首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   322517篇
  免费   5332篇
  国内免费   2470篇
电工技术   6614篇
技术理论   5篇
综合类   1187篇
化学工业   50899篇
金属工艺   13840篇
机械仪表   9973篇
建筑科学   8009篇
矿业工程   2083篇
能源动力   7219篇
轻工业   30960篇
水利工程   3593篇
石油天然气   7717篇
武器工业   283篇
无线电   33908篇
一般工业技术   62956篇
冶金工业   57794篇
原子能技术   7803篇
自动化技术   25476篇
  2021年   3208篇
  2020年   2229篇
  2019年   2746篇
  2018年   4695篇
  2017年   4633篇
  2016年   5108篇
  2015年   3607篇
  2014年   5842篇
  2013年   14378篇
  2012年   9622篇
  2011年   12517篇
  2010年   10055篇
  2009年   10865篇
  2008年   11615篇
  2007年   11700篇
  2006年   10274篇
  2005年   8967篇
  2004年   8205篇
  2003年   7706篇
  2002年   7622篇
  2001年   7710篇
  2000年   7311篇
  1999年   7185篇
  1998年   16017篇
  1997年   11768篇
  1996年   8940篇
  1995年   6844篇
  1994年   6237篇
  1993年   6119篇
  1992年   4782篇
  1991年   4642篇
  1990年   4744篇
  1989年   4657篇
  1988年   4309篇
  1987年   3769篇
  1986年   3779篇
  1985年   4203篇
  1984年   3940篇
  1983年   3711篇
  1982年   3276篇
  1981年   3468篇
  1980年   3168篇
  1979年   3374篇
  1978年   3250篇
  1977年   3495篇
  1976年   4478篇
  1975年   2936篇
  1974年   2750篇
  1973年   2778篇
  1972年   2370篇
排序方式: 共有10000条查询结果,搜索用时 203 毫秒
51.
Powder Metallurgy and Metal Ceramics - The infiltration of aluminum melts into porous metal skeletons produced by powder metallurgy methods, including 3D printing, under a pressure gradient was...  相似文献   
52.
As a solid state joining process, ultrasonic spot welding has been proven to be a promising technique for joining copper alloys. However, challenges still remain in employing ultrasonic spot welding to join copper alloys. This article comprehensively reviews the current state of ultrasonic spot welding of copper alloys with a number of critical issues including materials flow, plastic deformation, temperature distribution, vibration, relative motion, vertical displacement, interface friction coefficient, online monitoring technique, coupled with the macrostructure and microstructure, the mechanical properties and electrical conductivity. In addition, the future trends in this field are provided.  相似文献   
53.
Upper Barremian – Lower Aptian inner platform “Urgonian” limestones in the Mont de Vaucluse region, SE France, consist of alternating metre-scale microporous and tight intervals. This paper focuses on the influence of structural deformation on the reservoir properties of the Urgonian limestone succession in a study area near the town of Rustrel. Petrographic, petrophysical and structural data were recovered from five fully-cored boreholes, from the walls of a 100 m long underground tunnel, and from a 50 m long transect at a nearby outcrop. The data allowed reservoir property variations in the Urgonian limestones to be studied from core to reservoir scale. Eleven Reservoir Rock Types (RRTs) were identified based on petrographic features (texture, grain size), reservoir properties (porosity, permeability), and the frequency of structural discontinuities such as fractures, faults and stylolites. Tight and microporous reservoir rock types were distinguished. Tight reservoir rock types were characterised by early cementation of intergranular pore spaces and by the presence of frequent structural discontinuities. By contrast microporous reservoir rock types contained preserved intragranular microporosity and matrix permeability, but had very few structural discontinuities. Observed vertical alternations of microporous and tight rock types are interpreted to have been controlled by the early diagenesis of the Urgonian carbonates. Deformation associated with regional-scale tectonic phases, including Albian – Cenomanian “Durancian” uplift (∼105 to 96 Ma) and Pyrenean compression (∼55 to 25 Ma), resulted in the modification of the initial petrophysical properties of the Urgonian limestones. An early diagenetic imprint conditioned both the intensity of structural deformations and the associated circulations of diagenetic and meteoric fluids. Evolution of the Reservoir Rock Types is therefore linked both to the depositional conditions and to subsequent phases of structural deformation.  相似文献   
54.
55.
Pinhão seed is an unconventional source of starch and the pines grow up in native forests of southern Latin America. In this study, pinhão starch was adjusted at 15, 20 and 25% moisture content and heated to 100, 110 and 120 °C for 1 h. A decrease in λ max (starch/iodine complex) was observed as a result of increase in temperature and moisture content of HMT. The ratio of crystalline to amorphous phase in pinhão starch was determined via Fourier transform infra red by taking 1045/1022 band ratio. A decrease in crystallinity occurred as a result of HMT. Polarised light microscopy indicated a loss of birefringence of starch granules under 120 °C at 25% moisture content. Granule size distribution was further confirmed via scanning electron microscopy which showed the HMT effects. These results increased the understanding on molecular and structural properties of HMT pinhão starch and broadened its food and nonfood industrial applications.  相似文献   
56.
The viability and β‐galactosidase activity of four Lactobacillus strains in milk drink containing gums during 28 days of refrigerated storage at 4 °C were assessed. The population of Lactobacillus rhamnosus GGB101 and Lactobacillus rhamnosus GGB103 were maintained, whereas the population of Lactobacillus reuteri DSM20016 and Lactobacillus reuteri SD2112 significantly decreased. The recommended level of 6 log CFU g?1 was exceeded for all tested trains throughout storage. The highest viable number of Lactobacillus rhamnosus GGB103 (8.76 ± 0.03 log CFU mL?1) was obtained in the product containing carrageenan–maltodextrin. The addition of guar–locust bean–carrageenan led to 20‐fold increase in the level of β‐galactosidase activity for L. rhamnosus GGB101 (1208 ± 2.12 Miller units mL?1) compared to the control (61 ± 2.83 Miller units mL?1). Our results suggested that gums could be added to milk to improve viability and enhance β‐galactosidase activity of Lactobacillus.  相似文献   
57.
58.
59.
60.
基于香豆素类化合物在化妆品中的使用情况及其对人体健康的危害,采用C18色谱柱作为分析柱,通过优化试验条件建立了一种可准确、简便测定化妆品中多种香豆素类化合物的高效液相色谱法。试验结果表明,7种香豆素类化合物的保留时间和峰面积的相对标准偏差分别小于0.1%和2%,且检出限均低于40μg/L;通过样品加标试验,得到7种目标化合物的回收率为80%~94%。所建立方法具有快速、简便、准确、灵敏的特点,是测定化妆品中多种香豆素类化合物的有效方法。  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号