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   1738653篇
  免费   53576篇
  国内免费   21770篇
电工技术   54025篇
技术理论   45篇
综合类   31054篇
化学工业   319595篇
金属工艺   81751篇
机械仪表   60622篇
建筑科学   70527篇
矿业工程   22636篇
能源动力   58890篇
轻工业   122463篇
水利工程   20543篇
石油天然气   58729篇
武器工业   2916篇
无线电   227943篇
一般工业技术   301532篇
冶金工业   136414篇
原子能技术   37082篇
自动化技术   207232篇
  2022年   17560篇
  2021年   28366篇
  2020年   21349篇
  2019年   22193篇
  2018年   22805篇
  2017年   23188篇
  2016年   29333篇
  2015年   30129篇
  2014年   44968篇
  2013年   106451篇
  2012年   54517篇
  2011年   67294篇
  2010年   61407篇
  2009年   69110篇
  2008年   60716篇
  2007年   56490篇
  2006年   61411篇
  2005年   53392篇
  2004年   50170篇
  2003年   49114篇
  2002年   47891篇
  2001年   43212篇
  2000年   42031篇
  1999年   40978篇
  1998年   37374篇
  1997年   36260篇
  1996年   35163篇
  1995年   31915篇
  1994年   29753篇
  1993年   28352篇
  1992年   27118篇
  1991年   23629篇
  1990年   23772篇
  1989年   22634篇
  1988年   20917篇
  1987年   19041篇
  1986年   18220篇
  1985年   21431篇
  1984年   21980篇
  1983年   19902篇
  1982年   19036篇
  1981年   19048篇
  1980年   17625篇
  1979年   18208篇
  1978年   17438篇
  1977年   16545篇
  1976年   16404篇
  1975年   15758篇
  1974年   15305篇
  1973年   15366篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
The usage of cling wraps is emerging as an easy and cost-effective approach to protect fresh-cut fruits and vegetables from dust, whilst improving visual appeal on retail counters. This study focused on developing an alternate, protein-based packaging material as a food grade cling wrap for food packaging applications. Zein-based cling wraps were produced, and their physical and mechanical characteristics were evaluated and compared with conventionally used chitosan biopolymer films and commercial synthetic polymer films. Antioxidant potential of the prepared films was studied, and the effectiveness of the developed films as anti-browning cling wraps was evaluated using studies conducted on fresh-cut apple slices at ambient conditions. Anti-browning effects were in par with polymeric counterparts; however, zein cling wraps could better prevent weight loss in apple slices. Zein-based films can be adopted as biodegradable food grade cling wraps as an alternative to chitosan and synthetic polymeric materials.  相似文献   
972.
A method to calculate the height of a water-conducting fractured zone (HWCFZ) was developed based on the plate and shell theory, and the development of the HWCFZ in bedrock and Q2l loess strata is discussed in detail. First, the subsidence-deflection curve equation of the overlying stratum is theoretically derived, and then the ultimate deflection and free space height of rock strata are calculated. Moreover, the strata tensile strain is calculated by using integral calculus. In addition, the failure state of the rock is analyzed by comparing the theoretically calculated tensile strain with the experimentally measured yield tensile strain, allowing one to attain the maximum value of HWCFZ. This approach was tested at the Jinjitan coal mine; the theoretically predicted, experimentally measured, and numerically computed maximum HWCFZ values were 189.5, 187.3, and 188.5 m, respectively, demonstrating the accuracy of the proposed method. These results are highly significant for safe and environment-friendly coal mining in northwest Shaanxi, China.  相似文献   
973.
974.
975.
976.
Abstract

Preparation condition can affect the structure and the properties of nanofiber membrane. In order to explore suitable conditions to prepare the Fe3O4/PVDF nanofiber membrane with good hydrophobicity, the hydrophobicity of Fe3O4/PVDF nanofiber membranes obtained by electrospinning was investigated by changing preparation conditions like weight percentage of Fe3O4 nanoparticles, blending quality concentration of poly (vinylidene fluoride) (PVDF) and Fe3O4 nanoparticles, and positive voltage. And the variations of hydrophobicity of Fe3O4/PVDF nanofiber membranes modified by 1H, 1H, 2H, 2H-perfluorodecyl trimethoxysilane were studied. The results show that the hydrophobicity of Fe3O4/PVDF nanofiber membranes has changed under different preparation conditions. The contact angles of samples increased after a modification by 1H, 1H, 2H, 2H-perfluorodecyl trimethoxysilane, which indicates that the hydrophobicity of Fe3O4/PVDF nanofiber membranes has been enhanced.  相似文献   
977.
In reliability analysis, the stress-strength model is often used to describe the life of a component which has a random strength (X) and is subjected to a random stress (Y). In this paper, we considered the problem of estimating the reliability R=P [Y<X] when the distributions of both stress and strength are independent and follow exponentiated Pareto distribution. The maximum likelihood estimator of the stress strength reliability is calculated under simple random sample, ranked set sampling and median ranked set sampling methods. Four different reliability estimators under median ranked set sampling are derived. Two estimators are obtained when both strength and stress have an odd or an even set size. The two other estimators are obtained when the strength has an odd size and the stress has an even set size and vice versa. The performances of the suggested estimators are compared with their competitors under simple random sample via a simulation study. The simulation study revealed that the stress strength reliability estimates based on ranked set sampling and median ranked set sampling are more efficient than their competitors via simple random sample. In general, the stress strength reliability estimates based on median ranked set sampling are smaller than the corresponding estimates under ranked set sampling and simple random sample methods.  相似文献   
978.
Technical Physics Letters - A new method for epitaxial growth of cadmium sulfide (CdS) films in the metastable cubic phase by atomic-layer deposition on silicon substrates with a buffer layer of...  相似文献   
979.
Sidorov  G. V.  Myasoedov  N. F. 《Radiochemistry》2020,62(2):260-263
Radiochemistry - Reaction of solid-phase catalytic heterogeneous isotope exchange of 2-deoxy-D-glucose and its derivative, O(6)-(4-bromothiophenyl)guanine-C8-β-D-glucose with tritium has been...  相似文献   
980.
Russian Engineering Research - The theoretically possible reconfigurable parallel mechanisms are classified, in terms of the layout of guides on the base. Formulas are derived for the...  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