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   34226篇
  免费   2746篇
  国内免费   1199篇
电工技术   1584篇
综合类   1954篇
化学工业   6078篇
金属工艺   1615篇
机械仪表   1965篇
建筑科学   3062篇
矿业工程   628篇
能源动力   1113篇
轻工业   2146篇
水利工程   495篇
石油天然气   1886篇
武器工业   242篇
无线电   4236篇
一般工业技术   4526篇
冶金工业   1843篇
原子能技术   467篇
自动化技术   4331篇
  2024年   345篇
  2023年   584篇
  2022年   862篇
  2021年   1196篇
  2020年   969篇
  2019年   752篇
  2018年   846篇
  2017年   996篇
  2016年   914篇
  2015年   1153篇
  2014年   1489篇
  2013年   1901篇
  2012年   1980篇
  2011年   2146篇
  2010年   1807篇
  2009年   1808篇
  2008年   1762篇
  2007年   1740篇
  2006年   1777篇
  2005年   1603篇
  2004年   1109篇
  2003年   987篇
  2002年   983篇
  2001年   833篇
  2000年   912篇
  1999年   985篇
  1998年   972篇
  1997年   790篇
  1996年   787篇
  1995年   646篇
  1994年   506篇
  1993年   456篇
  1992年   315篇
  1991年   233篇
  1990年   239篇
  1989年   168篇
  1988年   142篇
  1987年   97篇
  1986年   78篇
  1985年   59篇
  1984年   49篇
  1983年   36篇
  1982年   33篇
  1981年   20篇
  1980年   20篇
  1979年   10篇
  1977年   10篇
  1976年   12篇
  1973年   8篇
  1970年   7篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
塔机多采用4根桩承载,施工既复杂,又增加材料用量.本项新技术采用单桩承台式基础来抵抗塔机的倾覆,保持整体稳定性,是在深回填土区和深基坑边施工塔机基础最经济合理的施工方法.该施工方法在重庆市区已实施8个塔机基础,回填土深度10~20m,取得良好的效果.该技术是塔机深基础新型的施工方法,技术先进,工艺简单,施工方便,具有创新性.  相似文献   
62.
The successive approximation register (SAR) is one of the most energy-efficient analog-to-digital converter (ADC) architecture for medium-resolution applications. However, its high energy efficiency quickly diminishes when the target resolution increases. This is because a SAR ADC suffers from several major error source, including the sampling kT/C noise, the comparator noise, and the DAC mismatch. These errors are increasing hard to address in high-resolution SAR ADCs. This paper reviews recent advances on error suppression techniques for SAR ADCs, including the sampling kT/C noise reduction, the noise-shaping (NS) SAR, and the mismatch error shaping (MES). These techniques aim to boost the resolution of SAR ADCs while maintaining their superior energy efficiency.  相似文献   
63.
建立雷诺方程的一种新概念   总被引:2,自引:2,他引:0  
针对工程应用中所存在的多种具体物理形式和多种工况条件的流体膜润滑型式,归纳给出了3类典型摩擦副流体膜润滑所对应的3种微圆柱流量物理模型、几何楔和有效法向速度差特征式的概念,由可压缩流微圆柱流量连续方程导出了有关的常用支承流体膜润滑广义雷诺方程。这样使分析方法和物理意义简明;同时还修正了此前长期被一些广为流传的专著或论文所忽视的有关问题;并给出了一些对基本形式雷诺方程润滑理论的实验验证。  相似文献   
64.
周军  沈林明 《华中建筑》2006,24(11):46-49
城市化进程不仅改变了传统土地组织结构与社会文化,也导致了日益严重的都市犯罪问题.特别是有些大城市随着城市发展出现了“城市死角”。该文主要探讨以合理的设计手法来倡导符合具体都市功能的环境设计,达到预防犯罪的目的,抵制城市死角。研究选取上海市典型的高架桥底舟固为模型,找出较为合理的设计通用手法来处理高架公园问题,旨在尽可能地使用城市集约空间,消除城市“死角”现象,  相似文献   
65.
介绍了国内第一套氨汽提尿素装置关键设备汽提塔的运行、倒头及垢层物理清洗情况。  相似文献   
66.
The ability of Pluronic F127 (PF127) conjugated with tetrapeptide Gly-Arg-Gly-Asp (GRGD) as a sequence of Arg-Gly-Asp (RGD) peptide to form the investigated potential hydrogel (hereafter referred to as 3DG bioformer (3BE)) to produce spheroid, biocompatibility, and cell invasion ability, was assessed in this study. The fibroblast cell line (NIH 3T3), osteoblast cell line (MG-63), and human breast cancer cell line (MCF-7) were cultured in the 3BE hydrogel and commercial product (Matrigel) for comparison. The morphology of spheroid formation was evaluated via optical microscopy. The cell viability was observed through cell counting Kit-8 assay, and cell invasion was investigated via Boyden chamber assay. Analytical results indicated that 3BE exhibited lower spheroid formation than Matrigel. However, the 3BE appeared biocompatible to NIH 3T3, MG-63, and MCF-7 cells. Moreover, cell invasion ability and cell survival rate after invasion through the 3BE was displayed to be comparable to Matrigel. Thus, these findings demonstrate that the 3BE hydrogel has a great potential as an alternative to a three-dimensional cell culture for drug screening applications.  相似文献   
67.
Mammalian adipose tissue can be divided into white and brown adipose tissue based on its colour, location, and cellular structure. Certain conditions, such as sympathetic nerve excitement, can induce the white adipose adipocytes into a new type of adipocytes, known as beige adipocytes. The process, leading to the conversion of white adipocytes into beige adipocytes, is called white fat browning. The dynamic balance between white and beige adipocytes is closely related to the body’s metabolic homeostasis. Studying the signal transduction pathways of the white fat browning might provide novel ideas for the treatment of obesity and alleviation of obesity-related glucose and lipid metabolism disorders. This article aimed to provide an overview of recent advances in understanding white fat browning and the role of BAT in lipid metabolism.  相似文献   
68.
Cinnamoyl-CoA reductase (CCR) is a pivotal enzyme in plant lignin synthesis, which has a role in plant secondary cell wall development and environmental stress defense. Alfalfa is a predominant legume forage with excellent quality, but the lignin content negatively affects fodder digestibility. Currently, there is limited information on CCR characteristics, gene expression, and its role in lignin metabolism in alfalfa. In this study, we identified 30 members in the CCR gene family of Medicago sativa. In addition, gene structure, conserved motif, and evolution analysis suggested MsCCR1–7 presumably functioned as CCR, while the 23 MsCCR-likes fell into three categories. The expression patterns of MsCCRs/MsCCR-likes suggested their role in plant development, response to environmental stresses, and phytohormone treatment. These results were consistent with the cis-elements in their promoters. Histochemical staining showed that lignin accumulation gradually deepened with the development, which was consistent with gene expression results. Furthermore, recombinant MsCCR1 and MsCCR-like1 were purified and the kinetic parameters were tested under four substrates. In addition, three-dimensional structure models of MsCCR1 and MsCCR-like1 proteins showed the difference in the substrate-binding motif H212(X)2K215R263. These results will be useful for further application for legume forage quality modification and biofuels industry engineering in the future.  相似文献   
69.
Vector beams, non-separable in spatial mode and polarisation, have emerged as enabling tools in many diverse applications, from communication to imaging. This a...  相似文献   
70.
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   
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