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   1512734篇
  免费   114260篇
  国内免费   17975篇
耳鼻咽喉   20261篇
儿科学   44849篇
妇产科学   41100篇
基础医学   215910篇
口腔科学   39669篇
临床医学   140358篇
内科学   287104篇
皮肤病学   29020篇
神经病学   113198篇
特种医学   58878篇
外国民族医学   506篇
外科学   221559篇
综合类   63156篇
现状与发展   56篇
一般理论   325篇
预防医学   106826篇
眼科学   36108篇
药学   121944篇
  195篇
中国医学   15051篇
肿瘤学   88896篇
  2021年   19176篇
  2020年   13477篇
  2019年   15758篇
  2018年   20175篇
  2017年   16223篇
  2016年   16927篇
  2015年   22108篇
  2014年   28845篇
  2013年   35540篇
  2012年   50149篇
  2011年   54478篇
  2010年   32192篇
  2009年   28547篇
  2008年   46680篇
  2007年   49698篇
  2006年   50305篇
  2005年   49625篇
  2004年   43846篇
  2003年   42443篇
  2002年   40809篇
  2001年   64133篇
  2000年   65990篇
  1999年   57275篇
  1998年   18137篇
  1997年   16534篇
  1996年   16050篇
  1995年   15096篇
  1994年   14013篇
  1992年   43400篇
  1991年   42466篇
  1990年   41629篇
  1989年   40318篇
  1988年   37588篇
  1987年   36637篇
  1986年   34871篇
  1985年   33046篇
  1984年   24493篇
  1983年   21266篇
  1982年   12625篇
  1979年   22917篇
  1978年   15992篇
  1977年   13842篇
  1976年   13063篇
  1975年   14313篇
  1974年   16803篇
  1973年   16189篇
  1972年   15441篇
  1971年   14330篇
  1970年   13303篇
  1969年   12801篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
141.
Background The appearance of eosinophils is a hallmark sign of the allergic late-phase response (LPR). Eosinophil cationic protein (ECP), a readily measurable product released from activated eosinophils, has so far not been evaluated in the ocular LPR. Objective Two sets of trials were performed in order to investigate changes of local and systemic eosinophil activity and their possible link with symptoms and hyper-reactivity in the allergic LPR in the eye. Methods In the first experiment, ECP was analysed in tears and serum and the clinical reaction was evaluated during a 72-h time–course after a single, high-dose allergen challenge out of season in one eye of 15 pollen-sensitized volunteers. In a second experiment, the hypothesis of an increased clinical response to an allergen challenge in an eye that had been provoked with allergen 48h previously was tested in nine sensitized individuals. Results In the first experiment, symptoms at 10 min and 2, 4, 6, 8 and 24 h significantly exceeded base line scores of the challenged eyes. Tear ECP was significantly elevated in challenged eyes compared to contralateral eyes at 6, 8 and 24 h. In addition, symptoms and ECP release correlated significantly at the 24-h evaluation. Serum ECP remained unchanged throughout the study period. In the second experiment, conjunctival hyperreactivity 48h after an allergen challenge was not confirmed. Conclusion ECP secretion occurs in the experimental ocular LPR and is in part associated with the magnitude of the clinical reaction, which suggests a truly pathogenic role of the activated eosinophil in pollen-induced allergic conjunctivitis.  相似文献   
142.
143.
The effects of daily oral administration of a high dose of 10 mg norethisterone acetate (NET-Ac.)/kg/day over 14 weeks on serum lipid and lipoprotein parameters as well as on blood coagulation were investigated in female monkeys (M. fascicularis). Measurements of lipids and lipoprotein cholesterol were performed in weeks —5 and — 1 before treatment and in weeks 4, 8 and 12 after treatment. In addition, various blood coagulation and fibrinolytic parameters were determined in weeks 11–14 after treatment with NET-Ac. Furthermore, the serum levels of norethisterone (NET) were determined in order to monitor the real systemic compound exposure and revealed that Cmax and AUC (0–3 h) values reached for norethisterone in this experiment in monkeys were about 25 times higher than those obtained after an oral contraceptive dose of NET-Ac. in women.

The results of lipid and lipoprotein cholesterol determinations showed decreases in serum total lipids, phospholipids, triglycerides and total cholesterol associated with similar decreases in HDL-, LDL- and VLDL-cholesterol fractions after NET-Ac.-treatment in monkeys. These effects were observed from week 4 onwards and maintained their magnitude up to week 12 after treatment. Since both HDL- and LDL-cholesterol fractions decreased, the HDL/LDL-ratio remained almost unchanged. Thus, the results obtained in this study after high-dose treatment with NET-Ac. in monkeys did not indicate any changes of lipid and lipoprotein parameters which in humans are supposed to be associated with an increased risk of cardiovascular lesions, namely a decrease in HDL- and increase in LDL-cholesterol fractions.

The results of blood coagulation and fibrinolytic parameters showed increased antithrombin-III and plasminogen levels besides minor changes in other parameters, thus indicating that NET-Ac. -treatment does not contribute to an increased risk of cardiovascular thrombotic events in the cynomolgus monkey.  相似文献   

144.
145.
146.
The phytotoxicity of heavy metals and pesticides was studied by using the fluorescence induction from the alga Dunaliella tertiolecta. The complementary area calculated from the variable fluorescence induction was used as a direct parameter to estimate phytotoxicity. The value of this parameter was affected when algae were treated with different concentrations of mercury, copper, atrazine, DCMU, Dutox, and Soilgard. The toxic effect of these pollutants was estimated by monitoring the decrease in the complementary area, which reflects photosystem II photochemistry. Further, the authors have demonstrated the advantage of using the complementary area as a parameter of phytotoxicity over using variable fluorescence yield. The complementary area of algal fluorescence can be used as a simple and sensitive parameter in the estimation of the phytotoxicity of polluted water.  相似文献   
147.
148.
149.
Falls among the elderly: epidemiology and prevention   总被引:1,自引:0,他引:1  
Harmful psychological and physical consequences may result when elderly people fall. I summarize the epidemiology of falls among elderly people and focus on three potentially remediable causes of falls: reduced peripheral neurosensation, the use of psychoactive medication, and environmental hazards. From 1960 to 1980, death rates from falls among white persons 75 years of age and older have decreased by more than 50%. Fall rates among community-dwelling elderly people increase with age and are greater for women than men. The death rates from falls, however, are now greater for men than women. Reduced peripheral neurosensation in the lower extremities may be a significant cause of falls among the elderly. Recreational walking or physical therapy may improve these deficits and lead to fewer falls. The use of psychoactive medications, most commonly benzodiazepine sedatives, is possibly associated with an increased risk of falls and hip fractures; greater caution in the use of these medications is warranted. The elimination or redesign of steps and curbs and the provision of hand railings and walking aids may be the most effective environmental approaches to preventing falls. These conclusions need further study in community-dwelling elderly populations.  相似文献   
150.
The relationship between stroke and physical disability was examined in a cohort of adult, Framingham, Massachusetts, residents who, between 1948 and 1951, were assembled for a longitudinal examination of cardiovascular disease. Multivariate analyses examined the amount of residual disability attributable to stroke among 2540 community-dwelling survivors, 27 years after their initial examination, after controlling for age, cardiovascular risk factors, other cardiovascular diseases, and eight general health conditions related to physical disability. Among men living in the community, a history of stroke explained 12% of the variance in physical disability. Suffering a stroke, however, was not as strongly related to physical disability among women living in the community, accounting for only 3% of the variance. Results suggest that although older men and women die from the same major causes, they may not be disabled by the same conditions.  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