全文获取类型
收费全文 | 13555篇 |
免费 | 1108篇 |
国内免费 | 562篇 |
专业分类
电工技术 | 717篇 |
技术理论 | 1篇 |
综合类 | 900篇 |
化学工业 | 2518篇 |
金属工艺 | 702篇 |
机械仪表 | 868篇 |
建筑科学 | 909篇 |
矿业工程 | 373篇 |
能源动力 | 390篇 |
轻工业 | 954篇 |
水利工程 | 247篇 |
石油天然气 | 670篇 |
武器工业 | 87篇 |
无线电 | 1497篇 |
一般工业技术 | 1866篇 |
冶金工业 | 633篇 |
原子能技术 | 170篇 |
自动化技术 | 1723篇 |
出版年
2024年 | 60篇 |
2023年 | 237篇 |
2022年 | 334篇 |
2021年 | 517篇 |
2020年 | 432篇 |
2019年 | 341篇 |
2018年 | 405篇 |
2017年 | 447篇 |
2016年 | 373篇 |
2015年 | 511篇 |
2014年 | 653篇 |
2013年 | 829篇 |
2012年 | 785篇 |
2011年 | 792篇 |
2010年 | 774篇 |
2009年 | 699篇 |
2008年 | 658篇 |
2007年 | 720篇 |
2006年 | 713篇 |
2005年 | 581篇 |
2004年 | 413篇 |
2003年 | 459篇 |
2002年 | 536篇 |
2001年 | 427篇 |
2000年 | 355篇 |
1999年 | 368篇 |
1998年 | 321篇 |
1997年 | 283篇 |
1996年 | 246篇 |
1995年 | 193篇 |
1994年 | 165篇 |
1993年 | 113篇 |
1992年 | 100篇 |
1991年 | 82篇 |
1990年 | 63篇 |
1989年 | 48篇 |
1988年 | 41篇 |
1987年 | 24篇 |
1986年 | 31篇 |
1985年 | 10篇 |
1984年 | 16篇 |
1983年 | 9篇 |
1982年 | 9篇 |
1981年 | 11篇 |
1980年 | 13篇 |
1979年 | 6篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1976年 | 8篇 |
1959年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
This paper analyses an asymptotic stability of a digitally redesigned control system when the states of the analogue and the digital control systems are approximately matched at every sampling point. The digital redesign is a simple method of converting a given analogue controller to an equivalent digital controller in the sense of state-matching. The concerned state-matching technique is to minimise the norm distance between the discretised closed-loop system matrix of linear analogue control system and that of linear digital control system. It is shown that (i) there exists an upper bound of the norm distance to guarantee the asymptotic stability of the digitally redesigned control system and (ii) the trajectories of the linear analogue and the linear digital control systems coincide at every sampling point if the norm distance is zero. Also, a robustness result is provided in the case that nonlinear perturbations occur in the analogue and the digital control systems. Moreover, design conditions for the developed stability analysis are proposed in terms of linear matrix inequalities. 相似文献
992.
We develop majorisation results that characterise changes in eigenvector components of a graph's adjacency matrix when its topology is changed. Specifically, for general (weighted, directed) graphs, we characterise changes in dominant eigenvector components for single- and multi-row incrementations. We also show that topology changes can be tailored to set ratios between the components of the dominant eigenvector. For more limited graph classes (specifically, undirected, and reversibly-structured ones), majorisations for components of the subdominant and other eigenvectors upon graph modifications are also obtained. 相似文献
993.
The eco-environment in the source region of the Yellow River in western China has been experiencing deterioration in the past decades. Vegetation affected by climate variables and anthropogenic activities is indicative of eco-environment well-being. To quantify temporal and spatial variations of vegetation coverage and analyse potential causes for the variations, we analysed the normalized difference vegetation index (NDVI), temperature and precipitation data from 2000 to 2007. We found that altitude and topographic aspects have a strong influence on vegetation coverage. Altitudes between 4500 and 4800 m and shady aspects provide more favourable environments for vegetation growth. Data show stronger vegetation growth within the temperature range of 4.5–5.5°C. Vegetation growth generally increases with precipitation. At higher elevations of 4800–5200 m, however, despite high precipitation rates, lower temperatures restrict growth. Local hydrology conditions are found to directly influence vegetation variations. Vegetation degradation increases with distance from surface water boundaries up to 4 km, but groundwater might serve as a reliable source for preventing vegetation from degrading. Finally, we found that the percentage of degradation decreases with increasing distance from residential loci up to 24 km, which suggests that overgrazing can be a lead cause for localized vegetation degradation. Findings of this study may have a broad implication in assessing vegetation variation and grassland restoration. 相似文献
994.
云环境中大量虚拟镜像带来的冗余会造成资源利用率降低,采用重复数据删除技术能缓解对存储空间以及网络带宽的需求,但同时也存在处理性能下降的问题。为此,提出一种基于堆叠文件系统的云计算存储优化方案。该方案利用可堆叠文件系统将用户对虚拟实例的少量修改信息存放于可读写盘中,将虚拟镜像存放于只读盘中,每次只保存用户对虚拟实例的少量修改信息,而无需保存整个实例。实验结果表明,该方案可在不影响性能的条件下降低存储容量,对文件系统性能的影响平均约为0.75%,在用户对虚拟实例只需少量修改的情况下,对存储容量的需求相比传统重复数据删除方案减少约35%。 相似文献
995.
为研究端羟基聚丁二烯(hydroxyl-terminated polybutadiene,HTPB)基浇注PBX炸药的固化反应特性确定其固化工艺参数,采用非等温DSC法研究HTPB基浇注PBX炸药粘接剂体系固化反应动力学.分别测试升温速率为5、10、15、20 K/min时的DSC数据,得出固化反应动力学方程,计算不同温度下的反应速率常数,绘制固化速率(dα/dt)~固化度(α)关系曲线,并给出常用HTPB基浇注固化炸药的固化温度范围.结果表明:相同固化度条件下,升温速率越大,固化反应速率越大,当固化度达到0.5时,固化反应速率达到最大值,此后逐渐降低,直至为零. 相似文献
996.
997.
Fengjie Cui Caixia Wan Yebo Li Zhe Liu Gireesh Rajashekara 《Food and Bioprocess Technology》2012,5(4):1278-1286
Lactic acid and cell production from whey permeate by Lactobacillus rhamnosus with different nutrient supplements were investigated in this study. Yeast extract was identified as the most effective nutrient
affecting lactic acid production. Increase in inoculum size from 0.05% to 1% (v/v) resulted in a substantial increase in lactic acid productivity from 0.66 to 0.83 g L−1 h−1 (P < 0.001). The optimal temperature for lactic acid production was 37 °C, while the highest cell production was obtained at
42 °C. When whey permeate and yeast extract concentrations were 6.8% (w/v) and 3 g L−1, respectively, lactic acid productivity reached 0.85 g L−1 h−1 after 48-h cultivation, which is 3.40 times of those without nutrient supplements. 相似文献
998.
云母微晶玻璃析晶动力学的研究 总被引:15,自引:5,他引:15
采用差热分析的方法,对TiO2作为晶核剂的氟金云母生晶玻璃的析晶动力学参数进行了测定。结果表明:TiO2使原始玻璃在晶化过程中产生了先析相钛酸镁,降低了氟金云母相的析晶活化能;氟金云母晶体以二维片层状方式生长,其生长过程受界面过程控制。 相似文献
999.
基于模态频率和神经网络的结构损伤检测 总被引:9,自引:0,他引:9
把结构损伤识别问题分为损伤辨识、损伤定位、损伤程度标定三个子模块,对每个子模块用模态参数构造对损伤敏感的标识量,并作为特征参数输入到神经网络中实现损伤识别。将优化的BP网络和频率相结合成功地实现了矩形梁的损伤检测,为结构健康监测研究提出一条新的技术途径。 相似文献
1000.