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   885867篇
  免费   11559篇
  国内免费   2285篇
电工技术   16256篇
综合类   790篇
化学工业   139058篇
金属工艺   34687篇
机械仪表   28054篇
建筑科学   21694篇
矿业工程   4989篇
能源动力   23122篇
轻工业   76595篇
水利工程   9298篇
石油天然气   16401篇
武器工业   52篇
无线电   102079篇
一般工业技术   174095篇
冶金工业   156179篇
原子能技术   18709篇
自动化技术   77653篇
  2021年   7964篇
  2020年   5810篇
  2019年   7453篇
  2018年   12524篇
  2017年   12730篇
  2016年   13534篇
  2015年   9093篇
  2014年   15060篇
  2013年   41594篇
  2012年   24025篇
  2011年   32858篇
  2010年   26033篇
  2009年   28979篇
  2008年   29783篇
  2007年   29432篇
  2006年   25853篇
  2005年   23483篇
  2004年   22661篇
  2003年   22100篇
  2002年   21382篇
  2001年   20971篇
  2000年   19757篇
  1999年   20037篇
  1998年   46150篇
  1997年   33541篇
  1996年   26306篇
  1995年   20354篇
  1994年   18236篇
  1993年   17736篇
  1992年   13583篇
  1991年   13023篇
  1990年   12772篇
  1989年   12366篇
  1988年   11857篇
  1987年   10460篇
  1986年   10205篇
  1985年   11975篇
  1984年   11045篇
  1983年   10102篇
  1982年   9274篇
  1981年   9315篇
  1980年   8900篇
  1979年   8939篇
  1978年   8630篇
  1977年   9839篇
  1976年   12729篇
  1975年   7588篇
  1974年   7258篇
  1973年   7214篇
  1972年   6118篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Factors affecting the performance of antacids F-MA 11, dihydroxy aluminum aminoacetate, magaldrate and magnesium hydroxide were studied in vitro using Schaub's acid neutralization test, a modified Reheis reaction velocity test and the USP test. From the results obtained it was evident that type and combination of antacid, the adjuvants and formulation techniques used in preparation of antacids affect their performance. The USP preliminary antacid test and acid neutralization test are not optimal in vitro tests to evaluate in vitro onset and duration of action of antacids.  相似文献   
992.
A method for measuring the characteristics of tunneling and impact ionization in thin-film electroluminescent emitters is suggested. This method makes it possible to find time dependences of the space-charge layer thickness near the anode and the length of the impact ionization region, to determine more exactly the time dependence of the field in the potential barrier at the cathode interface, the maximum depth of the surface states from which electron tunneling occurs, the minimum thickness of the barrier, and the electron tunneling probability, as well as the impact ionization rate for the deep centers related to structural defects of the phosphor layer.  相似文献   
993.
With the increasing demand for a proper and efficient XML data storage, XML-Enabled Database (XEnDB) has emerged as one of the popular solutions. It claims to combine the pros and limit the cons of the traditional Database Management Systems (DBMS) and Native XML Database (NXD). In this paper, we focus on XML data update management in XEnDB. Our aim is to preserve the conceptual semantic constraints and to avoid inconsistencies in XML data during update operations. In this current era when XML data interchange mostly occurs in a commercial setting, it is highly critical that data exchanged be correct at all times, and hence data integrity in XML data is paramount. To achieve our goal, we firstly classify different constraints in XML documents. Secondly, we transform these constraints into XML Schema with embedded SQL annotations. Thirdly, we propose a generic update methodology that utilizes the proposed schema. We then implement the method in one of the current XEnDB products. Since XEnDB has a Relational Model as the underlying data model, our update method uses the SQL/XML as a standard language. Finally, we also analyze the processing performance.  相似文献   
994.
995.
Deformation and attenuation of an ultrawideband radio pulse propagating along a single-wire line are analyzed as functions of the pulse initial duration. Variations in the longitudinal and transverse components of the pulse electric field with the distance from the line are determined. Features of the spatial distribution of the energy carried by the pulse near the line are revealed.  相似文献   
996.
In this paper, we propose a cognitive cellular system based on DS MC-CDMA to coexist with a number of narrow-band legacy systems in the same frequency range. If the bandwidth and the frequency location of each narrow-band system are known to this cognitive MC-CDMA, it is possible to mitigate their interfering effect in the cognitive receivers by adaptive transmission. We will develop an algorithm for calculating the adaptive transmission parameters and show that it combats interference in the channel effectively.  相似文献   
997.
Catalytic properties of composite amorphous carbon-platinum layers produced by magnetron cosputtering have been studied. The layers were characterized by electron microscopy, IR spectroscopy, ellipsometry, gravimetry, and spectrophotometric chemical analysis. The catalytic activity of the layers was studied in an air-hydrogen fuel cell by measuring its load and power characteristics.  相似文献   
998.
We demonstrate endless polarization stabilization with a control speed of up to 9 krad/s, over random Poincare sphere trajectories. These are in total >35 Mrad long, are composed in particular of difficult-to-track circles with all radii and orientations, and thereby include all possible worst cases. The maximum polarization mismatch and relative intensity errors are 0.13 rad and 0.43%, respectively. The controller runs on a field-programmable gate array and uses a commercial multistage LiNbO3 polarization transformer as the control device.  相似文献   
999.
Strong fiber Bragg gratings were written through the standard polymer coatings of "off-the-shelf" high numerical aperture single-mode optical fibers after a few seconds exposure with femtosecond pulse durations of infrared radiation through a phase mask. While writing through the acrylate coating, we obtained index modulations of up to 1.4 x 10-3 and 7 x 10-4 with and without H2 -loading, respectively.  相似文献   
1000.
DefibViz is a software application developed for defibrillation simulation and visualization. It exploits both surface techniques and methods for the interactive exploration of volumetric datasets for the analysis of transthoracic defibrillation simulation results. DefibViz has a graphical user interface for the specification of the shape, size, position, and applied voltage of a defibrillator's electrodes. An option is provided for using 3D slice plane widgets, which operate on the volumetric datasets, such that the distribution of the voltage gradient induced by an electric shock can be visually inspected in various tissues throughout the myocardium and torso. One goal of DefibViz is to enhance understanding of how electrode parameters relate to the change of the voltage gradient distribution throughout the heart, which may help lead to optimal defibrillator design. DefibViz is significant, in that, it is built by using an open-source graphics and visualization framework providing a platform for subsequent modifiability and extensibility. Moreover, it integrates simulation and visualization techniques, which previously required the running of several independent software executables, into an enhanced, seamless, and comprehensive software application.  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