全文获取类型
收费全文 | 42799篇 |
免费 | 4021篇 |
国内免费 | 2657篇 |
专业分类
电工技术 | 3402篇 |
技术理论 | 1篇 |
综合类 | 3590篇 |
化学工业 | 2412篇 |
金属工艺 | 3456篇 |
机械仪表 | 6758篇 |
建筑科学 | 1075篇 |
矿业工程 | 1884篇 |
能源动力 | 557篇 |
轻工业 | 5169篇 |
水利工程 | 373篇 |
石油天然气 | 577篇 |
武器工业 | 301篇 |
无线电 | 3033篇 |
一般工业技术 | 5671篇 |
冶金工业 | 1505篇 |
原子能技术 | 90篇 |
自动化技术 | 9623篇 |
出版年
2024年 | 263篇 |
2023年 | 908篇 |
2022年 | 1486篇 |
2021年 | 1696篇 |
2020年 | 1636篇 |
2019年 | 1280篇 |
2018年 | 1145篇 |
2017年 | 1416篇 |
2016年 | 1512篇 |
2015年 | 1633篇 |
2014年 | 2703篇 |
2013年 | 2249篇 |
2012年 | 3231篇 |
2011年 | 3323篇 |
2010年 | 2370篇 |
2009年 | 2499篇 |
2008年 | 2124篇 |
2007年 | 2851篇 |
2006年 | 2722篇 |
2005年 | 2237篇 |
2004年 | 1809篇 |
2003年 | 1521篇 |
2002年 | 1295篇 |
2001年 | 1108篇 |
2000年 | 879篇 |
1999年 | 698篇 |
1998年 | 519篇 |
1997年 | 430篇 |
1996年 | 344篇 |
1995年 | 319篇 |
1994年 | 275篇 |
1993年 | 216篇 |
1992年 | 175篇 |
1991年 | 132篇 |
1990年 | 115篇 |
1989年 | 118篇 |
1988年 | 74篇 |
1987年 | 29篇 |
1986年 | 27篇 |
1985年 | 12篇 |
1984年 | 7篇 |
1983年 | 15篇 |
1982年 | 13篇 |
1981年 | 6篇 |
1980年 | 9篇 |
1979年 | 7篇 |
1978年 | 5篇 |
1959年 | 5篇 |
1958年 | 3篇 |
1957年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
Influence of Storage Time and Temperature on Absorption of Flavor Compounds from Solutions by Plastic Packaging Materials 总被引:1,自引:0,他引:1
R. Van Willige D. Schoolmeester A. Van Ooij J. Linssen A. Voragen 《Journal of food science》2002,67(6):2023-2031
ABSTRACT: Linear low-density polyethylene (LLDPE), oriented polypropylene (OPP), polycarbonate (PC), polyethylene terephthalate (PET film and PET bottle), and polyethylene naphthalate (PEN) were stored in a model solution containing 10 flavor compounds at 4, 20, and 40 °C and flavor absorption by the plastic materials was followed in time. The absorption rate and/or total amount absorbed increased considerably with temperature from 4 to 40 °C. Depending on storage temperature, total flavor absorption by the polyolefins (LLDPE and OPP) was 3 to 2400 times higher than by the polyesters (PC, PET, and PEN). Therefore, in the factor of flavor absorption, polyesters are preferred over polyolefins as packaging material. 相似文献
122.
123.
124.
125.
Rubina H. Shreiner 《Journal of research of the National Institute of Standards and Technology》2002,107(5):393-399
The stability of solutions having an electrolytic conductivity, κ, of 5 μS/cm to 100 000 μS/cm packaged in glass screw-cap bottles, glass serum bottles, and glass ampoules was monitored for 1 year to 2 years. The conductivity was determined by measuring the ac resistance of the solution. Mass loss was also monitored for solutions packaged in bottles. The solutions were prepared using KCl in water (κ ≥100 μS/cm) or KCl in 30 % (by mass) n-propanol 70 % (by mass) water (κ ≤ 15 μS/cm). The conductivity changes were compared by packaging type and by nominal κ. The main causes of the κ changes are evaporation (screw-cap bottles) and leaching (screw-cap bottles, serum bottles, and ampoules). Evaporation is determined from mass loss data; leaching occurs from the glass container with no change in mass. The choice of optimal packaging, which depends on the conductivity level, is the packaging in which κ changes the least with time. Ampoules are the most suitable packaging for standards having nominal κ values of 500 μS/cm to 100 000 μS/cm. Screw-cap bottles are most suitable for standards having a nominal κ of 5 μS/cm to 100 μS/cm. 相似文献
126.
研究了支撑矢量机的分类机理,并利用支撑矢量机对雷达目标一维像进行了识别.识别的结果表明了该方法的优越性,并显示它可以对残缺不全的样本进行识别. 相似文献
127.
A. Rac 《Tribology International》1985,18(1):29-33
The wear of grey cast iron in dry sliding conditions has been studied with the aims of (1) finding the influence of working conditions on the wear rate, and (2) determining the region of speed and load where low wear is accomplished. Grey cast iron with flake and nodular graphite was submitted to investigation using a pin-on-disc machine. The results indicate that the flake graphite cast iron is more suitable for applications at speeds greater than 4 m s−1 and lower loads, while nodular cast iron has greater wear resistance at lower speeds in the range of loads investigated - from 50 N cm−2 to 200 N cm−2 相似文献
128.
The process of actuation is considered for the inertial element in the improved air-distributing system of pneumatic puncher whose dimensionless parameters are determined. 相似文献
129.
顾玲 《南方冶金学院学报》1992,13(2):134-139
根据振动理论建立了振动力学模型,并用等效刚度方法分析研究了弹性悬挂轮式工程机械行驶平稳性和振动特性。 相似文献
130.
一种简易的容积式灌装机 总被引:1,自引:0,他引:1
介绍了一种用于液体产品分装 ,易于使用的容积可调式灌装机的工艺原理及主要部件的结构 相似文献