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   17887篇
  免费   1262篇
  国内免费   343篇
耳鼻咽喉   129篇
儿科学   506篇
妇产科学   333篇
基础医学   1215篇
口腔科学   280篇
临床医学   1948篇
内科学   4958篇
皮肤病学   265篇
神经病学   872篇
特种医学   863篇
外科学   1644篇
综合类   1378篇
预防医学   1897篇
眼科学   518篇
药学   1517篇
  2篇
中国医学   265篇
肿瘤学   902篇
  2024年   42篇
  2023年   721篇
  2022年   1153篇
  2021年   1682篇
  2020年   1257篇
  2019年   1469篇
  2018年   1312篇
  2017年   775篇
  2016年   511篇
  2015年   508篇
  2014年   1283篇
  2013年   1050篇
  2012年   674篇
  2011年   803篇
  2010年   635篇
  2009年   613篇
  2008年   686篇
  2007年   634篇
  2006年   450篇
  2005年   414篇
  2004年   322篇
  2003年   283篇
  2002年   224篇
  2001年   159篇
  2000年   151篇
  1999年   139篇
  1998年   122篇
  1997年   115篇
  1996年   120篇
  1995年   112篇
  1994年   91篇
  1993年   89篇
  1992年   101篇
  1991年   75篇
  1990年   85篇
  1989年   77篇
  1988年   75篇
  1987年   43篇
  1986年   52篇
  1985年   68篇
  1984年   62篇
  1983年   36篇
  1982年   42篇
  1981年   37篇
  1980年   35篇
  1979年   30篇
  1978年   18篇
  1977年   23篇
  1976年   12篇
  1974年   7篇
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
111.
Odds ratio was used to evaluate relationship between sepsis in cattle less than 1 year old and mastitis in cows and erythrocyte glutathione peroxides (GSH-PX) activity as an indicator of selenium status. Data were from 178 blood samples collected from referred cases to Urmia University, Veterinary Teaching Hospital. Low activity of GSH-PX was significantly associated with higher odds of developing sepsis (P=0.005) in young cattle and mastitis (P=0.044) in adult cows. The odds ratios for the low activity of GSH-PX on incidence of sepsis and mastitis were 4.74 and 3.95, respectively. Selenium deficiency was associated with sepsis in young cattle and mastitis in cows, i.e., cattle with low activity of erythrocyte GSH-PX were at increased risk of sepsis and mastitis.  相似文献   
112.
The property of aerobic glycolysis commonly possessed by malignant cells points to a weakness in oxidative metabolism which has been equated in some tumours with partial uncoupling of oxidative phosphorylation. The suggestions are made, first, that this endogenous defect may account for spontaneous cell death , and, second, that its accentuation would inflict extensive tumour injury upon sensitive neoplasms. Certain drugs not in current use for the treatment of malignant disease are known to be able to interfere selectively with energy metabolism in sensitive tumours to such an extent that widespread necrotisation ensues. The drugs activate an endogenous destructive mechanism that appears to require oxygen. Liminal therapy, the maintenance of continuous destructive pressure on sensitive growths in such a manner that maximal anti-tumour activity in terms of interference with energy production is not achieved at any one time, and under conditions in which the oxygen supply is only partly depleted, is put forward as a possible means of achieving complete and selective tumour destruction .  相似文献   
113.
114.
新型MAO钛基生物材料的血液相容性研究   总被引:1,自引:1,他引:1  
目的初步评价新型钛基材料的血液相容性。方法采用新西兰大白兔新鲜全血,抗凝后分别与实验组和阳性对照、阴性对照组接触,用紫外-可见光分光光度计比色,评价各组的溶血率。实验符合国际化标准组织规定要求。结果新型微弧氧化钛基材料直接接触溶血率为0.79%,符合医用材料的溶血率不大于5%的要求。结论新型钛基材料具有良好的血液相容性。  相似文献   
115.
为了评价游离前列腺抗原(F PSA)/前列腺抗原(PSA)比值和PSA动态变化(年变化率)在前列腺癌诊断中的应用价值。本文应用ELISA追踪检测PSA在4~10μg/L范围患者在不同时段内PSA水平,并与正常人进行对照,利用ROC曲线,评价FPSA/PSA比值和PSA年变化率两项指标在前列腺癌诊断时的预示价值。结果表明:前列腺癌患者的FPSA/PSA比值和PSA年变化率与非前列腺癌组之间具有显著性差异(P〈0.001),当FPSA/PSA比值的临床判断值为0.21时,诊断灵敏度为93.5%,特异性为91.4%;当PSA年变化率的临床判断值为0.85%。诊断灵敏度为82.6%,诊断特异性为97.9%。前列腺增生患者FPSA/PSA比值与正常人之间无显著性差异(P〉0.05),而PSA年变化率与正常人比较具有显著性差异(P<0.001)。提示FPSA/PSA比值和PSA年变化率有助于PSA在4~10μg/L范围的患者前列腺癌的诊断。  相似文献   
116.
117.
Summary Effects of four days of intense physical activity on serum concentrations of total triglycerides, total cholesterol and apolipoproteins A-I, A-II, and B were studied in 35 well-trained young men. Serum total triglyceride levels decreased to 70% of baseline levels after 24 h, and fell further to 50% of baseline levels after 4 days. Serum levels of total cholesterol fell steadily to about 80% of baseline levels on the 4th day. Apo-B levels fell to 85% of baseline levels after 24 h, and remained at that level. Apo A-I fell to about 90%, and apo A-II to about 80% of baseline levels, causing a significant increase in the ratio of apo A-I to apo A-II. The intraindividual changes in apo B were positively correlated to changes in cholesterol during the first day (r=0.60). The changes in apo A-I and apo A-II had no significant correlation with changes in total cholesterol or triglycerides, or with one another, suggesting that apo A-I and apo A-II are metabolized independently during conditions of hard physical exercise.  相似文献   
118.
In order to study the quantitative structure/activity relationship of organic cation transport across the contraluminal side of the proximal renal tubule cell, the stopped-flow capillary microperfusion method was applied and the inhibitory potency (apparent K i values) of different homologous series of substrates against N 1-[3H]methylnicotinamide (NMeN+) transport was evaluated. Aniline and its ring- or N-substituted analogues as well as the aminonaphthalines do not interact with the contraluminal NMeN+ transporter except for the quaternary trimethylphenylammonium and pararosaniline, which bear a permanent positive charge, and for 1,8-bis-(dimethylamino)naphthaline, which forms an intramolecular hydrogen bond. If, however, one or more than one methylene group is interposed between the benzene ring and the amino group, the compounds interact with the contraluminal NMeN+ transporter in proportion to their hydrophobicity parameter, i.e. the octanol/water partition coefficient (log octanol). The catecholamines and other hydroxyl-substituted phenylethyl analogues also follow this rule. In addition, the N-heterocyclic pyridine, quinoline, isoquinoline and acridine analogues also interact with the contraluminal NMeN+ transporter, when their pK a values are higher than 5.0, and, an inverse correlation between pK a and log K i, NMeN was observed. An exception to this rule are those hydroxy compounds of pyridine, quinoline and isoquinoline that show tautomerism. These compounds slightly inhibit NMeN+ transport despite low pK a values. The quaternary nitrogen compounds of aniline and the N-heterocyclic analogues, as far as tested, all interact with the contraluminal NMeN+ transporter in relation to their hydrophobicity. The data indicate that the contraluminal NMeN+ transporter interacts with N-compounds according to their hydrophobicity and/or according to their basicity (affinity to protons). The reason for deviation of the aniline analogues and the OH-tautomeric heterocyclic N-compounds from this behaviour is discussed.  相似文献   
119.

Purpose

There is presently an ongoing debate on the relative merits of suggested criteria for spirometric airway obstruction. This study tests the null hypothesis that no superiority exists with the use of fixed ratio (FR) of forced expiratory volume in the first second (FEV1)/forced vital capacity (FVC) < 0.7 versus less than lower limit predicted (LLN) criteria with or without FEV1 <80% predicted in regards to future mortality.

Methods

In 1988–1994 the Third National Health and Nutrition Examination Survey (NHANES III) measured FEV1 and FVC with mortality follow-up data through December 31, 2011. For this survival analysis 7472 persons aged 40 and over with complete data formed the analytic sample.

Results

There were a total of 3554 deaths. Weighted Cox proportional hazards regression revealed an increased hazard ratio in persons with both fixed ratio and lower limit of normal with a low FEV1 (1.79, p < 0.0001), in those with fixed ratio only with a low FEV1 (1.77, p < 0.0001), in those with abnormal fixed ratio only with a normal FEV1 (1.28, p < 0.0001) compared with persons with no airflow obstruction (reference group). These remained significant after adjusting for demographic variables and other confounding variables.

Conclusions

The addition of FEV1 < 80% of predicted increased the prognostic power of the fixed ratio <0.7 and/or below the lower limit of predicted criteria for airway obstruction.  相似文献   
120.
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