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   1113篇
  免费   105篇
  国内免费   2篇
电工技术   16篇
化学工业   320篇
金属工艺   23篇
机械仪表   38篇
建筑科学   28篇
矿业工程   1篇
能源动力   61篇
轻工业   138篇
水利工程   8篇
石油天然气   3篇
无线电   88篇
一般工业技术   211篇
冶金工业   35篇
原子能技术   4篇
自动化技术   246篇
  2024年   1篇
  2023年   17篇
  2022年   57篇
  2021年   77篇
  2020年   36篇
  2019年   64篇
  2018年   52篇
  2017年   54篇
  2016年   58篇
  2015年   48篇
  2014年   43篇
  2013年   77篇
  2012年   90篇
  2011年   99篇
  2010年   73篇
  2009年   72篇
  2008年   60篇
  2007年   63篇
  2006年   24篇
  2005年   27篇
  2004年   27篇
  2003年   13篇
  2002年   13篇
  2001年   8篇
  2000年   2篇
  1999年   8篇
  1998年   10篇
  1997年   4篇
  1996年   8篇
  1995年   4篇
  1994年   2篇
  1993年   3篇
  1992年   4篇
  1990年   2篇
  1988年   1篇
  1987年   3篇
  1986年   1篇
  1985年   1篇
  1984年   3篇
  1982年   3篇
  1981年   3篇
  1979年   1篇
  1976年   1篇
  1975年   1篇
  1972年   1篇
  1957年   1篇
排序方式: 共有1220条查询结果,搜索用时 125 毫秒
101.
The present paper attempts to empirically study the cognitive impacts of Massive Multiplayer Online Role-Playing Games (MMORPGs) in uncontrolled contexts in light of the Cognitive Mediation Networks Theory, a new model of human intelligence that aims to explain cognition as the result of brain activity combined with the information-processing done by external structures such as tools, social groups and culture. A sample of 1280 students Brazilian high school students answered a form inquiring about socio-demographic information plus the use of computer games, and also was submitted to a short knowledge exam and a mini psychometric test. The findings indicated that, due to their underlying structure and sociocultural nature, MMORPGs are associated to a greater level of insertion into the Digital Age, higher levels of logical-numerical performance, and better scholastic ability. Finally, suggestions are made for future studies on the subject.  相似文献   
102.
Fucoidanase enzymes able to degrade fucoidan were produced by solid-state fermentation (SSF). The fermentation assays were initially carried out in a laboratory-scale rotating drum bioreactor, and two fungal strains (Aspergillus niger PSH and Mucor sp. 3P) and three algal substrates (untreated, autohydrolyzed, and microwave processed seaweed Fucus vesiculosus) were evaluated. Additionally, fermentations were carried out under rotational (10 rpm) and static conditions in order to determine the effect of the agitation on the enzyme production. Agitated experiments showed advantages in the induction of the enzyme when compared to the static ones. The conditions that promoted the maximum fucoidanase activity (3.82 U L?1) consisted in using Mucor sp. 3P as fungal strain, autohydrolyzed alga as substrate, and the rotational system. Such conditions were subsequently used in a 10 times larger scale rotating drum bioreactor. In this step, the effect of controlling the substrate moisture during the enzyme production by SSF was investigated. Moreover, assays combining the algal substrate with an inert support (synthetic fiber) were also carried out. Fermentation of the autohydrolyzed alga with the moisture content maintained at 80% during the fermentation with Mucor sp. 3P gave the highest enzyme activity (9.62 U L?1).  相似文献   
103.
A novel SBA-16-related synthesis of mesostructured silica containing framework aluminum is reported here. This material was successfully synthesized using aluminum sulphate and the pH-adjusting method. The structural and porosity properties of this novel material were studied by X-ray diffraction and N2 adsorption at 77 K. The Al insertion was determined by 27Al-MAS-NMR and the acidity was monitored by infrared spectroscopy of CO adsorption at 100 K.  相似文献   
104.
天生桥一级水电站混凝土面板堆石坝位移监测   总被引:1,自引:0,他引:1  
天生桥一级电站混凝土面板堆石坝的填筑坝体位移监测通过水管式沉降仪和水平位移计进行。坝本内安装了50支水管式沉降仪(瑞曲盒式)、31支水平位移计(钢丝型伸缩仪)和28支总压力计。监测结果表明,施工期末(1999年3月)最大坝体沉降是2.94m,相当于坝体高度的1.7%,施工期末堆石坝变形模量Erc平均45MPa,为最大坝体变形,促使上游边坡出现裂缝以及面板浇筑前上游边坡明显沉降。  相似文献   
105.
In order to optimize and improve the design of power devices with improved surge current safe operating area it is necessary to obtain a good correlation between measured and simulated space and time resolved temperature distributions. Therefore, an IR microscope capable of measuring the space and time resolved surface temperature distributions in Si power diodes operating under self-heating conditions has been developed. The minimum detectable spot size is 15 μm, while the signal rise time is detector limited to about 1 μs. The lower temperature detectivity limit is about 10°C over room temperature.

Using this instrument dynamic thermal phenomena in fast recovery 3.3 kV Si power diodes having radiation-induced recombination centers [Proceedings of the 7th EPE, Trondheim, 1997] subjected to 1.2 ms 400–2000 A/cm2 and 0.3–2 ms 2000 A/cm2 current pulses have been studied. The experimental results have been compared to results from 2D device simulations including surface recombination and carrier lifetime temperature dependence. The agreement between experimental and device simulation results (i.e. dynamic IV characteristics and time and space resolved temperature distributions) is very good up to a peak current density of 1500 A/cm2, and a reasonable good one for peak current densities up to 2000 A/cm2 (1.2 ms current pulses).  相似文献   

106.
Ultrathin strained-Si/strained-Ge heterostructures on insulator have been fabricated using a bond and etch-back technique. The substrate consists of a trilayer of 9 nm strained-Si/4 nm strained-Ge/3 nm strained-Si on a 400-nm-thick buried oxide. The epitaxial trilayer structure was originally grown pseudomorphic to a relaxed Si0.5Ge0.5 layer on a donor substrate. Raman analysis of the as-grown and final transferred layer structures indicates that there is little change in the strain in the Si and Ge layers after layer transfer. These ultrathin Si and Ge films have very high levels of strain (∼1.8% biaxial tension and 1.4% compression, respectively), and are suitable for enhanced-mobility field-effect transistor applications.  相似文献   
107.
This document presents new mechanisms for stability assessment in iterative controller tuning. Contrary to the usual approach adopted in robust model identification, the new mechanisms do not rely on plant models, but utilize information from the current closed-loop system to test if a newly designed controller will maintain loop stability. All controllers that satisfy the test are guaranteed to stabilize the actual plant.  相似文献   
108.
109.
Steven–Johnson Syndrome (SJS) and Toxic Epidermal Necrolysis (TEN) are severe adverse drug reactions, characterized by extensive epidermal detachment and erosions of mucous membrane. SJS/TEN is one of the most serious adverse reactions to Nevirapine (NVP) treatment, commonly used in developing countries as first-line treatment of human immunodeficiency virus infection. In the last years TRAF3IP2 gene variants had been described as associated with susceptibility to several diseases such as psoriasis and psoriatic arthritis. We hypothesized that this gene, involved in immune response and in NF-κB activation, could also be implicated in the SJS/TEN susceptibility. We performed a full resequencing of TRAF3IP2 gene in a population of patients treated with NVP. Twenty-seven patients with NVP-induced SJS/TEN and 78 controls, all from Mozambique, were enrolled. We identified eight exonic and three intronic already described variants. The case/control association analysis highlighted an association between the rs76228616 SNP in exon 2 and the SJS/TEN susceptibility. In particular, the variant allele (C) resulted significantly associated with a higher risk to develop SJS/TEN (p = 0.012 and OR = 3.65 (95% CI 1.33–10.01)). A multivariate analysis by logistic regression confirmed its significant contribution (p = 0.027, OR = 4.39 (95% CI 1.19–16.23)). In conclusion, our study suggests that a variant in TRAF3IP2 gene could be involved in susceptibility to SJS/TEN.  相似文献   
110.
Numerous studies have been focused to natural ingredients to maintain the quality and shell life of foods. Edibles coating, biodegradable ingredients, such as hydrocolloids and proteins can be used for coating fish with the purpose to suppress changes of quality during frozen storage. At the present time several developing of edibles packing, like glaze using hydrocolloids, (gelatin, carrageen, starch), that besides acts as protective film for food, they are economic, can be ingested by the consumer without toxicity risk, help to preserve organoleptics and nutritional characteristics of the product and, being biodegradable they contribute to the conservation of the atmosphere. The objective of the present study was to evaluate the incorporation ofhydrocolloids in the glazing tuna process as alternative of packing, to enhance its physical and chemical characteristics. Samples of tuna was glazed incorporating to its solutions of carrageen at 0.05, 0,1 and 0.15%, and gelatin at 0.5, 1%. The samples were shaped as square (15 cm3), frozen al -30 degrees C and glazed incorporating hydrocolloids submerging the sample its solutions at 0 degrees C by 30 seconds and storage at -10 degrees C by 0, 15 and 30 days. Proximal analysis results, soluble proteins, TBA, and color showed that all the samples glazed with hydrocolloids decrease deterioration of the tuna products respect to samples glazed without hydrocolloids; concluding that glazing adding hydrocolloids protects tuna for loss humidity and delays degradation of proteins. Moreover, carrageen shows to a better performance at the concentrations of 0.05% compared with the gelatin and the starch.  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