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   57255篇
  免费   9944篇
  国内免费   4705篇
电工技术   3517篇
技术理论   1篇
综合类   3460篇
化学工业   10280篇
金属工艺   3882篇
机械仪表   4217篇
建筑科学   3237篇
矿业工程   1604篇
能源动力   3395篇
轻工业   6963篇
水利工程   1214篇
石油天然气   1543篇
武器工业   1284篇
无线电   6376篇
一般工业技术   7244篇
冶金工业   1060篇
原子能技术   268篇
自动化技术   12359篇
  2024年   372篇
  2023年   2002篇
  2022年   3101篇
  2021年   3430篇
  2020年   3610篇
  2019年   2942篇
  2018年   2789篇
  2017年   3159篇
  2016年   3278篇
  2015年   3076篇
  2014年   3824篇
  2013年   4676篇
  2012年   6469篇
  2011年   5984篇
  2010年   3949篇
  2009年   4128篇
  2008年   2634篇
  2007年   3668篇
  2006年   3071篇
  2005年   1334篇
  2004年   547篇
  2003年   450篇
  2002年   457篇
  2001年   393篇
  2000年   280篇
  1999年   311篇
  1998年   146篇
  1997年   114篇
  1996年   140篇
  1995年   130篇
  1994年   85篇
  1993年   80篇
  1992年   80篇
  1991年   60篇
  1990年   64篇
  1989年   53篇
  1988年   95篇
  1987年   307篇
  1986年   285篇
  1985年   75篇
  1984年   51篇
  1983年   24篇
  1982年   30篇
  1981年   24篇
  1980年   27篇
  1979年   28篇
  1978年   21篇
  1977年   8篇
  1976年   11篇
  1951年   32篇
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
31.
Transglutaminase (TGase) was separated from the culture broth of an isolated strain of Streptoverticillium mobaraense. The crude enzyme was prepared by centrifugation, ultrafiltration, precipitation by alcohol, centrifugation and freeze‐drying. The yield after these processes was 65–70%. Then the enzyme was purified to homogeneity by chromatography on CM‐cellulose and Sephadex G‐75 on which the yields were about 70% and 80%, respectively; the purified folds reached 2.5–4.7 and 1.08–2.06, respectively. The molecular weight of this TGase was 39,500–40,100 Da by gel filtration chromatography. Optimum enzyme activity was observed in the pH range of 5.0–7.0, and it was maintained stable at 20–40C. The optimal temperature and pH was 52C and 6.0, respectively. At 1 mM and 5 mM metal ion or inhibitors concentration, TGase activity was strongly inhibited by Zn2+ and NEM, and not affected obviously by Ba2+, Ca2+, Co2+, Cu2+, Fe2+, Fe3+, Mg2+, Mn2+, Na+ as well as PMSF and EDTA. The effects of these additions on this TGase were compared with those of other microbial TGases.  相似文献   
32.
Pool boiling heat transfer from nano-porous surface immersed in a saturated FC-72 dielectric fluid has been experimentally studied at atmospheric pressure (101 kPa). The data obtained from nano-porous surface (Anodisc 25) of thickness about 70 μm made from aluminum oxide (Al2O3) obtained from Whatman, were compared to that of a plain surface (aluminum) of thickness about 105 μm. From the experimental data obtained it was evident that there is a reduction of about 30% in the incipient superheat for the applied power for nano-porous surface over plain surface. SEM photographs of the nano-porous coating were taken for determining the size of the pores.  相似文献   
33.
《Materials Letters》2007,61(11-12):2164-2166
By radiating a linear polyethylenimine–HAuCl4 aqueous solution with natural sunlight, we obtained polyelectrolyte-protected gold nanoparticles, and the size of such gold nanoparticles can be controlled by varying the molar ratio of polyelectrolyte to gold.  相似文献   
34.
Compressive creep tests in air were carried out on 1 cat.% Fe-doped alumina at a temperature T=1400 °C. Iron doping affected the plastic deformation by different ways in relation with Fe2+ cations population. Fe2+ cations sped up the deformation rates. FeAl2O4 spinel precipitates were identified and they were found (i) to interact with alumina grain boundaries (ii) to limit the grain growth within a range of strain. The Fe2+ cations underwent oxidation and this resulted in the dissolution of the some precipitates and in the decrease of deformation rates. It was suggested that deformation sped up this evolution through mass transport and that time was not a dominating parameter.  相似文献   
35.
建立垂直管吸收器管内泡式吸收过程中传热传质的数学物理模型,对其泡式吸收过程进行数值研究,获得泡式吸收方式的一些传热传质特性,为吸收器的优化设计提供一定理论指导。  相似文献   
36.
真空冷冻干燥技术在三七加工中的应用   总被引:1,自引:0,他引:1  
介绍了真空冷冻干燥的基本原理,并据三七的特点,探讨三七真空冷冻干燥的工艺流程及特点,简要分析了三七冷冻干燥的前景。  相似文献   
37.
A stable film made from hydroxyethylcellulose (HEC) on pyrolytic graphite (PG) electrode was employed for incorporating hemoglobin (Hb), myoglobin (Mb) and horseradish peroxidase (HRP), and the electrochemical characteristics of the proteins were studied correspondingly. Experimental results revealed that HEC film could greatly accelerate electron transfer between the proteins and electrode, and the proteins showed a thin layer electrochemical behavior in the film. Moreover, all the proteins in the film exhibited good catalytic activity towards the reduction of hydrogen peroxide (H2O2) in the low H2O2 concentration range. In the high concentration range, H2O2 would exhibit toxicity effect on the proteins. The electrochemical properties and electrocatalytic abilities of the three heme proteins in HEC film have been compared, and the optimal conditions for H2O2 biosensor fabrication have been obtained.  相似文献   
38.
39.
知识驱动的UG中的产品开发   总被引:2,自引:0,他引:2  
重点论述了UG中的KBE即KF模块的知识驱动产品开发设计过程及其关键技术,介绍了知识驱动自动化过程,实例剖析了UG中的KF在产品开发设计过程中的应用。  相似文献   
40.
The finite-difference time-domain method based on recursive convoltion method (RC-FDTD) for the electric anisotropic dispersive medium is discussed in detail. To exemplify the availability of the three-dimensional RC-FDTD algorithm, the backscattering Radar-Cross-Section(RCS) of a non-magnetized plasma sphere is computed, and the numerical results are the same as the one of the Shift Operater-FDTD method, and show that the RC-FDTD method is correct and efficient. In addition, the co-polarized and cross-polarized backscattering time-domain of a magnetized plasma sphere are obtained by the RC-FDTD algorithm. The results show that when the external magnetic field is implemented, the cross-polarized component appear, evidently.  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