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   106686篇
  免费   2591篇
  国内免费   465篇
电工技术   1102篇
综合类   2346篇
化学工业   16501篇
金属工艺   5567篇
机械仪表   4287篇
建筑科学   2613篇
矿业工程   566篇
能源动力   2101篇
轻工业   5579篇
水利工程   1355篇
石油天然气   362篇
武器工业   2篇
无线电   13220篇
一般工业技术   21486篇
冶金工业   4385篇
原子能技术   590篇
自动化技术   27680篇
  2023年   292篇
  2022年   333篇
  2021年   735篇
  2020年   542篇
  2019年   587篇
  2018年   15023篇
  2017年   13941篇
  2016年   10689篇
  2015年   1297篇
  2014年   1310篇
  2013年   1776篇
  2012年   4700篇
  2011年   11183篇
  2010年   9542篇
  2009年   6936篇
  2008年   8031篇
  2007年   8715篇
  2006年   1044篇
  2005年   1999篇
  2004年   1838篇
  2003年   1836篇
  2002年   1179篇
  2001年   669篇
  2000年   671篇
  1999年   549篇
  1998年   855篇
  1997年   533篇
  1996年   510篇
  1995年   319篇
  1994年   201篇
  1993年   194篇
  1992年   144篇
  1991年   143篇
  1990年   97篇
  1989年   100篇
  1988年   97篇
  1987年   71篇
  1986年   56篇
  1985年   49篇
  1984年   40篇
  1976年   43篇
  1968年   47篇
  1967年   40篇
  1966年   44篇
  1965年   44篇
  1959年   35篇
  1958年   37篇
  1957年   37篇
  1955年   63篇
  1954年   68篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
Metals and Materials International - This study investigated the influence of the initial grain size on the plastic deformation and tunnel defects that occurred from friction stir welding of...  相似文献   
42.
A facile sol–gel procedure has been developed for the synthesis of colloidal alumina nanocrystals. For the first time, optical characterization procedures were employed to study the quantum confinement effects in optical properties of the prepared Al2O3 sol. Accordingly, the hyperbolic band model was used to determine the optical band gap of colloidal alumina nanocrystals. X‐Ray diffraction pattern was used to study the crystallographic phase of the dried gel. Morphological characterization was performed using scanning electron microscopy (SEM). Inductively Coupled Plasma (ICP) emission spectroscopy was used to determination purity of the Al2O3 powder. High‐resolution TEM showed that the diameter of colloidal nanocrystals is about 10 nm. Photoluminescence spectroscopy demonstrated that quantum yields for colloidal nanocrystals are 68% with 300 nm excitation wavelength. The experimental observations confirm that highly stable alumina sol with strong UV emission was synthesized. The mentioned optical properties have not been reported before.  相似文献   
43.
44.
We study a maritime inventory routing problem, in which shipments between production and consumption nodes are carried out by a fleet of vessels. The vessels have specific capacities and can be chartered under different agreements. The inventory levels of all consumption nodes and some production nodes should be maintained within specified bounds; for the remaining production nodes, orders should be picked up within pre-defined time windows. We propose a discrete-time mixed-integer programming model. In the face of new information and uncertainty, this optimization model has to be re-solved, as the horizon is rolled forward. We discuss how to account for different sources of uncertainty. We present a rolling-horizon reoptimization framework that allows us to study different policies that impact the quality of the implemented solution, so we can identify the optimal set of policies.  相似文献   
45.
Over the past few decades, crystalline silicon solar cells have been extensively studied due to their high efficiency, high reliability, and low cost. In addition, these types of cells lead the industry and account for more than half of the market. For the foreseeable future, Si will still be a critical material for photovoltaic devices in the solar cell industry. In this paper, we discuss key issues, cell concepts, and the status of recent high-efficiency crystalline silicon solar cells.  相似文献   
46.
The majority of visualizations on the web are still stored as raster images, making them inaccessible to visually impaired users. We propose a deep‐neural‐network‐based approach that automatically recognizes key elements in a visualization, including a visualization type, graphical elements, labels, legends, and most importantly, the original data conveyed in the visualization. We leverage such extracted information to provide visually impaired people with the reading of the extracted information. Based on interviews with visually impaired users, we built a Google Chrome extension designed to work with screen reader software to automatically decode charts on a webpage using our pipeline. We compared the performance of the back‐end algorithm with existing methods and evaluated the utility using qualitative feedback from visually impaired users.  相似文献   
47.
48.
Vegetable soup (VS), a plant-based functional food, has been used as a traditional folk medicine and is attracting attention for its ability to enhance the immune response. β-Glucan, a well-established and effective immunomodulator, has synergistic effects when used in combination with some bioactive compounds. In the present study, we aimed to evaluate the synergistic immunomodulatory effects of the combination of VS and β-glucan on macrophage-mediated immune responses. β-Glucan was demonstrated to synergistically enhance the VS-stimulated immune response, including the production of interleukin-6, tumor necrosis factor-α, and nitric oxide, mainly through the mitogen-activated protein kinase pathway in macrophages. In addition, this combination has the potential for further development in functional foods with immune-enhancing activity.Supplementary InformationThe online version contains supplementary material available at 10.1007/s10068-021-00888-x.  相似文献   
49.
Gert Schubring 《NTM》2003,11(2):90-99
Enno Heeren Dirksen (1788–1850) was one of several mathematicians originating from Eastern Frisia at the end of the eighteenth century to acquire prominence in neohumanist reformed Prussia. While striving—like so many of his contemporaries—for more rigour in the foundations of calculus, his work is significant due to his unusual emphasis on the semiotic aspects of the basic concepts. As a clear-sighted propagator of Cauchy's conceptual innovations in Germany, his achievements in improving sign expressions of such concepts enabled him to clarify hitherto not differentiated multiple limit processes—although less successfully in constructive concept formation itself. The contribution is based on the analysis of Dirksen's published texts and on the numerous texts which remained drafts for his projected voluminousOrganon der gesamten Analysis.

Menso Folkerts zum 60. Geburtstag gewidmet  相似文献   
50.
A 10Gbit/s recirculating system is configured with Chirped Fiber Bragg Grating (CFBG) for the dispersion compensation. For the first time, the transmission distance in the loop reaches 1000km with bit error rate of 10-9. The effect of the group delay ripple of the fiber grating is also investigated in the recirculating systems, and it is shown that the transmission distance is limited to 4 cycles (4×167.1km ) in the loop with the power penalty fluctuation below 1.0dB. Thus the group delay ripple should be reduced to allow for the wavelength drift of±5GHz. At the end of this letter, the principles are given for designing long haul recirculating systems with dispersion compensation CFBG.  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