全文获取类型
收费全文 | 85302篇 |
免费 | 8355篇 |
国内免费 | 2168篇 |
专业分类
电工技术 | 616篇 |
综合类 | 3656篇 |
化学工业 | 40272篇 |
金属工艺 | 4124篇 |
机械仪表 | 1250篇 |
建筑科学 | 1150篇 |
矿业工程 | 1947篇 |
能源动力 | 10613篇 |
轻工业 | 4936篇 |
水利工程 | 200篇 |
石油天然气 | 1885篇 |
武器工业 | 650篇 |
无线电 | 3804篇 |
一般工业技术 | 14954篇 |
冶金工业 | 1980篇 |
原子能技术 | 418篇 |
自动化技术 | 3370篇 |
出版年
2024年 | 253篇 |
2023年 | 3495篇 |
2022年 | 2949篇 |
2021年 | 3434篇 |
2020年 | 4752篇 |
2019年 | 3741篇 |
2018年 | 3199篇 |
2017年 | 4006篇 |
2016年 | 4286篇 |
2015年 | 4649篇 |
2014年 | 6741篇 |
2013年 | 7251篇 |
2012年 | 6755篇 |
2011年 | 6644篇 |
2010年 | 4929篇 |
2009年 | 5072篇 |
2008年 | 2652篇 |
2007年 | 4342篇 |
2006年 | 3616篇 |
2005年 | 1896篇 |
2004年 | 1028篇 |
2003年 | 1113篇 |
2002年 | 1250篇 |
2001年 | 1086篇 |
2000年 | 719篇 |
1999年 | 802篇 |
1998年 | 413篇 |
1997年 | 209篇 |
1996年 | 347篇 |
1995年 | 305篇 |
1994年 | 202篇 |
1993年 | 181篇 |
1992年 | 182篇 |
1991年 | 170篇 |
1990年 | 202篇 |
1989年 | 234篇 |
1988年 | 383篇 |
1987年 | 863篇 |
1986年 | 823篇 |
1985年 | 241篇 |
1984年 | 52篇 |
1983年 | 30篇 |
1982年 | 47篇 |
1981年 | 22篇 |
1980年 | 16篇 |
1978年 | 17篇 |
1976年 | 16篇 |
1974年 | 16篇 |
1973年 | 17篇 |
1951年 | 105篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
251.
Recently, in our laboratory a closed form expression for the correlation function of the hard-sphere dimer fluid obtained
from Wertheims multidensity Ornstein-Zernike integral equation theory with Percus-Yevick approximation was presented by Kim
et al. [2001]. However, it is difficult to apply its expression to perturbation theory and vapor-liquid equilibria calculations,
since it is of very complex form. In this work, we present a simplified expression for the first shell of the radial distribution
function (RDF) of the hard-sphere dimer fluid using a series expansion of the analytical expression. The expansion is carried
out in terms of both the packing fraction and the radial distance. Expressions are also obtained for the coordination number
and its first and second derivatives as functions of radial distance and packing fraction. These expressions, which are useful
in perturbation theory, are simpler to use than those obtained from the starting equation, while giving good agreement with
the original expression results. Then we present an simplified equation of state for the square-well dimer fluid of variable
well width (λ) based on Barker-Henderson perturbation theory using its expression for the radial distribution function of
the hard-sphere dimer fluid, and test its expression with NVT and Gibbs ensemble Monte Carlo simulation data [Kim et al.,
2001]. 相似文献
252.
Natalia Andronova 《Polymer》2005,46(18):6746-6755
The synthesis and characterization of degradable polymeric networks for biomedical applications was performed. Cross-linked films of poly(ε-caprolactone) (PCL) and poly(1,5-dioxepan-2-one) (PDXO) having various mole fractions of monomers and different cross-link densities were successfully prepared using 2,2′-bis-(ε-caprolactone-4-yl) propane (BCP) as cross-linking agent. Reaction parameters were carefully examined to optimise the film-forming conditions. Networks obtained were elastomeric materials, easy to cast and remove from the mould. Effect of CL content and cross-link density on the final properties of the polymer network was evaluated. High CL content or degree of cross-linking led to increase in Young's modulus and decrease in elongation at break. An increase in crystalline domains in films having a higher CL content was observed by optical microscopy. A greater thermal stability was observed in films having a high CL content. The hydrophilicity of the materials could be tailored by changing the CL content. The surface of the films became rougher with higher CL content. 相似文献
253.
In the present study, various diffusive processes have been investigated during foaming of powdered precursors of polyimide. A detailed analysis of the powdered precursor's characteristics allows for an enhanced morphological understanding of the resulting microstructures and foam unit cell. Parameters that are central to the foaming process such as particle morphology, volatile concentration and sorption-desorption processes are evaluated. Isothermal and non-isothermal desorption experiments have been carried out by thermogravimetric analysis (TGA), and specific diffusive processes have been correlated to thermodynamic and kinetic transitions by means of modulated differential scanning calorimetry (MDSC) of the corresponding materials. It was found that two primary fluxes of volatiles, one out of the external surface of the particles (responsible for volatile desorption) and the other into the growing bubble (responsible for vapor supersaturation inside the bubble) compete against each other creating a competitive scenario that becomes the controlling factor for potential inflation within the precursor particles. 相似文献
254.
《Fuel Processing Technology》2005,87(1):71-76
Oil agglomeration of Sivas–Divriği (S–D) Uluçayır lignite fines was carried out using kerosene and kerosene–extract oil (which was obtained from lignite treated with microwave energy) mixture as a bridging oil. The effects of parameters such as the amount and type of bridging oil, microwave time and particle size on the agglomeration performance were investigated. The amount of kerosene was varied from 5 to 30 wt.% of the initial lignite loading. The values of the grade and recovery increased with an increase in the amount of kerosene added. Extract oil fraction of the lignite extract at various ratios in kerosene increased the agglomeration recovery from 95.88% to 98.55%. The effect of microwave time was investigated and it was found that the grade was also increased with increasing microwave time (4, 8 and 10 min). The grade of char (microwave time: 8 min) was increased in comparison with the original lignite while decreasing its recovery. Dense medium separations of the lignite were conducted and the results of their grade recovery performances were compared with those of agglomeration of the particles. During the inspection of particle size effect on the dense medium separation, the recovery was increased remarkably (from 12.07% to 89.50%) with increasing particle size, while decreasing the grade (from 0.732 to 0.697). In the oil agglomeration of lignite the recovery values were increased with increasing particle size. 相似文献
255.
《Materials Letters》2007,61(14-15):2904-2907
Large-scale uniform Ag microtubes with high length diameter ratios have been first successfully synthesized by a facile approach, using low-cost super fine glass fibers as templates. The samples were characterized by SEM and XRD. The investigations showed that calcining or adding of PEG-1000 and alcohol could greatly improve the mechanical strength of the sample. Especially the products exhibited favorable catalytic properties during the degradation of Rhodamine B by NaBH4. 相似文献
256.
高纯铝箔通常通过电化学扩面后用作铝电解电容器的阳极材料。利用铝箔(100)面隧道孔制备纳米模板。这种纳米模板的特点是制作简单、模板面积大,纳米阵列材料形状可控性强。还利用两步电化学侵蚀铝箔的特殊工艺,研制出纵横交错的TiO2纳米有序阵列材料。 相似文献
257.
Min Chan Kim Dong Won Lee Chang Kyun Choi 《Korean Journal of Chemical Engineering》2008,25(6):1239-1244
When a horizontal homogeneous solid is melted from below, convection can be induced in a thermally unstable melt layer. In
this study the onset of buoyancy-driven convection during time-dependent melting is investigated by using similarly transformed
disturbance equations. The critical Rayleigh numbers based on the melt-layer thickness are found numerically for various conditions.
For small superheats, the present predictions approach the well known results of classical Rayleigh-Bénard problems, that
is, critical Rayleigh numbers are located between 1,296 and 1,708, regardless of the Prandtl number. However, for high superheats
the critical Rayleigh number increases with an increase in phase change rate but with decrease in Prandtl number. 相似文献
258.
259.
Junwei Fu Zhengbiao Zhang Zhenping Cheng Jian Zhu Wei Zhang Xiulin Zhu 《Polymer Bulletin》2008,61(3):287-297
A novel reversible addition-fragmentation chain transfer (RAFT) reagent bearing triphenylamine (TPA)
group, 4-diphenylamino-dithiobenzoic acid benzyl ester (DDABE), was designed and synthesized. It was used
in the RAFT polymerizations of styrene (St) and methyl acrylate (MA) to prepare end-functionalized polymers.
The results of the polymerization showed that the RAFT polymerizations could be well controlled using DDABE
as the RAFT agent. Number-average molecular weight (Mn,GPC) increased linearly
with monomer conversion, and molecular weight distributions were relatively narrow (PDI<
1.50). The results of chain-extension reaction, 1H NMR spectra and UV/Vis
spectra confirmed that most of the polymers chains were end-capped by the functional triphenylamine
(TPA) groups. The effect of feed molar ratios of St/DDABE/AIBN on polymerization was investigated. 相似文献
260.
Qingzhao Yao Yuming Zhou Yanqing Sun Xiaoyun Ye 《Journal of Inorganic and Organometallic Polymers and Materials》2008,18(4):477-484
TiO2 hybrid molecular imprinted polymer (MIP) for ethofumesate using methacrylic acid (MAA) as the functional monomer and silane
coupling agent 3-(trimethoxysilyl) propylmethacrylate (KH570) as organic–inorganic connective bridge was synthesized via photo-excitation
method. Hydrogen bond was proved to act between MAA and ethofumesate for pre- and post-polymerization binding properties as
testified by UV spectrometric method. KH570 modified TiO2 nanoparticles were prepared via sonochemical reaction, which can accelerate hydrolysis, increase collision chance for the
reactive system and improve the dispersion of the nanoparticles. Scanning electron microscope (SEM), transmission electron
microscope (TEM), binding and the adsorption kinetics experiments as well as thermogravimetric analysis (TGA) were employed
for characterization. The results indicated that the hybrid MIP revealed a larger surface area and more ordered imprinting
cavities with improved thermal stability compared to organic-only MIP. Furthermore, faster adsorption kinetics and enhancive
adsorption capacity were achieved, which made it promising in chemical sensor applications. 相似文献