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   2113篇
  免费   100篇
  国内免费   1篇
电工技术   23篇
综合类   3篇
化学工业   426篇
金属工艺   28篇
机械仪表   19篇
建筑科学   130篇
矿业工程   3篇
能源动力   50篇
轻工业   203篇
水利工程   20篇
石油天然气   11篇
无线电   125篇
一般工业技术   436篇
冶金工业   419篇
原子能技术   17篇
自动化技术   301篇
  2023年   13篇
  2022年   12篇
  2021年   32篇
  2020年   28篇
  2019年   23篇
  2018年   35篇
  2017年   49篇
  2016年   58篇
  2015年   47篇
  2014年   60篇
  2013年   116篇
  2012年   99篇
  2011年   126篇
  2010年   81篇
  2009年   90篇
  2008年   104篇
  2007年   88篇
  2006年   77篇
  2005年   73篇
  2004年   59篇
  2003年   63篇
  2002年   54篇
  2001年   48篇
  2000年   32篇
  1999年   38篇
  1998年   47篇
  1997年   43篇
  1996年   52篇
  1995年   42篇
  1994年   36篇
  1993年   35篇
  1992年   27篇
  1991年   12篇
  1990年   20篇
  1989年   24篇
  1988年   23篇
  1987年   18篇
  1986年   20篇
  1985年   42篇
  1984年   26篇
  1983年   14篇
  1982年   32篇
  1981年   30篇
  1980年   27篇
  1979年   24篇
  1978年   17篇
  1977年   22篇
  1976年   12篇
  1975年   15篇
  1973年   16篇
排序方式: 共有2214条查询结果,搜索用时 15 毫秒
91.
Averaged n-Dependence Estimators (AnDE) is an approach to probabilistic classification learning that learns by extrapolation from marginal to full-multivariate probability distributions. It utilizes a single parameter that transforms the approach between a low-variance high-bias learner (Naive Bayes) and a high-variance low-bias learner with Bayes optimal asymptotic error. It extends the underlying strategy of Averaged One-Dependence Estimators (AODE), which relaxes the Naive Bayes independence assumption while retaining many of Naive Bayes’ desirable computational and theoretical properties. AnDE further relaxes the independence assumption by generalizing AODE to higher-levels of dependence. Extensive experimental evaluation shows that the bias-variance trade-off for Averaged 2-Dependence Estimators results in strong predictive accuracy over a wide range of data sets. It has training time linear with respect to the number of examples, learns in a single pass through the training data, supports incremental learning, handles directly missing values, and is robust in the face of noise. Beyond the practical utility of its lower-dimensional variants, AnDE is of interest in that it demonstrates that it is possible to create low-bias high-variance generative learners and suggests strategies for developing even more powerful classifiers.  相似文献   
92.
93.
94.
Three-dimensional cage-like mesoporous FDU-12 materials with large tuneable pore sizes ranging from 9.9 to 15.6 nm were prepared by varying the synthesis temperature from 100 to 200 °C for the aging time of just 2 h using a tri-block copolymer F-127(EO106PO70EO106) as the surfactant and 1,3,5-trimethyl benzene as the swelling agent in an acidic condition. The mesoporous structure and textural features of FDU-12-HX (where H denotes the hydrothermal method and X denotes the synthesis temperature) samples were elucidated and probed using x-ray diffraction, N2 adsorption, 29Si magic angle spinning nuclear magnetic resonance, scanning electron microscopy and transmission electron microscopy. It has been demonstrated that the aging time can be significantly reduced from 72 to 2 h without affecting the structural order of the FDU-12 materials with a simple adjustment of the synthesis temperature from 100 to 200 °C. Among the materials prepared, the samples prepared at 200 °C had the highest pore volume and the largest pore diameter. Lysozyme adsorption experiments were conducted over FDU-12 samples prepared at different temperatures in order to understand their biomolecule adsorption capacity, where the FDU-12-HX samples displayed high adsorption performance of 29 μmol g−1 in spite of shortening the actual synthesis time from 72 to 2 h. Further, the influence of surface area, pore volume and pore diameter on the adsorption capacity of FDU-12-HX samples has been investigated and results are discussed in correlation with the textural parameters of the FDU-12-HX and other mesoporous adsorbents including SBA-15, MCM-41, KIT-5, KIT-6 and CMK-3.  相似文献   
95.
96.
It is widely accepted that understanding the kinetics of steelmaking is a complex task, and reliable and validated kinetics models are required for developing successful steelmaking process models. Therefore, as an initial attempt, this paper analyses the applicability of first order kinetics to explain the steelmaking reaction kinetics using the published data in the IMproving Phosphorus Refining research report. The process data for 20 heats in a 6?tonne pilot plant were analysed for the removal of carbon, silicon, manganese and phosphorus using first order kinetics with static and dynamic equilibrium conditions. It was observed that the removal behaviour of silicon closely followed a first order kinetics relationship, while that of carbon only approximately followed a first order kinetics relationship. The removal of manganese did not show a good degree of fit with first order kinetics using static equilibrium condition, but a clear improvement was observed when calculated using dynamic equilibrium condition. In contrast, the kinetics of phosphorus oxidation did not follow any first order relationship.  相似文献   
97.
Nuclear reactors produce heat and thus can couple to heat storage systems to provide dispacthable electricity while the reactor operates at full power. Six classes of heat storage technologies couple to light-water reactors with steam cycles. Firebrick Resistance-Heated Energy Storage (FIRES) converts low-price electricity into high-temperature stored heat for industry or power. FIRES and brick recuperators coupled to nuclear brayton power cycles may enable high-temperature reactors to buy electricity when prices are low and sell electricity at higher price.  相似文献   
98.
Between 1997 and 2006, more than 4,300 serious burn injuries per year in the United States were associated with clothing. Ages 5–14 had the highest average annual burn injury rate, and ages 25–64 had the lowest rate. There were 120 deaths per year in the United States associated with clothing burns between 1999 and 2004. The death rate for those over 65 was six times the national average. The General Wearing Apparel Standard has regulated the flammability of clothing worn in the United States since 1953. Nearly all of the clothing-related injuries and deaths have occurred in fires involving apparel that complied with this Standard. Despite the size of this problem, there is no organized national activity under way to begin to address these casualties. Experience with the Children’s Sleepwear Flammability Standards, issued in the 1970s, suggests that safer garments can be manufactured that would prevent many clothing burn injuries and deaths. A more stringent up-to-date flammability standard, production of safer garments, use of warning labels, and educated consumers are needed.  相似文献   
99.
Bottled white wine may be exposed to UV-visible light for considerable periods of time before it is consumed. Light exposure may induce an off-flavor known as “sunlight” flavor, bleach the color of the wine, and/or increase browning and deplete sulfur dioxide. The changes that occur in bottled white wine exposed to light depend on the wine composition, the irradiation conditions, and the light exposure time. The light-induced changes in the aroma, volatile composition, color, and concentrations of oxygen and sulfur dioxide in bottled white wine are reviewed. In addition, the photochemical reactions thought to have a role in these changes are described. These include the riboflavin-sensitized oxidation of methionine, resulting in the formation of methanethiol and dimethyl disulfide, and the photodegradation of iron(III) tartrate, which gives rise to glyoxylic acid, an aldehyde known to react with flavan-3-ols to form yellow xanthylium cation pigments.  相似文献   
100.
While the chemical energy in fossil fuels has enabled the rapid rise of modern civilization, their utilization and accompanying anthropogenic CO2 emissions is occurring at a rate that is outpacing nature's carbon cycle. Its effect is now considered to be irreversible and this could lead to the demise of human society. This is a complex issue without a single solution, yet from the burgeoning global research activity and development in the field of CO2 capture and utilization, there is light at the end of the tunnel. In this article a couple of recent advances are illuminated. Attention is focused on the discovery of gas‐phase, light‐assisted heterogeneous catalytic materials and processes for CO2 photoreduction that operate at sufficiently high rates and conversion efficiencies, and under mild conditions, to open a new pathway for an energy transition from today's “fossil fuel economy” to a new and sustainable “CO2 economy”. Whichever of the competing CO2 capture and utilization approaches proves to be the best way forward for the development of a future CO2‐based solar fuels economy, hopefully this can occur in a period short enough to circumvent the predicted adverse consequences of greenhouse gas climate change.  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