首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   267814篇
  免费   28627篇
  国内免费   8977篇
电工技术   13093篇
技术理论   19篇
综合类   13297篇
化学工业   53557篇
金属工艺   13761篇
机械仪表   14472篇
建筑科学   16698篇
矿业工程   5742篇
能源动力   6299篇
轻工业   20920篇
水利工程   4693篇
石油天然气   13100篇
武器工业   1555篇
无线电   31304篇
一般工业技术   44508篇
冶金工业   14894篇
原子能技术   5491篇
自动化技术   32015篇
  2024年   1001篇
  2023年   3385篇
  2022年   6523篇
  2021年   9024篇
  2020年   7974篇
  2019年   8428篇
  2018年   9723篇
  2017年   10544篇
  2016年   10524篇
  2015年   11710篇
  2014年   13904篇
  2013年   17081篇
  2012年   15966篇
  2011年   16782篇
  2010年   14766篇
  2009年   14325篇
  2008年   13791篇
  2007年   12926篇
  2006年   11982篇
  2005年   10278篇
  2004年   8101篇
  2003年   7892篇
  2002年   7905篇
  2001年   7129篇
  2000年   6484篇
  1999年   5726篇
  1998年   4288篇
  1997年   3572篇
  1996年   3301篇
  1995年   2836篇
  1994年   2439篇
  1993年   1931篇
  1992年   1748篇
  1991年   1464篇
  1990年   1427篇
  1989年   1308篇
  1988年   1110篇
  1987年   996篇
  1986年   877篇
  1985年   795篇
  1984年   760篇
  1982年   715篇
  1979年   748篇
  1978年   784篇
  1977年   749篇
  1976年   768篇
  1975年   715篇
  1974年   729篇
  1973年   732篇
  1972年   710篇
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
1.
2.
This study was undertaken to develop a modified atmosphere package to control microbial growth in ready‐to‐eat (RTE) products stored at ambient temperature. Ethanol and/or limonene associated with modified atmosphere (CO2 : O2 : N2 = 30% : 5% : 65%) was used to inhibit the growth of total air‐borne microorganisms and Escherichia coli in RTE products stored at 25°C. The results indicated that 0.05% ethanol vapour in the headspace was effective to inhibit the growth of air‐borne microorganisms and E. coli at 25°C for 72 h in a model study, and the effectiveness was related to ethanol content. Both 73 ppm limonene and 0.05% ethanol vapour enhanced the bacteriostatic effect of modified atmosphere in RTE sushi roll products, and no off‐flavour was detected using this formulated gas; however, no significant inhibitory effect was observed for RTE cold noodle products. This study concludes that combinations of carbon dioxide, ethanol or limonene vapours are effective to inhibit microbial growth in RTE food at ambient temperature, and the outcome may be due to the hurdle effect. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   
3.
Amphiphilic magnetic microspheres ranging in diameter from 5 to 100 µm were prepared by dispersion copolymerization of styrene and poly(ethylene oxide) vinylbenzyl (PEO‐VB) macromonomer (MPEO) in the presence of Fe3O4 magnetic fluid. The effects of various polymerization parameters on the average particle size were systematically investigated. The average particle size was found to increase with increasing styrene concentration and initiator concentration. It also increased with decreasing stabilizer concentration and molecular weight of MPEO. The content of the hydroxyl groups localized in the microspheres ranged from 0.01 to 0.2 mmol g?1. © 2003 Society of Chemical Industry  相似文献   
4.
A locomotive cabin adsorption air‐conditioner has been equipped in #DF4B‐2369 locomotive; and has been successfully run for 2 years. It is powered by waste heat from the exhaust of the diesel engine. The influence on heat transfer is described by the equivalent heat transfer coefficient or thermal resistance of components inside the adsorber. The variation of adsorption capacity is expressed by a non‐equilibrium adsorption function. The dynamic heat transfer process of adsorption air‐conditioning system is treated with the lumped parameter method. Some typical running experimental results are present. The diesel engine rotating speed and locomotive speed influenced on the refrigeration system are discussed. The maximum mean refrigeration power is regarded as an objective function. Based on experiments and theoretical analysis, the running characteristics of the air‐conditioning system are optimized. Some techniques of performance improvement are suggested as well. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   
5.
华风气象影视大楼总面积4万平方米,根据空间功能不同分为办公大楼和商务写字楼两部分,办公大楼是集演播室、制作机房、办公室为一体的九层综合性建筑。设计师杨宇在刚接触到这个项目的时候,面对的是一个既成事实的建筑。  相似文献   
6.
徐玉 《世界电信》2004,17(10):29-32
主要对各国3G许可证与使用技术标准的抽绑政策.各国对2G/3G网络漫游的管制规定。以及3G网络之间共享的种类及实施方式等方面做了详尽的讲解,并进行比较和分析。  相似文献   
7.
Gas/liquid mass transfer has been investigated using a stirred vessel gas/liquid contactor using non‐Newtonian media and carbon dioxide as absorbent and gas phase, respectively. The volumetric mass transfer coefficients at different operational variables have been determined. Non‐Newtonian media (liquid phase) were prepared as aqueous solutions of sodium carboxymethyl cellulose salt. The influence of the rheological properties, polymer concentration, stirring rate, and gas flow rate on mass transfer was studied for these liquid phases. Kinematic viscosity and density experimental data were used to calculate the average molecular weight corresponding to the polymer employed. The Ostwald model has been used to fit the rheological behavior of aqueous solutions of the polymer employed as absorbent phase. Reasonably good agreement was found between the predictions of the proposed models and the experimental data of mass transfer coefficients.  相似文献   
8.
9.
In advancement of Pyrosil®‐technology a new kind of precursor delivery was developed, build and tested on real substrates. A Lab‐demonstrator was build to demonstrate the resources of the technology.  相似文献   
10.
Nucleation and growth mechanisms and kinetics of crystals of an amino acid salt were investigated in a methanol‐water system by measuring and evaluating the induction time as a function of the supersaturation ratio and temperature in batch salting out crystallization experiments. Discrimination between the possible crystallization mechanisms, and estimation of the kinetic parameters were carried out using nonlinear parameter identification. The results concerning the growth mechanism obtained were checked additionally by measuring the induction time as a function of number density of seed crystals.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号