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   1074篇
  免费   59篇
电工技术   2篇
化学工业   261篇
金属工艺   7篇
机械仪表   17篇
建筑科学   67篇
矿业工程   3篇
能源动力   23篇
轻工业   163篇
水利工程   7篇
石油天然气   3篇
无线电   47篇
一般工业技术   153篇
冶金工业   259篇
原子能技术   5篇
自动化技术   116篇
  2023年   14篇
  2022年   44篇
  2021年   77篇
  2020年   27篇
  2019年   28篇
  2018年   32篇
  2017年   40篇
  2016年   36篇
  2015年   18篇
  2014年   32篇
  2013年   62篇
  2012年   60篇
  2011年   56篇
  2010年   58篇
  2009年   52篇
  2008年   61篇
  2007年   38篇
  2006年   24篇
  2005年   24篇
  2004年   23篇
  2003年   26篇
  2002年   27篇
  2001年   15篇
  2000年   10篇
  1999年   12篇
  1998年   20篇
  1997年   16篇
  1996年   20篇
  1995年   18篇
  1994年   15篇
  1993年   10篇
  1992年   14篇
  1991年   5篇
  1990年   12篇
  1989年   9篇
  1988年   7篇
  1987年   9篇
  1986年   7篇
  1985年   9篇
  1984年   9篇
  1983年   9篇
  1982年   5篇
  1981年   5篇
  1979年   3篇
  1978年   6篇
  1977年   4篇
  1976年   3篇
  1974年   3篇
  1970年   3篇
  1964年   2篇
排序方式: 共有1133条查询结果,搜索用时 156 毫秒
71.
This study was a 5-year follow-up of obese children who participated in a family-based behavioral weight-control program targeting and reinforcing children and parents for weight loss (Epstein, Wing, Koeske, Andrasik, & Ossip, 1981). Children in the parent-plus-child group showed significantly greater weight reductions after 5 years (–22.7% overweight) than did children in a child-alone target group or in a no-target control group (4.3% and 8.2% overweight, respectively). One third of children in the parent-plus-child group were within 20% of normal weight in comparison with 5% of the children in the no-target control group. Height percentile decreased from the 72nd to the 60th percentile; these changes were negatively related to weight change. These children remained taller than the average child after weight loss, and children of short and medium-height parents were still relatively taller than their parents after 5 years. (23 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
72.
Assessed the effect of parent weight (obese/nonobese parent) and parent control vs child self-control on the weight loss of 41 obese 8–12 yr olds over a 3-yr period. Children of nonobese parents had significantly greater decrease in relative weight after 1 yr, but not after 3 yrs, than children of obese parents. Locus of control was not related to treatment outcome over the 3 yrs. Results suggest that parent weight was related to weight loss, but not weight maintenance, in obese children. (9 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
73.
74.
Two experiments examined long-term repetition priming in data entry. In each experiment, participants entered 4-digit numbers displayed as either words or numerals, and responded with digits (Experiment 1), or either digits or initial letters (Experiment 2). At test 1 week later, they entered old and new numbers, with the format changed for half of the old stimuli. Implicit memory was evidenced at test by faster entry of the old than the new numbers, regardless of whether the numbers were in the same or different format, suggesting that the abstract numerical meaning, not the surface form, contributes to repetition priming. Numbers presented as words in training had an advantage over numbers presented as numerals, regardless of response format, implying that type of processing also contributes to the effect and ruling out an explanation based on time spent processing numbers in word format. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
75.
The effects of a book reading technique called interactive book reading on the language and literacy development of 4 yr olds from low-income families were evaluated. Teachers read books to children and reinforced the vocabulary in the books by presenting concrete objects that represented the words and by providing children with multiple opportunities to use the book-related words. The teachers also were trained to ask open-ended questions and to engage children in conversations about the book and activities. This provided children with opportunities to use language and learn vocabulary in a meaningful context. Children who were in the interactive book reading intervention group scored significantly better than children in the comparison group on Peabody Picture Vocabulary Test—III and other measures of receptive and expressive language. Book reading and related activities can promote the development of language and literacy skills in young children. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
76.
77.
Refutes R. F. Baumeister's (see record 1989-14054-001) argument that the inclusion of sex-difference findings in research reports is undesirable from both political and scientific standpoints. A number of advantages stem from the study of sex differences. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
78.

Background

Risks from electromagnetic devices are of considerable concern. Electrohypersensitive (EHS) persons attribute a variety of rather unspecific symptoms to the exposure to electromagnetic fields. The pathophysiology of EHS is unknown and therapy remains a challenge.

Objectives

Heavy metal load has been discussed as a potential factor in the symptomatology of EHS patients. The main objective of the study was to test the hypothesis of a link between EHS and heavy metal exposure.

Methods

We measured lead, mercury and cadmium concentrations in the blood of 132 patients (n = 42 males and n = 90 females) and 101 controls (n = 34 males and n = 67 females).

Results

Our results show that heavy metal load is of no concern in most cases of EHS but might play a role in exceptional cases.

Conclusions

The data do not support the general advice to heavy metal detoxification in EHS.  相似文献   
79.
Protected Working Capacity Envelope (PWCE) has been proposed to simplify resource management and traffic control for survivable WDM networks. In a PWCE-based network, part of the link capacity is reserved for accommodating working routes, and the remaining capacity is reserved for backup routes. The shortest path routing is applied in PWCE-based networks. An arrival call is accepted only when each link along the shortest path has a free working channel. Such a working path routing scheme greatly simplifies the call admission control process for dynamic traffic, and it is especially suitable for implementation in a distributed manner among network nodes. In this article, we investigate two protection strategies: Bundle Protection (BP) and Individual Protection (IDP). In BP, only one backup path can be used to protect a failure component, whereas multiple backup paths can be used in IDP. We formulate four mixed integer non-linear programming (MINLP) problems using BP and IDP strategies for single link and single node failure protection. Each model is designed to determine link metrics for shortest working path routing, working and backup channel assignments, and backup path planning. Our objective is to minimize call-blocking probability on the bottleneck link. Since these models are highly non-linear and non-convex, it is difficult to obtain exact global optimal solutions. We propose a Simulated Annealing-based Heuristic (SAH) algorithm to obtain near optimal solutions. This SAH adopts the concepts of simulated annealing as well as the bi-section technique to minimize call-blocking probabilities. To evaluate the performance, we made simulation comparisons between SAH and the unity link weight assignment scheme. The results indicate that SAH can greatly reduce call-blocking probabilities on benchmark and the randomly generated networks.  相似文献   
80.
Mountaintop coal mining (MCM) in the Southern Appalachian forest region greatly impacts both soil and aquatic ecosystems. Policy and practice currently in place emphasize water quality and soil stability but do not consider upland soil health. Here we report soil organic carbon (SOC) measurements and other soil quality indicators for reclaimed soils in the Southern Appalachian forest region to quantify the health of the soil ecosystem. The SOC sequestration rate of the MCM soils was 1.3 MgC ha(-1) yr(-1) and stocks ranged from 1.3 ± 0.9 to 20.9 ± 5.9 Mg ha(-1) and contained only 11% of the SOC of surrounding forest soils. Comparable reclaimed mining soils reported in the literature that are supportive of soil ecosystem health had SOC stocks 2.5-5 times greater than the MCM soils and sequestration rates were also 1.6-3 times greater. The high compaction associated with reclamation in this region greatly reduces both the vegetative rooting depth and infiltration of the soil and increases surface runoff, thus bypassing the ability of soil to naturally filter groundwater. In the context of environmental sustainability of MCM, it is proposed that the entire watershed ecosystem be assessed and that a revision of current policy be conducted to reflect the health of both water and soil.  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