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   2394830篇
  免费   173548篇
  国内免费   3519篇
耳鼻咽喉   33071篇
儿科学   78092篇
妇产科学   63938篇
基础医学   352548篇
口腔科学   66902篇
临床医学   214419篇
内科学   466446篇
皮肤病学   53083篇
神经病学   188933篇
特种医学   89349篇
外国民族医学   490篇
外科学   360980篇
综合类   48010篇
现状与发展   12篇
一般理论   862篇
预防医学   185716篇
眼科学   55637篇
药学   177989篇
  11篇
中国医学   4885篇
肿瘤学   130524篇
  2021年   20495篇
  2019年   20772篇
  2018年   28712篇
  2017年   21501篇
  2016年   24017篇
  2015年   26944篇
  2014年   37962篇
  2013年   56361篇
  2012年   77994篇
  2011年   82997篇
  2010年   48944篇
  2009年   46011篇
  2008年   77272篇
  2007年   82223篇
  2006年   82938篇
  2005年   80374篇
  2004年   76830篇
  2003年   73860篇
  2002年   71374篇
  2001年   109621篇
  2000年   112244篇
  1999年   94140篇
  1998年   27273篇
  1997年   23863篇
  1996年   24241篇
  1995年   22841篇
  1994年   20992篇
  1993年   19786篇
  1992年   72175篇
  1991年   70232篇
  1990年   68542篇
  1989年   65792篇
  1988年   60409篇
  1987年   59229篇
  1986年   55309篇
  1985年   53079篇
  1984年   39373篇
  1983年   33460篇
  1982年   19882篇
  1979年   35923篇
  1978年   25692篇
  1977年   21250篇
  1976年   20353篇
  1975年   21845篇
  1974年   26184篇
  1973年   24832篇
  1972年   23229篇
  1971年   22076篇
  1970年   20271篇
  1969年   19335篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
The aim of the present study was to explore differences in the clinical expression, clinical diagnoses and management of airway diseases in a primary-care setting. Patients aged >or=35 yrs who had ever smoked were enrolled when they presented for any reason to one of eight rural primary-care practices. Respiratory symptom questionnaires and spirometry were administered. In total, 1,034 patients had acceptable and reproducible spirometry, of whom 550 (53%) were males and 484 (47%) were females. Males smoked more than females (41.2 versus 29.2 pack-yrs) respectively, and were more likely to have a pre-bronchodilator forced expiratory volume in one second/forced vital capacity <0.70 at 22.4 versus 11.8%, respectively. However, more females than males reported breathlessness (51.0 versus 42.8%, respectively), a prior diagnosis compatible with airflow obstruction and taking respiratory medications (23.4 versus 14.9%, respectively). In conclusion, the current results suggest that females are more likely than males to report breathlessness and be prescribed respiratory medications independent of differences in the severity of airflow obstruction.  相似文献   
72.
A very high ventilatory response to hypoxia is believed necessary to reach extreme altitude without oxygen. Alternatively, the excessive ventilation could be counterproductive by exhausting the ventilatory reserve early on. To test these alternatives, 11 elite climbers (2004 Everest-K2 Italian Expedition) were evaluated as follows: 1) at sea level, and 2) at 5,200 m, after 15 days of acclimatisation at altitude. Resting oxygen saturation, minute ventilation, breathing rate, hypoxic ventilatory response, maximal voluntary ventilation, ventilatory reserve (at oxygen saturation = 70%) and two indices of ventilatory efficiency were measured. Everest and K2 summits were reached 29 and 61 days, respectively, after the last measurement. Five climbers summited without oxygen, the other six did not, or succeeded with oxygen (two climbers). At sea level, all data were similar. At 5,200 m, the five summiters without oxygen showed lower resting minute ventilation, breathing rate and ventilatory response to hypoxia, and higher ventilatory reserve and ventilatory efficiency, compared to the other climbers. Thus, the more successful climbers had smaller responses to hypoxia during acclimatisation to 5,200 m, but, as a result, had greater available reserve for the summit. A less sensitive hypoxic response and a greater ventilatory efficiency might increase ventilatory reserve and allow sustainable ventilation in the extreme hypoxia at the summit.  相似文献   
73.
74.
75.
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   
76.
77.
78.
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   
79.
Although melanocytic skin lesions have been recognized since antiquity, their literature was limited to Caucasians. To date, the clinicopathologic features of these lesions in Egyptians are still unknown. To define these features, diagnostic records of the melanocytic skin lesions received at the Pathology Department, Assuit University Hospitals (1989-2004) were reviewed. The lesions examined included 12 benign naevi (BN), 10 dysplastic naevi (DN), and 21 cutaneous malignant melanomas (CMMs). The DN and CMMs were more common in men than in women (2 : 1 and 1.5 : 1, respectively) while BN were more common in women (2 : 1). The average age incidence was 33+/-5, 38+/-7 and 54+/-3 years, for BN, DN and CMM, respectively. The lower limb (13/21, 62%), head and neck (7/21, 33%) were the most common sites for CMMs. The average size (mm) was 2+/-0.3, 4+/-0.6 and 21+/-0.3 for BN, DN and CMMs, respectively. Recurrence occurred in 10% of CMMs. Histologically, CMMs were of nodular type and composed of epithelioid (7/21, 33%), spindle cells (1/21, 5%), or mixed cells (13/21, 62%). The mean tumour thickness (Breslow) was 6+/-0.5 mm. CMMs included two of 21(9%), three of 21(14%), six of 21(38%), and 10 of 21(38%) with Clark level II, III, IV and V. In Egypt, CMM is the third most common cutaneous neoplasm following squamous and basal cell carcinomas. Compared with Western societies, melanoma has a male sex predilection, similar histological features but different topographical distribution and rare incidence. The striking difference from Western series is the incidence of nodular melanoma - in the West this represents 15-30% of melanomas, with superficial spreading being the majority. Another key difference from the West is the 'sun-bed' culture of the West and the desire to have suntans. This is the first study that reports the clinicopathologic features of melanocytic skin lesions in Egypt.  相似文献   
80.
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