全文获取类型
收费全文 | 206645篇 |
免费 | 2215篇 |
国内免费 | 568篇 |
专业分类
电工技术 | 3514篇 |
综合类 | 141篇 |
化学工业 | 31949篇 |
金属工艺 | 10296篇 |
机械仪表 | 7019篇 |
建筑科学 | 3998篇 |
矿业工程 | 2161篇 |
能源动力 | 4649篇 |
轻工业 | 12899篇 |
水利工程 | 2921篇 |
石油天然气 | 7726篇 |
武器工业 | 22篇 |
无线电 | 21591篇 |
一般工业技术 | 45284篇 |
冶金工业 | 34462篇 |
原子能技术 | 6624篇 |
自动化技术 | 14172篇 |
出版年
2021年 | 2059篇 |
2019年 | 2008篇 |
2018年 | 3690篇 |
2017年 | 3724篇 |
2016年 | 4004篇 |
2015年 | 2243篇 |
2014年 | 3789篇 |
2013年 | 8757篇 |
2012年 | 5697篇 |
2011年 | 7232篇 |
2010年 | 5873篇 |
2009年 | 6516篇 |
2008年 | 6627篇 |
2007年 | 6509篇 |
2006年 | 5586篇 |
2005年 | 5135篇 |
2004年 | 4641篇 |
2003年 | 4565篇 |
2002年 | 4390篇 |
2001年 | 4482篇 |
2000年 | 4193篇 |
1999年 | 4205篇 |
1998年 | 10202篇 |
1997年 | 7196篇 |
1996年 | 5515篇 |
1995年 | 4140篇 |
1994年 | 3607篇 |
1993年 | 3854篇 |
1992年 | 2991篇 |
1991年 | 2999篇 |
1990年 | 2892篇 |
1989年 | 2860篇 |
1988年 | 2871篇 |
1987年 | 2511篇 |
1986年 | 2576篇 |
1985年 | 2866篇 |
1984年 | 2697篇 |
1983年 | 2563篇 |
1982年 | 2306篇 |
1981年 | 2269篇 |
1980年 | 2351篇 |
1979年 | 2364篇 |
1978年 | 2389篇 |
1977年 | 2491篇 |
1976年 | 2885篇 |
1975年 | 2197篇 |
1974年 | 2073篇 |
1973年 | 2171篇 |
1972年 | 1945篇 |
1971年 | 1761篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
Androstenedione labeled with tritium at positions 1 and 2 was prepared. The molar radioactivity of the sample prepared using homogeneous catalysts was as high as 1.4-1.5 PBq mol-
1. [1,2-3H]Androst-4-ene-3,17-dione can be converted into the [1-3H]steroid with the molar radioactivity of 0.9 PBq mol-
1. 相似文献
142.
It is essential in the simulation of power electronics applications to model magnetic components accurately. In addition to modeling the nonlinear hysteresis behavior, eddy currents and winding losses must be included to provide a realistic model. In practice the losses in magnetic components give rise to significant temperature increases which can lead to major changes in the component behavior. In this paper a model of magnetic components is presented which integrates a nonlinear model of hysteresis, electro-magnetic windings and thermal behavior in a single model for use in circuit simulation of power electronics systems. Measurements and simulations are presented which demonstrate the accuracy of the approach for the electrical, magnetic and thermal domains across a variety of operating conditions, including static thermal conditions and dynamic self heating 相似文献
143.
Aluminum and magnesium alloys are the base structural materials in aircraft and spacecraft engineering. The main stages of the development and introduction of light alloys are described. 相似文献
144.
Determination of dislocation densities in HCP metals from X-ray diffraction line-broadening analysis
Griffiths M. Sage D. Holt R. A. Tome C. N. 《Metallurgical and Materials Transactions A》2002,33(13):859-865
X-Ray diffraction (XRD) line-broadening analysis has been performed on highly textured Zr-2.5Nb specimens which had been deformed
in tensile tests to produce well-controlled dislocation structures. An iterative deconvolution method has been applied to
extract the broadening function for the material, using as standards, a Zr single crystal and a 0 pct deformed specimen. In
both cases, for specific tensile tests, a significant contribution to the basal line braodening was observed, which was clearly
not directly related to the dislocation structure generated by the deformation, i.e., so-called c-component dislocations having a component of their Burgers vectors perpendicular to the basal plane. Calculations showed
that the extent of basal line broadening cannot be attributed to the secondary effect of strain from a-type dislocations, i.e., dislocations with Burgers vectors parallel with the basal plane. It is concluded that most of the line broadening observed
was the result of intergranular strain distributions. These distributions are most prominent for grains oriented with their
c-axes perpendicular to the tensile-deformation axis and resulted in basal-plane line broadening even when there were few,
if any, c-component dislocations present.
This article is based on a presentation made in the symposium entitled “Defect Properties and Mechanical Behavior of HCP Metals
and Alloys” at the TMS Annual Meeting, February 11–15, 2001, in New Orleans, Louisiana, under the auspices of the following
ASM committees: Materials Science and Critical Technology Sector, Structural Materials Division, Electronic, Magnetic & Photonic
Materials Division, Chemistry & Physics of Materials Committee, Joint Nuclear Materials Committee, and Titanium Committee. 相似文献
145.
146.
The kinetics of changes in the bound water content in dietetic sucrose-free sponge cakes (DC) during storage was investigated. The effect of edible films of polymyxan, pectin, xanthan, and carboxymethylcellulose upon this kinetics was also investigated. The quantitative changes in both states of water (slightly bound water and strongly bound water) were registered by combined dynamic analysis (thermogravimetry analysis, TGA, and differential thermal analysis, DTA). The moisture changes in DC crumb were analyzed by drying out to constant mass. The rate constants were determined according the equation q = qoe-kt. The values of rate constants 'k', in day-1, concerning the different edible films were as follows: for crumb moisture is (8.00 ≤ k ≤ 12.47) × 10-3, for bound water is (3.07 ≤ kw ≤ 6.26) × 10-2, for slightly bound water is (4.22 ≤ k1 ≤ 8.49) × 10-2 and for strongly bound water is (2.02 ≤ k2 ≤ 5.62) × 10-2 as compared to 18.53 × 10-3, 7.16 × 10-2, 9.04 × 10-2, and 5.36 × 10-2 in the uncovered DC, respectively. The best water-retaining effect in respect to crumb moisture during storage was ascertained in the use of polymyxan and xanthan films. The lowest rate constant values for bound water and its two states were measured for DC covered with pectin. The relation between the kinetics of both bound water states during storage and ageing of the crumb of DC covered with different edible films and the crumb microstructure was represented. By means of scanning electron microscope was read the smallest change in crumb microstructure of pectin-covered DC on the sixth day of storage. 相似文献
147.
N. A. Sivov A. I. Martynenko G. N. Bondarenko M. P. Filatova E. Yu. Kabanova N. I. Popova A. N. Sivov E. B. Kruts’ko 《Petroleum Chemistry》2006,46(1):41-59
Structures and compositions of the monomers guanidine acrylate and guanidine methacrylate, their homopolymers, and copolymers with diallyldimethylammonium chloride enriched in acrylate comonomer units were determined. It was shown that ampholytic copolymers, owing to their ionic nature, contained comonomeric guanidine acrylate or methacrylate units and diallyldimethylammonium chloride units, as well as the acrylate comonomer with the diallyl counterion and polymeric acrylate and diallyl ion pairs. It follows from IR and 1H NMR data that guanidine methacrylate has the same structure (with two hydrogen bonds) in the solid state and in solutions. Guanidine acrylate structures in the solid state and in dimethylsulfoxide are identical and analogous to guanidine methacrylate structure in this solvent. In water, the guanidine acrylate structure has another type of hydrogen bonding (with one hydrogen bond, where the proton is shifted toward the guanidine group). These features of hydrogen bonding of guanidine acrylate and guanidine methacrylate are also retained in their homopolymers and copolymers with diallyldimethylammonium chloride. It was shown that the thermal stability of the copolymers was higher than that of their homopolymers, confirming the formation of intramolecular ion pairs of oppositely charged units of ampholytic copolymers. Moreover, the thermal stability of guanidine methacrylate-diallyldimethylammonium chloride copolymers is higher than that of guanidine acrylate-diallyldimethylammonium chloride copolymers. 相似文献
148.
149.
H. Furuse N. Mori H. Kubo H. Momose M. Kondow 《Journal of Materials Science: Materials in Electronics》2007,18(1):81-85
We have measured optical transmittance through germanium in the mid-infrared region at room temperature using the Osaka free-electron laser (FEL). In spite of the fact that germanium is transparent in the mid-infrared region, we observed strong suppression of optical transmission under high-intensity FEL excitation. We found that the observed suppression is due to optical absorption in germanium. To analyze the experimental results, we have calculated optical transmittance of germanium within Keldysh theory 相似文献
150.
Model-driven development - Guest editor's introduction 总被引:1,自引:0,他引:1