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   580篇
  免费   19篇
  599篇
  2016年   6篇
  2015年   16篇
  2014年   18篇
  2013年   26篇
  2012年   16篇
  2011年   20篇
  2010年   27篇
  2009年   28篇
  2008年   14篇
  2007年   16篇
  2006年   13篇
  2005年   16篇
  2004年   15篇
  2001年   7篇
  2000年   7篇
  1999年   7篇
  1998年   13篇
  1997年   12篇
  1996年   9篇
  1995年   12篇
  1994年   7篇
  1993年   9篇
  1992年   6篇
  1991年   7篇
  1989年   9篇
  1988年   15篇
  1987年   7篇
  1985年   6篇
  1984年   11篇
  1983年   7篇
  1982年   18篇
  1981年   6篇
  1980年   5篇
  1979年   8篇
  1978年   6篇
  1977年   9篇
  1976年   7篇
  1975年   8篇
  1974年   7篇
  1973年   6篇
  1972年   10篇
  1959年   9篇
  1958年   11篇
  1957年   5篇
  1955年   7篇
  1954年   7篇
  1953年   10篇
  1952年   6篇
  1951年   8篇
  1950年   6篇
排序方式: 共有599条查询结果,搜索用时 9 毫秒
501.
Central processing of inertial sensory information about head attitude and motion in space is crucial for motor control. Vestibular signals are coded relative to a non-inertial system, the head, that is virtually continuously in motion. Evidence for transformation of vestibular signals from head-fixed sensory coordinates to gravity-centered coordinates have been provided by studies of the vestibulo-ocular reflex. The underlying central processing depends on otolith afferent information that needs to be resolved in terms of head translation related inertial forces and head attitude dependent pull of gravity. Theoretical solutions have been suggested, but experimental evidence is still scarce. It appears, along these lines, that gaze control systems are intimately linked to motor control of head attitude and posture.  相似文献   
502.
Complete coding regions of the 18S rRNA gene of an enteropneust hemichordate and an echinoid and ophiuroid echinoderm were obtained and aligned with 18S rRNA gene sequences of all major chordate clades and four outgroups. Gene sequences were analyzed to test morphological character phylogenies and to assess the strength of the signal. Maximum- parsimony analysis of the sequences fails to support a monophyletic Chordata; the urochordates form the sister taxon to the hemichordates, and together this clade plus the echinoderms forms the sister taxon to the cephalochordates plus craniates. Decay, bootstrap, and tree-length distribution analyses suggest that the signal for inference of dueterostome phylogeny is weak in this molecule. Parsimony analysis of morphological plus molecular characters supports both monophyly of echinoderms plus enteropneust hemichordates and a sister group relationship of this clade to chordates. Evolutionary parsimony does not support chordate monophyly. Neighbor-joining, Fitch-Margoliash, and maximum-likelihood analyses support a chordate lineage that is the sister group to an echinoderm-plus-hemichordate lineage. The results illustrate both the limitations of the 18S rRNA molecule alone for high- level phylogeny inference and the importance of considering both molecular and morphological data in phylogeny reconstruction.   相似文献   
503.
504.
Further Observations on Light and Spore Discharge in Certain Pyrenomycetes   总被引:1,自引:0,他引:1  
A ‘spore-clock’ for studying the hourly rate ofspore discharge over a 24-hour period is described. A numberof the experiments reported in this paper have involved theuse of this apparatus. In Sordaria fimicola there is a distinct positive light-dischargereaction in a dark-conditioned culture, the rate of spore dischargeincreasing steeply to a peak 2–3 hours after brief stimulationby bright light. Although darkening a light-conditioned cultureleads to an immediate decrease in the rate of discharge, thereis no evidence of a delayed negative dark-discharge reaction. In S. verruculosa with a 12-hours light: 12-hours dark dailyreëgime, more spores are discharged in the dark than inthe light periods if the intensity of illumination is low. Withhigher light intensity there is no significant difference betweenthe number of spores discharged in light and dark periods. Asin S. fimicola there is a positive light-discharge reaction,the interval between stimulus and maximum response being muchlonger (8–12 hours). When a dark-conditioned culture istransferred to light for 48 hours and then returned to darknessfor a further 48 hours it is apparent that not only is therea positive light-discharge reaction but also a negative dark-dischargeresponse. The ‘plateau’ level of discharge is essentiallythe same in light and darkness. It is confirmed that in Hypoxylon fuscum light inhibits discharge.  相似文献   
505.
Abstract.  A pheromone sprayer and an electroantennogram (EAG) are used to study sensory adaptation in the antennae of male obliquebanded leafrollers, Choristoneura rosaceana and oriental fruit moths, Grapholita molesta , to the main pheromone compounds ( Z )-11-tetradecen-1-yl acetate ( Z 11-14:Ac) and ( Z )-8-dodecen-1-yl acetate ( Z 8-12:Ac), respectively. The atomization of 0.125, 0.25, 0.5 or 1 μL ethanol min−1 into the EAG air delivery tube at an airflow rate of 2 L min−1, with resultant concentrations of 6.25, 12.5, 25 or 50 × 10−5μL ethanol mL air−1, respectively, does not affect the EAG response of C. rosaceana or C. molesta after a 30-min exposure period. The atomization of 0.125 μL min−1 of a solution of 8 mg Z 11-14:Ac mL−1 ethanol into the EAG air delivery tube at an airflow rate of 2 L min−1, with a resultant concentration of 0.5 ng pheromone mL−1 air, reduces the EAG response of C. rosaceana by approximately 70% after a 15-min exposure period. An additional 15 min of exposure to pheromone does not result in increased sensory adaptation. Antennae recover 32% of the lost responsiveness when exposed to pheromone-free air for 15 min. The atomization of 0.125 μL min−1 of a solution of 8 mg Z 8-12:Ac mL−1 ethanol into the EAG air delivery tube at an airflow rate of 2 L min−1, with a resultant concentration of 0.5 ng pheromone mL−1 air, reduces the EAG response of C. molesta antenna by approximately 80% after a 15- or 30-min exposure period. The antennae of this species do not recover responsiveness when exposed to pheromone-free air for 15 min.  相似文献   
506.

Background  

Lymphocyte function-associated antigen-1 (LFA-1, CD11a/CD18, alphaLbeta2), the most abundant and widely expressed beta2-integrin, is required for many cellular adhesive interactions during the immune response. Many studies have shown that LFA-1 is centrally involved in the pathogenesis of several diseases caused by Repeats-in-toxin (RTX) -producing bacteria.  相似文献   
507.
The cellular and subcellular distribution of Ni within leaves of Hybanthus floribundus (Lindley) F. Muell, a hyperaccumulator of Ni, was investigated at relatively high spatial resolution using energy‐dispersive X‐ray microanalysis (EDAX). Elemental distribution maps showed that Ni was predominantly localized in the vacuoles of epidermal cells in the leaves. Quantification of Ni revealed concentrations up to 275 mmol kg?1 (embedded tissue) in some epidermal vacuoles. The accumulation of Ni in these cells was associated with a decrease in the concentration of Na and K. There was no indication that Ni was associated with P, S or Cl in the vacuoles. Ni was also concentrated on the outside of cell walls throughout the leaves, indicating that apoplastic compartmentation is also involved in Ni tolerance and accumulation in this plant.  相似文献   
508.

Introduction

IL-1β is a proinflammatory cytokine driving joint inflammation as well as systemic signs of inflammation, such as fever and acute phase protein production.

Methods

ACZ885, a fully human monoclonal antibody that neutralizes the bioactivity of human IL-1β, was generated to study the potent and long-lasting neutralization of IL-1β in mechanistic animal models as well as in a proof-of-concept study in patients with rheumatoid arthritis (RA).

Results

The mouse IL-1 receptor cross-reacts with human IL-1β, and it was demonstrated that ACZ885 can completely suppress IL-1β-mediated joint inflammation and cartilage destruction in mice. This observation prompted us to study the safety, tolerability and pharmacodynamic activity of ACZ885 in RA patients in a small proof-of-concept study – the first to be conducted in humans. Patients with active RA despite treatment with stable doses of methotrexate were enrolled in this dose escalation study. The first 32 patients were split into four cohorts of eight patients each (six were randomly assigned to active treatment and two to placebo). ACZ885 doses were 0.3, 1, 3 and 10 mg/kg, administered intravenously on days 1 and 15. To explore efficacy within 6 weeks of treatment, an additional 21 patients were randomly assigned to the 10 mg/kg cohort, resulting in a total of 20 patients dosed with 10 mg/kg and 15 patients treated with placebo. There was clinical improvement (American College of Rheumatology 20% improvement criteria) at week 6 in the 10 mg/kg treatment group; however, this did not reach statistical significance (P = 0.085). A statistically significant reduction in disease activity score was observed after 4 weeks in the 10 mg/kg group. Onset of action was rapid, because most responders exhibited improvement in their symptoms within the first 3 weeks. C-reactive protein levels decreased in patients treated with ACZ885 within 1 week. ACZ885 was well tolerated. Three patients receiving ACZ885 developed infectious episodes that required treatment. No anti-ACZ885 antibodies were detected during the study.

Conclusion

ACZ885 administration to methotrexate-refractory patients resulted in clinical improvement in a subset of patients. Additional studies to characterize efficacy in RA and to determine the optimal dose regimen appear warranted.

Trial Registration

ClinicalTrials.gov identifier NCT00619905.  相似文献   
509.
510.
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