全文获取类型
收费全文 | 196409篇 |
免费 | 18980篇 |
国内免费 | 10512篇 |
专业分类
电工技术 | 17106篇 |
技术理论 | 9篇 |
综合类 | 20248篇 |
化学工业 | 17800篇 |
金属工艺 | 7529篇 |
机械仪表 | 17550篇 |
建筑科学 | 20446篇 |
矿业工程 | 7105篇 |
能源动力 | 7971篇 |
轻工业 | 13705篇 |
水利工程 | 7572篇 |
石油天然气 | 8754篇 |
武器工业 | 2560篇 |
无线电 | 18173篇 |
一般工业技术 | 18326篇 |
冶金工业 | 7304篇 |
原子能技术 | 2688篇 |
自动化技术 | 31055篇 |
出版年
2024年 | 826篇 |
2023年 | 2424篇 |
2022年 | 4841篇 |
2021年 | 5649篇 |
2020年 | 5974篇 |
2019年 | 4922篇 |
2018年 | 4889篇 |
2017年 | 6136篇 |
2016年 | 7323篇 |
2015年 | 7884篇 |
2014年 | 12664篇 |
2013年 | 12505篇 |
2012年 | 14757篇 |
2011年 | 16112篇 |
2010年 | 11633篇 |
2009年 | 11735篇 |
2008年 | 11208篇 |
2007年 | 13543篇 |
2006年 | 11706篇 |
2005年 | 9868篇 |
2004年 | 8278篇 |
2003年 | 7008篇 |
2002年 | 5622篇 |
2001年 | 4660篇 |
2000年 | 3965篇 |
1999年 | 3289篇 |
1998年 | 2781篇 |
1997年 | 2359篇 |
1996年 | 1920篇 |
1995年 | 1586篇 |
1994年 | 1426篇 |
1993年 | 1082篇 |
1992年 | 955篇 |
1991年 | 706篇 |
1990年 | 590篇 |
1989年 | 505篇 |
1988年 | 422篇 |
1987年 | 286篇 |
1986年 | 242篇 |
1985年 | 228篇 |
1984年 | 258篇 |
1983年 | 249篇 |
1982年 | 203篇 |
1981年 | 103篇 |
1980年 | 100篇 |
1979年 | 68篇 |
1978年 | 54篇 |
1977年 | 48篇 |
1976年 | 43篇 |
1959年 | 34篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
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
32.
试论循环水装置的经济性及其成本分析 总被引:2,自引:1,他引:1
通过对循环水装置的投资和成本分析,阐述了建设该装置的经济性和社会意义。 相似文献
33.
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
34.
J. B. Quinn G. E. Schumacher L. W. Schultheis 《Journal of Failure Analysis and Prevention》2004,4(1):41-46
Several days after heart surgery, a patient discovered his upper right canine tooth had broken at the root. Such tooth damage,
recognized post-operatively, is usually assumed to be caused by blunt mechanical force from an instrument used by the anesthesiologist
during placement of a breathing tube at the start of surgery.
In this case, the patient had saved the crown portion of the broken tooth, and it was possible to examine the root fracture
characteristics. The curvature and direction of the crack path and natural tooth situation suggested that failure could be
described through a cantilever beam model. This was confirmed when a whole extracted sample tooth was embedded and broken
by a measured force in a manner consistent with the model. The resulting fracture surface matched that of the patient’s broken
canine tooth. However, the high load and force direction necessary to fracture the root was inconsistent with forces applied
during the anesthesia procedure. The failure analysis and further investigation indicated tooth clenching on the breathing
tube during recovery was the likely cause of fracture.
This paper presents an alternate explanation for intubation-related dental injury, demonstrates the practicality of fractographic
analysis of biological materials, and introduces a methodology for simulating in vitro tooth settings for mechanical testing. 相似文献
35.
基于直升机目标旋转部件的调制模型,本文针对防空雷达提出了分析直升机信号特征的一种新方法——WVD法,并对直升机目标旋转部件调制回波信号在不同噪声情况下加以仿真分析,结果表明:用WVD分析雷达回波中直升机信号特征是一种非常有效的方法。 相似文献
36.
硅微机械梳齿静电谐振器的建模与分析 总被引:5,自引:2,他引:3
基于参数化的计算机辅助设计(CAD)软件,对硅微机械梳齿静电谐振器进行了实体建模,以有限元分析软件为工具,进行了谐振器的模态分析,静态分析和谐响应分析,初步揭示了谐振器的静、动态特性,有助于改善设计效率和质量,展示了计算机辅助工程(CAE)技术在微机电系统(MEMS)研究中的重要作用。 相似文献
37.
Ying Tan 《The Journal of VLSI Signal Processing》2002,32(1-2):45-54
In this paper, we propose a new approach for signal detection in wireless digital communications based on the neural network with transient chaos and time-varying gain (NNTCTG), and give a concrete model of the signal detector after appropriate transformations and mappings. It is well known that the problem of the maximum likelihood signal detection can be described as a complex optimization problem that has so many local optima that conventional Hopfield-type neural networks fail to solve. By refraining from the serious local optima problem of Hopfield-type neural networks, the NNTCTG makes use of the time-varying parameters of the recurrent neural network to control the evolving behavior of the network so that the network undergoes the transition from chaotic behavior to gradient convergence. It has richer and more flexible dynamics rather than conventional neural networks only with point attractors, so that it can be expected to have much ability to search for globally optimal or near-optimal solutions. After going through a transiently inverse-bifurcation process, the NNTCTG can approach the global optimum or the neighborhood of global optimum of our problem. Simulation experiments have been performed to show the effectiveness and validation of the proposed neural network based method for the signal detection in digital communications. 相似文献
38.
39.
40.
一种基于三次样条函数求离子浓度的自动算法 总被引:1,自引:0,他引:1
本文提出了一种用三次样条函数模拟双次标准加入法测量方程,直接求解离子浓度的自动算法。比较了三咱不同边界条件下用要池数计算离子浓度的结果。造出节点区间两极端点的二阶导数为零时的三次样条函数为最佳模拟函数。并讨论了该方法在实际分析中误差的来源及消除办法。经对一系列文献数据的验算对比,表明本法完全可代替传统的迭代法和查图法,且能方便地设置在智能化的电位分析系统中。 相似文献