全文获取类型
收费全文 | 96034篇 |
免费 | 10872篇 |
国内免费 | 6291篇 |
专业分类
电工技术 | 8851篇 |
技术理论 | 7篇 |
综合类 | 11289篇 |
化学工业 | 8835篇 |
金属工艺 | 2843篇 |
机械仪表 | 4977篇 |
建筑科学 | 10746篇 |
矿业工程 | 4323篇 |
能源动力 | 2977篇 |
轻工业 | 8191篇 |
水利工程 | 4519篇 |
石油天然气 | 8111篇 |
武器工业 | 1353篇 |
无线电 | 8986篇 |
一般工业技术 | 8823篇 |
冶金工业 | 3519篇 |
原子能技术 | 1196篇 |
自动化技术 | 13651篇 |
出版年
2024年 | 456篇 |
2023年 | 1434篇 |
2022年 | 2832篇 |
2021年 | 3339篇 |
2020年 | 3432篇 |
2019年 | 2800篇 |
2018年 | 2794篇 |
2017年 | 3227篇 |
2016年 | 3799篇 |
2015年 | 3952篇 |
2014年 | 6167篇 |
2013年 | 6085篇 |
2012年 | 7184篇 |
2011年 | 7665篇 |
2010年 | 5655篇 |
2009年 | 5775篇 |
2008年 | 5413篇 |
2007年 | 6489篇 |
2006年 | 5814篇 |
2005年 | 5026篇 |
2004年 | 4064篇 |
2003年 | 3512篇 |
2002年 | 2794篇 |
2001年 | 2484篇 |
2000年 | 1960篇 |
1999年 | 1647篇 |
1998年 | 1291篇 |
1997年 | 1128篇 |
1996年 | 960篇 |
1995年 | 812篇 |
1994年 | 685篇 |
1993年 | 479篇 |
1992年 | 350篇 |
1991年 | 311篇 |
1990年 | 255篇 |
1989年 | 239篇 |
1988年 | 188篇 |
1987年 | 102篇 |
1986年 | 79篇 |
1985年 | 61篇 |
1984年 | 76篇 |
1983年 | 51篇 |
1982年 | 41篇 |
1981年 | 30篇 |
1980年 | 21篇 |
1979年 | 22篇 |
1977年 | 15篇 |
1964年 | 17篇 |
1961年 | 18篇 |
1959年 | 17篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
111.
通过对减振器结构设计的理论分析,建立了减振器的数学模型,同时通过设计的模拟装置对减振效果进行了实测,效果良好。 相似文献
112.
探讨水资源承载力综合评估和多目标计算理论在城市规划中的应用。运用灰色多层次综合评估模型对惠州市水资源承载力进行定性的综合评价,应用多目标规划理论对城市经济发展规划不同方案下的惠州市水资源承载力作了定量计算。 相似文献
113.
Oleuropein Inhibits LDL Oxidation Induced by Cooking Oil Frying By-products and Platelet Aggregation Induced by Platelet-Activating Factor 总被引:1,自引:0,他引:1
Oleuropein, a polyphenolic glucoside, constituent of olive fruit and oil, has been previously shown to exhibit, in vitro, potent properties as a biological antioxidant. In the present paper, two new properties are demonstrated in vitro as well, concerning its vascular protection activity, against the atheromatic lesion formation and its blood antithrombotic effect. Firstly, it was found that the oxidation of low-density lipoproteins (LDL), induced by different quantities of total polar materials (TPM), was inhibited by 10 μ M (final concentration) of oleuropein, revealing approx. 50% protection. Secondly, platelet-rich human plasma aggregation, induced by either the platelet-activating factor or adenosine diphospate or arachidonic acid, was inhibited by oleuropein. The 10 μ M (final concentration) of oleuropein was proven to be the most effective among the tested concentrations against LDL oxidation, while an IC50=0.41 mM was calculated for its inhibitory activity against platelet aggregation induced by 0.7 μ M platelet-activating factor. 相似文献
114.
Ting Gang Zhu Uttiya Chowdhury Michael M. Wong Jonathan C. Denyszyn Russell D. Dupuis 《Journal of Electronic Materials》2002,31(5):406-410
In this paper, we report the study of the electrical characteristics of GaN and AlGaN vertical p-i-n junctions and Schottky
rectifiers grown on both sapphire and SiC substrates by metal-organic chemical-vapor deposition. For GaN p-i-n rectifiers
grown on SiC with a relatively thin “i” region of 2 μm, a breakdown voltage over 400 V, and forward voltage as low as 4.5
V at 100 A/cm2 are exhibited for a 60-μm-diameter device. A GaN Schottky diode with a 2-μm-thick undoped layer exhibits a blocking voltage
in excess of ∼230 V at a reverse-leakage current density below 1 mA/cm2, and a forward-voltage drop of 3.5 V at a current density of 100 A/cm2. It has been found that with the same device structure and process approach, the leakage current of a device grown on a SiC
substrate is much lower than a device grown on a sapphire substrate. The use of Mg ion implantation for p-guard rings as planar-edge
terminations in mesageometry GaN Schottky rectifiers has also been studied. 相似文献
115.
Development of a recurrent Sigma-Pi neural network rainfall forecasting system in Hong Kong 总被引:1,自引:1,他引:0
At the moment, weather forecasting is still an art — the experience and intuition of forecasters play a significant role in determining the quality of forecasting. This paper describes the development of a new approach to rainfall forecasting using neural networks. It deals with the extraction of information from radar images and an evaluation of past rain gauge records to provide shortterm rainfall forecasting. All of the meteorological data were provided by the Royal Observatory of Hong Kong (ROHK). Preprocessing procedures were essential for this neural network rainfall forecasting. The forecast of the rainfall was performed every half an hour so that a storm warning signal can be delivered to the public in advance. The network architecture is based on a recurrent Sigma-Pi network. The results are very promising, and this neural-based rainfall forecasting system is capable of providing a rain storm warning signal to the Hong Kong public one hour ahead. 相似文献
116.
X. Wang S. B. Lambert 《Fatigue & Fracture of Engineering Materials & Structures》1997,20(12):1637-1655
Abstract— A Fourier series approach is proposed to calculate stress intensity factors using weight functions for semi-elliptical surface cracks in flat plates subjected to two-dimensional stress distributions. The weight functions were derived from reference stress intensity factors obtained by three-dimensional finite element analyses. The close form weight functions derived are suitable for the calculation of stress intensity factors for semi-elliptical surface cracks in flat plates under two-dimensional stress distributions with the crack aspect ratio in the range of 0.1 ≤ a/c ≤ 1 and relative depth in the range of 0 ≤ a/t ≤ 0.8. Solutions were verified using several two-dimensional non-linear stress distributions; the maximum difference being 6%. 相似文献
117.
采用MC6805系列单片机并充分利用其定时器,选择测频法或测周法,可以实现定范围、高精度频率测量。此种方法只占用1个内部定时器,节省了硬件开销。 相似文献
118.
本文介绍的基于信息的智能控制理论的发展过程,主要分为智能控制的信息指标和智能控制的信息结构分析两部分,文中在最后对这套理论可能的发展方向进行了探讨。 相似文献
119.
120.
Management of multidimensional discrete data 总被引:1,自引:0,他引:1
Peter Baumann Ph.D. 《The VLDB Journal The International Journal on Very Large Data Bases》1994,3(4):401-444
Spatial database management involves two main categories of data: vector and raster data. The former has received a lot of in-depth investigation; the latter still lacks a sound framework. Current DBMSs either regard raster data as pure byte sequences where the DBMS has no knowledge about the underlying semantics, or they do not complement array structures with storage mechanisms suitable for huge arrays, or they are designed as specialized systems with sophisticated imaging functionality, but no general database capabilities (e.g., a query language). Many types of array data will require database support in the future, notably 2-D images, audio data and general signal-time series (1-D), animations (3-D), static or time-variant voxel fields (3-D and 4-D), and the ISO/IEC PIKS (Programmer's Imaging Kernel System) BasicImage type (5-D). In this article, we propose a comprehensive support ofmultidimensional discrete data (MDD) in databases, including operations on arrays of arbitrary size over arbitrary data types. A set of requirements is developed, a small set of language constructs is proposed (based on a formal algebraic semantics), and a novel MDD architecture is outlined to provide the basis for efficient MDD query evaluation. 相似文献