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   23658篇
  免费   2896篇
  国内免费   1299篇
电工技术   2157篇
综合类   2311篇
化学工业   2057篇
金属工艺   523篇
机械仪表   1517篇
建筑科学   3053篇
矿业工程   350篇
能源动力   900篇
轻工业   4859篇
水利工程   691篇
石油天然气   853篇
武器工业   296篇
无线电   1570篇
一般工业技术   3026篇
冶金工业   1186篇
原子能技术   467篇
自动化技术   2037篇
  2024年   74篇
  2023年   516篇
  2022年   957篇
  2021年   1226篇
  2020年   1155篇
  2019年   1012篇
  2018年   891篇
  2017年   1060篇
  2016年   1104篇
  2015年   1162篇
  2014年   1429篇
  2013年   1561篇
  2012年   2047篇
  2011年   2078篇
  2010年   1305篇
  2009年   1274篇
  2008年   1123篇
  2007年   1255篇
  2006年   1110篇
  2005年   921篇
  2004年   711篇
  2003年   618篇
  2002年   457篇
  2001年   408篇
  2000年   322篇
  1999年   291篇
  1998年   253篇
  1997年   191篇
  1996年   164篇
  1995年   173篇
  1994年   133篇
  1993年   123篇
  1992年   108篇
  1991年   73篇
  1990年   74篇
  1989年   54篇
  1988年   48篇
  1987年   39篇
  1986年   27篇
  1985年   30篇
  1984年   26篇
  1983年   13篇
  1982年   22篇
  1980年   24篇
  1979年   22篇
  1965年   15篇
  1964年   19篇
  1963年   15篇
  1961年   13篇
  1957年   14篇
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
991.
The proliferation of the Internet has given birth to a number of complaint web sites where dissatisfied and frustrated consumers can easily articulate their opinions and comments on products, services, or companies. Little attention, however, has been paid to the influence of online complaints on potential consumers’ behaviors. This study attempts to provide the understanding of causal attribution process in the online complaining behaviors. The results showed that informational factors, such as vividness and consensus, facilitated consumers’ attribution to companies’ responsibility for the negative events, and subsequently led to changing their evaluation of the companies. In addition, we found that corporate response strategies to online complaints should be different from the conventional response strategies.  相似文献   
992.
The number of deaths in road traffic accidents in Spain exceeds three thousand people each year. Public authorities have implemented some policies with the aim to reducing this number. Among them, the improvement of road quality standards and some legal changes encouraging careful driving behavior. However, less attention has been focused on one of the issues that may be critical to reducing the number of fatalities caused by traffic accidents: a quick emergency medical care. In this paper, we use a sample of more than 1400 accidents occurred on Spanish roads in May 2004. Our objective is to analyze to which extent a reduction of the time interval between the crash and the arrival of the emergency services to the crash scene is related to a lower probability of death. Our results suggest that a 10 min reduction of the medical response time can be statistically associated with an average decrease of the probability of death by one third, both on motorways and conventional roads.  相似文献   
993.
Abstract

The delignification response in cooking and the impact of bleaching on earlywood and latewood were studied. Spruce earlywood and latewood chips were pulped by the kraft process and subsequently treated with one bleaching chemical at a time. In cooking, latewood required a higher alkali charge to reach the same kappa number. No difference in the light absorption coefficient between the different fiber types was observed. After oxygen delignification the earlywood fibers had a higher light absorption coefficient at the same kappa number. The difference in light absorbing material was maintained when bleaching was performed with chlorine dioxide, ozone, and peracetic acid. Hydrogen peroxide decreased the light absorbing structures in the earlywood to the same level as for latewood. The earlywood pulp had a higher brightness at a given kappa number than the latewood. The higher brightness remained through all bleaching operations and was primarily due to a higher light scattering ability.  相似文献   
994.
谢敏 《四川建材》2013,(6):94-95
从建筑结构模型的阻尼值出发,探讨了阻尼对反应听谱的影响,对几种特殊结构的阻尼进行了分析,因此,设计中应结合结构体系材料选取合适的阻尼比数值。  相似文献   
995.
BaZrxTi1?xO3 (x = 0.2, 0.25, 0.3) ceramics were prepared by a citrate method. The ferroelectric phase transition behavior and bias electric-field-induced dielectric nonlinearity of the ceramics were investigated. With increasing zirconium content, the phase transition behavior of the ceramics changed from a diffusion phase transition to relaxor-like behavior. Applying bias electric field in diverse manners led to differing effects on the dielectric nonlinearity, depending on the zirconium content of the ceramics. These dielectric phenomena were related to the polarization response of polar nano-regions (PNRs) embedded in the ceramics, which are macroscopically in the paraelectric state at room temperature. The characteristic parameters of PNRs were determined by fitting the dielectric constants under bias electric field to a multipolarization mechanism model. It was found that the size of PNRs was decreased with increasing zirconium content. The evolution of the phase transition behavior and dielectric nonlinearity with zirconium content was interpreted in relation to the size change of PNRs.  相似文献   
996.
该文介绍比例伺服传动技术上的一款具有突破性的产品,DF plus比例阀.该产品采用了全新专利的阀芯驱动技术——音圈驱动技术VCD(Voice Coil Drive),使该阀具有伺服阀的动态特性,比例阀的可靠耐用等优点,在最大流量下该阀仍具有极好的动态特性,适用于高精度的液压传动系统的压力,速度和位置控制.  相似文献   
997.
998.
Nylon-polystyrene microcapsules with immobilized ferroelectric liquid crystalline segments were prepared, and the permeability control of the encapsulated core material was investigated under an external electric field. A ferroelectric liquid crystal monomer possessing both mesogenicity and chirality effectively responded to an external electrical field. Permeation of the material (oxprenolol) contained in the inner aqueous core of the microcapsules was enhanced under a feeble electric field (2 V). Furthermore, it was found that the permeability of the microcapsules without the ferroelectric liquid crystal group did not depend on the external electrical field. In order to clarify the controlled release mechanism of the core material, the transmittance was quantitatively evaluated under an external electric field using a handmade polarized light transmittance apparatus.  相似文献   
999.
The effects of butadiene/styrene ratio, monomer distribution, and molecular weight distribution and branching on the pressure sensitive adhesive properties of butadiene/ styrene radial teleblock copolymers are reported. Styrene content of polymers with varying structures shows a close relation with tack response, and styrene content and structure affect solution viscosity and shear adhesion. When part of the styrene is incorporated into the polybutadiene segment to yield a block progressively enriched in styrene (tapered block), solution viscosity and shear adhesion are reduced. When the butadiene segment is replaced by a block of randomly copolymerized butadiene and styrene, the polymers provide lower solution viscosities and shear adhesion but unchanged tack.

The molecular weight distribution of the radial teleblock polymers can vary from broad, highly branched compositions to narrow molecular weight distributions of almost Iinear polymers. The latter have relatively high solution viscosity and low shear adhesion, whereas the former polymers produce moderate solution viscosity but high shear adhesion. Tack is generally unaffected.  相似文献   
1000.
Gravity dam is a typical structure that has been frequently used in the fields of water conservancy engineering, and the safety of the structure has received widespread attention recently. Due to earthquakes or other reasons, gravity dams normally have damage such as cracks in practical service. Damage in the structures can alter the structural dynamic behavior and seriously affect structural performance. Maintaining safety and integrity of the gravity dam structures requires a better understanding of dynam...  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