首页 | 官方网站   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   4444篇
  免费   4篇
  国内免费   1篇
工业技术   4449篇
  2021年   2篇
  2019年   2篇
  2018年   1篇
  2017年   3篇
  2015年   2篇
  2014年   1篇
  2013年   7篇
  2012年   7篇
  2011年   14篇
  2010年   3篇
  2009年   19篇
  2008年   20篇
  2007年   19篇
  2006年   13篇
  2005年   14篇
  2004年   4篇
  2003年   13篇
  2002年   4篇
  2001年   9篇
  2000年   9篇
  1999年   140篇
  1998年   1418篇
  1997年   786篇
  1996年   517篇
  1995年   261篇
  1994年   233篇
  1993年   253篇
  1992年   33篇
  1991年   40篇
  1990年   38篇
  1989年   49篇
  1988年   49篇
  1987年   28篇
  1986年   26篇
  1985年   26篇
  1984年   5篇
  1983年   11篇
  1982年   12篇
  1981年   17篇
  1980年   36篇
  1979年   5篇
  1978年   5篇
  1977年   88篇
  1976年   193篇
  1975年   6篇
  1973年   2篇
  1972年   1篇
  1970年   1篇
  1969年   1篇
  1965年   1篇
排序方式: 共有4449条查询结果,搜索用时 156 毫秒
61.
62.
63.
PAHCF and Women and Infants Hospital have been working together for many years to provide high quality, accessible prenatal and obstetrical care to low-income, inner-city residents in the Providence area. Many of these patients have multiple medical, social, and nutritional problems that place them at increased risk for poor pregnancy outcomes. The PAHCF sites offer convenient locations, evening hours, and culturally-sensitive, bilingual staffs; together the five sites provided prenatal care to nearly 1200 patients last year. Women and Infants Ambulatory Care Department provided prenatal care to an additional 1800 women in 1991, including all high risk patients referred for complications or diagnostic evaluations. All patients deliver at Women and Infants, then return to their original source of care for postpartum followup and family planning services. Patient records are readily transferred between the sites, eliminating the need for unnecessary duplication of information or laboratory tests. This close collaboration is mutually beneficial to both the health care providers and the patients whom they serve.  相似文献   
64.
Creation of a dynamic levator aponeurosis fold or double eye adds to the beauty of the East Asian. The eyes are larger and less puffy, and the eyelashes appear longer and curve up and out instead of down. The distance from the ciliary border to the eyebrow is decreased and more in proportion. The Mongolian trait is preserved.  相似文献   
65.
66.
Bacterial collagenase was used to study the susceptibility of dermal sheep collagen (DSC) cross-linked with a mixture of the water-soluble carbodiimide 1-ethyl-3-(3-dimethyl aminopropyl)-carbodiimide hydrochloride and N-hydroxysuccinimide (E/N-DSC) towards enzymatic degradation. Contrary to non-cross-linked DSC (N-DSC), which had a rate of weight-loss of 18.1% per hour upon degradation, no weight loss was observed for E/N-DSC during a 24 h degradation period. The tensile strength of the E/N-DSC samples decreased during this time period, resulting in partially degraded samples having 80% of the initial tensile strength remaining. The susceptibility of E/N-DSC samples towards enzymatic degradation could be controlled by varying the degree of cross-linking of the samples. Ethylene oxide sterilization of E/N-DSC samples made the material more resistant against degradation compared with non-sterilized E/N-DSC samples. This may be explained by a decrease of the adsorption of bacterial collagenase onto the collagen owing to reaction of ethylene oxide with remaining free amine groups in the collagen matrix.  相似文献   
67.
Autonomic dysfunction in insulin-dependent diabetic (IDDM) patients has been associated with abnormalities of left ventricular function and an increased risk of sudden death. A group of 30 patients with IDDM and 30 age, sex and blood pressure matched control subjects underwent traditional tests of autonomic function. In addition, baroreceptor-cardiac reflex sensitivity (BRS) was assessed using time domain (sequence) analysis of systolic blood pressure and pulse interval data recorded non-invasively using the Finapres beat-to-beat blood pressure recording system. 'Up BRS' sequences-increases in systolic blood pressure associated with lengthening of R-R interval, and 'down BRS' sequences-decreases in systolic blood pressure associated with shortening of R-R interval were identified and BRS calculated from the regression of systolic blood pressure on R-R interval for all sequences. We also assessed heart rate variability using power spectral analysis and, after expressing components of the spectrum in normalised units, assessed sympathovagal balance from the ratio of low to high frequency powers. IDDM subjects underwent 2-D echocardiography to assess left ventricular mass index. Standard tests of autonomic function revealed no differences between IDDM patients and control subjects, but dramatic reductions in baroreceptor-cardiac reflex sensitivity were detected in IDDM patients. 'Up BRS' when supine was 11.2 +/- 1.5 ms/mmHg (mean +/- SEM) compared with 20.4 +/- 1.95 in control subjects (p < 0.003) and when standing was 4.1 +/- 1.9 vs 7.6 +/- 2.7 ms/mmHg (p < 0.001). Down BRS when supine was 11.5 +/- 1.2 vs 22 +/- 2.6 (p < 0.001) and standing was 4.4 +/- 1.9 vs 7.3 +/- 2.5 ms/mmHg (p < 0.003). There were significant relations between impairment of the baroreflex and duration of diabetes (p < 0.001) and poor glycaemic control (p < 0.001). From a fast Fourier transformation of supine heart rate data and using a band width of 0.05-0.15 Hz as low-frequency and 0.2-0.35 Hz as high frequency total spectral power of R-R interval variability was significantly reduced in the IDDM group for both low-frequency (473 +/- 62.8 vs 746.6 +/- 77.6 ms2 p = 0.002) and high frequency bands 125.2 +/- 12.9 vs 459.3 +/- 89.8 ms2 p < 0.0001. When the absolute powers were expressed in normalised units the ratio of low frequency to high frequency power (a measure of sympathovagal balance) was significantly increased in the IDDM group (2.9 +/- 0.53 vs 4.6 +/- 0.55, p < 0.002 supine: 3.8 +/- 0.49 vs 6.6 +/- 0.55, p < 0.001 standing). Thus, time domain analysis of baroreceptor-cardiac reflex sensitivity detects autonomic dysfunction more frequently in IDDM patients than conventional tests. Impaired BRS is associated with an increased left ventricular mass index and this abnormality may have a role in the increased incidence of sudden death seen in young IDDM patients.  相似文献   
68.
69.
Both poverty and other factors associated with race are related to child health. However, the mechanisms of these relationships have not been adequately specified. The purpose of this study was to explore the relationship of the social environment to child health status in black and white children and further, to explore whether the patterns of the effects of social class were different by race. This study provides further evidence that the social environment is strongly associated with child health status. Several risk factors are similar for both white and black children: mothers who view their own health as fair or poor are much more likely to rate their children in poor health. The presence of childhood chronic medical conditions is independently associated with poor health status regardless of race. However, the relative importance of several social risks for poor health status differs between white and black children. Specifically, while low family income is a consistent risk factor for poor health among white children, low income alone is not a risk factor for black children. Among black children, other social risks that are associated with poverty, such as low maternal education and a mother's perception of her own health as poor, increased the risk of poorer health in the child.  相似文献   
70.
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-23

京公网安备 11010802026262号