全文获取类型
收费全文 | 34540篇 |
免费 | 4883篇 |
国内免费 | 2190篇 |
专业分类
电工技术 | 18398篇 |
技术理论 | 1篇 |
综合类 | 2579篇 |
化学工业 | 908篇 |
金属工艺 | 655篇 |
机械仪表 | 1585篇 |
建筑科学 | 564篇 |
矿业工程 | 559篇 |
能源动力 | 1044篇 |
轻工业 | 265篇 |
水利工程 | 371篇 |
石油天然气 | 593篇 |
武器工业 | 220篇 |
无线电 | 8718篇 |
一般工业技术 | 1776篇 |
冶金工业 | 564篇 |
原子能技术 | 337篇 |
自动化技术 | 2476篇 |
出版年
2024年 | 94篇 |
2023年 | 525篇 |
2022年 | 783篇 |
2021年 | 1041篇 |
2020年 | 1187篇 |
2019年 | 940篇 |
2018年 | 931篇 |
2017年 | 1397篇 |
2016年 | 1469篇 |
2015年 | 1792篇 |
2014年 | 2354篇 |
2013年 | 2062篇 |
2012年 | 2878篇 |
2011年 | 3166篇 |
2010年 | 2214篇 |
2009年 | 2308篇 |
2008年 | 2316篇 |
2007年 | 2621篇 |
2006年 | 2336篇 |
2005年 | 1808篇 |
2004年 | 1335篇 |
2003年 | 1164篇 |
2002年 | 934篇 |
2001年 | 858篇 |
2000年 | 668篇 |
1999年 | 484篇 |
1998年 | 341篇 |
1997年 | 317篇 |
1996年 | 276篇 |
1995年 | 216篇 |
1994年 | 185篇 |
1993年 | 158篇 |
1992年 | 107篇 |
1991年 | 85篇 |
1990年 | 66篇 |
1989年 | 48篇 |
1988年 | 41篇 |
1987年 | 27篇 |
1986年 | 16篇 |
1985年 | 14篇 |
1984年 | 17篇 |
1983年 | 9篇 |
1982年 | 7篇 |
1981年 | 6篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1975年 | 2篇 |
1972年 | 1篇 |
1959年 | 1篇 |
1956年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
Hajime Tomita 《Electrical Engineering in Japan》2015,190(3):1-8
In this investigation, the nature of the electrostatic discharge (ESD) that occurs when a charged object moves toward a stationary grounded object is experimentally clarified. The spark lengths, discharge currents, and induced voltages in a magnetic probe were measured when a charged metallic spherical electrode connected to a 422 pF capacitor approached a stationary grounded object, which was the current target, for different moving speeds of the charged metallic spherical electrode in a range of 1 mm/s to 100 mm/s. The charge voltages of the capacitor were +6.5 kV and +10 kV. Based on the results, the average gap length shortened with the speed of the spherical electrode. The average peak values of the discharge current and the induced voltage were likely to increase with the speed of the spherical electrode. The average rise times of the discharge current and the induced voltage were likely to drop with the speed of the spherical electrode. The relation between the spark length and the discharge current due to the ESD can be explained qualitatively by using an equation derived from the spark resistance formula proposed by Rompe and Weizel. 相似文献
22.
《Microelectronics Journal》2015,46(11):1012-1019
This paper presents a voltage reference generator architecture and two different realizations of it that have been fabricated within a standard 0.18 μm CMOS technology. The architecture takes the advantage of utilizing a sampled-data amplifier (SDA) to optimize the power consumption. The circuits achieve output voltages on the order of 190 mV with temperature coefficients of 43 ppm/°C and 52.5 ppm/°C over the temperature range of 0 to 120°C without any trimming with a 0.8 V single supply. The power consumptions of the circuits are less then 500 nW while occupying an area of 0.2 mm2 and 0.08 mm2, respectively. 相似文献
23.
Since researchers began studying the mechanism of flavonoids’ anticancer activity, little attention has been focused on the modulation of redox state in cells as a potential chemotherapeutic strategy. However, recent studies have begun identifying that the anticancer effect of flavonoids occurs both in their antioxidative activity which scavenges ROS and their prooxidative activity which generates ROS. Against this backdrop, this study attempts to achieve a comprehensive analysis of the individual and separate study findings regarding flavonoids’ modulation of redox state in cancer cells. It focuses on the mechanism behind the anticancer effect, and mostly on the modulation of redox potential by flavonoids such as quercetin, hesperetin, apigenin, genistein, epigallocatechin-3-gallate (EGCG), luteolin and kaempferol in both in vitro and animal models. In addition, the clinical applications of and bioavailability of flavonoids were reviewed to help build a treatment strategy based on flavonoids’ prooxidative potential. 相似文献
24.
ABSTRACTThe RF output power dissipated per unit area is calculated using Runge-Kutta method for the high-moderate-moderate-high (n+-n-p-p+) doping profile of double drift region (DDR)-based impact avalanche transit time (IMPATT) diode by taking different substrate at Ka band. Those substrates are silicon, gallium arsenide, germanium, wurtzite gallium nitride, indium phosphide and 4H-silicon carbide. A comparative study regarding power dissipation ability by the IMPATT using different material is being presented thereby modelling the DDR IMPATT diode in a one-dimensional structure. The IMPATT based on 4H-SiC element has highest power density in the order of 1010 Wm?2 and the Si-based counterpart has lowest power density of order 106 Wm?2 throughout the Ka band. So, 4H-SiC-based IMPATT should be preferable over others for the power density preference based application. This result will be helpful to estimate the power density of the IMPATT for any doping profile and to select the proper element for the optimum design of the IMPATT as far as power density is concerned in the Ka band. Also, we have focused on variation of power density with different junction temperatures and modelled the heat sink with analysis of thermal resistances. 相似文献
25.
垦71井区三维VSP资料波场分离方法应用研究 总被引:8,自引:5,他引:3
三维VSP资料是多偏移距VSP资料,资料中多种类型的波叠合在一起形成复杂波场。从复杂波场中分离出单一的保幅反射波波场是三维VSP波场分离的重要工作。常规二维VSP波场处理方法单一,难以适用于复杂的三维波场处理。针对三维VSP资料的波场特点,以分离上行反射P波为例,将单一波场分离方法加以适当组合,对垦71井区三维VSP实际资料进行了应用研究。结果表明,波场分离处理中叠加消去法和中值滤波相结合以及F—K滤波和中值滤波相结合的方法克服了单一方法的缺陷,波场处理后获得了波组特征明显、波场清晰单一的上行反射P波保幅波场,取得了较好的波场分离效果。 相似文献
26.
基于CVSD编码的无线语音系统方案的设计 总被引:2,自引:0,他引:2
简要介绍了连续可变斜率增量(CVSD)调制的原理。与目前应用较为广泛的其它语音编码方式相比较,CVSD拥有更优的数字特性。着重介绍了由CML公司研制开发的基于CVSD的语音编码芯片———CMX649的特点及相关的应用方式。CMX649能够成功地应用在广泛的语音编码系统中,尤其适合无线语音系统应用。在此基础上,给出了一种实用性很强的低成本、低功耗无线语音系统的设计与应用方案。该方案可提供清晰可靠的语音传输,可广泛应用于农村地区,具有广阔的市场空间。 相似文献
27.
文章介绍了3种宽带数字储频的基本结构,分析了宽带数字储频的一个重要指标——量化噪声,根据输出信号频谱的杂散电平比较了三种结构的优劣。 相似文献
28.
本文对焦炉煤气加压控制系统进行了分析,在焦炉煤气加压机控制系统中运用变频调速技术对其进行改造,从而实现煤气加压机运转的自动调节,有效地稳定了焦炉煤气母管压力,保证了安全运行,并且达到节约能源的效果。解决了两台鼓风机并列运行,靠调节回流阀无法实现压力恒定这个始终困扰焦炉生产的难题。 相似文献
29.
30.
为了提高注入剖面测井的准确性,研制了一种新型注入剖面组合测井仪。该仪器由流量处理单元、伽马处理单元、井温处理单元、磁性定位处理单元、调制式传输、电源电路六部分组成。一次下井可同时测取流量、伽马、井温、磁性定位四组参数。具有测取资料精度高、单芯电缆传输、流量可单点测量也可连续测量以厦现场监测和维修方便等特点。 相似文献