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   524篇
  免费   22篇
电工技术   2篇
化学工业   66篇
机械仪表   6篇
建筑科学   18篇
能源动力   4篇
轻工业   72篇
水利工程   6篇
石油天然气   3篇
无线电   15篇
一般工业技术   64篇
冶金工业   232篇
自动化技术   58篇
  2023年   5篇
  2022年   2篇
  2021年   5篇
  2020年   3篇
  2019年   3篇
  2018年   7篇
  2017年   10篇
  2016年   13篇
  2015年   3篇
  2014年   16篇
  2013年   22篇
  2012年   14篇
  2011年   24篇
  2010年   22篇
  2009年   21篇
  2008年   30篇
  2007年   25篇
  2006年   31篇
  2005年   20篇
  2004年   20篇
  2003年   24篇
  2002年   33篇
  2001年   10篇
  2000年   13篇
  1999年   12篇
  1998年   7篇
  1997年   11篇
  1996年   8篇
  1995年   11篇
  1994年   15篇
  1993年   11篇
  1992年   12篇
  1991年   5篇
  1990年   6篇
  1989年   12篇
  1988年   6篇
  1987年   5篇
  1986年   7篇
  1985年   11篇
  1984年   3篇
  1983年   6篇
  1982年   6篇
  1981年   3篇
  1980年   1篇
  1979年   3篇
  1978年   3篇
  1977年   3篇
  1975年   2篇
  1967年   1篇
排序方式: 共有546条查询结果,搜索用时 15 毫秒
61.
Conducted interviews with 39 psychologists and psychology students to examine attitudes toward reporting child abuse cases to the authorities. Ss were almost equally divided in their decisions about reporting; the majority considered the child's life the most important, with confidentiality ranked second, and the law ranked third. Those who considered the law the most important issue (31%) chose always to report the abuse. Those who considered the law the least important issue (41%) saw the spirit of the law as more important than the letter and based their decision on their perception of the consequences for the child. (9 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
62.
Health, leisure and beauty activities are increasing in popularity, with a particular emphasis on self-help and alternative health practices. One product type that has increased sales with this expansion is the hand-held electric massager. These are products that use vibration as a means of alleviating muscular strains and pains, as well as promoting relaxation. Paradoxically, these products are extremely popular as gifts, but are soon discarded. A multi-disciplinary research team was commissioned by a British manufacturer of electrical consumer products to investigate user attitudes and perceptions of existing massagers, to identify areas of user dissatisfaction. The manufacturer was also concerned about a possible stigma attached to these products because of an association with sex aids. This paper provides an account of the perceptions of both consumers and therapists regarding the use of these products. Identifying the differences between the perceptions of consumers and therapists should help provide a basis for effective integration of user needs, manufacturer requirements, designers' skills and sound therapeutic practice. The results provide insight to support the development of more effective hand-held massagers.  相似文献   
63.
82 preschoolers' (40–62 mo old) rates of behavior were observed toward play activities (e.g. dolls, trucks) and teacher-related variables. Results show that both sexes increased rates of participation in response to teacher presence in male and female sex-typed activity areas during free play. Girls, however, responded more consistently to teacher presence than did boys, who modulated their responses according to both the sex typing of the activity and the sex of the teacher. Findings indicate that typically observed teacher behavior during free play may contribute significantly to reported patterns of sex-differentiated play. (13 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
64.
The U.S. Geological Survey produces a variety of resource information for the United States. This includes many data bases of particular interest to planners such as land use and terrain information prepared by the National Mapping Division, water quantity and quality data collected by Water Resources Division, and coal resource information gathered by the Geologic Division. These data are stored in various forms, and information on their availability can be obtained from appropriate offices in the U.S. Geological Survey as well as from USGS Circular 777. These data have been used for the management, development, and monitoring of our Nation's resources by Federal, State, and local agencies.  相似文献   
65.
Metallized, flexible polymeric reflector materials are much lighter and potentially less expensive than the conventional glass/metal mirrors often used in solar thermal concentrators such as heliostats and parabolic dishes and troughs. Unweathered silvered-PMMA reflectors have a solar reflectance at least as high as glass reflectors, but their environmental durability needs to be demonstrated. ECP-305, a silvered-PMMA film available commercially from the 3M Company and developed in collaboration with the National Renewable Energy Laboratory, is the current state of the art. Important progress has been made in overcoming the three primary mechanisms causing ECP-305 to lose reflectance. These mechanisms are: (1) photon-induced silver corrosion, (2) surface soiling, and (3) a form of delamination called tunneling. Given the progress in resolving these performance lifetime issues, silvered-PMMA films should meet the reflectance and durability goals.  相似文献   
66.
BACKGROUND: One of the realities of apple distribution for long‐term stored fruit is that a controlled‐atmosphere (CA) storage room will be unsealed and fruit held in air storage and marketed over several weeks. This work was conducted to determine the effect of post‐CA air storage of whole fruit on potential shelf life for fresh‐cut apple slices. RESULTS: Fresh‐cut slices of ‘Spartan’ and ‘Delicious’ apples held in post‐CA air storage for 2 or 4 weeks showed the least changes in cut surface color as compared with those made from apples immediately on removal from CA. Shelf life was most improved by post‐CA air storage in the ‘Spartan’ apples, which were more advanced in maturity as compared with the ‘Delicious’ apples. Internal ethylene concentration, firmness, and respiration changed significantly with post‐CA air storage, suggesting a relationship between physiological status of the whole fruit and shelf life of slices made from that fruit. CONCLUSION: The results support the hypothesis that apples had suppressed physiological activity in CA storage and are susceptible to accelerated deterioration upon cutting. Holding fruit for 2 weeks in air storage allowed recovery of physiological activity, which resulted in greater resistance to deterioration in response to fresh‐cut processing. Copyright © 2010 Crown in the right of Canada. Published by JohnWiley & Sons, Ltd  相似文献   
67.
Abstract

The KRYPTOS competition is an annual codebreaking competition for undergraduates. Debuting in 2011 with 49 participants from three states, after nine years we have seen over 1,000 students from 32 states and seven different countries. KRYPTOS will hold its tenth competition in April of 2020. Here we present some of the puzzles participants have found most elusive and challenge you to beat the clock on our fastest solver.  相似文献   
68.
69.
Cytosolic phospholipase A2α (cPLA2α) may play a critical role in neuropsychiatric and neurodegenerative disorders associated with oxidative stress and neuroinflammation. An effective PET radioligand for imaging cPLA2α in living brain might prove useful for biomedical research, especially on neuroinflammation. We selected four high‐affinity (IC50 2.1–12 nm ) indole‐5‐carboxylic acid‐based inhibitors of cPLA2α, namely 3‐isobutyryl‐1‐(2‐oxo‐3‐(4‐phenoxyphenoxy)propyl)‐1H‐indole‐5‐carboxylic acid ( 1 ); 3‐acetyl‐1‐(2‐oxo‐3‐(4‐(4‐(trifluoromethyl)phenoxy)phenoxy)propyl)‐1H‐indole‐5‐carboxylic acid ( 2 ); 3‐(3‐methyl‐1,2,4‐oxadiazol‐5‐yl)‐1‐(2‐oxo‐3‐(4‐phenoxyphenoxy)propyl)‐1H‐indole‐5‐carboxylic acid ( 3 ); and 3‐(3‐methyl‐1,2,4‐oxadiazol‐5‐yl)‐1‐(3‐(4‐octylphenoxy)‐2‐oxopropyl)‐1H‐indole‐5‐carboxylic acid ( 4 ), for labelling in carboxyl position with carbon‐11 (t1/2=20.4 min) to provide candidate PET radioligands for imaging brain cPLA2α. Compounds [11C] 1 – 4 were obtained for intravenous injection in adequate overall yields (1.1–5.5 %) from cyclotron‐produced [11C]carbon dioxide and with moderate molar activities (70–141 GBq μmol?1) through the use of Pd0‐mediated [11C]carbon monoxide insertion on iodo precursors. Measured logD7.4 values were within a narrow moderate range (1.9–2.4). After intravenous injection of [11C] 1 – 4 in mice, radioactivity uptakes in brain peaked at low values (≤0.8 SUV) and decreased by about 90 % over 15 min. Pretreatments of the mice with high doses of the corresponding non‐radioactive ligands did not alter brain time–activity curves. Brain uptakes of radioactivity after administration of [11C] 1 to wild‐type and P‐gp/BCRP dual knock‐out mice were similar (peak 0.4 vs. 0.5 SUV), indicating that [11C] 1 and others in this structural class, are not substrates for efflux transporters.  相似文献   
70.

Background

Dietary strategies that help patients adhere to a weight reduction diet may increase the likelihood of weight loss maintenance and improved long-term health outcomes. Regular nut consumption has been associated with better weight management and less adiposity. The objective of this study was to compare the effects of a walnut-enriched reduced-energy diet to a standard reduced-energy-density diet on weight, cardiovascular disease risk factors, and satiety.

Methods

Overweight and obese men and women (n =?100) were randomly assigned to a standard reduced-energy-density diet or a walnut-enriched (15% of energy) reduced-energy diet in the context of a behavioral weight loss intervention. Measurements were obtained at baseline and 3- and 6-month clinic visits. Participants rated hunger, fullness and anticipated prospective consumption at 3 time points during the intervention. Body measurements, blood pressure, physical activity, lipids, tocopherols and fatty acids were analyzed using repeated measures mixed models.

Results

Both study groups reduced body weight, body mass index and waist circumference (time effect p <?0.001 for each). Change in weight was ?9.4 (0.9)% vs. -8.9 (0.7)% (mean [SE]), for the standard vs. walnut-enriched diet groups, respectively. Systolic blood pressure decreased in both groups at 3 months, but only the walnut-enriched diet group maintained a lower systolic blood pressure at 6 months. The walnut-enriched diet group, but not the standard reduced-energy-density diet group, reduced total cholesterol and low-density lipoprotein cholesterol (LDL-C) at 6 months, from 203 to 194 mg/dL and 121 to 112 mg/dL, respectively (p <?0.05). Self-reported satiety was similar in the groups.

Conclusions

These findings provide further evidence that a walnut-enriched reduced-energy diet can promote weight loss that is comparable to a standard reduced-energy-density diet in the context of a behavioral weight loss intervention. Although weight loss in response to both dietary strategies was associated with improvements in cardiovascular disease risk factors, the walnut-enriched diet promoted more favorable effects on LDL-C and systolic blood pressure.

Trial registration

The trial is registered at (NCT02501889).
  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