全文获取类型
收费全文 | 3603篇 |
免费 | 239篇 |
国内免费 | 2篇 |
出版年
2023年 | 22篇 |
2022年 | 40篇 |
2021年 | 87篇 |
2020年 | 60篇 |
2019年 | 82篇 |
2018年 | 106篇 |
2017年 | 91篇 |
2016年 | 128篇 |
2015年 | 180篇 |
2014年 | 162篇 |
2013年 | 237篇 |
2012年 | 225篇 |
2011年 | 226篇 |
2010年 | 157篇 |
2009年 | 145篇 |
2008年 | 170篇 |
2007年 | 151篇 |
2006年 | 164篇 |
2005年 | 127篇 |
2004年 | 137篇 |
2003年 | 108篇 |
2002年 | 112篇 |
2001年 | 85篇 |
2000年 | 77篇 |
1999年 | 75篇 |
1998年 | 29篇 |
1997年 | 30篇 |
1996年 | 24篇 |
1995年 | 37篇 |
1994年 | 22篇 |
1993年 | 24篇 |
1992年 | 38篇 |
1991年 | 42篇 |
1990年 | 34篇 |
1989年 | 37篇 |
1988年 | 32篇 |
1987年 | 33篇 |
1986年 | 38篇 |
1985年 | 25篇 |
1984年 | 14篇 |
1981年 | 14篇 |
1979年 | 18篇 |
1978年 | 15篇 |
1977年 | 16篇 |
1975年 | 16篇 |
1974年 | 23篇 |
1973年 | 17篇 |
1971年 | 11篇 |
1969年 | 13篇 |
1968年 | 14篇 |
排序方式: 共有3844条查询结果,搜索用时 437 毫秒
161.
162.
Determinant Factors of Untreated Dental Caries and Lesion Activity in Preschool Children Using ICDAS
Tássia Cristina de Almeida Pinto-Sarmento Mauro Henrique Abreu Monalisa Cesarino Gomes Edja Maria Melo de Brito Costa Carolina Castro Martins Ana Flávia Granville-Garcia Saul Martins Paiva 《PloS one》2016,11(2)
The aim of the present study was to investigate determinant factors associated with the presence of dental caries and lesion activity in preschool children. A population-based, cross-sectional study was carried out with 843 children of aged three to five years enrolled at public and private preschools in the city of Campina Grande, Brazil. A questionnaire addressing socio-demographic data and oral health care was self-administered by parents/caregivers. Three dentists previously calibrated examined the children for the diagnosis of dental caries and lesion activity using the International Caries Detection and Assessment System (ICDAS). Nutritional status was evaluated based on the body mass index. Logistic regression analysis for complex samples was performed (α = 5%). The prevalence of dental caries was 66.3%. Among the children with caries, 88.0% had active lesions. Dental caries was more prevalent in girls (OR = 1.53, 95%CI: 1.05–2.23), in children from families with a monthly household income ≤US$312.50 (OR = 2.38, 95%CI: 1.65–3.43) and those whose mothers had up to eight years of schooling (OR = 1.55, 95%CI: 1.07–2.23). Lesion activity was significantly associated with mother’s schooling ≤ 8 years (OR = 2.15, 95%CI: 1.15–4.00). The prevalence rates of dental caries and lesion activity were high and mainly associated with a lower socioeconomic status and mother’s schooling. 相似文献
163.
Jilson L. Almeida-Junior Leonardo Gil-Santana Carolina A. M. Oliveira Simone Castro Aparecida S. Cafezeiro Carla Daltro Eduardo M. Netto Hardy Kornfeld Bruno B. Andrade 《PloS one》2016,11(4)
BackgroundDiabetes mellitus (DM) has been associated with increased risk for pulmonary tuberculosis (PTB) in endemic settings but it is unknown whether PTB risk is also increased by pre-DM. Here, we prospectively examined the association between glucose metabolism disorder (GMD) and PTB in patients with respiratory symptoms at a tuberculosis primary care reference center in Brazil.MethodsOral glucose tolerance test was performed and levels of fasting plasma glucose and glycohemoglobin (HbA1c) were measured in a cohort of 892 individuals presenting with respiratory symptoms of more than two weeks duration. Patients were also tested for PTB with sputum cultures. Prevalence of pre-DM and DM (based on HbA1c) was estimated and tested for association with incident PTB. Other TB risk factors including smoking history were analyzed.ResultsThe majority of the study population (63.1%) exhibited GMD based on HbA1c ≥5.7%. Patients with GMD had higher prevalence of PTB compared to normoglycemic patients. Individuals with DM exhibited increased frequency of TB-related symptoms and detection of acid-fast bacilli in sputum smears. Among patients with previous DM diagnosis, sustained hyperglycemia (HbA1c ≥7.0%) was associated with increased TB prevalence. Smoking history alone was not significantly associated with TB in our study population but the combination of smoking and HbA1c ≥7.0% was associated with 6 times higher odds for PTB.ConclusionsSustained hyperglycemia and pre-DM are independently associated with active PTB. This evidence raises the question whether improving glycemic control in diabetic TB patients would reduce the risk of TB transmission and simultaneously reduce the clinical burden of disease. A better understanding of mechanisms underlying these associations, especially those suggesting that pre-DM may be a factor driving susceptibility to TB is warranted. 相似文献
164.
Jhonathan Pedroso Rigal dos Santos Renato Coelho de Castro Vasconcellos Luiz Paulo Miranda Pires Marcio Balestre Renzo Garcia Von Pinho 《PloS one》2016,11(4)
New proposals for models and applications of prediction processes with data on molecular markers may help reduce the financial costs of and identify superior genotypes in maize breeding programs. Studies evaluating Genomic Best Linear Unbiased Prediction (GBLUP) models including dominance effects have not been performed in the univariate and multivariate context in the data analysis of this crop. A single cross hybrid construction procedure was performed in this study using phenotypic data and actual molecular markers of 4,091 maize lines from the public database Panzea. A total of 400 simple hybrids resulting from this process were analyzed using the univariate and multivariate GBLUP model considering only additive effects additive plus dominance effects. Historic heritability scenarios of five traits and other genetic architecture settings were used to compare models, evaluating the predictive ability and estimation of variance components. Marginal differences were detected between the multivariate and univariate models. The main explanation for the small discrepancy between models is the low- to moderate-magnitude correlations between the traits studied and moderate heritabilities. These conditions do not favor the advantages of multivariate analysis. The inclusion of dominance effects in the models was an efficient strategy to improve the predictive ability and estimation quality of variance components. 相似文献
165.
Henrique Roman Ramos Inácio de Loiola M. Junqueira-de-Azevedo Juliana Branco Novo Karen Castro Clara Guerra Duarte Ricardo A. Machado-de-ávila Carlos Chavez-Olortegui Paulo Lee Ho 《PLoS neglected tropical diseases》2016,10(3)
BackgroundEnvenoming by coral snakes (Elapidae: Micrurus), although not abundant, represent a serious health threat in the Americas, especially because antivenoms are scarce. The development of adequate amounts of antielapidic serum for the treatment of accidents caused by snakes like Micrurus corallinus is a challenging task due to characteristics such as low venom yield, fossorial habit, relatively small sizes and ophiophagous diet. These features make it difficult to capture and keep these snakes in captivity for venom collection. Furthermore, there are reports of antivenom scarcity in USA, leading to an increase in morbidity and mortality, with patients needing to be intubated and ventilated while the toxin wears off. The development of an alternative method for the production of an antielapidic serum, with no need for snake collection and maintenance in captivity, would be a plausible solution for the antielapidic serum shortage.ConclusionHere we describe that the genetic immunisation with a synthetic multiepitope gene followed by booster doses with recombinant protein is a promising approach to develop an alternative antielapidic serum against M. corallinus venom without the need of collection and the very challenging maintenance of these snakes in captivity. 相似文献
166.
Virtual reconstruction of the Early Pleistocene mandible ATD6‐96 from Gran Dolina‐TD6‐2 (Sierra De Atapuerca,Spain)
下载免费PDF全文
![点击此处可从《American journal of physical anthropology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
167.
Asier Largo‐Gosens Antonio Encina María de Castro Hugo Mélida José L. Acebes Penélope García‐Angulo Jesús M. Álvarez 《Physiologia plantarum》2016,157(2):193-204
The cellulose biosynthesis inhibitor 2,6‐dichlorobenzonitrile (DCB) has been widely used to gain insights into cell wall composition and architecture. Studies of changes during early habituation to DCB can provide information on mechanisms that allow tolerance/habituation to DCB. In this context, maize‐cultured cells with a reduced amount of cellulose (~20%) were obtained by stepwise habituation to low DCB concentrations. The results reported here attempt to elucidate the putative role of an antioxidant strategy during incipient habituation. The short‐term exposure to DCB of non‐habituated maize‐cultured cells induced a substantial increase in oxidative damage. Concomitantly, short‐term treated cells presented an increase in class III peroxidase and glutathione S‐transferase activities and total glutathione content. Maize cells habituated to 0.3–1 µM DCB (incipient habituation) were characterized by a reduction in the relative cell growth rate, an enhancement of ascorbate peroxidase and class III peroxidase activities, and a net increment in total glutathione content. Moreover, these cell lines showed increased levels of glutathione S‐transferase activity. Changes in antioxidant/conjugation status enabled 0.3 and 0.5 µM DCB‐habituated cells to control lipid peroxidation levels, but this was not the case of maize cells habituated to 1 μM DCB, which despite showing an increased antioxidant capacity were not capable of reducing the oxidative damage to control levels. The results reported here confirm that exposure and incipient habituation of maize cells to DCB are associated with an enhancement in antioxidant/conjugation activities which could play a role in incipient DCB habituation of maize‐cultured cells. 相似文献
168.
Effects of different arbuscular mycorrhizal fungal backgrounds and soils on olive plants growth and water relation properties under well‐watered and drought conditions
下载免费PDF全文
![点击此处可从《Plant, cell & environment》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Monica Calvo‐Polanco Iván Sánchez‐Castro Manuel Cantos José Luis García Rosario Azcón Juan Manuel Ruiz‐Lozano Carmen R. Beuzón Ricardo Aroca 《Plant, cell & environment》2016,39(11):2498-2514
The adaptation capacity of olive trees to different environments is well recognized. However, the presence of microorganisms in the soil is also a key factor in the response of these trees to drought. The objective of the present study was to elucidate the effects of different arbuscular mycorrhizal (AM) fungi coming from diverse soils on olive plant growth and water relations. Olive plants were inoculated with native AM fungal populations from two contrasting environments, that is, semi‐arid – Freila (FL) and humid – Grazalema (GZ) regions, and subjected to drought stress. Results showed that plants grew better on GZ soil inoculated with GZ fungi, indicating a preference of AM fungi for their corresponding soil. Furthermore, under these conditions, the highest AM fungal diversity was found. However, the highest root hydraulic conductivity (Lpr) value was achieved by plants inoculated with GZ fungi and growing in FL soil under drought conditions. So, this AM inoculum also functioned in soils from different origins. Nine novel aquaporin genes were also cloned from olive roots. Diverse correlation and association values were found among different aquaporin expressions and abundances and Lpr, indicating how the interaction of different aquaporins may render diverse Lpr values. 相似文献
169.
170.
Osmoconditioning prevents the onset of microtubular cytoskeleton and activation of cell cycle and is detrimental for germination of Jatropha curcas L. seeds
下载免费PDF全文
![点击此处可从《Plant biology (Stuttgart, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
P. R. Ribeiro P. C. T. Vasconcelos L. G. Fernandez R. D. de Castro 《Plant biology (Stuttgart, Germany)》2016,18(6):1053-1057
- Jatropha curcas is an oilseed crop renowned for its tolerance to a diverse range of environmental stresses. In Brazil, this species is grown in semiarid regions where crop establishment requires a better understanding of the mechanisms underlying appropriate seed, seedling and plant behaviour under water restriction conditions. In this context, the objective of this study was to investigate the physiological and cytological profiles of J. curcas seeds in response to imbibition in water (control) and in polyethylene glycol solution (osmoticum).
- Seed germinability and reactivation of cell cycle events were assessed by means of different germination parameters and immunohistochemical detection of tubulin and microtubules, i.e. tubulin accumulation and microtubular cytoskeleton configurations in water imbibed seeds (control) and in seeds imbibed in the osmoticum.
- Immunohistochemical analysis revealed increasing accumulation of tubulin and appearance of microtubular cytoskeleton in seed embryo radicles imbibed in water from 48 h onwards. Mitotic microtubules were only visible in seeds imbibed in water, after radicle protrusion, as an indication of cell cycle reactivation and cell proliferation, with subsequent root development. Imbibition in osmoticum prevented accumulation of microtubules, i.e. activation of cell cycle, therefore germination could not be resumed.
- Osmoconditioned seeds were able to survive re‐drying and could resume germination after re‐imbibition in water, however, with lower germination performance, possibly due to acquisition of secondary dormancy. This study provides important insights into understanding of the physiological aspects of J. curcas seed germination in response to water restriction conditions.