全文获取类型
收费全文 | 25003篇 |
免费 | 2300篇 |
国内免费 | 928篇 |
专业分类
电工技术 | 1218篇 |
综合类 | 1028篇 |
化学工业 | 4382篇 |
金属工艺 | 1583篇 |
机械仪表 | 1845篇 |
建筑科学 | 1306篇 |
矿业工程 | 596篇 |
能源动力 | 927篇 |
轻工业 | 1843篇 |
水利工程 | 334篇 |
石油天然气 | 958篇 |
武器工业 | 115篇 |
无线电 | 3454篇 |
一般工业技术 | 4191篇 |
冶金工业 | 1397篇 |
原子能技术 | 220篇 |
自动化技术 | 2834篇 |
出版年
2024年 | 86篇 |
2023年 | 473篇 |
2022年 | 735篇 |
2021年 | 1196篇 |
2020年 | 894篇 |
2019年 | 762篇 |
2018年 | 899篇 |
2017年 | 887篇 |
2016年 | 957篇 |
2015年 | 1010篇 |
2014年 | 1285篇 |
2013年 | 1568篇 |
2012年 | 1679篇 |
2011年 | 1882篇 |
2010年 | 1581篇 |
2009年 | 1516篇 |
2008年 | 1401篇 |
2007年 | 1155篇 |
2006年 | 1095篇 |
2005年 | 949篇 |
2004年 | 724篇 |
2003年 | 708篇 |
2002年 | 666篇 |
2001年 | 569篇 |
2000年 | 509篇 |
1999年 | 515篇 |
1998年 | 536篇 |
1997年 | 388篇 |
1996年 | 358篇 |
1995年 | 276篇 |
1994年 | 219篇 |
1993年 | 145篇 |
1992年 | 113篇 |
1991年 | 84篇 |
1990年 | 85篇 |
1989年 | 71篇 |
1988年 | 49篇 |
1987年 | 40篇 |
1986年 | 36篇 |
1985年 | 25篇 |
1984年 | 16篇 |
1983年 | 11篇 |
1982年 | 10篇 |
1981年 | 14篇 |
1980年 | 10篇 |
1979年 | 5篇 |
1978年 | 7篇 |
1977年 | 7篇 |
1976年 | 10篇 |
1975年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
介绍了一种日常参数智能控制器的研制及研制过程中的几个重要问题的解决方法。特别是用于城市照明及美化城市的彩灯的开、关时间智能控制方面,给出了依据当地绝对时间、经度、纬度进行昼夜时间计算的方法,使之在不接光电传感器情况下可跟踪季节的昼夜变化。控制系统采用89C2051单片机,配有时钟日历芯片DS12887,系统体积小、功能强、可靠性高。 相似文献
42.
Ki Hyun Kim Yong Hoon Kang Byoungho Lee 《Photonics Technology Letters, IEEE》1997,9(12):1610-1612
A photorefractive volume hologram was recorded and probed using light diffracted from a tapered optical fiber as a reference beam. A single-mode fiber (SMF) was chemically etched and tapered to give a complicated beam pattern, and it is shown that the tapered optical fiber can be utilized to increase the storage density of the volume hologram. Spatial selectivity of the volume hologram with this method was increased by two times compared to the normal SMF referencing, which is due to the fact that the complicated beam pattern has little correlation with its shifted version 相似文献
43.
DH Kang CL Coe DO McCarthy NN Jarjour EA Kelly RR Rodriguez WW Busse 《Canadian Metallurgical Quarterly》1997,17(8):481-487
T cell cytokines play an important role in mediating airway inflammation in asthma. The predominance of a Th2 cytokine profile, particularly interleukin (IL)-4 and IL-5, is associated with the pathogenesis and course of asthma. The aim of this study was to test the hypothesis that a stressful life event alters the pattern of cytokine release in asthmatic individuals. Thirteen healthy controls and 21 asthmatic adolescents gave blood samples three times over a semester: midsemester, during the week of final examinations, and 2-3 weeks after examinations. Interferon-gamma (IFN-gamma), IL-2, IL-4, and IL-5 were measured from supernatants of cells stimulated with PHA/PMA for 24 h. Cells from asthmatic subjects released significantly more IL-5 during the examination and postexamination periods, whereas cells from healthy controls released significantly more IL-2 during the midsemester and examination periods, thereby indicating a bias for a Th2-like pattern in asthmatics and a Th1-like pattern in healthy controls. IL-4 and IL-5 production showed a marked decrease during and after examinations in healthy controls, whereas this decline was absent in asthmatics. The ratios of IFN-gamma:IL-4 and IFN-gamma:IL-5 also revealed significant changes in the profile of cytokine release across the semester. These results indicate differential cytokine responses in asthmatics that may become pronounced during periods of cellular activation. 相似文献
44.
2Mbit/s高速信令链路在移动通信七号信令网中的应用 总被引:1,自引:0,他引:1
通过对2Mbit/s高速信令链路原理、特点的介绍,阐明了该技术在现阶段使用的实际意义,并给出了2Mbit/s高速信令链路在移动通信七号信令网中的应用。 相似文献
45.
46.
47.
48.
49.
LiFePO4 is a potential candidate for the cathode material of the lithium secondary batteries. A co-precipitation method was adopted to prepare LiFePO4 because it is simple and cheap. Nitrogen gas was needed to prevent oxidation of Fe2+ in the aqueous solution. The co-precipitated precursor shows the high reactivity with the reductive gas, and the single phase of LiFePO4 is successfully synthesized with the aid of carbon under less reductive conditions. LiFePO4 fine powder prepared by co-precipitation method shows high rate capability, impressive specific capacity and cycle property. 相似文献
50.
Seo K. Heiblum M. Knoedler C.M. Oh J.E. Pamulapati J. Bhattacharya P. 《Electron Device Letters, IEEE》1989,10(2):73-75
A high-gain ballistic hot-electron device is described. The GaAs-AlGaAs heterostructure device, with a 21-mm-thick pseudomorphic In 0.12Ga0.88As base, had a current gain of 27 at 77 K and 41 at 4.2 K. As characteristically seen in ballistic devices, transfer into the L valley limited the maximum gain. The Γ-L valley separation in the strained In0.12Ga0.88As was estimated to be about 380 meV 相似文献