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   2599篇
  免费   144篇
  国内免费   1篇
  2744篇
  2023年   2篇
  2022年   17篇
  2021年   21篇
  2020年   16篇
  2019年   24篇
  2018年   37篇
  2017年   29篇
  2016年   50篇
  2015年   89篇
  2014年   104篇
  2013年   192篇
  2012年   167篇
  2011年   157篇
  2010年   103篇
  2009年   119篇
  2008年   163篇
  2007年   174篇
  2006年   173篇
  2005年   171篇
  2004年   165篇
  2003年   167篇
  2002年   198篇
  2001年   31篇
  2000年   21篇
  1999年   21篇
  1998年   34篇
  1997年   27篇
  1996年   24篇
  1995年   18篇
  1994年   19篇
  1993年   26篇
  1992年   26篇
  1991年   17篇
  1990年   15篇
  1989年   11篇
  1988年   11篇
  1987年   2篇
  1986年   10篇
  1985年   7篇
  1984年   7篇
  1983年   10篇
  1982年   21篇
  1981年   12篇
  1980年   10篇
  1978年   3篇
  1977年   7篇
  1976年   5篇
  1970年   3篇
  1969年   2篇
  1968年   2篇
排序方式: 共有2744条查询结果,搜索用时 0 毫秒
51.
PurposeThe Glaucoma Stereo Analysis Study (GSAS), a cross sectional multicenter collaborative study, used a stereo fundus camera to assess various morphological parameters of the optic nerve head (ONH) in glaucoma patients and investigated the relationships between these parameters and patient characteristics.ResultsPatient characteristics included refractive error of −3.38±3.75 diopters, intraocular pressure (IOP) of 13.6±2.6 mmHg, and visual field mean deviation (MD) of −4.71±3.26 dB. Representative ONH parameters included a horizontal disc width of 1.66±0.28 mm, vertical disc width of 1.86±0.23 mm, disc area of 2.42±0.63 mm2, cup area of 1.45±0.57 mm2, and cup volume of 0.31±0.22 mm3. Correlation analysis revealed significant negative associations between vertical cup-to-disc ratio (0.82±0.08) and MD (r = −0.40, P<0.01) and between disc tilt angle (10.5±12.5 degrees) and refractive error (r = −0.36, P<0.01). Seventy-five percent of the eyes had a positive value for rim decentering (0.30±0.42), indicating that rim thinning manifested more often as an inferior lesion than a superior lesion.ConclusionWe used stereoscopic analysis to establish a database of ONH parameters, which may facilitate future studies of glaucomatous changes in ONH morphology.  相似文献   
52.
The membrane topology of Om45 in the yeast mitochondrial outer membrane (OM) is under debate. Here, we confirm that Om45 is anchored to the OM from the intermembrane space (IMS) by its N-terminal hydrophobic segment. We show that import of Om45 requires the presequence receptors, Tom20 and Tom22, and the import channel of Tom40. Unlike any of the known OM proteins, Om45 import requires the TIM23 complex in the inner membrane, a translocator for presequence-containing proteins, and the membrane potential (ΔΨ). Therefore, Om45 is anchored to the OM via the IMS by a novel import pathway involving the TIM23 complex.  相似文献   
53.

Background

It is time-consuming to obtain the square root of airway wall area of the hypothetical airway with an internal perimeter of 10 mm (√Aaw at Pi10), a comparable index of airway dimensions in chronic obstructive pulmonary disease (COPD), from all airways of the whole lungs using 3-dimensional computed tomography (CT) analysis. We hypothesized that √Aaw at Pi10 differs among the five lung lobes and √Aaw at Pi10 derived from one certain lung lobe has a high level of agreement with that derived from the whole lungs in smokers.

Methods

Pulmonary function tests and chest volumetric CTs were performed in 157 male smokers (102 COPD, 55 non-COPD). All visible bronchial segments from the 3rd to 5th generations were segmented and measured using commercially available 3-dimensional CT analysis software. √Aaw at Pi10 of each lung lobe was estimated from all measurable bronchial segments of that lobe.

Results

Using a mixed-effects model, √Aaw at Pi10 differed significantly among the five lung lobes (R2 = 0.78, P<0.0001). The Bland-Altman plots show that √Aaw at Pi10 derived from the right or left upper lobe had a high level of agreement with that derived from the whole lungs, while √Aaw at Pi10 derived from the right or left lower lobe did not.

Conclusion

In male smokers, CT-derived airway wall area differs among the five lung lobes, and airway wall area derived from the right or left upper lobe is representative of the whole lungs.  相似文献   
54.
Cynomolgus macaques (Macaca fascicularis, Mafa) have emerged as important animal models for biomedical research, necessitating a more extensive characterization of their major histocompatibility complex polymorphic regions. The current information on the polymorphism or diversity of the polygenetic Mafa class I A loci is limited in comparison to the more commonly studied rhesus macaque Mafa class I A loci. Therefore, in this paper, to better elucidate the degree and types of polymorphisms and genetic differences of Mafa-A1 among three native Southeast Asian populations (Indonesian, Vietnamese, and Filipino) and to investigate how the allele differences between macaques and humans might have evolved to affect their respective immune responses, we identified 83 Mafa-A loci-derived alleles by DNA sequencing of which 66 are newly described. Most alleles are unique to each population, but seven of the most frequent alleles were identical in sequence to some alleles in other macaque species. We also revealed (1) the large and dynamic genetic and structural differences and similarities in allelic variation by analyzing the population allele frequencies, Hardy-Weinberg’s equilibrium, heterozygosity, nucleotide diversity profiles, and phylogeny, (2) the difference in genetic structure of populations by Wright’s FST statistic and hierarchical analysis of molecular variance, and (3) the different demographic and selection pressures on the three populations by performing Tajima’s D test of neutrality. The large level of diversity and polymorphism at the Mafa-A1 was less evident in the Filipino than in the Vietnam or the Indonesian populations, which may have important implications in animal capture, selection, and breeding for medical research.  相似文献   
55.
We describe here the discovery and biological profile of a series of isoindolinone derivatives as developed mGluR1 antagonists. Our combined strategy of rapid parallel synthesis and conventional medicinal optimization successfully led to N-cyclopropyl 22 and N-isopropyl isoindolinone analogs 21 and 23 with improved in vivo DMPK profiles. Moreover the most advanced analog 23 showed an oral antipsychotic-like effect at a dose of 1 mg/kg in an animal model.  相似文献   
56.
An alarm pheromone released from stressed conspecifics evokes behavioral and autonomic responses in rats. We have previously reported that male Wistar rats show behavioral changes including increased sniffing, walking and rearing, and decreased resting as well as exaggerated response of body temperature to a novel environment [known as stress-induced hyperthermia (SIH)] when they are exposed to an alarm pheromone released from other male rats receiving foot shocks. The purpose of the present study was to examine the role of testosterone in the production and release of the alarm pheromone using these behavioral and autonomic responses in recipient rats. Three groups of alarm pheromone donors were presented, namely, intact males, castrated males, and testosterone-implanted castrated males. The effects of the alarm pheromone on the autonomic responses did not differ among the three groups, regardless of the donor's steroidal milieu, whereas behavioral responses were altered by castrating the donor males and the effects were restored by testosterone implantation. These results suggest that the alarm pheromone released from stressed male rats can be classified into at least two categories according to the androgen dependency of their production and/or release.  相似文献   
57.
Abstract: Changes in extracellular levels of acetylcholine (ACh) and choline (Ch) in the striatum of rats were examined by in vivo microdialysis after intraperitoneal injections of drugs. A dopamine D2 antagonist, sulpiride (20 mg/kg), and a muscarinic antagonist, atropine (3.5 mg/kg), increased ACh levels and decreased Ch levels. On the contrary, the D2 agonist (±)-2-( N -phenylethyl- N -propyl)amino-5-hydroxytetralin (N-434; 5 mg/kg) and an anesthetic, pentobarbital (50 mg/kg), decreased ACh levels and increased Ch levels. Perfusion of 10 µ M hemicholinium-3 (HC-3), a Ch uptake inhibitor, through the striatum induced a complete inhibition of ACh release and increased Ch levels in all drug-treated groups. The degree of relative increase in the level of Ch induced by HC-3 differed among the drug-pretreated groups; compared with the control group, the relative increase was larger in the sulpiride- and atropine-treated groups and smaller in the N-434 and pentobarbital-treated groups. Thus, we demonstrated reciprocal relations between extracellular concentrations of Ch and ACh after treatments by drugs. The data suggest that in the striatum, which is rich in cholinergic innervation, the extracellular Ch concentration is to a large extent determined by activity of the cholinergic transmission reflected in high-affinity choline uptake.  相似文献   
58.

Objectives

The Japanese Orthopaedic Association (JOA) score is widely used to assess the severity of clinical symptoms in patients with cervical compressive myelopathy, particularly in East Asian countries. In contrast, modified versions of the JOA score are currently accepted as the standard tool for assessment in Western countries. The objective of the present study is to compare these scales and clarify their differences and interchangeability and verify their validity by comparing them to other outcome measures.

Materials and Methods

Five institutions participated in this prospective multicenter observational study. The JOA and modified JOA (mJOA) proposed by Benzel were recorded preoperatively and at three months postoperatively in patients with cervical compressive myelopathy who underwent decompression surgery. Patient reported outcome (PRO) measures, including Japanese Orthopaedic Association Cervical Myelopathy Evaluation Questionnaire (JOACMEQ), the Short Form-12 (SF-12) and the Neck Disability Index (NDI), were also recorded. The preoperative JOA score and mJOA score were compared to each other and the PRO values. A Bland-Altman analysis was performed to investigate their limits of agreement.

Results

A total of ninety-two patients were included. The correlation coefficient (Spearman’s rho) between the JOA and mJOA was 0.87. In contrast, the correlations between JOA/mJOA and the other PRO values were moderate (|rho| = 0.03 – 0.51). The correlation coefficient of the recovery rate between the JOA and mJOA was 0.75. The Bland-Altman analyses showed that limits of agreement were 3.6 to -1.2 for the total score, and 55.1% to -68.8% for the recovery rates.

Conclusions

In the present study, the JOA score and the mJOA score showed good correlation with each other in terms of their total scores and recovery rates. Previous studies using the JOA can be interpreted based on the mJOA; however it is not ideal to use them interchangeably. The validity of both scores was demonstrated by comparing these values to the PRO values.  相似文献   
59.
Objective: Several lines of evidence suggest important roles for adiponectin in glucose and lipid metabolism and atherosclerosis. However, the mechanisms regulating serum adiponectin levels and adiponectin production are still not completely understood. Our aim was to determine whether adiponectin synthesis is physiologically regulated by the sympathetic nervous system (SNS). Research Methods and Procedures: Mice were exposed to cold (4 °C) for 12 hours and for 24 hours with or without inhibition of noradrenaline synthesis or pan‐β adrenergic function, followed by measurement of serum adiponectin concentrations and levels of adiponectin and uncoupling protein (UCP) 1 expressions in various white adipose tissues (WATs). Results: Cold exposure significantly reduced serum adiponectin concentrations without changing body weights or WAT sizes in either subcutaneous or intra‐abdominal fat tissues. The serum adiponectin reduction was associated with a decrease in adiponectin mRNA expression in subcutaneous, epididymal, and mesenteric fat tissues. In these adipose tissues, UCP1 expression was markedly enhanced, suggesting SNS activation in these tissues. Administration of α‐methyl‐p‐tyrosine or a combination of SR59230A and propranolol reversed the cold‐exposure‐induced decreases in serum adiponectin concentrations and adiponectin mRNA expression in these tissues. In contrast, in retroperitoneal fat, the effects of cold exposure on adiponectin and UCP1 expressions were strikingly weak but were not reversed by SNS inhibitors. Discussion: SNS physiologically regulates serum adiponectin levels and adiponectin synthesis in WATs in vivo, although responsiveness to SNS stimulation differs markedly among WATs. Sympathetic activation might be involved in development of the metabolic syndrome by modulation of serum adiponectin concentrations.  相似文献   
60.
Caveolin, a 20-24 kDa integral membrane protein, is a principal component of caveolar domains. Caveolin-1 is expressed predominantly in endothelial cells, fibroblasts, and adipocytes, while the expression of caveolin-3 is confined to muscle cells. However, their localization in various muscles has not been well documented. Using double-immunofluorescence labeling and confocal laser microscopy, we examined the localization of caveolins-1 and 3 in adult monkey skeletal, cardiac and uterine smooth muscles and the co-immunolocalization of these caveolins with dystrophin, which is a product of the Duchenne muscular dystrophy gene. In the skeletal muscle tissue, caveolin-3 was localized along the sarcolemma except for the transverse tubules, and co-immunolocalized with dystrophin, whereas caveolin-1 was absent except in the blood vessels of the muscle tissue. In cardiac muscle cells, caveolins-1 and -3 and dystrophin were co-immunolocalized on the sarcolemma and transverse tubules. In uterine smooth muscle cells, caveolin-1, but not caveolin-3, was co-immunolocalized with dystrophin on the sarcolemma.  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