全文获取类型
收费全文 | 551920篇 |
免费 | 6381篇 |
国内免费 | 1680篇 |
专业分类
电工技术 | 10164篇 |
综合类 | 2988篇 |
化学工业 | 78988篇 |
金属工艺 | 21043篇 |
机械仪表 | 16120篇 |
建筑科学 | 13298篇 |
矿业工程 | 2085篇 |
能源动力 | 13433篇 |
轻工业 | 45178篇 |
水利工程 | 5122篇 |
石油天然气 | 6445篇 |
武器工业 | 15篇 |
无线电 | 70544篇 |
一般工业技术 | 103799篇 |
冶金工业 | 98720篇 |
原子能技术 | 8467篇 |
自动化技术 | 63572篇 |
出版年
2021年 | 3268篇 |
2019年 | 3184篇 |
2018年 | 19071篇 |
2017年 | 17904篇 |
2016年 | 14871篇 |
2015年 | 4375篇 |
2014年 | 6739篇 |
2013年 | 21008篇 |
2012年 | 13886篇 |
2011年 | 23996篇 |
2010年 | 19790篇 |
2009年 | 19073篇 |
2008年 | 20991篇 |
2007年 | 21801篇 |
2006年 | 13176篇 |
2005年 | 13294篇 |
2004年 | 13022篇 |
2003年 | 12754篇 |
2002年 | 11807篇 |
2001年 | 11902篇 |
2000年 | 11329篇 |
1999年 | 12043篇 |
1998年 | 31095篇 |
1997年 | 21618篇 |
1996年 | 16854篇 |
1995年 | 12751篇 |
1994年 | 11404篇 |
1993年 | 11138篇 |
1992年 | 8045篇 |
1991年 | 7760篇 |
1990年 | 7534篇 |
1989年 | 7288篇 |
1988年 | 6964篇 |
1987年 | 5753篇 |
1986年 | 5948篇 |
1985年 | 6880篇 |
1984年 | 6169篇 |
1983年 | 5692篇 |
1982年 | 5171篇 |
1981年 | 5492篇 |
1980年 | 4941篇 |
1979年 | 4773篇 |
1978年 | 4596篇 |
1977年 | 5499篇 |
1976年 | 7200篇 |
1975年 | 3950篇 |
1974年 | 3795篇 |
1973年 | 3760篇 |
1972年 | 3141篇 |
1971年 | 2764篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
22.
Barbara M. Johnston Peter R. Johnston 《International journal for numerical methods in engineering》2003,56(4):589-607
Accurate numerical evaluation of integrals arising in the boundary element method is fundamental to achieving useful results via this solution technique. In this paper, a number of techniques are considered to evaluate the weakly singular integrals which arise in the solution of Laplace's equation in three dimensions and Poisson's equation in two dimensions. Both are two‐dimensional weakly singular integrals and are evaluated using (in a product fashion) methods which have recently been used for evaluating one‐dimensional weakly singular integrals arising in the boundary element method. The methods used are based on various polynomial transformations of conventional Gaussian quadrature points where the transformation polynomial has zero Jacobian at the singular point. Methods which split the region of integration into sub‐regions are considered as well as non‐splitting methods. In particular, the newly introduced and highly accurate generalized composite subtraction of singularity and non‐linear transformation approach (GSSNT) is applied to various two‐dimensional weakly singular integrals. A study of the different methods reveals complex relationships between transformation orders, position of the singular point, integration kernel and basis function. It is concluded that the GSSNT method gives the best overall results for the two‐dimensional weakly singular integrals studied. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
23.
Chloride doped polyaniline conducting polymer films have been prepared in a protic acid medium (HCl) by potentiodynamic method
in an electrochemical cell and studied by cyclic voltammetry and FTIR techniques. The FTIR spectra confirmed Cl- ion doping in the polymers. The polymerization rate was found to increase with increasing concentration of aniline monomer.
But the films obtained at high monomer concentration were rough having a nonuniform flaky polyaniline distribution. Results
showed that the polymerization rate did not increase beyond a critical HCl concentration. Cyclic voltammetry suggested that,
the oxidation-reduction current increased with an increase in scan rate and that the undoped polyaniline films were not hygroscopic
whereas chloride doped polyaniline films were found to be highly hygroscopic. 相似文献
24.
Tanabe A. Nakahara Y. Furukawa A. Mogami T. 《Solid-State Circuits, IEEE Journal of》2003,38(1):107-113
A redundant multivalued logic is proposed for high-speed communication ICs. In this logic, serial binary data are received and converted into parallel redundant multivalued data. Then they are restored into parallel binary data. Because of the multivalued data conversion, this logic makes it possible to achieve higher operating speeds than that of a conventional binary logic. Using this logic, a 1:4 demultiplexer (DEMUX, serial-parallel converter) IC was fabricated using a 0.18-/spl mu/m CMOS process. The IC achieved an operating speed of 10 Gb/s with a supply voltage of only 1.3 V and with power consumption of 38 mW. This logic may achieve CMOS communication ICs with an operating speed several times greater than 10 Gb/s. 相似文献
25.
Hook T.B. Brown J. Cottrell P. Adler E. Hoyniak D. Johnson J. Mann R. 《Electron Devices, IEEE Transactions on》2003,50(9):1946-1951
Lateral scattering of retrograde well implants is shown to have an effect on the threshold voltage of nearby devices. The threshold voltage of both NMOSFETs and PMOSFETs increases in magnitude for conventional retrograde wells, but for triple-well isolated NMOSFETs the threshold voltage decreases for narrow devices near the edge of the well. Electrical data, SIMS, and SUPREM4 simulations are shown that elucidate the phenomenon. 相似文献
26.
Reducing CIC filter complexity 总被引:1,自引:0,他引:1
This paper provides several tricks to reduce the complexity and enhance the usefulness of cascaded integrator-comb (CIC) filters. The first trick shows a way to reduce the number of adders and delay elements in a multi-stage CIC interpolation filter. The result is a multiplierless scheme that performs high-order linear interpolation using CIC filters. The second trick shows a way to eliminate the integrators from CIC decimation filters. The benefit is the elimination of unpleasant data word growth problems. 相似文献
27.
W. Shieh R. Hui X. Yi 《Photonics Technology Letters, IEEE》2006,18(10):1122-1124
We perform a systematic measurement of the degree-of-polarization (DOP) and eye-closure penalty for optical signals with orthogonal polarizations. We find that the symmetry of DOP is maintained for the orthogonal polarizations under both first and higher order polarization-mode dispersion (PMD), whereas the symmetry of eye-closure penalty is broken under second-order PMD. An orthogonal polarization pair can have large disparity of eye-closure penalty despite an identical DOP. We also demonstrate a novel approach to estimate the maximum eye-closure penalty asymmetry with three orthogonal polarizations on the Poincare/spl acute/ sphere. 相似文献
28.
Piedade M. Sousa L. A. de Almeida T. M. Germano J. da Costa B. A. Lemos J. M. Freitas P. P. Ferreira H. A. Cardoso F. A. 《IEEE transactions on circuits and systems. I, Regular papers》2006,53(11):2384-2395
This paper presents a hand-held microsystem based on new fully integrated magnetoresistive biochips for biomolecular recognition (DNA hybridization, antibody antigen interaction, etc.). Magnetoresistive chip surfaces are chemically treated, enabling the immobilization of probe biomolecules such as DNA or antibodies. Fluid handling is also integrated in the biochip. The proposed microsystem not only integrates the biochip, which is an array of 16times16 magnetoresistive sensors, but it also provides all the electronic circuitry for addressing and reading out each transducer. The proposed architecture and circuits were specifically designed for achieving a compact, programmable and portable microsystem. The microsystem also integrates a hand-held analyzer connected through a wireless channel. A prototype of the system was already developed and detection of magnetic nanoparticles was obtained. This indicates that the system may be used for magnetic label based bioassays 相似文献
29.
R. Urata R. Takahashi T. Nakahara K. Takahata H. Suzuki 《Photonics Technology Letters, IEEE》2006,18(1):67-69
We propose an optically clocked transistor array optoelectronic integrated circuit (OEIC) for both serial-to-parallel and parallel-to-serial conversion (demux/mux), enabling an interface between high-speed asynchronous burst optical labels and CMOS circuitry for optical label swapping. Dual functionality of the OEIC reduces size, power, and cost of the optical label swapper. The capability for greater than 20-Gb/s conversion operation is demonstrated. 相似文献
30.
The objective of this study was to compare methane production and characteristics of digested material in anaerobic digestion concepts according to the Animal By-Products Regulation (ABP-Regulation) of the EC (hygienisation of biowaste for 1 hour at 70 degrees C, particle size < 12 mm) and Finnish national regulations (treatment temperature 55 degrees C, feeding interval 24 h, hydraulic retention time (HRT) 20 d, particle size < 40 mm) and with small variations in treatment methods for treating manure and biowaste. Moreover, the survival of three different salmonella bacteria in these processes was studied. Hygienisation of biowaste prior to digestion at 35 degrees C enhanced methane production by 14-18% compared to similar treatment without hygienisation. The differences in treatment temperature, HRT and hygienisation of biowaste prior to digestion did not significantly affect the characteristics of digested material. The concepts according to the ABP-Regulation and Finnish national regulations were effective in destroying salmonella bacteria to an undetectable level. 相似文献