全文获取类型
收费全文 | 13952篇 |
免费 | 2245篇 |
国内免费 | 1127篇 |
专业分类
电工技术 | 3696篇 |
综合类 | 1402篇 |
化学工业 | 1794篇 |
金属工艺 | 315篇 |
机械仪表 | 885篇 |
建筑科学 | 562篇 |
矿业工程 | 286篇 |
能源动力 | 397篇 |
轻工业 | 1140篇 |
水利工程 | 138篇 |
石油天然气 | 435篇 |
武器工业 | 188篇 |
无线电 | 1887篇 |
一般工业技术 | 1289篇 |
冶金工业 | 222篇 |
原子能技术 | 85篇 |
自动化技术 | 2603篇 |
出版年
2024年 | 100篇 |
2023年 | 312篇 |
2022年 | 446篇 |
2021年 | 545篇 |
2020年 | 603篇 |
2019年 | 475篇 |
2018年 | 476篇 |
2017年 | 573篇 |
2016年 | 581篇 |
2015年 | 690篇 |
2014年 | 825篇 |
2013年 | 812篇 |
2012年 | 987篇 |
2011年 | 1089篇 |
2010年 | 825篇 |
2009年 | 839篇 |
2008年 | 850篇 |
2007年 | 1089篇 |
2006年 | 930篇 |
2005年 | 747篇 |
2004年 | 638篇 |
2003年 | 559篇 |
2002年 | 441篇 |
2001年 | 385篇 |
2000年 | 340篇 |
1999年 | 257篇 |
1998年 | 198篇 |
1997年 | 152篇 |
1996年 | 134篇 |
1995年 | 88篇 |
1994年 | 84篇 |
1993年 | 59篇 |
1992年 | 59篇 |
1991年 | 25篇 |
1990年 | 29篇 |
1989年 | 19篇 |
1988年 | 7篇 |
1987年 | 11篇 |
1986年 | 6篇 |
1985年 | 10篇 |
1984年 | 5篇 |
1983年 | 7篇 |
1982年 | 7篇 |
1980年 | 4篇 |
1979年 | 1篇 |
1974年 | 2篇 |
1964年 | 1篇 |
1959年 | 1篇 |
1955年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 281 毫秒
151.
碘化钾水溶液中碘在活性炭上的吸附等温线 总被引:1,自引:0,他引:1
测定了碘化钾水溶液中碘在活性炭上的吸附平衡数据,证明碘在液固两相中的平衡关系可用Freundlich方程式拟合,其平衡方程式为:x/m=0.381C 相似文献
152.
以功率MOSFET和IGBT为代表的、集高频、高压和大电流于一身的功率半导体复合器件,表明传统电力电子技术已经进入现代电力电子时代,开关电源的工作频率得以大大提高,一些新技术的应用更是进一步提升了开关电源的性能。开关电源拥有更广阔的发展空间和应用前景。 相似文献
153.
何祥锋 《网络安全技术与应用》2014,(1):88-89,91
作为一种主动防御的网络安全技术,蜜罐技术已经成为诱骗攻击者非常有效实用的方法。本文从蜜罐技术的定义、分类、发展情况以及主要技术等方面进行比较系统的解释,最后介绍在网络安全中的应用。 相似文献
154.
155.
156.
Tjeenk Marjjke Leuveling; Bulsink Yvonne B. M.; Slotboom Arend J.; Verheij Hubertus M.; Haas Gerard H.de; Demleitner Gaby; Gotz Friedrich 《Protein engineering, design & selection : PEDS》1994,7(4):579-583
The Staphylococcus hyicus lipase is an acyl hydrolase with broadsubstrate specificity including neutral glycerides and phospholipids.To obtain further insight into the mechanism of action of thisenzyme, we tested several sulfonyl fluorides as active site-directedinhibitors. The enzyme is resistant to the well-known serineprotease/esterase inhibitor phenylmethanesulfonyl fluoride (PMSF),but is rapidly inactivated by hexadecylsulfonyl fluoride. Thekinetics of inactivation were studied in Triton X-100 micelles.Inactivation is fast and the rate of inactivation is constantover the pH range where this lipase is active. Metal ions likeCa2+ and Sr2+ do not appreciably influence the rate of inactivation,although the enzymatic activity is significantly increased,suggesting a structural role for these ions. The S.hyicus lipasecontains a consensus sequence G-H/Y-S-X-G. Substitution by site-directedmutagenesis of this serine (Ser369) by a cysteine resulted ina mutant with only 0.2% residual activity. The activity of thismutant could not be inhibited with water-soluble sulfhydrylreagents either in the presence or absence of Triton X-100 micelles.In the presence of Triton X-100 micelles, inactivation of themutant occurred with 4-nitrophenylhexadecyl disulfide (t1/2= 125 min) while the wild-type enzyme does not react at all.We conclude that Ser369 is the active site residue and thatin water this residue is inaccessible. Only after interfacialactivation Ser369 (or Cys369) becomes exposed and reacts withirreversible inhibitors. 相似文献
157.
Creaser E.H.; Murali C.; Britt K.A. 《Protein engineering, design & selection : PEDS》1990,3(6):523-526
By protein engineering we have investigated changes to two aminoacid residues (Trp93 and Ser48) in the substrate pocket of yeastalcohol dehydrogenase 1. Upon changing Thr48 to serine we producedan enzyme which has markedly greater activity towards aliphaticalcohols with chain length up to 8, together with a generalincrease in catalytic activity (V/K). Changes at position 93were less pronounced, with the Phe enzyme being more activethan the parent towards the range of alcohols but with the alanineenzyme showing very little difference from the wild-type. Enzymeswith the double changes at 48 and 93 showed increased activitytowards alcohols with 38 carbons but the increases werenot additive over the single changes. The enzymes with changesat the two positions would metabolize both stereoisomers of2-octanol whereas the parent ADH would attack only one of them.None of the engineered enzymes would attack cyclohexanol oraromatic alcohols. The results are in general agreement withthe prediction that reducing the size of amino acids in thesubstrate pocket would enhance the ability to oxidize alcoholslarger than ethanol. 相似文献
158.
基于神经网络监督控制的拥塞控制算法研究 总被引:2,自引:2,他引:0
提出了一个基于神经网络控制的主动队列管理(AQM)算法;研究了TCP/AQM拥塞控制系统的可逆性,并利用一种神经网络监督控制结构进行了AQM算法的设计。算法由一个三层前馈结构的神经网络控制器(neural network controller,NNC)和一个反馈控制器(feedback controller,FC)组成。NNC作为一个前馈控制器,通过FC产生的教师信号进行学习,以建立被控对象的逆动力学模型。仿真结果表明,提出的算法与PI(proportional-integral)算法相比,无论在瞬态性能 相似文献
159.
160.
In order to improve the pyrotechnical reagent with potassium perchlorate,composite catalyst of active carbon supporting transition metal oxides (TMO),Fe2O3 and CuO,were prepared and added into pyrotechnical reagent with potassium perchlorate.Accelerating rate calorimeter (ARC) was used to study the catalysis of pyrotechnical reagent which is consisted of potassium perchlorate and composite catalyst.Composite catalyst of both Fe2O3 and CuO supported by active carbon can catalyze pyrotechnical reagent with potassium perchlorate.Furthermore,it can lower the apparent activation energy and accelerate the reaction with a smaller quantity than that with Fe2O3 and CuO.The maximal reaction rate of pyrotechnical reagent with potassium perchlorate mixed with Fe2O3/active carbon and CuO/active carbon is 8.31 min-1 and 9.13 min-1,which is 1.74 times and 1.91 times of pyrotechnical reagent mixed with no catalyst;time to maximal rate was 18.99 min and 1.96 min respectively,which is lower than pyrotechnical reagent mixed with no catalyst by 86.46% and 98.67% ;the apparent activation energy is 368.10 kJ·mol-1 and 325.29 kJ·mol-1,which is lower than pyrotechnical reagent mixed with no catalyst by 31.89% and 39.81% respectively. 相似文献