全文获取类型
收费全文 | 431461篇 |
免费 | 3610篇 |
国内免费 | 821篇 |
专业分类
电工技术 | 6352篇 |
综合类 | 2507篇 |
化学工业 | 66666篇 |
金属工艺 | 24440篇 |
机械仪表 | 15876篇 |
建筑科学 | 8485篇 |
矿业工程 | 5045篇 |
能源动力 | 7245篇 |
轻工业 | 20675篇 |
水利工程 | 6911篇 |
石油天然气 | 16874篇 |
武器工业 | 31篇 |
无线电 | 39144篇 |
一般工业技术 | 98912篇 |
冶金工业 | 53871篇 |
原子能技术 | 13856篇 |
自动化技术 | 49002篇 |
出版年
2021年 | 3525篇 |
2019年 | 3470篇 |
2018年 | 20784篇 |
2017年 | 19931篇 |
2016年 | 17145篇 |
2015年 | 4472篇 |
2014年 | 7035篇 |
2013年 | 14438篇 |
2012年 | 12740篇 |
2011年 | 21278篇 |
2010年 | 17971篇 |
2009年 | 16405篇 |
2008年 | 17707篇 |
2007年 | 18368篇 |
2006年 | 9151篇 |
2005年 | 9195篇 |
2004年 | 8895篇 |
2003年 | 8719篇 |
2002年 | 7906篇 |
2001年 | 7367篇 |
2000年 | 7262篇 |
1999年 | 6605篇 |
1998年 | 13077篇 |
1997年 | 10009篇 |
1996年 | 7507篇 |
1995年 | 5918篇 |
1994年 | 5403篇 |
1993年 | 5599篇 |
1992年 | 4652篇 |
1991年 | 4757篇 |
1990年 | 4861篇 |
1989年 | 4672篇 |
1988年 | 4569篇 |
1987年 | 4433篇 |
1986年 | 4362篇 |
1985年 | 4563篇 |
1984年 | 4404篇 |
1983年 | 4292篇 |
1982年 | 4019篇 |
1981年 | 4210篇 |
1980年 | 4141篇 |
1979年 | 4424篇 |
1978年 | 4735篇 |
1977年 | 4798篇 |
1976年 | 5755篇 |
1975年 | 4338篇 |
1974年 | 4388篇 |
1973年 | 4464篇 |
1972年 | 4054篇 |
1971年 | 3688篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
Intensive use of the benchmark simulation model No. 1 (BSM1), a protocol for objective comparison of the effectiveness of control strategies in biological nitrogen removal activated sludge plants, has also revealed a number of limitations. Preliminary definitions of the long-term benchmark simulation model No. 1 (BSM1_LT) and the benchmark simulation model No. 2 (BSM2) have been made to extend BSM1 for evaluation of process monitoring methods and plant-wide control strategies, respectively. Influent-related disturbances for BSM1_LT/BSM2 are to be generated with a model, and this paper provides a general overview of the modelling methods used. Typical influent dynamic phenomena generated with the BSM1_LT/BSM2 influent disturbance model, including diurnal, weekend, seasonal and holiday effects, as well as rainfall, are illustrated with simulation results. As a result of the work described in this paper, a proposed influent model/file has been released to the benchmark developers for evaluation purposes. Pending this evaluation, a final BSM1_LT/BSM2 influent disturbance model definition is foreseen. Preliminary simulations with dynamic influent data generated by the influent disturbance model indicate that default BSM1 activated sludge plant control strategies will need extensions for BSM1_LT/BSM2 to efficiently handle 1 year of influent dynamics. 相似文献
12.
It was found that vanadyl porphyrin complexes synthesized from petroleum metal porphyrin concentrates stimulated epoxidation during the olefin oxygenation process. The yields of obtained oxiranes turned out to be 38–75%, depending on the olefin structure. An epoxidation mechanism that suggests the formation of a protonated dioxygen adduct as an intermediate during oxygenation of olefins in the presence of vanadyl porphyrin complexes was proposed. An analogy is drawn between the epoxide formation reaction upon the catalytic oxygenation of olefins and the Prilezhaev reaction. 相似文献
13.
The Magnitogorsk Metallurgical Combine has conducted a study of the effect of technological factors on the hydrogen content
of chromium-nickel-molybdenum steel after vacuum degassing. It was established that the most important factor is the hydrogen
content of the steel before the degassing operation. The study also determined the effects of the circulation coefficient,
the duration of the degassing operation, and the vacuum used in the treatment.
__________
Translated from Metallurg, No. 7, pp. 68–69, July, 2006. 相似文献
14.
The basic methods of verifying continuous automatic belt weighers are described. A comparative analysis of these methods on the basis of experimental studies is made and ways of implementing the results in industry are recommended. 相似文献
15.
Yu. I. Golovin D. V. Lopatin R. K. Nikolaev A. V. Umrikhin 《Technical Physics Letters》2004,30(5):426-428
The effect of crystal orientation on the photogeneration of free charge carriers was studied for C60 single crystals in a weak magnetic field. The photoconductivity sharply depends on the orientation of magnetic field with
respect to the crystallographic directions, showing a 5–8% increase for seven axes of the C60 crystal. 相似文献
16.
V. G. Deibuk 《Semiconductors》2003,37(10):1151-1155
The miscibility gaps and the critical temperatures of spinodal decomposition of ternary semiconducting Ga-In-Sb, Ga-In-P, and In-As-Sb systems are calculated by taking into account the deformation energy and the effect of plastic relaxation caused by the misfit dislocations. It is shown that taking into consideration elastic energy narrows the ranges of spinodal decomposition and lowers its critical temperature. The introduction of the phenomenological parameter into Matthews-Blakeslee formula makes it possible to reach a satisfactory agreement between theoretically calculated values of critical thickness of epitaxial films and the experimental data. 相似文献
17.
Ferrite particles coated with biocompatible phases can be used for hyperthermia treatment of cancer. We have synthesized substituted
calcium hexaferrite, which is not stable on its own but is stabilized with small substitution of La. Hexaferrite of chemical
composition (CaO)0.75(La203)0.20(Fe2O3)6 was prepared using citrate gel method. Hydroxyapatite was prepared by precipitating it from aqueous solution of Ca(NO3)2 and (NH4)2HPO4 maintaining pH above 11. Four different methods were used for coating of hydroxyapatite on ferrite particles. SEM with EDX
and X-ray diffraction analysis shows clear evidence of coating of hydroxyapatite on ferrite particles. These coated ferrite
particles exhibited coercive field up to 2 kOe, which could be made useful for hysteresis heating in hyperthermia. Studies
by culturing BHK-21 cells and WBC over the samples show evidence of biocompatibility. SEM micrographs and cell counts give
clear indication of cell growth on the surface of the sample. Finally coated ferrite particle was implanted in Kasaulli mouse
to test its biocompatibility. The magnetic properties and biocompatibility studies show that these hydroxyapatite coated ferrites
could be useful for hyperthermia. 相似文献
18.
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
19.
Rogin J. Kouchev I. Brenna G. Tschopp D. Qiuting Huang 《Solid-State Circuits, IEEE Journal of》2003,38(12):2239-2248
A 2-GHz direct-conversion receiver for wide-band code division multiple access (WCDMA) is presented. It includes two low-noise amplifiers (LNAs), an I/Q demodulator, and two sixth-order baseband channel select filters with programmable gain. Quadrature local oscillator (LO) signals are generated on chip in a frequency divider flip-flop. An external interstage filter between the LNAs rejects transmitter leakage to relax demodulator linearity requirements. A low-voltage demodulator topology improves linearity as well as demodulator output pole accuracy. The active-RC baseband filter uses a programmable servo loop for offset compensation and provides an adjacent channel rejection of 39 dB. Programmable gain over 71-dB range in 1-dB steps is merged with the filter to maximize dynamic range. An automatic on-chip frequency calibration scheme provides better than 1.5% corner frequency accuracy. The receiver is integrated in a 0.13-/spl mu/m CMOS process with metal-insulator-metal (MIM) capacitors. Measured receiver performance includes a 6.5-dB noise figure, IIP2 of +27 dBm, and IIP3 of -8.6 dBm. Power consumption is 45 mW. 相似文献
20.
The application of barrier discharges at atmospheric pressure in air expands on the market of plasma technology, because it is an ecological and cost‐effective alternative to other processes of surface treatment. These plasmas usually consist of a multitude of spatially and temporally localized filaments, whose distribution should be as even as possible for homogeneous treatment. This holds especially for the plasma treatment of sensitive goods such as wool or other textiles. In equipment for continuous pass of material the barrier arrangements often consist of a system cylinder – cylinder or cylinder – plane, whereby the gap width changes locally. Space distribution and intensity of filaments has been investigated by means of short‐time photography and spatially resolved measurement of current distribution and energy distribution derived from it. The local dependency found can be explained by means of a capacitive equivalent circuit. 相似文献