全文获取类型
收费全文 | 112042篇 |
免费 | 9059篇 |
国内免费 | 4644篇 |
专业分类
电工技术 | 6259篇 |
技术理论 | 9篇 |
综合类 | 7044篇 |
化学工业 | 18932篇 |
金属工艺 | 6047篇 |
机械仪表 | 7141篇 |
建筑科学 | 8092篇 |
矿业工程 | 3502篇 |
能源动力 | 3286篇 |
轻工业 | 7303篇 |
水利工程 | 1756篇 |
石油天然气 | 7662篇 |
武器工业 | 834篇 |
无线电 | 12389篇 |
一般工业技术 | 13887篇 |
冶金工业 | 5658篇 |
原子能技术 | 1139篇 |
自动化技术 | 14805篇 |
出版年
2024年 | 532篇 |
2023年 | 2005篇 |
2022年 | 3531篇 |
2021年 | 4848篇 |
2020年 | 3616篇 |
2019年 | 3040篇 |
2018年 | 3593篇 |
2017年 | 3860篇 |
2016年 | 3219篇 |
2015年 | 4313篇 |
2014年 | 5522篇 |
2013年 | 6542篇 |
2012年 | 6969篇 |
2011年 | 7688篇 |
2010年 | 6709篇 |
2009年 | 6055篇 |
2008年 | 6104篇 |
2007年 | 5719篇 |
2006年 | 5747篇 |
2005年 | 5120篇 |
2004年 | 3382篇 |
2003年 | 3013篇 |
2002年 | 2774篇 |
2001年 | 2418篇 |
2000年 | 2569篇 |
1999年 | 2968篇 |
1998年 | 2498篇 |
1997年 | 2005篇 |
1996年 | 1961篇 |
1995年 | 1645篇 |
1994年 | 1338篇 |
1993年 | 970篇 |
1992年 | 776篇 |
1991年 | 597篇 |
1990年 | 452篇 |
1989年 | 352篇 |
1988年 | 312篇 |
1987年 | 193篇 |
1986年 | 166篇 |
1985年 | 133篇 |
1984年 | 97篇 |
1983年 | 68篇 |
1982年 | 65篇 |
1981年 | 52篇 |
1980年 | 48篇 |
1979年 | 25篇 |
1978年 | 15篇 |
1977年 | 18篇 |
1976年 | 16篇 |
1973年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
A self-aligned diffusion process has been demonstrated in the fabrication of n-InP JFETs on semi-insulating InP. This process utilises the anisotropic and selective etching properties of InP/GaInAs materials. Using this technique, sub-micrometre gate lengths can be achieved even with conventional photolithography. Devices with trans-conductance of >35mS/mm, leakage current of < 10nA/mm and gate capacitance of <0.7pF/mm have been fabricated with a cutoff frequency of 7 GHz. 相似文献
62.
Jian Song Chongcheng Fan 《Lightwave Technology, Journal of》1995,13(3):546-550
A simplified formula for the dispersion limit of single-mode-fiber intensity modulation/direct detection (IM/DD) systems is derived for arbitrary given normalized pulse width U, eye opening penalty X and source linewidth enhancement factor α. From the comparison with published theoretical analyses, computer simulation and experimental data, its validity and the limits of existing formulae are shown. Using this simple and general formula, one can easily obtain the dispersion limit of various fiber types under different working conditions in IM/DD systems 相似文献
63.
研究了温度及气体压力对漂移室(工作于正比区)气体放大倍数的影响,温度和气体压力的变化范围分别是5 ̄40℃及90 ̄105kPa。用实验数据拟合得到了函数关系并测量了几种饱和度下函数中的参数值。 相似文献
64.
Infiltration and localization of preferential infiltration zones at the dam abutment are measured using radioactive tracer tests of flow in boreholes,meanwhile interconnection between boreholes and the energing water points is analysed.The theory and practice of radioactive tracer synthetic detective method are described to give methods and calculation formulae used under the condition of stable flow in single well to measure permeability coefficient and hydrostatic heads.Major single hole techniques including measurement for seepage line,velocity,rate of seepage flow and relationship of recharge of groundwater in aquifers are introduced briefly.The possibilities offered by natureal tracers are analysed,uincluding electric-conduct,pH-value and temperature of water as well as stable isotopes(D,^18O) and tritium.Furthermore,the sensibilities of this theory and methods were confirmed by detecting seepage flow field of Xinanjiang Dam. 相似文献
65.
服务器虚拟化大大提高了服务器的资源利用率,对客户来说是十分有利的。但是,也带来了一些诸如破坏正常的网络架构、可能致使系统服务器超载等信息安全风险,需要采取一定的影响策略予以解决。能采取的影响策略有:安装兼容性杀毒软件、不间断地进行服务器硬件的容量分析等。 相似文献
66.
席殊书屋、第三级书局走了,风入松、纸老虎世纪城店关了,我没太在意。2010年10月底,有着36家连锁店的光合作用竟然也宣告倒闭了!我终于淡定不起来了。清华大学出版社零售产品经理王川(简称川)清华大学出版社图书编辑刘青(简称刘)记者Justdo(简称J)新华书店+网购是必然趋势J:光合作用倒闭了,你们惊讶吗?刘:其实我挺惊讶,因为我常去,特别是五道口那家店,从刚开业起就经常去逛。 相似文献
67.
Applied Intelligence - Personnel performance is a key factor to maintain core competitive advantages. Thus, predicting personnel future performance is a significant research domain in human... 相似文献
68.
Neural Computing and Applications - Most traditional genetic programming methods that handle symbolic regression are random algorithms without memory and direction. They repeatedly search for the... 相似文献
69.
Interactive genetic algorithms are effective methods of solving optimization problems with implicit (qualitative) criteria by incorporating a user's intelligent evaluation into traditional evolution mechanisms. The heavy evaluation burden of the user, however, is crucial and limits their applications in complex optimization problems. We focus on reducing the evaluation burden by presenting a semi-supervised learning assisted interactive genetic algorithm with large population. In this algorithm, a population with many individuals is adopted to efficiently explore the search space. A surrogate model built with an improved semi-supervised learning method is employed to evaluate a part of individuals instead of the user to alleviate his/her burden in evaluation. Incorporated with the principles of the improved semi-supervised learning, the opportunities of applying and updating the surrogate model are determined by its confidence degree in estimation, and the informative individuals reevaluated by the user are selected according to the concept of learning from mistakes. We quantitatively analyze the performance of the proposed algorithm and apply it to the design of sunglasses lenses, a representative optimization problem with one qualitative criterion. The empirical results demonstrate the strength of our algorithm in searching for satisfactory solutions and easing the evaluation burden of the user. 相似文献
70.