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   1293篇
  免费   59篇
  国内免费   3篇
电工技术   25篇
化学工业   266篇
金属工艺   27篇
机械仪表   26篇
建筑科学   39篇
矿业工程   4篇
能源动力   83篇
轻工业   106篇
水利工程   11篇
石油天然气   11篇
无线电   139篇
一般工业技术   249篇
冶金工业   156篇
原子能技术   22篇
自动化技术   191篇
  2023年   9篇
  2022年   35篇
  2021年   64篇
  2020年   30篇
  2019年   46篇
  2018年   43篇
  2017年   61篇
  2016年   52篇
  2015年   33篇
  2014年   64篇
  2013年   97篇
  2012年   68篇
  2011年   89篇
  2010年   57篇
  2009年   58篇
  2008年   51篇
  2007年   44篇
  2006年   34篇
  2005年   17篇
  2004年   25篇
  2003年   22篇
  2002年   17篇
  2001年   22篇
  2000年   13篇
  1999年   19篇
  1998年   41篇
  1997年   28篇
  1996年   18篇
  1995年   17篇
  1994年   23篇
  1993年   18篇
  1992年   6篇
  1991年   5篇
  1990年   7篇
  1989年   6篇
  1988年   6篇
  1987年   7篇
  1986年   5篇
  1985年   12篇
  1983年   6篇
  1982年   9篇
  1981年   9篇
  1980年   8篇
  1979年   7篇
  1977年   10篇
  1976年   8篇
  1974年   3篇
  1973年   4篇
  1972年   7篇
  1971年   3篇
排序方式: 共有1355条查询结果,搜索用时 15 毫秒
1.
2.
We analysed the ground deformation across two blocks defined by the Rio-Patras fault from 1993 to 2017 using multi-temporal Synthetic Aperture Radar Interferometry (InSAR) techniques. Our main objective was to contribute to the assessment of seismic hazard near the large city of Patras. Multiple data-sets were used, each one covering different temporal periods. Descending and ascending acquisitions, providing different viewing geometries contribute to fully determine the ground displacement in 3D. The data-sets used are from the European Space Agency’s (ESA) European Remote Sensing (ERS), Environmental Satellite (ENVISAT) and SENTINEL-1 as well as German Aerospace Center (DLR) ’s TERRASAR-X missions. Considering ESA’s missions covering both acquisition geometries and long periods, the southern block, showing lack of a sufficient number of scatterers does not allow the displacement characterization. In contrary, the northern block is characterized by a high number of scatterers having values of maximum likehood ranging from ?3.5 to ?4.3 mm year?1 for ascending geometry and from ?1.6 to ?2.7 mm year?1 for the descending one. The fact that both geometries show negative values of displacements are consistent with downlift movement and at the same time the quantitative differentiation probably indicates an horizontal component as well.  相似文献   
3.
The case-based learning (CBL) approach has gained attention in medical education as an alternative to traditional learning methodology. However, current CBL systems do not facilitate and provide computer-based domain knowledge to medical students for solving real-world clinical cases during CBL practice. To automate CBL, clinical documents are beneficial for constructing domain knowledge. In the literature, most systems and methodologies require a knowledge engineer to construct machine-readable knowledge. Keeping in view these facts, we present a knowledge construction methodology (KCM-CD) to construct domain knowledge ontology (i.e., structured declarative knowledge) from unstructured text in a systematic way using artificial intelligence techniques, with minimum intervention from a knowledge engineer. To utilize the strength of humans and computers, and to realize the KCM-CD methodology, an interactive case-based learning system(iCBLS) was developed. Finally, the developed ontological model was evaluated to evaluate the quality of domain knowledge in terms of coherence measure. The results showed that the overall domain model has positive coherence values, indicating that all words in each branch of the domain ontology are correlated with each other and the quality of the developed model is acceptable.  相似文献   
4.
Clean Technologies and Environmental Policy - The concentration of any disinfectant is a major parameter which is used to evaluate the quality of water. Chlorine is the most common disinfecting...  相似文献   
5.
By distinguishing among mobile and immobile dislocations and operating within the framework of continuum mechanics it is possible to derive a set of partial differential equations of the diffusion-reaction type for the evolution of dislocation species. On examining the competition between gradient dependent terms modelling the motion of dislocations and nonlinear terms modelling their interactions, it is shown that stable solutions are possible. The wavelength turns out to be a material property in agreement with observations. The discussion is limited to one dimension, that is to glide of straight dislocations in the slip direction, and the model corresponds physically to the ladder-like structure of persistent slip bands.  相似文献   
6.
The non-uniformity of the air temperatures and the slow flow rate at the plane collector exit constitute the main cause of the limitations of the solar drying systems. In order to obtain an uniform and a variable flow rate for different uses, a hot air generator using concentrated solar radiation is proposed. To improve the thermal efficiency of the generator, a study of the influence of different shape parameters is realized. The generator is simulated in the laboratory while investigating the flow induced by a circular disc heated uniformly by Joule effect at constant temperature. This disc is placed at the entrance of an open ended vertical cylinder of a larger diameter. Thermal radiation emitted by the hot disc heats the cylinder wall. The heating of the fluid at the cylinder-inlet generates a thermosiphon flow around the one created by the hot disc. The comparison of the velocity and the temperature profiles of the resulting flow permits to determine the influence of the cylinder height, the vertical source-cylinder spacing and the radius ratio, on the resulting flow at the system exit. Thus, a judicious choice of the shape parameters entails an improvement of the flow rate as well as the thermal flux absorbed by the air and a good homogenization of the air temperature at the generator exit.  相似文献   
7.
Alpha 1 antitrypsin deficiency (AT) is an autosomal recessive disease associated with chronic liver disease in adults and children and emphysema in adults. The disease is one of the most common inherited disorders of the Caucasian population of North Europe and North America and is the most common genetic reason for pediatric orthotopic liver transplantation (OLTx), although it is a rare indication in adults. The natural history of the disease is unpredictable and the pathogenesis of the liver injury unclear. Thirty-five patients with histologically apparent alpha 1 AT accumulation in the liver (22 adults, 13 children) have been transplanted in this center. Clinical features were correlated with the pretransplant phenotype, serum alpha 1 antitrypsin levels and potential precipitating factors. All children were PiZZ homozygotes, most of whom had presented with neonatal hepatitis. The majority of adult patients were heterozygotes presenting with portal hypertension and liver cirrhosis. Current one-year posttransplant survival figures are 73% for adults and 87.5% for children. Replacement of the cirrhotic liver results in acquisition of the donor phenotype, a rise in serum levels of alpha 1 antitrypsin, and apparent prevention of associated disease.  相似文献   
8.
Infrared and UV–vis studies of metallocene immobilization on silica are reported here. The results have indicated changes in the Zr coordination sphere of metallocene depending on the immobilization route used. The reaction of [(Cp)2ZrCl2] with silica formed [(Cp)2ZrCl]+[SiO] species. The same metallocene, reacting with TMA modified silica, formed monomethylated and dimethylated species by the substitution of chloro for methyl ligands, stabilized on the surface by interaction with “MAO-like” species (methylaluminoxane, MAO). These monomethylated and dimethylated cationic zirconium species are the active centers for the polymerization reaction. Different order of TMA addition in the silica modification step generated surface species of a similar nature, differing in their relative quantities. The highest amount of these active species was obtained when the support was added to the TMA solution rather than adding the TMA solution to the silica support. This was the most significant parameter affecting catalytic activity in ethylene polymerization.  相似文献   
9.
As the manned exploration of space continues, many complex structural components are being developed to construct the orbital platforms that will be used to house communication hardware, personnel, and manufacturing complexes. These components are extremely flexible and complex in their behavior. There is a need for a simple method for determining the dynamic characteristics of these space structures with a minimum of effort. A mathematical model of one of these structural elements, an articulating truss beam, has been developed to predict its dynamic response. Assumptions of the force interaction between the beam elements and the joints have been made for using this model. Algorithms are provided to determine the flexibility matrix of the truss beam for use in the equation of motion. The natural frequencies obtained from using this method are compared with those obtained by the finite element method. An experimental procedure is planned to validate the results from the theoretical method.  相似文献   
10.
In the present work, the composition of H- 13 tool steel was modified with respect to the vanadium content to include an addition of niobium to obtain improved austenite grain size control without altering the tempering response of the steel. Optical metallography and transmission electron microscopy (TEM) observation of extraction replicas showed that the new steel had a smaller austenite grain size and a finer carbide size distribution than the vanadium steel, which indicates a higher potential toughness.  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