全文获取类型
收费全文 | 33411篇 |
免费 | 2127篇 |
国内免费 | 1118篇 |
专业分类
电工技术 | 2113篇 |
综合类 | 3881篇 |
化学工业 | 8429篇 |
金属工艺 | 1383篇 |
机械仪表 | 2298篇 |
建筑科学 | 1457篇 |
矿业工程 | 1200篇 |
能源动力 | 758篇 |
轻工业 | 1603篇 |
水利工程 | 500篇 |
石油天然气 | 3069篇 |
武器工业 | 220篇 |
无线电 | 2214篇 |
一般工业技术 | 2095篇 |
冶金工业 | 1805篇 |
原子能技术 | 299篇 |
自动化技术 | 3332篇 |
出版年
2024年 | 31篇 |
2023年 | 181篇 |
2022年 | 286篇 |
2021年 | 556篇 |
2020年 | 496篇 |
2019年 | 417篇 |
2018年 | 564篇 |
2017年 | 700篇 |
2016年 | 742篇 |
2015年 | 657篇 |
2014年 | 1983篇 |
2013年 | 1659篇 |
2012年 | 2379篇 |
2011年 | 1692篇 |
2010年 | 1566篇 |
2009年 | 1862篇 |
2008年 | 1988篇 |
2007年 | 2966篇 |
2006年 | 3197篇 |
2005年 | 2417篇 |
2004年 | 1359篇 |
2003年 | 1613篇 |
2002年 | 1164篇 |
2001年 | 1032篇 |
2000年 | 989篇 |
1999年 | 853篇 |
1998年 | 632篇 |
1997年 | 490篇 |
1996年 | 400篇 |
1995年 | 324篇 |
1994年 | 261篇 |
1993年 | 208篇 |
1992年 | 170篇 |
1991年 | 138篇 |
1990年 | 101篇 |
1989年 | 87篇 |
1988年 | 81篇 |
1987年 | 64篇 |
1986年 | 43篇 |
1985年 | 71篇 |
1984年 | 50篇 |
1983年 | 28篇 |
1982年 | 36篇 |
1981年 | 19篇 |
1980年 | 29篇 |
1979年 | 20篇 |
1978年 | 16篇 |
1977年 | 11篇 |
1976年 | 7篇 |
1975年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 750 毫秒
111.
本文介绍一种能够解决有语言障碍的人汉语发音问题的计算机软件系统,此系统采用电报和五笔画编码方案作为汉字输入方法,自建了一套汉字录入和检索体系,并利用Microsoft公司的Speech SDK4.0和Concatenated Text-to-Speech Engine建立了专用的语音库,本系统使得有语言障碍的人可以与其他正常人之间进行正常的交流,从而避免了使用哑语带来的不便。 相似文献
112.
将8098单片机所特有的用软件来实现A/D,D/A及PWM信号输出的特性应用在模拟式移相电路中,展示了模拟式移相电路改造成具有智能化特点的一条有效途径。 相似文献
113.
本文介绍了降秩因子分析(RAFA)方法,它是从一个多组分混合物中直接定量计算其中某一组分,而不必知道其它组分的物种及含量的一种定量分析的数学方法。它适用于双线性的数据。本实验首先将荧光分光光度计与外接计算机相连,以获得样品的激发-发射矩阵(EEM),再用RAFA方法对蒽、萘、菲、芘、芴、(艹屈)六种标样的一至五组分的混合物进行定量分析,获得满意的结果。 相似文献
114.
Measuring shape: ellipticity, rectangularity, and triangularity 总被引:1,自引:0,他引:1
Paul L. Rosin 《Machine Vision and Applications》2003,14(3):172-184
115.
The primary purpose of this work is to review the literature about what is and is not known about using ethylene vinyl acetate (EVA0 copolymer as the encapsulant (or pottant) material in photovoltaic (PV) modules. Secondary purposes include elucidating the complexity of the encapsulation problem, providing an overview about encapsulation of PV cells and modules, providing a historical overview of the relevant research and development on EVA, summarizing performance losses reported for PV systems deployed since ca. 1981, and summarizing the general problems of polymer stability in a solar environment. We also provide a critical review of aspects of reported work for cases that we believe are important.Failure modes resolved in the early work to establish reliability of deployed modules and the purposes and properties of pottants, are summarized. Typical performance losses in large field-deployed, large-scale systems ranging from 1% to 10% per year are given quantitatively, and qualitative reports of EVA discoloration are summarized with respect to ultraviolet (UV), world-wide location and site dependence.The general stability of polymers and their desirable bulk properties for solar utilization are given. The stabilization formulation for EVA, its effectiveness, and changes in it during degradation are discussed. The degradation mechanisms for the base resin, e.g., unstabilized Elvax 150TM, and stabilized EVA are indicated for literature dating to the early 1950s, and the role played by unsaturated chromophores is indicated. The limited number of studies relating discoloration and PV cell efficiency are summarized.Observed degradation of EVA or the unstabilized base resin in the laboratory and examples used to measure the degradation are summarized in sections entitled: (1) thermally-induced degradation; (2) photodegradation and photothermal degradation of EVA in different temperature regimes; (3) photobleaching and photodegradation of the UV absorber and cross-linking agent; (4) acetic acid and metal and metal-oxide catalyzed oxidative degradation; and (5) discolaration and PV cell efficiency losses.Processing effects/influences on EVA stability are discussed in sections entitled: (1) EVA raw materials and extruded, uncured films; (2) thermal encapsulation processes; (3) effects of lamination, curing, and curing peroxide on gel content and chromophores formed; and (4) incomplete shielding of curing-generated chromophores. A summary is given for the limited number of accelerated lifetime testing efforts and examples of erroneous service lifetime predictions for EVA are discussed. The known factors that effect the discoloration rate of several EVA formulations are discussed in which the reduction in rate by using UV-absorbing superstrates is a prime example. A summary is given of what is and is not known about EVA degradation mechanisms, degradation from exposures in field-deployed modeules and/or laboratory testing, and factors that contribute to EVA stability or degradation. Finally, conclusions about using Elvax 150 in EVA formulations are summarized, and future prospects for developing the next-generation pottant for encapsulating PV modules are discussed. 相似文献
116.
117.
J. A. Jimenez-Tejada J. A. Lopez-Villanueva P. Cartujo J. Vicente J. E. Carceller 《Journal of Electronic Materials》1992,21(9):883-886
The energy levels introduced by Pt in silicon have been measured in a non-abruptp
+-n junction using constant-capacitance thermal-emission rate measurements and a numerical simulation of high frequency-capacitance.
Two levels have been detected with activation energies of:E
c -E
T = 0.22 eV with acceptor character andE
T -E
v = 0.34 eV with donor character. The sample preparation and diffusion of Pt is similar to previous works in which an acceptor
levelE
c -E
T = 0.34 eV was found instead of or besides a donorlike levelE
T -E
v = 0.34 eV. Our numerical calculation of the shallow-impurity profile points to the existence of a gradual transition near
the metallurgical junction for these samples. We have demonstrated that the well-known model of an abrupt junction is not
appropriate for these types of junctions, and could lead to errors in the location attributed to the detected levels. Simulation
of the electrical behavior leads to the non-existence of the acceptor levelE
c −E
T = 0.34 eV located in then-side of the junction. 相似文献
118.
TORGILS FOSSEN ØYVIND M. ANDERSEN DAG OLAV ØVSTEDAL ATLE T. PEDERSEN ÅSE RAKNES 《Journal of food science》1996,61(4):703-706
Three red onion (Allium cepa) cultivars, top onion (A. cepa var. vivi-parum), A. altaicum and chive (A. schoenoprasum) contained several or all of the following anthocyanins: 3-(6′-malonyl-3′-glucosylglucoside), 3-(3′,6′-dimalonylglucoside), 3-(6′-malonylglucoside), 3-(3′-malonyl-glucoside), 3-(3′-glucosylglucoside) and 3-glucoside of cyanidin. Trace amounts of two pelargonidin derivatives and the 3,5-diglucosides of cyanidin and peonidin were for the first time reported in red onion. Carbon NMR data showed that the sugars of the 3-(6′-malonyl-3′-glu-cosylglucoside), 3-(6′-malonylglucoside) and 3-glucoside of cyanidin were pyranoses. Substitution either by sugar or acid in the sugar 3-position of an anthocyanin has never been reported outside the genus Allium. 相似文献
119.
钨在铂电极上成核动力学研究 总被引:3,自引:0,他引:3
采用循环伏安法和计时电流法研究了钨在KF-B2O3-K2WO4(62-37-1m/o)熔体中(T=795℃)铂电极上成核动力学过程。实验结果表明:该过程符合扩散步骤控制的半球形三维晶核连续成核长大的动力学规律。 相似文献
120.