全文获取类型
收费全文 | 124408篇 |
免费 | 9192篇 |
国内免费 | 8099篇 |
专业分类
电工技术 | 8528篇 |
技术理论 | 2篇 |
综合类 | 8314篇 |
化学工业 | 26078篇 |
金属工艺 | 11722篇 |
机械仪表 | 8608篇 |
建筑科学 | 4783篇 |
矿业工程 | 2220篇 |
能源动力 | 3833篇 |
轻工业 | 8853篇 |
水利工程 | 760篇 |
石油天然气 | 4742篇 |
武器工业 | 2143篇 |
无线电 | 12862篇 |
一般工业技术 | 14525篇 |
冶金工业 | 5702篇 |
原子能技术 | 1457篇 |
自动化技术 | 16567篇 |
出版年
2024年 | 292篇 |
2023年 | 1639篇 |
2022年 | 2374篇 |
2021年 | 3462篇 |
2020年 | 3092篇 |
2019年 | 3002篇 |
2018年 | 2823篇 |
2017年 | 3681篇 |
2016年 | 3915篇 |
2015年 | 4062篇 |
2014年 | 5793篇 |
2013年 | 6736篇 |
2012年 | 7210篇 |
2011年 | 8554篇 |
2010年 | 7065篇 |
2009年 | 7901篇 |
2008年 | 7453篇 |
2007年 | 8647篇 |
2006年 | 8338篇 |
2005年 | 6930篇 |
2004年 | 6084篇 |
2003年 | 5714篇 |
2002年 | 4870篇 |
2001年 | 3979篇 |
2000年 | 3493篇 |
1999年 | 2794篇 |
1998年 | 2115篇 |
1997年 | 1699篇 |
1996年 | 1499篇 |
1995年 | 1397篇 |
1994年 | 1223篇 |
1993年 | 1027篇 |
1992年 | 789篇 |
1991年 | 453篇 |
1990年 | 326篇 |
1989年 | 292篇 |
1988年 | 188篇 |
1987年 | 126篇 |
1986年 | 120篇 |
1985年 | 87篇 |
1984年 | 73篇 |
1983年 | 50篇 |
1982年 | 56篇 |
1981年 | 66篇 |
1980年 | 34篇 |
1979年 | 23篇 |
1978年 | 23篇 |
1977年 | 21篇 |
1976年 | 26篇 |
1975年 | 18篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
E. A. Fitzgerald Y. -H. Xie D. Brasen M. L. Green J. Michel P. E. Freeland B. E. Weir 《Journal of Electronic Materials》1990,19(9):949-955
We have grown Ge x Si1-x (0 <x < 0.20,1000–3000Å thick) on small growth areas etched in the Si substrate. Layers were grown using both molecular beam epitaxy (MBE) at 550° C and rapid thermal chemical vapor deposition (RTCVD) at 900° C. Electron beam induced current images (EBIC) (as well as defect etches and transmission electron microscopy) show that 2800Å-thick, MBE Ge0.19Si0.81 on 70-μm-wide mesas have zerothreading and nearly zero misfit dislocations. The Ge0.19Si{0.81} grown on unpatterned, large areas is heavily dislocated. It is also evident from the images that heterogeneous nucleation of misfit dislocations is dominant in this composition range. 1000Å-thick, RTCVD Ge0.14Si0.86 films deposited on 70 μm-wide mesas are also nearly dislocation-free as shown by EBIC, whereas unpatterned areas are more heavily dislocated. Thus, despite the high growth temperatures, only heterogeneous nucleation of misfit dislocations occurs and patterning is still effective. Photoluminescence spectra from arrays of GeSi on Si mesas show that even when the interface dislocation density on the mesas is high, growth on small areas results in a lower dislocation density than growth on large areas. 相似文献
952.
In this investigation we consider the formation of Cooper pairs near the oxygen-deficient sites in Y-Ba-Cu-O ceramic superconductors which would give rise to an energy-dependent potential as seen by conduction charge carriers. It is shown that Cooper pairs could be formed under such conditions, resulting in a supercurrent. We use the Bogoliubov transformation technique to calculate the energy gap, the energy difference, and the transition temperature of the model superconductor using certain data obtained from previous experiments. Numerical analysis shows that the superconducting current can be explained by the presence of such oscillating Cooper pairs. 相似文献
953.
An opportunity arose in 1985 to become involved in a transition of working practice from hard copy to VDT. Over a two-year period, 161 VDT users and 65 control subjects in the same office environment were regularly and routinely examined for symptoms of asthenopia. The analysis of data shows that there are no significant differences in type, number and frequency of the work-related symptoms between VDT users and non-VDT users. It appears that reporting of symptoms within the group may be random, although certain symptoms do appear more frequently than others. Additionally, it appears that there is a significant difference between male and female users in the frequency of symptom reporting. 相似文献
954.
Process monitoring in additive manufacturing may allow components to be certified cheaply and rapidly and opens the possibility of healing defects, if detected. Here, neural networks (NNs) and convolutional neural networks (CNNs) are trained to detect flaws in layerwise images of a build, using labeled XCT data as a ground truth. Multiple images were recorded after each layer before and after recoating with various lighting conditions. Classifying networks were given a single image or multiple images of various lighting conditions for training and testing. CNNs demonstrated significantly better performance than NNs across all tasks. Furthermore, CNNs demonstrated improved generalizability, i.e., the ability to generalize to more diverse data than either the training or validation data sets. Specifically, CNNs trained on high-resolution layerwise images from one build showed minimal loss in performance when applied to data from an independent build, whereas the performance of the NNs degraded significantly. CNN accuracy was also demonstrated to be a function of flaw size, suggesting that smaller flaws may be produced by mechanisms that do not alter the surface morphology of the build plate. CNNs demonstrated accuracies of 93.5 % on large (>200 μm) flaws when testing and training on components from the same build and accuracies of 87.3 % when testing on a previously unseen build. Finally, evidence linking the formation of large lack-of-fusion defects to the presence of process ejecta is presented. 相似文献
955.
956.
随着信息化浪潮的发展,SSL协议的应用非常普遍,但是在SSL协议应用的工程实践中也发现了一些应用模式所导致的问题,文章首先介绍了SSL协议的安全技术应用,重点分析了其中安全技术问题的表现,并通过国产密码算法与SSL协议之间应用兼容性的问题分析,提出了一些SSL协议应用模式的建议。 相似文献
957.
针对基于PLC的带式输送机控制系统存在体积大、PLC程序更改不方便、成本高等问题,提出了一种基于嵌入式技术的带式输送机控制系统的设计方案;详细介绍了该系统中嵌入式本质安全控制机、控制驱动器、远程I/O模块的硬件及软件设计。实际应用表明,该系统解决了基于PLC的带式输送机控制系统存在的问题,具有较好的稳定性、灵活性和友好性。 相似文献
958.
研究了嵌入式三轴运动控制系统的以太网通信问题;采用LM3S9B92微控制器设计主控制器和各轴电动机控制器,通过移植实时操作系统μC/OS-Ⅱ和TCP/IP协议栈LwIP,实现主控制器与各轴电机控制器之间的信息交互;按电动机控制数据传输紧急程度要求不同,在以太网MAC层之上建立调度表,优先传输紧急数据,提高三轴运动控制系统实时性;实验结果表明嵌入式三轴运动控制系统实现了以太网数据的无差错传输,并且在重载情况下时间延迟大约为系统改进前的72%,改进了系统的实时性。 相似文献
959.
介绍了利用NIOSⅡ软核处理器设计嵌入式测试系统的两类系统架构,详细讲述了基于NIOSⅡ软核处理器的嵌入式测试系统软硬件设计方法;最后结合EP2C8Q-208C8型FPGA芯片,利用Verilog语言描述A/D芯片的工作时序逻辑,利用NIOSⅡ软核处理器设计串口处理单元,将A/D采集的数据通过串口发送到计算机显示。实践表明,利用NIOS II软核处理器设计嵌入式测试系统,具有开发周期短,系统集成度高,功能灵活多样等特点,与传统利用单片机设计嵌入式测试系统相比,具有时钟频率高、运行速度快、调试方便等特点,是一种值得推广的嵌入式测试系统设计方法。 相似文献
960.