全文获取类型
收费全文 | 358771篇 |
免费 | 3964篇 |
国内免费 | 1703篇 |
专业分类
电工技术 | 5532篇 |
综合类 | 2830篇 |
化学工业 | 51165篇 |
金属工艺 | 15732篇 |
机械仪表 | 11374篇 |
建筑科学 | 8492篇 |
矿业工程 | 2122篇 |
能源动力 | 8041篇 |
轻工业 | 25885篇 |
水利工程 | 4234篇 |
石油天然气 | 6119篇 |
武器工业 | 43篇 |
无线电 | 42432篇 |
一般工业技术 | 71841篇 |
冶金工业 | 53323篇 |
原子能技术 | 7728篇 |
自动化技术 | 47545篇 |
出版年
2021年 | 2153篇 |
2019年 | 2063篇 |
2018年 | 17629篇 |
2017年 | 16608篇 |
2016年 | 13582篇 |
2015年 | 3066篇 |
2014年 | 4552篇 |
2013年 | 12120篇 |
2012年 | 10068篇 |
2011年 | 18790篇 |
2010年 | 15489篇 |
2009年 | 14068篇 |
2008年 | 15626篇 |
2007年 | 16614篇 |
2006年 | 7902篇 |
2005年 | 8383篇 |
2004年 | 8251篇 |
2003年 | 8086篇 |
2002年 | 7211篇 |
2001年 | 6923篇 |
2000年 | 6644篇 |
1999年 | 6807篇 |
1998年 | 16339篇 |
1997年 | 11602篇 |
1996年 | 8957篇 |
1995年 | 6851篇 |
1994年 | 6023篇 |
1993年 | 6059篇 |
1992年 | 4406篇 |
1991年 | 4202篇 |
1990年 | 4073篇 |
1989年 | 4055篇 |
1988年 | 3759篇 |
1987年 | 3387篇 |
1986年 | 3392篇 |
1985年 | 3739篇 |
1984年 | 3461篇 |
1983年 | 3217篇 |
1982年 | 3024篇 |
1981年 | 3038篇 |
1980年 | 3030篇 |
1979年 | 2829篇 |
1978年 | 2869篇 |
1977年 | 3141篇 |
1976年 | 4096篇 |
1975年 | 2416篇 |
1974年 | 2379篇 |
1973年 | 2396篇 |
1972年 | 2018篇 |
1971年 | 1781篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
ABSTRACTIn recent times, the applications of multimedia are rising in a greedy mode and hence the amount of video transactions is also increasing exponentially. This has shouted great demands on effective models on video encoding and also for reducing the transmission channel congestion. This research work introduces a managing technique termed weighted encoding for High-Efficiency Video Coding (HEVC). HEVC, also termed as MPEG-H Part 2 and H.265 is a video compression standard that is widely utilized AVC (H.264 or MPEG-4 Part 10). When compared to AVC, HEVC grants double the ratio of data compression at a similar level of quality of the video or considerably enhanced video quality at a similar bit rate. This work intends to optimize the weight that adopted in HEVC for encoding. For this, this paper proposes a new Iterative based propagation update in the water wave Optimization Algorithm (IPU-WWO), which is the improved form of Water wave Optimization (WWO). The performance of proposed IPU-WWO is compared over other conventional methods like Artificial Bee Colony (ABC), Firefly (FF), Particle Swarm Optimization (PSO) and Genetic Algorithm (GA) with respect to Peak Signal to Noise Ratio (PSNR). By doing the encoding process, it minimizes the video size with perceptually better quality video or PSNR. 相似文献
2.
3.
The main factors that determine the uniformity with which smelting products are tapped from a blast furnace are the rate of accumulation of the products in the hearth and the tapping rate. The first parameter is in turn determined by the stability of the furnace’s operation and can vary significantly even over the course of 24 h. The second parameter is determined mainly by the condition of the iron notch, the maintenance it receives, any changes that occur in the diameter of the channel of the notch, and the quality of the materials used to form the notch. Recommendations are presented to optimize tapping of the smelting products. 相似文献
4.
P. B. Lovyrev A. I. Lavrov V. A. Babkin A. N. Aminov S. M. Melekhin Yu. P. Kazantsev P. M. Korol’kov 《Metallurgist》2006,50(3-4):152-157
Specifications require that all the welds in 12-m-diam. decomposers with a capacity of 3600 m3 be subjected to high-temperature tempering before going into service in order to alleviate the stresses from the welding
operation. Specialists at the organizations VNIIPTkhimnefteapparatury and VNIImontazhspetsstroi have proposed out-of-furnace
volumetric (complete) of the assembled decomposer with the use of special heaters. The use of this heating method has shortened
assembly operations while providing the welds with a highquality heat treatment and reducing the stresses overall (including
welding stresses, stresses from assembly of the decomposer, etc.) The technology ensures uniform heating of the housing of
the decomposer and provides for close control over the process. The experience gained in heat-treating decomposers can also
be used in the construction of other containers that come into contact with corrosive media.
__________
Translated from Metallurg, No. 3, pp. 61–64, March, 2006. 相似文献
5.
P. Cofta 《BT Technology Journal》2006,24(2):214-218
Trust is the key element of commerce, both for traditional models and — more recently — for eCommerce. Unlike its traditional
counterpart, eCommerce relies on trust being created and maintained with the help of digital devices and services. Convergence
brings significant changes to the way people interact through digital media by offering ubiquitous and seamless communication.
This has a significant impact on the way trust is established and maintained, with consequent impact upon eCommerce. This
paper identifies a number of the most important challenges to trust in eCommerce as well as trust-related aspects of key enablers
of eCommerce. From this perspective, the paper studies an impact of convergence on trust within eCommerce to identify several
positive relationships. 相似文献
6.
K.P. Pipe R.J. Ram 《Photonics Technology Letters, IEEE》2003,15(4):504-506
By measuring the total energy flow from an optical device, we can develop new design strategies for thermal stabilization. Here we present a comprehensive model for heat exchange between a semiconductor laser diode and its environment that includes the mechanisms of conduction, convection, and radiation. We perform quantitative measurements of these processes for several devices, deriving parameters such as a laser's heat transfer coefficient, and then demonstrate the feasibility of thermal probing for the nondestructive wafer-scale characterization of optical devices. 相似文献
7.
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
8.
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
9.
10.
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