全文获取类型
收费全文 | 447255篇 |
免费 | 5267篇 |
国内免费 | 1848篇 |
专业分类
电工技术 | 8352篇 |
综合类 | 634篇 |
化学工业 | 62660篇 |
金属工艺 | 17358篇 |
机械仪表 | 12976篇 |
建筑科学 | 9844篇 |
矿业工程 | 2194篇 |
能源动力 | 10948篇 |
轻工业 | 34343篇 |
水利工程 | 4447篇 |
石油天然气 | 8068篇 |
武器工业 | 47篇 |
无线电 | 56465篇 |
一般工业技术 | 87535篇 |
冶金工业 | 92306篇 |
原子能技术 | 10354篇 |
自动化技术 | 35839篇 |
出版年
2021年 | 3174篇 |
2019年 | 3135篇 |
2018年 | 5322篇 |
2017年 | 5374篇 |
2016年 | 5649篇 |
2015年 | 3738篇 |
2014年 | 6498篇 |
2013年 | 18762篇 |
2012年 | 10675篇 |
2011年 | 14729篇 |
2010年 | 11637篇 |
2009年 | 13529篇 |
2008年 | 14142篇 |
2007年 | 14234篇 |
2006年 | 12519篇 |
2005年 | 11669篇 |
2004年 | 11669篇 |
2003年 | 11251篇 |
2002年 | 10866篇 |
2001年 | 11300篇 |
2000年 | 10613篇 |
1999年 | 11474篇 |
1998年 | 30341篇 |
1997年 | 20799篇 |
1996年 | 15997篇 |
1995年 | 11949篇 |
1994年 | 10450篇 |
1993年 | 10484篇 |
1992年 | 7312篇 |
1991年 | 7026篇 |
1990年 | 6849篇 |
1989年 | 6673篇 |
1988年 | 6140篇 |
1987年 | 5333篇 |
1986年 | 5385篇 |
1985年 | 6023篇 |
1984年 | 5416篇 |
1983年 | 4962篇 |
1982年 | 4643篇 |
1981年 | 4799篇 |
1980年 | 4575篇 |
1979年 | 4277篇 |
1978年 | 4272篇 |
1977年 | 4916篇 |
1976年 | 6545篇 |
1975年 | 3653篇 |
1974年 | 3526篇 |
1973年 | 3507篇 |
1972年 | 2977篇 |
1971年 | 2589篇 |
排序方式: 共有10000条查询结果,搜索用时 10 毫秒
101.
L. Gao P. Hrter Ch. Linsmeier J. Gstttner R. Emling D. Schmitt-Landsiedel 《Materials Science in Semiconductor Processing》2004,7(4-6):331
Deposition of Ag films by direct liquid injection-metal organic chemical vapor deposition (DLI-MOCVD) was chosen because this preparation method allows precise control of precursor flow and prevents early decomposition of the precursor as compared to the bubbler-delivery. Silver(I)-2,2-dimethyl-6,6,7,7,8,8,8-heptafluoro-3,5-octanedionato-triethylphosphine [Ag(fod)(PEt3)] as the precursor for Ag CVD was studied, which is liquid at 30 °C. Ag films were grown on different substrates of SiO2/Si and TiN/Si. Argon and nitrogen/hydrogen carrier gas was used in a cold wall reactor at a pressure of 50–500 Pa with deposition temperature ranging between 220 °C and 350 °C. Ag films deposited on a TiN/Si diffusion barrier layer have favorable properties over films deposited on SiO2/Si substrate. At lower temperature (220 °C), film growth is essentially reaction-limited on SiO2 substrate. Significant dependence of the surface morphology on the deposition conditions exists in our experiments. According to XPS analysis pure Ag films are deposited by DLI-MOCVD at 250 °C by using argon as carrier gas. 相似文献
102.
We propose a standardization procedure that provides a convenient, quantitative and reproducible laboratory-based method for measuring the state of polarization (SOP) fluctuations produced by polarization varying devices. This method is based on the SOP distributions generated by commercial polarization scramblers. We show that these devices generate distributions of the maximum change of the SOP (in a given sample time) that follow Rayleigh statistics, which scale linearly with scrambling frequency and the sample time. We use this procedure to measure the SOP fluctuations in a short length of coiled fiber subject to mechanical perturbations. 相似文献
103.
Korolev I. A. Alekseenko N. N. Porodnov B. T. Sapunov V. A. Savel'ev D. V. 《Measurement Techniques》2003,46(9):865-871
The design of a sylphon bellows sensor and the basic circuits of an LC-generator and of a microprocessor unit are presented. An analytical pressure–frequency conversion function and a special method of adjusting the sensor ensure an error of less than 0.05%. The dynamic range is up to 105. The instruments developed cover the ranges 103, 104, and 105 Pa. 相似文献
104.
Neil P. Soice Adrian C. Maladono Doreen Y. Takigawa Arlan D. Norman William B. Krantz Alan R. Greenberg 《应用聚合物科学杂志》2003,90(5):1173-1184
Selected aromatic amides were used to model the chemical reactivity of aromatic polyamides found in thin‐film composite reverse osmosis (RO) membranes. Chlorination and possible amide bond cleavage of aromatic amides upon exposure to aqueous chlorine, which can lead to membrane failure, were investigated. Correlations are made of the available chlorine concentration, pH, and exposure time with chemical changes in the model compounds. From the observed reactivity trends, insights are obtained into the mechanism of RO membrane performance loss upon chlorine exposure. Two chemical pathways for degradation are shown, one at constant pH and another that is pH‐history dependent. An alternative strategy is presented for the design of chlorine‐resistant RO membranes, and an initial performance study of RO membranes incorporating this strategy is reported. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1173–1184, 2003 相似文献
105.
Honour Index (HoI), a method to evaluate research performance within different research fields, was derived from the impact
factor (IF). It can be used to rate and compare different categories of journals. HoI was used in this study to determine
the scientific productivity of stem cell research in the Asian Four Dragons (Hong Kong, Singapore, South Korea and Taiwan)
from 1981 to 2001. The methodology applied in this study represents a synthesis of universal indicator studies and bibliometric
analyses of subfields at the micro-level. We discuss several comparisons, and conclude the developmental trend in stem cell
research for two decades.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
106.
107.
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
108.
B. Pantchev P. Danesh K. Antonova B. Schmidt D. Grambole J. Baran 《Journal of Materials Science: Materials in Electronics》2003,14(10-12):751-752
The hydrogen content, its depth distribution, and its bonding configuration have been studied in hydrogenated amorphous silicon prepared by plasma-enhanced chemical vapor deposition with hydrogen-diluted silane. Nuclear reaction analysis and infrared spectroscopy were used to determine the total amount of hydrogen and its bonded component, respectively. It has been established that the total concentration of hydrogen does not depend on the film thickness, and has a uniform depth profile. The concentration of bonded hydrogen changes with the film thickness within the measurement accuracy. The data obtained suggest the presence of molecular (non-bonded) hydrogen, uniformly distributed in concentration across the film thickness. 相似文献
109.
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
110.
A common computing-core representation of the discrete cosine transform and discrete sine transform is derived and a reduced-complexity algorithm is developed for computation of the proposed computing-core. A parallel architecture based on the principle of distributed arithmetic is designed further for the computation of these transforms using the common-core algorithm. The proposed scheme not only leads to a systolic-like regular and modular hardware for computing these transforms, but also offers significant improvement in area-time efficiency over the existing structures. The structure proposed here is devoid of complicated input/output mapping and does not involve any complex control. Unlike the convolution-based structures, it does not restrict the transform length to be a prime or multiple of prime and can be utilized as a reusable core for cost-effective, memory-efficient, high-throughput implementation of either of these transforms 相似文献