全文获取类型
收费全文 | 294455篇 |
免费 | 23307篇 |
国内免费 | 11580篇 |
专业分类
电工技术 | 16458篇 |
技术理论 | 20篇 |
综合类 | 17050篇 |
化学工业 | 50240篇 |
金属工艺 | 16010篇 |
机械仪表 | 18356篇 |
建筑科学 | 23895篇 |
矿业工程 | 8170篇 |
能源动力 | 8452篇 |
轻工业 | 18173篇 |
水利工程 | 4749篇 |
石油天然气 | 17680篇 |
武器工业 | 2086篇 |
无线电 | 34925篇 |
一般工业技术 | 36581篇 |
冶金工业 | 15372篇 |
原子能技术 | 3001篇 |
自动化技术 | 38124篇 |
出版年
2024年 | 1239篇 |
2023年 | 4658篇 |
2022年 | 8426篇 |
2021年 | 11449篇 |
2020年 | 8611篇 |
2019年 | 7227篇 |
2018年 | 7892篇 |
2017年 | 8999篇 |
2016年 | 8289篇 |
2015年 | 10913篇 |
2014年 | 13869篇 |
2013年 | 17572篇 |
2012年 | 17832篇 |
2011年 | 19959篇 |
2010年 | 16885篇 |
2009年 | 16442篇 |
2008年 | 15797篇 |
2007年 | 15132篇 |
2006年 | 15850篇 |
2005年 | 14005篇 |
2004年 | 9327篇 |
2003年 | 8435篇 |
2002年 | 7792篇 |
2001年 | 7038篇 |
2000年 | 7063篇 |
1999年 | 8083篇 |
1998年 | 7239篇 |
1997年 | 5972篇 |
1996年 | 5537篇 |
1995年 | 4612篇 |
1994年 | 3837篇 |
1993年 | 2872篇 |
1992年 | 2305篇 |
1991年 | 1689篇 |
1990年 | 1344篇 |
1989年 | 1161篇 |
1988年 | 885篇 |
1987年 | 636篇 |
1986年 | 501篇 |
1985年 | 395篇 |
1984年 | 260篇 |
1983年 | 239篇 |
1982年 | 199篇 |
1981年 | 172篇 |
1980年 | 153篇 |
1979年 | 112篇 |
1978年 | 64篇 |
1977年 | 63篇 |
1976年 | 77篇 |
1975年 | 38篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
浅谈火灾调查的边缘化趋势 总被引:1,自引:0,他引:1
从火灾调查实际工作状态出发,提出火灾调查存在地位边缘化的趋势,并在分析边缘化趋势原因的基础上提出了相应的对策,供火灾调查同仁探讨。 相似文献
992.
A Subcarriers Allocation Scheme for Cognitive Radio Systems Based on Multi-Carrier Modulation 总被引:1,自引:0,他引:1
Tao Luo Tao Jiang Weidong Xiang Hsiao-Hwa Chen 《Wireless Communications, IEEE Transactions on》2008,7(9):3335-3340
Cognitive radio (CR) is a dynamic spectrum access technology as a solution to spectrum under-utilization problem in some licensed bands. Operating over an exceedingly wide spectrum, CR systems usually adopt multi-carrier modulation (MCM) to implement flexible channelization. Consequently, efficient channel allocation scheme becomes extremely important to an MCM based CR (MCM-CR) system. In this paper, a maximum likelihood detection model is developed to detect the presence and locations of licensed users (LUs) signals in the frequency domain. Performance of the detection model, including the optimal detection region, detection probability and false alarm probability, is analyzed. A one-order two-state Markovian chain model is proposed to predict channel status information. In particular, a novel subcarrier allocation scheme for MCM-CR systems is proposed, taking into account the confidence of channel estimation, quality of services (QoS) of rental users (RUs) and throughput. To validate the analytical results, simulations have been conducted to show effectiveness of the proposed scheme. 相似文献
993.
Ultrasound backscattered signals for object detection could be too weak to be perceived when superposed to strong reflection signals, and could also be complicated either in time or frequency domain. These peculiarities raise a challenge for signal processing methods. In this paper four signal processing methods were studied to detect objects in containers. Root mean squares (RMS) method was better in object detection but needed to combine other methods to increase detection success rate. Variance, center frequency pressure ratio (CFPR) and backscattered amplitude integral (BAI) methods have similar overall detection ratings. The optimal signal size, to increase the detection ability, corresponded approximately to the length of reverberation signals before it was dissipated. 相似文献
994.
重构在框架开发中的研究与应用 总被引:2,自引:0,他引:2
框架和应用能够通过重构相互促进,应用和框架的并行开发可以加速框架的开发过程.从框架与应用的中间层,框架与应用的接口的结构和形式等方面,对此过程中的重构方法进行了讨论,提出了几种适应于框架与应用并行开发的重构手段. 相似文献
995.
The Y2O3: Yb3 , Er3 microstructures were fabricated by a hydrothermal method without surfactants.The microstructures structure was characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM,KYKY 1000B).The up-conversion luminescence spectra were studied under 978 nm laser diode excitation.In Yb3 and Er3 codoped Y2 O3 microcrystals, the relative intensity of green emission became stronger as the morphology of sample changed from wires to films. 相似文献
996.
997.
Gregory S. Ho Chen Huang Emily A. Carter 《Current Opinion in Solid State & Materials Science》2007,11(5-6):57-61
Orbital-free density functional theory (OF-DFT) can be made to scale linearly with sample size, allowing thousands of atoms to be treated explicitly with quantum mechanics. State-of-the-art kinetic energy density functionals and ion–electron pseudopotentials are used to obtain accurate structural property predictions for nanoparticles, nanowires, extended surfaces, and nanoindentation of simple metals. 相似文献
998.
活性污泥数学模型入流组分测定及应用 总被引:2,自引:0,他引:2
阐述了活性污泥1号模型人流组分的分析方法,并用这些方法测定了西安市城市污水水质。实验结果表明测定方法操作简单、准确可靠,能为利用模型进行污水处理厂的设计、模拟及管理提供入流组分分析依据, 相似文献
999.
Squeeze-film effects of perforated plates for small amplitude vibration are analyzed through modified Reynolds equation (MRE).
The analytical analysis reckons in most important influential factors: compressibility of the air, border effects, and the
resistance caused by vertical air flow passing through perforated holes. It is found that consideration of air compressibility
is necessary for high operating frequency and small ratio of the plate width to the attenuation length. The analytical results
presented in this paper agree with ANSYS simulation results better than that under the air incompressibility assumption. The
analytical analysis can be used to estimate the squeeze-film effects causing damping and stiffness added to the system. Since
the value of Reynolds number involved in this paper is low (< 1), inertial effects are neglected. 相似文献
1000.
Optical Splitting Trees for High-Precision Monocular Imaging 总被引:1,自引:0,他引:1
McGuire M. Matusik W. Pfister H. Chen B. Hughes J.F. Nayar S.K. 《Computer Graphics and Applications, IEEE》2007,27(2):32-42
In this article, we consider the design of monocular multiview optical systems that form optical splitting trees, where the optical path topology takes the shape of a tree because of recursive beam splitting. Designing optical splitting trees is challenging when it requires many views with specific spectral properties. We introduce a manual design paradigm for optical splitting trees and a computer-assisted design tool to create efficient splitting-tree cameras. The tool accepts as input a specification for each view and a set of weights describing the user's relative affinity for efficiency, measurement accuracy, and economy. An optimizer then searches for a design that maximizes these weighted priorities. Our tool's output is a splitting-tree design that implements the input specification and an analysis of the efficiency of each root-to-leaf path. Automatically designed trees appear comparable to those designed by hand; we even show some cases where they are superior. With the help of the optimizer, the system demonstrates high dynamic range, focusing, matting, and hybrid imaging implemented on a single, reconfigurable camera containing eight sensors 相似文献