiproton one.Dedicated to the memory of M. Gmitro. 相似文献
107.
The contrast of interference pattern formed by two circularly polarized waves and by a linearly polarized wave and a circularly polarized one is discussed. The results are compared with that by two linear beams. It shows that the use of circular light in holographic fabrication of three-dimensional periodic microstructures may remove the necessity of beam ratio and polarization optimization needed in the interference of three linear noncoplanar beams and improve the uniform contrast of resultant pattern simultaneously. 相似文献
108.
R. Euler B. Fricke T. Morović W. -D. Sepp A. Rosén 《Zeitschrift für Physik A Hadrons and Nuclei》1980,297(2):101-104
Total energy SCF calculations were performed for noble gas difluorides in a relativistic procedure and compared with analogous non-relativistic calculations. The discrete variational method with numerical basis functions was used. Rather smooth potential energy curves could be obtained. The theoretical Kr-F and Xe-F bond distances were calculated to be 3.5 a.u. and 3.6 a.u. which should be compared with the experimental values of 3.54 a.u. and 3.7 a.u. Although the dissociation energies are off by a factor of about five it was found that ArF2 may be a stable molecule. Theoretical ionization energies for the outer levels reproduce the experimental values for KrF2 and XeF2 to within 2 eV. 相似文献
109.
Z.X. Cheng S.J. ZhangF. Song H.C. GuoJ.R. Han H.C. Chen 《Journal of Physics and Chemistry of Solids》2002,63(11):2011-2017
Erbium and ytterbium codoped double tungstates NaY(WO4)2 crystals were prepared by using Czochralski (CZ) pulling method. The absorption spectra in the region 290-2000 nm have been recorded at room temperature. The Judd-Ofelt theory was applied to the measured values of absorption line strengths to evaluate the spontaneous emission probabilities and stimulated emission cross sections of Er3+ ions in NaY(WO4)2 crystals. Intensive green and red lights were measured when the sample were pumped by a 974 nm laser diode (LD), especially, the intensities of green upconversion luminescence are very strong. The mechanism of energy transfer from Yb3+ to Er3+ ions was analyzed. Energy transfer and nonradiative relaxation played an important role in the upconversion process. Photoexcited luminescence experiments are also fulfilled to help analyzing the transit processes of the energy levels. 相似文献
110.
C. Zălinescu 《Mathematical Methods of Operations Research》1991,35(4):291-298
In this paper there is stated a result on sets in ordered linear spaces which can be used to show that some properties of the sets are inherited by their convex hulls under suitable conditions. As applications one gives a characterization of weakly efficient points and a duality result for nonconvex vector optimization problems. 相似文献