全文获取类型
收费全文 | 51443篇 |
免费 | 6128篇 |
国内免费 | 3092篇 |
专业分类
电工技术 | 12875篇 |
技术理论 | 1篇 |
综合类 | 5218篇 |
化学工业 | 1703篇 |
金属工艺 | 1174篇 |
机械仪表 | 4608篇 |
建筑科学 | 2049篇 |
矿业工程 | 1159篇 |
能源动力 | 963篇 |
轻工业 | 955篇 |
水利工程 | 806篇 |
石油天然气 | 1034篇 |
武器工业 | 606篇 |
无线电 | 12742篇 |
一般工业技术 | 3700篇 |
冶金工业 | 645篇 |
原子能技术 | 398篇 |
自动化技术 | 10027篇 |
出版年
2024年 | 240篇 |
2023年 | 693篇 |
2022年 | 1116篇 |
2021年 | 1427篇 |
2020年 | 1510篇 |
2019年 | 1126篇 |
2018年 | 1085篇 |
2017年 | 1491篇 |
2016年 | 1656篇 |
2015年 | 2120篇 |
2014年 | 3414篇 |
2013年 | 3042篇 |
2012年 | 4233篇 |
2011年 | 4483篇 |
2010年 | 3371篇 |
2009年 | 3472篇 |
2008年 | 3417篇 |
2007年 | 4034篇 |
2006年 | 3582篇 |
2005年 | 3081篇 |
2004年 | 2419篇 |
2003年 | 1981篇 |
2002年 | 1448篇 |
2001年 | 1300篇 |
2000年 | 994篇 |
1999年 | 780篇 |
1998年 | 547篇 |
1997年 | 467篇 |
1996年 | 403篇 |
1995年 | 370篇 |
1994年 | 299篇 |
1993年 | 214篇 |
1992年 | 153篇 |
1991年 | 119篇 |
1990年 | 114篇 |
1989年 | 113篇 |
1988年 | 69篇 |
1987年 | 41篇 |
1986年 | 35篇 |
1985年 | 34篇 |
1984年 | 43篇 |
1983年 | 27篇 |
1982年 | 35篇 |
1981年 | 13篇 |
1980年 | 13篇 |
1979年 | 13篇 |
1978年 | 7篇 |
1977年 | 4篇 |
1976年 | 3篇 |
1959年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Javier Ramírez Antonio García Uwe Meyer-Bäse Fred Taylor Antonio Lloris 《The Journal of VLSI Signal Processing》2003,33(1-2):171-190
Currently there are design barriers inhibiting the implementation of high-precision digital signal processing (DSP) objects with field programmable logic (FPL) devices. This paper explores overcoming these barriers by fusing together the popular distributed arithmetic (DA) method with the residue number system (RNS) for use in FPL-centric designs. The new design paradigm is studied in the context of a high-performance filter bank and a discrete wavelet transform (DWT). The proposed design paradigm is facilitated by a new RNS accumulator structure based on a carry save adder (CSA). The reported methodology also introduces a polyphase filter structure that results in a reduced look-up table (LUT) budget. The 2C-DA and RNS-DA are compared, in the context of a FPL implementation strategy, using a discrete wavelet transform (DWT) filter bank as a common design theme. The results show that the RNS-DA, compared to a traditional 2C-DA design, enjoys a performance advantage that increases with precision (wordlength). 相似文献
2.
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
3.
介绍一种基于快速平台测井要求的多通道核能谱测井仪设计方案。复杂可编程逻辑器件的应用使仪器功能增强,规模减小。该系统可对岩性密度长短源距脉冲信号、自然γ能谱脉冲信号进行多道脉冲幅度分析,并对补偿中子测井信号及井下多路常规模拟信号、脉冲信号进行数字化采集。数据传输采用曼彻斯特编码,传输方式可选择20kB/s半双工(兼容Atlas 3508)或下行20kB/s、上行41.66或93.75kB/s全双工方式(兼容Atlas WTS),适应挂接到不同测井系统的需要。 相似文献
4.
5.
根据某雷达系统对测量信号的快速传输要求,提出采用滑动帧的处理方法并在FPGA中实现,克服了传统帧处理难以满足快速传输要求的不足。阐述了滑动帧结构的构造思想,详述了滑动帧结构的特点及具体功能模块的实现。根据实际应用需求构造了滑动帧结构处理器,试验和应用结果表明设计可行有效,能充分满足实时数据传输的要求。 相似文献
6.
Hydroprocessing catalysts based on Ni, Co, Mo and W are used in various refinery processing applications where several deactivation mechanisms become of importance (coke formation, active phase sintering, metals deposition, poisoning) in the catalyst's life cycle. The life cycle of commercial hydroprocessing catalysts is very complex and includes the catalyst production, sulfidation, use, oxidative regeneration followed by re-sulfidation and reuse or, if reuse is not possible, recycling or disposal. To understand the changes in catalyst properties taking place during a life cycle, the catalyst quality in the different stages can be best monitored by using advanced analytical techniques. The catalyst's life cycle is further complicated by numerous technical, environmental and organizational issues involved. In principle, different companies can be involved in each of the life cycle steps. Leading catalyst manufacturers, together with specialized firms, offer refineries a total catalyst management concept, starting with the purchase of the fresh catalyst and ending with its final recycling or disposal. Total catalyst management includes a broad range of services, ensuring optimal timing during the change-out process, reliable, smooth and safe operations, minimal downtime and maximum catalyst and unit performance. 相似文献
7.
轻便型γ能谱测井仪几个关键技术问题的探讨 总被引:1,自引:0,他引:1
为研制性能好,功能强,微机化学程度高的轻便型γ能谱测井仪,针对非油气测井工作的井口径小(〈φ60mm)井身浅(〈1000m)等特点,探讨了γ能谱测井仪的轻便化,测量精度,信号传输技术,稳谱技术及微机化等关键技术问题。 相似文献
8.
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
9.
10.
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