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   4049篇
  免费   68篇
  国内免费   1篇
电工技术   32篇
综合类   2篇
化学工业   515篇
金属工艺   69篇
机械仪表   19篇
建筑科学   58篇
矿业工程   1篇
能源动力   28篇
轻工业   182篇
水利工程   6篇
石油天然气   3篇
无线电   137篇
一般工业技术   334篇
冶金工业   2513篇
原子能技术   21篇
自动化技术   198篇
  2022年   25篇
  2021年   39篇
  2020年   22篇
  2019年   31篇
  2018年   28篇
  2017年   25篇
  2016年   43篇
  2015年   33篇
  2014年   38篇
  2013年   62篇
  2012年   65篇
  2011年   90篇
  2010年   47篇
  2009年   51篇
  2008年   62篇
  2007年   85篇
  2006年   68篇
  2005年   47篇
  2004年   48篇
  2003年   52篇
  2002年   35篇
  2001年   46篇
  2000年   48篇
  1999年   108篇
  1998年   813篇
  1997年   457篇
  1996年   323篇
  1995年   202篇
  1994年   154篇
  1993年   166篇
  1992年   33篇
  1991年   35篇
  1990年   45篇
  1989年   51篇
  1988年   69篇
  1987年   44篇
  1986年   33篇
  1985年   32篇
  1984年   18篇
  1983年   15篇
  1982年   26篇
  1981年   24篇
  1980年   22篇
  1979年   17篇
  1978年   13篇
  1977年   51篇
  1976年   137篇
  1975年   21篇
  1974年   13篇
  1973年   18篇
排序方式: 共有4118条查询结果,搜索用时 0 毫秒
111.

Object   

Histology is the gold standard for confirming thermally induced necrosis. Generally, however, no specimen is obtained from thermal ablation therapy for pathological examination. The aim of this study was to provide evidence for the relationship between temperatures reached and resulting tissue coagulation during laser ablation in a near-physiological ex vivo lung tumor model by combining viability staining and direct temperature measurement.  相似文献   
112.
113.
114.
With the continuous reduction in the availability of extractive metallurgical curricula in colleges and universities, the concern has in part been from where will the next generation of extractive metallurgists come? One objective of this article is to emphasize the fact that extractive metallurgy is, in fact, one of many areas of chemical engineering technology. Thus, although the extractive metallurgist may have disappeared in name, its activity is alive and well, subsumed in the field of chemical engineering. One goal of this lecture is to demonstrate the applicability of chemical engineering principles to what is typically considered ??the field of extractive metallurgy.?? Two processes will be described that have supplanted typical pyrometallurgical fire refining of precious metals, particularly silver. The origins of fire refining can be traced back to biblical times. There are numerous references to it in the old testament: Ezekiel 22:20, ??As men gather silver and bronze and iron and lead and tin into a furnace to blow the fire upon it in order melt it??; Jeremiah 6:29, ??The bellows blow fiercely; the lead is consumed by the fire; in vain the refining goes on??; and Malachi 3:2 (The Oxford Annotated Bible with the Apocrypha), ??For he is like a refiners fire.?? Many references to it will also be found in ??De Re Metallurgica?? and as well in Lazarus Ercker??s 1574 Manual ??Treatise on Ores and Refining.?? Today, fire refining has been improved greatly by innovative furnace design, new fluxing technologies, and the improved use of oxygen. However, fundamentally, the process chemistry has not changed much in the last millennium. Illustrations of hydrometallurgical processing of silver-bearing inputs will be provided by the treatment of sulfated silver-bearing materials and chlorinated slimes. The first of these technologies will be described briefly as practiced by the Phelps Dodge Refining Corporation for several years. The second, the treatment of silver chloride-bearing inputs, will be described in detail to demonstrate how typical chemical engineering unit process and unit operations have supplanted classic smelting and fire refining techniques. The Kennecott Copper Company, which has operated a hydrometallurgical circuit successfully for the recovery of high-purity silver from the slimes wet chlorination residue, has permitted me to provide some operation information and results using the technology. Both Phelps Dodge and Kennecott should be recognized for their forward-looking attitude in undertaking the conversion of conceptual chemistry into successful, full-scale plants. The process as employed at Phelps Dodge is discussed at length in reference (J.E. Hoffmann and B. Wesstrom: Hydrometallurgy, 1994, vol. 94, pp. 69?C105).  相似文献   
115.
Based on the information needs of stakeholders (from animal feed to consumers, including the authorities and organizations involved) an integrated IT-system without structural fractures and barriers shall be developed. It will be designed to enable the merging, internal exchange and utilization of relevant data and parameters. Subprojects of the interdisciplinary research consortium cover the entire supply chain and also address cross-section issues, such as logistics, costs and benefits, veterinarian services, quality assurance systems, a comprehensive IT-solution including data format standards (agroXML), and requirements for sustainability. Substantial added value has been generated from intensive interdisciplinary co-operation. The interdisciplinary research project IT FoodTrace () aims at achieving traceability and quality assurance along the food chain of “meat and meat products”. The aim of this paper is the presentation of (a) the complexity of underlying problems, (b) the project structure, (c) available results from selected sub-projects and (d) the added values from interdisciplinary co-operation. Selected findings include an optimized single animal data collection and information management in livestock systems, benefits gained by linking animal-health-related information to an integrated animal-health system, requirements and features of an integrated IT-System, including consequences for data protection and security, and findings from a Delphi-based cost–benefit-analysis of an integrated quality assurance and traceability system.  相似文献   
116.
The endurance limit of carbonitrided specimens of 18CrNiMo7‐6 and 20MnCr5 case hardening steels were examined under bending conditions. Four variants were manufactured differing in heat treatment and surface conditions. Besides conventional gas carburised variants, carbonitrided specimens with a low and a raised nitrogen content of 0.2 and 0.45% at the surface as well as a carbonitrided and ground variant were examined. The specimens were tested with stress ratios R = –1 and 0. Depending on the nitrogen content cyclic loading evokes compressive residual stresses at the specimens' surfaces, caused by elastic‐plastic deformation. Specimens of the ground variant show additionally a decrease of the residual austenite content when cycled. The induced compressive residual stresses are substantially responsible for high endurance limits at both stress ratios and are the key for understanding the beneficial effect of carbonitriding in this regard.  相似文献   
117.
Overexpression of the histone lysine demethylase KDM4A, which regulates H3K9 and H3K36 methylation states, has been related to the pathology of several human cancers. We found that a previously reported hydroxamate‐based histone deacetylase (HDAC) inhibitor (SW55) was also able to weakly inhibit this demethylase with an IC50 value of 25.4 μm . Herein we report the synthesis and biochemical evaluations, with two orthogonal in vitro assays, of a series of derivatives of this lead structure. With extensive chemical modifications on the lead structure, also by exploiting the versatility of the radical arylation with aryldiazonium salts, we were able to increase the potency of the derivatives against KDM4A to the low‐micromolar range and, more importantly, to obtain demethylase selectivity with respect to HDACs. Cell‐permeable derivatives clearly showed a demethylase‐inhibition‐dependent antiproliferative effect against HL‐60 human promyelocytic leukemia cells.  相似文献   
118.
Cupuassu fat is a good candidate for partial substitution of cocoa butter in many products, including emulsions. However, for such use it is necessary to know the characteristics of the products prepared with cupuassu fat. Therefore, the main goal of this work is to characterize emulsions prepared with cupuassu fat using the surfactants Tween® 60, Tween® 80 and Tween® 85 as emulsifiers. The emulsions were prepared at 43 °C with addition of 0.5 or 1.5 % (w/v) of surfactant and compared with an emulsion without surfactant. All emulsions were analysed by conductivity, stability, pH, optical microscopy, rheology and oxidative stability. It was verified that the emulsions prepared with Tween® 60 and Tween® 80 have higher stability, smaller droplet size and higher apparent viscosity. Also, these properties are positively influenced by the concentration of the surfactant. On the other hand, emulsions prepared with Tween 85 or without surfactant reached unsatisfactory results. The rheological behaviour of the emulsions was adequately described by both Herschel-Bulkley and Mizhari-Berki models revealing pseudoplastic character. These emulsions also present strong gel behaviour, with storage modulus higher than loss modulus. In conclusion, cupuassu fat can be used as oil phase for emulsions products and this characterization helps to understand their behaviour in order to increase their use in food industry.  相似文献   
119.
Here, the spatial distribution of the bacterial flora along the murine alimentary tract was evaluated using high throughput sequencing in wild-type and Tff3-deficient (Tff3KO) animals. Loss of Tff3 was linked to increased dextran sodium sulfate-induced colitis. This systematic study shows the results of 13 different regions from the esophagus to the rectum. The number of bacterial species (richness) increased from the esophagus to the rectum, from 50 to 200, respectively. Additionally, the bacterial community structure changed continuously; the highest changes were between the upper/middle and lower gastrointestinal compartments when comparing adjacent regions. Lactobacillus was the major colonizer in the upper/middle gastrointestinal tract, especially in the esophagus and stomach. From the caecum, a drastic diminution of Lactobacillus occurred, while members of Lachnospiraceae significantly increased. A significant change occurred in the bacterial community between the ascending and the transverse colon with Bacteroidetes being the major colonizers with relative constant abundance until the rectum. Interestingly, wild-type and Tff3KO animals did not show significant differences in their bacterial communities, suggesting that Tff3 is not involved in alterations of intraluminal or adhesive microbiota but is obviously important for mucosal protection, e.g., of the sensitive stem cells in the colonic crypts probably by a mucus plume.  相似文献   
120.
In chemical process engineering, fast gas-liquid reactions often suffer from an inefficient distribution of gas and therefore mixing and mass transfer performance. This study deals with the possibility of influencing the local gas holdup and bubble size distribution in a gas-liquid process using additively manufactured lattice structures (AMLS). The used measuring technique to study bubble size, velocity, and the local gas holdup is a photo-optical needle probe. By using AMLS, a significant radial homogenization of the local gas holdup and the mean bubble size is achieved. Furthermore, it can be demonstrated that the bubble size can be tailored by the geometry of the inserted structure. It is illustrated that the mean bubble velocities are lowered within the lattice resulting in a higher residence time of the dispersed phase with an impact on the mass transfer performance within the AMLS.  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