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   43594篇
  免费   4367篇
  国内免费   2991篇
电工技术   1789篇
综合类   3789篇
化学工业   7403篇
金属工艺   2261篇
机械仪表   1666篇
建筑科学   4770篇
矿业工程   1832篇
能源动力   1606篇
轻工业   4732篇
水利工程   1372篇
石油天然气   2250篇
武器工业   435篇
无线电   5218篇
一般工业技术   6768篇
冶金工业   2178篇
原子能技术   942篇
自动化技术   1941篇
  2024年   255篇
  2023年   836篇
  2022年   1389篇
  2021年   1668篇
  2020年   1691篇
  2019年   1560篇
  2018年   1331篇
  2017年   1706篇
  2016年   1619篇
  2015年   1706篇
  2014年   2425篇
  2013年   2642篇
  2012年   2946篇
  2011年   3142篇
  2010年   2387篇
  2009年   2459篇
  2008年   2286篇
  2007年   2736篇
  2006年   2551篇
  2005年   2103篇
  2004年   1784篇
  2003年   1562篇
  2002年   1364篇
  2001年   1079篇
  2000年   1006篇
  1999年   777篇
  1998年   616篇
  1997年   585篇
  1996年   485篇
  1995年   414篇
  1994年   362篇
  1993年   302篇
  1992年   235篇
  1991年   197篇
  1990年   168篇
  1989年   138篇
  1988年   101篇
  1987年   65篇
  1986年   45篇
  1985年   32篇
  1984年   36篇
  1983年   22篇
  1982年   19篇
  1981年   12篇
  1980年   20篇
  1979年   22篇
  1965年   5篇
  1963年   5篇
  1959年   9篇
  1951年   7篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
李长智  郭杰 《纺织器材》2003,30(5):46-49
论述了普通胶辊表面不处理的性能特点和存在问题,技术措施和合理工艺参数,提高了成纱条干水平,减少缠绕和磨损。  相似文献   
52.
王政富  鞠泳 《山西建筑》2003,29(11):32-33
阐述了时空效应规律在软土深基坑工程中的运用情况,实践证明,运用时空效应规律,能可靠而合理地利用土体自身在基坑开挖过程中控制土体位移的潜力而达到保护环境的目的。  相似文献   
53.
On the elemental effect of AlCoCrCuFeNi high-entropy alloy system   总被引:1,自引:0,他引:1  
The AlCoCrCuFeNi high-entropy alloy system was synthesized using a well-developed arc melting and casting method. Their elemental effect on microstructures and hardness was investigated with X-ray diffraction, scanning electron microscopy and Vickers hardness testing. The alloys exhibit quite simple FCC and BCC solid solution phases. Co, Cu and Ni elements enhance the formation of the FCC phase while Al and Cr enhance that of the BCC phase in the alloy system. BCC phases form a spinodal structure during cooling. Copper tends to segregate at the interdendrite region and forms a Cu-rich FCC phase. Low copper content renders the interdendrite as a thin film and the as-cast structure like recrystallized grain structure. The formation of BCC phases significantly increases the hardness level of the alloy system. The strengthening mechanism is discussed.  相似文献   
54.
It is demonstrated that scattering of mobile charge carriers by fluctuations of local spin density in the normal state of SC-cuprates results in anomalous contribution to the transport phenomena (Hall and Nernst effects are included). Depending on their sign and magnitude, they can change value and sign of the corresponding effect measured.  相似文献   
55.
单壁纳米碳管/纳米铝基复合材料的增强效果   总被引:12,自引:0,他引:12  
用半连续氢电弧法和活性氢等离子蒸发法分别制备出单壁纳米碳管(SWNTs)和纳米A1粉体,然后用提纯后的SWNTs和纳米A1粉体制备出SWNTs含量(质量分数)分别为0、2.5%、5.0%、7.5%和10.0%的单壁纳米碳管/纳米铝基块体复合材料.SWNTs对高强度纳米A1基体具有显著的增强作用,当SWNTs含量小于5.0%时,材料的硬度随着SWNTs含量的提高线性上升.其中5%SWNTs和纳米A1的复合增强效果最好,其硬度可达2.89GPa,大约是粗晶A1(0.15GPa)的20倍.当SWNTs含量超过5.0%时,增强效果开始缓慢的下降.讨论了单壁纳米碳管增强纳米铝基复合材料的强化机制.  相似文献   
56.
One of the most frequently cited reasons for conducting a meta-analysis is the increase in statistical power that it affords a reviewer. This article demonstrates that fixed-effects meta-analysis increases statistical power by reducing the standard error of the weighted average effect size (T?.) and, in so doing, shrinks the confidence interval around T?.. Small confidence intervals make it more likely for reviewers to detect nonzero population effects, thereby increasing statistical power. Smaller confidence intervals also represent increased precision of the estimated population effect size. Computational examples are provided for 3 effect-size indices: d (standardized mean difference), Pearson's r, and odds ratios. Random-effects meta-analyses also may show increased statistical power and a smaller standard error of the weighted average effect size. However, the authors demonstrate that increasing the number of studies in a random-effects meta-analysis does not always increase statistical power. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
57.
Academically selective schools are intended to affect academic self-concept positively, but theoretical and empirical research demonstrates that the effects are negative. The big-fish--little-pond effect (BFLPE), an application of social comparison theory to educational settings, posits that a student will have a lower academic self-concept in an academically selective school than in a nonselective school. This study, the largest cross-cultural study of the BFLPE ever undertaken, tested theoretical predictions for nationally representative samples of approximately 4,000 15-year-olds from each of 26 countries (N=103,558) who completed the same self-concept instrument and achievement tests. Consistent with the BFLPE, the effects of school-average achievement were negative in all 26 countries (M beta=-.20, SD=.08), demonstrating the BFLPE's cross-cultural generalizability. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
58.
To clarify whether motion information per se has a separable influence on action control, the authors investigated whether irrelevant direction of motion of stimuli whose overall position was constant over time would affect manual left-right responses (i.e., reveal a motion-based Simon effect). In Experiments 1 and 2, significant Simon effects were obtained for sine-wave gratings moving in a stationary Gaussian window. In Experiment 3, a direction-based Simon effect with random-dot patterns was replicated, except that the perceived direction of motion was based on the displacement of single elements. Experiments 4 and 5 studied motion-based Simon effects to point-light figures that walked in place--displays requiring high-level analysis of global shape and local motion. Motion-based Simon effects occurred when the displays could be interpreted as an upright human walker, showing that a high-level representation of motion direction mediated the effects. Thus, the present study establishes links between high-level motion perception and action. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
59.
Generation effect (generated words are better memorized than read words) of anagrams, rhymes, and associates of target words was examined in young, elderly, and very old subjects. Experiments 1 and 2 showed that only young subjects benefit from the generation effect in a free-recall test when the rule is of a phonological nature. Experiments 3, 4, and 5 showed that the generation effect of rhymes was due to a resources-dependent self-initiated process. Experiments 4 and 5 showed that in a divided-attention situation, generation effect of rhymes is not significant in young subjects, but that the generation effect of semantic associates remains significant for both groups (Experiment 5). The results are discussed within the environmental support framework and the transfer-appropriate processing framework. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
60.
To find the exact probability distribution of the global maximum or minimum of a random field within a bounded domain is a pending problem even for Gaussian fields. Except for very special examples of fields, recourse must be taken to approximate reasoning or asymptotic considerations to be judged with respect to accuracy by simulations. In this paper, the problem is addressed through a functional equation that leads to the definition of a class of distribution functions that depend solely on process or field characteristics and domain quantities that can be calculated explicitly. This distribution function class is studied for Gaussian processes in earlier works by the author and it has been obtained explicitly for Gaussian fields on rectangular domains in the plane. Simulation studies show that rather good predictions are obtained for sufficiently smooth wide band Gaussian processes and fields. In this paper, the distribution function is obtained in general for Gaussian fields over arbitrary bounded domains with piecewise continuous and differentiable boundaries, and as in earlier works the distribution function is tested against empirical distribution functions obtained by simulation of sample functions of a smooth approximately Gaussian field, herein called a broken line Hino field. For completeness this particular field type is defined in appendix a and appendix b. The paper concludes with a statistical application on data for plain concrete tensile strength.  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