全文获取类型
收费全文 | 16761篇 |
免费 | 2116篇 |
国内免费 | 1283篇 |
专业分类
化学 | 5395篇 |
晶体学 | 74篇 |
力学 | 538篇 |
综合类 | 56篇 |
数学 | 157篇 |
物理学 | 5882篇 |
无线电 | 8058篇 |
出版年
2024年 | 30篇 |
2023年 | 105篇 |
2022年 | 228篇 |
2021年 | 324篇 |
2020年 | 400篇 |
2019年 | 262篇 |
2018年 | 324篇 |
2017年 | 492篇 |
2016年 | 548篇 |
2015年 | 591篇 |
2014年 | 1012篇 |
2013年 | 1106篇 |
2012年 | 1086篇 |
2011年 | 1119篇 |
2010年 | 847篇 |
2009年 | 1014篇 |
2008年 | 1178篇 |
2007年 | 1090篇 |
2006年 | 1070篇 |
2005年 | 1079篇 |
2004年 | 979篇 |
2003年 | 870篇 |
2002年 | 693篇 |
2001年 | 627篇 |
2000年 | 506篇 |
1999年 | 410篇 |
1998年 | 343篇 |
1997年 | 338篇 |
1996年 | 250篇 |
1995年 | 228篇 |
1994年 | 190篇 |
1993年 | 136篇 |
1992年 | 121篇 |
1991年 | 99篇 |
1990年 | 79篇 |
1989年 | 47篇 |
1988年 | 27篇 |
1987年 | 45篇 |
1986年 | 45篇 |
1985年 | 61篇 |
1984年 | 30篇 |
1983年 | 27篇 |
1982年 | 37篇 |
1981年 | 35篇 |
1980年 | 19篇 |
1979年 | 7篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1957年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 806 毫秒
71.
72.
73.
Hirohisa Yokota Kenji Kamoto Jun-ichi Igarashi Norihiko Mouri Yutaka Sasaki 《Optical Review》2002,9(1):9-12
A new configuration for an ASE reduction filter in EDFA repeaters for WDM optical transmission systems using optical fiber grating couplers (FGCs) was proposed and first demonstrated. The filtering characteristics of the proposed filter for amplified single wavelength signal and 2-channel WDM signals using EDFA were identified. It was found that the filter was effective to improve SNR in optical domain by reducing ASE noise. The required FGC characteristics for the filter were theoretically predicted under the condition that the total filter loss did not exceed 3 dB. More than 70% of drop efficiency was required in each FGC for the application of the proposed filter to an 8-channel WDM system using EDFA repeaters. 相似文献
74.
The prepared amorphous
γ-ZrP\SiO2 composite had a complicated composition,
since a part of γ-ZrP is converted to α-form during the exfoliation
of it. The γ-ZrP\SiO2 composite have specific surface
area of 421 m2g–1.
The acidic P–OH groups of the lamellae species placed on the surface
(it is ≈1.0 meq g–1), do not destroy until
the temperature of 1030 K. During the thermal treatment the total mass loss
of 7.79% was found. This value corresponds to 0.42 mole of H2O
per molecule unit. The water loss process was found very slow, because of
the placing of bilamellar species in the composite. 相似文献
75.
本文提出等效远场的可变孔径方法,由测量光纤远场累积分布求得模场半径。并且利用Petermann关于模场半径的新定义,推出了一种对非高斯模场分布也适用的求模场半径的方法。实验表明,这种测量方法简便可靠,在不同的制备端面下,重复测量的标准误差小于0.04μm。 相似文献
76.
A simple method of determining ultra-trace Au in natural water was presented by using graphite furnace atomic absorption spectrophotometry (GFAAS) after in situ enrichment with thiol cotton fiber (TCF). The sample solution was adjusted to pH 1.5-2.0 with HCl, then the water sample was passed through a column packed with 0.10-0.20 g TCF and the flow rate was controlled at 20-40 ml min−1. The effects of interferences, such as complexing and oxidizing agents and other elements adsorbed on TCF were overcome by chemical treatments prior to the desorption of Au. The adsorbed Au was adsorbed with 2.0 ml hot acid, then it was extracted with 1.00 ml methyl isobutylketone (MIBK). For a 5 l water sample, the detection limit of Au is 0.02 ng l−1. The relative standard deviation (R.S.D.) for the determination of 1.44 ng l−1 Au was 9.4%.The method was applied to determine ultra-trace Au both in suspended phase and soluble phase in natural water, the concentrations of total Au in natural water samples range from 0.51 to 67.82 ng l−1. The recovery of added 0.50-6.00 ng l−1 Au was 80-95%. The method is useful in prospecting for Au deposits by means of hydrogeochemical methods. The enrichment is carried out in the field, and then the determination of Au is completed later in the laboratory. 相似文献
77.
A method is developed for a stress analysis in an infinite elastic body containing two neighboring periodically cophasaly curved fibers located along two parallel lines. The stress distribution is studied when the body is loaded at infinity by uniformly distributed normal forces in the fiber direction. The investigation is carried out within the framework of a piecewise homogeneous body model with the use of exact three-dimensional equations of elasticity theory. Numerical results related to the stress distribution considered and the influence of interaction between the fibers on this distribution are given. 相似文献
78.
79.
AbbasA. Zaman 《Particle & Particle Systems Characterization》2003,20(5):342-350
Effects of a low molecular weight physically adsorbed polyethylene oxide (PEO) and the range of the electrostatic repulsion on the rheological behavior of silica dispersions (as a model system) has been investigated. Particular attention is given to the evolution of the rheological behavior with increasing the polymer concentration in the system and also effectiveness of the polymer as a dispersant under extreme conditions (high ionic strength). Results indicate that at small separation distances and low polymer coverage, the polymer chains are long enough to adsorb on the surface of two particles simultaneously causing bridging flocculation in the system and hence increasing the viscosity and linear viscoelastic functions of the dispersion. A significant increase was observed in the viscosity of the dispersion at salt concentrations high enough to eliminate electrostatics between the particles. Under these conditions,the viscosity of the system increased significantly when PEO was added to the dispersion showing that at high electrolyte concentrations, a neutral polymer such as PEO is not able to stabilize the system. 相似文献
80.
Sean D. Brooks M. F. Mahmood J. A. Donaldson 《Journal of Mathematical Modelling and Algorithms》2004,3(1):19-29
A numerical investigation, based on the split-step Fourier transform algorithm of all optical switching of solitons in a low
birefringent optical fiber is presented. The numerical algorithm is described in detail.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献