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   2209篇
  免费   125篇
  国内免费   79篇
电工技术   13篇
综合类   183篇
化学工业   156篇
金属工艺   43篇
机械仪表   46篇
建筑科学   157篇
矿业工程   126篇
能源动力   65篇
轻工业   106篇
水利工程   106篇
石油天然气   863篇
武器工业   2篇
无线电   20篇
一般工业技术   94篇
冶金工业   271篇
原子能技术   6篇
自动化技术   156篇
  2024年   4篇
  2023年   16篇
  2022年   27篇
  2021年   55篇
  2020年   58篇
  2019年   46篇
  2018年   52篇
  2017年   71篇
  2016年   66篇
  2015年   59篇
  2014年   122篇
  2013年   186篇
  2012年   141篇
  2011年   166篇
  2010年   100篇
  2009年   105篇
  2008年   86篇
  2007年   120篇
  2006年   123篇
  2005年   109篇
  2004年   100篇
  2003年   101篇
  2002年   79篇
  2001年   78篇
  2000年   49篇
  1999年   51篇
  1998年   50篇
  1997年   23篇
  1996年   30篇
  1995年   27篇
  1994年   12篇
  1993年   12篇
  1992年   9篇
  1991年   10篇
  1990年   3篇
  1988年   3篇
  1986年   6篇
  1984年   5篇
  1983年   6篇
  1980年   3篇
  1976年   3篇
  1965年   2篇
  1963年   3篇
  1962年   2篇
  1961年   5篇
  1960年   6篇
  1959年   2篇
  1958年   2篇
  1957年   3篇
  1954年   5篇
排序方式: 共有2413条查询结果,搜索用时 0 毫秒
1.
王念喜  李雪雁 《油气井测试》2006,15(2):18-20,24
大牛地气田为低渗-致密气田,因存在启动压力梯度等因素,修正等时试井曲线按常规方法处理出现异常,无法准确获取气井的产能方程.采用LIT法和异常曲线校正法对气田异常试井资料进行了重新处理,最终获得气井产能方程,为同类气藏产能试井可能出现的异常资料处理解释探索了新的途径.  相似文献   
2.
Abstract. This paper examines the capacity of the research designs of 37 empirical studies of information systems (IS) effectiveness to provide a basis for the development of theories about behaviour related to IS effectiveness. The power of each study to support causal inference was evaluated in terms of (a) its handling of the time dimension, (b) its ability to weigh differences and (c) its resistance to internal validity threats that pose alternative explanations for its reported findings. Of the reviewed studies, 29.7% could account for the time dimension, 32.4% employed a comparison group and 16.2% were not susceptible to any internal validity threats. Only 13.5% of the studies combined an accounting for the time dimension with the use of a comparison group. Of these, however, only 5.4% were also invulnerable to internal validity threats. The research designs of nearly 95% of these published studies were deficient in supporting causal inference. In those studies, suggestions that one variable was causally related to another variable could not be substantiated. Encouragement for the future capacity of IS effectiveness research to support causal inference was found in a trend towards the use of quasiexperimental designs. Recommendations are made regarding ways to increase the inferential capacity of research designs employed in the study of IS effectiveness.  相似文献   
3.
Abstract. This paper examines critically the function point analysis mark II (FPA mark II) method of measuring the functionality of information systems. Although the focus of the paper is on FPA mark II as devised by Symons, both this and the Albrecht method, from which the FPA mark II was developed, are briefly discussed. The published attempts to validate FPA mark II are reviewed and then the problems encountered by the author in applying the approach are described. The final part of the paper is concerned with the fit between SSADM and FPA mark II.  相似文献   
4.
Suitability of sweet sorghum in Greece, where irrigation supply during crop development is limited as rainfall is scarce and evapotranspiration loss is high, is examined in relation with radiation availability. A two-year field experiment was conducted, in central Greece, imposing four soil water regimes via different irrigation treatments: (1) Highly irrigated, (2) Highly irrigated till anthesis when irrigation stopped, (3) Medium irrigated, and (4) Low irrigated. It was found that above-ground dry biomass production from non-water-stressed sweet sorghum plants suggests a high productivity potential among C4 crops. Under water shortage, radiation use efficiency may be significantly lower. Radiation use efficiency seems to be linearly related to water consumption. Stressed plants (probably except severely stressed) seem to use available water more efficiently than unstressed plants. The slope of the line relating dry matter produced and water evapotranspired increases the sooner the stress is sensed. Yield reduction resulting from post-anthesis irrigation stopage is very little. High water use efficiency values tend to be related with low radiation use efficiency values.  相似文献   
5.
在对中美两国的职工持股计划进行分析后,本文认为职工持股计划在中国,理论上可行,但在实践中 需要谨慎行事。  相似文献   
6.
依据升平气田的试井资料,建立了气井产能与压差之间的二次项产能方程。运用此方程可以预测升平气田的单井产能,并且建立了压差平方与kh值相关的气田综合产能方程。当求得气田的平均kh值后,利用该方法可以求得气田的平均产能或生产压差。  相似文献   
7.
In this report, the scientific productivity of Year 2006 of chemical engineering professionals in Taiwan was analyzed carefully with information retrieved from the database of the ISI Web of Science. The distributions of number of authors with x publication versus the number of publication x follows a general power-law trend, which coincidently comply with the Pareto distribution. The power-law indices found ranges from −1.64 to −2.22, which is consistent with values reported in the literature investigated for periods of 1907–1916 and 1969–2004.  相似文献   
8.
Pressure to compress the development life cycle and reduce the duration and resources committed to testing lead to experimentation in testing at the NASA Goddard Space Flight Centerís Software Engineering Laboratory. This study investigates the trend to reduce developer testing and increasingly rely upon inspection techniques and independent functional testing to shorten the development life cycle, improve testing productivity, and improve software quality.An approach is developed to conduct this comparison. In particular, the problem faced by software researchers, having a comprehensive characterization of software projects so similar types may be identified for comparative studies, is addressed using expert opinion.  相似文献   
9.
1 INTRODUCTION Porphyridium cruentum is a kind of unicellular microalgae, which can live widely in freshwater, marine, brackish, and soil environment[1]. Great attention has been paid to its potential economic value such as the high content of essential high unsaturated fatty acids, especially arachidonic acid (AA) and eicosapentaenoic acid (EPA) (ca 50% in the total fatty acids), ploysaccharides, and synthetic pigments, especially phycoerythrin (PE)[2,3]. During cultivation, the cells…  相似文献   
10.
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