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   253417篇
  免费   2817篇
  国内免费   870篇
电工技术   4817篇
综合类   193篇
化学工业   36229篇
金属工艺   9513篇
机械仪表   7547篇
建筑科学   6085篇
矿业工程   880篇
能源动力   7250篇
轻工业   21148篇
水利工程   2203篇
石油天然气   3231篇
武器工业   15篇
无线电   34320篇
一般工业技术   50017篇
冶金工业   48649篇
原子能技术   5077篇
自动化技术   19930篇
  2021年   2185篇
  2020年   1572篇
  2019年   1928篇
  2018年   3288篇
  2017年   3320篇
  2016年   3412篇
  2015年   2235篇
  2014年   3979篇
  2013年   11521篇
  2012年   6261篇
  2011年   8618篇
  2010年   6933篇
  2009年   7911篇
  2008年   8418篇
  2007年   8314篇
  2006年   7383篇
  2005年   6510篇
  2004年   6294篇
  2003年   6566篇
  2002年   6052篇
  2001年   6524篇
  2000年   5986篇
  1999年   6397篇
  1998年   16526篇
  1997年   11433篇
  1996年   8806篇
  1995年   6614篇
  1994年   5914篇
  1993年   5855篇
  1992年   4137篇
  1991年   4024篇
  1990年   3857篇
  1989年   3650篇
  1988年   3563篇
  1987年   3019篇
  1986年   2943篇
  1985年   3211篇
  1984年   2928篇
  1983年   2829篇
  1982年   2637篇
  1981年   2544篇
  1980年   2462篇
  1979年   2305篇
  1978年   2108篇
  1977年   2606篇
  1976年   3564篇
  1975年   1764篇
  1974年   1729篇
  1973年   1665篇
  1972年   1465篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
The theory of characteristic modes for aperture problems is used in this paper to solve the equivalent magnetic current and aperture fields due to a conducting cylinder with multiple slots. It is assumed that these slots are illuminated by either a transverse electric (TE) or a transverse magnetic (TM) plane wave and the media inside and outside the cylinder exhibit different electromagnetic properties. The formulation is given for the general case and numerical results for a limited number of slots are presented  相似文献   
42.
This short paper discusses the method of effectively canceling equal status normal mode noise not only on a sensor line but also on a transmission line of an optical instrument using a sensor with a sensordummy resistance  相似文献   
43.
Crosstalk between microstrip transmission lines   总被引:1,自引:0,他引:1  
Methods for prediction of crosstalk between microstrip transmission lines are reviewed and simplified for the weak-coupling case. Classical coupled transmission line theory is used for uniform lines, and potential and induced EMF methods are used for crosstalk between nonuniform lines. It is shown that the potential method is equivalent to classical coupled transmission line theory for the case of uniform lines. An experiment was performed for uniform coupled microstrip lines for frequencies from 50 MHz to 5 GHz, and good agreement between theory and measurement was obtained for both near- and far-end crosstalk  相似文献   
44.
45.
An instrument is proposed for continuously tracking the Sun and measuring its height by the use of a laser gyrometer as measuring converter. The accuracy in photoelectric sighting on the Sun is improved by greatly reducing the light fluxes to be compared by screening out the central part of the Sun's image in the focal plane. Translated from Izmeritel'naya Tekhnika, No. 3, pp. 7–9, March, 1994.  相似文献   
46.
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   
47.
Subcellular localization directed by specific A kinase anchoring proteins (AKAPs) is a mechanism for compartmentalization of cAMP-dependent protein kinase (PKA). Using a two-hybrid screen, a novel AKAP was isolated. Because it interacts with both the type I and type II regulatory subunits, it was defined as a dual specific AKAP or D-AKAP1. Here we report the cloning and characterization of another novel cDNA isolated from that screen. This new member of the D-AKAP family, D-AKAP2, also binds both types of regulatory subunits. A message of 5 kb pairs was detected for D-AKAP2 in all embryonic stages and in all adult tissues tested. In brain, skeletal muscle, kidney, and testis, a 10-kb mRNA was identified. In testis, several small mRNAs were observed. Therefore, D-AKAP2 represents a novel family of proteins. cDNA cloning from a mouse testis library identified the full length D-AKAP2. It is composed of 372 amino acids which includes the R binding fragment, residues 333-372, at its C-terminus. Based on coprecipitation assays, the R binding domain interacts with the N-terminal dimerization domain of RIalpha and RIIalpha. A putative RGS domain was identified near the N-terminal region of D-AKAP2. The presence of this domain raises the intriguing possibility that D-AKAP2 may interact with a Galpha protein thus providing a link between the signaling machinery at the plasma membrane and the downstream kinase.  相似文献   
48.
A case of endometrioid carcinoma arising from endometriosis of the sigmoid colon is reported. The patient had been treated with unopposed continuous estrogen injection for twenty years after bilateral salpingo-oophorectomy because of severe endometriosis. The pathology, pertinent literature and implications of the present case are discussed.  相似文献   
49.
The impact of crosstalk in an arrayed-waveguide N×N wavelength multiplexer is investigated precisely in relation to its application to wavelength-routing N×N all optical networks. In such systems multiple crosstalk light which has the same wavelength as the signal results in signal-crosstalk beat noise. We confirm that the noise is Gaussian and obtain the relation between crosstalk and power penalty. It is shown that the crosstalk must be less than -38 dB for a 16×16 system to keep the power penalty below 1 dB at a bit error rate of 10-9  相似文献   
50.
The one-dimensional (1D) position-sensitive superheated-liquid-droplet dosimeter (SLDD) has been fabricated and tested in the laboratory. The 1D SLDD is fabricated from a 9.525-mm OD, 6.35-mm ID, 20-cm long, Plexiglas-walled tube filled with a mixture of superheated-liquid Freon droplets and host medium glycerol. Washer-shaped piezoelectric acoustic transducers are positioned at both ends of the tube; they determine the number and positions of the acoustic events when the superheated-liquid droplets evaporate upon neutron irradiation. The SLDD is irradiated with the 137Cs and 60Co γ-sources, as well as 252Cf neutron source to test for its radiation response and spatial resolution. The SLDD based on the Freon-134a superheated-liquid droplets operating at 20°C and 1 atm is found to be ideal for measuring absorbed neutron dose. This study also proves that the positions of the radiation-induced nucleation acoustic events can be linearly determined from the differences in the transmission times received by the acoustic transducers on the 1D SLDD. The spatial resolution of the neutron depth-dose is 1 mm due the finite response time (1 μs) of the piezoelectric acoustic transducers.  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