全文获取类型
收费全文 | 45323篇 |
免费 | 7112篇 |
国内免费 | 5675篇 |
专业分类
电工技术 | 3201篇 |
技术理论 | 3篇 |
综合类 | 5196篇 |
化学工业 | 3803篇 |
金属工艺 | 3415篇 |
机械仪表 | 3442篇 |
建筑科学 | 3022篇 |
矿业工程 | 1509篇 |
能源动力 | 917篇 |
轻工业 | 1250篇 |
水利工程 | 950篇 |
石油天然气 | 2323篇 |
武器工业 | 440篇 |
无线电 | 5136篇 |
一般工业技术 | 4611篇 |
冶金工业 | 2412篇 |
原子能技术 | 191篇 |
自动化技术 | 16289篇 |
出版年
2024年 | 380篇 |
2023年 | 967篇 |
2022年 | 1836篇 |
2021年 | 1931篇 |
2020年 | 2018篇 |
2019年 | 1693篇 |
2018年 | 1412篇 |
2017年 | 1674篇 |
2016年 | 1854篇 |
2015年 | 2030篇 |
2014年 | 3065篇 |
2013年 | 2802篇 |
2012年 | 3580篇 |
2011年 | 3742篇 |
2010年 | 2814篇 |
2009年 | 2928篇 |
2008年 | 2681篇 |
2007年 | 3216篇 |
2006年 | 2857篇 |
2005年 | 2330篇 |
2004年 | 1926篇 |
2003年 | 1699篇 |
2002年 | 1453篇 |
2001年 | 1200篇 |
2000年 | 1104篇 |
1999年 | 890篇 |
1998年 | 707篇 |
1997年 | 629篇 |
1996年 | 495篇 |
1995年 | 429篇 |
1994年 | 379篇 |
1993年 | 226篇 |
1992年 | 214篇 |
1991年 | 177篇 |
1990年 | 164篇 |
1989年 | 142篇 |
1988年 | 81篇 |
1987年 | 39篇 |
1986年 | 37篇 |
1985年 | 40篇 |
1984年 | 33篇 |
1983年 | 26篇 |
1982年 | 26篇 |
1981年 | 19篇 |
1980年 | 17篇 |
1979年 | 22篇 |
1978年 | 11篇 |
1977年 | 10篇 |
1964年 | 12篇 |
1957年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
ABSTRACTIn this paper, we review some algebraic control system. Precisely, linear and bilinear systems on Euclidean spaces and invariant and linear systems on Lie groups. The fourth classes of systems have a common issue: to any class, there exists an associated subgroup. From this object, we survey the controllability property. Especially, from those coming from our contribution to the theory. 相似文献
2.
ABSTRACTThis paper proposes the multiple-hypotheses image segmentation and feed-forward neural network classifier for food recognition to improve the performance. Initially, the food or meal image is given as input. Then, the segmentation is applied to identify the regions, where a particular food item is located using salient region detection, multi-scale segmentation, and fast rejection. Then, the features of every food item are extracted by the global feature and local feature extraction. After the features are obtained, the classification is performed for each segmented region using a feed-forward neural network model. Finally, the calorie value is computed with the aid of (i) food volume and (ii) calorie and nutrition measure based on mass value. The experimental results and performance evaluation are validated. The outcome of the proposed method attains 0.947 for Macro Average Accuracy (MAA) and 0.959 for Standard Accuracy (SA), which provides better classification performance. 相似文献
3.
蔡存岭 《石油化工管理干部学院学报》2006,(1):72-74
论述了当前腐败现象的表现和特点,分析了产生腐败现象的主要原因,提出了治理腐败现象的对策措施: 建立有效的教育机制、严格的用人机制、规范的决策机制、健全的管理机制、完善的监督机制和有力的责任追究机制,建立科学的法人治理结构并实行纪检监察机构派驻制。 相似文献
4.
5.
Analysis of non-stationary electrochemical oscillations emerges utilization of the techniques allowing an observation of time evolution of their parameters such as instantaneous frequency, amplitude or frequency band. An algorithm of extraction of these parameters can be based on one of linear or quadratic time-frequency representations of oscillations record. In this paper, the authors present representatives of such transformations (Choi-Williams and Cone-shaped) originating from one of the most popular joint time-frequency energy distribution—Wigner-Ville distribution. Short introduction to the mathematics of the topic discussed is provided, then the authors present an example of application in the analysis of current oscillations of copper dissolution process. 相似文献
6.
基于子波变换的涡街流量传感器信号分析 总被引:6,自引:0,他引:6
长期以来 ,如何提取潜在噪声下的涡街流量信号一直是个问题。流体流速脉动 ,局部阻力 ,随机振动———所有这些因素都给解决这一问题带来难度。文章应用子波变换消噪理论 ,从软件滤波的角度分析了强噪声干扰下的涡街流量信号 ,并提出了单支重构计数方法。分析结果表明 ,这种方法对低流速流量计量效果很好 ,能够有效地扩展量程下限 相似文献
7.
The present empirical investigation had a 3-fold purpose: (a) to cross-validate L. R. Offermann, J. K. Kennedy, and P. W. Wirtz's (1994) scale of Implicit Leadership Theories (ILTs) in several organizational settings and to further provide a shorter scale of ILTs in organizations; (b) to assess the generalizability of ILTs across different employee groups, and (c) to evaluate ILTs' change over time. Two independent samples were used for the scale validation (N1 = 500 and N2 = 439). A 6-factor structure (Sensitivity, Intelligence, Dedication, Dynamism, Tyranny, and Masculinity) was found to most accurately represent ELTs in organizational settings. Regarding the generalizability of ILTs, although the 6-factor structure was consistent across different employee groups, there was only partial support for total factorial invariance. Finally, evaluation of gamma, beta, and alpha change provided support for ILTs' stability over time. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
8.
本文提出了一种基于信息融合的物体三维特征的提取方法,该方法利用两幅互相配准的三维测距图像和灰度图像,来提取多面体的三维特征。首先,通过分析灰度图像中的灰度变化及测距图像中的测距值变化,分别求取各自图像中物体的特征点及特征边;然后,利用两配准图像之间的对应关系,求得所有特征点、面与多边形在三维测距图像中的三维表示;接着,通过分析三维测距图像中所测得的各候选平面上特定点与边处的曲率及法向,验证候选平面 相似文献
9.
In the oxidation of TiAl alloys, the role of scale-growth stresses formed during oxidation has, thus far, been unknown. In the present paper the oxide-growth stresses were investigated by the deflection-test method in monofacial oxidation (DTMO) accompanied by acoustic-emission measurements. On unmodified surfaces the growth stresses are compressive and reach levels of around –100 MPa. At the same time, significant acoustic emission occurs indicating that even under isothermal conditions, stresses are relieved by a scale-cracking mechanism. For oxide scales on TiAl surfaces, which had been ion implanted with chlorine before oxidation, a very thin protective alumina layer is formed which, however, develops growth stresses in the range of several GPa, accompanied by intensive acoustic emission. In all stress–time curves, a dynamic situation is observed. This consists of phases of stress relief by scale microcracking and phases of stresses increase due to crack healing and further oxide growth. As a result, the level of stress as a function of oxidation time, is characterized by an oscillating course. 相似文献
10.
介绍了天线近场测量的基本原理和HD-1型平面近场测试系统,并对近场测量在实际天线测试中的应用情况、发展方向和应用前景等作了简单的描述。 相似文献