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   76085篇
  免费   5366篇
  国内免费   2969篇
电工技术   4562篇
技术理论   21篇
综合类   13677篇
化学工业   6230篇
金属工艺   2423篇
机械仪表   4307篇
建筑科学   13130篇
矿业工程   4268篇
能源动力   1791篇
轻工业   4015篇
水利工程   4771篇
石油天然气   3070篇
武器工业   445篇
无线电   5062篇
一般工业技术   4463篇
冶金工业   3591篇
原子能技术   471篇
自动化技术   8123篇
  2024年   208篇
  2023年   503篇
  2022年   1087篇
  2021年   1219篇
  2020年   1356篇
  2019年   1065篇
  2018年   1094篇
  2017年   1484篇
  2016年   1801篇
  2015年   2273篇
  2014年   5387篇
  2013年   3805篇
  2012年   5132篇
  2011年   5641篇
  2010年   4547篇
  2009年   5062篇
  2008年   4601篇
  2007年   6038篇
  2006年   5673篇
  2005年   4842篇
  2004年   3998篇
  2003年   3417篇
  2002年   2789篇
  2001年   2326篇
  2000年   1983篇
  1999年   1465篇
  1998年   963篇
  1997年   768篇
  1996年   708篇
  1995年   604篇
  1994年   515篇
  1993年   394篇
  1992年   367篇
  1991年   234篇
  1990年   212篇
  1989年   204篇
  1988年   148篇
  1987年   101篇
  1986年   82篇
  1985年   53篇
  1984年   54篇
  1983年   32篇
  1982年   20篇
  1981年   40篇
  1980年   22篇
  1979年   23篇
  1978年   10篇
  1977年   10篇
  1975年   12篇
  1973年   7篇
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
11.
孔子是否删诗,这是一个历史遗留问题。司马迁首言在前,孔颖达怀疑在后。宋之后,争议遂起,延至近代。今人夏传才先生断日:孔子是否删诗,“在没有发掘出新史料的情况下,哪怕再争论八百年,也是搞不清楚的”。以此止息纷争。话虽不错,但问题并没有解决。我认为,在没有发掘出新史料的情况下,可以从《左传》入手,来考察孔子是否删诗。  相似文献   
12.
大学在办学资源、办学过程、办学质量、办学形象的竞争中出现大量的不良倾向。大学的不良竞争是由于政府主导资源配置、资源和制度供给不足、大学系统重构等因素导致。必须通过控制主体、控制手段的转变和控制对象的发展形成新的控制机制,以保证大学竞争的秩序化和规范化。  相似文献   
13.
To obtain more biologically relevant data there is a growing interest in the use of living cells for assaying the biological activity of unknown chemical compounds. Density ‘multiplex’ cell‐based assays, where different cell types are mixed in one well and simultaneously investigated upon exposure to a certain compound are beginning to emerge. To be able to identify the cells they should be attached to microscopic carriers that are encoded. This paper investigates how digitally encoded microparticles can be loaded with cells while keeping the digital code in the microcarriers readable. It turns out that coating the surface of the encoded microcarriers with polyelectrolytes using the layer‐by‐layer (LbL) approach provides the microcarriers with a ‘highly functional’ surface. The polyelectrolyte layer allows the growth of the cells, allows the orientation of the cell loaded microcarriers in a magnetic field, and does not hamper the reading of the code. It has further been shown that the cells growing on the polyelectrolyte layer can become transduced by adenoviral particles hosted by the polyelectrolyte layer. It is concluded that the digitally encoded microparticles are promising materials for use in biomedical and pharmaceutical in‐vitro research where cells are used as tools.  相似文献   
14.
We propose a general modeling framework to evaluate the performance of cache consistency algorithms. In addition to the usual hit rate, we introduce the hit* rate as a consistency measure, which captures the fraction of non-stale downloads from the cache. We apply these ideas to the analysis of the fixed TTL consistency algorithm in the presence of network delays. The hit and hit* rates are evaluated when requests and updates are modeled by renewal processes. Classical results on the renewal function lead to various bounds.  相似文献   
15.
16.
Copper slag is a by‐product generated during smelting to extract copper metal from the ore. The copper slag obtained may exhibit pozzolanic activity and may therefore be used in the manufacture of addition‐containing cements. In this paper the effect of the incorporation of the copper slag in cement is measured. Blends of copper slag with Portland cement generally possess properties equivalent to Portland cement containing fly ash, but very different to the silica fume incorporation. Copper slag and fly ash reduce the heat of hydration more effectively than silica fume in mortars. The replacement of 30% cement by copper slag reduces the flexural and compressive strength in a similar way to fly ash; however, after 28 days, the reduction is less than the percentage of substitution. Hydrated calcium aluminate phases were analysed using scanning electron microscopy (SEM) and X‐ray diffraction (XRD) techniques. The pozzolanic activity of copper slag is similar to that of fly ash and higher than silica fume. In the presence of low water/cement ratios, certain pozzolanic materials produce a very compact cement paste that limits the space available for hydration products, a determining factor in the formation of hydrated calcium aluminates. SEM was found to be a useful analytical technique when aluminates are formed and can be clearly detected by XRD. Copyright © 2008 Society of Chemical Industry  相似文献   
17.
会计政策选择类型在理论上大体可分为机会主义型和效率(或有效契约)型。会计政策选择具有效率性,但也为经理人员的机会主义行为打开了大门。在我国,由于企业缺乏一系列有效的激励约束机制,会计政策选择的机会主义仍然严重。为此,必须建立适合我国企业有效的激励约束机制。  相似文献   
18.
High cycle fatigue of bolted connections Extensive tests regarding the influences on the fatigue of bolt‐nut‐connections of preloading with torsion, of preloading with yielding, of loading with superimposed bending and of the tested lot are processed. These influences are not yet known according to VDI 2230. New testing devices were designed for these tests, which allow a far less expensive operation and may easily be used for bolts of diameters up to M100 and testing frequencies up to 1000 Hz. The validity of fatigue resistance according to VDI 2230 is specified with respect to the test results. The determined influence of the tested lots is unexpectedly high. The manufacturing process of bolts should be improved to minimize this influence.  相似文献   
19.
Announces the 2007 recipient of the Gold Medal Award for Life Achievement in the Practice of Psychology: Patricia M. Bricklin. A brief biography, highlighting areas of special focus in Bricklin's work, is provided. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
20.
Announces the 2007 recipient of the Gold Medal Award for Life Achievement in the Psychology in the Public Interest: Rhoda K. Unger. A brief biography, highlighting areas of special focus in Unger's work, is provided. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  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