全文获取类型
收费全文 | 2498篇 |
免费 | 227篇 |
国内免费 | 4篇 |
专业分类
电工技术 | 39篇 |
综合类 | 2篇 |
化学工业 | 678篇 |
金属工艺 | 111篇 |
机械仪表 | 75篇 |
建筑科学 | 55篇 |
矿业工程 | 11篇 |
能源动力 | 84篇 |
轻工业 | 423篇 |
水利工程 | 17篇 |
石油天然气 | 13篇 |
无线电 | 103篇 |
一般工业技术 | 638篇 |
冶金工业 | 73篇 |
原子能技术 | 23篇 |
自动化技术 | 384篇 |
出版年
2023年 | 25篇 |
2022年 | 32篇 |
2021年 | 82篇 |
2020年 | 73篇 |
2019年 | 73篇 |
2018年 | 139篇 |
2017年 | 121篇 |
2016年 | 113篇 |
2015年 | 132篇 |
2014年 | 167篇 |
2013年 | 368篇 |
2012年 | 135篇 |
2011年 | 168篇 |
2010年 | 161篇 |
2009年 | 132篇 |
2008年 | 69篇 |
2007年 | 50篇 |
2006年 | 47篇 |
2005年 | 18篇 |
2004年 | 27篇 |
2003年 | 20篇 |
2002年 | 22篇 |
2001年 | 26篇 |
2000年 | 36篇 |
1999年 | 19篇 |
1998年 | 17篇 |
1997年 | 28篇 |
1996年 | 25篇 |
1995年 | 22篇 |
1994年 | 22篇 |
1993年 | 21篇 |
1992年 | 15篇 |
1991年 | 18篇 |
1990年 | 9篇 |
1989年 | 11篇 |
1988年 | 12篇 |
1986年 | 11篇 |
1985年 | 16篇 |
1984年 | 21篇 |
1983年 | 22篇 |
1982年 | 15篇 |
1981年 | 22篇 |
1980年 | 10篇 |
1979年 | 17篇 |
1978年 | 17篇 |
1977年 | 11篇 |
1976年 | 23篇 |
1975年 | 11篇 |
1974年 | 15篇 |
1973年 | 10篇 |
排序方式: 共有2729条查询结果,搜索用时 15 毫秒
31.
Summary The synthesis is reported of copolymers of styrene with methacrylic acid and of methyl methacrylate with methacrylic acid by radical copolymerization, of copolymers of methyl methacrylate with methacrylic acid by partial alkaline hydrolysis of poly(methyl methacrylate), and of block copolymers of styrene with methacrylic acid. Modified titration curves of all these copolymers were recorded in water and water-ethanol solutions. In a solution containing 50 mass.% ethanol, only small differences could be observed between the potentiometric behaviour of the individual copolymers and polymethacrylic acid. Also, there were no essential differences in any of the solvents used between the potentiometric behaviour of block copolymers of styrene with methacrylic acid, on the one hand, and polymethacrylic acid, on the other. On the contrary, maxima and minima were always observed on the modified titration curves of statistical copolymers with a higher content of the hydrophobic comonomer in solutions with a high water content. Thus, using the modified titration curves, it is possible to decide whether a given copolymer is of the block or statistical type. 相似文献
32.
The study of hydration of expansive cement prepared from 64% portland cement clinker, 23% metakaolinite and 13% CaSO4.2H2O is described. It was found that in the course of a 10-day hydration period, all the gypsum entered the reaction with the formation of ettringite. In 7–10 days, after the termination of the expansion processes, typical stalk-like crystals were transformed into leaf-shaped or other formations. Ettringite was identified even after 4 months of hydration. Monosulphate (3CaO.Al2O3.CaSO4.12H2O) was found in none of the investigated high-expansion cement paste samples. 相似文献
33.
Summary The electrical conductivity of polyphenylacetylenes and polyhalophenylacetylenes was measured in dependence on the temperature and on the type of catalyst used for polymerization. The electrical conductivity increased with increasing temperature. The energy gap was calculated from the temperature dependence on the electrical conductivity; it decreased with increasing number of conjugated double bonds in the polymer chain and with the regularity of structure of the polymer. The number of double bonds, cyclization and configurations were determined by 1H and 13C-NMR. In polyphenylacetylenes only aliphatic carbons deriving from cyclohexadiene units were found but no such units were found in polyhalophenylacetylenes. By UV-vis measurement the number of conjugated double bonds in segments was estimated. The synthesized polymers were amorphous. Their molecular weight was between 2000 and 74.000. 相似文献
34.
M. Hartmanová V. Šály F. Hanic M. Pisarčík H. Ullmann 《Journal of Materials Science》1991,26(16):4313-4317
The investigation of microstructure, some electrical and optical parameters of transparent ThO2-15 mol % yo1.5 ceramics has shown: (a) a very low porosity, close to zero; (b) a higher electrical conductivity than is usual for ThO2 ceramics of the same composition, with the activation energy 1.12 eV; (c) a relative permittivity r 33 under the given conditions; (d) confirmation of a single-phase fluorite-type cubic structure by means of Raman and infrared spectra. 相似文献
35.
Peter Tatarko Fabrizio Valenza Hakan Ünsal Alexandra Kovalčíková Jaroslav Sedláček Pavol Šajgalík 《Journal of the European Ceramic Society》2021,41(5):3051-3060
The wettability and infiltration of molten ZrSi2 and ZrSi2-Lu2O3 alloys into Cf/SiC and B4C-infiltrated Cf/SiC composites were investigated to understand the interfacial interactions that occur during the development of Cf/SiC-ZrC and Cf/SiC-ZrB2-ZrC-Lu2O3 materials. A significant evaporation of Si from the liquid affected the wetting behaviour of the alloy when tested in a vacuum at 1670 °C. The better wetting and spreading of the alloy over the surface was observed for the composites with lower overall porosity (12 %). On the other hand, the formation of an outer dense layer, followed up by the uniform infiltrated region up to ~ 1 mm was observed for the Cf/SiC with higher porosity (21 %). The infiltrated alloy reacted with SiC matrix to form ZrC or with B4C-infiltrated SiC matrix to form ZrB2-ZrC-SiC. The Lu2O3 particles were not wetted by the melt, and were pushed away of the reaction zone by the solidification front. 相似文献
36.
37.
38.
Inductive Logic Programming (ILP) deals with the problem of finding a hypothesis covering positive examples and excluding negative examples, where both hypotheses and examples are expressed in first-order logic. In this paper we employ constraint satisfaction techniques to model and solve a problem known as template ILP consistency, which assumes that the structure of a hypothesis is known and the task is to find unification of the contained variables. In particular, we present a constraint model with index variables accompanied by a Boolean model to strengthen inference and hence improve efficiency. The efficiency of models is demonstrated experimentally. 相似文献
39.
Knowing the estimation of a statistical process’s parameters for measured network traffic is very important as it can then be further used for the statistical analyses and modeling of network traffic in simulation tools. It is for this reason that different estimation methods are proposed that allow estimations of the statistical processes of network traffic. One of them is our own histograms comparison (EMHC) based method that can be used to estimate statistical data-length process parameters from measured packet traffic. The main part of EMHC method is Mapping Algorithm with Fragmentation Mimics (MAFM). 相似文献
40.
Eigenvalue analysis of size effect for cohesive crack model 总被引:1,自引:0,他引:1
The paper analyses the effect of structure size on the nominal strength of the structure that is implied by the cohesive (or fictitious) crack model proposed for concrete by Hillerborg et al. A new method to calculate the maximum load of geometrically similar structures of different sizes without calculating the entire load-deflection curves is presented. The problem is reduced to a matrix eigenvalue problem, in which the structure size for which the maximum load occurs at the given (relative) length of the cohesive crack is obtained as the smallest eigenvalue. Subsequently, the maximum load, nominal strength and load-point displacement are calculated from the matrix equilibrium equation. The nonlinearity of the softening stress-displacement law is handled by iteration. For a linear softening law, the eigenvalue problem is linear and independent of the matrix equilibrium equation, and the peak load can then be obtained without solving the equilibrium equation. The effect of the shape of the softening law is studied, and it is found that the size effect curve is not very sensitive to it. The generalized size effect law proposed earlier by Baant, which describes a transition between the horizontal and inclined asymptotes of strength theory and linear elastic fracture mechanics, is found to fit the numerical results very well. Finally some implications for the determination of fracture energy from the size effect tests are discussed. The results are of interest for quasibrittle materials such as concrete, rocks, sea ice and modern tough ceramics. 相似文献