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   26672篇
  免费   1698篇
  国内免费   26篇
电工技术   164篇
综合类   10篇
化学工业   5573篇
金属工艺   428篇
机械仪表   558篇
建筑科学   812篇
矿业工程   52篇
能源动力   506篇
轻工业   5469篇
水利工程   313篇
石油天然气   119篇
武器工业   1篇
无线电   1044篇
一般工业技术   4325篇
冶金工业   5394篇
原子能技术   66篇
自动化技术   3562篇
  2024年   66篇
  2023年   278篇
  2022年   271篇
  2021年   716篇
  2020年   657篇
  2019年   669篇
  2018年   1236篇
  2017年   1208篇
  2016年   1258篇
  2015年   965篇
  2014年   1108篇
  2013年   2302篇
  2012年   1766篇
  2011年   1562篇
  2010年   1272篇
  2009年   1089篇
  2008年   1144篇
  2007年   1052篇
  2006年   668篇
  2005年   558篇
  2004年   532篇
  2003年   508篇
  2002年   432篇
  2001年   323篇
  2000年   261篇
  1999年   312篇
  1998年   1898篇
  1997年   1191篇
  1996年   728篇
  1995年   394篇
  1994年   301篇
  1993年   318篇
  1992年   87篇
  1991年   74篇
  1990年   61篇
  1989年   59篇
  1988年   82篇
  1987年   73篇
  1986年   63篇
  1985年   72篇
  1984年   61篇
  1983年   35篇
  1982年   36篇
  1981年   60篇
  1980年   59篇
  1978年   30篇
  1977年   104篇
  1976年   207篇
  1975年   33篇
  1973年   38篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
62.
García J  Mas D  Dorsch RG 《Applied optics》1996,35(35):7013-7018
A method for the calculation of the fractional Fourier transform (FRT) by means of the fast Fourier transform (FFT) algorithm is presented. The process involves mainly two FFT's in cascade; thus the process has the same complexity as this algorithm. The method is valid for fractional orders varying from -1 to 1. Scaling factors for the FRT and Fresnel diffraction when calculated through the FFT are discussed.  相似文献   
63.
64.
Excess Volumes,V E, and excess viscosities, E, at 293.15 and 313.15 K are reported for binary mixtures of some cyclic ethers (tetrahydrofuran, tetrahydropyran, 2-methyltetrahydrofuran and 2,5-dimethyltetrahydrofuran) + bromocyclohexane. These properties were obtained from density and viscosity measurements. E and E show negatives values for all the mixtures.  相似文献   
65.
1.5% Capsaicin (Cap) or Vehicle was respectively used to treat the right or left sciatic nerve in 20 Sprague-Dawley rats. On the seventh day, the 20 rats were at random divided into electroacupuncture (EA) group and non-EA group, the spinal cord corresponding to the afferent segments of sciatic nerve was taken out for observing the changes of acetylcholinesterase (AChE) activity and [3H]-quinuelidinylbenzylate (QNB) binding sites in the spinal dorsal horn (SDH). The results were as follows: (1) EA "Huantiao" could enhance AChE activity in the SDH and decrease [3H]-QNB binding sites; (2) Cap treating sciatice nerve could weaken AChE activity in the SDH and merease [3H]-QNB binding sites; (3) Cap treatment could inhibit or partially inhibit the actions of EA as above. The results indicated that ACh participated in the primary afferent of acupuncture information and might exist in Cap-sensitive neurons.  相似文献   
66.
In the last years different classification systems for hospitalized patients have been developed in the United States, that allow to evaluate different aspects of any Hospital: The quality, the efficacy and the efficiency. The classification of "The Diagnosis Related Groups" (DRG) relates the hospitalized patients with the expenses that they generate, and it is the most used in Europe. In the version DRG-All Patient, all the diagnoses and procedures of the hospitalized patients, using the International Classification of Diseases, are divided in to 25 Major Diagnostic Categories (MDC) where each one excludes all the others. We describe the behavior with respect to the age, sex and stay of all the GDR integrated in the CDM 6 and 7: diseases and disorders of the digestive tract, and diseases and disorders of the hepatobiliary system and the pancreas. The study has been carried out with a national data base of two millions of cases seen from 214 acute-care Hospitals. The MDC number 6 is the most frequent, with an important number of patients in the pediatric age; it is more frequent in males; the average stay is 8.59 days and 19 GDR (36.5%) have a variation coefficient greater than one. The other MDC, number 7 is less frequent, the majority of the patients are between 60-80 years of age, the average stay is 12.2 days with a coefficient of variation greater than one in 4 GDR (17.4%). Clinical Services should know the characteristics and behavior of their patients, as well as the comparison with the national data bases. This may allow a control of the quality and the costs by using a common "language" with the managers.  相似文献   
67.
68.
The additive model of multiattribute value theory is widely used in multicriteria choice problems. But often it is not easy to obtain precise values for the scaling weights or the alternatives’ value in each function. Several decision rules which require weaker information, such as ordinal information, have been proposed to select an alternative under these circumstances. We propose new decision rules and test them using Monte-Carlo simulation, considering that there is ordinal information both on the scaling weights and on the alternatives’ values. Results show the new rules constitute a good approximation. We provide guidelines about how to use these rules in a context of selecting a subset of the most promising alternatives, considering the contradictory objectives of keeping a low number of alternatives yet not excluding the best one.  相似文献   
69.
An adaptive, real-time, traffic monitoring system   总被引:1,自引:0,他引:1  
In this paper we describe a computer vision-based traffic monitoring system able to detect individual vehicles in real-time. Our fully integrated system first obtains the main traffic variables: counting, speed and category; and then computes a complete set of statistical variables. The objective is to investigate some of the difficulties impeding existing traffic systems to achieve balanced accuracy in every condition; i.e. day and night transitions, shadows, heavy vehicles, occlusions, slow traffic and congestions. The system we present is autonomous, works for long periods of time without human intervention and adapts automatically to the changing environmental conditions. Several innovations, designed to deal with the above circumstances, are proposed in the paper: an integrated calibration and image rectification step, differentiated methods for day and night, an adaptive segmentation algorithm, a multistage shadow detection method and special considerations for heavy vehicle identification and treatment of slow traffic. A specific methodology has been developed to benchmark the accuracy of the different methods proposed.  相似文献   
70.
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