全文获取类型
收费全文 | 19905篇 |
免费 | 1715篇 |
国内免费 | 870篇 |
专业分类
电工技术 | 1377篇 |
技术理论 | 2篇 |
综合类 | 1239篇 |
化学工业 | 3365篇 |
金属工艺 | 1100篇 |
机械仪表 | 1176篇 |
建筑科学 | 1422篇 |
矿业工程 | 513篇 |
能源动力 | 639篇 |
轻工业 | 1510篇 |
水利工程 | 396篇 |
石油天然气 | 1027篇 |
武器工业 | 141篇 |
无线电 | 2211篇 |
一般工业技术 | 2545篇 |
冶金工业 | 1049篇 |
原子能技术 | 265篇 |
自动化技术 | 2513篇 |
出版年
2024年 | 56篇 |
2023年 | 316篇 |
2022年 | 486篇 |
2021年 | 805篇 |
2020年 | 644篇 |
2019年 | 514篇 |
2018年 | 594篇 |
2017年 | 639篇 |
2016年 | 606篇 |
2015年 | 778篇 |
2014年 | 989篇 |
2013年 | 1170篇 |
2012年 | 1243篇 |
2011年 | 1434篇 |
2010年 | 1188篇 |
2009年 | 1159篇 |
2008年 | 1176篇 |
2007年 | 1194篇 |
2006年 | 1104篇 |
2005年 | 939篇 |
2004年 | 674篇 |
2003年 | 609篇 |
2002年 | 656篇 |
2001年 | 526篇 |
2000年 | 439篇 |
1999年 | 428篇 |
1998年 | 383篇 |
1997年 | 320篇 |
1996年 | 299篇 |
1995年 | 242篇 |
1994年 | 214篇 |
1993年 | 146篇 |
1992年 | 124篇 |
1991年 | 84篇 |
1990年 | 50篇 |
1989年 | 68篇 |
1988年 | 47篇 |
1987年 | 35篇 |
1986年 | 21篇 |
1985年 | 21篇 |
1984年 | 14篇 |
1983年 | 11篇 |
1982年 | 11篇 |
1981年 | 5篇 |
1980年 | 4篇 |
1978年 | 4篇 |
1976年 | 7篇 |
1975年 | 3篇 |
1967年 | 2篇 |
1957年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 140 毫秒
51.
52.
J. Chen J. B. Xu K. Xue J. An N. Ke W. Cao H. B. Xia J. Shi D. C. Tian 《Microelectronics Reliability》2005,45(1):137-142
Transition-metal compound TiC60 thin films were grown by co-deposition from two separated sources of fullerene C60 powder and titanium. Study of structural properties of the films, by Raman spectroscopy, atomic force microscopy, and scanning tunneling spectroscopy reveals that the films have a deformed C60 structure with certain amount of sp3 bonds and a rough surface with a large number of nanoclusters. z–V tunnelling spectroscopic measurements suggest that several charge transport mechanisms are involved in as the tip penetrates into the thin film. Conventional field electron emission (FEE) measurements show a high emission current density of 10 mA/cm2 and a low turn-on field less than 8 V/μm, with the field enhancement factors being 659 and 1947 for low-field region and high-field region, respectively. By exploiting STM tunneling spectroscopy, local FEE on nanometer scale has also been characterized in comparison with the conventional FEE. The respective field enhancement factors are estimated to be 99–355 for a gap varying from 36 to 6 nm. The enhanced FEE of TiC60 thin films can be ascribed to structural variation of C60 in the films and the electrical conducting paths formed by titanium nanocrystallites embedded in C60 matrix. 相似文献
53.
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
54.
Nguyen An Tien I. Ya. Mittova O. V. Almjasheva S. A. Kirillova V. V. Gusarov 《Glass Physics and Chemistry》2008,34(6):756-761
Nanocrystalline LaFeO3 is prepared by the dehydration of coprecipitated lanthanum and iron(III) hydroxides. It is shown that the behavior of the samples during heating and the size distribution of LaFeO3 nanocrystals can be considerably different depending on the scheme used for coprecipitation of lanthanum and iron hydroxides; independently of the method employed for coprecipitation of the initial compounds, sintering of the samples at 950°C leads to the formation of lanthanum orthoferrite crystals up to 100 nm in size. 相似文献
55.
We present a numerical study of the packing of uniform spheres under three-dimensional vibration using the discrete element method (DEM), focusing on the effects of vibration condition (amplitude and frequency) and inter-particle frictions (sliding and rolling frictions). The results are analysed in terms of packing density, coordination number (CN), radial distribution function (RDF) and pore structure. It is shown that increasing either the vibration amplitude or frequency causes packing density to increase initially to a maximum and then decrease. Both vibration frequency and amplitude should be considered to characterize the effect of vibration process on packing structure. The sliding and rolling frictions between particles can decrease packing density since they dissipate energy, although the effect of rolling friction is less significant. In line with the change of packing density, microstructural properties such as CN, RDF and pore distribution also change: a looser packing often corresponds to smaller CN, less peaked RDF and larger but more widely distributed pores. 相似文献
56.
1977年4月间,台北天母地区有22栋5层楼的公寓住宅,在广告攻势展开的第4天,即开始接受订购。到了订购的第3天,即达成10O%的销售成绩。其立竿见影效果之高,销售速度之快,为众房地产商所瞩目。这批公寓住宅的投资兴建者是台湾信托投资公司。其特色是采取凹型设计,数幢房屋合围着一块百余坪的空地。将这块空地再设计成一座小花园,即形成数幢房屋合围着一片有百余坪的绿地花园,对住户而言,颇为理想。设计完成后,台湾信托就准备刊播广告进行销售。广告代理商经过多次会商确定广告战略:1、强调这是金融业所兴建销售的房屋。2、强调房屋具有别墅的… 相似文献
57.
功率因数校正技术越来越成为电源行业研究的热点。文中介绍了适用于雷达等设备的250W带功率因数校正整流电源模块的设计,分析了其中升压电感器设计、主开关管保护、控制电路消振、散热设计和表面贴装等关键技术,完成了实验研究,获得了满意的试验结果。 相似文献
58.
59.
本文介绍了由西门子S7—226PLC与MM440变频器组成的电气控制系统在光缆护套机速度控制中的应用。并对该系统的控制原理作了详细的阐述。 相似文献
60.
A good understanding of environmental effects on structural modal properties is essential for reliable performance of vibration-based damage diagnosis methods. In this paper, a method of combining principal component analysis (PCA) and support vector regression (SVR) technique is proposed for modeling temperature-caused variability of modal frequencies for structures instrumented with long-term monitoring systems. PCA is first applied to extract principal components from the measured temperatures for dimensionality reduction. The predominant feature vectors in conjunction with the measured modal frequencies are then fed into a support vector algorithm to formulate regression models that may take into account thermal inertia effect. The research is focused on proper selection of the hyperparameters to obtain SVR models with good generalization performance. A grid search method with cross validation and a heuristic method are utilized for determining the optimal values of SVR hyperparameters. The proposed method is compared with the method directly using measurement data to train SVR models and the multivariate linear regression (MLR) method through the use of long-term measurement data from a cable-stayed bridge. It is shown that PCA-compressed features make the training and validation of SVR models more efficient in both model accuracy and computational costs, and the formulated SVR model performs much better than the MLR model in generalization performance. When continuously measured data is available, the SVR model formulated taking into account thermal inertia effect can achieve more accurate prediction than that without considering thermal inertia effect. 相似文献