全文获取类型
收费全文 | 16293篇 |
免费 | 1288篇 |
国内免费 | 754篇 |
专业分类
电工技术 | 348篇 |
综合类 | 830篇 |
化学工业 | 4801篇 |
金属工艺 | 1297篇 |
机械仪表 | 501篇 |
建筑科学 | 501篇 |
矿业工程 | 174篇 |
能源动力 | 418篇 |
轻工业 | 3717篇 |
水利工程 | 92篇 |
石油天然气 | 585篇 |
武器工业 | 74篇 |
无线电 | 1083篇 |
一般工业技术 | 1482篇 |
冶金工业 | 675篇 |
原子能技术 | 382篇 |
自动化技术 | 1375篇 |
出版年
2024年 | 56篇 |
2023年 | 263篇 |
2022年 | 478篇 |
2021年 | 479篇 |
2020年 | 490篇 |
2019年 | 496篇 |
2018年 | 420篇 |
2017年 | 508篇 |
2016年 | 613篇 |
2015年 | 608篇 |
2014年 | 794篇 |
2013年 | 1029篇 |
2012年 | 1125篇 |
2011年 | 1201篇 |
2010年 | 953篇 |
2009年 | 932篇 |
2008年 | 835篇 |
2007年 | 1033篇 |
2006年 | 915篇 |
2005年 | 715篇 |
2004年 | 616篇 |
2003年 | 591篇 |
2002年 | 590篇 |
2001年 | 512篇 |
2000年 | 420篇 |
1999年 | 312篇 |
1998年 | 234篇 |
1997年 | 204篇 |
1996年 | 159篇 |
1995年 | 137篇 |
1994年 | 88篇 |
1993年 | 80篇 |
1992年 | 65篇 |
1991年 | 53篇 |
1990年 | 54篇 |
1989年 | 34篇 |
1988年 | 45篇 |
1987年 | 32篇 |
1986年 | 24篇 |
1985年 | 27篇 |
1984年 | 19篇 |
1983年 | 13篇 |
1982年 | 9篇 |
1981年 | 15篇 |
1980年 | 11篇 |
1979年 | 11篇 |
1977年 | 9篇 |
1975年 | 6篇 |
1972年 | 3篇 |
1951年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
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
32.
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
33.
以己二酰二氯和不同取代基的苯肼合成了N,N'-二芳基己二酰二肼类中间体,然后在N-溴丁二酰亚胺(NBS)/吡啶氧化体系下室温合成了8种己二酰基双偶氮化合物。第一步反应条件为:n(己二酰二氯):n(取代苯肼)=1:2,反应温度0-5℃,反应时间4 h,收率80%-93%;第二步反应条件为:n(N,N’-二芳基己二酰二肼):n(NBs/吡啶)=1:2,氧化反应时间0.5-1.0 h,收率80%-94%。并用元素分析、IR、1H NMR对合成的中间产物及目标化合物进行了表征。 相似文献
34.
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
35.
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
36.
张田林 《青岛科技大学学报(自然科学版)》1994,(3)
DCPTA是近年来新发现的一种植物生长调节剂。对农作物具有明显的增产增质效果。文中就其新的合成方法进行了研究。 相似文献
37.
谈国新 《华中科技大学学报(城市科学版)》1994,(2)
本文提出了一种基于自然数线性八叉树的优化构造算法。该算法以活动结点表为中间辅助结构,在图像输入过程中直接生成基于N码的八叉树叶结点.与常规构造算法相比,新提出的优化构造算法省去了N码的计算及合并过程,从而具有较高的时空效率. 相似文献
38.
氨合成塔出口氨含量偏低原因分析及对策 总被引:1,自引:0,他引:1
阐述UHDE合成塔运行现状 ,分析氨净值达不到设计值的原因 ,提出相应的解决措施 相似文献
39.
Auguste Commeyras Hlne Collet Laurent Boiteau Jacques Taillades Odile Vandenabeele‐Trambouze Herv Cottet Jean‐Philippe Biron Raphaël Plasson Louis Mion Olivier Lagrille Herv Martin Franck Selsis Michel Dobrijevic 《Polymer International》2002,51(7):661-665
Addressing the still open question of the prebiotic origin of sequential macromolecules (peptides, nucleic acids) on the primitive Earth, we describe a molecular engine (the primary pump), which works at ambient temperature and continuously generates, elongates and complexifies sequential peptides. This new scenario is based on a cyclic reaction sequence, whose keystep is the activation of amino acids into their N‐carboxyanhydrides (NCA) through nitrosation by NOx. This process could have taken place on tidal beaches; it requires a buffered ocean, emerged land and a nitrosating atmosphere. With the help of geochemical studies and computer simulations of atmosphere photochemistry, we show that the primitive Earth during the Hadean may have satisfied all these requirements. © 2001 Society of Chemical Industry. 相似文献
40.
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