全文获取类型
收费全文 | 2145篇 |
免费 | 70篇 |
国内免费 | 1篇 |
学科分类
工业技术 | 2216篇 |
出版年
2021年 | 38篇 |
2020年 | 13篇 |
2019年 | 19篇 |
2018年 | 33篇 |
2017年 | 36篇 |
2016年 | 42篇 |
2015年 | 19篇 |
2014年 | 54篇 |
2013年 | 108篇 |
2012年 | 90篇 |
2011年 | 112篇 |
2010年 | 83篇 |
2009年 | 104篇 |
2008年 | 98篇 |
2007年 | 99篇 |
2006年 | 82篇 |
2005年 | 70篇 |
2004年 | 62篇 |
2003年 | 62篇 |
2002年 | 74篇 |
2001年 | 33篇 |
2000年 | 32篇 |
1999年 | 38篇 |
1998年 | 51篇 |
1997年 | 48篇 |
1996年 | 43篇 |
1995年 | 40篇 |
1994年 | 34篇 |
1993年 | 35篇 |
1992年 | 31篇 |
1991年 | 34篇 |
1990年 | 36篇 |
1989年 | 29篇 |
1988年 | 24篇 |
1987年 | 27篇 |
1986年 | 25篇 |
1985年 | 42篇 |
1984年 | 34篇 |
1983年 | 18篇 |
1982年 | 26篇 |
1981年 | 20篇 |
1980年 | 17篇 |
1979年 | 29篇 |
1978年 | 23篇 |
1977年 | 24篇 |
1976年 | 22篇 |
1975年 | 22篇 |
1974年 | 14篇 |
1973年 | 18篇 |
1971年 | 11篇 |
排序方式: 共有2216条查询结果,搜索用时 265 毫秒
1.
Thiamine Deficiency Complex (TDC) is an ongoing problem impacting salmonine health in various waterbodies, including Lake Ontario. The prevalence of TDC has been variable and explanations for differences are limited. In the current study, thiamine concentrations were measured in eggs, liver tissue, and muscle tissue sampled from brown trout (Salmo trutta), Chinook salmon (Oncorhynchus tshawytscha), coho salmon (O. kisutch), lake trout (Salvelinus namaycush), and steelhead trout (O. mykiss) that were collected from Lake Ontario and its surrounding tributaries. The occurrence of TDC was measured for each species based on TDC-induced offspring mortality rates under laboratory conditions. TDC-induced offspring mortality was observed for all species except brown trout. For affected species, egg free thiamine (Th) was consistently low compared to lake trout collected from Lake Superior that are considered thiamine replete. In addition, species with the lowest percentages of Th in their eggs were the most susceptible to TDC, suggesting that limited thiamine reserves in the form of Th may cause TDC-induced offspring mortality. Lastly, our results show that egg thiamine concentrations have yearly variation and increased for all species throughout the study. Reasons for such variation are undetermined; but, if egg thiamine concentrations continue to increase, the impacts of TDC on these salmonine species may lessen. Future monitoring is needed for determining if thiamine concentrations are increasing and the potential impacts that may have on the entire Lake Ontario fishery. 相似文献
2.
3.
Magnetic Resonance Materials in Physics, Biology and Medicine - To show the relevance of a simple finite difference transmission line model to help design safe implanted cables in 1.5T MRI’s... 相似文献
4.
5.
Pierre Yves Le Gac Morgane Broudin Gérard Roux Jacques Verdu Peter Davies Bruno Fayolle 《Polymer》2014
Tensile properties and crack propagation properties, especially critical strain energy release rate in mode I, GIC, have been used to investigate fracture properties of elastomers and their relationships with microstructure. These investigations were mainly based on a series of comparisons: first, the behaviour of polychloroprene rubber (CR), undergoing stress hardening due to strain induced crystallization (SIC) and oxidative crosslinking (OCL) was compared with that of chlorinated polyethylene (CPE), which undergoes SIC but not OCL, and with a polyurethane based on hydroxyl terminated polybutadiene (PU) which undergoes OCL but not SIC. Comparisons were also made on CR between fracture behaviour at ambient temperature, where SIC occurs and at 100 °C where there is no SIC. Finally, oxidative crosslinking was used to vary in a continuous way the crosslink density in CR and PU, in order to evaluate the role of crosslinking in fracture behaviour. 相似文献
6.
Bulletin of Engineering Geology and the Environment - Un appareil appelé SAIGNOFOR a été développé pour évaluer la résistance à la compression des terrains... 相似文献
7.
Biological hazards associated with the collection of solid and compostable waste have not been well characterized in North America. This is an issue because workers who handle such materials may be exposed to bioaerosols (airborne bacteria and fungi) and dusts resulting in infections or allergic diseases. We conducted a personal sampling campaign for culturable bacteria and fungi in the breathing zones of waste collectors in a variety of typical work settings (scenarios) in the province of Quebec, Canada. Total culturable bacterial and fungal counts were analyzed and compared to ambient environmental levels (background) to determine the degree of incremental exposure among workers. In several scenarios, worker exposure counts were significantly (p < or = 0.05) higher than ambient levels measured upwind, with the highest personal exposures to bacteria observed for urban compostable waste collectors (median = 50,300 Colony Forming Units/m(3) of air (CFU/m(3))). On the other hand, fungal counts collected on an every-other-week cycle were highest among a group of rural compostable waste collectors (median = 101,700 CFU/m(3)). Similar exposures to culturable bacteria and fungi have been reported in European workers who showed such adverse health effects as nausea, diarrhea, upper respiratory tract irritation, and allergy. Therefore, it may be necessary to modify certain work practices in order to minimize exposure. Recommendations include automation of waste and compost collection, use of personal protective equipment including goggles, gloves, and disposable masks, and meticulous personal hygiene. 相似文献
8.
Specific cationic photoinitiators for near UV and visible LEDs: Iodonium versus ferrocenium structures 下载免费PDF全文
Haifaa Mokbel Joumana Toufaily Tayssir Hamieh Frederic Dumur Damien Campolo Didier Gigmes Jean Pierre Fouassier Joanna Ortyl Jacques Lalevée 《应用聚合物科学杂志》2015,132(46)
Two iodonium salts based on a coumarin chromophore are investigated for polymerization upon light emitting diode irradiations (LEDs). They work as one‐component photoinitiators. They initiate the cationic polymerization of epoxides (under air) and vinylethers (laminate) upon exposure to violet LEDs (385 and 405 nm). Excellent polymerization profiles are recorded. Their efficiency is quite similar to that of a ferrocenium salt. Interpenetrating polymer networks can also be obtained through a concomitant cationic/radical photopolymerization of an epoxy/acrylate blend monomer. The light absorption properties of these new salts as well as the involved photochemical mechanisms are investigated for the first time through electron spin resonance, laser flash photolysis, steady state photolysis experiments. Molecular orbital calculations are also used to shed some light on the initiation mechanisms. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42759. 相似文献
9.
Extensive N‐methylation of chitosan: evaluating the effects of the reaction conditions by using response surface methodology 下载免费PDF全文
Tonimar DA Senra Danilo M Santos Jacques Desbrières Sergio P Campana‐Filho 《Polymer International》2015,64(11):1617-1626
The effects of reaction time, concentration of aqueous sodium hydroxide and molar ratio iodomethane/chitosan on the yield of the reaction of chitosan with iodomethane in N‐methyl‐2‐pyrrolidone (NMP) at 25.0 ± 0.1 °C, as well as on the characteristics of the resulting N,N,N‐trimethylchitosan (TMCh), were evaluated by using full‐factorial 23 design analysis and response surface methodology. This study also aimed to determine the reaction conditions allowing the production of water‐soluble TMCh presenting a high average degree of quaternization and intrinsic viscosity at high reaction yield. 1H NMR spectroscopy was employed for structural characterization, including the determination of average degrees of acetylation () and quaternization (), while capillary viscometry was used to determine intrinsic viscosity [η]. The results show that when the extensive N‐methylation is carried out for 24 h in NMP/15% NaOH (w/v) employing a lower excess of iodomethane (CH3I/Ch = 9), water‐soluble highly substituted ( = 46.0%) TMCh ([η] = 213.0 mL g?1) can be produced in high yield (81.8%). The highly significant mathematical models resulting from this study describe the dependence of the experimental responses on the reaction conditions and allow the characteristics and properties of the resulting TMCh to be defined by properly choosing the reaction conditions. © 2015 Society of Chemical Industry 相似文献
10.
Comparative study on volatile compounds,fatty acids,squalene and quality parameters from whole fruit,pulp and seed oils of two tunisian olive cultivars using chemometrics 下载免费PDF全文