首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   5093篇
  免费   81篇
  国内免费   7篇
电工技术   194篇
综合类   2篇
化学工业   899篇
金属工艺   118篇
机械仪表   110篇
建筑科学   99篇
矿业工程   2篇
能源动力   107篇
轻工业   405篇
水利工程   26篇
石油天然气   10篇
无线电   529篇
一般工业技术   872篇
冶金工业   1349篇
原子能技术   118篇
自动化技术   341篇
  2023年   19篇
  2022年   48篇
  2021年   80篇
  2020年   43篇
  2019年   49篇
  2018年   58篇
  2017年   41篇
  2016年   70篇
  2015年   42篇
  2014年   85篇
  2013年   231篇
  2012年   133篇
  2011年   210篇
  2010年   143篇
  2009年   176篇
  2008年   178篇
  2007年   152篇
  2006年   170篇
  2005年   142篇
  2004年   139篇
  2003年   150篇
  2002年   138篇
  2001年   99篇
  2000年   90篇
  1999年   139篇
  1998年   494篇
  1997年   342篇
  1996年   257篇
  1995年   135篇
  1994年   131篇
  1993年   146篇
  1992年   63篇
  1991年   61篇
  1990年   61篇
  1989年   57篇
  1988年   49篇
  1987年   32篇
  1986年   56篇
  1985年   60篇
  1984年   40篇
  1983年   44篇
  1982年   40篇
  1981年   45篇
  1980年   40篇
  1979年   28篇
  1978年   17篇
  1977年   29篇
  1976年   50篇
  1975年   13篇
  1973年   14篇
排序方式: 共有5181条查询结果,搜索用时 0 毫秒
11.
Y. Inoue  Y. Watanabe 《Catalysis Today》1993,16(3-4):487-494
A poled ferroelectric LiNbO3 single crystal with high spontaneous polarization was employed as a catalyst support, and the static and dynamic effects of the polar substrate surfaces on the adsorptive and catalytic properties of thin film catalysts deposited were shown. For the static effect, it was demonstrated that the surface conductivity of copper and metal-free phthalocyanine films increased by the adsorption of NO gas, to a larger extent, when the substrate was the negative polar surface, compared to the positive one. The role of the polar substrates is explained In terms of a band bending model. For the dynamic effect, the Rayleigh surface acoustic wave generated on the LiNbO3 substrate was shown to enhance the catalytic activity for ethanol oxidation on Cu and Ag thin film catalysts deposited on the propagation path. It is proposed that the catalyst activation is mainly due to an electric Held produced. The use of poled LiNbO3 is suggested to be effective for the development of a device-type catalyst with activity controllable functions.  相似文献   
12.
13.
14.
Lithium naphthalene reacts with acetic acid to give α-anion of lithium acetate. The reaction of this anion with various ketones gives the corresponding β-hydroxy-acids in good yield.  相似文献   
15.
The crystalline complex between poly(γ-methyl l-glutamate) (PMLG) and dimethyl phthalate (DMP) has been formed in films cast from a solution in dichloroethane. It has the stoichiometry of 1 mol of DMP to three or four residues of PMLG and shows two definite characteristics in X-ray diffraction patterns; one is the large hexagonal unit cell with the edge of around 28 Å and another the ‘extra’ 5.07 Å meridional reflection which can not be interpreted by a PMLG α-helical conformation. The structural examination for the films with various DMP contents is carried out by X-ray, viscoelastic, and d.s.c. measurements and the following structure is proposed for the crystalline complex. Four PMLG are associated to form a group which is hexagonally packed and DMP molecules, located in the gaps between groups, form a specific favourable helical structure along PMLG chains in which the van der Waals stacking of benzene rings of DMP is significant.  相似文献   
16.
In order to investigate the steric effect of the substituents to determine the product distribution, disubstituted cyclohexenes were hydrogenated over several transition metal catalysts. Some cyclohexenes which have two large substituents at the vicinal carbon atoms, at least one of which is trigonal, were not hydrogenated over Raney Ni at all but were hydrogenated over Pt catalyst under our experimental conditions. Presumably, the stereoselectivity depends on the competitive operation of the torsional angle strain and the catalyst hindrance with substituents. In the hydrogenation over Pd catalyst, thermodynamically more stable products were dominant at the standard condition but at high substrate to catalyst ratio the less stable products were slightly preferred. No appreciable stereoselectivity was observed in the hydrogenation of 1,4-disubstituted cyclohexenes.  相似文献   
17.
Type-A zeolite evenly covered with hydroxyapatite thin layers was prepared using hydrothermal treatment at 120°C for 8 h under autogenous pressure. The hydroxyapatite needlelike nanocrystals, 100–200 nm in diameter and 30 nm in thickness, were grown under the reaction between discharged Ca2+ ions from type-A zeolite and PO43− ions in (NH4)3PO4 solution. The preferential orientations of the c -axis of hydroxyapatite crystals perpendicular to a zeolite surface were observed using transmission electron microscopy. The crystal structure of type-A zeolite was not destroyed under the reaction, but the surface morphology was changed only with complete covering of scaly hydroxyapatite particles.  相似文献   
18.
In this study known mixtures of four or five fatty acid methyl esters were analyzed collaboratively by gas chromatography with flame ionization detectors. The experimental data was treated statistically to examine inter- and intralaboratory scattering. More-over the effect of the use of correction factors was investigated. Even if only the specific analytical values that scattered a little were chosen, the averages of such values did not always approach the actual values. In some laboratories a sort of regularity was observed in the deviation of analytical values from real values throughout the analyses of four samples. The application of correction factors to the analytical values obtained by these laboratories resulted in a considerable decrease of interlaboratory scattering and deviation from the real values. When a constant amount of sample was injected, intralaboratory scattering was decreased, whereas interlaboratory scattering was not. Injection of large sample sizes caused deviation. From this collaborative study it was recommended that 0.5–1.0 μl of 20% solution be injected. Presented at the JOCS-AOCS Joint Meeting, Los Angeles, April 1972.  相似文献   
19.
We propose an explanatory mechanism for multilayered neural networks (NN). In spite of the effective learning capability as a uniform function approximator, the multilayered NN suffers from unreadability, i.e., it is difficult for the user to interpret or understand the "knowledge" that the NN has by looking at the connection weights and thresholds obtained by backpropagation (BP). This unreadability comes from the distributed nature of the knowledge representation in the NN. In this paper, we propose a method that reorganizes the distributed knowledge in the NN to extract approximate classification rules. Our rule extraction method is based on the analysis of the function that the NN has learned, rather than on the direct interpretation of connection weights as correlation information. More specifically, our method divides the input space into "monotonic regions" where a monotonic region is a set of input patterns that belongs to the same class with the same sensitivity pattern. Approximate classification rules are generated by projecting these monotonic regions.  相似文献   
20.
With the progress of electronics technology, the development of civilian UAV (unmanned aerial vehicle) applications becomes possible. In addition, smartphones have rapidly gained popularity and become very important due to the simple operability and mobility. Hence, there is a need to have an easy and flexible way to control a UAV using such technology. In this study, a remote controller using an iOS device is developed for a quadrotor to enable remote control with easy operations. Four basic programs for obtaining compass information, controlling a gimbal, autopilot function for return, and video preview function are developed and implemented for an iOS device. The basic functionalities of the programs are evaluated and confirmed through experiments using a quadrotor and an iOS device.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号