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   34026篇
  免费   2140篇
  国内免费   167篇
电工技术   524篇
技术理论   1篇
综合类   129篇
化学工业   7680篇
金属工艺   1231篇
机械仪表   1920篇
建筑科学   759篇
矿业工程   54篇
能源动力   1419篇
轻工业   2787篇
水利工程   158篇
石油天然气   138篇
武器工业   10篇
无线电   5701篇
一般工业技术   6984篇
冶金工业   2485篇
原子能技术   439篇
自动化技术   3914篇
  2024年   44篇
  2023年   407篇
  2022年   596篇
  2021年   1040篇
  2020年   766篇
  2019年   791篇
  2018年   1068篇
  2017年   999篇
  2016年   1193篇
  2015年   960篇
  2014年   1504篇
  2013年   2220篇
  2012年   2156篇
  2011年   2612篇
  2010年   2014篇
  2009年   2026篇
  2008年   1911篇
  2007年   1446篇
  2006年   1303篇
  2005年   1171篇
  2004年   1058篇
  2003年   939篇
  2002年   893篇
  2001年   806篇
  2000年   682篇
  1999年   713篇
  1998年   1081篇
  1997年   706篇
  1996年   631篇
  1995年   420篇
  1994年   321篇
  1993年   251篇
  1992年   187篇
  1991年   176篇
  1990年   149篇
  1989年   160篇
  1988年   112篇
  1987年   108篇
  1986年   102篇
  1985年   81篇
  1984年   68篇
  1983年   64篇
  1982年   43篇
  1981年   51篇
  1980年   50篇
  1979年   28篇
  1978年   20篇
  1977年   42篇
  1976年   58篇
  1975年   27篇
排序方式: 共有10000条查询结果,搜索用时 5 毫秒
61.
Characterisation of a BioFET for detection of albumin in a mixture of human urine is presented. To avoid electrolyte effect of the urine, it was measured in PBS (phosphate buffer saline) at a fixed pH after albumin binding. The drain current was modulated by the albumin bound to the anti-albumin immobilised on the gate surface of the BioFET. The current variation ratio was likely to be proportional to the concentration of the albumin in the range 50-250 mg/1. The results show the feasibility of the BioFET as a urinary albumin sensor.  相似文献   
62.
Orbital-free density functional theory (OF-DFT) can be made to scale linearly with sample size, allowing thousands of atoms to be treated explicitly with quantum mechanics. State-of-the-art kinetic energy density functionals and ion–electron pseudopotentials are used to obtain accurate structural property predictions for nanoparticles, nanowires, extended surfaces, and nanoindentation of simple metals.  相似文献   
63.
64.
A sweeping operation called polygonal extrusion is defined to improve the modeling power of CSG-based modeling. It is assumed that a 2D cross-sectional polygon (sweeping polygon) moves in space while its containing plane is kept orthogonal to the tangent direction of the trajectory curve, a planar polygonal chain having no self-intersections. The objective of the paper is to compute the boundary of the swept volume of the sweeping polygon as a set of polygons (or triangles). The most significant challenge to accomplishing this objective is the problem of trimming the swept volume. To solve the trimming problem, 2D-curve offsetting methods are employed. Two algorithms are presented for polygonal extrusion that are based on different offsetting methods, the Voronoi diagram and PWID offset. The proposed algorithms have been implemented and tested with various examples. Published online: 28 January 2003  相似文献   
65.
A new dynamic buffer allocation strategy based on the notion of marginal gains is presented for the buffer cache that is used by the operating system to store frequently accessed disk blocks in main memory, and the performance of the proposed strategy is compared with those of previous allocation strategies. In the proposed strategy, marginal gain values are predicted by exploiting functions that approximate the expected number of buffer hits per unit time. Experimental results from both trace-driven simulation and an actual implementation in the FreeBSD operating system show that the proposed strategy accurately predicts the marginal gain values for various workloads resulting in significantly improved buffer hit ratios.  相似文献   
66.
Presented in this paper is a topology reconstruction algorithm from a set of unorganized trimmed surfaces. Error-prone small geometric elements are handled to give proper topological information. It gives complete topology to topologically complete models, and it is also tolerant to incomplete models. The proposed algorithm is vertex-based in that clues for topological information are searched from the set of vertices first, not from that of edges.  相似文献   
67.
Bibliometric analysis of tsunami research   总被引:3,自引:0,他引:3  
The use of the bibilometric analytical technique for examining tsunami research does not exist in the literature. The objective of the study was to perform a bibliometric analysis of all tsunami-related publications in the Science Citation Index (SCI). Analyzed parameters included document type, language of publication, publication output, authorship, publication patterns, distribution of subject category, distribution of author keywords, country of publication, most-frequently cited article, and document distribution after the Indonesia tsunami. The US and Japan produced 53% of the total output where the seven major industrial countries accounted for the majority of the total production. English was the dominant language, comprising 95% of articles. A simulation model was applied to describe the relationship between the number of authors and the number of articles, the number of journals and the number of articles, and the percentage of total articles and the number of times a certain keyword was used. Moreover the tsunami publication patterns in the first 8 months after the Indonesia tsunami occurred on 26 December 2004 indicated a high percentage of non-article publications and more documents being published in journals with higher impact factors.  相似文献   
68.
Effects of austenitizing treatment temperatures on aqueous corrosion properties of martensitic stainless steels were investigated by electrochemical tests (potentiodynamic test, potentiostatic test and electrochemical impedance spectroscopy), and surface analyses (optical microscopy and XRD). The results of potentiodynamic test revealed that the breakdown potential increased with the increased austenitizing temperature, indicating increased relative resistance to initiation of localized corrosion. EIS measurements showed that MSS3 (1030 °C) exhibits larger polarization resistance value than MSS1 (970 °C) and MSS2 (1000 °C) at passive and breakdown states. This was caused by decreasing the amount of Cr-rich M23C6 carbide which acts as preferential sites for pitting corrosion.  相似文献   
69.
Understanding how aging influences cognition across different cultures has been hindered by a lack of standardized, cross-referenced verbal stimuli. This study introduces a database of such item-level stimuli for both younger and older adults, in China and the United States, and makes 3 distinct contributions. First, the authors specify which item categories generalize across age and/or cultural groups, rigorously quantifying differences among them. Second, they introduce novel, powerful methods to measure between-group differences in freely generated ranked data, the rank-ordered logit model and Hellinger Affinity. Finally, a broad archive of tested, cross-linguistic stimuli is now freely available to researchers: data, similarity measures, and all stimulus materials for 105 categories and 4 culture-by-age groups, comprising over 10,000 fully translated unique item responses. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
70.
This paper proposes a new LDMOSFET structure with a trenched sinker for high‐power RF amplifiers. Using a low‐temperature, deep‐trench technology, we succeeded in drastically shrinking the sinker area to one‐third the size of the conventional diffusion‐type structure. The RF performance of the proposed device with a channel width of 5 mm showed a small signal gain of 16.5 dB and a maximum peak power of 32 dBm with a power‐added efficiency of 25% at 2 GHz. Furthermore, the trench sinker, which was applied to the guard ring to suppress coupling between inductors, showed an excellent blocking performance below ?40 dB at a frequency of up to 20 GHz. These results confirm that the proposed trenched sinker should be an effective technology both as a compact sinker for RF power devices and as a guard ring against coupling.  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