全文获取类型
收费全文 | 29197篇 |
免费 | 3034篇 |
国内免费 | 1922篇 |
专业分类
电工技术 | 3271篇 |
技术理论 | 5篇 |
综合类 | 3192篇 |
化学工业 | 3455篇 |
金属工艺 | 881篇 |
机械仪表 | 1309篇 |
建筑科学 | 3847篇 |
矿业工程 | 1085篇 |
能源动力 | 1107篇 |
轻工业 | 1934篇 |
水利工程 | 1193篇 |
石油天然气 | 2537篇 |
武器工业 | 235篇 |
无线电 | 2262篇 |
一般工业技术 | 3089篇 |
冶金工业 | 1434篇 |
原子能技术 | 660篇 |
自动化技术 | 2657篇 |
出版年
2024年 | 109篇 |
2023年 | 372篇 |
2022年 | 941篇 |
2021年 | 1142篇 |
2020年 | 975篇 |
2019年 | 757篇 |
2018年 | 773篇 |
2017年 | 920篇 |
2016年 | 1089篇 |
2015年 | 1150篇 |
2014年 | 1757篇 |
2013年 | 1992篇 |
2012年 | 2048篇 |
2011年 | 2320篇 |
2010年 | 1727篇 |
2009年 | 1814篇 |
2008年 | 1661篇 |
2007年 | 1957篇 |
2006年 | 1746篇 |
2005年 | 1505篇 |
2004年 | 1211篇 |
2003年 | 1022篇 |
2002年 | 915篇 |
2001年 | 763篇 |
2000年 | 602篇 |
1999年 | 523篇 |
1998年 | 408篇 |
1997年 | 334篇 |
1996年 | 310篇 |
1995年 | 248篇 |
1994年 | 202篇 |
1993年 | 134篇 |
1992年 | 110篇 |
1991年 | 88篇 |
1990年 | 91篇 |
1989年 | 81篇 |
1988年 | 83篇 |
1987年 | 39篇 |
1986年 | 24篇 |
1985年 | 19篇 |
1984年 | 32篇 |
1982年 | 15篇 |
1981年 | 11篇 |
1980年 | 11篇 |
1964年 | 10篇 |
1962年 | 7篇 |
1961年 | 8篇 |
1960年 | 9篇 |
1959年 | 11篇 |
1955年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
松辽盆地南部深层火山岩识别及成藏条件分析 总被引:14,自引:0,他引:14
松辽盆地北部徐深1井在营城组火山岩获得油气突破后,在松辽盆地南部长岭断陷针对火山岩部署了长深1井。在长深1井营城组火山岩地层测试获4.6×105m3/d的工业气流,推算无阻流量1.5×106m3/d以上,预示松辽盆地南部深层火山岩气藏是下步勘探开发的主要领域。通过大量的火山岩岩心资料,利用岩石学、矿物学、测井和地震地层学等多学科技术,首次在松辽盆地南部建立了火山岩识别标准,在东南隆起区部署探井1口,在火山岩中见到了较好的气显示,取得很好的效果。 相似文献
32.
本文回顾了PCB制造常用的环氧树脂及其增强材料的性能和用途。同时,还介绍了代用树脂材料和代用增强材料的最新进展,如改性环氧树脂、无卤树脂、Thermount、PTFE、氰酸酯等,并就其性能进行了探讨。 相似文献
33.
一种零电压转换有源功率因数校正电路的研究 总被引:1,自引:0,他引:1
提出了一种基于UC3854的零电压转换有源功率因数校正(ZVT-APFC)的控制电路实现方案,介绍了ZVT电路工作原理,着重分析了由分立元件构成的辅助开关管的驱动电路,通过实验证实了驱动电路的稳定性和可靠性,并通过效率比较验证了ZVT-APFC电路的优良性能。与采用UC3855的电路相比,该电路方案具有简单、可靠、成本低等优点。 相似文献
34.
The present empirical investigation had a 3-fold purpose: (a) to cross-validate L. R. Offermann, J. K. Kennedy, and P. W. Wirtz's (1994) scale of Implicit Leadership Theories (ILTs) in several organizational settings and to further provide a shorter scale of ILTs in organizations; (b) to assess the generalizability of ILTs across different employee groups, and (c) to evaluate ILTs' change over time. Two independent samples were used for the scale validation (N1 = 500 and N2 = 439). A 6-factor structure (Sensitivity, Intelligence, Dedication, Dynamism, Tyranny, and Masculinity) was found to most accurately represent ELTs in organizational settings. Regarding the generalizability of ILTs, although the 6-factor structure was consistent across different employee groups, there was only partial support for total factorial invariance. Finally, evaluation of gamma, beta, and alpha change provided support for ILTs' stability over time. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
35.
36.
通过对减振器结构设计的理论分析,建立了减振器的数学模型,同时通过设计的模拟装置对减振效果进行了实测,效果良好。 相似文献
37.
Oleuropein Inhibits LDL Oxidation Induced by Cooking Oil Frying By-products and Platelet Aggregation Induced by Platelet-Activating Factor 总被引:1,自引:0,他引:1
Oleuropein, a polyphenolic glucoside, constituent of olive fruit and oil, has been previously shown to exhibit, in vitro, potent properties as a biological antioxidant. In the present paper, two new properties are demonstrated in vitro as well, concerning its vascular protection activity, against the atheromatic lesion formation and its blood antithrombotic effect. Firstly, it was found that the oxidation of low-density lipoproteins (LDL), induced by different quantities of total polar materials (TPM), was inhibited by 10 μ M (final concentration) of oleuropein, revealing approx. 50% protection. Secondly, platelet-rich human plasma aggregation, induced by either the platelet-activating factor or adenosine diphospate or arachidonic acid, was inhibited by oleuropein. The 10 μ M (final concentration) of oleuropein was proven to be the most effective among the tested concentrations against LDL oxidation, while an IC50=0.41 mM was calculated for its inhibitory activity against platelet aggregation induced by 0.7 μ M platelet-activating factor. 相似文献
38.
Ting Gang Zhu Uttiya Chowdhury Michael M. Wong Jonathan C. Denyszyn Russell D. Dupuis 《Journal of Electronic Materials》2002,31(5):406-410
In this paper, we report the study of the electrical characteristics of GaN and AlGaN vertical p-i-n junctions and Schottky
rectifiers grown on both sapphire and SiC substrates by metal-organic chemical-vapor deposition. For GaN p-i-n rectifiers
grown on SiC with a relatively thin “i” region of 2 μm, a breakdown voltage over 400 V, and forward voltage as low as 4.5
V at 100 A/cm2 are exhibited for a 60-μm-diameter device. A GaN Schottky diode with a 2-μm-thick undoped layer exhibits a blocking voltage
in excess of ∼230 V at a reverse-leakage current density below 1 mA/cm2, and a forward-voltage drop of 3.5 V at a current density of 100 A/cm2. It has been found that with the same device structure and process approach, the leakage current of a device grown on a SiC
substrate is much lower than a device grown on a sapphire substrate. The use of Mg ion implantation for p-guard rings as planar-edge
terminations in mesageometry GaN Schottky rectifiers has also been studied. 相似文献
39.
X. Wang S. B. Lambert 《Fatigue & Fracture of Engineering Materials & Structures》1997,20(12):1637-1655
Abstract— A Fourier series approach is proposed to calculate stress intensity factors using weight functions for semi-elliptical surface cracks in flat plates subjected to two-dimensional stress distributions. The weight functions were derived from reference stress intensity factors obtained by three-dimensional finite element analyses. The close form weight functions derived are suitable for the calculation of stress intensity factors for semi-elliptical surface cracks in flat plates under two-dimensional stress distributions with the crack aspect ratio in the range of 0.1 ≤ a/c ≤ 1 and relative depth in the range of 0 ≤ a/t ≤ 0.8. Solutions were verified using several two-dimensional non-linear stress distributions; the maximum difference being 6%. 相似文献
40.
水溶性防氧化剂在SMT用印制板上的应用 总被引:1,自引:0,他引:1
水溶性的防氧化剂是一种有机可焊性保护剂。其方法是在印制板完全阻焊、字符层的印刷,并经电检之后,通过表面浸渍在裸铜的贴片位或通孔内形成一种耐热性的有机可焊性膜层。这种有机、可焊、耐热的膜层,膜厚可达0.3-0.5mm,其分解的温度可达约300℃,传统的印制板的热风整平法亦无法满足QFP愈来愈密集的需求,同时也无法满足SMD表面平整度的要求,更无法适应PCB薄型化生产。烷基苯并咪唑的OSP法能弥补这项缺陷,因而在PCB业乃至SMT产业中得到了广泛的应用。 相似文献