全文获取类型
收费全文 | 1172篇 |
免费 | 31篇 |
国内免费 | 59篇 |
专业分类
电工技术 | 30篇 |
综合类 | 23篇 |
化学工业 | 248篇 |
金属工艺 | 145篇 |
机械仪表 | 37篇 |
建筑科学 | 75篇 |
矿业工程 | 6篇 |
能源动力 | 49篇 |
轻工业 | 120篇 |
水利工程 | 4篇 |
石油天然气 | 49篇 |
武器工业 | 3篇 |
无线电 | 44篇 |
一般工业技术 | 238篇 |
冶金工业 | 66篇 |
原子能技术 | 26篇 |
自动化技术 | 99篇 |
出版年
2024年 | 1篇 |
2023年 | 12篇 |
2022年 | 17篇 |
2021年 | 36篇 |
2020年 | 33篇 |
2019年 | 21篇 |
2018年 | 29篇 |
2017年 | 32篇 |
2016年 | 40篇 |
2015年 | 40篇 |
2014年 | 83篇 |
2013年 | 118篇 |
2012年 | 70篇 |
2011年 | 99篇 |
2010年 | 50篇 |
2009年 | 70篇 |
2008年 | 70篇 |
2007年 | 66篇 |
2006年 | 56篇 |
2005年 | 60篇 |
2004年 | 50篇 |
2003年 | 45篇 |
2002年 | 30篇 |
2001年 | 17篇 |
2000年 | 27篇 |
1999年 | 19篇 |
1998年 | 22篇 |
1997年 | 6篇 |
1996年 | 7篇 |
1995年 | 7篇 |
1994年 | 9篇 |
1993年 | 5篇 |
1992年 | 6篇 |
1991年 | 1篇 |
1990年 | 4篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1986年 | 1篇 |
1970年 | 1篇 |
排序方式: 共有1262条查询结果,搜索用时 15 毫秒
91.
The objective of this paper is to describe and interpret the results from a public opinion poll about elderly drivers to provide useful information regarding future challenges related to elderly drivers. The introduction describes demographic developments, factors affecting elderly drivers, crash rates of elderly drivers and characteristics of crashes of elderly drivers. This information is used to provide a context to interpret the results of the public opinion poll. A total of 1238 drivers completed the interview, which required an average of approximately 15 min per respondent. It was administered by telephone to a random sample of Canadian drivers by Opinion Search Inc., in September 2007. Criteria for inclusion were having a valid driver's license and having driven in the past 30 days. Data were weighted according to region, gender and age to avoid bias. Univariate frequency distributions, their 95% confidence intervals and Chi-square statistics were calculated taking account of the stratified and weighted sampling design. Also, multivariate logistic regression was performed, accounting for the design effects of the used sampling design. Lower levels of concern about the issue of elderly drivers were found among the public at large and especially among elderly drivers. While general support for actions to protect elderly drivers was high, elderly drivers were less supportive for a measure requiring them to complete training to maintain their driving privileges. The results from this survey are contrasted against what is known from the literature about the issue of elderly drivers and conclusions regarding future challenges are drawn. 相似文献
92.
Shrinkage of repair material, especially in patching repairs, is the major factor inducing cracking in concrete repairs. Induced cracks in repair materials are due to restrained shrinkage. Although in usual practice, the free shrinkage of the repair mortar is measured, in reality, cracking is not due to free shrinkage. It is well known that cracking is due to restrained shrinkage. It is very hard to measure the restrained shrinkage; therefore, to overcome this problem a restraint factor (R) is used to modify the free shrinkage and come up with the restrained shrinkage. The restraint factor is influenced by the surface and boundary condition.In this study, the restraint factor for patching repair with different boundary conditions (with eaves and without eaves) and surface condition (rough and smooth) of the substrate concrete is investigated.The results show that the restraint factor R lies between 0.1 and 0.94; with an increase of restraint, the restraint factor is increased. In situations with a high level of restraint (eaves at the perimeter and a rough surface of substrate), the average R is 0.83. while with a low level of restraint (without eaves at the perimeter and a smooth surface of the substrate), the average R is 0.22. 相似文献
93.
94.
In this paper we present a Monte Carlo approach for the evaluation of plant maintenance strategies and operating procedures under economic constraints. The proposed Monte Carlo simulation model provides a flexible tool which enables one to describe many of the relevant aspects for plant management and operation such as aging, repair, obsolescence, renovation, which are not easily captured by analytical models. The maintenance periods are varied with the age of the components. Aging is described by means of a modified Brown–Proschan model of imperfect (deteriorating) repair which accounts for the increased proneness to failure of a component after it has been repaired. A model of obsolescence is introduced to evaluate the convenience of substituting a failed component with a new, improved one. The economic constraint is formalized in terms of an energy, or cost, function; optimization studies are then performed using the maintenance period as the control parameter. 相似文献
95.
Chunbao Li Guanghong Zhou Xinglian Xu 《International Journal of Food Science & Technology》2008,43(5):838-845
This study was designed to explore the changes of meat quality characteristics and intramuscular connective tissue of beef semitendinosus muscle during postmortem aging for Chinese Yellow bulls. Semitendinosus muscles were obtained at day 4 postmortem and then further aged for different periods. Chemical determinations, histological and mechanical measurements were performed for the raw and cooked steaks on days 4, 11, 14, 21, and 28 postmortem, respectively. The results showed that postmortem aging resulted in an increase in moisture content and collagen solubility, a decrease in filtering residues, primary perimysial thickness, fibre diameter, Warner‐Bratzler shear force, and transition temperature of the endomysium. The synergic effects of the myofibril and the intramuscular connective tissue determined the tenderness of aged beef. 相似文献
96.
Kezban Candogan Suhendra Kartika Foster B. Wardlaw James C. Acton 《European Food Research and Technology》2008,227(6):1651-1661
Beef sausage mixes were inoculated with either Pediococcus acidilactici with Staphylococcus xylosus or P. acidilactici with S. carnosus, subdivided and then held for 0, 24, 48 or 72 h at 8–10 °C prior to fermentation. After aging (pre-fermentation holding),
the mixes were fermented for 16 h ending at 41 °C. Moisture, protein and fat contents of all sausage mixes did not differ
due to holding effects over all starter cultures. The pH of mixes followed the same pattern for all mixes, declining (p < 0.05) from approximately 5.8 to pH 5.2–5.3 at 72 h aging and to 4.4–4.5 after fermentation. Total acidity of the mixes
followed an inverse pattern to pH, increasing (p < 0.05) after fermentation although there was no effect due to type of starter culture. Aging had no effect on nonprotein
nitrogen (NPN) content as ΔNPN among all cultures. After fermentation, however, sausages held 72 h and inoculated with S. carnosus had higher NPN contents compared to P. acidilactici alone (p < 0.05) and with S. xylosus (p < 0.10). The same effects of starter cultures on changes in total amino acid concentration were observed. Concentrations
of individual amino acids showed increases depending on pre-fermentation aging period (0 h versus 72 h) followed by fermentation. 相似文献
97.
就硫化氢与丁腈橡胶和氢化丁腈橡胶的不饱和双键,以及与丙烯腈侧基的老化反应的机理作了介绍。研究表明:氢化丁腈橡胶具有优异的耐硫化氢性能,适合用来生产石油钻探领域的相关橡胶制品。 相似文献
98.
Oliver I. Strube Daniel Briesenick Johannes Brikmann Bruno Hüsgen 《Polymer-Plastics Technology and Engineering》2015,54(5):494-498
We present an in-depth investigation of contaminated silicone molds by use of scanning electron microscopy, that provides additional insight into the aging process of the molds. The molds lifetime in vacuum casting processes of polyurethane is limited due to contamination with the diisocyanate compound of the PUR resin. SEM investigations, combined with FIB cross-sections and EDX measurements show that three different types of particles are distributed in the contaminated silicone matrix. The particles differ in shape and size, with a range from 50 nm to 50 µm. This explains the loss in transparency and the hardened haptics of contaminated molds. 相似文献
99.
A waterborne aliphatic polyurethane-based coating was studied for accelerated ultra-violet (UV), water (WT), and thermal (TH) aging for a period of 1000 h. To monitor the coating durability, samples were tested every 200 h. ATR-FTIR spectroscopy was used to monitor the chemical changes occurring during the aging process. UV–vis with integrating sphere was used to track the change in diffused reflectance, while the optical microscope and the scanning white light interferometry (SWLI) were used for surface characterization. FTIR studies of coatings subjected to UV exposure indicated a decrease in functional groups such as CONH, CH, CO, and COC. The appearance of functional groups such as NH is attributed to chain scission of the polyurethane binder in the coating. Investigation of the degradation mechanism in water and thermal aging showed physical effects through water penetration and the mismatch in the coefficient of thermal expansion as the primary causes of degradation. In all aging scenarios, the reduction of reflectivity was largely due to physical defects caused by the different aging mechanisms. 相似文献
100.
在己内酰胺水解开环聚合过程中加入一定量的光稳定剂(UV-791),合成改性聚己内酰胺(PA6)树脂.研究了UV-791对PA6光稳定性、热氧稳定性、末端氨基含量的影响.结果表明,UV-791的加入能明显提高PA6的耐紫外光及热氧稳定性,空气氛围下的起始分解温度提升26℃左右;在185℃空气氛围下老化30 min,改性PA6相对黏度下降百分比极低(UV-791含量0.2%时,相对黏度仅下降了1.3%),热氧稳定性明显得到改善.同时,加入量为0.05%时,端氨基含量提高了7.4 mmol/kg.而UV-791对PA6的熔融温度与结晶温度影响不大. 相似文献