全文获取类型
收费全文 | 3016篇 |
免费 | 95篇 |
国内免费 | 1篇 |
学科分类
工业技术 | 3112篇 |
出版年
2021年 | 54篇 |
2020年 | 27篇 |
2019年 | 45篇 |
2018年 | 47篇 |
2017年 | 53篇 |
2016年 | 51篇 |
2015年 | 48篇 |
2014年 | 75篇 |
2013年 | 204篇 |
2012年 | 109篇 |
2011年 | 143篇 |
2010年 | 132篇 |
2009年 | 121篇 |
2008年 | 142篇 |
2007年 | 136篇 |
2006年 | 141篇 |
2005年 | 124篇 |
2004年 | 81篇 |
2003年 | 86篇 |
2002年 | 76篇 |
2001年 | 47篇 |
2000年 | 50篇 |
1999年 | 46篇 |
1998年 | 62篇 |
1997年 | 51篇 |
1996年 | 51篇 |
1995年 | 51篇 |
1994年 | 54篇 |
1993年 | 41篇 |
1992年 | 39篇 |
1991年 | 22篇 |
1990年 | 35篇 |
1989年 | 38篇 |
1988年 | 35篇 |
1987年 | 37篇 |
1986年 | 43篇 |
1985年 | 42篇 |
1984年 | 39篇 |
1983年 | 35篇 |
1982年 | 24篇 |
1981年 | 33篇 |
1980年 | 22篇 |
1979年 | 26篇 |
1978年 | 22篇 |
1977年 | 21篇 |
1976年 | 29篇 |
1975年 | 20篇 |
1974年 | 15篇 |
1973年 | 26篇 |
1971年 | 15篇 |
排序方式: 共有3112条查询结果,搜索用时 15 毫秒
1.
Dr. Lalit N. Goswami Dr. Tyson J. Olds Dr. Terri G. Monk Dr. Quinn L. Johnson Dr. James P. Dilger Dr. Mohammed A. Shanawaz Dr. Satish S. Jalisatgi Dr. M. Frederick Hawthorne Dr. George R. Kracke 《ChemMedChem》2019,14(11):1108-1114
We synthesized a family of neuromuscular blocking agents (NMB) based on decamethonium, but containing a carborane cluster in the methylene chain between the two quaternary ammonium groups. The carborane cluster isomers o-NMB, m-NMB, and p-NMB were tested in animals for neuromuscular block and compared with agents used clinically: rocuronium and decamethonium. All three isomers caused reversible muscle weakness in mice as determined by grip strength and inverted screen tests, with a potency rank of p-NMB > rocuronium > decamethonium > m-NMB > o-NMB. The mechanism of action of the compounds was determined by using the in vitro rat phrenic nerve hemi-diaphragm preparation and electrophysiologic measurements in cells. Neostigmine reversed hemi-diaphragm weakness caused by the three isomers and rocuronium, but not succinylcholine. In electrophysiologic recordings of currents through acetylcholine receptor channels, the carborane compounds did not activate channel activity but did inhibit channel activation by acetylcholine. These results demonstrate that the carborane neuromuscular blocking agents are non-depolarizers in contrast to the depolarizing action of the parent compound. 相似文献
2.
3.
Scientometrics - U.S. university engagement with Africa in various areas including global health, education, environment, and agriculture has grown in the last 15 years. However, there is... 相似文献
4.
Brandon J. Hathaway Jane H. Davidson 《International Journal of Hydrogen Energy》2021,46(29):15257-15267
High efficiency solar steam gasification of biomass is carried out in a prototype molten salt reactor for solar-only and solar-autothermal hybrid operation. Previous demonstration of the prototype 3-kW solar gasifier for steam gasification of cellulose at stoichiometric conditions demonstrated thermal efficiency of 44% during continuous operation at 1200 K. The present work expands the range of operating conditions to consider two challenges. Hybridization between solar and autothermal modes of operation is accomplished by adding oxygen directly to the reactor. Control of the H2:CO ratio of the product gas is accomplished through in-situ steam shifting. Hybridization stabilized temperatures for variations in radiative input as large as a 30% reduction in power, corresponding to conditions where both sensible and chemical heat demands for the process were fully met by exothermic heat release with no significant challenges. Peak efficiencies and carbon conversion values observed are 45% and 99.5% respectively. The resulting product gas stream composition was shifted from a hydrogen and carbon monoxide ratio of 1:1 with stoichiometric steam delivery to a ratio of 1.7:1 with steam at nine times the stoichiometric amount, only slightly lower than equilibrium predictions. The results demonstrate very favorable attributes for the molten salt reactor in a continuous fuel production process. 相似文献
5.
6.
Presented here is an investigation of the structure–property relationships of crosslinked networks using three bi-functional glycidyl ether aromatic epoxy resins, two bi-aryl and one tri-aryl, cured with bi- and tri-aryl amines. Subtle changes to the monomer chemistry including changing aromatic substitution patterns from meta to para, methylene to isopropyl and isopropyl to ether were explored. Changing an epoxy resin backbone from methylene to isopropyl enhances backbone rigidity thus increasing glass transition temperature (Tg), yield strength, and strain despite reducing modulus. Changing meta-substitution to para increases Tg and yield strain while leaving strength unaffected and reducing modulus. Changing isopropyl linkages to ether reduces modulus, strength, Tg, and yield strain reflecting increased molecular flexibility. Using three instead of two aromatic rings increases the molecular weight between crosslinks thereby decreasing Tg and yield strain while increasing modulus and strength. Despite the complexities of multiple systems for varying epoxy resins and amine hardeners, the effect upon network properties is explained in terms of short- and long-range molecular and segmental mobility, crosslink density, and equilibrium packing density. © 2020 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48874. 相似文献
7.
William Huddleston Frederick Dynys Alp Sehirlioglu 《Journal of the American Ceramic Society》2020,103(3):1527-1535
Sintering of LiNi0.33Mn0.33Co0.33O2 cathode material was investigated for potential application in all-electric aerospace propulsion systems utilizing new architectural concepts. All-solid-state batteries, while inherently safe, may not reach the high energy density required for next generation propulsion systems. To meet this performance requirement, multifunctionality of sintered active material may achieve systems level weight savings through simultaneous load bearing and electrochemical energy storage performance. The effects of sintering conditions on structural stability, chemistry, densification, grain size, fracture strength and electrical conductivity were quantified for the active cathode material. X-ray diffraction and inductively coupled plasma results indicated the structure and stoichiometry were maintained across the range of processing conditions to facilitate intercalation. Densification was achieved by sintering at 1050°C in ambient atmosphere, but grain coarsening was observed for higher temperatures and longer hold times. Mechanical strength was improved with reduction in porosity, but excessive grain growth decreased strength, providing a maximum of 50 MPa for samples sintered at 1050°C for 10 hours. Electrical conductivity initially improved with densification, but significantly diminished as the microstructure coarsened. The optimal sintering condition of 1050°C maximized mechanical fracture strength and electrical conductivity, with shorter sintering times preferred. 相似文献
8.
9.
Frederick W. Mowrer 《Fire Technology》2002,38(1):33-56
Enclosure smoke filling and management are addressed from the standpoint of the volumetric flow rates commonly used for mechanical ventilation system design. In this context, fire-induced gas expansion is treated as a volumetric source term. A two-layer analysis developed previously for enclosure smoke filling without mechanical ventilation is extended to consider the impact of mechanical ventilation on smoke layer descent rates and conditions within the smoke layer. A spreadsheet-based model of enclosure smoke filling developed in conjunction with the previous unventilated analysis is also extended to consider both mechanical extraction and injection systems. Some implications of mechanical ventilation on the development and descent of a smoke layer in an enclosure fire are discussed. 相似文献
10.
Richard W. Gilpin Susan B. Dillon Patricia Keyser Alice Androkites Mary Berube Nichola Carpendale Jane Skorina James Hurley Adele M. Kaplan 《Water research》1985,19(7):839-848
Continuous ultraviolet light (u.v.) and chemical disinfection of circulating water systems were evaluated. Direct comparisons of the biocidal effectiveness of u.v. light vs halogenation were tested with Legionella spp and Pseudomonas aeruginosa because of their association with the acquisition of overt clinical disease from water-containing appliances. Findings indicated that six species of Legionella and P. aeruginosa were killed by a moderate level of u.v. radiation. L. pneumophila and other bacteria in a circulating water system were effectively killed by a biocidal u.v. light. However, free chlorine levels needed to kill Legionella, Pseudomonas, and Flavobacterium within 1 min were found to be greater than 4 mg ml?1. Data from a long-term field trial with u.v. light treatment of evaporative condenser water showed a significant reduction in numbers of bacteria. Ultraviolet disinfection of hospital hydrotherapy whirlpools confirmed the utility of this mode of disinfection under circumstances where chlorination may not be practical for medical reasons. These findings were confirmed during investigations of halogenated or u.v.-treated public hot tub/whirlpools. The effectiveness of routine chemical disinfection for controlling microbial flora in a cooling tower was also evaluated. The 2 month survey indicated that the numbers of bacteria, including Legionella, were not affected by two biocides that were used. The observations made during this investigation support the conclusion that u.v. light disinfection of water-containing systems may be an appropriate alternative or supplement to chemical biocides. 相似文献