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   1453篇
  免费   103篇
  国内免费   15篇
耳鼻咽喉   12篇
儿科学   26篇
妇产科学   25篇
基础医学   279篇
口腔科学   60篇
临床医学   121篇
内科学   354篇
皮肤病学   18篇
神经病学   174篇
特种医学   33篇
外科学   155篇
综合类   4篇
预防医学   108篇
眼科学   11篇
药学   126篇
中国医学   6篇
肿瘤学   59篇
  2023年   18篇
  2022年   40篇
  2021年   97篇
  2020年   39篇
  2019年   62篇
  2018年   68篇
  2017年   49篇
  2016年   49篇
  2015年   46篇
  2014年   72篇
  2013年   95篇
  2012年   112篇
  2011年   109篇
  2010年   68篇
  2009年   38篇
  2008年   75篇
  2007年   54篇
  2006年   56篇
  2005年   64篇
  2004年   60篇
  2003年   66篇
  2002年   47篇
  2001年   31篇
  2000年   30篇
  1999年   21篇
  1998年   4篇
  1997年   6篇
  1996年   11篇
  1995年   5篇
  1993年   2篇
  1992年   5篇
  1991年   9篇
  1990年   4篇
  1989年   6篇
  1988年   6篇
  1987年   9篇
  1986年   3篇
  1985年   11篇
  1984年   5篇
  1983年   3篇
  1982年   3篇
  1981年   1篇
  1980年   5篇
  1979年   1篇
  1978年   1篇
  1974年   2篇
  1970年   2篇
  1968年   1篇
排序方式: 共有1571条查询结果,搜索用时 0 毫秒
81.
Zellweger syndrome (ZS) and some peroxisomal diseases are severe inherited disorders mainly characterized by neurological symptoms and cerebellum abnormalities, whose pathogenesis is poorly understood. Biochemically, these diseases are mainly characterized by accumulation of pristanic acid (Prist) and other fatty acids in the brain and other tissues. In this work, we evaluated the in vitro influence of Prist on redox homeostasis by measuring lipid, protein, and DNA damage, as well as the antioxidant defenses and the activities of aconitase and α-ketoglutarate dehydrogenase in cerebellum of 30-day-old rats. The effect of Prist on DNA damage was also evaluated in blood of these animals. Some parameters were also evaluated in cerebellum from neonatal rats and in cerebellum neuronal cultures. Prist significantly increased malondialdehyde (MDA) levels and carbonyl formation and reduced sulfhydryl content and glutathione (GSH) concentrations in cerebellum of young rats. It also caused DNA strand damage in cerebellum and induced a high micronuclei frequency in blood. On the other hand, this fatty acid significantly reduced α-ketoglutarate dehydrogenase and aconitase activities in rat cerebellum. We also verified that Prist-induced increase of MDA levels was totally prevented by melatonin and attenuated by α-tocopherol but not by the nitric oxide synthase inhibitor Nω-nitro-l-arginine methyl ester, indicating the involvement of reactive oxygen species in this effect. Cerebellum from neonate rats also showed marked alterations of redox homeostasis, including an increase of MDA levels and a decrease of sulfhydryl content and GSH concentrations elicited by Prist. Finally, Prist provoked an increase of dichlorofluorescein (DCFH) oxidation in cerebellum-cultivated neurons. Our present data indicate that Prist compromises redox homeostasis in rat cerebellum and blood and inhibits critical enzymes of the citric acid cycle that are susceptible to free radical attack. The present findings may contribute to clarify the pathogenesis of the cerebellar alterations observed in patients affected by ZS and some peroxisomal disorders in which Prist is accumulated.  相似文献   
82.

Purpose

The aim of this study was to highlight the challenges for early diagnosis and the difficulties observed in surgical treatment of patients with transsphenoidal meningoencephalocele associated with cleft lip and/or palate.

Method

We evaluated six male patients treated over the course of 4 years. Five patients presented encephalic herniation with nonfunctional brain tissue; one of these presented herniation of the pituitary gland and cerebral ventricles.

Results

All the patients received surgical treatment for the cleft lip and/or palate. Only one patient underwent repair of the meningoencephalocele, via nasal endoscopy. There were no postprocedural clinical or surgical complications.

Conclusion

The tendency is to avoid neurosurgery, opting for periodic follow-up with magnetic resonance imaging. In the presence of cleft palate, palatoplasty is essential to protect the meningoencephalocele.
  相似文献   
83.
ABSTRACT

Functional recovery following general nerve reconstruction is often associated with poor results. Comparing to rat and mice experimental studies, there are much fewer investigations on nerve regeneration and repair in the sheep, and there are no studies on this subject using gait analysis in the sheep model as an assessment tool. Additionally, this is the first study evaluating obstacle negotiation and the compensatory strategies that take place at each joint in response to the obstacle during locomotion in the sheep model. This study aims to get kinematic data to serve as a template for an objective assessment of the ankle joint motion in future studies of common peroneal nerve (CP) injury and repair in the ovine model. Our results show that a moderately high obstacle set to 10% of the sheep’s hindlimb length was associated to several spatial and temporal strategies in order to increase hoof height during obstacle negotiating. Sheep efficiently cleared an obstacle by increasing knee, ankle and metatarsophalangeal flexion during swing, whereas the hip joint is not affected. This study establishes the bounds of normal motion in the neurologically intact hindlimb when approached and cleared an obstacle and provides baseline data for further studies of peripheral nerve research in the ovine model.  相似文献   
84.
ObjectiveTo provide empirical evidence to assess whether having immigrant parents is a source of variation in health status and in health services’ utilization among children.MethodThe analysis was based on the sample of children from the Catalan Health Survey, 2006. Modelling of health status and use of health services was developed from the specification of distinct probabilistic models.ResultsThe results indicate that the children of immigrants had a significantly fewer chronic diseases, while perceived health status, according to the self-evaluation of the parents or responsible person, was worse if both parents belonged to this group. Significant differences were found in the utilization of distinct health services.ConclusionsThe analyses developed suggest that parental origin leads to differences in the utilization of the various levels of the Spanish health system. While no widespread pattern of increased or decreased utilization of the whole system was identified, differences were found in the number of specialist visits and admissions. Statements of the child's perceived health status were influenced by immigrant families’ socioeconomic conditions, which probably affected outcomes.  相似文献   
85.
Diphenyl diselenide (PhSe)2 is an organic selenium compound that has been little studied. In this study we investigated the effects of (PhSe)2 (0.1-3 microM) in a classical model of in vitro brain ischemia, which consists of exposing rat hippocampal slices to oxygen-glucose deprivation (OGD). Hippocampal slices were exposed for 60 min to OGD and the cellular viability (performed by MTT assay) as well as the immunocontent of nitric oxide synthase inducible (iNOS) were evaluated after 180 min of a recovery period. OGD decreased cellular viability by 50% and increased more than twice the immunocontent of iNOS of hippocampal slices. (PhSe)2 (1 and 3 microM) added during OGD and the recovery period abolished both effects. These results demonstrate for the first time the neuroprotective effects of (PhSe)2. Although the selenium analog--ebselen--has been widely used in ischemia models, our results suggest that other selenoorganic compounds could be investigated as pharmacological tools against brain disorders.  相似文献   
86.
Adenine and guanine nucleotides have been shown to exert multiple roles in central and peripheral nervous systems, and the sequential breakdown of these nucleotides by enzymatic systems is an important step in the modulation of their extracellular effects. The aim of this study was to investigate whether nucleotide hydrolysis also occurs in the cerebrospinal fluid (CSF) of rats. CSF was able to hydrolyze all guanine and adenine nucleotides investigated (2.0 mM): GDPADP=ATP=GTPAMP=GMP. More detailed studies with the diphosphate nucleotides showed that the hydrolysis of ADP and GDP was linear with incubation time and protein concentration. The apparent KM (Henry–Michaelis–Menten constant) and V (maximal velocity) values for ADP and GDP were 164.3±54.7 μM and 12.2±3.8 nmol Pi/min per mg protein, and 841.0±90.2 μM and 22.8±8.0 nmol Pi/min per mg protein. The sum of ADP, GDP and UDP hydrolysis (2.0 mM) upon individual incubations with CSF was similar to the hydrolysis observed when all three nucleotides were incubated together. This pattern of hydrolysis strongly suggests the involvement of more than one enzyme activity. The higher maximum activity for GDP and UDP compared to ADP is compatible with presence of a soluble NTDPase5.  相似文献   
87.
This study analyses the serogroups/types (SGTs) and resistance to penicillin and erythromycin of 3921 strains isolated from 1990 to 1999 in children aged 0-14 y in Spanish hospitals of all the autonomous communities. Based on the age of the children, strains have been divided into five groups: 0-6 mo, > 6-1 y, > 1-2 y, > 2-5 y and > 5 y. While only eight SGTs were responsible for 80% of the infections in children from 6 mo to 2 y of age, this number increased to 11 and 16 for the groups > 2-5 y and > 5-14 y, respectively. SGTs 6, 14 and 19 were prevalent in blood and otic exudates. SGTs 1, 4, 5, 12 and 18 were more frequent in invasive disease but serotype 3 was clearly associated with otitis. Serotypes I and 5 were quite significant in children of over 2 y of age, and this should be taken into account in future vaccine formulations. CONCLUSION: Although high, the rate of penicillin resistance in the paediatric population has remained stable in recent years. Conversely, erythromycin resistance is still increasing in our country. Coverage by the 7-valent vaccine was 78 and 81% for blood and otic isolates, respectively. These coverage levels would be increased by 9% and 3% if 9-valent (plus 1 + 5 serotypes) were used and by an additional 2.6% and 7.6% using the 11-valent (plus 3 + 7) formulation.  相似文献   
88.
89.
Two cases of peripelvic hemorrhage simulating tumors (Antopol-Goldman lesion) are reported. In the 2 cases, nephrectomies were performed. With more knowledge of this lesion, and of its rapid disappearance, a waiting period and repeated intravenous pyelogram might prevent some unnecessary surgery.  相似文献   
90.
Oral and intraperitoneal administration of the nucleoside guanosine have been shown to prevent quinolinic acid- (QA) and alpha-dendrotoxin-induced seizures, impair memory, and impair anxiety in rats and mice. We investigated the effect of 2-weeks ad lib orally administered guanosine (0.5 mg/ml) on seizures induced by QA, inhibitory avoidance memory, and locomotor performance in rats. We also studied the mechanism of action of guanosine through the measurement of its concentration in the cerebrospinal fluid (CSF) and its effect on glutamate uptake in cortical slices of rats. QA produced seizures in 85% of rats, an effect partially prevented by guanosine (53% of seizures; P = 0.0208). Guanosine also impaired retention on the inhibitory avoidance task (P = 0.0278) and decreased locomotor activity on the open field test (P = 0.0101). The CSF guanosine concentration increased twofold in the treated group compared to that in the vehicle group (P = 0.0178). Additionally, QA promoted a 30% decrease in glutamate uptake as compared to that with intracerebroventricular saline administration, an effect prevented by guanosine in animals protected against QA-induced seizures. Altogether, these findings suggest a potential role of guanosine for treating diseases involving glutamatergic excitotoxicity such as epilepsy. These effects seem to be related to modulation of glutamate uptake.  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