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   749篇
  免费   17篇
  国内免费   1篇
电工技术   8篇
化学工业   136篇
金属工艺   9篇
机械仪表   10篇
建筑科学   17篇
矿业工程   1篇
能源动力   16篇
轻工业   69篇
水利工程   13篇
石油天然气   2篇
无线电   52篇
一般工业技术   134篇
冶金工业   202篇
原子能技术   3篇
自动化技术   95篇
  2024年   4篇
  2023年   3篇
  2022年   6篇
  2021年   8篇
  2020年   8篇
  2019年   10篇
  2018年   14篇
  2017年   13篇
  2016年   10篇
  2015年   7篇
  2014年   15篇
  2013年   40篇
  2012年   27篇
  2011年   44篇
  2010年   28篇
  2009年   33篇
  2008年   39篇
  2007年   34篇
  2006年   29篇
  2005年   28篇
  2004年   26篇
  2003年   26篇
  2002年   28篇
  2001年   17篇
  2000年   20篇
  1999年   18篇
  1998年   24篇
  1997年   24篇
  1996年   23篇
  1995年   20篇
  1994年   17篇
  1993年   23篇
  1992年   6篇
  1991年   3篇
  1990年   11篇
  1989年   4篇
  1988年   11篇
  1987年   7篇
  1986年   8篇
  1985年   7篇
  1984年   11篇
  1983年   6篇
  1982年   3篇
  1977年   3篇
  1976年   6篇
  1974年   2篇
  1973年   4篇
  1971年   1篇
  1970年   4篇
  1957年   1篇
排序方式: 共有767条查询结果,搜索用时 15 毫秒
1.
OBJECTIVES: To determine age-specific prevalence of hypertension and blood pressure (BP) levels in relation to diet and lifestyle factors in North Indians. DESIGN AND SETTING: Cross-sectional survey in 20 randomly selected streets in Moradabad, North India. SUBJECTS AND METHODS: A total of 1806 subjects from North India (904 males and 902 females) age range 25-64 years. The survey methods were as follows: dietary diaries for 7 days food intake record; BP measurements; physician administered questionnaire and anthropometric measurements. Diagnosis of hypertension was based on new World Health Organization/International Society of Hypertension (WHO/ISH) criteria. Risk factors were assessed based on WHO guidelines. RESULTS: The prevalence of hypertension according to WHO/ISH criteria was 23.7% and by old WHO criteria 13.3%. In the WHO/ISH hypertensive group, isolated diastolic hypertension was present in 47.3% males and 40.6% females. Males have a slightly higher prevalence than females in the young age group, however, the prevalence rates are comparable in the older age groups. In both sexes, the prevalence rates and BP level increased with older age. Multivariate analysis revealed that age, higher body mass index, central obesity and higher socioeconomic status were independently and strongly associated with hypertension in both sexes. Higher dietary fat and salt intake and lower physical activity were weakly but significantly associated with hypertension. CONCLUSION: Association of higher socioeconmic status, higher body mass index and central obesity in North Indian adults with higher fat intake, lower physical activity and higher prevalence and level of hypertension indicate that these populations may benefit by decreasing the dietary fat intake and increasing physical activity, with an aim to decrease central obesity for decreasing hypertension in North Indians.  相似文献   
2.
3.
This paper describes the distributed system, network and software architecture, the application development environment, the performance, and the early lessons learned on the ATM LAN testbed Mercuri established at the Honeywell Technology Center, to develop distributed multimedia technologies for real-time control applications. We have developed a client-server-based software architecture on Sun Sparcstation-2s connected by a Fore Systems' ASX-100 ATM switch, with video processing handled by Parallax's X Video cards. The architecture enables network-transparent applications and provides simple primitives for multimedia capture, display, transmission, storage, and retrieval. A real-time multimedia-in-the-loop control application was developed as the vehicle for testing the capabilities and performance of the network. Our test measurements focus on the end-user-level performance metrics such as message throughput and round-trip delay as well as video-frame jitter under no-load and load conditions. Our results show that the maximum burst throughput that can be supported at the user level is 48 Mb/s using AAL 5, while round-trip delays for 4-kbyte messages are about 3 ms. Our experience reveals a number of performance bottlenecks and open issues in using commercial ATM switches for practical applications. Our conclusions are outlined  相似文献   
4.
5.
Hydrogenolysis of a carbobenzyloxy group (CBz) was studied utilizing molecular hydrogen in the presence of carbon-supported palladium catalyst. It was demonstrated that the kinetics of the reaction are greatly influenced by the presence of the CO2 by-product. It was found out that the presence of CO2 determines whether the reaction is first or zero order since it causes deactivation of the catalyst via inhibition. The effect of potassium carbonate (K2CO3) and triethylamine (TEA) as additives was investigated. A considerable solvent effect was also observed that may be explained by the variation of dispersion of the catalyst from one solvent to another.  相似文献   
6.
Although the association between marital conflict and child adjustment problems has been well documented, there is no empirical evidence that conflict actually causes maladjustment. The investigation of causation requires theoretically and empirically informed longitudinal research. Two topics are addressed to facilitate such research. First, how marital conflict may lead to adjustment problems is outlined, with a focus on constructs that are likely to be critical to any theory on this topic. Second, several issues are identified that need to be addressed in longitudinal research on the mechanisms underlying the link between marital and child problems. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
7.
Patterns of smoking cessation using 6- and 12-mo follow-up data are reported for 1,261 primary care patients randomized to 3 physician-delivered smoking interventions: advice only (AO), counseling (CI), and counseling plus availability of nicotine-containing gum (CI?+?NCG). One-week point-prevalence cessation rates at 12 mo did not differ among the interventions: AO (15.2%), CI (12.9%) and CI?+?NCG (16.7%). However, maintained cessation rates (abstinent at both 6 and 12 mo) increased with intervention intensity: AO (6.0%), CI (7.8%), and CI?+?NCG (10.0%): Test of trend χ–2?=?5.06, p?=?.02. CI?+?NCG was significantly higher than AO (p?=?.02). The findings support the following conclusions: Brief physician delivered intervention with availability of nicotine-containing gum can have a beneficial long-term effect on smoking cessation, and cohort data as well as point-prevalence rates are important when assessing the long-term impact of lifestyle interventions. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
8.
To investigate the relationship of severity of pediatric closed head injury (CHI), the contribution of frontal lobe lesions, and age at testing (6–10 yr olds vs 11–15 yr olds) to cognitive deficit, 134 head-injured patients were given the Tower of London (TOL) task and underwent magnetic resonance imaging. 89 normal controls were given the TOL for comparison. Severity of CHI and age at testing were strongly related to cognitive performance on the TOL, including the frequency of breaking the rules. Volume of frontal lobe lesion (but not extrafrontal lesion) contributed to the prediction of perfomance on the TOL even after severity of injury was taken into account. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
9.
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