全文获取类型
收费全文 | 2040篇 |
免费 | 52篇 |
国内免费 | 16篇 |
专业分类
电工技术 | 83篇 |
综合类 | 50篇 |
化学工业 | 339篇 |
金属工艺 | 110篇 |
机械仪表 | 208篇 |
建筑科学 | 113篇 |
矿业工程 | 106篇 |
能源动力 | 275篇 |
轻工业 | 366篇 |
水利工程 | 19篇 |
石油天然气 | 61篇 |
无线电 | 73篇 |
一般工业技术 | 194篇 |
冶金工业 | 41篇 |
原子能技术 | 21篇 |
自动化技术 | 49篇 |
出版年
2024年 | 2篇 |
2023年 | 44篇 |
2022年 | 75篇 |
2021年 | 57篇 |
2020年 | 70篇 |
2019年 | 62篇 |
2018年 | 64篇 |
2017年 | 72篇 |
2016年 | 42篇 |
2015年 | 50篇 |
2014年 | 109篇 |
2013年 | 124篇 |
2012年 | 81篇 |
2011年 | 154篇 |
2010年 | 100篇 |
2009年 | 101篇 |
2008年 | 108篇 |
2007年 | 107篇 |
2006年 | 90篇 |
2005年 | 71篇 |
2004年 | 85篇 |
2003年 | 62篇 |
2002年 | 72篇 |
2001年 | 53篇 |
2000年 | 41篇 |
1999年 | 36篇 |
1998年 | 27篇 |
1997年 | 23篇 |
1996年 | 19篇 |
1995年 | 19篇 |
1994年 | 21篇 |
1993年 | 18篇 |
1992年 | 11篇 |
1991年 | 17篇 |
1990年 | 8篇 |
1989年 | 5篇 |
1988年 | 3篇 |
1986年 | 1篇 |
1983年 | 3篇 |
1982年 | 1篇 |
排序方式: 共有2108条查询结果,搜索用时 15 毫秒
31.
32.
切削液的使用带来了许多负面问题,鉴于环境考虑,研究绿色加工技术将是机械制造业必须重视的课题.干式切削是解决途径之一,它不用切削液,可完全消除切削液带来的一系列负面影响.本文通过选用一些新型刀具,在干式切削条件下对不同的刀具材料、刀具几何参数和切削用量进行试验比较,以寻求适用于干式切削的刀具材料与切削规律. 相似文献
33.
Anselmo Eduardo Diniz Adilson Jos de Oliveira 《International Journal of Machine Tools and Manufacture》2004,44(10):1061-1067
The main objective of using cutting fluids in machining operations is the reduction of temperature in the cutting region to increase tool life. However, the advantages offered by cutting fluids have been strongly debated because of their negative effects on the economic aspect, the environment and the health of workers using them. A trend to solve these problems is cutting without fluid, a method named dry cutting, which has been made possible due to technological innovations. This work aims to seek conditions in which dry cutting is satisfactory compared with the flood of fluid (called here wet cutting) usually used. Aiming at this goal, several experiments were carried out varying parameters such as cutting speed, feed, depth of cut and tool material in rough turning of ABNT 1045 steel in dry and wet cutting. The analysis of the results showed that wet turning is, as expected, better for tool life. The second conclusion is that dry cutting cannot be used with large depth of cut. But the main conclusion is that, if the tool material is changed to a more wear resistant one, dry cutting can be used with results very similar to those obtained with a flood of fluid. 相似文献
34.
35.
针对大型等离子体干法刻蚀生产设备的工艺特点,根据公司的生产实际需求,对原有损坏机台控制系统进行了重新改造设计。基于真空系统、工艺气体混合调节系统、射频微波放电系统、传动控制系统和终点检测系统等各子系统的控制难点及实现过程,设计了以三菱Q06 PLC为核心和In Touch 10.0为上位机监控软件的等离子体干法刻蚀设备控制系统。在In Touch 10.0平台上,搭建了等离子体干法刻蚀系统的监控界面,通过上位机处理大量生产制程数据和归档重要配方参数,实现生产工艺流程各个环节的实时监控、设备工作运行状态的参数显示和系统的故障报警等功能。 相似文献
36.
DCS系统在新型干法水泥生产线中的应用 总被引:2,自引:2,他引:0
刘成基 《自动化与仪器仪表》2009,(1):67-70
介绍了在新型干法水泥生产线中全厂全线采用DCS系统进行设计应用,对企业降低费用、提高效率和生产率具有十分重大意义。 相似文献
37.
A scalable approach to mapping annual land cover at 250 m using MODIS time series data: A case study in the Dry Chaco ecoregion of South America 总被引:3,自引:0,他引:3
Matthew L. Clark T. Mitchell Aide George Riner 《Remote sensing of environment》2010,114(11):2816-2832
Land use and land cover (LULC) maps from remote sensing are vital for monitoring, understanding and predicting the effects of complex human-nature interactions that span local, regional and global scales. We present a method to map annual LULC at a regional spatial scale with source data and processing techniques that permit scaling to broader spatial and temporal scales, while maintaining a consistent classification scheme and accuracy. Using the Dry Chaco ecoregion in Argentina, Bolivia and Paraguay as a test site, we derived a suite of predictor variables from 2001 to 2007 from the MODIS 250 m vegetation index product (MOD13Q1). These variables included: annual statistics of red, near infrared, and enhanced vegetation index (EVI), phenological metrics derived from EVI time series data, and slope and elevation. For reference data, we visually interpreted percent cover of eight classes at locations with high-resolution QuickBird imagery in Google Earth. An adjustable majority cover threshold was used to assign samples to a dominant class. When compared to field data, we found this imagery to have georeferencing error < 5% the length of a MODIS pixel, while most class interpretation error was related to confusion between agriculture and herbaceous vegetation. We used the Random Forests classifier to identify the best sets of predictor variables and percent cover thresholds for discriminating our LULC classes. The best variable set included all predictor variables and a cover threshold of 80%. This optimal Random Forests was used to map LULC for each year between 2001 and 2007, followed by a per-pixel, 3-year temporal filter to remove disallowed LULC transitions. Our sequence of maps had an overall accuracy of 79.3%, producer accuracy from 51.4% (plantation) to 95.8% (woody vegetation), and user accuracy from 58.9% (herbaceous vegetation) to 100.0% (water). We attributed map class confusion to limited spectral information, sub-pixel spectral mixing, georeferencing error and human error in interpreting reference samples. We used our maps to assess woody vegetation change in the Dry Chaco from 2002 to 2006, which was characterized by rapid deforestation related to soybean and planted pasture expansion. This method can be easily applied to other regions or continents to produce spatially and temporally consistent information on annual LULC. 相似文献
38.
As urban development increases, a need is emerging to understand and predict river behaviour in order to focus rehabilitation efforts and protect the natural river system while preserving urban infrastructure. Stream assessment methods are reviewed to demonstrate the need for a physically based and objective method that is also accessible in terms of time, data requirements and expertise. The case of Highland Creek near Toronto, Canada, is used to demonstrate a new type of initial stream assessment method that is based on the concept of stream power and performed entirely in a geographic information system using information from a digital elevation model (DEM). The results from this analysis are tested against existing information for Highland Creek. This includes a hydraulic model (Hydraulic Engineering Center's ‘River Analysis System’), field‐measured slopes, air photos and the geomorphic effects of an extreme flood. In addition, the results are presented in map form to demonstrate the effectiveness of visualizing the stream‐power distribution over the entire basin and also the usefulness of overlaying stream power onto other available information. The slopes extracted from the DEM are found to be statistically similar to those from a one‐dimensional hydraulic model and field‐measured slopes. Individual peaks in slope as well as locations of stream‐power maxima and minima are found to correlate to actual channel features as seen in air photos. The extreme flood event of August 2005 caused a dramatic change in channel form at the exact location of maximum energy predicted by the DEM‐based stream‐power analysis. The case of Highland Creek illustrates how this approach yields a useful outcome for understanding stream dynamics and stability as part of a stream assessment process. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
39.
地下水埋深变化是地下水系统动态变化最主要的表现形式之一,通过预测地下水埋深分析地下水系统未来演变趋势,对合理开发、持续利用地下水资源有着重要的现实意义。本文选取2000-2010年渭北旱塬区的两个典型监测井的地下水埋深数据,用灰色GM(1,1)理论建立预测模型,并对该监测井的地下水埋深进行短期预测。经检验,该模型具有较高的预测精度,说明采用灰色理论预测渭北旱塬区监测井地下水埋深的方法可行。 相似文献
40.