全文获取类型
收费全文 | 77765篇 |
免费 | 20776篇 |
国内免费 | 1457篇 |
专业分类
电工技术 | 3308篇 |
综合类 | 1176篇 |
化学工业 | 25815篇 |
金属工艺 | 3203篇 |
机械仪表 | 2681篇 |
建筑科学 | 2877篇 |
矿业工程 | 612篇 |
能源动力 | 2603篇 |
轻工业 | 8273篇 |
水利工程 | 484篇 |
石油天然气 | 609篇 |
武器工业 | 84篇 |
无线电 | 13540篇 |
一般工业技术 | 24413篇 |
冶金工业 | 1656篇 |
原子能技术 | 176篇 |
自动化技术 | 8488篇 |
出版年
2024年 | 58篇 |
2023年 | 265篇 |
2022年 | 278篇 |
2021年 | 839篇 |
2020年 | 3279篇 |
2019年 | 5856篇 |
2018年 | 5389篇 |
2017年 | 6097篇 |
2016年 | 5950篇 |
2015年 | 5778篇 |
2014年 | 6037篇 |
2013年 | 6830篇 |
2012年 | 5976篇 |
2011年 | 6130篇 |
2010年 | 4815篇 |
2009年 | 4456篇 |
2008年 | 4346篇 |
2007年 | 4366篇 |
2006年 | 3966篇 |
2005年 | 3251篇 |
2004年 | 2981篇 |
2003年 | 2706篇 |
2002年 | 2593篇 |
2001年 | 2198篇 |
2000年 | 1948篇 |
1999年 | 1185篇 |
1998年 | 475篇 |
1997年 | 377篇 |
1996年 | 275篇 |
1995年 | 253篇 |
1994年 | 200篇 |
1993年 | 174篇 |
1992年 | 151篇 |
1991年 | 136篇 |
1990年 | 89篇 |
1989年 | 54篇 |
1988年 | 47篇 |
1987年 | 32篇 |
1986年 | 29篇 |
1985年 | 25篇 |
1984年 | 20篇 |
1983年 | 12篇 |
1982年 | 13篇 |
1981年 | 11篇 |
1979年 | 7篇 |
1978年 | 8篇 |
1976年 | 9篇 |
1975年 | 7篇 |
1974年 | 9篇 |
1957年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
Studies on the deactivations and initiations of gas phase polymerizations of 1,3‐butadiene have been achieved by Monte Carlo simulation. Initiation and deactivation control the reaction before and after the peak of the polymerization rate, respectively. The influence of polymerization temperature has been studied. Monte Carlo modeling of polymerization kinetics and mechanism was confirmed by the agreement of experimental data and simulation results of polymerizations run with a temporary evacuation of monomer. The balance of catalysts and active chains is established by both initiation and chain transfer reactions with cocatalyst, which causes a ‘pseudo‐stability’ stage. © 2003 Society of Chemical Industry 相似文献
62.
From its foundation until 2004, ETRI has registered over 1,000 US patents. This letter analyzes the characteristics of these patents and addresses the explanatory factors affecting their citation counts. For explanatory variables, research team related variables, invention specific variables, and geographical domain related variables are suggested. Zero‐altered count data models are used to test the impact of independent variables. A key finding is that technological cumulativeness, the scale of invention, outputs in the electronic field, and the degree of dependence on the US technology domain positively affect the citation counts of ETRI‐invented US patents. The magnitude of international presence appears to negatively affect the citation counts of ETRI‐invented US patents. 相似文献
63.
64.
M. Benkerri R. Halimi A. Bouabellou N. Benouattas 《Materials Science in Semiconductor Processing》2004,7(4-6):319
In this work, the solid state reaction between a thin film of copper and silicon has been studied using Rutherford backscattering spectroscopy, X-ray diffraction, scanning electron microscopy and microprobe analysis. Cu films of 400 and 900 Å thicknesses are thermally evaporated on Si(1 1 1) substrates, part of them had previously been implanted with antimony ions of 5×1014 or 5×1015 at. cm−2 doses. The samples are heat-treated in vacuum at temperatures in the range 200–700 °C for various times. The results show the growth and formation of Cu3Si and Cu4Si silicides under crystallites shape dispatched on the sample surface, independently of the implantation dose. On the other hand, it is established that the copper layer is less and less consumed as the antimony dose increases, resulting in the accumulation of Sb+ ions at silicide/Si interface and in the silicide layer close to surface. The exposure of samples to air at room temperature shows the stability of Cu4Si phase whereas the Cu3Si silicide disappears to the benefit of the silicon dioxide formation. The observed phenomena are discussed. 相似文献
65.
We have developed new photopolymers that have superior waterproof properties and that can easily interact with polyfunctional acrylate compounds, thus serving as hydrophobic photocrosslinking reagents. Acryloylmorpholine monomers whose homopolymers were less moisture absorbing than the usual water‐soluble polymers but were still water soluble to a good degree, were copolymerized with other acryloyl monomers. We then introduced the photosensitive (meth)acryloyl group to side chains of the resulting polymers. Among six copolymers examined, the copolymers composed of acryloyl morpholine, hydroxyethyl acrylate, ethyl, or methyl methacrylate, and methacryloyl isocyanate were found to have nicely balanced hydrophilicity and waterproof properties, in addition to good compatibility with hydrophobic photocrosslinking reagents. The composite polymers thus obtained were confirmed to be promising photopolymers usable even in a highly humid environment. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 684–692, 2003 相似文献
66.
67.
Polymer networks in which poly(propylene imine) dendrimers (Astramol?) are connected to each other by linear polytetrahydrofuran (polyTHF) segments, were prepared by two methods. The first method was a one‐step procedure in which bifunctionally living polyTHF, obtained by initiation of the THF polymerization with trifluoromethane sulfonic anhydride (triflic anhydride), was reacted with an amino‐dendrimer. This reaction was very fast but did not allow formation of the end products. The second method was a two‐step procedure. In a first step, living polyTHF, prepared with acryloyloxybutyl triflate as initiator, was grafted on an amino‐dendrimer, to form a star‐like, acrylate‐terminated polyTHF multi‐macromonomer with the dendrimer as core. In a second step, networks were obtained by Michael addition between the acrylate end‐groups and unreacted amino‐groups of the dendrimer. This cross‐linking reaction occurred spontaneously upon heating of the solution of the multi‐macromonomer with gelation times varying from a few minutes to a few hours, depending on the temperature and the composition of the prepolymers. With this method it was possible to prepare networks in the form of coatings or films. © 2003 Society of Chemical Industry 相似文献
68.
69.
Measurement Method of the Thickness Uniformity for Polymer Films 总被引:1,自引:0,他引:1
YANGHong-liang RENQuan FANYun-zheng 《半导体光子学与技术》2003,9(2):128-132
Several methods for investigating the thickness uniformity of polymer thin films are presented as well their measurement principles.A comparison of these experimental methods is given.The cylindrical lightwave feflection method is found to can obtain the thickness distribution along a certain direction.It is simple and suitable method to evaluate the film thickness uniformity. 相似文献
70.
The motional transition and heterogeneity of semi‐interpenetrating networks (SIPNs) based on polyurethane (PU) with carboxylic groups and methacrylic copolymer (PM) with tertiary amine groups were studied by the electron spin resonance (ESR) spin probe method. The concentration of functional groups in both prepolymers varied from 0 to 0.45 mmol g?1. Spin‐probed SIPNs show that the temperature‐dependent spectra are sensitive to polymer interactions imposed by functional groups. These interactions determine the free volume distribution in the matrix and temperature at which motional transition takes place. The fraction of free volume increases with functional group concentration and reaches its maximum at 0.25 mmol g?1. Further increases in the functional group concentration reduce the free volume. The results of the networks with strong interactions are discussed in terms of the interference of the plasticizing effect of the PU component and the formation of possible cluster cross‐links, which restricts segmental motions. Copyright © 2003 Society of Chemical Industry 相似文献