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   30652篇
  免费   2247篇
  国内免费   1102篇
电工技术   1470篇
技术理论   2篇
综合类   1707篇
化学工业   5301篇
金属工艺   1846篇
机械仪表   1999篇
建筑科学   2393篇
矿业工程   1000篇
能源动力   803篇
轻工业   1802篇
水利工程   533篇
石油天然气   2065篇
武器工业   213篇
无线电   3246篇
一般工业技术   3778篇
冶金工业   1636篇
原子能技术   356篇
自动化技术   3851篇
  2024年   121篇
  2023年   562篇
  2022年   915篇
  2021年   1278篇
  2020年   1049篇
  2019年   802篇
  2018年   983篇
  2017年   988篇
  2016年   946篇
  2015年   1155篇
  2014年   1462篇
  2013年   1809篇
  2012年   1895篇
  2011年   1932篇
  2010年   1745篇
  2009年   1706篇
  2008年   1581篇
  2007年   1565篇
  2006年   1669篇
  2005年   1376篇
  2004年   891篇
  2003年   846篇
  2002年   751篇
  2001年   631篇
  2000年   675篇
  1999年   812篇
  1998年   704篇
  1997年   628篇
  1996年   561篇
  1995年   461篇
  1994年   357篇
  1993年   264篇
  1992年   196篇
  1991年   159篇
  1990年   116篇
  1989年   101篇
  1988年   80篇
  1987年   53篇
  1986年   53篇
  1985年   29篇
  1984年   29篇
  1983年   19篇
  1982年   20篇
  1981年   11篇
  1980年   9篇
  1979年   2篇
  1971年   1篇
  1970年   2篇
  1966年   1篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
对喷射成形高温合金的组织形成及其从雾化过程的树枝晶向等轴晶组织的演变过程进行了分析,结果表明,半液态层中发生的枝晶破碎,重熔所造成的核心增殖作用为等轴晶组织的形成提供了大量结晶核心,在此基础上枝晶臂的合并,粗化以及未严重固相枝晶的粗化和均匀化产生了喷射成形材料所持有的非枝非等轴晶组织。  相似文献   
142.
In the chemical looping with oxygen uncoupling (CLOU) process,CuO is a promising material due to the high oxygen carrier capacity and exothermic reaction in fuel reactor but limited by the low melting point.The combustion rate of carbon is faster than the decoupling rate of oxygen carrier (OC).Hence,high tem-perature tolerance and rapid oxygen release rate of CuO modified by three different ores were investi-gated in this study.The kinetics analysis of oxygen decoupling with Cu-based oxygen carriers was also evaluated.Results showed that CuO modified by chrysolite had faster oxygen release rate than that of CuO.Limestone showed obvious positive effect on the oxidization process.The selected OCs could keep stable in at least 20 cycles,for about 1200 min.Shrinking core model (SCM) fitted well for the decoupling process in the temperature range of 1123-1223 K.Reduction rate kinetic information may aid in the development of chemical looping with oxygen uncoupling (CLOU) technologies during reactor design and process modeling.Ternary doped copper oxide with chrysolite and limestone could improve the reactivity of CuO in decoupling and coupling process and also improve the high temperature tolerance.  相似文献   
143.
Increasing numbers of miRNAs have been observed as oncogenes or tumor suppressors in colorectal cancer (CRC). It was recently reported that hsa-miR-106b-5p (miR-106b) promoted CRC cell migration and invasion. However, there were also studies showing contradictory results. Therefore, in the present study, we further explore the role of miR-106b and its downstream networks in the carcinogenesis of CRC. We observed that the expression of miR-106b is significantly increased in Pan-Cancer and CRC tissues compared with normal tissues from The Cancer Genome Atlas (TCGA) database. Furthermore, we used Transwell, Cell Counting Kit-8, and colony formation assays to clarify that miR-106b promotes the migratory, invasive, and proliferative abilities of CRC cells. For the first time, we systematically screened the target mRNAs and lncRNAs of miR-106b using TCGA database and the bioinformatics algorithms. Dual-luciferase reporter assay confirmed that NR2F2-AS1 and PLEKHO2 are the direct targets of miR-106b. Furthermore, NR2F2-AS1 acts as a competing endogenous RNA (ceRNA) to regulate PLEKHO2 expression by sponging miR-106b. The results of Gene set enrichment analysis (GSEA) and Western blot indicated that they play important roles in CRC progression by regulating MAPK pathway. Thus, miR-106b/NR2F2-AS1/PLEKHO2/MAPK signaling axis may suggest the potential usage in CRC treatment.  相似文献   
144.
Here, zinc-neutralized ethylene propylene diene monomer (EPDM) ionomers with different neutralization levels are prepared through melt blending, and are then incorporated with polyamide 1012 (PA1012) to fabricate PA1012/EPDM ionomer blends. Interestingly, complex crosslinking networks are formed in the blends due to the construction of sacrificial bonds (Zn2+-carboxyl, Zn2+-amide). The as-formed network structure and sacrificial bond endow the PA/EPDM blends with largely enhanced toughness (16 times higher than that of neat PA), as well as balanced strength and stiffness. Meanwhile, the rheological behaviors of PA1012/EPDM ionomer blends indicate their relative low melting viscosity, which can avoid the processing shortcomings of plastics toughened with rubber. Moreover, PA1012/EPDM ionomer blends show obvious gelation behavior, and a maximum notched Izod impact strength exhibited at the gel point, in which unique double network structure can be observed obviously, indicating that there is a corresponding correlation between the rheological and mechanical parameters. Furthermore, the supper-toughening mechanism of PA1012/EPDM ionomer blends at gel point is explored, which origins from the large deformation and cavitation of rubber particles and the destruction of special double network morphologies. This study provides a novel and effective strategy to fabricate PA materials with outstanding toughness and excellent strength simultaneously.  相似文献   
145.
Bcl-2 and Mcl-1, the two arms of the anti-apoptotic Bcl-2 family proteins, have been identified as key regulators of apoptosis and effective therapeutic targets of cancer. However, no small-molecular probe is capable of profiling and visualizing both Bcl-2 and Mcl-1 simultaneously in situ. Herein, we report a multifunctional molecular probe (BnN3-OPD-Alk) by a “three-in-one” molecular designing strategy, which integrated the Bcl-2/Mcl-1 binding ligand, fluorescent reporter group and photoreactive group azido into the same scaffold. BnN3-OPD-Alk exhibited sub-micromolar affinities to Bcl-2/Mcl-1 and bright green self-fluorescence. It was then successfully applied for Bcl-2/Mcl-1 labeling, capturing, enriching, and bioimaging both in vitro and in cells. This strategy could facilitate the precise early diagnosis and effective therapy of dual Bcl-2/Mcl-1-related diseases.  相似文献   
146.
钨尾矿微晶玻璃的形状记忆效应   总被引:1,自引:1,他引:1  
研究了钨尾矿微晶玻璃的形状记忆效应(SME),并用X射线衍射法(XRD)作了相分析。结果表明,钨尾矿微晶玻璃具有明显的SME;恢复应变随回复保温温度升高而增加;该材料随着变形量的减小,形状恢复率随之上升  相似文献   
147.
Rapidly quenching embrittlement (RQE) sometimes appears in Fe73.5Cu1Nb3Si13.5B9 nanocrystalline soft magnetic alloy (FINEMET) during production process. As a re-sult of RQE the ductility of the as-quenched ribbon drops seriously. The mechanism of RQE has been elucidated in the recent works of current authors. It was believed that RQE is due to the structural relaxation but not related to a-Fe(Si) crystallization. In this paper, the high resolution TEM (HRTEM) method and image digital processing were applied to analyze the HRTEM images of two FINEMET rapidly quenched ribbons with different thicknesses in detail. In the thinner ductile sample, the ordering domains with the size of about 3nm are observed. In the thicker RQE sample, the metastable nanocrystalline domains with the size of 18nm are observed along with the structural relaxation. These domains seem to have Fe3B-like metastable phase struc-ture on nanometer scale. The result indicates that the local atomic ordering regions extend when RQE induced  相似文献   
148.
A NEW CHELATING EXTRACTANT H 106   总被引:6,自引:0,他引:6  
本文介绍了异羟肟酸型螯合萃取剂 H106的稳定性及其在金属萃取中的行为,研究了用 H106进行金属萃取的机理和萃合物的稳定常数.实验结果表明,H106的稳定性很高,对金属的萃取性能很好.H106是一种一元弱酸,在试验条件下,它通过氧-氧配位,与金属离子形成内络盐 MeL_n.其对各金属离子的萃取能力强弱与金属络合物积累稳定常数的大小顺序相一致.在一定条件下,在萃取中表现出极佳的选择性.用 H106由湿法炼锌厂置换渣的硫酸浸出液中回收 Ga 和 Ge 已获得十分满意的结果.也可以用于微量钛测定和其他许多方面.  相似文献   
149.
本文介绍了一种新型仿真转台用叶片式无脉动连续回转电液伺服马达的工作原理,并提出为验证马达性能的非线性PI和微分前馈的复合控制策略,并通过试验对马达的性能进行了验证。  相似文献   
150.
中国有色金属再生资源回收利用及展望   总被引:2,自引:0,他引:2  
一、有色金属再生资源利用现状我国是有色金属资源短缺的国家,节约和合理使用资源显得特别重要。世界上工业发达国家对再生资源利用相当重视。近10年来世界再生铜产量已占原生铜产量的40%~55%,美国约占本国原生铜产量的60%,日本约占45%,德国约占80%。世界再生铝产量也占原生铝产量的30%~50%,美国约占本国原生铝的50%,日本约占90%,德国约占45%。世界再生铅产量也占原生铅产量的40%~60%,美国约占本国原生铅的75%,日本约占60%,德国约占55%。锌、镍、镁、锡、锑等再生资源也得到不同程度的利用。  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