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   5481篇
  免费   328篇
  国内免费   198篇
电工技术   155篇
综合类   564篇
化学工业   805篇
金属工艺   150篇
机械仪表   338篇
建筑科学   676篇
矿业工程   128篇
能源动力   175篇
轻工业   327篇
水利工程   141篇
石油天然气   513篇
武器工业   22篇
无线电   325篇
一般工业技术   667篇
冶金工业   184篇
原子能技术   91篇
自动化技术   746篇
  2024年   13篇
  2023年   52篇
  2022年   106篇
  2021年   138篇
  2020年   173篇
  2019年   134篇
  2018年   112篇
  2017年   165篇
  2016年   170篇
  2015年   251篇
  2014年   365篇
  2013年   364篇
  2012年   371篇
  2011年   460篇
  2010年   326篇
  2009年   317篇
  2008年   271篇
  2007年   332篇
  2006年   298篇
  2005年   218篇
  2004年   212篇
  2003年   170篇
  2002年   164篇
  2001年   109篇
  2000年   109篇
  1999年   104篇
  1998年   70篇
  1997年   85篇
  1996年   82篇
  1995年   51篇
  1994年   27篇
  1993年   24篇
  1992年   19篇
  1991年   21篇
  1990年   17篇
  1989年   15篇
  1988年   13篇
  1987年   11篇
  1986年   6篇
  1985年   8篇
  1984年   4篇
  1983年   5篇
  1982年   3篇
  1964年   4篇
  1962年   3篇
  1960年   2篇
  1959年   7篇
  1957年   3篇
  1956年   3篇
  1955年   2篇
排序方式: 共有6007条查询结果,搜索用时 15 毫秒
41.
王兵  闫丽  王巍 《自动化应用》2012,(6):36-37,42
介绍以西门子S7-300/200PLC、WINCC6.0、MM440变频器、6SE70系列变频器等产品为基础建立的莱钢新区炼钢厂西门子自动化实验室。  相似文献   
42.
周慧芬 《物联网技术》2012,(6):77-78,81
针对目前高校实验室管理需求,设计了一种高校实验室信息管理系统。该系统以ASP.NET为开发平台,采用B/S模式设计,通过SQL Server数据库支持,可实现对实验室各种信息的全面管理。同时可以更加完善实验教学等诸环节,为教与学提供良好的发展平台。  相似文献   
43.
研究了由次氯酸钠和溴化钠催化氧化乳酸乙酯合成丙酮酸乙酯新工艺。并通过正交试验设计方法 ,得出最佳实验操作条件 :温度为 30℃以下 ,反应时间为 8h ,溴化钠与乳酸乙酯的摩尔比为 1∶2 ,盐酸与溴化钠的摩尔比为1∶1. 4,不采用光照 ,并由此得到丙酮酸乙酯最好收率为 82 . 86 %(文献值为 80 . 2 %) ,乳酸乙酯的转化率为10 0 %。  相似文献   
44.
匡科 《广东化工》2007,34(3):99-100
《检测和校准实验室能力认可准则》分为l5项管理要素和10项技术要素。作者结合实验室的实际工作,从认可准则管理要求中的组织、管理体系、文件控制、纠正措施、内部审核和管理评审等几个方面有效地推进了实验室质量管理体系的建设,促进实验室的规范化管理。  相似文献   
45.
North Carolina rock phosphate (NCRP) (highly carbonate—substituted apatite) was ground to produce three samples with different particle size distributions. The effectiveness of these fertilizers was compared with the effectiveness of superphosphate in a field experiment and three glasshouse experiments using lateritic soils from south-western Australia. Non-reactive Queensland rock phosphate (low carbonate-substituted apatite from the Duchess deposit) was also used in the pot experiments. Bicarbonate-soluble phosphorus extracted from the soil is widely used in Western Australia to predict plant yields from previously-applied fertilizer dressings. For both field and pot experiments bicarbonate-extractable phosphorus (soil test value) was measured and related to subsequent plant yields.As calculated from the initial slope of the relationship between yield and the level of P applied, finely powdered NCRP was about 5–32% as effective as freshly-applied superphosphate in the year of application and also for two years after application in the field experiment, and for two successive crops in the three pot experiments. For both field and pot experiments, finely powdered NCRP, was at best, 1.5–2.0 times as effective as granular NCRP. Relative to freshly-applied superphosphate, the effectiveness of rock phosphates usually decreased with increasing level of application.For each of the crops in the field experiment, the relationships between yield and phosphorus content of plants (i.e. internal efficiency curves) were similar for all fertilizers. Thus the low effectiveness of the rock phosphates relative to superphosphate was solely due to much less phosphorus being taken up by plants. By contrast, in the pot experiments internal efficiency curves differed for different fertilizers. This is attributed to differences in the rate of phosphorus uptake by plant roots during the early stages of plant growth.For both field and pot experiments, soil test calibrations (the relationship between yield and soil test value) differed for rock phosphates and superphosphate. For superphosphate, soil test calibrations also differed for the three different years after the initial application of this fertilizer in the field experiment. For the second crop in the pot experiment, soil test calibrations differed for superphosphate applied at different times (before the first and the second crop). These results point out the difficulty of applying soil testing procedures to soils that have experienced different histories of fertilizer application.  相似文献   
46.
In manufacturing industries, the quality of a product depends on the combined effect of multiple input variables working singly or together and therefore attention has been given on process capability indices to shift from single to multivariate domain. In case of multivariable domain the capability to incorporate uncertainties at the time of decision making becomes necessary. Fuzzy system is introduced to take care of this requirement. In this article the process parameters of soap manufacturing industries have been analyzed. The process capability is determined using Fuzzy Inference System rule editor based on a set of justified if then statements as applicable for the process. The data has been collected in linguistic form to derive its process capability, using a set of justified rules and the effect of each factor has been determined using Design of Experiments (DoE) and analysis of variance technique (ANOVA) for improving the soap quality from perspective of its softness. This article ventures to propose a new methodology by integrating Fuzzy with DoE providing better result followed by DoE and Fuzzy Inference system in isolation.  相似文献   
47.
Abstract. This paper is concerned with the problem of joint determination of the state dimension and autoregressive order of models with Markov‐switching parameters. A model selection procedure is proposed which is based on optimization of complexity‐penalized likelihood criteria. The efficacy of the procedure is evaluated by means of Monte Carlo experiments.  相似文献   
48.
Correlations between shear resistance and the mechanical properties of pressure sensitive adhesives are studied by measuring the deformation behaviour in the static and the dynamic shear test and determining the dynamic shear modulus of the adhesive. For polymers with low or moderate viscosities, the shear strain vs. time characteristics in a static shear test and, accordingly, the static shear strength, can be evaluated from the master curves of the dynamic shear modulus or the dynamic viscosity. The dynamic shear strength also can be calculated. These exact calculations cannot be applied to highly viscous or slightly crosslinked polymers. On the basis of the model experiments, empirical correlations between shear strength and the dynamic shear modulus are established which seem to be generally valid.  相似文献   
49.
The reaction pathway of the ammoxidation of toluene on (VO)2P2O7 used as catalyst and the interaction of potential intermediates with the pyrophosphate were studied by spectroscopic techniques (FTIR, EPR), temperature-programmed chemisorptions/ reactions (TPD, TPRS) and transient studies such as the temporal analysis of products (TAP) technique. NH3 is chemisorbed on the catalyst surface, forming three different species, i.e., NH 4 + ions located on BrØnsted sites, coordinatively bound NH3 on Lewis sites and NH 2 groups, presumably P-NH2. Toluene that is probably adsorbed on Lewis sites reacts in a first step to a benzyl radical. A subsequent partial oxidation by interaction of VIV=O groups generates a V...O=CH-C6H5 surface structure. This benzaldehyde-like surface species reacts with adsorbed NH3 according to a Langmuir-Hinshelwood mechanism. TAP experiments on ammonium-containing vanadium phosphates revealed that NH 4 + ions could act as potential N-insertion species. No formation of benzylamine as well as the generation of V=NH surface groups as possible intermediates or N-insertion sites were observed.  相似文献   
50.
In the area of nonlinear predictive control, several control schemes using artificial neural networks have been proposed. In this work, the issues relating to the information contents of the data used to train the neural network components of these nonlinear predictive control schemes are considered. This raises questions about the design of experiments. A class of feedback-feedforward nonlinear controller based on the model predictive structure (also known as Internal Model Control, IMC, structure) is investigated. The implementation and performance of these neural network based controllers, together with comparisons to other nonlinear and linear controllers, are illustrated on two nonlinear continuous-stirred-tank-reactor simulations.  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