首页 | 官方网站   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   1780篇
  国内免费   59篇
  完全免费   383篇
工业技术   2222篇
  2020年   3篇
  2019年   16篇
  2018年   79篇
  2017年   86篇
  2016年   100篇
  2015年   91篇
  2014年   148篇
  2013年   107篇
  2012年   180篇
  2011年   191篇
  2010年   138篇
  2009年   135篇
  2008年   135篇
  2007年   129篇
  2006年   157篇
  2005年   112篇
  2004年   86篇
  2003年   66篇
  2002年   38篇
  2001年   52篇
  2000年   38篇
  1999年   35篇
  1998年   24篇
  1997年   22篇
  1996年   13篇
  1995年   9篇
  1994年   8篇
  1993年   6篇
  1992年   1篇
  1991年   7篇
  1990年   4篇
  1989年   1篇
  1987年   1篇
  1985年   1篇
  1984年   2篇
  1963年   1篇
排序方式: 共有2222条查询结果,搜索用时 46 毫秒
1.
新疆阜康县草地资源产量动态监测模型的研究   总被引:4,自引:0,他引:4       下载免费PDF全文
利用NOAA/AVHHR数据和地面实测产量值,分析、模拟了鲜草重量和植被指数之间的数理关系,并对草地产量进行了模拟预报。结果表明,采用两种植被指数和七种经验公式所选出的最优预报模型,在地势比较平坦,草地类型变化不大的地区,可以较准确地反映草地产量的变化;但在地形复杂、草地类型变化较大的地区,模型稳定性变差,不适合于草地产量的预报。  相似文献   
2.
烟碱含量近红外光谱预测模型的评价   总被引:2,自引:1,他引:1  
以烟碱为例,建立了近红外光谱的预测模型,采用回归分析法和假设检验法对该模型的预测效果进行了系统的评价。结果表明,该模型对烟草样品烟碱含量的预测效果良好,模型预测值与化学测定值之间不存在显著性差异。  相似文献   
3.
油气田中CO2腐蚀的预测模型   总被引:1,自引:0,他引:1  
综述了油气田中CO2腐蚀速率的预测模型.关于CO2腐蚀速率的预测模型主要包括经验模型(Empirical models),半经验模型(Semi—empirical models)和机理模型(Mechanistic models)三类.经验模型是根据实验室和油气田现场腐蚀数据建立的预测模型,这类模型比较简洁,与现场的试验数据吻合较好.半经验模型先根据腐蚀过程中的化学、电化学过程和介质的传输过程建立腐蚀速率相关的动力学模型,然后利用实验室数据以及现场数据确定各因素的影响因子.机理模型主要是应用腐蚀热力学、动力学以及物质扩散动力学,基于CO2腐蚀机理建立腐蚀速率的预测模型.由于CO2腐蚀的影响因素很多,腐蚀机理异常复杂,要建立准确、普适的预测模型较为困难.目前这三类预测模型均存在一定的不完善性,应对其进行更深入的研究和改进.  相似文献   
4.
长治市需水预测研究   总被引:2,自引:0,他引:2  
文中用人工神经网络预测模型对长治市近期国民经济发展对水的需求进行了预测。  相似文献   
5.
油井小层含水率预测方法研究   总被引:1,自引:1,他引:0  
本文在对影响油井含水的地质及开发因素分析的基础上,用数值模拟方法建立了油水井间不同砂体连通关系下,油井小层含水率预测模型。通过对大庆油田小井距试验区501井萨Ⅱ7+8和葡I1+2两个单采油层含水率的预测及中区西部密井网试验区单层测试资料的验证,其结果与实际含水率符合较好。  相似文献   
6.
The growth responses of a vegetative inoculum of Bacillus cereus as influenced by varying conditions of temperature, pH value and sodium chloride concentration (% w/v) and carbon dioxide concentration (% v/v) were determined in laboratory medium. Growth curves in concentrations of NaCl in the range 0.5–10.5% (w/v), pH values in the range 4.5–7.0, CO2 concentrations in the range 10–80% (v/v) and storage temperatures from 10 °C to 30 °C were fitted using the regime of Baranyi et al. (1993). A response surface model was prepared and predictions of doubling time, growth rate, lag time and time to 1000-fold increase could be obtained for any set of conditions within the matrix studied. This model is included in Food MicroModel Version 1. Predicted doubling times from the model were compared to observed doubling times in the literature and the model was found to give realistic estimates of doubling time for a range of foods including milk, meat and poultry and carbohydrate-based products.  相似文献   
7.
以全国20余省、区的17种作物种质资源为材料,利用近红外漫反射光谱分析仪快速测定其粗蛋白、粗脂肪、粗淀粉、赖氨酸、单宁、沉淀值、硬度等籽粒品质性状。建立了41个定标模型,获得较高的预测决定系数(0.95~0.99)和较小的标准偏差(0.19~0.50)。同时,对17种作物的7240份作物种质资源进行了快速测定,筛选出645份优异作物种质资源。文中还对关键技术进行了讨论。  相似文献   
8.
MOSFET的热载流子效应及其表征技术   总被引:1,自引:0,他引:1  
赵要  胡靖  许铭真  谭长华 《微电子学》2003,33(5):432-438
介绍了热载流子引起MOS器件退化的机制及其退化模型、最大应力模式和典型的寿命预测模型等,并对器件退化的表征技术进行了概述。  相似文献   
9.
A program of experimental and analytical tasks has been conducted to define the linkage(s) between microstructural characteristics and fatigue performance in an aluminum alloy typically used for airframe structural applications. The first goal was to develop data for quantitatively linking measurable characteristics of material microstructure with long-term fatigue performance. The second goal was to develop models to predict fatigue performance based on the microstructural characteristics. The work focused on several process variants of aluminum alloy 7050-T7451 plate. This material was chosen because of its widespread use for flight-critical airframe structural components, and the particular characteristics associated with the manufacturing, service and maintenance of thick section components. Within the framework of this objective, life-limiting microstructural features have been identified and ranked by severity, and models to quantitatively describe the evolution and growth of macrostructural cracks from those features have been developed.The modeling framework has been applied to predict the cyclic lifetime of the 7050 alloy process variants based on the populations of life-limiting microstructural features. In addition, the models have been used to show how changes in the material characteristics may affect the fatigue performance. This includes predictions of the effect of changing the life-limiting microfeature size and shape distributions, and the effect of changing material strength properties.The use of this modeling approach to probabilistically describe the implications of changes in the microstructure has been demonstrated, thereby allowing the effects of material pedigree to be predictively linked with the structural integrity of end components. The modeling framework has potential applications in airframe design support processes, and as a tool for use in material and product form selection processes.  相似文献   
10.
Accident prediction models for roads with minor junctions   总被引:2,自引:0,他引:2  
The purpose of this study was to develop and validate a method for predicting expected accidents on main roads with minor junctions where traffic counts on the minor approaches are not available. The study was based on data for some 3800 km of highway in the U.K. including more than 5000 minor junctions. The highways consisted of both single and dual-carriageway roads in urban and rural areas. Generalized linear modelling was used to develop regression estimates of expected accidents for six highway categories and an empirical Bayes procedure was used to improve these estimates by combining them with accident counts. Accidents on highway sections were shown to be a non-linear function of exposure and minor junction frequency. For the purposes of estimating expected accidents, while the regression model estimates were shown to be preferable to accident counts, the best results were obtained using the empirical Bayes method. The latter was the only method that produced unbiased estimates of expected accidents for high-risk sites.  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-23

京公网安备 11010802026262号