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   18603篇
  免费   1007篇
  国内免费   30篇
电工技术   188篇
综合类   16篇
化学工业   4386篇
金属工艺   353篇
机械仪表   339篇
建筑科学   685篇
矿业工程   34篇
能源动力   553篇
轻工业   2831篇
水利工程   139篇
石油天然气   44篇
无线电   997篇
一般工业技术   3007篇
冶金工业   2956篇
原子能技术   101篇
自动化技术   3011篇
  2024年   34篇
  2023年   137篇
  2022年   484篇
  2021年   618篇
  2020年   371篇
  2019年   423篇
  2018年   698篇
  2017年   647篇
  2016年   684篇
  2015年   484篇
  2014年   713篇
  2013年   1198篇
  2012年   1136篇
  2011年   1269篇
  2010年   916篇
  2009年   869篇
  2008年   872篇
  2007年   752篇
  2006年   646篇
  2005年   556篇
  2004年   432篇
  2003年   407篇
  2002年   359篇
  2001年   272篇
  2000年   266篇
  1999年   260篇
  1998年   1056篇
  1997年   635篇
  1996年   445篇
  1995年   262篇
  1994年   227篇
  1993年   227篇
  1992年   87篇
  1991年   92篇
  1990年   80篇
  1989年   78篇
  1988年   71篇
  1987年   61篇
  1986年   55篇
  1985年   69篇
  1984年   55篇
  1983年   52篇
  1982年   60篇
  1981年   72篇
  1980年   56篇
  1979年   30篇
  1978年   35篇
  1977年   75篇
  1976年   96篇
  1973年   27篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
102.
103.
104.
The adolescent's breaking of the voice is the result of the substitution of the chest voice (or heavy mechanism) for the head voice (or light mechanism). In cases of late breaking, the voice is abnormally high-pitched and feeble, often with a distorted timbre, while the larynx is normal and pubescent. Such people are generally not fully aware of their voices' real nature. Therapy classically resorts to laryngeal manipulations, of which a new technique is put forward. Another therapeutic approach is based, on the one hand, on critical listening compared with a control male voice, thus enabling the subject to become aware of his own voice, and, on the other hand, on high intensity work which helps passing from head to chest voice.  相似文献   
105.
The objective of this study is to describe usual medical management and costs associated with recurrent respiratory infections in subjects with chronic obstructive bronchitis in France. A prospective survey was performed in Autumn 1994 on a national sample of private practice pulmonologists (N = 71). Two hundred forty-four patients, presenting at least one infection of the lower respiratory tract, were included. Bronchitis was the most frequent acute exacerbation observed (94%). Pneumonia concerned 9% of the patients. Biological tests, X-rays and pulmonary function tests were prescribed for, respectively, 59, 65 and 45% of the patients. Following the visit, 15 patients were hospitalized (6%). The direct medical cost per acute exacerbation was estimated 3,289 francs (1994 value) of which 60% were hospital-related. An average 10.4 day sick-leave was prescribed to 21% of patients in employment. For those patients, this sick-leave was associated to an extra-cost of 1,264-1,876 francs for Social Security and of 0-2,553 francs out of pocket per episode varying according to their Benefit Regimen.  相似文献   
106.
107.
108.
109.
To compare the value of echocardiography and magnetic resonance imaging (MRI) in the assessment of the amount and extent of hypertrophy in hypertrophic cardiomyopathy (HC) and, second, to correlate the degree of hypertrophy, as assessed by MRI, with clinical and electrocardiographic parameters, 30 consecutive patients (16 men and 14 women, aged 20 to 74 years) with HC were studied. Measurements of left ventricular wall thickness were performed at 11 predetermined segments (5 basal, 5 midventricular, and 1 apical) by 2-dimensional echocardiography and MRI. Two parameters derived from MRI studies were considered as indicators of the degree and extent of hypertrophy: (1) mean of the measured wall thickness at the 11 segments, and (2) the number of segments with thickness > 15 mm. Results showed that, from a total of 330 myocardial segments, thickness could be measured by echocardiography in 221 (67%), whereas MRI allowed measurement of 320 segments (97%). When compared with clinical and electrocardiographic data, no correlation was found regarding mean wall thickness and number of hypertrophied segments by MRI except for the presence of an abnormal electrocardiographic repolarization pattern. It is concluded that MRI allows a better assessment of the degree and extension of left ventricular hypertrophy than echocardiography in HC. Despite the precise information on hypertrophy provided by MRI, the amount and degree of hypertrophy bears no correlation with most of the clinical data in these patients.  相似文献   
110.
1. We investigated the effect of exercise on plasma adrenomedullin, atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) concentrations and studied the relationship between these peptides and haemodynamic parameters in nine patients with old myocardial infarction (MI) and in eight normal subjects. 2. The exercise protocol consisted of two fixed work loads (40 and 80 W) for 4 min each and venous blood samples were taken at rest, during each exercise stage and after exercise while monitoring the mean arterial pressure (MAP) and heart rate (HR). In MI, pulmonary arterial pressure (PAP), pulmonary capillary wedge pressure (PCWP), left ventricular end-diastolic pressure (LVEDP) and cardiac output (CO) were measured throughout exercise. 3. Adrenomedullin levels did not significantly increase with exercise. Adrenomedullin levels correlated with PAP and PCWP at rest (P < 0.05). Atrial natriuretic peptide levels correlated with PAP, PCWP and LVEDP throughout exercise (P < 0.05) but, on multiple regression analysis, PCWP correlated only with ANP (P < 0.01). Brain natriuretic peptide levels correlated with LVEDP throughout exercise (P < 0.01) and its increment correlated closely with basal BNP levels at rest (P < 0.01). 4. These results suggest that adrenomedullin does not respond to the acute haemodynamic changes of exercise, whereas ANP responds to it and PCWP is the major stimulus factor. Brain natriuretic peptide responds to exercise in proportion to the basal synthesis of BNP in patients with left ventricular dysfunction and LVEDP may play a role in increasing BNP during exercise.  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