首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   1486766篇
  免费   26954篇
  国内免费   7846篇
电工技术   35351篇
技术理论   5篇
综合类   7391篇
化学工业   271778篇
金属工艺   64527篇
机械仪表   42072篇
建筑科学   46364篇
矿业工程   11777篇
能源动力   50317篇
轻工业   112420篇
水利工程   14957篇
石油天然气   38327篇
武器工业   367篇
无线电   196728篇
一般工业技术   280052篇
冶金工业   146204篇
原子能技术   33926篇
自动化技术   169003篇
  2021年   16024篇
  2020年   12096篇
  2019年   14808篇
  2018年   15293篇
  2017年   14594篇
  2016年   21210篇
  2015年   17804篇
  2014年   29140篇
  2013年   88442篇
  2012年   35806篇
  2011年   48019篇
  2010年   42974篇
  2009年   51337篇
  2008年   44987篇
  2007年   42245篇
  2006年   45306篇
  2005年   39528篇
  2004年   41202篇
  2003年   41034篇
  2002年   40326篇
  2001年   36852篇
  2000年   35488篇
  1999年   34063篇
  1998年   39149篇
  1997年   35854篇
  1996年   33076篇
  1995年   29352篇
  1994年   27735篇
  1993年   27589篇
  1992年   25987篇
  1991年   22938篇
  1990年   23313篇
  1989年   22384篇
  1988年   20926篇
  1987年   19191篇
  1986年   18533篇
  1985年   21874篇
  1984年   22259篇
  1983年   20187篇
  1982年   19179篇
  1981年   19281篇
  1980年   17841篇
  1979年   18479篇
  1978年   17697篇
  1977年   17115篇
  1976年   17742篇
  1975年   15958篇
  1974年   15509篇
  1973年   15554篇
  1972年   13044篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
861.
862.
The mass and charge identification of secondary particles with Z < 4 by a large CsI(T1) scintillation detector is performed using pulse shape analysis and time-of-flight methods. The dependence of the light output on E, A and Z is studied in the energy range of 1–20 MeV/A and special attention is paid to the integration time of the photomultiplier anode signal. It is found that the behaviour of the calibration curves strongly depends on the choice of the integration time interval.  相似文献   
863.
Heterostructure Acoustic Charge Transport (HACT) devices have been fabricated with a new nondestructive sense (NDS) electrode structure that provides for the recovery of base-band signals without the use of an integrating capacitor. This electrode structure provides an output signal comprising an RF carrier at the SAW frequency, amplitude modulated by the sampled input signal which has been delayed by a period proportional to the output electrodes distance from the input diode. The output of the NDS electrode structure is subsequently demodulated to provide the base-band signal  相似文献   
864.
A therapist's theoretical orientation is likely to influence every facet of the therapeutic process. We explore the relationship of therapeutic orientation and self-monitoring style. To test the hypothesis that high self-monitors would be more eclectic than low self-monitors, we surveyed 30 intake therapists at a child guidance center. Results supported the hypothesis; those frequently using more than one orientation had higher self-monitoring scores. Furthermore, self-monitoring correlated negatively with psychoanalytic endorsement, but in a positive direction with behavioral, systems and eclectic endorsements. Results are discussed in terms of training needs of those differing in self-monitoring style. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
865.
866.
ABSTRACT: The objective of this work was to observe the microstructure of feta cheese using confocal scanning laser microscopy. Low fat cheese and cheese containing capsule-producing cultures were made. The protein network was observed using the reflectance mode of the confocal microscope. Fat was stained by Nile red dye diluted with whey. More even distribution of fat with a larger number of smaller globules was observed in cheese made with noncapsule-forming culture compared to that made with the capsule-forming culture. Nonfat cheese had compact structure when made with noncapsule-forming culture which contrasted with the open structure observed in cheese made with the capsule-forming culture  相似文献   
867.
This paper proposes a method to reduce the vibration of the three-phase HB-type stepping motor with cogging torque by the feedforward compensation control. The compensation signal to suppress the vibration of the motor frame is obtained by the repetitive controller installing an online Fourier transformer and utilizing an acceleration sensor attached to the motor frame or an acoustic sensor such as a microphone placed close to the frame. The sensor is used only for the acquisition of the feedforward compensation data. The feedforward compensation signal at an arbitrary operating point is derived from the amplitude and phase data of the frequency components and the operating point data. Compensation data obtained by the repetitive controller is applied to the operating point changed by reference frequency and load condition in steady state. The compensation signal for the new operating point will be generated from compensation data utilizing polynomial equation approximation and linear interpolation method. The effectiveness of this proposed method is confirmed by the experimental results.  相似文献   
868.
Spatial and temporal variations in vegetation dielectric properties strongly influence the microwave backscatter characteristics of forested landscapes. This paper examines the relationship between xylem tissue dielectric constant, xylem sap flux density, and xylem sap chemical composition as measured in the stems of two Norway Spruce (Picea abies [L.] Karst.) trees in the Fichtelgebirge region of Northern Bavaria, Germany. Dielectric constant and xylem sap flux were monitored continuously from June through October 1995, at several heights along the tree trunks. At the end of the measurement series, each tree was harvested, and its xylem sap extracted and analyzed to determine the concentrations of amino acids and cations. Results show that the sap flux density was correlated with vapor pressure deficit (VPD) at all heights in the stem. In contrast, the xylem tissue dielectric constant is influenced by VPD but can exhibit a significant temporal lag relative to changes in VPD. This lag varies with position along the tree trunk. The temporal variability of the dielectric constant is compared with both trees at several positions along the tree trunks. Results of xylem sap chemical analysis are presented. We show that spatial and temporal variability in the xylem tissue dielectric constant is influenced not only by water content, but by variations in xylem sap chemistry as well. This has important implications for microwave remote sensing of forested landscapes, as useful information may be acquired regarding stand physiology and water relations and where variations in dielectric properties within individual trees and across geographic areas can be significant error sources for forest inventory mapping.  相似文献   
869.
Schmitt  M.P. 《Electronics letters》1998,34(18):1725-1726
A new hybrid automatic repeat request scheme employing packet combining based on the Viterbi decoder is presented. It is shown that the proposed form of combining, together with a rearrangement of the signal constellation, can outperform similar forms of packet combining such as average diversity combining  相似文献   
870.
This paper presents a high-speed, small-area circuit specifically designed to identify the levels in the read out operation of a flash multilevel memory. The circuit is based on the analog computation of the Euclidean distance between the current read out from a memory cell and the reference currents that represent the different logic levels. An experimental version of the circuit has been integrated in a standard double-metal 0.7-μm CMOS process with a die area of only 140×100 μm2. Operating under a 5-V power supply, this circuit identifies the read-out current of a memory cell, and associates it with the appropriate logic level in 9 ns  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号