全文获取类型
收费全文 | 424389篇 |
免费 | 73996篇 |
国内免费 | 47534篇 |
专业分类
电工技术 | 32516篇 |
技术理论 | 5篇 |
综合类 | 21428篇 |
化学工业 | 62483篇 |
金属工艺 | 34790篇 |
机械仪表 | 12980篇 |
建筑科学 | 17348篇 |
矿业工程 | 14299篇 |
能源动力 | 13387篇 |
轻工业 | 45093篇 |
水利工程 | 9843篇 |
石油天然气 | 17525篇 |
武器工业 | 3743篇 |
无线电 | 55562篇 |
一般工业技术 | 76064篇 |
冶金工业 | 53174篇 |
原子能技术 | 6607篇 |
自动化技术 | 69072篇 |
出版年
2024年 | 2727篇 |
2023年 | 4618篇 |
2022年 | 5833篇 |
2021年 | 7277篇 |
2020年 | 9781篇 |
2019年 | 19813篇 |
2018年 | 22486篇 |
2017年 | 23748篇 |
2016年 | 23856篇 |
2015年 | 21644篇 |
2014年 | 21933篇 |
2013年 | 27683篇 |
2012年 | 23057篇 |
2011年 | 21706篇 |
2010年 | 18613篇 |
2009年 | 16202篇 |
2008年 | 15106篇 |
2007年 | 14724篇 |
2006年 | 12653篇 |
2005年 | 11357篇 |
2004年 | 13715篇 |
2003年 | 11955篇 |
2002年 | 11647篇 |
2001年 | 10985篇 |
2000年 | 10134篇 |
1999年 | 9913篇 |
1998年 | 16686篇 |
1997年 | 12933篇 |
1996年 | 10544篇 |
1995年 | 8801篇 |
1994年 | 7775篇 |
1993年 | 7452篇 |
1992年 | 6375篇 |
1991年 | 5529篇 |
1990年 | 5199篇 |
1989年 | 5043篇 |
1988年 | 4498篇 |
1987年 | 3313篇 |
1986年 | 3309篇 |
1985年 | 3611篇 |
1984年 | 3465篇 |
1983年 | 3182篇 |
1982年 | 2848篇 |
1981年 | 3055篇 |
1980年 | 2755篇 |
1979年 | 2899篇 |
1978年 | 2834篇 |
1977年 | 2881篇 |
1976年 | 3903篇 |
1975年 | 2635篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
981.
Apparent carbon aromaticities, fa, of some asphaltenes have been measured by n.m.r. in solution and compared with those obtained by the CP/MAS technique on solid samples. The aromaticities were also measured for several Alberta plains coals. From the 1H solution spectra and 13C solid nmr spectra of asphaltenes, some of their skeletal features, not obtainable from solution spectra only, have been suggested. 相似文献
982.
Plastic deformation and fracture of binary TiAl-base alloys 总被引:4,自引:0,他引:4
The mechanical behavior of binary TiAl alloys containing 46 to 60 at. pct Al has been studied in bulk materials preparedvia rapid solidification processing. Bending and tensile tests were carried out at room temperature as a function of Al concentration.
A few alloys were also tested from liquid nitrogen temperature to ∼ 1000°C. Deformation substructures were studied by analytical
transmission electron microscopy and fracture modes by scanning electron microscopy (SEM). It was found that both microstructure
and composition strongly affect the mechanical behavior of TiAl-base alloys. A duplex structure, which contains both primary
y grains and transformedγ/α
2 lamellar grains, is more deformable than a single-phase or a fully transformed structure. The highest plasticities are observed
in duplex alloys containing 48–50 at. pct Al after heat treatment in the center of theγ + α phase field. The deformation of these duplex alloys is facilitated by 1/2[110] slip and {111} twinning, but very limited
superdislocation slip occurs. The twin deformation is suggested to result from a lowered stacking fault energy due to oxygen
depletion or an intrinsic change in chemical bonding. Other factors, such as grain size and grain boundary chemistry and structure,
are important from a fracture point of view. The results on the deformation and fracture modes as a function of test temperature
are also discussed. 相似文献
983.
984.
Joos F. Miguel Snaddon Robert W. L. Johnson Neil A. 《Industry Applications, IEEE Transactions on》1985,(6):1366-1372
Droplet growth is examined in a water-in-oil type emulsion where the droplets are subjected exclusively to viscous and dielectrophoretic forces. The latter are produced by the interaction of the droplets with an otherwise uniformly imposed electric field. Theoretical considerations are presented as a basis for understanding and interpreting the experiments. An emulsion consisting of deionized water droplets in a silicone oil of specific gravity I is subjected to a uniform 60 Hz, ac electrostatic field. Initially, the droplets are fairly monodisperse with mean diameters of approximately 25 , sm. The changes in droplet size distributions with time are examined with a laser diffraction system for water volume fractions ranging from 0.001 to 0.1 and applied fields ranging from 52 to 520 kVm-1. The average droplet size increases exponentially with time; we examine the exponent's dependence on average field strength and droplet volume fraction. 相似文献
985.
986.
A 1.3 ?m laser in a compact disc package is coupled to single-mode fibre using two graded-index lenses in a nearly confocal scheme. An increase in the alignment tolerance at the lens-lens interface by a factor of six suggests the design for a potentially very low-cost connectorised laser package. The coupling efficiency of approx. 6% (?12 dB) is shown to be adequate for local loop applications. 相似文献
987.
Canham R.O. Smith S.L. Tyrrell A.M. 《Vision, Image and Signal Processing, IEE Proceedings -》2005,152(6):741-749
Complex and highly distorted line drawings are produced by subjects attempting the Rey Complex Figure test, a clinical test of neuropsychological assessment. However, the marking scheme conventionally employed can be subjective and unreliable. In this paper, the first stages in automating this scoring system are investigated using a robust technique to locate a reduced set of scoring sections and a knowledge-based system that employs spatial metrics and fuzzy approximation techniques. Testing the technique using clinical data produced encouraging results that support the argument that this is a feasible approach for implementing a fully automated system, and that in its current state, can be immediately applied in a semi-automated system. 相似文献
988.
Measurements of gel time of the epoxy system DGEBA(n=0)/m-XDA were carried out using rheometry and dielectric analysis with the objective of checking the validity of Mangion-Johari equation (DEA) and Harran-Laudouard criterium (rheometry) for gel time determination. In this work, gel times obtained by rheometry and dielectric analysis are compared and conversions at gel time calculated. From the experimental results obtained for gel times it was found a reasonable agreement between the two techniques that lead to gel conversion values very close to those obtained using Flory equation. 相似文献
989.
Based on the basic operating principal and the technology characteristic of electron beam physical vapor deposition(EBPVD) technique, EBPVD was used to prepare the micro-layer composites. The effect on the substrate preheating temperature was taken into accounts and the finite element analysis package ANSYS was used to simulate the internal stress field and the potential displacement changing tendency. The results show that one of the most important quality factors on the judgment of micro-layer composites is the adhesion between the substrate and the deposition layers as well as among the different deposition layers. Besides the existance of temperature gradient through the thickness of layers, the main reason for the internal stress in micro-layer composites is the mismatch of various properties of the layer and the substrate of different thermal expansions and crystal lattice types. With the increase of substrate preheating temperature, the inter-laminar shear stress also takes on a tendency of increase but the axial residual stress decrease. 相似文献
990.
Nucleation of solidification in liquid droplets 总被引:2,自引:0,他引:2
Analytical and numerical methods have been developed to analyze the solidification kinetics of a mass of liquid droplets dispersed
in a fluid or solid matrix using classical nucleation theory. The resulting analytical expressions and numerical calculations
can be compared directly with calorimetric measurements of the droplet solidification exotherms to obtain information about
the nucleation mechanism. With increasing contact angle at the solid-liquid-matrix triple point, the solidification onset,
peak, and end temperatures and exothermic peak height all decrease sharply and the droplet solidification exotherms become
broader. Decreasing either the droplet radius or the number of potential catalytic nucleation sites produces a similar but
smaller effect. Distributions in droplet radius, contact angle, and nucleation sites have no effect on the solidification
peak temperature, but the droplet solidification exotherms become broader and more symmetric. The solidification onset temperature
is independent of cooling rate in the calorimeter, but the solidification peak and end temperatures decrease and the exothermic
peak height increases with increasing cooling rate. Predicted droplet solidification exotherms are in excellent agreement
with detailed experimental measurements on 10-nm-radius Cd droplets embedded in a solid Al matrix. Analytical predictions
give best-fit values of 43 deg and 430 for the contact angle and the number of potential catalytic nucleation sites per droplet,
respectively; numerical predictions give best-fit values of 43 deg and 750 for the contact angle and the number of potential
catalytic nucleation sites per droplet, respectively. 相似文献