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   242403篇
  免费   2699篇
  国内免费   427篇
电工技术   4307篇
综合类   257篇
化学工业   39711篇
金属工艺   9393篇
机械仪表   7418篇
建筑科学   5492篇
矿业工程   1394篇
能源动力   5195篇
轻工业   25000篇
水利工程   2488篇
石油天然气   5099篇
武器工业   32篇
无线电   25137篇
一般工业技术   44940篇
冶金工业   45500篇
原子能技术   5956篇
自动化技术   18210篇
  2021年   2156篇
  2019年   2044篇
  2018年   3526篇
  2017年   3458篇
  2016年   3727篇
  2015年   2260篇
  2014年   3948篇
  2013年   10246篇
  2012年   6208篇
  2011年   8388篇
  2010年   6615篇
  2009年   7297篇
  2008年   7626篇
  2007年   7751篇
  2006年   6923篇
  2005年   6076篇
  2004年   5840篇
  2003年   5624篇
  2002年   5698篇
  2001年   5583篇
  2000年   5395篇
  1999年   5317篇
  1998年   12626篇
  1997年   8933篇
  1996年   6900篇
  1995年   5351篇
  1994年   4757篇
  1993年   4634篇
  1992年   3672篇
  1991年   3393篇
  1990年   3600篇
  1989年   3477篇
  1988年   3307篇
  1987年   2897篇
  1986年   2935篇
  1985年   3374篇
  1984年   3221篇
  1983年   2894篇
  1982年   2740篇
  1981年   2825篇
  1980年   2721篇
  1979年   2628篇
  1978年   2684篇
  1977年   2949篇
  1976年   3811篇
  1975年   2369篇
  1974年   2244篇
  1973年   2376篇
  1972年   1972篇
  1971年   1859篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
The authors present a practical extension to typestate checking, which is capable of proving programs free of uninitialized variable errors even when these programs contain conditionally initialized variables where the initialization of a variable depends upon the equality of one or more tag variables to a constant. The user need not predeclare the relationship between a conditionally initialized variable and its tags, and this relationship may change from one point in the program to another. The technique generalizes liveness analysis to conditional liveness analysis. Like typestate checking, this technique incorporates a dataflow analysis algorithm in which each point in a program is labeled with a lattice point describing statically tracked information, including the initialization of variables. The labeling is then used to check for programming errors such as referencing a variable which may be uninitialized  相似文献   
992.
993.
994.
The electroluminescence and stimulated emission of lasers with one layer of InAs quantum dots (QD’s) grown in a single molecular-beam epitaxial process on vicinal GaAs(001) surfaces misoriented in the direction [010] by 2, 4 and 6° are investigated. It is discovered that an increase in the misorientation angle leads to a blue shift and a decrease in the full width at half maximum (FWHM) of the electroluminescence spectrum. This effect is attributed to a decrease in the size of the quantum dots and improvement in their size uniformity. A strong dependence of the threshold current density on the width of the spontaneous luminescence spectrum is discovered. The room-temperature threshold current density of the lasers with one layer of quantum dots and the spontaneous luminescence spectrum having the smallest FWHM (54 meV) equals 210 A/cm2. Fiz. Tekh. Poluprovodn. 32, 1482–1486 (December 1998)  相似文献   
995.
Deals with the use of neural networks to solve linear and nonlinear programming problems. The dynamics of these networks are analyzed. In particular, the dynamics of the canonical nonlinear programming circuit are analyzed. The circuit is shown to be a gradient system that seeks to minimize an unconstrained energy function that can be viewed as a penalty method approximation of the original problem. Next, the implementations that correspond to the dynamical canonical nonlinear programming circuit are examined. It is shown that the energy function that the system seeks to minimize is different than that of the canonical circuit, due to the saturation limits of op-amps in the circuit. It is also noted that this difference can cause the circuit to converge to a different state than the dynamical canonical circuit. To remedy this problem, a new circuit implementation is proposed.  相似文献   
996.
1. Occupational health nurses need a general knowledge of psychiatric medications to work effectively with clients and their off site health providers. 2. Acquiring an understanding of the major classes of medications--anti-psychotic, anti-anxiety, anti-depressant, and antimanic--is important. 3. It is helpful to understand under what conditions and with which conditions psychotropic medications are helpful.  相似文献   
997.
It is shown that the electrical breakdown voltages of polycarbonate film/metal foil capacitors can be increased. This can be achieved by briefly exposing the metal foil in these spirally wound film foil sections to a low-pressure, low-temperature gas plasma. Exposure of tin/lead foil to a 96% CF4/4% O2 gas plasma for four min, for example, produced >500% increase in breakdown voltage of sealed polycarbonate capacitors  相似文献   
998.
E. Ohashi  I. Karube 《Food Control》1993,4(4):183-188
This article presents an overview of the results of a five-year research project on sensors for the food industry in Japan. This project was a government-sponsered research programme involving the food industry and the instrumentation industry, coordinated by the Japanese Ministry of Agriculture, Forestry and Fisheries. The programme focussed on 17 food processing operations and quality control tasks, where the need for an on-line (or rapid at-line) measurement had been established. The instrument development work employed biosensors pH and gas sensors, optical-imaging devices, as well as near-infrared, microwave, ultrasound and mechanical resonance techniques, together with robotics and advanced data-processing techniques.  相似文献   
999.
In right middle cerebral territory infarction a new sign, excessive closure of the right eye ipsilateral to the lesion and mild closure of the left eye on command, was noted. The excessive ipsilateral eye closure was not observed on spontaneous eye closure.  相似文献   
1000.
A multivariate statistical method, correspondence factorial (CF) analysis, was used to examine the correlations among the protein binding and cell proliferation effects of a series of 36 di- and triphenylethylenes (DPEs and TPEs). The analysis was applied to a study which measured their competition for estradiol binding to cytosol estrogen receptor (ER), their influence on protein kinase C (PKC) activity under different conditions of enzyme activation, their ability to promote the growth of a breast cancer cell line and to inhibit growth at high concentrations (cytotoxicity). The CF analysis revealed several levels of correlation. First, it distinguished those molecules within the population that stimulated rather than inhibited PKC activity. Second, it made apparent a strong correlation between cytotoxicity and inhibition of Ca++ and phosphatidylserine-dependent PKC activity, which was most marked when the enzyme had been activated by diacylglycerol indicating that PKC inhibition under physiological conditions might contribute to the overall cytotoxicity of these compounds. Third, a lower level of correlation was established between competition for ER binding and cytotoxicity. Taken together, the results suggest that MCF7 cells might be most sensitive to a cytotoxic effect of TPEs (via PKC and other targets) when they at the same time decrease estrogen-stimulated proliferation via an ER-mediated antiestrogenic effect.  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