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   43888篇
  免费   4394篇
  国内免费   2013篇
电工技术   2675篇
技术理论   6篇
综合类   3543篇
化学工业   7289篇
金属工艺   2259篇
机械仪表   2675篇
建筑科学   3553篇
矿业工程   1052篇
能源动力   1197篇
轻工业   4871篇
水利工程   922篇
石油天然气   2022篇
武器工业   401篇
无线电   4860篇
一般工业技术   4670篇
冶金工业   1701篇
原子能技术   583篇
自动化技术   6016篇
  2025年   6篇
  2024年   488篇
  2023年   796篇
  2022年   1294篇
  2021年   1792篇
  2020年   1392篇
  2019年   1071篇
  2018年   1249篇
  2017年   1370篇
  2016年   1280篇
  2015年   1782篇
  2014年   2214篇
  2013年   2682篇
  2012年   3079篇
  2011年   3344篇
  2010年   2960篇
  2009年   2886篇
  2008年   2922篇
  2007年   2654篇
  2006年   2534篇
  2005年   2171篇
  2004年   1502篇
  2003年   1154篇
  2002年   1118篇
  2001年   932篇
  2000年   874篇
  1999年   907篇
  1998年   730篇
  1997年   604篇
  1996年   526篇
  1995年   461篇
  1994年   334篇
  1993年   251篇
  1992年   220篇
  1991年   162篇
  1990年   114篇
  1989年   105篇
  1988年   89篇
  1987年   47篇
  1986年   57篇
  1985年   27篇
  1984年   23篇
  1983年   13篇
  1982年   13篇
  1981年   15篇
  1980年   18篇
  1979年   8篇
  1976年   7篇
  1975年   4篇
  1951年   2篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
51.
52.
Nephrotoxicity is the dose-limiting factor of cisplatin treatment. Magnesium isoglycyrrhizinate (MgIG) has been reported to ameliorate renal ischemia–reperfusion injury. This study aimed to investigate the protective effect and possible mechanisms of MgIG against cisplatin-induced nephrotoxicity from the perspective of cellular pharmacokinetics. We found that cisplatin predominantly accumulated in mitochondria of renal tubular epithelial cells, and the amount of binding with mitochondrial DNA (mtDNA) was more than twice that with nuclear DNA (nDNA). MgIG significantly lowered the accumulation of cisplatin in mitochondria and, in particular, the degree of target-binding to mtDNA. MgIG notably ameliorated cisplatin-induced changes in mitochondrial membrane potential, morphology, function, and cell viability, while the magnesium donor drugs failed to work. In a mouse model, MgIG significantly alleviated cisplatin-caused renal dysfunction, pathological changes of renal tubules, mitochondrial ultrastructure variations, and disturbed energy metabolism. Both in vitro and in vivo data showed that MgIG recovered the reduction of NAD+-related substances and NAD+-dependent deacetylase sirtuin-3 (SIRT3) level caused by cisplatin. Furthermore, SIRT3 knockdown weakened the protective effect of MgIG on mitochondria, while SIRT3 agonist protected HK-2 cells from cisplatin and specifically reduced platinum-binding activity with mtDNA. In conclusion, MgIG reduces the target-binding amount of platinum to mtDNA and exerts a protective effect on cisplatin-induced renal injury through SIRT3, which may provide a new strategy for the treatment of cisplatin-induced nephrotoxicity.  相似文献   
53.
Transmembrane proteins participate in various physiological activities in plants, including signal transduction, substance transport, and energy conversion. Although more than 20% of gene products are predicted to be transmembrane proteins in the genome era, due to the complexity of transmembrane domains they are difficult to reliably identify in the predicted protein, and they may have different overall three-dimensional structures. Therefore, it is challenging to study their biological function. In this review, we describe the typical structures of transmembrane proteins and their roles in plant growth, development, and stress responses. We propose a model illustrating the roles of transmembrane proteins during plant growth and response to various stresses, which will provide important references for crop breeding.  相似文献   
54.
The central nervous system (CNS) controls and regulates the functional activities of the organ systems and maintains the unity between the body and the external environment. The advent of co-culture systems has made it possible to elucidate the interactions between neural cells in vitro and to reproduce complex neural circuits. Here, we classified the co-culture system as a two-dimensional (2D) co-culture system, a cell-based three-dimensional (3D) co-culture system, a tissue slice-based 3D co-culture system, an organoid-based 3D co-culture system, and a microfluidic platform-based 3D co-culture system. We provide an overview of these different co-culture models and their applications in the study of neural cell interaction. The application of co-culture systems in virus-infected CNS disease models is also discussed here. Finally, the direction of the co-culture system in future research is prospected.  相似文献   
55.
Cashmere is initiated and develops in the fetal stages and the number and density of secondary hair follicles (SHFs) determine cashmere production and quality. Growing evidence indicates that both microRNA (miRNA) and long non-coding RNA (lncRNA) play an indispensable role in hair follicle (HF) growth and development. However, little is known about miRNAs, lncRNAs, and their functions as well as their interactions during cashmere initiation and development. Here, based on lncRNA and miRNA high-throughput sequencing and bioinformatics analysis, we identified 10,485 lncRNAs, 40,639 mRNAs, and 605 miRNAs in cashmere goat skin during HF induction, organogenesis, and cytodifferentiation stages. Among them, 521 lncRNAs, 5976 genes, and 204 miRNAs were differentially expressed (DE). KEGG analysis of DE genes indicated that ECM–receptor interaction and biosynthesis of amino acids were crucial for HF development. Notch, TGF-beta, and Wnt signaling pathways were also identified, which are conventional pathways associated with HF growth and development. Then, the ceRNA regulatory network was constructed, and the impact of lncRNA H19 was investigated in dermal papilla (DP) cells. The MTT, CCK-8, and EdU assays showed that the viability and proliferation of DP cells were promoted by H19, and mechanistic studies suggested that H19 performed its function through the chi-miR-214-3p/β-catenin axis. The present study created a resource for lncRNA, miRNA, and mRNA studies in cashmere morphogenesis. It could contribute to a better understanding of the molecular mechanism of ncRNAs involved in the regulation of HF growth and development.  相似文献   
56.
对带式输送机日常生产应用中受料段产生的缓冲托辊磨损、撒料等常见问题进行相关分析,结合带式输送机受料段的结构特点和应用情况进行相应改进,以达到提高带式输送机使用效率、延长输送机使用寿命的目的.  相似文献   
57.
路向阳  孙丽娟  方向前  胡进  贾丽娟 《光电工程》2018,45(6):170739-1-170739-7
由于弹性波传播动力学方程较复杂,若通过材料参数设计控制弹性波的传播路径,难以获得准确的设计结果。通常在对弹性波材料进行设计时,需要根据实际情况(如高频条件),对动力学方程进行简化或者近似才可以设计出基于弹性波的相应器件。由于这种设计方法的阻抗匹配和介质材料的无损要求难以满足,使得在设计弹性波传播器件过程中出现散射现象,而且往往散射的波形还是频变的信号,因此,在评价弹性波器件设计优劣时,散射现象的大小标志着设计效果的好坏,成为评价设计的手段和工具。但是,散射现象往往仅根据肉眼观察,难以准确地描述,无法给出定量的结果进行说明。为此,本文提出的分数阶Fourier变换(FRFT)对频变信号具有良好的聚焦特性,可利用频率变化的调频率,定量描述散射效应的大小,给出弹性波传播控制散射效应的一种定量的描述方法,降低散射程度认知的盲目性,为简化材料介质参数的设计提供依据。  相似文献   
58.
为开发出高性能生物医用干式电极,提出了利用激光微铣-重铸加工方法,实现了表面具有微结构阵列特征的新型金属干式电极的制造成形。在分析电极表面微观形貌的基础上,研究了电极表面的润湿性能,并重点研究了扫描间距、扫描速度和扫描次数等加工参数对大肠杆菌粘附性能的影响规律。研究结果表明:在一定工艺参数条件下所加工出具有微结构阵列特征的电极的接触角可达150°以上,表现出超疏水的特性。在不同扫描间隙和扫描次数条件下加工出的电极对大肠杆菌的粘附性能具有较大影响,在选择0.1 mm扫描间隙时,电极表面粘附的大肠杆菌数量最少,适当增加扫描次数,也能够有效地减少电极表面大肠杆菌的粘结,从而发挥较好的抗菌效果。通过改变扫描速度加工出的电极则对大肠杆菌的粘附性能影响不大。  相似文献   
59.
张强  赵江海  袁雅薇  方世辉 《光电工程》2017,44(11):1107-1115
针对单一传感器在动态场景感知问题上的局限性,设计了一种融合激光与视觉的实现系统,并对运动检测中的背景显露区误判问题和融合中不同传感器间点云的失配问题分别提出了改进算法。在运动检测上,首先基于视觉的背景差分算法对激光进行前景点分拣,再以激光前景点为启发信息进行视觉前景聚类。在融合失配问题上,首先基于栅格失配度分别对激光和视觉点云进行聚类分割,再以激光为基准,逐一将对应的视觉点云与之配准,滤除噪声后所得到的矫正点云可用于场景重建进行进一步验证。实验结果表明,改进算法所获得的融合前景对"影子"有更好的鲁棒性;较之整体配准的矫正,改进算法在平均失配度上降低了约75%,在y和z方向上的偏移比收敛了至少5%。  相似文献   
60.
Arbitrary micro-scale three-dimensional (3D) structures fabrication is a dream to achieve many exciting goals that have been pursued for a long time. Among all these applications, the direct 3D printing to fabricate human organs and integrated photonic circuits are extraordinary attractive as they can promote the current technology to a new level. Among all the 3D printing methods available, two-photon polymerization (2PP) is very competitive as it is the unique method to achieve sub-micron resolution to make any desired tiny structures. For the conventional 2PP, the building block is the photoresist. However, the requirement for the building block is different for different purposes. It is very necessary to investigate and improve the photoresist properties according to different requirements. In this paper, we presented one hybrid method to modify the mechanical strength and light trapping efficiency of the photoresist, which transfers the photoresist into the micro-concretes. The micro-concrete structure can achieve ±22% strength modification via a silica nano-particles doping. The structures doped with gold nano-particles show tunable plasmonic absorption. Dye doped hybrid structure shows great potential to fabricate 3D micro-chip laser.  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