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   2654篇
  免费   178篇
  国内免费   6篇
电工技术   43篇
综合类   6篇
化学工业   665篇
金属工艺   50篇
机械仪表   42篇
建筑科学   89篇
矿业工程   1篇
能源动力   107篇
轻工业   287篇
水利工程   7篇
石油天然气   2篇
无线电   279篇
一般工业技术   487篇
冶金工业   244篇
原子能技术   42篇
自动化技术   487篇
  2023年   24篇
  2022年   41篇
  2021年   73篇
  2020年   56篇
  2019年   52篇
  2018年   70篇
  2017年   76篇
  2016年   73篇
  2015年   91篇
  2014年   111篇
  2013年   175篇
  2012年   153篇
  2011年   250篇
  2010年   162篇
  2009年   146篇
  2008年   149篇
  2007年   107篇
  2006年   102篇
  2005年   90篇
  2004年   71篇
  2003年   90篇
  2002年   55篇
  2001年   35篇
  2000年   38篇
  1999年   47篇
  1998年   75篇
  1997年   36篇
  1996年   51篇
  1995年   23篇
  1994年   41篇
  1993年   34篇
  1992年   28篇
  1991年   19篇
  1990年   18篇
  1989年   12篇
  1988年   12篇
  1987年   11篇
  1986年   7篇
  1985年   10篇
  1984年   7篇
  1983年   10篇
  1982年   7篇
  1980年   6篇
  1979年   6篇
  1978年   7篇
  1977年   10篇
  1976年   22篇
  1975年   7篇
  1974年   7篇
  1970年   5篇
排序方式: 共有2838条查询结果,搜索用时 31 毫秒
11.
Ovarian failure is heterogeneous in etiology and may occur at various points in a woman's life. As such, it may interfere with fertility. Clinical presentation ranges from complete cessation of menses to oligomenorrhea to the continuation of menses with elevated gonadotropins. Various therapies have been used in an attempt to induce fertility, including sex steroids and gonadotropin-releasing hormone agonists to suppress circulating gonadotropin alone or in combination with estrogen or gonadotropin-releasing hormone agonists to induce ovulation. Corticosteroids are also used to overcome autoimmunity. Randomized therapeutic trials are rare and fail to demonstrate any significant improvement in ovulation and pregnancy rates. Donor oocytes have demonstrated high success rates and have proven to be useful in patients with both premature ovarian failure and natural menopause. Pregnancies have been initiated and maintained in women through 60 years of age. Thus, for those accepting of the technique, oocyte donation appears to be the treatment of choice for hypergonadotropic hypogonadism.  相似文献   
12.
The equivalent inclusion method (EIM) assuming linear elasticity is used to calculate the mechanical interactions between spherical rubber particles in an amorphous matrix, as in a rubber toughened polymer. The influences of the various calculation parameters are examined and it is shown that the method can provide reliable results with regard to the level of hydrostatic stress in the particles. Damage of the material is simulated by replacing the most stressed particles by voids. Numerical simulations for several hundreds of interacting particles give information on the kinetics and spatial organisation of the damage. It appears that, as the volume fraction of particles increases from 10 to 20%, the spatial configuration of the damage evolves from a localised to a diffuse mode. These results are discussed in relation to the efficiency of rubber toughening.  相似文献   
13.
Zusammenfassung Eine einfache Formel zur n?herungsweisen Berechnung der Axialspannungen eines Rohres infolge der von einer Temperaturschichtung im Rohrinnern hervorgerufenen Temperaturfelder wird vorgestellt. Die Formel basiert auf der konventionellen Balkentheorie. Durch Vergleiche der von der N?herungsformel gelieferten Axialspannungen mit den Axialspannungen, die mit Hilfe von Finite-Elemente-Rechnungen erhalten werden, wird gezeigt, da? die N?herungsformel die maximalen Axialspannungen ausreichend genau wiedergibt.  相似文献   
14.
15.
The paper reports the results of on-site regeneration catalytic bed of the natural gas reformer in a 5 kW PEM fuel cell system. The Ni catalyst previously poisoned by sulphur from the available natural gas, could be re-activated by injection of pure water steam, following the method developed for industrial reformers using the same metal catalyst: this method was shown to be perfectly efficient, provided no natural gas was fed during the operation. Results of the tests conducted are presented and discussed in relation to published data on S-sorption on Ni surfaces.  相似文献   
16.
When designing an accurate automated guidance system for vehicles, a major problem is sliding and pseudo-sliding effects. This is especially the case in agricultural applications, where five-centimetre accuracy with respect to the desired trajectory is required, although the vehicles are moving on slippery ground. It has been established that RTK GPS was a very suitable sensor to achieve automated guidance with such high precision: several control laws have been designed for vehicles equipped with this sensor, and provide the expected guidance accuracy as long as the vehicles do not slide. In previous work, further control developments have been proposed to take sliding into account: guidance accuracy in slippery environments has been shown to be preserved, except transiently at the beginning/end of curves. In this paper, the design of this control law is first recalled and discussed. A Model Predictive Control method is then applied in order to preserve accuracy of guidance even during these curvature transitions. Finally, the overall control scheme is implemented, and improvements with respect to previous guidance laws are demonstrated through full-scale experiments.  相似文献   
17.
Biochips are miniaturized, highly ordered analysis systems which offer the unique advantage of highly parallel analysis of thousands of analytes at the same time. Although this technique has been enthusiastically developed and has promised to improve and speed up numerous biological assays, the quality control of chip manufacture, chip analysis and data management has received less attention.

The following article compares three epoxy-containing chip surfaces (ARChip Epoxy, 3D-Link™, and EasySpot) with respect to their autofluorescence, immobilization capacity, background fluorescence and hybridization efficiency. Since data collected from biochip experiments are random snapshots with errors, inherently noisy and incomplete, we tried to evaluate technical factors causing variability and to set up quality control procedures for chip manufacture and chip analysis. Variabilities caused by arraying, glass substrate and polymer coating, fluorescent label and experimental conditions are discussed in details.  相似文献   

18.
Oxidation catalysts are modeled by oxide single crystals, thin oxide films, as well as supported oxide nanoparticles. We characterize the surface of those materials using a variety of surface sensitive techniques including scanning tunneling microscopy and spectroscopy, photoelectron spectroscopy, infrared spectroscopy, and thermal desorption spectroscopy. We find temperature dependent structural transformations from V2O5(001) to V2O3(0001) via V6O13(001). V2O3(0001) is found to be vanadyl terminated in an oxygen ambient and it loses the vanadyl termination after electron bombardment. It is shown that the concentration of vanadyl groups controls the selectivity of the methanol oxy-dehydrogenation towards formaldehyde. A proposal for the mechanism is made. The results on single crystalline thin films are compared with similar measurements on deposited vanadia nanoparticles. The experimental results are correlated with theoretical calculations and models.  相似文献   
19.
New generations of automobiles will include driver assistance systems requiring powerful, low-cost processors to handle video/camera applications and to enable fast, convenient application development. Shrinking feature sizes on processors already in development will bring substantial increases in system speed and functionality.  相似文献   
20.
This paper presents the results of the Réseau futé (smart net) project, the goal of which is to use distributed AI and multi-agent techniques for network management and supervision. More precisely, these techniques have been applied to the partial automation of the dynamic processing (what is known about a network is always incomplete and can change at any time) of alarms and of various event notifications received by network management platforms. The system that we propose is able for example to automatically handle some alarms or to filter events of no-interest for a given operator. To achieve this goal, an assistant, or interface agent according to the model proposed by Patti Maes [MK93], has been realized. The goal of the assistant is first to learn, by observation, the behavior of the network supervision operator and second to reproduce such a behavior when the conditions in which the behavior has been learned are detected again. The learned information are stored using chronicles [Gha94]. A chronicle is a data-structure allowing programmers to represent sequences of events while taking temporal knowledge into account. Our assistant has been implemented and tested within Magenta which is a program, written in Smalltalk, that simulates (in a simplified way) a network management platform. This program respects roughly the gdmo and cmis standards.  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