全文获取类型
收费全文 | 45289篇 |
免费 | 4441篇 |
国内免费 | 2158篇 |
专业分类
电工技术 | 11664篇 |
技术理论 | 1篇 |
综合类 | 3771篇 |
化学工业 | 889篇 |
金属工艺 | 751篇 |
机械仪表 | 3914篇 |
建筑科学 | 1166篇 |
矿业工程 | 1001篇 |
能源动力 | 1094篇 |
轻工业 | 412篇 |
水利工程 | 509篇 |
石油天然气 | 784篇 |
武器工业 | 404篇 |
无线电 | 11707篇 |
一般工业技术 | 2053篇 |
冶金工业 | 398篇 |
原子能技术 | 213篇 |
自动化技术 | 11157篇 |
出版年
2025年 | 284篇 |
2024年 | 895篇 |
2023年 | 855篇 |
2022年 | 1076篇 |
2021年 | 1285篇 |
2020年 | 1537篇 |
2019年 | 1209篇 |
2018年 | 1141篇 |
2017年 | 1566篇 |
2016年 | 1873篇 |
2015年 | 2311篇 |
2014年 | 3546篇 |
2013年 | 3025篇 |
2012年 | 4324篇 |
2011年 | 4126篇 |
2010年 | 3037篇 |
2009年 | 2843篇 |
2008年 | 2806篇 |
2007年 | 2908篇 |
2006年 | 2356篇 |
2005年 | 1841篇 |
2004年 | 1458篇 |
2003年 | 1153篇 |
2002年 | 843篇 |
2001年 | 776篇 |
2000年 | 564篇 |
1999年 | 455篇 |
1998年 | 342篇 |
1997年 | 294篇 |
1996年 | 260篇 |
1995年 | 190篇 |
1994年 | 159篇 |
1993年 | 116篇 |
1992年 | 88篇 |
1991年 | 60篇 |
1990年 | 62篇 |
1989年 | 63篇 |
1988年 | 31篇 |
1987年 | 19篇 |
1986年 | 13篇 |
1985年 | 15篇 |
1984年 | 22篇 |
1983年 | 14篇 |
1982年 | 20篇 |
1981年 | 4篇 |
1980年 | 4篇 |
1979年 | 5篇 |
1978年 | 4篇 |
1976年 | 3篇 |
1975年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
J. Gegner 《Materialwissenschaft und Werkstofftechnik》2003,34(3):290-297
Chemical Composition and Microstructure of Polymer‐Derived Glasses and Ceramics in the Si–C–O System. Part 2: Characterization of microstructure formation by means of high‐resolution transmission electron microscopy and selected area diffraction Liquid or solid silicone resins represent the economically most interesting class of organic precursors for the pyrolytic production of glass and ceramics materials on silicon basis. As dense, dimensionally stable components can be cost‐effectively achieved by admixing reactive filler powders, chemical composition and microstructure development of the polymer‐derived residues must be exactly known during thermal decomposition. Thus, in the present work, glasses and ceramics produced by pyrolysis of the model precursor polymethylsiloxane at temperatures from 525 to 1550 °C are investigated. In part 1, by means of analytical electron microscopy, the bonding state of silicon was determined on a nanometre scale and the phase separation of the metastable Si–C–O matrix into SiO2, C and SiC was proved. The in‐situ crystallization could be considerably accelerated by adding fine‐grained powder of inert fillers, such as Al2O3 or SiC, which permits effective process control. In part 2, the microstructure is characterized by high‐resolution transmission electron microscopy and selected area diffraction. Turbostratic carbon and cubic β‐SiC precipitate as crystallization products. Theses phases are embedded in an amorphous matrix. Inert fillers reduce the crystallization temperature by several hundred °C. In this case, the polymer‐derived Si–C–O material acts as a binding agent between the powder particles. Reaction layer formation does not occur. On the investigated pyrolysis conditions, no crystallization of SiO2 was observed. 相似文献
2.
Sanghoon Lee Chris Podilchuk Vidhya Krishnan Alan C. Bovik 《The Journal of VLSI Signal Processing》2003,34(1-2):149-166
By exploiting new human-machine interface techniques, such as visual eyetrackers, it should be possible to develop more efficient visual multimedia services associated with low bandwidth, dynamic channel adaptation and robust visual data transmission. In this paper, we introduce foveation-based error resilience and unequal error protection techniques over highly error-prone mobile networks. Each frame is spatially divided into foveated and background layers according to perceptual importance. Perceptual importance is determined either through an eye tracker or by manually selecting a region of interest. We attempt to improve reconstructed visual quality by maintaining the high visual source throughput of the foveated layer using foveation-based error resilience and error correction using a combination of turbo codes and ARQ (automatic reQuest). In order to alleviate the degradation of visual quality, a foveation based bitstream partitioning is developed. In an effort to increase the source throughput of the foveated layer, we develop unequal delay-constrained ARQ (automatic reQuest) and rate compatible punctured turbo codes where the punctual pattern of RCPC (rate compatible punctured convolutional) codes in H.223 Annex C is used. In the simulation, the visual quality is significantly increased in the area of interest using foveation-based error resilience and unequal error protection; (as much as 3 dB FPSNR (foveal peak signal to noise ratio) improvement) at 40% packet error rate. Over real-fading statistics measured in the downtown area of Austin, Texas, the visual quality is increased up to 1.5 dB in PSNR and 1.8 dB in FPSNR at a channel SNR of 5 dB. 相似文献
3.
文中严格地讨论了任意截面形状,任意模式的柱形谐振腔Q值与构成该谐振器的传输线衰减常数间的关系,给出了更一般的公式,推广了Davidson和Sim-monds^[1]、Barlow和Cullen^[2]以及Yeh和Shimabukuro^[3,4]的结果。 相似文献
4.
P. T. Tsilingiris 《国际能源研究杂志》1991,15(9):723-730
The paper describes the calculation of the beam solar radiation transmission across the uniform salinity upper convecting zone (UCZ) and the salinity stratified gradient zone (GZ), when the extinction coefficient is not only wavelength but also salinity-concentration dependent, assuming that the effect of scattering to be negligible. The results are useful in determining the effects of dissolved salt ions on pure water transmission, at least according to the existing measured data in the literature. 相似文献
5.
TAN Zuo-wen 《通讯和计算机》2007,4(5):40-46
Signcryption is a public key or asymmetric cryptographic method that provides simultaneously both message confidentiality and integrity at a lower computational and communication cost. This paper presents a (t, n) threshold proxy signcryption scheme in which no less than t proxy agents in the proxy group can produce the signcryption cryptogram. combines the functionality of threshold proxy signing and encryption. The proposed scheme combines the functionality of both threshold proxy signing and encryption, and provides fair protection for the sender and the proxy agents. This scheme is secure against attack of public key substitution. It also satisfies security properties such as confidentiality and authenticity. 相似文献
6.
7.
8.
9.
忽翔 《安徽电气工程职业技术学院学报》2014,(3):18-23
架空输电线路项目扩容改造,当采用倍容导线时,需在技术和经济上对倍容导线进行比较分析。文章对这种导线的种类、特性情况作了介绍,通过在220kV线路上对倍容导线的选择分析,为同类案例的处理提供了借鉴和参考。 相似文献
10.
白日昕 《计算机光盘软件与应用》2011,(13)
随着电子通信技术的发展,分布式测控系统也应运而生,并且规模在逐渐的扩大。在大的发展趋势前提下,监测数据在远距离传输的时候,如何保证其高效、安全、可靠地传输,已经成为计算机产业热议的话题。嵌入式以太网的实现为数据传输系统的设计创造了有利条件。 相似文献