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   30364篇
  免费   980篇
  国内免费   27篇
电工技术   205篇
综合类   10篇
化学工业   6410篇
金属工艺   475篇
机械仪表   592篇
建筑科学   916篇
矿业工程   53篇
能源动力   720篇
轻工业   6034篇
水利工程   344篇
石油天然气   134篇
武器工业   2篇
无线电   1182篇
一般工业技术   4675篇
冶金工业   5654篇
原子能技术   90篇
自动化技术   3875篇
  2024年   288篇
  2023年   357篇
  2022年   401篇
  2021年   865篇
  2020年   756篇
  2019年   776篇
  2018年   1267篇
  2017年   1236篇
  2016年   1304篇
  2015年   996篇
  2014年   1188篇
  2013年   2412篇
  2012年   1879篇
  2011年   1761篇
  2010年   1418篇
  2009年   1262篇
  2008年   1274篇
  2007年   1182篇
  2006年   768篇
  2005年   656篇
  2004年   607篇
  2003年   578篇
  2002年   487篇
  2001年   385篇
  2000年   302篇
  1999年   348篇
  1998年   2017篇
  1997年   1257篇
  1996年   783篇
  1995年   439篇
  1994年   335篇
  1993年   339篇
  1992年   103篇
  1991年   79篇
  1990年   64篇
  1989年   63篇
  1988年   86篇
  1987年   86篇
  1986年   73篇
  1985年   79篇
  1984年   65篇
  1983年   37篇
  1982年   41篇
  1981年   64篇
  1980年   62篇
  1978年   31篇
  1977年   107篇
  1976年   213篇
  1975年   35篇
  1973年   39篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
It is described the case of a patient with Ovarian Cystadenoma in whom a 3.5 cm nodular lesion was accidentally detected in her left suprarenal gland. She had no signs of hypercortisolism or any other suprarenal pathology and was symptomless. Determinations in the urine of 24 hours of Cortisol, Adrenaline and Noradrenaline, 17-ketosteroids and Tetrahydroaldosterone were normal. Daily rhythm and plasmatic determinations of ACTH, cortisol and 11-deoxycortisol were normal. The Dexamethasone suppression test was also normal. In the suprarenal gammagraphy it appeared an intense captation by left suprarenal without visualization of right gland. A left suprarenalectomy was performed and the anatomopathological analysis showed a clear cell corticoadrenal adenoma. Therefore the only data of the function of suprarenal adenoma was the one coming from gammagraphy. We thought that the adenoma was responsible of practically all the corticoadrenal function without reaching pathological levels, meeting the criteria of "pre-Cushing" syndrome or subclinical Cushing, due to the fact that the contralateral gland was not seen in the gammagraphy. Therefore in the characterization of certain tumors which appear clinically and biochemically as non functional, the suprarenal gammagraphy could be a technique of great usefulness for the diagnosis.  相似文献   
72.
73.
The study analyzes variables that influence the water management model based on a simultaneous relationship between competing demands in the Marina Baja of Alicante, using a methodology that directly links together urban and irrigation demands, making them relevant to each other from a socioeconomic point of view. The paper identifies the relevant variables of this model and the agent behaviour in a closed and joint system. It also aims to demonstrate that by considering water demands for different yet simultaneous uses and regarding clean and reclaimed waters as integrated resources, the system could remain in equilibrium without external water supplies.  相似文献   
74.
In this paper, we present a heterogeneous parallel solver of a high frequency single level Fast Multipole Method (FMM) for the Helmholtz equation applied to acoustic scattering. The developed solution uses multiple GPUs to tackle the compute bound steps of the FMM (aggregation, disaggregation, and near interactions) while the CPU handles a memory bound step (translation) using OpenMP. The proposed solver performance is measured on a workstation with two GPUs (NVIDIA GTX 480) and is compared with that of a distributed memory solver run on a cluster of 32 nodes (HP BL465c) with an Infiniband network. Some energy efficiency results are also presented in this work.  相似文献   
75.
Two key aspects of the Knowledge Society are the interconnection between the actors involved in the decision making processes and the importance of the human factor, particularly the citizen’s continuous learning and education. This paper presents a new module devoted to knowledge extraction and diffusion that has been incorporated into a previously developed decision making tool concerning the Internet and related with the multicriteria selection of a discrete number of alternatives (PRIOR-Web). Quantitative and qualitative procedures using data and text mining methods have been employed in the extraction of knowledge. Graphical visualisation tools have been incorporated in the diffusion stage of the methodological approach suggested when dealing with decision making in the Knowledge Society. The resulting collaborative platform is being used as the methodological support for the cognitive democracy known as e-cognocracy.  相似文献   
76.
In this paper we deal with the observer-based asymptotic synchronization problem for a class of chaotic oscillators. Some results based on a differential algebraic approach are used in order to determine the algebraic observability of unknown variables. The strategy consists of proposing a slave system (observer) which tends to follow asymptotically the master system. The methodology is tested in the real-time asymptotic synchronization of the Colpitts oscillator by means of a proportional reduced order observer (PROO) of free-model type.  相似文献   
77.
78.
The synthesis and properties of sulfur-doped nanocrystalline diamond films were investigated. The films were deposited by hot-filament chemical vapor deposition on Mo substrates using methane, hydrogen, and hydrogen disulfide. The nanocrystalline nature of the material arises from the induction of continuous secondary nucleation in the chemical vapor deposition environment. Complementary characterization tools were employed in order to obtain a comprehensive and coherent understanding of the correlations between the structural and electronic properties. In particular, sulfur-doped nanocrystalline diamond films show n-type Hall conductivity, enhanced field emission properties, and insensitivity to ion radiation. It was found that n-type doping of the tetragonally-bonded carbon matrix together with a nano network of trigonally-bonded carbon are crucial elements for enhanced field emission from nanocrystalline diamond. These conclusions and the corresponding supporting evidence are discussed.  相似文献   
79.
The second-order stiffness matrix and corresponding loading vector of a prismatic beam–column subjected to a constant axial load and supported on a uniformly distributed elastic foundation (Winkler type) along its span with its ends connected to elastic supports are derived in a classical manner. The stiffness coefficients are expressed in terms of the ballast coefficient of the elastic foundation, applied axial load, support conditions, bending, and shear deformations. These individual parameters may be dropped when the appropriate effect is not considered; therefore, the proposed model captures all the different models of beams and beam–columns including those based on the theories of Bernoulli–Euler, Timoshenko, Rayleigh, and bending and shear.The expressions developed for the load vector are also general for any type or combinations of transverse loads including concentrated and partially nonuniform distributed loads. In addition, the transfer equations necessary to determine the transverse deflections, rotations, shear, and bending moments along the member are also developed and presented.  相似文献   
80.
This study examined the mediating role of service climate in the prediction of employee performance and customer loyalty. Contact employees (N=342) from 114 service units (58 hotel front desks and 56 restaurants) provided information about organizational resources, engagement, and service climate. Furthermore, customers (N=1,140) from these units provided information on employee performance and customer loyalty. Structural equation modeling analyses were consistent with a full mediation model in which organizational resources and work engagement predict service climate, which in turn predicts employee performance and then customer loyalty. Further analyses revealed a potential reciprocal effect between service climate and customer loyalty. Implications of the study are discussed, together with limitations and suggestions for future research. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  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