全文获取类型
收费全文 | 21785篇 |
免费 | 4297篇 |
国内免费 | 2098篇 |
专业分类
化学 | 8681篇 |
晶体学 | 625篇 |
力学 | 836篇 |
综合类 | 120篇 |
数学 | 327篇 |
物理学 | 17591篇 |
出版年
2024年 | 44篇 |
2023年 | 247篇 |
2022年 | 417篇 |
2021年 | 439篇 |
2020年 | 515篇 |
2019年 | 345篇 |
2018年 | 429篇 |
2017年 | 753篇 |
2016年 | 865篇 |
2015年 | 734篇 |
2014年 | 1276篇 |
2013年 | 1883篇 |
2012年 | 1394篇 |
2011年 | 1468篇 |
2010年 | 1113篇 |
2009年 | 1416篇 |
2008年 | 1691篇 |
2007年 | 1532篇 |
2006年 | 1432篇 |
2005年 | 1333篇 |
2004年 | 1133篇 |
2003年 | 973篇 |
2002年 | 902篇 |
2001年 | 815篇 |
2000年 | 745篇 |
1999年 | 680篇 |
1998年 | 549篇 |
1997年 | 562篇 |
1996年 | 430篇 |
1995年 | 395篇 |
1994年 | 349篇 |
1993年 | 275篇 |
1992年 | 246篇 |
1991年 | 164篇 |
1990年 | 125篇 |
1989年 | 122篇 |
1988年 | 86篇 |
1987年 | 77篇 |
1986年 | 48篇 |
1985年 | 36篇 |
1984年 | 41篇 |
1983年 | 13篇 |
1982年 | 30篇 |
1981年 | 20篇 |
1980年 | 9篇 |
1979年 | 7篇 |
1975年 | 5篇 |
1973年 | 10篇 |
1970年 | 2篇 |
1957年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
101.
Recently, molecular imaging has been rapidly developed to studyphysiological and pathological processes in vivo at the cellularand molecular levels. Among molecular imaging modalities, opticalimaging has attracted a major attention for its unique advantages.In this paper, we establish a mathematical framework for multispectralbioluminescence tomography (BLT) that allows simultaneous studiesof multiple optical reporters. We show solution existence, uniquenessand continuous dependence on data as well as the limiting behaviourswhen the regularization parameter approaches zero or when thepenalty parameter approaches infinity. Then, we propose twonumerical schemes for multispectral BLT and derive error estimatesfor the corresponding solutions. 相似文献
102.
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
103.
This paper presents results of studies on dc electrical conductivity and transference number measurements on potassium bromate
(KBrO3) complexed polyvinyl chloride (PVC) films prepared by solution cast technique. Temperature dependence of dc electrical conductivity
and transference number data indicated the dominance of ion type charge transport in these specimens. The magnitude of conductivity
increased with increase in concentration of the salt and temperature. Using this (PVC + KBrO3) electrolyte, solid-state electrochemical cells were fabricated, and their discharge profiles were studied under a constant
load of 100 kΩ. Several cell profiles such as open circuit voltage, short circuit current, power density, and energy density
associated with these cells were evaluated and were reported. The features of complexation of the electrolytes were studied
by X-ray diffraction and Fourier transform infrared spectroscopy.
Paper presented at the Third International Conference on Ionic Devices (ICID 2006), Chennai, Tamilnadu, India, Dec. 7–9, 2006 相似文献
104.
Optical trapping forces of polystyrene microspheres are analyzed both theoretically and experimentally, and comparisons are
made between the two. Discrepancies are mainly caused by straight-ray approximation for axial trapping, and by trapping-position
vertical displacement due to gravity for transverse trapping. 相似文献
105.
This work proposes and demonstrates the feasibility of gray image encryption using multiple polarization encoding, in which
the cascaded twisted nematic liquid crystal devices sandwiched between a crossed polarizer pair are used to implement exclusive
OR (XOR) logical encryption and decryption. The polarization encoding scheme provides a multichannel XOR logic operation to
secure bit-plane images derived from a gray image, according to the adiabatic following properties of twisted nematic liquid
crystal devices. Experimental data reveal that the multiple polarization encoding schemes for gray image encryption and decryption
are performed with acceptable image quality by selecting appropriate polarization orientation and modulation conditions. Both
analytic and experimental results are presented and discussed. 相似文献
106.
107.
This paper gives a critical review on the applications of ToF SIMS in the areas of polymer additive characterization and in the study of polymer blends and interfaces. Polymer additives can readily be identified by ToF SIMS using their parent molecular ions or characteristic fragments. This analytical capability has been successfully applied to monitor the migration or segregation of additives during polymer processing. ToF SIMS is an ideal analytical tool for the study of polymer blends and interfaces because it is able to provide information on both surface composition and morphology. In combination with other analytical techniques such as AFM and XPS, ToF SIMS chemical imaging capability has opened up new horizons in the investigation of complex polymer blend systems. Finally the main advantages and limitations of ToF SIMS in these application areas are also discussed. 相似文献
108.
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
109.
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
110.