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   3426552篇
  免费   255913篇
  国内免费   9198篇
耳鼻咽喉   46433篇
儿科学   113183篇
妇产科学   95727篇
基础医学   481706篇
口腔科学   94743篇
临床医学   314599篇
内科学   673618篇
皮肤病学   81387篇
神经病学   282353篇
特种医学   130779篇
外国民族医学   1111篇
外科学   512349篇
综合类   74061篇
现状与发展   7篇
一般理论   1334篇
预防医学   267489篇
眼科学   77699篇
药学   248286篇
  8篇
中国医学   7249篇
肿瘤学   187542篇
  2019年   27430篇
  2018年   38481篇
  2017年   29543篇
  2016年   33948篇
  2015年   38234篇
  2014年   53271篇
  2013年   79976篇
  2012年   106716篇
  2011年   113197篇
  2010年   67825篇
  2009年   64740篇
  2008年   105213篇
  2007年   111633篇
  2006年   113483篇
  2005年   109204篇
  2004年   104725篇
  2003年   100984篇
  2002年   97565篇
  2001年   165392篇
  2000年   169450篇
  1999年   142488篇
  1998年   41206篇
  1997年   36692篇
  1996年   36715篇
  1995年   35506篇
  1994年   32418篇
  1993年   30338篇
  1992年   110006篇
  1991年   105600篇
  1990年   102325篇
  1989年   98569篇
  1988年   90419篇
  1987年   88582篇
  1986年   82967篇
  1985年   79400篇
  1984年   59539篇
  1983年   50464篇
  1982年   30174篇
  1981年   26900篇
  1979年   52627篇
  1978年   37247篇
  1977年   31389篇
  1976年   29243篇
  1975年   30830篇
  1974年   36711篇
  1973年   35095篇
  1972年   32985篇
  1971年   30504篇
  1970年   28346篇
  1969年   26991篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
Clinicopathological and electron microscopical findings of eight cases of enzootic nasal adenocarcinoma of sheep, diagnosed solely in one big flock in Slovenia between years 2001 and 2003 are described. All affected sheep were female, their mean age was 4.5 ± 1.5 years and they either belonged to the Istrian pramenka breed (five sheep) or were crossbreeds (three sheep). Tumours that arose from the ethmoid area of the nasal cavity were unilateral in six cases (75%) and bilateral in two cases (25%). All tumours were classified as adenocarcinomas by histopathological examination and they displayed either a combination of tubular and papillary growth or less often solely tubular proliferation. No metastases were detected in regional lymph nodes, brain or other organs. Electron microscopical studies performed on the reprocessed paraffin‐embedded tissues revealed the presence of the virus‐like particles with an average diameter between 70 and 90 nm.  相似文献   
993.
994.
995.
996.
997.
Perforator flaps are perfused through a long vessel whose calibre decreases from its origin to the skin, because all branches have been sealed, resulting in a conduit with resistances in series, rather than a tree with resistances in parallel, as in the normal systemic circulation. This study was planned to assess whether the differences between perforator flap and normal systemic vasculature have an impact on haemodynamic parameters in perforator flaps and on their clinical significance. The study was performed on 10 patients. Echo-colour-Doppler measurement of diameters, velocity of flow and calculations of flow rate were made at the level of flap pedicle artery and skin perforator artery, pre- and post-operatively in each patient. Statistical analysis used the Wilcoxon matched pairs signed sum rank test. Our data show that in the donor area pre-operatively, blood velocity in skin artery perforator is lower that in the corresponding pedicle artery, whereas post-operatively, in perforator flaps, blood velocity in the perforator is higher than in the pedicle. The difference was statistically significant (P<0.01). There is an inversion of the gradient of blood velocity between pedicle artery and perforator artery compared to normal circulation. Furthermore, in normal circulation flow through the perforator was found smaller than that at the pedicle, whereas in perforator flaps, flow through the perforator is smaller but is a greater proportion of the flow through the pedicle and the difference is statistically significant (P<0.01). Therefore, the velocity of blood and the rate of flow reaching the skin are higher in perforator flaps than in normal circulation.  相似文献   
998.
Abstract Chorea is a rare complication of polycythaemia vera. Polycythaemic chorea occurs predominantly in females and usually in generalised form. We present a 66-year-old woman with acute onset hemichorea-ballism with no vascular pathology in the basal ganglia region. A clear relationship was observed between the onset of chorea and worsening of haematological parameters in the patient. After repeated phlebotomies the patient's clinical status was improved. Polycythaemic chorea must be considered, especially in the elderly, as early diagnosis leads to effective treatment and prevention of complications.  相似文献   
999.
A new semi-empirical formula for the evaluation of (n,(3)He) reaction cross-sections at the energy of 14.6 and 20 MeV is presented. Formula was derived using the analytical expression for the evaluation of the (3)He spectrum within the frame of pre-equilibrium exciton model. The systematics obtained is compared with the empirical formula for the (n,(3)He) reaction cross-section.  相似文献   
1000.
SETTING: Tuberculosis (TB) cases reported from nine districts of Madrid, where the percentage of immigrant population varied from 1.9% in 1996 to 12.2% in 2003. OBJECTIVE: To describe the trends in TB incidence from 1994 to 2003. DESIGN: Observational study. RESULTS: Between 1994-1995 and 2002-2003, the TB rate decreased from 48.5 (95% CI 45.8-51.1) to 23.3 per 100000 population (95% CI 21.5-25.1) (P < 0.001). The percentage of TB cases co-infected with HIV decreased from 55.9% in 1994 to 14.3% in 2003 (P < 0.001), whereas TB cases in foreigners increased from 2.6% in 1994 to 33.7% in 2003 (P < 0.001). CONCLUSION: Although the TB rates showed a marked decrease in the study period, the increasing impact of immigration contributed to slowing down the trend.  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