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   37398篇
  免费   1350篇
  国内免费   57篇
电工技术   392篇
综合类   29篇
化学工业   7490篇
金属工艺   748篇
机械仪表   762篇
建筑科学   2009篇
矿业工程   114篇
能源动力   1090篇
轻工业   3029篇
水利工程   450篇
石油天然气   130篇
武器工业   5篇
无线电   2596篇
一般工业技术   6313篇
冶金工业   6689篇
原子能技术   274篇
自动化技术   6685篇
  2023年   274篇
  2022年   469篇
  2021年   778篇
  2020年   544篇
  2019年   645篇
  2018年   804篇
  2017年   716篇
  2016年   861篇
  2015年   777篇
  2014年   1080篇
  2013年   2432篇
  2012年   1729篇
  2011年   2129篇
  2010年   1697篇
  2009年   1596篇
  2008年   1843篇
  2007年   1815篇
  2006年   1619篇
  2005年   1457篇
  2004年   1203篇
  2003年   1151篇
  2002年   1073篇
  2001年   715篇
  2000年   562篇
  1999年   598篇
  1998年   611篇
  1997年   598篇
  1996年   559篇
  1995年   582篇
  1994年   530篇
  1993年   518篇
  1992年   501篇
  1991年   295篇
  1990年   423篇
  1989年   393篇
  1988年   320篇
  1987年   356篇
  1986年   314篇
  1985年   422篇
  1984年   422篇
  1983年   321篇
  1982年   296篇
  1981年   281篇
  1980年   273篇
  1979年   270篇
  1978年   247篇
  1977年   226篇
  1976年   207篇
  1975年   194篇
  1974年   173篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
52.
The intestinal epithelium is a principal site for environmental agents’ detection. Several inflammation- and stress-related signalling pathways have been identified as key players in these processes. However, it is still unclear how the chronic intake of inadequate nutrients triggers inflammatory signalling pathways in different intestinal regions. We aimed to evaluate the impact of unhealthy dietary patterns, starting at a younger age, and the association with metabolic dysfunction, intestinal inflammatory response, and obesity in adulthood. A rat model was used to evaluate the effects of the consumption of sugary beverages (HSD) and a Western diet (WD), composed of ultra-processed foods. Both diets showed a positive correlation with adiposity index, but a positive correlation was found between the HSD diet and the levels of blood glucose and triglycerides, whereas the WD diet correlated positively with triglyceride levels. Moreover, a distinct inflammatory response was associated with either the WD or HSD diets. The WD induced an increase in TLR2, TLR4, and nuclear factor-kappa B (NF-κB) intestinal gene expression, with higher levels in the colon and overexpression of the inducible nitric oxide synthase. In turn, the HSD diet induced activation of the TLR2-mediated NF-κB signalling pathway in the small intestine. Altogether, these findings support the concept that early intake of unhealthy foods and nutrients are a main exogenous signal for disturbances of intestinal immune mechanisms and in a region-specific manner, ultimately leading to obesity-related disorders in later life.  相似文献   
53.
Alzheimer’s disease (AD) is the most common form of dementia, but there is still no available treatment. Δ9-tetrahydrocannabinol (THC) is emerging as a promising therapeutic agent. Using THC in conventional high doses may have deleterious effects. Therefore, we propose to use an ultra-low dose of THC (ULD-THC). We previously published that a single injection of ULD-THC ameliorated cognitive functioning in several models of brain injuries as well as in naturally aging mice. Here, 5xFAD AD model mice received a single treatment of ULD-THC (0.002 mg/kg) after disease onset and were examined in two separate experiments for cognitive functions, neurotropic, and inflammatory factors in the hippocampus. We show that a single injection of ULD-THC alleviated cognitive impairments in 6- and 12-month-old 5xFAD mice. On the biochemical level, our results indicate an imbalance between the truncated TrkB receptor isoform and the full receptor, with AD mice showing a greater tendency to express the truncated receptor, and ULD-THC improved this imbalance. We also investigated the expression of three AD-related inflammatory markers and found an ameliorating effect of ULD-THC. The current research demonstrates for the first time the beneficial effects of a single ultra-low dose of THC in a mouse model of AD after disease onset.  相似文献   
54.
参考人体行走电压的测试标准IEC 61340-4-5, 搭建了电缆由线轴上绕下并在地板上拖拽积累的电压的测试系统, 测量了六类非屏蔽网线的电压波形.基于实测电缆电压波形, 提出了电缆电压的RC等效电路模型, 并分析了模型参数对电缆电压时域波形的影响.进行了电缆充电后对金属靶的放电实验, 测量了电缆放电事件的电流波形、瞬态电场和瞬态磁场波形, 分析了电缆放电事件对电子设备的影响.根据测量的电缆放电事件的电流波形, 对比了GJB 151B中CS 115电缆束注入脉冲激励传导敏感度的电流波形, 二者电流波形有一定的相似性, 但是对于较长电缆在电流的强度和宽度方面都会大于CS 115规定的限值.因此, 提出了电缆放电事件的防护方法, 并对相关标准的改进方面提出了初步建议.  相似文献   
55.
Color vision is used throughout medicine to interpret the health and status of tissue. Ionizing radiation used in radiation therapy produces broadband white lig...  相似文献   
56.
近来,如果稍稍留意就会看到,Linux正日益迅速地被用作手机开发的平台,依托Linux进行手机应用的开发正方兴未艾。尽管现在已有不少国家把Linux作为开发重点,但中国却一直走在移动Linux应用开发的前沿。现在,整个亚洲和欧洲众多大公司已经确定要使Linux在手机市场占据一席之地。这将为中国主要的手机厂商带来更多重要商机。  相似文献   
57.
In the present paper, new results using in situ video are presented regarding boiling water reactor (BWR) control blade degradation up to 1750 K at the beginning of a nuclear severe accident. Energy-dispersive X-ray spectrometry (EDS) mapping indicated stratification of the absorber blade melt with formation of a chromium and boride-enriched layer. High-content-B- and C-containing material with increased melting temperature acted like a shielding and was found to prevent further relocation of control blade claddings. The interacted layers around the B4C-granules prevented direct steam attack of residual B4C. The results provide new insights for understanding of the absorber blade degradation mechanism under reducing conditions specific to Fukushima Dai-Ichi Unit 2 resulting from prolonged steam starvation.  相似文献   
58.
大数据时代对大容量磁盘的需求日益增长,而在对现有的磁盘不进行较大改动的前提下,叠瓦式磁记录技术SMR是提高磁盘存储容量的最佳选择.近年来,兴起了一种新的磁记录技术——交错式磁记录技术IMR,它可以获得比SMR更高的存储密度和随机写性能.首先介绍了SMR磁盘的内部叠瓦式结构以及由此带来的数据写放大问题,并对缓解数据写放大问题的数据管理方式、性能特性评测以及基于SMR的上层应用系统方面的研究进展进行了概述;然后对新兴的IMR磁盘内部结构及其数据写放大问题进行了介绍,并对其将来的研究方向做了一定的分析和展望;最后对SMR磁盘和IMR磁盘在存储密度、数据写性能等方面进行了比较分析.当前有很多基于SMR磁盘的上层应用系统,这表明SMR磁盘可以高效地替代传统磁盘来构建大型的存储系统,而IMR磁盘的优势也将使其未来的发展前景可期.  相似文献   
59.
In this work, we deepen in the characterization of two protic ionic liquids (PILs), ethylammonium nitrate (EAN) and propylammonium nitrate (PAN). With this aim, we determined the influence of inorganic nitrate salts addition on their physical properties and their electrochemical potential window (EPW). Thus, experimental measurements of electrical conductivity, density, viscosity, refractive index and surface tension of mixtures of {EAN or PAN + LiNO3, Ca(NO3)2, Mg(NO3)2 or Al(NO3)3} at a temperature range between 5 and 95 °C are presented first, except for the last two properties which were measured at 25 °C. In the second part, the corresponding EPWs were determined at 25 °C by linear sweep voltammetry using three different electrochemical cells. Effect of the salt addition was associated mainly with the metal cation characteristics, so, generally, LiNO3 showed the lower influence, followed by Ca(NO3)2, Mg(NO3)2 or Al(NO3)3. The results obtained for the EAN + LiNO3 mixtures, along with those from a previous work, allowed us to develop novel predictive equations for most of the presented physical properties as functions of the lithium salt concentration, the temperature and the water content. Electrochemical results showed that a general order of EPW can be established for both PILs, although exceptions related to measurement conditions and the properties of the mixtures were found.  相似文献   
60.
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