全文获取类型
收费全文 | 74819篇 |
免费 | 8557篇 |
国内免费 | 4659篇 |
专业分类
电工技术 | 7672篇 |
技术理论 | 3篇 |
综合类 | 7701篇 |
化学工业 | 11093篇 |
金属工艺 | 2620篇 |
机械仪表 | 4838篇 |
建筑科学 | 9789篇 |
矿业工程 | 2485篇 |
能源动力 | 6011篇 |
轻工业 | 3279篇 |
水利工程 | 6855篇 |
石油天然气 | 4838篇 |
武器工业 | 667篇 |
无线电 | 3042篇 |
一般工业技术 | 5852篇 |
冶金工业 | 3614篇 |
原子能技术 | 1463篇 |
自动化技术 | 6213篇 |
出版年
2024年 | 311篇 |
2023年 | 1053篇 |
2022年 | 2007篇 |
2021年 | 2386篇 |
2020年 | 2521篇 |
2019年 | 2208篇 |
2018年 | 2083篇 |
2017年 | 2553篇 |
2016年 | 2827篇 |
2015年 | 2949篇 |
2014年 | 4323篇 |
2013年 | 4787篇 |
2012年 | 5183篇 |
2011年 | 5896篇 |
2010年 | 4155篇 |
2009年 | 4521篇 |
2008年 | 4223篇 |
2007年 | 5042篇 |
2006年 | 4624篇 |
2005年 | 4032篇 |
2004年 | 3323篇 |
2003年 | 2887篇 |
2002年 | 2393篇 |
2001年 | 2018篇 |
2000年 | 1713篇 |
1999年 | 1386篇 |
1998年 | 1177篇 |
1997年 | 978篇 |
1996年 | 882篇 |
1995年 | 754篇 |
1994年 | 647篇 |
1993年 | 476篇 |
1992年 | 402篇 |
1991年 | 247篇 |
1990年 | 245篇 |
1989年 | 197篇 |
1988年 | 139篇 |
1987年 | 100篇 |
1986年 | 74篇 |
1985年 | 54篇 |
1984年 | 60篇 |
1983年 | 40篇 |
1982年 | 27篇 |
1981年 | 13篇 |
1980年 | 30篇 |
1979年 | 20篇 |
1977年 | 5篇 |
1975年 | 4篇 |
1959年 | 22篇 |
1951年 | 24篇 |
排序方式: 共有10000条查询结果,搜索用时 156 毫秒
111.
淤泥质土状亚粘土的一些特征 总被引:1,自引:0,他引:1
珠江三角洲软土地区存在一种灰色亚粘土,其工程性能与淤泥、淤泥质土相似,但两者的物理力学性质却有明显的不同,这是一种在规范土名定义上处于过渡或边缘状态的粘性土,不是严格定义上的淤泥质土,也不是正常沉积的一般粘性土,土的强度和工程性质与淤泥质土类似,应该近沿海地区淤泥和淤泥质土对待,不应看成一般粘性土。 相似文献
112.
113.
The kinetics of changes in the bound water content in dietetic sucrose-free sponge cakes (DC) during storage was investigated. The effect of edible films of polymyxan, pectin, xanthan, and carboxymethylcellulose upon this kinetics was also investigated. The quantitative changes in both states of water (slightly bound water and strongly bound water) were registered by combined dynamic analysis (thermogravimetry analysis, TGA, and differential thermal analysis, DTA). The moisture changes in DC crumb were analyzed by drying out to constant mass. The rate constants were determined according the equation q = qoe-kt. The values of rate constants 'k', in day-1, concerning the different edible films were as follows: for crumb moisture is (8.00 ≤ k ≤ 12.47) × 10-3, for bound water is (3.07 ≤ kw ≤ 6.26) × 10-2, for slightly bound water is (4.22 ≤ k1 ≤ 8.49) × 10-2 and for strongly bound water is (2.02 ≤ k2 ≤ 5.62) × 10-2 as compared to 18.53 × 10-3, 7.16 × 10-2, 9.04 × 10-2, and 5.36 × 10-2 in the uncovered DC, respectively. The best water-retaining effect in respect to crumb moisture during storage was ascertained in the use of polymyxan and xanthan films. The lowest rate constant values for bound water and its two states were measured for DC covered with pectin. The relation between the kinetics of both bound water states during storage and ageing of the crumb of DC covered with different edible films and the crumb microstructure was represented. By means of scanning electron microscope was read the smallest change in crumb microstructure of pectin-covered DC on the sixth day of storage. 相似文献
114.
针对武钢热轧厂层流冷却系统能耗高,水压不稳,系统反应慢,供水泵工作效率低等缺陷,进行系统改造。提高了系统的控制精度和产品质量,节能降耗取得了明显的效果。 相似文献
115.
在不同频率流量和阻水程度条件下,采用一维明渠非恒定流网河数学模型,分析规划中的佛山市桥梁群对区间河道洪季行洪、枯季水环境的影响,计算洪季不同频率洪峰流量下规划桥梁群对区间河道行洪洪水位、分流比的影响,枯季时规划桥梁群对区间河道过流量、分流比的影响,结果表明,利用一维网河数学模型计算佛山市中心组团规划桥梁群对区间河道断面平均水位、流量和流速的影响,结果有足够的数值精度,是可信的。 相似文献
116.
117.
118.
H. Luo 《Microsystem Technologies》2006,12(4):324-329
This paper focuses on tracking, reconstruction and motion estimation of a well-defined MEMS optical switch from a microscopic
view. For out-of-view reconstruction, a homography capable of transforming feature points and feature lines between a microscopic
image and a CAD model of the switch is implemented. The homography between two sequential microscopic images is decomposed
and factorized for motion estimation. Optical flow has also been explored to provide rough estimations of rotation centre
and angle. The paper also illustrates motion parameter optimization principles to deal with uncertainty inherent in micro
world. After non-linear optimization, estimation accuracy for rotation angle and rotation centre can reach 0.06° and pixel
level, respectively. 相似文献
119.
V. Anjos M.J.V. Bell E.F. da Silva Jr. R.W.A. Franco I.A. Esquef 《Microelectronics Journal》2005,36(11):977-980
In this paper we report the use of photothermal techniques such as Thermal lens (TL) spectrometry, Photoacoustic and heat capacity, ρcp, to determine the thermo-optical parameters, such as thermal conductivity (K), thermal diffusivity (D), specific heat (cp) and the optical path dependence with temperature (ds/dT), of an undoped polycrystalline 3C-SiC. To our knowledge, this is the first time that Thermal lens technique is used for wide band-gap systems. Results obtained for the polycrystalline sample with TL technique indicates that ds/dT is negative at room temperature. Moreover, the obtained values of thermal diffusivity and thermal conductivity are in good agreement with that found in the literature, indicating that the phototermal techniques can be used to obtain the referred parameters in circumstances where other techniques cannot be used, for example, in harsh environments. 相似文献
120.
Lawrence K. Forbes Graeme C. Hocking Simon Wotherspoon 《Journal of Engineering Mathematics》2004,48(1):69-91
Rainwater can collect in a lens-shaped region within the rock of a tropical island, and may be separated from the underlying salt water by a sharp interface. This paper presents a nonlinear theory for determining the shape of this interface. The island is assumed to be saturated with rain, and provision is made for the outflow of rain-water through the sides of the island. The effect of a bore well on the shape of the interface is investigated, and the problem is solved using a spectral method. An integral-equation method is also presented for the case when the island has infinite width. 相似文献