全文获取类型
收费全文 | 118192篇 |
免费 | 3527篇 |
国内免费 | 1423篇 |
专业分类
电工技术 | 2311篇 |
技术理论 | 4篇 |
综合类 | 3895篇 |
化学工业 | 17333篇 |
金属工艺 | 6297篇 |
机械仪表 | 4754篇 |
建筑科学 | 3888篇 |
矿业工程 | 1328篇 |
能源动力 | 2315篇 |
轻工业 | 5818篇 |
水利工程 | 1711篇 |
石油天然气 | 1376篇 |
武器工业 | 146篇 |
无线电 | 14584篇 |
一般工业技术 | 21231篇 |
冶金工业 | 5342篇 |
原子能技术 | 655篇 |
自动化技术 | 30154篇 |
出版年
2024年 | 114篇 |
2023年 | 474篇 |
2022年 | 902篇 |
2021年 | 1234篇 |
2020年 | 962篇 |
2019年 | 830篇 |
2018年 | 15218篇 |
2017年 | 14199篇 |
2016年 | 10750篇 |
2015年 | 1692篇 |
2014年 | 1656篇 |
2013年 | 2333篇 |
2012年 | 5113篇 |
2011年 | 11616篇 |
2010年 | 10046篇 |
2009年 | 7372篇 |
2008年 | 8619篇 |
2007年 | 9448篇 |
2006年 | 1708篇 |
2005年 | 2461篇 |
2004年 | 2232篇 |
2003年 | 2359篇 |
2002年 | 1946篇 |
2001年 | 1292篇 |
2000年 | 1016篇 |
1999年 | 796篇 |
1998年 | 1050篇 |
1997年 | 728篇 |
1996年 | 641篇 |
1995年 | 498篇 |
1994年 | 411篇 |
1993年 | 347篇 |
1992年 | 267篇 |
1991年 | 249篇 |
1990年 | 226篇 |
1989年 | 203篇 |
1988年 | 180篇 |
1987年 | 154篇 |
1986年 | 129篇 |
1985年 | 129篇 |
1984年 | 110篇 |
1983年 | 77篇 |
1982年 | 70篇 |
1981年 | 59篇 |
1980年 | 81篇 |
1978年 | 60篇 |
1977年 | 58篇 |
1976年 | 76篇 |
1955年 | 71篇 |
1954年 | 69篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
Sang-Mok Lee Woo-Jin Chang Ah-Rom Choi Yoon-Mo Koo 《Korean Journal of Chemical Engineering》2005,22(5):687-690
Ionic liquids are compounds that composed only of ions and are liquid at room temperature. Thus, it is normally named room
temperature ionic liquid (RTIL). In this study, the application of RTILs to the extractive fermentation of biomaterials was
investigated as a substitute of organic solvents. The relative toxicity of the RTILs on the growth ofE. coli was tested. The inhibition of cell growth in the presence of various ionic liquids was measured using solid and liquid culture,
and EC50 of each RTILs was calculated. The number of viable and total cells was measured by the number of colonies and optical density,
respectively. Effective concentrations of toxicity (EC50) in these tested systems were similar with conventional solvents, such as acetone, acetonitrile, and ethanol. The viability
ofE. coli was affected by the polarity and ionic properties of ionic liquids. The resistance of the microorganisms against ionic liquids
was different with the cations and anions composing ionic liquids. No general influence of the anionic compound of the ionic
liquids was found on toxicity comparing with distinctive influence of cationic moiety. 相似文献
992.
993.
Robert A. Moreau David B. Johnston Kevin B. Hicks 《Journal of the American Oil Chemists' Society》2007,84(11):1039-1044
All commercial corn oil is obtained by pressing corn germ and/or extracting the germ with hexane. In the current study, six
types of corn oil were prepared by extracting corn germ, corn fiber and ground corn, each with hexane or with ethanol. The
levels of lutein, zeaxanthin and other carotenoids were quantitatively analyzed in the six corn oils. The levels of lutein + zeaxanthin
in the oil ranged from 2.3 μg/g for hexane-extracted corn germ oil to 220.9 μg/g for ethanol-extracted ground corn oil. These
results indicate that a diet that includes 30 g (~2 tbsp) per day of the unrefined corn oil obtained by extracting ground
corn with ethanol would provide ~6 mg of lutein + zeaxanthin, the daily dosage that is currently considered to be necessary
to slow the progression of age-related macular degeneration.
Mention of trade names or commercial products in this publication is solely for the purpose of providing specific information
and does not imply recommendation or endorsement by the U.S. Department of Agriculture. 相似文献
994.
The combination of styrene-acrylonitrile-glycidyl methacrylate (SAG) reactive copolymer and sodium lauryl sulfonate catalyst is able to function as an effective in situ compatibilizer for the otherwise immiscible and incompatible polymer blends of phenoxy and acrylonitrile-butadiene-styrene (ABS). The copolymer formed from the reaction between phenoxy and SAG under melt blending conditions tends to reduce interfacial tension in the melt and results in finer morphological domains of the blends. The presence of this in situ formed compatibilizer also raises the interphase adhesion of the blends and results in significant improvements in mechanical properties. © 1994 John Wiley & Sons, Inc. 相似文献
995.
996.
Migration kinetics of straight-chain oligomers and antioxidants from several polyolefins at different temperatures into various solvents have been studied by radioactive tracer techniques. Anhydrous ethanol appears to be a well suited food-oil or liquid-fat simulant for extracting different types of migrants from polyolefins. Pure and mixed triglycerides are also good oil or fat simulants, but the triglycerides offer no simpler analytical procedures than the use of oil or fat themselves. n-Octanol may also be considered as a reasonable oil or fat simulant; however, its action depends somewhat on the choice of migrants. The accelerating action of n-heptane over that of oil or simulants is quantitatively demonstrated. The accelerating effects are greater for migration systems with lower diffusion coefficients. The diffusion coefficients for migration into n-heptane are about 20 times greater than the diffusion coefficients into ethanol or oil for otherwise identical migration systems yielding diffusion coefficients of about 10?7 cm2s?1 into oil or ethanol. For systems yielding diffusion coefficients into oil or ethanol of about 10?12 cm2s?1, the corresponding diffusion coefficients into n-heptane are about 1000 times greater. The molecular weight distributions (MWDs) of the n-heptane and ethanol extracts of polyolefins have been analysed. n-Heptane can not only accelerate the migration of the individual migrant but also remove oligomer species that are slightly soluble or present at low levels in the oil or simulant extracts. 相似文献
997.
Mesoporous molecular sieve MCM-41 with a Si/Al ratio of 35 was obtained by hydrothermal synthesis using a gel mixture with a molar composition of 6 SiO20.1 Al2O31 hexadecyltrimethylammonium chloride 0.25 dodecyltrimethylammonium bromide 0.25 tetrapropylammonium bromide0.15 (NH4)2O1.5 Na2O300 H2O. The MCM-41 sample was calcined in O2 flow at 813 K and subsequently ion exchanged with Ca2+. A small Pt cluster has been supported on the MCM-41 sample following a procedure using ion exchange of Pt(NH3)
4
2+
. The Pt(NH3)
4
2+
ion supported on MCM-41 has been activated in O2 flow at 593 K and subsequently reduced with Fh flow at 573 K, in the same way used for the preparation of a Pt cluster entrapped inside the supercage of zeolite NaY. The resulting Pt cluster supported on the MCM-41 shows hydrogen chemisorption oftotal two H atoms per Pt at 296 K (based on the total amount of Pt) and high catalytic activity for hydrogenolysis of ethane. The chemical shift in129Xe NMR spectroscopy of adsorbed xenon indicates that the Pt cluster is located inside the mesoporous molecular sieve. 相似文献
998.
999.
Extraction of Lipids from Municipal Wastewater Plant Microorganisms for Production of Biodiesel 总被引:2,自引:0,他引:2
Stephen Dufreche R. Hernandez T. French D. Sparks M. Zappi E. Alley 《Journal of the American Oil Chemists' Society》2007,84(2):181-187
Municipal wastewater treatment plants in the USA produce over 6.2 × 106 t of dried sewage sludge every year. This microorganism-rich sludge is often landfilled or used as fertilizer. Recent restrictions
on the use of sewage sludge, however, have resulted in increased disposal problems. Extraction of lipids from sludge yields
an untapped source of cheap feedstock for biodiesel production. Solvents used for extraction in this study include n-hexane, methanol, acetone, and supercritical CO2. The gravimetric yield of oil was low for nonpolar solvents, but use of polar solvents gave a considerably increased yield;
however, the percentage of saponifiable material was less. Extraction of lipids with a mixture of n-hexane, methanol, and acetone gave the largest conversion to biodiesel compared with other solvent systems, 4.41% based on
total dry weight of sludge. In situ transesterification of dried sludge resulted in a yield of 6.23%. If a 10% dry weight
yield of fatty acid methyl esters is assumed, the amount of biodiesel available for production in the USA is 1.4 × 106 m3/year. Outfitting 50% of municipal wastewater plants for lipid extraction and transesterification could result in enough biodiesel
production to replace 0.5% of the national petroleum diesel demand (0.7 × 106 m3). 相似文献
1000.