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   44524篇
  免费   1592篇
  国内免费   739篇
电工技术   2068篇
综合类   2347篇
化学工业   7522篇
金属工艺   2639篇
机械仪表   3895篇
建筑科学   3557篇
矿业工程   2645篇
能源动力   1723篇
轻工业   5236篇
水利工程   1380篇
石油天然气   4604篇
武器工业   29篇
无线电   1000篇
一般工业技术   1655篇
冶金工业   2129篇
原子能技术   219篇
自动化技术   4207篇
  2024年   34篇
  2023年   145篇
  2022年   411篇
  2021年   628篇
  2020年   662篇
  2019年   694篇
  2018年   671篇
  2017年   479篇
  2016年   412篇
  2015年   275篇
  2014年   587篇
  2013年   967篇
  2012年   615篇
  2011年   1718篇
  2010年   1192篇
  2009年   1433篇
  2008年   1510篇
  2007年   1818篇
  2006年   2295篇
  2005年   2288篇
  2004年   2725篇
  2003年   2944篇
  2002年   3506篇
  2001年   3426篇
  2000年   2978篇
  1999年   3041篇
  1998年   2306篇
  1997年   2060篇
  1996年   1456篇
  1995年   1019篇
  1994年   652篇
  1993年   471篇
  1992年   265篇
  1991年   160篇
  1990年   143篇
  1989年   112篇
  1988年   64篇
  1987年   53篇
  1986年   37篇
  1985年   47篇
  1984年   30篇
  1983年   35篇
  1982年   40篇
  1981年   34篇
  1980年   35篇
  1979年   32篇
  1977年   65篇
  1976年   98篇
  1975年   24篇
  1973年   28篇
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
1.
A set of novel hydrazone derivatives were synthesized and analyzed for their biological activities. The compounds were tested for their inhibitory effect on the phosphorylating activity of the protein kinase CK2, and their antioxidant activity was also determined in three commonly used assays. The hydrazones were evaluated for their radical scavenging against the DPPH, ABTS and peroxyl radicals. Several compounds have been identified as good antioxidants as well as potent protein kinase CK2 inhibitors. Most hydrazones containing a 4-N(CH3)2 residue or perfluorinated phenyl rings showed high activity in the radical-scavenging assays and possess nanomolar IC50 values in the kinase assays.  相似文献   
2.
This study investigates the behavior of fruit and vegetable samples during drying. The experimental data are fitted to several different thin-layer drying models. Regression analysis is used to determine model parameters, while statistical indicators serve to evaluate the goodness of fit. The power function model gives the best fit for all examined samples. Based on this model, different drying and heat storage technologies can be combined to ensure that the required residual moisture content of an agricultural product is reached. It is demonstrated on the case of a specific Togolese processing plant that under favorable conditions, fossil fuel consumption can be decreased by 33 %.  相似文献   
3.
Recent advancements in isolation and stacking of layered van der Waals materials have created an unprecedented paradigm for demonstrating varieties of 2D quantum materials. Rationally designed van der Waals heterostructures composed of monolayer transition-metal dichalcogenides (TMDs) and few-layer hBN show several unique optoelectronic features driven by correlations. However, entangled superradiant excitonic species in such systems have not been observed before. In this report, it is demonstrated that strong suppression of phonon population at low temperature results in a formation of a coherent excitonic-dipoles ensemble in the heterostructure, and the collective oscillation of those dipoles stimulates a robust phase synchronized ultra-narrow band superradiant emission even at extremely low pumping intensity. Such emitters are in high demand for a multitude of applications, including fundamental research on many-body correlations and other state-of-the-art technologies. This timely demonstration paves the way for further exploration of ultralow-threshold quantum-emitting devices with unmatched design freedom and spectral tunability.  相似文献   
4.
5.
In this study, AA7075 aluminum matrix composites reinforced with the combination of SiC, Al2O3, and B4C particles were fabricated by the liquid metal infiltration method. The effects of the relative ratio of B4C and Al2O3 particles on the microstructural, wear, and corrosion features of the composite samples were analyzed using XRD, light metal microscopy, SEM, EDS, Brinell hardness, ball-on-disc type tribometer, and potentiodynamic polarization devices. It was determined that infiltration occurred more successfully, and homogenously distributed particles with reduced porosity were obtained as the amount of Al2O3 increased. Worn surface studies revealed that the specimens were predominantly worn by abrasion and adhesion. The increase in B4C/Al2O3 ratio caused a decrease in the hardness and wear strength, whereas it increased the corrosion resistance.  相似文献   
6.
A silica-based glass-ceramic, with Y2Ti2O7 as the major crystalline phase, is designed, characterised and tested as an oxidation-protective coating for a titanium suboxide (TiOx) thermoelectric material at temperatures of up to 600 °C. The optimised sinter-crystallisation treatment temperatures are found to be 1300 °C and 855 °C for a duration of 30 min, and this treatment leads to a glass-ceramic with cubic Y2Ti2O7 and CaAl2Si2O8 as crystalline phases. An increase of ~270 °C in the dilatometric softening temperature is observed after devitrification of the parent glass, thus further extending its working temperature range.Excellent adhesion of the glass-ceramic coating to the thermoelectric material is maintained after exposure to a temperature of 600 °C for 120 h under oxidising conditions, thus confirming the effectiveness of the T1 glass-ceramic in protecting the TiOx material.  相似文献   
7.
Journal of Low Temperature Physics - This study modeled and investigated the magnetocaloric effect in Ni2MnGa Heusler alloy characterized by its magnetic entropy change (ΔSm) and its...  相似文献   
8.
针对和成矿业井下原矿含泥量和含水量较大,且矿泥中存在绿泥石、高岭土等黏土类矿物,造成供矿系统粘堵严重,系统台时量仅为设计水平一半的问题,对原矿进行了洗矿工艺研究。通过洗矿工艺,将原矿中的矿块和矿泥分离,实现矿块和矿泥按粒度分选,彻底解决了供矿系统粘堵严重的问题,稳定了磨选系统给矿量。  相似文献   
9.
为了综合回收现有南非铜尾矿中的有价铁元素,在试验室对该铜尾矿进行了回收铁的可选性试验研究。研究结果表明:该铜尾矿铁品位为59.36%,磁性铁含量为57.99%,当原矿磨矿细度为-0.074 mm 58%时,经两次磁选后,可获得产率为88.95%,铁品位为65.69%,铁回收率为98.43%的铁精矿。  相似文献   
10.
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