全文获取类型
收费全文 | 41558篇 |
免费 | 3015篇 |
国内免费 | 2026篇 |
专业分类
电工技术 | 2062篇 |
技术理论 | 1篇 |
综合类 | 3043篇 |
化学工业 | 8047篇 |
金属工艺 | 3100篇 |
机械仪表 | 2561篇 |
建筑科学 | 4906篇 |
矿业工程 | 1953篇 |
能源动力 | 1718篇 |
轻工业 | 2501篇 |
水利工程 | 862篇 |
石油天然气 | 1265篇 |
武器工业 | 750篇 |
无线电 | 2348篇 |
一般工业技术 | 6835篇 |
冶金工业 | 2761篇 |
原子能技术 | 458篇 |
自动化技术 | 1428篇 |
出版年
2024年 | 138篇 |
2023年 | 433篇 |
2022年 | 1011篇 |
2021年 | 1265篇 |
2020年 | 1203篇 |
2019年 | 933篇 |
2018年 | 911篇 |
2017年 | 1227篇 |
2016年 | 1235篇 |
2015年 | 1198篇 |
2014年 | 2062篇 |
2013年 | 2045篇 |
2012年 | 2516篇 |
2011年 | 2822篇 |
2010年 | 2238篇 |
2009年 | 2510篇 |
2008年 | 2118篇 |
2007年 | 3130篇 |
2006年 | 2797篇 |
2005年 | 2537篇 |
2004年 | 2069篇 |
2003年 | 1939篇 |
2002年 | 1594篇 |
2001年 | 1312篇 |
2000年 | 1147篇 |
1999年 | 904篇 |
1998年 | 694篇 |
1997年 | 562篇 |
1996年 | 481篇 |
1995年 | 390篇 |
1994年 | 346篇 |
1993年 | 244篇 |
1992年 | 142篇 |
1991年 | 104篇 |
1990年 | 77篇 |
1989年 | 78篇 |
1988年 | 55篇 |
1987年 | 21篇 |
1986年 | 14篇 |
1985年 | 19篇 |
1984年 | 7篇 |
1983年 | 10篇 |
1982年 | 6篇 |
1981年 | 7篇 |
1980年 | 5篇 |
1975年 | 4篇 |
1959年 | 4篇 |
1956年 | 3篇 |
1955年 | 4篇 |
1951年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
72.
73.
本对影响氧化铝熟料单筒冷却机冷却效率的因素进行了分析,并提出了相应的节能技术改造措施,取得了明显的节能效益。 相似文献
74.
Termites live in a material world: exploration of their ability to differentiate between food sources. 下载免费PDF全文
Ra Inta Joseph C S Lai Eugene W Fu Theodore A Evans 《Journal of the Royal Society Interface》2007,4(15):735-744
Drywood termites are able to assess wood size using vibratory signals, although the exact mechanism behind this assessment ability is not known. Important vibratory characteristics such as the modal frequencies of a wooden block depend on its geometry and boundary conditions; however, they are also dependent on the material characteristics of the block, such as mass, density and internal damping. We report here on choice experiments that tested the ability of the drywood termite Cryptotermes secundus to assess wooden block size using a solid wooden block paired with a composite block, the latter made of either wood and aluminium or wood and rubber. Each composite block was constructed to match mass or low-frequency vibratory modes (i.e. fundamental frequency) of the solid wooden block. The termites always chose the blocks with more wood; they moved to the solid wooden blocks usually within a day and then tunnelled further into the solid wooden block by the end of the experiment. Termites offered composite blocks of wood and rubber matched for mass were the slowest to show a preference for the solid wooden block and this preference was the least definitive of any treatment, which indicated that mass and/or damping may play a role in food assessment. This result clearly shows that the termites were not fooled by composite blocks matched for mass or frequency, which implies that they probably employ more than a single simple measure in their food assessment strategy. This implies a degree of sophistication in their ability to assess their environment hitherto unknown. The potential importance of alternative features in the vibrational signals is discussed. 相似文献
75.
分析了当前家装存在的破坏结构,一味追求奢华,施工质量差等种种误区,提出了搞好家庭装修的关键环节,对促进家装行业健康发展有积极的意义。 相似文献
76.
对采用粉末冶金与化学热处理相结合的方法研制的电触头材料进行了理化性能、显微组织和抗氧化性能试验,探讨其机理及对性能的影响因素。试验表明:所研制的触头的理化性能基本达到了国标规定的相近触头的指标,其显微组织和抗氧比性能则优于国标规定。A_(c4)加速模拟电寿命试验的结果证实该种触头材料应用前景良好。 相似文献
77.
核测井仪器受套管剩磁的影响比较严重,常常用在探测器的周围缠绕多层坡莫合金带的方法进行磁屏蔽,由于缠绕的坡莫合金圆筒不能闭合,加上缠绕过程中坡莫合金带的形变造成材料本身磁导率的下降,传统的磁屏蔽方法的效果不好。本文介绍一种简单易行、磁屏蔽效果较好的方法,实验的结果说明用电工纯铁做探测器的外壳可以达到令人满意的效果。 相似文献
78.
79.
Laura M. Haas Michael J. Carey Miron Livny Amit Shukla 《The VLDB Journal The International Journal on Very Large Data Bases》1997,6(3):241-256
In this paper, we re-examine the results of prior work on methods for computing ad hoc joins. We develop a detailed cost model for predicting join algorithm performance, and we use the model to develop cost formulas
for the major ad hoc join methods found in the relational database literature. We show that various pieces of “common wisdom” about join algorithm
performance fail to hold up when analyzed carefully, and we use our detailed cost model to derive op
timal buffer allocation schemes for each of the join methods examined here. We show that optimizing their buffer allocations
can lead to large performance improvements, e.g., as much as a 400% improvement in some cases. We also validate our cost model's
predictions by measuring an actual implementation of each join algorithm considered. The results of this work should be directly
useful to implementors of relational query optimizers and query processing systems.
Edited by M. Adiba. Received May 1993 / Accepted April 1996 相似文献
80.