全文获取类型
收费全文 | 129497篇 |
免费 | 3620篇 |
国内免费 | 466篇 |
专业分类
电工技术 | 1103篇 |
综合类 | 2354篇 |
化学工业 | 21576篇 |
金属工艺 | 5639篇 |
机械仪表 | 3954篇 |
建筑科学 | 3560篇 |
矿业工程 | 652篇 |
能源动力 | 2370篇 |
轻工业 | 11570篇 |
水利工程 | 1658篇 |
石油天然气 | 555篇 |
武器工业 | 7篇 |
无线电 | 10949篇 |
一般工业技术 | 23259篇 |
冶金工业 | 12838篇 |
原子能技术 | 526篇 |
自动化技术 | 31013篇 |
出版年
2024年 | 92篇 |
2023年 | 389篇 |
2022年 | 831篇 |
2021年 | 1302篇 |
2020年 | 931篇 |
2019年 | 1113篇 |
2018年 | 15652篇 |
2017年 | 14587篇 |
2016年 | 11434篇 |
2015年 | 1938篇 |
2014年 | 1938篇 |
2013年 | 3601篇 |
2012年 | 5716篇 |
2011年 | 11987篇 |
2010年 | 10307篇 |
2009年 | 7538篇 |
2008年 | 8577篇 |
2007年 | 9331篇 |
2006年 | 1479篇 |
2005年 | 2395篇 |
2004年 | 2228篇 |
2003年 | 2134篇 |
2002年 | 1447篇 |
2001年 | 758篇 |
2000年 | 834篇 |
1999年 | 764篇 |
1998年 | 3239篇 |
1997年 | 2188篇 |
1996年 | 1479篇 |
1995年 | 850篇 |
1994年 | 698篇 |
1993年 | 773篇 |
1992年 | 291篇 |
1991年 | 307篇 |
1990年 | 205篇 |
1989年 | 227篇 |
1988年 | 229篇 |
1987年 | 201篇 |
1986年 | 165篇 |
1985年 | 216篇 |
1984年 | 168篇 |
1983年 | 131篇 |
1982年 | 164篇 |
1981年 | 178篇 |
1980年 | 190篇 |
1979年 | 97篇 |
1978年 | 97篇 |
1977年 | 351篇 |
1976年 | 744篇 |
1973年 | 84篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
101.
Serdar Akbayrak Yalçın Tonbul Saim Özkar 《International Journal of Hydrogen Energy》2021,46(27):14259-14269
Herein, we report the use of tungsten(VI) oxide (WO3) as support for Rh0 nanoparticles. The resulting Rh0/WO3 nanoparticles are highly active and stable catalysts in H2 generation from the hydrolysis of ammonia borane (AB). We present the results of our investigation on the particle size distribution, catalytic activity and stability of Rh0/WO3 catalysts with 0.5%, 1.0%, 2.0% wt. Rh loadings in the hydrolysis reaction. The results reveal that Rh0/WO3 (0.5% wt. Rh) is very promising catalyst providing a turnover frequency of 749 min?1 in releasing 3.0 equivalent H2 per mole of AB from the hydrolysis at 25.0 °C. The high catalytic activity of Rh0/WO3 catalyst is attributed to the reducible nature of support. The report covers the results of kinetics study as well as comparative investigation of activity, recyclability, and reusability of colloidal(0) nanoparticles and Rh0/WO3 (0.5 % wt. Rh) catalyst in the hydrolysis reaction. 相似文献
102.
103.
Meza-Espinoza Libier de los Ángeles Vivar-Vera María de Lourdes García-Magaña María Sáyago-Ayerdi Sonia G. Chacón-López Alejandra Becerrea-Verdín Eduardo M. Montalvo-González Efigenia 《Food science and biotechnology》2018,27(2):509-517
Food Science and Biotechnology - The enzymatic activity and partial characterization of proteases from Bromelia karatas fruits were evaluated and compared with Bromelia pinguin proteases. The... 相似文献
104.
Gert Schubring 《NTM》2003,11(2):90-99
Enno Heeren Dirksen (1788–1850) was one of several mathematicians originating from Eastern Frisia at the end of the eighteenth
century to acquire prominence in neohumanist reformed Prussia. While striving—like so many of his contemporaries—for more
rigour in the foundations of calculus, his work is significant due to his unusual emphasis on the semiotic aspects of the
basic concepts. As a clear-sighted propagator of Cauchy's conceptual innovations in Germany, his achievements in improving
sign expressions of such concepts enabled him to clarify hitherto not differentiated multiple limit processes—although less
successfully in constructive concept formation itself.
The contribution is based on the analysis of Dirksen's published texts and on the numerous texts which remained drafts for
his projected voluminousOrganon der gesamten Analysis.
Menso Folkerts zum 60. Geburtstag gewidmet 相似文献
Menso Folkerts zum 60. Geburtstag gewidmet 相似文献
105.
Yang Aiying Wang Ziyu Zhang Zhaoyi Chen Zhangyuan Wu Deming 《电子科学学刊(英文版)》2003,20(6):461-466
A 10Gbit/s recirculating system is configured with Chirped Fiber Bragg Grating (CFBG) for the dispersion compensation. For the first time, the transmission distance in the loop reaches 1000km with bit error rate of 10-9. The effect of the group delay ripple of the fiber grating is also investigated in the recirculating systems, and it is shown that the transmission distance is limited to 4 cycles (4×167.1km ) in the loop with the power penalty fluctuation below 1.0dB. Thus the group delay ripple should be reduced to allow for the wavelength drift of±5GHz. At the end of this letter, the principles are given for designing long haul recirculating systems with dispersion compensation CFBG. 相似文献
106.
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
107.
The tensile elastic modulus (E), yield stress (σY) and microhardness (MH) of neat and binary and ternary blends of glassy semicrystalline ethylene–vinyl alcohol copolymer (EVOH), a glassy amorphous polyamide and a semicrystalline nylon‐containing ionomer covering a broad range of properties were examined. The tests were carried out on dry and water‐equilibrated samples to produce stiffer and softer materials, respectively. From the results, more accurate linear correlations were found to describe adequately the microhardness, modulus and yield stress of these strongly self‐associated polymers through hydrogen bonding. Copyright © 2003 Society of Chemical Industry 相似文献
108.
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
109.
110.
Real-time multimedia applications have to use forward error correction (FEC) anderror concealment techniques to cope with
losses in today’s best-effort Internet. The efficiency of these solutions is known however to depend on the correlation between
losses in the media stream. In this paper we investigate how the packet size distribution affects the packet loss process,
that is, the distribution of the number of lost packets in a block, the related FEC performance and the average loss run length.
We present mathematical models for the loss process of the MMPP+M/D/1/K and the MMPP+M/M/1/K queues; we validate the models
via simulations, and compare the results to simulation results with an MPEG-4 coded video trace. We conclude that the deterministic
packet size distribution (PSD) not only results in lower stationary loss probability than the exponential one, but also gives
a less correlated loss process, both at a particular average link load and at a particular stationary loss probability as
seen by the media stream.Our results show that for applications that can only measure the packet loss probability, the effects
of the PSD on FEC performance are higher in access networks, where a single multimedia stream might affect the multiplexing
behavior. Our results show that the effects of the PSD on FEC performance are higher in access networks, where a single multimedia
stream might affect the multiplexing behavior and thus can improve the queuing performance by decreasing the variance of its
PSD. 相似文献