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   17458篇
  免费   1847篇
  国内免费   808篇
电工技术   5977篇
综合类   1287篇
化学工业   1205篇
金属工艺   277篇
机械仪表   1308篇
建筑科学   314篇
矿业工程   274篇
能源动力   3585篇
轻工业   76篇
水利工程   473篇
石油天然气   1609篇
武器工业   251篇
无线电   1064篇
一般工业技术   505篇
冶金工业   185篇
原子能技术   521篇
自动化技术   1202篇
  2024年   37篇
  2023年   173篇
  2022年   345篇
  2021年   458篇
  2020年   550篇
  2019年   426篇
  2018年   423篇
  2017年   563篇
  2016年   646篇
  2015年   680篇
  2014年   1071篇
  2013年   962篇
  2012年   1408篇
  2011年   1531篇
  2010年   1061篇
  2009年   1075篇
  2008年   1027篇
  2007年   1282篇
  2006年   1106篇
  2005年   945篇
  2004年   806篇
  2003年   662篇
  2002年   565篇
  2001年   494篇
  2000年   430篇
  1999年   288篇
  1998年   217篇
  1997年   163篇
  1996年   149篇
  1995年   121篇
  1994年   74篇
  1993年   66篇
  1992年   69篇
  1991年   45篇
  1990年   38篇
  1989年   50篇
  1988年   21篇
  1987年   19篇
  1986年   11篇
  1985年   12篇
  1984年   15篇
  1983年   5篇
  1982年   8篇
  1981年   6篇
  1980年   2篇
  1979年   1篇
  1978年   1篇
  1976年   1篇
  1959年   4篇
  1951年   1篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
The spinal ejaculation generator (SEG) is located in the central gray (lamina X) of the rat lumbar spinal cord and plays a pivotal role in the ejaculatory reflex. We recently reported that SEG neurons express the oxytocin receptor and are activated by oxytocin projections from the paraventricular nucleus of hypothalamus (PVH). However, it is unknown whether the SEG responds to oxytocin in vivo. In this study, we analyzed the characteristics of the brain–spinal cord neural circuit that controls male sexual function using a newly developed in vivo electrophysiological technique. Optogenetic stimulation of the PVH of rats expressing channel rhodopsin under the oxytocin receptor promoter increased the spontaneous firing of most lamina X SEG neurons. This is the first demonstration of the in vivo electrical response from the deeper (lamina X) neurons in the spinal cord. Furthermore, we succeeded in the in vivo whole-cell recordings of lamina X neurons. In vivo whole-cell recordings may reveal the features of lamina X SEG neurons, including differences in neurotransmitters and response to stimulation. Taken together, these results suggest that in vivo electrophysiological stimulation can elucidate the neurophysiological response of a variety of spinal neurons during male sexual behavior.  相似文献   
2.
文章介绍了海外某大型火力发电厂发生的一起发电机定子接地故障的分析和处理过程,对发电厂类似故障的处理和海外发电厂的运行和维护提供了参考。  相似文献   
3.
介绍了浙江石油化工有限公司新建的3 Mt/a柴油加氢精制装置,其配套使用中国石化石油化工科学研究院有限公司开发的催化剂级配技术,并实施了可根据原料供应及市场产品需求情况灵活调整切换的2种生产技术方案。1 a的安稳生产运行结果表明:该装置以直馏柴油为主原料,通过分馏塔的馏分切割及其侧线抽出,实现了稳产国Ⅵ柴油并兼产喷气燃料技术方案的工业化应用;在实施以兼产喷气燃料为主的生产技术方案时,通过调整常一线柴油的掺炼量,不仅可以生产含硫量小于10.0 μg/g的精制柴油产品,同时兼产所得到的喷气燃料产品含硫量小于0.5 μg/g,赛波特颜色号值大于30;在实施主产精制柴油组分方案时,通过掺炼质量分数为20%~40%的催化柴油,并使所提炼得到的精制柴油组分含硫量小于6.0 μg/g的前提下,这些精制柴油组分产品既可直接作为满足国Ⅵ柴油产品出厂待售,也可作为柴油调和组分储存待用于产品的进一步优化。  相似文献   
4.
吕薇  姜根山  刘月超  张伟 《声学技术》2022,41(6):789-795
为了研究温度分布对于管阵列结构中的声透射特性的影响,以核电站的实际工况为背景,构建了不同的温度场以及周期性变化的非均匀温度场,利用有限元方法进行数值模拟。结果表明:(1)温度分布会改变管阵列声透射频谱的“禁带”宽度以及中心频率位置。在同一介质中,温度变化对频率较高位置的影响大于频率较低的位置。(2)在同样为10℃的温度差下,当水的平均声速为1 653 m·s-1、饱和水蒸气的平均声速为522.5 m·s-1时,介质为水时的禁带宽度及中心频率位置变化较大,即声速大的介质的频谱对于温度的变化更敏感。(3)当温度差在10℃以内,在周期性变化的非均匀温度场和与均匀温度场中管阵列声透射特性在第一中心频率23 996.1 Hz之前,两频谱差别很小,在第一禁带之后会出现明显区别。该研究成果对完善核电站应用的声学检测提供了理论基础。  相似文献   
5.
As one of the cleanest energies, hydrogen has attracted much attention over the past decade. Hydrogen can be produced using water electrolysis in a Proton Exchange Membrane Electrolysis Cell (PEMEC). In the present study, the performance of the PEMEC, powered by the Photovoltaic-Thermal (PVT) system, is scrutinized. It is considered that the PVT system provides the required electrical power of the PEMEC and preheats the feedwater. A comprehensive numerical model of the coupled PVT-PEMEC system is developed. The model is used to investigate the effect of various operating parameters, including solar radiation intensity, inlet feedwater temperature, and feedwater mass flow rate, on the hydrogen production and operating voltage of the PEMEC at various Exchange Current Densities (ECDs). Furthermore, the effect of integration of Phase Change Material (PCM) and Thermoelectric Generator (TEG) on the hydrogen production of the system is evaluated. According to the obtained results, the PVT-TEG-PEMEC system outperforms other systems in hydrogen production. However, integration of the PVT-PEMEC system with PCM has a negligible effect on its hydrogen production.  相似文献   
6.
《Ceramics International》2022,48(8):10852-10861
Carbon cloth was used as a flexible substrate for bismuth telluride (Bi2Te3) particles to provide flexibility and improve the overall thermoelectric performance. Bi2Te3 on carbon cloth (Bi2Te3/CC) was synthesized via a hydrothermal reaction with various reaction times. After over 12 h, the Bi2Te3 particles showed a clear hexagonal shape and were evenly adhered to the carbon cloth. Selenium (Se) atoms were doped into the Bi2Te3 structure to improve its thermoelectric performance. The electrical conductivity increased with increasing Se-dopant content until 40% Se was added. Moreover, the maximum power factor was 1300 μW/mK2 at 473 K for the 30% Se-doped sample. The carbon cloth substrate maintained its electrical resistivity and flexibility after 2000 bending cycles. A flexible thermoelectric generator (TEG) fabricated using the five pairs of 30% Se-doped sample showed an open-circuit voltage of 17.4 mV and maximum power output of 850 nW at temperature difference ΔT = 30 K. This work offers a promising approach for providing flexibility and improving the thermoelectric performance of inorganic thermoelectric materials for wearable device applications using flexible carbon cloth substrate for low temperature range application.  相似文献   
7.
On-site hydrogen production through steam-methane reforming (SMR) from city gas or natural gas is believed to be a cost-effective way for hydrogen-based infrastructure due to high cost of hydrogen transportation. In recent years, there have been a lot of on-site hydrogen fueling stations under design or construction in China. This study introduces current developments and technology prospects of skid-mounted SMR hydrogen generator. Also, technical solutions and economic analysis are discussed based on China's first on-site hydrogen fueling station project in Foshan. The cost of hydrogen product from skid-mounted SMR hydrogen generator is about 23 CNY/kg with 3.24 CNY/Nm3 natural gas. If hydrogen price is 60 CNY/kg, IRR of on-site hydrogen fueling station project reaches to 10.8%. While natural gas price fall to 2.3 CNY/Nm3, the hydrogen cost can be reduced to 18 CNY/kg, and IRR can be raised to 13.1%. The conclusion is that skid-mounted SMR technology has matured and is developing towards more compact and intelligent design, and will be a promising way for hydrogen fueling infrastructures in near future.  相似文献   
8.
周赛  李龙  刘宜树 《同位素》2019,32(3):171-177
与裂变型99Mo-99mTc发生器相比,凝胶型99Mo-99mTc发生器制备99mTc具有工艺简单、产生的放射性废物容易处理、对环境影响小等优点。本文主要论述了凝胶型99Mo-99mTc发生器与裂变型99Mo-99mTc发生器的区别,堆照生产99Mo原料和凝胶材料的研究进展,凝胶结构以及凝胶组分等多种条件因素对凝胶型99Mo-99mTc发生器性能的影响等,并对低比活度99Mo生产99mTc的研究进展进行综述。  相似文献   
9.
针对幅频特性信息采集的专用仪器价格昂贵的问题,自主研制了基于通用信号源和频谱仪的幅频特性测试系统,运用LabVIEW编程语言设计了测试系统软件,实现了仪器的自动控制,数据的自动处理、分析、显示和存储等功能。对前置功率放大器进行了实际测试,将测试结果和Agilent N5230A矢量网络分析仪的测试结果进行了对比,验证了所开发的幅频特性测试系统的有效性。  相似文献   
10.
《Oil and Energy Trends》2019,44(8):37-45
Current data of world oil demand. This includes international bunkers and refinery fuel. Updated on a monthly basis. Current data of oil demand from counties such as Canada, the United States of America, Japan, OECD Europe, Belgium, France, Germany, Italy, Netherlands, Spain, Sweden, the United Kingdom, Australia, Mexico, Republic of Korea, and Turkey. Updated on a monthly basis. Current data for crude oil and refined product stocks in Canada, Chile, Mexico, the United States (Western Hemisphere), France, Germany, Italy, Netherlands, Spain, the United Kingdom and Other Europe (Europe), Japan, Republic of Korea, Other Pacific (Asia-Pacific), and Total OECD (Table 12.1) Current data for refined product stocks in the OECD Western Hemisphere, OECD Europe, OECD Asia-Pacific and Total OECD. Products include gasoline, diesel and gasoil, and heavy fuel oil. Updated on a monthly basis (Table 12.2).  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