全文获取类型
收费全文 | 38598篇 |
免费 | 2731篇 |
国内免费 | 1463篇 |
专业分类
电工技术 | 1839篇 |
技术理论 | 2篇 |
综合类 | 2236篇 |
化学工业 | 6405篇 |
金属工艺 | 2117篇 |
机械仪表 | 2258篇 |
建筑科学 | 2939篇 |
矿业工程 | 917篇 |
能源动力 | 879篇 |
轻工业 | 2277篇 |
水利工程 | 516篇 |
石油天然气 | 2593篇 |
武器工业 | 201篇 |
无线电 | 4576篇 |
一般工业技术 | 4757篇 |
冶金工业 | 2967篇 |
原子能技术 | 402篇 |
自动化技术 | 4911篇 |
出版年
2024年 | 141篇 |
2023年 | 623篇 |
2022年 | 928篇 |
2021年 | 1398篇 |
2020年 | 1054篇 |
2019年 | 882篇 |
2018年 | 961篇 |
2017年 | 1146篇 |
2016年 | 1036篇 |
2015年 | 1346篇 |
2014年 | 1718篇 |
2013年 | 2199篇 |
2012年 | 2144篇 |
2011年 | 2446篇 |
2010年 | 2204篇 |
2009年 | 2028篇 |
2008年 | 2021篇 |
2007年 | 2008篇 |
2006年 | 2030篇 |
2005年 | 1766篇 |
2004年 | 1202篇 |
2003年 | 1046篇 |
2002年 | 1011篇 |
2001年 | 867篇 |
2000年 | 899篇 |
1999年 | 1128篇 |
1998年 | 1251篇 |
1997年 | 1014篇 |
1996年 | 908篇 |
1995年 | 688篇 |
1994年 | 583篇 |
1993年 | 440篇 |
1992年 | 346篇 |
1991年 | 263篇 |
1990年 | 198篇 |
1989年 | 172篇 |
1988年 | 146篇 |
1987年 | 107篇 |
1986年 | 80篇 |
1985年 | 63篇 |
1984年 | 57篇 |
1983年 | 31篇 |
1982年 | 42篇 |
1981年 | 27篇 |
1980年 | 21篇 |
1979年 | 11篇 |
1978年 | 6篇 |
1977年 | 22篇 |
1976年 | 47篇 |
1970年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
贴片机脱机编程的快捷方法 总被引:7,自引:4,他引:3
SMT生产线中的大多数加工设备均为数控设备。它们编程所需要的大多数特征数据均可从CAD设计系统中得到。文章介绍了如何从CAD设计系统中导出X、Y坐标数据,并转换成贴片数据的方法和思路,以期引起更多的同行加入到这方面的研究中。 相似文献
3.
Disciplinary and linguistic considerations for academic Web linking: An exploratory hyperlink mediated study with Mainland China and Taiwan 总被引:4,自引:0,他引:4
The Web has become an important means of academic information exchange and can be used to give new insights into patterns
of informal scholarly communication. This study develops new methods to examine patterns of university Web linking, focusing
on Mainland China and Taiwan, and including language considerations. Multiple exploratory investigations into Web links were
conducted between universities in these two places. Firstly, inlinks were counted to each university Web site from its national
peers using four alternative Web document models. The results were shown to correlate significantly with research productivity
in Taiwan but not in the Mainland, although in the latter case less reliable institutional data could have been the cause.
For Taiwan, this is the first evidence of a scholarly association with academic linking for a non-English speaking region.
It was then ascertained that the same link counts associated more strongly with scientific than social scientific research
productivity in Taiwan. This confirms the general assumption of greater Web use by the hard sciences. We then investigated
Taiwan-Mainland university cross-links, and found that although English is extensively used on the Web, there was no evidence
that it was the language of preference for informal scholarly communication between the two areas.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
4.
Ching-Wen Tang Chi-Yang Chang 《Electronics letters》2002,38(15):801-803
A novel chip-type ceramic balun designed in the 2.4 GHz ISM band frequency is presented. A buried capacitor is included in the balun, so that the length of the coupled transmission lines can be reduced and can be designed very easily. A meander or spiral broadside coupled-line is adopted to realise the proposed LTCC multi-layer balun. The measured performances of phase and amplitude balance for this LTCC-MLC balun show a good match with computer simulation 相似文献
5.
一种实现最佳用户检测的非线性优化神经网络 总被引:2,自引:0,他引:2
本文提出并讨论了实现码分多址(CDMA)系统上最佳多用户检测(MUD)的一种神经网络方法。该方法通过将最佳多用户检测视为非线性优化组合问题,利用神经网络能有效求解非线性优化问题的优势,导出了一种非线性优化神经网络来实现最佳多用户检测,理论分析和计算机模拟表明,所提出的神经网络具有可实时应用的动态性能和较传统方法优越得多的误码率性能和抗多址干扰的性能。 相似文献
6.
The systemic, coronary and regional vascular responses to the K+ATP channel opener lemakalim were compared to other potent vasodilators (i.e., nifedipine, adenosine, nitroglycerin and acetylcholine). Experiments were performed in 12 conscious dogs 2 to 4 weeks after implantation of aortic catheters and flow probes on the ascending aorta, left circumflex coronary, celiac, mesenteric, renal and iliac arteries, and solid-state miniature pressure gauges in the left ventricular cavity. Dose-response curves induced by bolus injection (i.v.) were examined. For doses that reduced total peripheral resistance by 22%, lemakalim reduced celiac (-28 +/- 2%), mesenteric (-24 +/- 3%), renal (-17 +/- 3%) and iliac (-18 +/- 3%) vascular resistances (i.e., by amounts similar to those observed with the other vasodilators, except for adenosine, which increased renal resistance). At these doses, lemakalim induced a greater decrease (-52 +/- 3%) (P < .05) in coronary resistance, as compared with nifedipine (-35 +/- 3%), adenosine (-38 +/- 3%), nitroglycerin (-25 +/- 2%) and acetylcholine (-32 +/- 3%). However, when near maximal vasodilation was elicited, adenosine elicited the greatest (P < .05) decrease in coronary resistance (-81 +/- 1%), as compared with lemakalim (-74 +/- 2%), nifedipine (-67 +/- 2%), nitroglycerin (-63 +/- 2%) and acetylcholine (-72 +/- 1%). Both the time to maximal increases in regional blood flow and the time for recovery in all vascular beds were significantly prolonged for lemakalim compared with the other vasodilators. Thus, the K+ATP channel opener lemakalim dilates the coronary bed out of proportion to other vascular beds, is relatively more potent at lower doses than other vasodilators and exhibits a delayed and more prolonged action in all regional vascular beds. 相似文献
7.
8.
9.
SF Zakharov SH Kwok H Sokoloff HT Chang SP Radko A Chrambach 《Canadian Metallurgical Quarterly》1998,19(10):1625-1630
An automated gel electrophoresis apparatus, recently available commercially, allows one to follow the band during electrophoresis in real time, and lends itself therefore to an evaluation of bandwidth as a function of migration time (the dispersion coefficient), resolution and band shape. These determinations assume the constancy of band area with migration time and at various gel concentrations. The purpose of the present study was to verify these assumptions. Representative proteins and sodium dodecyl sulfate (SDS)-proteins, either natively fluorescent or fluorescein carboxylate labeled, were found to exhibit band areas which approach constancy as a function of migration time in both agarose and polyacrylamide gel electrophoresis, provided that (i) the protein concentration under the band was low enough to obviate self-quenching of fluorescence; (ii) the separation of the protein of interest from contaminants had progressed sufficiently during the time at which band areas were measured; (iii) the baseline under the peak was sufficiently well defined. However, band areas decrease with increasing gel concentration. Protein peaks exhibited leading and trailing tails. The ratio of the combined tail area to total area appeared to be near-constant at varying migration times. However, that ratio increases with increasing gel concentration. The tail area does not appear to be an artifact of fluorometric detection since it is reproduced upon fluorimetric analysis of the protein eluted from gel slices after electrophoresis. However, it may be due to photochemical destruction under the conditions of repetitive fluorometric peak detection. 相似文献
10.