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   2125篇
  免费   117篇
  国内免费   28篇
耳鼻咽喉   31篇
儿科学   38篇
妇产科学   79篇
基础医学   326篇
口腔科学   40篇
临床医学   166篇
内科学   407篇
皮肤病学   12篇
神经病学   242篇
特种医学   111篇
外科学   356篇
综合类   11篇
一般理论   2篇
预防医学   99篇
眼科学   7篇
药学   172篇
中国医学   1篇
肿瘤学   170篇
  2022年   21篇
  2021年   30篇
  2020年   26篇
  2019年   43篇
  2018年   37篇
  2017年   26篇
  2016年   35篇
  2015年   28篇
  2014年   53篇
  2013年   67篇
  2012年   88篇
  2011年   84篇
  2010年   65篇
  2009年   52篇
  2008年   98篇
  2007年   66篇
  2006年   76篇
  2005年   91篇
  2004年   74篇
  2003年   85篇
  2002年   79篇
  2001年   71篇
  2000年   66篇
  1999年   58篇
  1998年   35篇
  1997年   21篇
  1996年   19篇
  1995年   27篇
  1993年   17篇
  1992年   45篇
  1991年   39篇
  1990年   26篇
  1989年   41篇
  1988年   30篇
  1987年   18篇
  1986年   44篇
  1985年   34篇
  1984年   38篇
  1983年   35篇
  1982年   22篇
  1979年   33篇
  1978年   20篇
  1977年   21篇
  1976年   17篇
  1974年   30篇
  1972年   25篇
  1971年   18篇
  1970年   17篇
  1968年   20篇
  1966年   23篇
排序方式: 共有2270条查询结果,搜索用时 15 毫秒
1.
INTRODUCTION H pylori infection is an established risk factor for development of gastric cancer[1,2]. According to the model of carcinogenesis of the intestinal type adenocarcinoma proposed by Correa, the multi-step development starts from the condition o…  相似文献   
2.
Patients with bulimia (binge-purge syndrome) frequently complain that they consume a very restrictive diet to avoid gaining weight. To investigate this claim, 23 hospitalized bulimic patients were assessed daily for body weight, caloric intake, macronutrient diet content, activity measures, and body composition estimates during weight-stable periods. Bulimic patients ate fewer kilocalories per kilogram body weight (22.1 +/- 4.6 kcal/kg) than did age-matched normal women (29.7 +/- 6.5 kcal/kg) but had similar activity levels and body composition. Clinical variables, such as history of laxative abuse, anorexia, or obesity, and physiological characteristics, such as body weight, activity level, or dietary content, could not account for this difference in caloric consumption. Bulimic patients tended to eat a diet lower in fat and higher in protein than did control subjects. These results agree with observations of increased efficiency of caloric utilization in obese patients and support patient complaints of a tendency to gain weight easily.  相似文献   
3.
The effect of olestra on vitamin D status was assessed in a 6-wk, double-blind, placebo-controlled study involving 202 free-living adults. Subjects consumed a total of 20 g/d of olestra or triglycerides in cookies eaten at each meal. A 20-micrograms ergocalciferol capsule was taken with each morning meal. Serum 25-hydroxyergocalciferol (25-OHD2) concentrations rose from approximately 5.7 to 39.0 and 31.7 nmol/L in the placebo and olestra groups, respectively, at week 6. At week 6, 25-OHD2 contributed 46-54% to total serum 25-OHD concentration compared with 11% at baseline. The 19% decrease in serum 25-OHD2 concentrations produced by olestra in this study is equivalent to a decrease of approximately 1.2 nmol/L under nonsupplemented dietary conditions. Ingesting 20 g olestra/d in the diet is thus not expected to affect vitamin D nutritional status.  相似文献   
4.
Angiogenesis and patency of blood vessels were analyzed qualitatively in solid CNS and peripheral tissue syngeneic, allogeneic, and xenogeneic grafts and in individual cell suspension grafts of astrocytes, fibroblasts, PC12, and three additional tumor cell lines placed intracerebrally in adult host mice. Postgrafting survival times were 1 day through 4 weeks. The patency of graft vessels was determined in sections from immersion-fixed tissues incubated to reveal the endogenous peroxidase activity of host red cells trapped within the lumen of blood vessels. Additionally, horseradish peroxidase (HRP) was administered intravenously to live hosts; HRP labels host brain and graft vessels on the luminal surface and reveals the presence or absence of a blood-brain barrier (BBB) within the grafts. The origins of blood vessels supplying solid tissue xenografts were identified immunohistochemically with primary antibodies against host (athymic AKR mice) and donor (fetal Lewis rats) major histocompatibility complex (MHC) class I. Blood vessels supplying solid CNS grafts at 1-7 days post-transplantation were identified ultrastructurally and possessed interendothelial tight junctional complexes; however, they were not perfused with either host blood or blood-borne HRP prior to 8 days. Graft vessels at 10 days were outlined consistently by peroxidase-positive red cells in immersion-fixed material and labeled with blood-borne HRP. These vessels provided a BBB to the circulating HRP and exhibited interendothelial tight junctions. Evidence of angiogenesis within solid anterior pituitary grafts and the variety of cell suspension grafts was obtained prior to 3 days post-transplantation in immersion-fixed preparations; the vessels, with the notable exception of those supplying astrocyte cell suspensions, failed to present a BBB to blood-borne peroxidase. Endothelia in the solid pituitary allografts and the PC12 cell grafts were highly fenestrated and exhibited open interendothelial junctions; those in the tumor and fibroblast cell grafts, for the most part, appeared nonfenestrated, and many possessed open interendothelial junctional complexes. Immunostaining for host and donor MHC class I revealed that donor blood vessels predominate over host vessels in CNS xenografts and supply pituitary xenografts exclusively; in both preparations, donor vessels were not identified within the host CNS. Because cell suspension grafts were derived from endothelia-free preparations grown in culture, blood vessels supplying these grafts were necessarily of host CNS origin and manifested a morphological transformation from a BBB to a non-BBB endothelium. The data suggest that angiogenesis in solid CNS grafts placed into the adult host CNS, compared to similarly placed solid peripheral tissue/cell suspension grafts, is not rapid.(ABSTRACT TRUNCATED AT 400 WORDS)  相似文献   
5.
6.
A previously developed method for achieving patient relocation in fractionated stereotactic radiotherapy (attachment of an infrared fiducial system to a bite tray) relies on the integrity of a bite tray system that incorporates moulding to the patient's upper dentition. Reproducible and accurate patient positioning requires stability of the bite tray and mould during the full treatment process, both during the time the bite tray is inserted in the patient's mouth, and between separate bite tray insertions. The optimum construction method for a stable reproducible tray has not been sufficiently investigated. We undertook a study to identify factors which might influence the integrity of the hard palate bite tray system. Reprosil Fast Set Putty was used to construct 3 impression conditions; teeth only; teeth and alveolar sulcus; and teeth, alveolar sulcus, and the hard palate. Reproducibility was assessed by volunteers inserting the impressions multiple times and recording the locations of 8 standard reference points. Our results showed the optimal impression technique (i.e., the one that led to the smallest ranges in positional and rotational errors) was that which incorporated the teeth, alveolar sulcus, and hard palate.  相似文献   
7.
8.
This paper reviews the results of toxicity studies conducted in laboratory animals to evaluate the safety of the herbicide trifluralin (TFL). The data show that TFL is slightly toxic following single oral exposure. Testing for embryotoxicity in rats and rabbits indicated no teratogenic potential, and many different mutagenicity tests showed that TFL was non-genotoxic. Subchronic and chronic toxicity testing in rats, mice and dogs indicated that TFL was haematotoxic (anaemia and methaemoglobinaemia), particularly in the dog, and slightly hepatotoxic. No-observed-effect levels of 4.8 and 41 mg/kg body weight/day, respectively, were determined in dogs and rats exposed chronically to TFL. Oncogenicity studies in rats and mice revealed no carcinogenic potential. Since the data for TFL indicated no mutagenic or other special toxicological risks, it is suggested that a safety factor of 100 could be used for the determination of the acceptable daily intake of TFL, which would be 0.05 mg/kg body weight/day.  相似文献   
9.
Patients with anorexia nervosa have neuroendocrine and behavioral alterations that starvation and weight loss are thought to cause, or contribute to, since they are reversed by weight restoration. We have found that anorexics have starvation-related disturbances of neuropeptide Y (NPY), corticotropin-releasing hormone (CRH), and beta-endorphin, as determined by their measurements in cerebrospinal fluid. The relationship between these neuropeptides and several symptoms in anorexia, together with findings in experimental animals, raise a possibility that changes in the activity of these neuropeptides contribute to neuroendocrine and behavioral alterations in anorexia. Specifically, a disturbance of central nervous system CRH activity is likely to be responsible for hypercortisolemia, while a disturbance of central nervous system NPY may contribute to amenorrhea. In addition, disturbances of these neuropeptides could contribute to other symptoms such as increased physical activity, hypotension, reduced sexual interest, depression, and pathological feeding behavior.  相似文献   
10.
The purpose of this study was to determine whether disruption of early social attachment alters the activity of brain biogenic amine systems in rhesus monkeys (Macaca mulatta). Male rhesus monkey infants were deprived of maternal interaction, peer interaction, or both, during the first 22 months of life. Cerebrospinal fluid (CSF) was collected under rigorously controlled conditions approximately every month and assayed for levels of norepinephrine (NE), its major metabolite, and the metabolites of dopamine and serotonin. Mother-Deprived infants had lower levels of CSF NE than Mother-Reared infants. Mother-Deprived infants also failed to develop the same pattern of intercorrelations between compounds and month-to-month stability in levels of neurotransmitter and metabolites in CSF as the Mother-Reared infants. Finally, there were changes in CSF NE levels associated with social separation and social group formation. The brain NE system appears to be sensitive to changes in the social environment. Its level of activity, as reflected in levels of NE in CSF, appears to depend on both the prevailing social environment and the prior rearing environment.  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