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   29469篇
  免费   3709篇
  国内免费   1430篇
电工技术   4017篇
技术理论   3篇
综合类   1511篇
化学工业   2897篇
金属工艺   1058篇
机械仪表   768篇
建筑科学   1618篇
矿业工程   387篇
能源动力   5464篇
轻工业   5012篇
水利工程   961篇
石油天然气   1164篇
武器工业   203篇
无线电   2151篇
一般工业技术   2828篇
冶金工业   580篇
原子能技术   172篇
自动化技术   3814篇
  2024年   294篇
  2023年   1011篇
  2022年   1467篇
  2021年   1629篇
  2020年   1647篇
  2019年   1506篇
  2018年   1200篇
  2017年   1321篇
  2016年   1272篇
  2015年   1326篇
  2014年   2089篇
  2013年   1833篇
  2012年   2135篇
  2011年   2219篇
  2010年   1524篇
  2009年   1408篇
  2008年   1269篇
  2007年   1482篇
  2006年   1400篇
  2005年   1099篇
  2004年   991篇
  2003年   799篇
  2002年   647篇
  2001年   519篇
  2000年   435篇
  1999年   358篇
  1998年   290篇
  1997年   218篇
  1996年   204篇
  1995年   160篇
  1994年   155篇
  1993年   115篇
  1992年   109篇
  1991年   70篇
  1990年   49篇
  1989年   47篇
  1988年   45篇
  1987年   40篇
  1986年   35篇
  1985年   46篇
  1984年   27篇
  1983年   22篇
  1982年   20篇
  1981年   15篇
  1980年   9篇
  1979年   7篇
  1977年   7篇
  1976年   7篇
  1975年   7篇
  1974年   8篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
132.
��Ѩ���´����⽨�⼼��   总被引:9,自引:2,他引:7  
丁国生 《天然气工业》2003,23(2):106-108
我国的西气东输工程从新疆塔里木油田到上海,管线长度达4000公里,为确保对长江三角洲地区安全稳定的供气,就必须在长江三角洲地区建设地下储气库,从而保证在管线故障期间应急供气,同时利用地下储气库调节冬季和夏季用气量的差异,保证长输管线的高效、平稳运行。在长江三角洲地区经地库址选择,目前准备将常州盆地的金坛盐矿用以建设地下储气库。盐穴地下储气库主要选择在盐层或盐兵上,利用水溶方式形成地下溶腔进行储气,选择合适的建库地址要结合地质、水、工程等诸多因素,造腔过程中需要采取一系列控制技术,在造腔过程中还要及时采取声纳测井技术进行跟踪监测,造腔过程的检测及腔体完成后的密封安全性检测是气库能否投入运行的关键。  相似文献   
133.
研究了三种贮氢合金 L a Ni5、L a Ni4 .7Al0 .3、Ml Ni4 .5Al0 .5被 10 0× 10 - 6 CO毒化后的分形特征 ,求出这三种合金在含 10 0× 10 - 6 CO的氢中循环 ,分维分别为 0 .2 5 4 7、0 .170 9、0 .0 72 5。可以较好的解释合金被毒化的宏观现象。  相似文献   
134.
可燃气体冷冻储存安全性分析   总被引:1,自引:0,他引:1  
根据烃类和其它可燃气体液化储存的特性,比较了气体液化冷冻储存和压力液化储存在设备出现泄漏时的可燃气体释放量、释放速率和扩散范围指出,可燃气体液化冷冻储存与压力液化储存相比。储存压力低,即使出现泄漏,因其泄漏量少。泄漏速率低,扩散范围小,因而可燃气体液化冷冻储存比压力液化储存更为安全。  相似文献   
135.
Distributed active storage architectures are designed to offload user-level processing to the peripheral from the host servers. In this paper, we report preliminary investigation on performance and fault recovery designs, as impacted by emerging storage interconnect protocols and state-of-the-art storage devices. Empirical results obtained using validated device-level and interconnect data demonstrate the significance of the said parameters on the overall system performance and reliability.  相似文献   
136.
A Ml (NiCoMnA1)5 hydrogen storage alloys was prepared by double-roller rapid quenching.Its microstructure, electrochemically and kinetic characteristic were studied.A uniform crystal phase with CaCu5 structure could be detected by XRD analyses, whose average grain size is 30 ~ 50 nm and the ratio of c/a of nano-crystal hydrogen storage alloy is larger.The hydrogen absorption/desertion p - C isotherms of alloy show that its fiat-performance is perfect and the magnetic stagnant effect is very little.An simulate cell is used for electrochemical measurement.Electrode is 10C, the capacity decreasing rate via the 450 cycles at 7C is less than 20%.  相似文献   
137.
Samples of chicken meat from spent laying hens were obtained by four different methods: (1) manual deboning of whole carcasses; (2) manual deboning of skinned carcasses; (3) mechanical deboning of whole carcasses; and (4) mechanical deboning of skinned carcasses. The meat was packaged, frozen and stored at ?18 °C for up to 3 months. Functional properties studied were pH, emulsifying capacity (EC) and water‐holding capacity (WHC) and, in addition, pigment concentration was investigated. Sensory properties included aroma, colour, texture and overall acceptability, as judged by a trained panel using a nine‐point hedonic scale. Removal of the skin prior to deboning by either method gave significantly higher values (P < 0.05) for EC, while WHC values were not significantly different among the experimental treatments, despite higher pH values for mechanically‐deboned meat, with and without skin. Pigment concentrations were highest in meat from Treatment 4 and lowest for Treatment 1, but values for both methods of deboning were affected by the presence of skin. There were no significant differences between treatments for any of the sensory properties studied. Changes occurring in the meat during frozen storage are described.  相似文献   
138.
The mechanism of slip and its consequence in the process of energy storage during uniaxial tension of austenitic steel was studied. The interpretation of the energy storage process in terms of the slip development and microscopic shear band formation is presented.  相似文献   
139.
Aliquots of serum collected in a large case-control study of cervical cancer were stored at −70°C for up to 4 years during implementation of the study. When 500 μL serum aliquots were thawed in preparation for carotenoid and vitamin A assays, volumes were noticeably variable and fell below 500 μL in the majority of the samples. We were concerned about evaporation/sublimation during storage of the samples because loss of water would concentrate the analytes of interest. We evaluated the use of density and sodium ion concentration measurements to confirm its occurrence. We found that serum density was an unreliable indicator of extent of volume loss since the anticipated increases in density due to evaporation were of the same magnitude as inter-individual variation in serum density. In contrast, Na+ concentration is tightly regulated and would rise if water had been lost from the samples. In a representative sample of serum aliquots from the case-control study, 24 of 25 vials contained less than 500 μL of serum. The mean sodium ion concentration (138.1 ± 3.6 mmol/L) was within the normal range for human serum of 136–145 mmol/L, and no correlation was observed between serum volume and Na+ concentration. These results strongly suggest that the observed low volumes were not due to evaporative losses. Instead, the variably low volumes of serum aliquots were probably due to pipetting errors in the initial aliquotting resulting from the use of air-displacement pipettes.  相似文献   
140.
S. L. Grossman  S. Davidi  Haim Cohen   《Fuel》1995,74(12):1772-1775
Bituminous coal piles stored in the open air can undergo autocatalytic heating accompanied by the emission of small but appreciable amounts of molecular hydrogen. When the coal is contained in a confined space and the temperature reaches 40°C, accumulation of hydrogen is expected. This process has been observed for a wide variety of bituminous coals. The amount of hydrogen gas expected to accumulate in the air pocket above the coal cargo in ship holds (assuming that the coal's temperature approaches 40°C during the voyage) has been calculated. The results clearly indicate that in most cases the hydrogen concentration will be appreciably above the lower explosion limit in air. Hence when bituminous coals are stored in a confined space (e.g. a ship hold), the explosive risk of hydrogen should be taken into account.  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