全文获取类型
收费全文 | 18367篇 |
免费 | 2313篇 |
国内免费 | 1401篇 |
专业分类
电工技术 | 5124篇 |
综合类 | 1584篇 |
化学工业 | 778篇 |
金属工艺 | 518篇 |
机械仪表 | 1193篇 |
建筑科学 | 525篇 |
矿业工程 | 444篇 |
能源动力 | 340篇 |
轻工业 | 461篇 |
水利工程 | 219篇 |
石油天然气 | 295篇 |
武器工业 | 214篇 |
无线电 | 3632篇 |
一般工业技术 | 1073篇 |
冶金工业 | 437篇 |
原子能技术 | 205篇 |
自动化技术 | 5039篇 |
出版年
2024年 | 80篇 |
2023年 | 227篇 |
2022年 | 366篇 |
2021年 | 499篇 |
2020年 | 591篇 |
2019年 | 474篇 |
2018年 | 435篇 |
2017年 | 637篇 |
2016年 | 750篇 |
2015年 | 796篇 |
2014年 | 1128篇 |
2013年 | 1192篇 |
2012年 | 1470篇 |
2011年 | 1628篇 |
2010年 | 1188篇 |
2009年 | 1212篇 |
2008年 | 1190篇 |
2007年 | 1425篇 |
2006年 | 1233篇 |
2005年 | 1037篇 |
2004年 | 806篇 |
2003年 | 678篇 |
2002年 | 582篇 |
2001年 | 476篇 |
2000年 | 401篇 |
1999年 | 333篇 |
1998年 | 240篇 |
1997年 | 185篇 |
1996年 | 154篇 |
1995年 | 143篇 |
1994年 | 90篇 |
1993年 | 80篇 |
1992年 | 64篇 |
1991年 | 54篇 |
1990年 | 42篇 |
1989年 | 36篇 |
1988年 | 29篇 |
1987年 | 13篇 |
1986年 | 22篇 |
1985年 | 18篇 |
1984年 | 9篇 |
1983年 | 7篇 |
1982年 | 9篇 |
1981年 | 6篇 |
1980年 | 9篇 |
1979年 | 5篇 |
1978年 | 3篇 |
1977年 | 4篇 |
1976年 | 7篇 |
1959年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
91.
二滩电厂表孔采用弧形门,启闭形式为双缸液压启闭机.自投入运行以来,运行状况良好.汛期启闭方式已由原来的现地手动操作过渡到远方控制自动启闭.在闸门起落的过程中,由于工况的不同,两缸会出现不同步现象,因此设计中考虑了纠偏回路.本文简单介绍了二滩电厂表孔液压启闭机的原理和故障情况. 相似文献
92.
93.
Using airborne laser scanning to monitor tree migration in the boreal-alpine transition zone 总被引:1,自引:0,他引:1
The boreal tree line is expected to advance upwards into the mountains and northwards into the tundra due to global warming. The major objective of this study was to find out if it is possible to use high-resolution airborne laser scanner data to detect very small trees — the pioneers that are pushing the tree line up into the mountains and out onto the tundra. The study was conducted in a sub-alpine/alpine environment in southeast Norway. A total of 342 small trees of Norway spruce, Scots pine, and downy birch with tree heights ranging from 0.11 to 5.20 m were precisely georeferenced and measured in field. Laser data were collected with a pulse density of 7.7 m− 2. Three different terrain models were used to process the airborne laser point cloud in order to assess the effects of different pre-processing parameters on small tree detection. Greater than 91% of all trees > 1 m tall registered positive laser height values regardless of terrain model. For smaller trees (< 1 m), positive height values were found in 5-73% of the cases, depending on the terrain model considered. For this group of trees, the highest rate of trees with positive height values was found for spruce. The more smoothed the terrain model was, the larger the portion of the trees that had positive laser height values. The accuracy of tree height derived from the laser data indicated a systematic underestimation of true tree height by 0.40 to 1.01 m. The standard deviation for the differences between laser-derived and field-measured tree heights was 0.11-0.73 m. Commission errors, i.e., the detection of terrain objects — rocks, hummocks — as trees, increased significantly as terrain smoothing increased. Thus, if no classification of objects into classes like small trees and terrain objects is possible, many non-tree objects with a positive height value cannot be separated from those actually being trees. In a monitoring context, i.e., repeated measurements over time, we argue that most other objects like terrain structures, rocks, and hummocks will remain stable over time while the trees will change as they grow and new trees are established. Thus, this study indicates that, given a high laser pulse density and a certain density of newly established trees, it would be possible to detect a sufficient portion of newly established trees over a 10 years period to claim that tree migration is taking place. 相似文献
94.
95.
近年来,电驱动已成为石油钻机的主要驱动形式,是钻机自动化、智能化的坚实平台。文章就电动钻机的部分工作理论作初步剖析,包括钻机工作机组对电驱动的要求,可控硅直流电驱动和交流变频电驱动的工作原理,直流电动机和交流变频电动机等的特性分析,电动机的四象限运行和能耗制动原理等。 相似文献
96.
97.
A mechanism of synchronization of components of distributed systems in which communications are based on a common time schedule
for all system components is illustrated by examples of simple Time-Triggered Protocols. For parametric linear models of synchronization,
the optimization problem is considered for a parameter that should exclude the overlapping of messages in communication channels.
The results of using numeric methods for estimation of the optimal value of this parameter are described.
__________
Translated from Kibernetika i Sistemnyi Analiz, No. 3, pp. 24–32, May–June 2006. 相似文献
98.
99.
银河仿真Ⅱ型机YH-F2是高性能的全数字仿真计算机,处理机间通讯是YH-F2采用的关键技术之一。本文分三个部分介绍了YH-F2的处理机间通讯:①处理机通讯指令,③处理机间数据传输,③I/O处理机IOP与通讯控制处理机CCP之间的通讯。 相似文献
100.
Kosuke Kurokawa 《Electrical Engineering in Japan》1993,113(4):54-65
Solar radiation has an irregularly varying factor due to a basic day and night cycle and climatic conditions. For such conditions a data sampling interval is important to ensure the accuracy of energy monitoring in a photovoltaic system. While treating a system monitoring equipment as a black box. the author has developed the method of calibrating an energy-integrating function. At first for various input waveforms, the relationship between sampling intervals and quasi-integration outputs have been examined by trapezoidal rule. In the numerical simulation the phases of the sampling clock also are considered Then it is concluded that a sampling interval can be inspected through outside observation only by using a rectangular single pulse. By applying the pulse to the energy-integrating process, two kinds of integrated outputs can be obtained for different sampling phases. The calculated difference between both outputs can uniquely give the sampling interval being inspected. Conditions to ensure measuring accuracy are discussed and the validity of this method has been demonstrated experimentally. Practical calibrating procedures also are proposed for the integrating function of PV system monitoring. 相似文献