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   29744篇
  免费   3208篇
  国内免费   1854篇
电工技术   2287篇
技术理论   1篇
综合类   2351篇
化学工业   4395篇
金属工艺   1627篇
机械仪表   1919篇
建筑科学   2589篇
矿业工程   848篇
能源动力   841篇
轻工业   2116篇
水利工程   680篇
石油天然气   1431篇
武器工业   338篇
无线电   3788篇
一般工业技术   3400篇
冶金工业   1290篇
原子能技术   410篇
自动化技术   4495篇
  2024年   183篇
  2023年   570篇
  2022年   1082篇
  2021年   1543篇
  2020年   1118篇
  2019年   923篇
  2018年   1035篇
  2017年   1040篇
  2016年   891篇
  2015年   1312篇
  2014年   1649篇
  2013年   1823篇
  2012年   2101篇
  2011年   2240篇
  2010年   2122篇
  2009年   1892篇
  2008年   1832篇
  2007年   1743篇
  2006年   1580篇
  2005年   1311篇
  2004年   972篇
  2003年   1003篇
  2002年   1113篇
  2001年   972篇
  2000年   677篇
  1999年   517篇
  1998年   347篇
  1997年   268篇
  1996年   210篇
  1995年   175篇
  1994年   129篇
  1993年   120篇
  1992年   82篇
  1991年   38篇
  1990年   39篇
  1989年   39篇
  1988年   34篇
  1987年   17篇
  1986年   9篇
  1985年   9篇
  1984年   8篇
  1983年   8篇
  1982年   5篇
  1981年   7篇
  1980年   6篇
  1979年   4篇
  1959年   6篇
  1951年   2篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
The practical application of sodium metal batteries (SMBs) is hampered due to the inferior interfacial stability between Na metal and conventional electrolytes....  相似文献   
92.
The culture of keratinocytes on flexible membranes has been proposed as a means to simplify, accelerate and improve the efficiency with which proliferating cells are delivered to full thickness or non-healing skin defects. The purpose of this article was to study the ability of chitosan-gelatin manbranes to facilitate the growth of human keratinocytes. The membranes with different chitosan contents were studied. The surface properties of chitosan-gelatin membranes were investigate by SEM, and water contact angle test. The mechanical property of the membranes was tested. Data implied that gelatin could make the membranes more flexible and hydrophilic than chitosan membranes, which may regulate the seeded cells behavior. Loading human keratinocytes on chitosan-gelatin membranes, cells attachment, spread, and growth were investigated by light microscopy, SEM, and MTT test. The results suggested that the adhesion and proliferation of keratinocytes seeded on chitosan-gelatin membranes were same as on tissue culture plate, in which gelatin could modify the interaction between keratinocytes and chitosan membranes. Therefore, chitosan-gelatin membrane is a good candidate for keratinocytes delivery system.  相似文献   
93.
Li L  Li T  Wang S  Zhu S  Zhang X 《Nano letters》2011,11(10):4357-4361
On the basis of a novel phase modulation method by in-plane diffraction processes, a well-designed nanoarray on metal surface is proposed to realize a broad band focusing (bandwidth ~100 nm) and a demultiplexing element (resolution ~12 nm) of surface plasmon polariton (SPP) waves. Moreover, sublattice arrays are developed to achieve an improved demultiplexer and confocal SPP beams. The proposed scheme with implemented functionalities is designed totally in planar dimension, which is free of the SPP coupling process and indicates more practical application in photonic integrations.  相似文献   
94.
燃烧器是锅炉燃烧系统的重要组成部分,针对湖南金信公司4'煤粉锅炉出现的燃烧不稳、不能负压运行、锅炉容易熄火、渣可燃物含量高等问题进行了分析,选择钝体燃烧器来代替普通直流燃烧器,设计出了一种新型钝体燃烧器,运行结果表明,飞灰含碳量Cfh=13.6%,较改前降低了5.4%,锅炉效率从76.74%提高到80.54%.该燃烧器具有较强的稳燃和负荷调节能力等优越性能,具有较好经济效益并有推广应用价值.  相似文献   
95.
Plasma behaviour and the scaling relations in a coaxial plasma opening switch (POS) using hydrogen plasma are studied self-consistently based on the two-dimensional magnetohydrodynamic (MHD) equations in conjunction with the generalized Ohm's law. The vacuum region on the right of POS is included in the model and the influence of downstream flow on the conduction characteristics is discussed. It is found that with the penetration of magnetic field, the pure hydrogen plasma is pushed downstream significantly; and POS still conducts current after the magnetic field arrives at the load edge of POS, which is different from the previous experimental results in a multispecies POS. It is because that the noticeable downstream plasma in the pure hydrogen POS may continue to conduct the current, while in the multispecies POS, the downstream plasma is unimportant so that the conduction phase ends soon after the magnetic field reaches the load edge. The scaling relation obtained from the simulations including the downstream region is consistent with the experimental results.  相似文献   
96.
三维CAD在虚拟环境中有着广泛的应用,其模型数据由于具有复杂的结构且拥有较多的冗余信息而不能高效的运用到虚拟环境的构建中。基于此,针对虚拟场景渲染对数据模型的要求,给出了三维CAD模型数据优化及重组方法,该方法能去除冗余信息,优化文件结构,丰富数据内容,且能够有效地提高虚拟环境的绘制效率。  相似文献   
97.
小目标检测作为目标检测中一项极具挑战性的项目, 广泛分布于日常生活中, 在视频监控场景中, 距离摄像头约20 m远处的行人人脸就可以被认为是小目标. 由于人脸可能相互遮挡并容易受到噪声和天气光照条件的影响, 现有的目标检测模型在这类小目标上的性能劣于中大型目标. 针对此类问题, 本文提出了改进后的YOLOv7模型, 添加了高分辨率检测头, 并基于GhostNetV2对骨干网络进行了改造; 同时基于BiFPN和SA注意力模块替换PANet结构, 增强多尺度特征融合能力; 结合Wasserstein距离改进了原来的CIoU损失函数, 降低了小目标对锚框位置偏移的敏感性. 本文在公开数据集VisDrone2019以及自制的视频监控数据集上进行了对比实验. 实验表明, 本文提出的改进方法mAP指标在VisDrone2019数据集上提高到了50.1%, 在自制视频监控数据集上高于现有方法1.6个百分点, 有效提高了小目标检测的能力, 并在GTX1080Ti上达到了较好的实时性.  相似文献   
98.
Circular RNAs (circRNAs), a class of new endogenous non-coding RNAs (ncRNAs), are closely related to the carcinogenic process and play a critical role in tumor metastasis. CircRNAs can lay the foundation for tumor metastasis via promoting tumor angiogenesis, make tumor cells gain the ability of migration and invasion by regulating epithelial-mesenchymal transition (EMT), interact with immune cells, cytokines, chemokines, and other non-cellular components in the tumor microenvironment, damage the normal immune function or escape the immunosuppressive network, and further promote cell survival and metastasis. Herein, based on the characteristics and biological functions of circRNA, we elaborated on the effect of circRNA via circRNA-associated competing endogenous RNA (ceRNA) network by acting as miRNA/isomiR sponges on tumor angiogenesis, cancer cell migration and invasion, and interaction with the tumor microenvironment (TME), then explored the potential interactions across different RNAs, and finally discussed the potential clinical value and application as a promising biomarker. These results provide a theoretical basis for the further application of metastasis-related circRNAs in cancer treatment. In summary, we briefly summarize the diverse roles of a circRNA-associated ceRNA network in cancer metastasis and the potential clinical application, especially the interaction of circRNA and miRNA/isomiR, which may complicate the RNA regulatory network and which will contribute to a novel insight into circRNA in the future.  相似文献   
99.
宁研彤  陈想  冯一佳 《轮胎工业》2024,44(7):0430-0433
以245/45R18 100W轮胎为例,研究缆型钢丝圈替代六角形钢丝圈在半钢轿车子午线轮胎中的应用。结果表明,采用缆型钢丝圈生产工艺性能良好,可有效减小轮胎质量,降低滚动阻力,提高抗撞击性能,显著增强轮胎在使用过程中的抗风险能力。  相似文献   
100.
踢球阶梯式程序教学法是指在踢球教学中按照踢球技术动作难度设定一定的程序,指导学生逐步提高踢球技术水平的教学方法。实践证明,踢球阶梯式程序教学法比传统踢球教学法有明显的成效。  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