全文获取类型
收费全文 | 8391篇 |
免费 | 660篇 |
国内免费 | 311篇 |
专业分类
电工技术 | 187篇 |
综合类 | 398篇 |
化学工业 | 1632篇 |
金属工艺 | 501篇 |
机械仪表 | 241篇 |
建筑科学 | 311篇 |
矿业工程 | 62篇 |
能源动力 | 189篇 |
轻工业 | 3289篇 |
水利工程 | 26篇 |
石油天然气 | 155篇 |
武器工业 | 32篇 |
无线电 | 571篇 |
一般工业技术 | 473篇 |
冶金工业 | 244篇 |
原子能技术 | 133篇 |
自动化技术 | 918篇 |
出版年
2024年 | 36篇 |
2023年 | 130篇 |
2022年 | 283篇 |
2021年 | 268篇 |
2020年 | 247篇 |
2019年 | 245篇 |
2018年 | 232篇 |
2017年 | 265篇 |
2016年 | 309篇 |
2015年 | 330篇 |
2014年 | 453篇 |
2013年 | 606篇 |
2012年 | 689篇 |
2011年 | 709篇 |
2010年 | 489篇 |
2009年 | 504篇 |
2008年 | 444篇 |
2007年 | 536篇 |
2006年 | 448篇 |
2005年 | 347篇 |
2004年 | 290篇 |
2003年 | 262篇 |
2002年 | 250篇 |
2001年 | 200篇 |
2000年 | 152篇 |
1999年 | 89篇 |
1998年 | 82篇 |
1997年 | 78篇 |
1996年 | 59篇 |
1995年 | 43篇 |
1994年 | 37篇 |
1993年 | 39篇 |
1992年 | 28篇 |
1991年 | 16篇 |
1990年 | 28篇 |
1989年 | 20篇 |
1988年 | 20篇 |
1987年 | 10篇 |
1986年 | 8篇 |
1985年 | 13篇 |
1984年 | 9篇 |
1983年 | 7篇 |
1982年 | 6篇 |
1981年 | 7篇 |
1980年 | 7篇 |
1979年 | 8篇 |
1977年 | 7篇 |
1976年 | 3篇 |
1975年 | 4篇 |
1959年 | 2篇 |
排序方式: 共有9362条查询结果,搜索用时 0 毫秒
11.
Laurus nobilis L., commonly known as daphne tree, is an evergreen that belongs to the Lauraceae family. Daphne trees produce grape-sized
shiny purplish berries having three parts: flesh, skin, and an inner kernel (single seed). This study examines supercritical
CO2 (SC-CO2) extraction of oil from daphne seeds. The oil yield of ground seeds varied from 14 to 28% depending on the method and particle
size used for oil recovery. Yields were similar for both petroleum ether and SC-CO2 extraction. The extraction yield decreased significantly with increasing particle size. The amount of extract collected increased
exponentially with increasing SC-CO2 pressure. The highest extraction yield was obtained at the highest temperature studied, 75°C. More than 45% of the oil was
lauric acid. SC-CO2 is a viable technique to obtain high-purity L. nobilis L. seed oil, which is a potential ingredient for the cosmetic industry. 相似文献
12.
An experiment to remove re-deposited layers and to release hydrogen using a glow discharge in oxygen (O-GDC) has been performed in the HT-7 superconducting tokamak. In the absence of magnetic fields, the O-GDC wall conditioning had produced rapid, controlled co-deposit removal. Average removal rates, 5.2 × 1022 H-atoms/h, 5.65 × 1021 D-atoms/h and 5.53 × 1022 C-atoms/h, respectively, were obtained during 145 min O-GDC experiment in the pressure range 0.5-1.5 Pa. The corresponding removal rate of co-deposited films was ∼1.19 μm/day (26.5 g/day for carbon) based on an area of 12 m2. Compared to thermo-oxidation and O-ICR experiment, high pressure O-GDC wall conditioning promoted the oxidation and improved the C and D atoms removal. In the O-GDC experiment, the removal rates of H-atoms and D-atoms as H2O, HDO and D2O were higher than that of H2 and D2 by factors of about 20 and 50, respectively. During the 145 min O-GDC experiment, about 14.5% O-atoms were converted into carbon oxides and hydroxides, and about 5.37 × 1022 O-atoms were adsorbed on the walls corresponding to a coverage of 4.5 × 1021 O/m2 on an wall area of 12 m2. In a 100 min helium glow discharge (He-GDC) following the O-GDC experiment, 1.53 × 1022 O-atoms, about 28.5% oxygen retained on the walls, were removed. The removal rate of H-atoms in He-GDC cleaning after O-GDC experiment was lower than that in He-GDC cleaning before O-GDC experiment, which indicates that the O-GDC wall conditioning had effectively reduced hydrogen retention on the walls. 相似文献
13.
介绍了作者研制的应用于固态雷达发射机上的L波段500W固态功放组件的工作原理、用途及其主要技术指标。描述了功放组件的设计过程和测试结果。该功放组件在窄脉宽条件下实现了快速上升沿,性能优良,工作稳定可靠。 相似文献
14.
The equilibrium moisture content (EMC) characteristics of high oleic sunflower seeds and kernels between 10 and 55°C were determined by equilibrating the samples to known relative humidities (RH) above saturated salt solutions. EMC of the kernels was lower than that of seeds in the range of 11 to 96% ERH and at 25 and 40°C. Hysteresis effect was found for the EMC properties of seeds and kernels at 25°C. Four EMC-ERH models (modified Henderson, Chung-Pfost, Halsey, and Guggenheim-Anderson-de Boer) and their estimated parameters were evaluated for goodness of fit. GAB and Halsey equations showed the best fitting of experimental data although GAB equation adjusted for temperature described the EMC data the best. Components of the seed as oil content or hull/kernel ratio did not explain the slight differences in EMC found between the varieties. 相似文献
15.
Core–shell type nanoparticles of poly(L ‐lactide)/poly(ethylene glycol) (LE) diblock copolymer were prepared by a dialysis technique. Their size was confirmed as 40–70 nm using photon correlation spectroscopy. The 1H‐NMR analysis confirmed the formation of core–shell type nanoparticles and drug loading. The particle size, drug loading, and drug release rate of the LE nanoparticles were slightly changed by the initial solvents that were used. The drug release behavior of LE core–shell type nanoparticles showed an initial burst during the first 12 h and then a sustained release until 100 h. The degradation behavior of LE block copolymer nanoparticles was divided into three phases: the initial rapid degradation phase, the stationary phase, and the rapid degradation phase until complete degradation. It was suggested that lidocaine release kinetics were predominantly governed by the diffusion mechanism in the initial burst phase and after that by both of the diffusion and degradation mechanisms. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2625–2634, 2002 相似文献
16.
A. Murua 《Computing》1997,59(1):43-61
A class of half-explicit methods for index 2 differential-algebraic systems in Hessenberg form is proposed, which takes advantage
of the partitioned structure of such problems. For this family of methods, which we call partitioned half-explicit Runge-Kutta
methods, a better choice in the parameters of the method than for previously available half-explicit Runge-Kutta methods can
be made. In particular we construct a family of 6-stage methods of order 5, and determine its parameters (based on the coefficients
of the successful explicit Runge-Kutta method DOPRI5) in order to optimize the local error coefficients. Numerical experiments
demonstrate the efficiency of this method for the solution of constrained multi-body systems. 相似文献
17.
An endoprotease was purified from melon fruit (Cucumis melo L.) by ammonium sulfate precipitation, gel filtration and ion-exchange chromatography using t-butyloxycarbonyl-Ala-Ala-Pro-Leu p-nitroanilide as a substrate. The molecular weight was estimated as 26,000 and isoelectric point pH 9.5. It preferentially hydrolyzed peptide bonds of the carboxyl terminal sides of Leu, Ala, His, Gin, and Am. Activity was strongly inhibited by diisopropyl phosphofluoridate, indicating the serine protease nature of the enzyme. The migration distance on electrophoresis, molecular weight and substrate specificity differed from cucumisin, a known protease from melon. This unusual protease may have potential for special food treatment applications. 相似文献
18.
An experimental investigation under cold condition was made to study the effects of some operating/design parameters and non-mechanical L valve configuration on the solid circulation rate in a 4.5 m tall, 0.15 m diameter circulating fluidized bed with riser flow rate varying from 1400 litres/min to 2000 litres/min and bed inventory from 15 kg to 25 kg of sand of average sizes 200 μm, 400 μm and 500 μm. Solid circulation rate was estimated by measuring velocity of sand particle travelling through a vertical Perspex tube section at the bottom of the return leg. It was found to be in the range of 2.8 to 12.3kg/m2s, 0.07 to 9.1kg/m2s and 0.12 to 2.23kg/m2s for sand sizes of 200 μm, 400 μm and 500 μm, respectively for a horizontal L valve. Two mathematical correlations have been developed from the experimental results to predict solid circulation rate as a function of riser flow rate, aeration flow rate, total bed inventory and particle size used. 相似文献
19.
HCPL-260L/060L是美国安捷伦科技有限公司推出的高速数字光电耦合器。该器件的逻辑电平与LVTTL/LVCMOS兼容 ,并具有输出使能端。文中详细介绍了HCPL -260L/060L的引脚功能、内部结构、主要特点、使用要求和注意事项 ,给出了它与LVTTL器件的典型接口电路及隔离的3.3VRS232接口电路。 相似文献
20.