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   34010篇
  免费   868篇
  国内免费   66篇
电工技术   366篇
综合类   35篇
化学工业   6788篇
金属工艺   858篇
机械仪表   622篇
建筑科学   1842篇
矿业工程   247篇
能源动力   1016篇
轻工业   2764篇
水利工程   335篇
石油天然气   207篇
武器工业   2篇
无线电   2149篇
一般工业技术   5197篇
冶金工业   7576篇
原子能技术   322篇
自动化技术   4618篇
  2022年   196篇
  2021年   386篇
  2020年   332篇
  2019年   399篇
  2018年   489篇
  2017年   509篇
  2016年   521篇
  2015年   463篇
  2014年   736篇
  2013年   2132篇
  2012年   1241篇
  2011年   1590篇
  2010年   1169篇
  2009年   1258篇
  2008年   1436篇
  2007年   1467篇
  2006年   1256篇
  2005年   1172篇
  2004年   1052篇
  2003年   1025篇
  2002年   1031篇
  2001年   634篇
  2000年   616篇
  1999年   604篇
  1998年   889篇
  1997年   664篇
  1996年   699篇
  1995年   607篇
  1994年   601篇
  1993年   589篇
  1992年   490篇
  1991年   325篇
  1990年   441篇
  1989年   431篇
  1988年   386篇
  1987年   433篇
  1986年   388篇
  1985年   521篇
  1984年   491篇
  1983年   445篇
  1982年   466篇
  1981年   452篇
  1980年   364篇
  1979年   366篇
  1978年   332篇
  1977年   337篇
  1976年   336篇
  1975年   319篇
  1974年   243篇
  1973年   279篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
The ears of lizards are highly directional. The directionality is generated by strong acoustical coupling of the eardrums. A simple lumped-parameter model of the ear followed by binaural comparisons has been shown to perform successful phonotaxis in robot implementations. However, such a model will produce localization errors in the form of response bias if the ears are asymmetrical. We have evaluated how large errors are generated by asymmetry using simulations of the ear model in Mathematica 5.2. The study shows that the effect of asymmetry is minimal around the most directional frequency of the ear, but that biases reduce the useful bandwidth of localization. This work was presented in part at the First European Workshop on Artificial Life and Robotics, Vienna, Austria, July 12–13, 2007  相似文献   
102.
103.
D-ribose, a naturally occurring pentose carbohydrate, has been shown to replenish high- energy phosphates following myocardial ischemia and high intensity, repetitive exercise. Human studies have mainly involved short-term assessment, including potential toxicity. Reports describing adverse effects of D-ribose with prolonged ingestion have been lacking. Therefore, this study assessed the toxicity of extended consumption of D-ribose in healthy adults. Nineteen subjects ingested 20 grams/Day (10 grams, twice a Day) of ribose with serial measurements of biochemical and hematological parameters at Days 0, 7, and 14. No significant toxic changes over the 14-day assessment period occurred in complete blood count, albumin, alkaline phosphatase, gamma glutamyltransferase, alanine amiotransferase, and aspartate aminotransferase. However, D-ribose did produce an asymptomatic, mild hypoglycemia of short duration. Uric acid levels increased at Day 7, but decreased to baseline values by Day 14. D-ribose consumption for 14 days appears not to produce significant toxic changes in both hematological and biochemical parameters in healthy human volunteers.  相似文献   
104.
This study evaluates characteristics associated with alcohol consumption or alcohol-related problems in an elderly population, as detected by CAGE questionnaire and self-reported alcohol intake respectively. Data were obtained from a multidimensional study carried out in a community-dwelling population aged 70-75 (n = 1205, 389 males and 816 females) living in the city center of Brescia, in northern Italy. All information was gathered by self-report. Male gender, better mood, daily function, somatic health, not living alone, and being married were significantly associated with self-reported alcohol consumption. Male gender, poorer cognitive function, and income dissatisfaction were significantly associated with alcohol problems as detected by CAGE. Data suggest that self-report of alcohol intake, though intrinsically loaded with imperfect internal consistency, does not necessarily indicate risk of alcoholism; on the contrary, it can reveal the positive psychological attitude of the drinking habit. CAGE questionnaire, which is sensitive to alcohol related problems, is associated with poor psychosocial conditions.  相似文献   
105.
Argues that children's failure on one of Piaget's best known tasks, conservation of solid quantity, reflects ignorance of physical properties rather than inadequate reasoning ability. The evidence for conservation itself, seen from the child's position, is analyzed. It is emphasized that children can learn and enjoy the concepts and methods of physics at much earlier ages than current orthodoxies would indicate. (French abstract) (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
106.
107.
In this paper a fuller and clear derivation of the weight vector theory of Coriolis mass flowmeters is given indicating its potential for the prediction of velocity profile effects in both the traditional kind of meter (vibrating tube) and the compact kind (vibrating element inside a duct).  相似文献   
108.
Psychotherapy with adolescent clients (ACs) is difficult for at least 2 reasons: ACs frequently do not trust adults and ACs are often poorly motivated for treatment. Consequently there may be significant problems eliciting the cooperation needed to implement successfully various psychotherapeutic treatment techniques (PTTs) with ACs in general, and treatment-resistant ACs in particular. Several PTTs designed to capture ACs' attention, further the psychotherapeutic alliance, and facilitate cooperation are presented. PTTs include siding with the AC, teaching strategic skills, exploring moral dilemmas, wagering on cognitions and behaviors, and alternative communication strategies. Case illustrations are provided to demonstrate the effectiveness of PTTs. It is recommended that psychotherapists consistently review the quality of their relationship with ACs to facilitate successful implementation of PTTs. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
109.
Two cases of cystic hygroma arising as a primary lesion in the chest are presented. Because of calcifications discovered on CT and because of the anterior location of the mass in both cases, teratoma was the first diagnostic consideration. However, after surgical removal, histologic study determined that both lesions were cystic hygromas with areas of scattered calcification probably secondary to hemorrhage. These cases are presented because of the remarkable similarity of their imaging features to those of teratoma.  相似文献   
110.
To provide insight into the stream of Medicare payments over time, a sixteen-year longitudinal study examines three age cohorts of beneficiaries, looking separately at beneficiaries who died during the study period and those who survived. The common wisdom that a small minority of the population accounts for a large majority of health care expenditures is tempered when health care use is examined over an extended period of time. By putting high average costs in the final years of life in the context of a cohort's total lifetime experience, the study shows a leveling of spending over time, resulting in a lower concentration of health care resources on a small fraction of the population.  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