全文获取类型
收费全文 | 4483篇 |
免费 | 419篇 |
国内免费 | 1篇 |
专业分类
4903篇 |
出版年
2023年 | 34篇 |
2022年 | 58篇 |
2021年 | 90篇 |
2020年 | 55篇 |
2019年 | 88篇 |
2018年 | 97篇 |
2017年 | 80篇 |
2016年 | 158篇 |
2015年 | 222篇 |
2014年 | 281篇 |
2013年 | 280篇 |
2012年 | 397篇 |
2011年 | 361篇 |
2010年 | 235篇 |
2009年 | 197篇 |
2008年 | 251篇 |
2007年 | 238篇 |
2006年 | 231篇 |
2005年 | 249篇 |
2004年 | 232篇 |
2003年 | 226篇 |
2002年 | 192篇 |
2001年 | 33篇 |
2000年 | 31篇 |
1999年 | 44篇 |
1998年 | 64篇 |
1997年 | 41篇 |
1996年 | 40篇 |
1995年 | 41篇 |
1994年 | 30篇 |
1993年 | 28篇 |
1992年 | 40篇 |
1991年 | 23篇 |
1990年 | 22篇 |
1989年 | 12篇 |
1988年 | 22篇 |
1987年 | 21篇 |
1986年 | 9篇 |
1985年 | 14篇 |
1984年 | 20篇 |
1983年 | 12篇 |
1982年 | 13篇 |
1981年 | 11篇 |
1980年 | 5篇 |
1979年 | 13篇 |
1978年 | 4篇 |
1977年 | 4篇 |
1976年 | 4篇 |
1974年 | 7篇 |
1970年 | 6篇 |
排序方式: 共有4903条查询结果,搜索用时 15 毫秒
101.
Anett Richter Will Osborne Sarah Hnatiuk Alison Rowell 《Journal of Insect Conservation》2013,17(6):1093-1104
The conservation and management of endangered species requires an adequate understanding of their biology and ecology. Although there has been an increasing appreciation in Australia of the need for greater efforts to conserve insects, there is only limited information available that can be used to underpin conservation efforts. The endangered golden sun moth, Synemon plana (Lepidoptera: Castniidae) is a flagship species endemic to natural temperate grassland in south-eastern Australia. Most populations of this species are at considerable risk from habitat loss, weed invasion and inadequate management. Despite the considerable knowledge that exists about the species biology and ecology, efforts to improve the species conservation status are hampered because there are still critical gaps in our understanding of the species’ natural history. In particular, the ecology of the larvae is not known. Our study examined the abundance, population structure and reproductive biology of the moths in a broad sample of both natural temperate and exotic grassland remnants in and near Canberra in the Australian Capital Territory (ACT) in south-eastern Australia. The results fill critical gaps in the knowledge needed to achieve effective conservation management. From our findings, it is clear that the species inhabits grasslands dominated by a mixture of native wallaby grasses (Rytidosperma spp. (formerly Austrodanthonia)) and spear grasses (Austrostipa spp.). In contrast to earlier suggestions that S. plana is entirely confined to natural temperate grassland, mature and immature life stages of the species were also present in grasslands comprised entirely of the exotic Chilean needlegrass (Nassella neesiana). Most of the S. plana populations surveyed in the ACT were characterised by low relative abundance with only very few large populations being recorded. The conservation of exotic grasslands as substitute habitat for S. plana is discussed and suggestions regarding future monitoring and research of the species are provided. 相似文献
102.
103.
Alison Brognaux Jörg Bugge Friedel H. Schwartz Philippe Thonart Samuel Telek Frank Delvigne 《Journal of industrial microbiology & biotechnology》2013,40(7):679-686
Cell density and cell viability have been followed on-line by using a three-dimensional optical reflectance method (3D-ORM) probe. This method has allowed to highlight the differences between a well-mixed and a scale-down bioreactor configured in order to reproduce mixing deficiencies during a fed-batch culture of Escherichia coli. These differences have been observed both for the obscuration factor (OBF) and the coincidence probability delivered by the probe. These parameters are correlated to flow cytometry measurement based on the PI-uptake test and cell density based on optical density measurement. This first set of results has pointed out the fact that the 3D-ORM probe is sensitive to sub-lethal injuries encountered by microbial cells in process-related conditions. The effect of lethal injuries has been further investigated on the basis of additional experiments involving heat stress and a sharp increase of the OBF has been observed indicating that cells are effectively injured by the increase of temperature. However, further improvement of the probe are needed in order to give access to single-cell measurements. 相似文献
104.
105.
Alison L. Towerton Rodney P. Kavanagh Trent D. Penman Christopher R. Dickman 《Ecological Management & Restoration》2013,14(1):54-58
Predation on native vertebrates and livestock by the European Red Fox (Vulpes vulpes) remains a significant problem in many parts of Australia. Coordinated approaches to fox control are most effective in protecting these assets and involve placement of baits across the landscape by private and public land managers. However, participation in such programmes varies seasonally and the spatial coverage of baiting is often difficult to determine. Here, we describe a geographic information systems‐based system that assists land managers to collect and use spatial information, minimizing gaps in bait coverage and maximizing bait encounters by foxes to increase the effectiveness of pest control. The coordination of data collection and reporting between land managers should facilitate more effective adaptive management by allowing better strategic planning and increasing landholder involvement, which should, in turn, improve the programme's efficacy, provided other critical conditions and resources are met. 相似文献
106.
Portia C. Mutevedzi Alison J. Rodger Paul Kowal Makandwe Nyirenda Marie-Louise Newell 《PloS one》2013,8(10)
Background
The association of HIV with chronic morbidity and inflammatory markers (cytokines) in older adults (50+years) is potentially relevant for clinical care, but data from African populations is scarce.Objective
To examine levels of chronic morbidity by HIV and ART status in older adults (50+years) and subsequent associations with selected pro-inflammatory cytokines and body mass index.Methods
Ordinary, ordered and generalized ordered logistic regression techniques were employed to compare chronic morbidity (heart disease (angina), arthritis, stroke, hypertension, asthma and diabetes) and cytokines (Interleukins-1 and -6, C-Reactive Protein and Tumor Necrosis Factor-alpha) by HIV and ART status on a cross-sectional random sample of 422 older adults nested within a defined rural South African population based demographic surveillance.Results
Using a composite measure of all morbidities, controlling for age, gender, BMI, smoking and wealth quintile, HIV-infected individuals on ART had 51% decreased odds (95% CI:0.26-0.92) of current morbidity compared to HIV-uninfected. In adjusted regression, compared to HIV-uninfected, the proportional odds (aPOR) of having elevated inflammation markers of IL6 (>1.56pg/mL) was nearly doubled in HIV-infected individuals on (aPOR 1.84; 95%CI: 1.05-3.21) and not on (aPOR 1.94; 95%CI: 1.11-3.41) ART. Compared to HIV-uninfected, HIV-infected individuals on ART had >twice partial proportional odds (apPOR=2.30;p=0.004) of having non-clinically significant raised hsCRP levels(>1ug/mL); ART-naïve HIV-infected individuals had >double apPOR of having hsCRP levels indicative of increased heart disease risk(>3.9ug/mL;p=0.008).Conclusions
Although HIV status was associated with increased inflammatory markers, our results highlight reduced morbidity in those receiving ART and underscore the need of pro-actively extending these services to HIV-uninfected older adults, beyond mere provision at fixed clinics. Providing health services through regular community chronic disease screening would ensure health care reaches all older adults in need. 相似文献107.
James J. Lewis Katherine L. Fielding Alison D. Grant Violet N. Chihota Flora Popane Mariette Luttig Dorothy Muller Leonie Coetzee Gavin J. Churchyard 《PloS one》2013,8(11)
Setting
The “Thibela TB” cluster randomised trial of community-wide isoniazid preventive therapy (IPT) to reduce tuberculosis incidence in the South African gold mines.Objectives
To determine the proportion of participants eligible for IPT and the reasons and risk factors for ineligibility, to inform the scale-up of IPT.Design
Cross-sectional survey of participants in intervention clusters (mine shafts) consenting to tuberculosis screening and assessment for eligibility to start IPT.Results
Among 27,126 consenting participants, 94.7% were male, the median age was 41 years, 12.2% reported previous tuberculosis, 0.6% reported ever taking IPT and 2.5% reported currently taking antiretroviral therapy. There were 24,430 (90.1%) assessed as eligible to start IPT, of whom 23,659 started IPT. The most common reasons for ineligibility were having suspected tuberculosis that was subsequently confirmed by a positive smear and/or culture (n=705), excessive alcohol consumption (n=427) and being on tuberculosis treatment at time of initial screen (n=241). Ineligibility was associated with factors including older age, female gender, prior history of tuberculosis and being in “HIV care”. However, at least 78% were eligible for IPT in all of these sub-groups.Conclusions
The vast majority of participants in this community-wide intervention were eligible for IPT. 相似文献108.
Alexander C. Phillips Alison Sleigh Catherine J. McAllister Soren Brage T. Adrian Carpenter Graham J. Kemp Anthony J. Holland 《PloS one》2013,8(12)
Down’s syndrome (DS) is a developmental disorder associated with intellectual disability (ID). We have previously shown that people with DS engage in very low levels of exercise compared to people with ID not due to DS. Many aspects of the DS phenotype, such as dementia, low activity levels and poor muscle tone, are shared with disorders of mitochondrial origin, and mitochondrial dysfunction has been demonstrated in cultured DS tissue. We undertook a phosphorus magnetic resonance spectroscopy (31P-MRS) study in the quadriceps muscle of 14 people with DS and 11 non-DS ID controls to investigate the post-exercise resynthesis kinetics of phosphocreatine (PCr), which relies on mitochondrial respiratory function and yields a measure of muscle mitochondrial function in vivo. We found that the PCr recovery rate constant was significantly decreased in adults with DS compared to non-DS ID controls (1.7±0.1 min−1 vs 2.1±0.1 min−1 respectively) who were matched for physical activity levels, indicating that muscle mitochondrial function in vivo is impaired in DS. This is the first study to investigate mitochondrial function in vivo in DS using 31P-MRS. Our study is consistent with previous in vitro studies, supporting a theory of a global mitochondrial defect in DS. 相似文献
109.
Mark S. Dworkin Caryn E. Peterson Weihua Gao Angel Mayor Robert Hunter Edna Negron Alison Fleury C. Lynn Besch 《PloS one》2013,8(10)