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   3551篇
  免费   342篇
  2023年   12篇
  2022年   10篇
  2021年   59篇
  2020年   33篇
  2019年   50篇
  2018年   53篇
  2017年   51篇
  2016年   71篇
  2015年   135篇
  2014年   140篇
  2013年   205篇
  2012年   259篇
  2011年   251篇
  2010年   141篇
  2009年   117篇
  2008年   227篇
  2007年   233篇
  2006年   207篇
  2005年   220篇
  2004年   192篇
  2003年   176篇
  2002年   152篇
  2001年   58篇
  2000年   39篇
  1999年   57篇
  1998年   61篇
  1997年   52篇
  1996年   35篇
  1995年   41篇
  1994年   29篇
  1993年   30篇
  1992年   29篇
  1991年   38篇
  1990年   28篇
  1989年   27篇
  1988年   15篇
  1987年   26篇
  1986年   21篇
  1985年   25篇
  1984年   18篇
  1983年   14篇
  1982年   18篇
  1981年   20篇
  1980年   17篇
  1979年   13篇
  1978年   14篇
  1977年   14篇
  1974年   18篇
  1973年   15篇
  1972年   13篇
排序方式: 共有3893条查询结果,搜索用时 15 毫秒
101.

Introduction

This cluster randomised trial evaluated an intervention to decrease x-ray referrals and increase giving advice to stay active for people with acute low back pain (LBP) in general practice.

Methods

General practices were randomised to either access to a guideline for acute LBP (control) or facilitated interactive workshops (intervention). We measured behavioural predictors (e.g. knowledge, attitudes and intentions) and fear avoidance beliefs. We were unable to recruit sufficient patients to measure our original primary outcomes so we introduced other outcomes measured at the general practitioner (GP) level: behavioural simulation (clinical decision about vignettes) and rates of x-ray and CT-scan (medical administrative data). All those not involved in the delivery of the intervention were blinded to allocation.

Results

47 practices (53 GPs) were randomised to the control and 45 practices (59 GPs) to the intervention. The number of GPs available for analysis at 12 months varied by outcome due to missing confounder information; a minimum of 38 GPs were available from the intervention group, and a minimum of 40 GPs from the control group. For the behavioural constructs, although effect estimates were small, the intervention group GPs had greater intention of practising consistent with the guideline for the clinical behaviour of x-ray referral. For behavioural simulation, intervention group GPs were more likely to adhere to guideline recommendations about x-ray (OR 1.76, 95%CI 1.01, 3.05) and more likely to give advice to stay active (OR 4.49, 95%CI 1.90 to 10.60). Imaging referral was not statistically significantly different between groups and the potential importance of effects was unclear; rate ratio 0.87 (95%CI 0.68, 1.10) for x-ray or CT-scan.

Conclusions

The intervention led to small changes in GP intention to practice in a manner that is consistent with an evidence-based guideline, but it did not result in statistically significant changes in actual behaviour.

Trial Registration

Australian New Zealand Clinical Trials Registry ACTRN012606000098538  相似文献   
102.

Background

The Ca2+-activated K+ channel KCa3.1 is expressed in several structural and inflammatory airway cell types and is proposed to play an important role in the pathophysiology of asthma. The aim of the current study was to determine whether inhibition of KCa3.1 modifies experimental asthma in sheep.

Methodology and Principal Findings

Atopic sheep were administered either 30 mg/kg Senicapoc (ICA-17073), a selective inhibitor of the KCa3.1-channel, or vehicle alone (0.5% methylcellulose) twice daily (orally). Both groups received fortnightly aerosol challenges with house dust mite allergen for fourteen weeks. A separate sheep group received no allergen challenges or drug treatment. In the vehicle-control group, twelve weeks of allergen challenges resulted in a 60±19% increase in resting airway resistance, and this was completely attenuated by treatment with Senicapoc (0.25±12%; n = 10, P = 0.0147). The vehicle-control group had a peak-early phase increase in lung resistance of 82±21%, and this was reduced by 58% with Senicapoc treatment (24±14%; n = 10, P = 0.0288). Senicapoc-treated sheep also demonstrated reduced airway hyperresponsiveness, requiring a significantly higher dose of carbachol to increase resistance by 100% compared to allergen-challenged vehicle-control sheep (20±5 vs. 52±18 breath-units of carbachol; n = 10, P = 0.0340). Senicapoc also significantly reduced eosinophil numbers in bronchoalveolar lavage taken 48 hours post-allergen challenge, and reduced vascular remodelling.

Conclusions

These findings suggest that KCa3.1-activity contributes to allergen-induced airway responses, inflammation and vascular remodelling in a sheep model of asthma, and that inhibition of KCa3.1 may be an effective strategy for blocking allergen-induced airway inflammation and hyperresponsiveness in humans.  相似文献   
103.
The plant pathogen Erwinia amylovora can be divided into two host-specific groupings; strains infecting a broad range of hosts within the Rosaceae subfamily Spiraeoideae (e.g., Malus, Pyrus, Crataegus, Sorbus) and strains infecting Rubus (raspberries and blackberries). Comparative genomic analysis of 12 strains representing distinct populations (e.g., geographic, temporal, host origin) of E. amylovora was used to describe the pan-genome of this major pathogen. The pan-genome contains 5751 coding sequences and is highly conserved relative to other phytopathogenic bacteria comprising on average 89% conserved, core genes. The chromosomes of Spiraeoideae-infecting strains were highly homogeneous, while greater genetic diversity was observed between Spiraeoideae- and Rubus-infecting strains (and among individual Rubus-infecting strains), the majority of which was attributed to variable genomic islands. Based on genomic distance scores and phylogenetic analysis, the Rubus-infecting strain ATCC BAA-2158 was genetically more closely related to the Spiraeoideae-infecting strains of E. amylovora than it was to the other Rubus-infecting strains. Analysis of the accessory genomes of Spiraeoideae- and Rubus-infecting strains has identified putative host-specific determinants including variation in the effector protein HopX1Ea and a putative secondary metabolite pathway only present in Rubus-infecting strains.  相似文献   
104.
Nipah virus (NiV) (Genus Henipavirus) is a recently emerged zoonotic virus that causes severe disease in humans and has been found in bats of the genus Pteropus. Whilst NiV has not been detected in Australia, evidence for NiV-infection has been found in pteropid bats in some of Australia’s closest neighbours. The aim of this study was to determine the occurrence of henipaviruses in fruit bat (Family Pteropodidae) populations to the north of Australia. In particular we tested the hypothesis that Nipah virus is restricted to west of Wallace’s Line. Fruit bats from Australia, Papua New Guinea, East Timor and Indonesia were tested for the presence of antibodies to Hendra virus (HeV) and Nipah virus, and tested for the presence of HeV, NiV or henipavirus RNA by PCR. Evidence was found for the presence of Nipah virus in both Pteropus vampyrus and Rousettus amplexicaudatus populations from East Timor. Serology and PCR also suggested the presence of a henipavirus that was neither HeV nor NiV in Pteropus alecto and Acerodon celebensis. The results demonstrate the presence of NiV in the fruit bat populations on the eastern side of Wallace’s Line and within 500 km of Australia. They indicate the presence of non-NiV, non-HeV henipaviruses in fruit bat populations of Sulawesi and Sumba and possibly in Papua New Guinea. It appears that NiV is present where P. vampyrus occurs, such as in the fruit bat populations of Timor, but where this bat species is absent other henipaviruses may be present, as on Sulawesi and Sumba. Evidence was obtained for the presence henipaviruses in the non-Pteropid species R. amplexicaudatus and in A. celebensis. The findings of this work fill some gaps in knowledge in geographical and species distribution of henipaviruses in Australasia which will contribute to planning of risk management and surveillance activities.  相似文献   
105.

Background

People with Cystic Fibrosis (CF) in the UK and elsewhere are increasingly surviving into adulthood, yet there is little research on the employment consequences of having CF. We investigated, for the first time in a UK-wide cohort, longitudinal employment status, and its association with deprivation, disease severity, and time in hospital.

Methods

We did a longitudinal registry study of adults with CF in the UK aged 20 to 40 (3458 people with 15,572 observations between 1996 and 2010), using mixed effects models.

Results

Around 50% of adults with CF were in employment. Male sex, higher lung function and body mass index, and less time in hospital were associated with improved employment chances. All other things being equal, being in the most deprived quintile was associated with a reduction of employment prevalence of 17.6 percentage points compared to the prevalence in the least deprived quintile. Having poor lung function was associated with a reduced employment prevalence of 7.2 percentage points compared to the prevalence for people with relatively good lung function. Acting synergistically, deprivation modifies the effect of lung function on employment chances – poor lung function in the least deprived group was associated with a 3 percentage point reduction in employment chances, while poor lung function in the most deprived quintile was associated with a 7.7 point reduction in employment chances.

Conclusions

Greater deprivation, disease severity, and time in hospital are all associated with employment chances in adults with CF. Furthermore, our analysis suggests that deprivation amplifies the harmful association of disease severity on employment. Future studies should focus on understanding and mitigating the barriers to employment faced by people with CF.  相似文献   
106.
Rapid, efficient, and robust quantitative analyses of dynamic apoptotic events are essential in a high-throughput screening workflow. Currently used methods have several bottlenecks, specifically, limitations in available fluorophores for downstream assays and misinterpretation of statistical image data analysis. In this study, we developed cytochrome-C (Cyt-C) and caspase-3/-8 reporter cell lines using lung (PC9) and breast (T47D) cancer cells, and characterized them from the response to apoptotic stimuli. In these two reporter cell lines, the spatial fluorescent signal translocation patterns served as reporters of activations of apoptotic events, such as Cyt-C release and caspase-3/-8 activation. We also developed a vision-based, tunable, automated algorithm in MATLAB to implement the robust and accurate analysis of signal translocation in single or multiple cells. Construction of the reporter cell lines allows live monitoring of apoptotic events without the need for any other dyes or fixatives. Our algorithmic implementation forgoes the use of simple image statistics for more robust analytics. Our optimized algorithm can achieve a precision greater than 90% and a sensitivity higher than 85%. Combining our automated algorithm with reporter cells bearing a single-color dye/fluorophore, we expect our approach to become an integral component in the high-throughput drug screening workflow.  相似文献   
107.
108.
Dengue virus is a major human pathogen that has four serotypes (DENV1 to -4). Here we report the cryoelectron microscopy (cryo-EM) structures of immature and mature DENV1 at 6- and 4.5-Å resolution, respectively. The subnanometer-resolution maps allow accurate placement of all of the surface proteins. Although the immature and mature viruses showed vastly different surface protein organizations, the envelope protein transmembrane (E-TM) regions remain in similar positions. The pivotal role of the E-TM regions leads to the identification of the start and end positions of all surface proteins during maturation.  相似文献   
109.
This paper presents findings from original research exploring the impact on Muslim men of a child sexual exploitation scandal that attracted significant attention to the northern English town where they live and contributed to a sustained detrimental effect on local community relations. It foregrounds men’s accounts to reveal their agency and resilience in responding to racism that they identified as resulting from the scandal. It reveals how their accounts disrupt dominant discourses foregrounding Muslim self-segregation and lack of integration, demonstrating positive attachments and claims to localized space, and commitment to belonging. In doing so, it shows how men’s responses to racism challenge racialized forms of knowledge about Muslims. The paper draws attention to the significance of localized forms of belonging in facilitating the inclusion of Muslim minorities. It also highlights the importance of centring Muslim men as historically speaking subjects in accounts of issues involving them.  相似文献   
110.
The anti-apartheid struggle was characterized by tensions between the opposing ideologies of non-racialism (exemplified by the Freedom Charter) and racialism (exemplified by Black Consciousness). These tensions have remained prevalent in public policies and discourse, and in the writings of social scientists, in the post-apartheid period. In this paper I examine some ways in which issues of whether, when, and how race matters become visible in everyday interactions in South Africa, and what insights this may offer with respect to these ongoing tensions. Specifically, I employ an ethnomethodological, conversation analytic approach to examine some ways in which racial categories are treated as resources for action or constraints on action. I conclude by arguing that these findings point to the contingent and situational operation of a practical non-racialism (as well as practical racialism), and thus to the achievement of these ideologies in the moment-by-moment unfolding of interactions.  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