全文获取类型
收费全文 | 850篇 |
免费 | 68篇 |
出版年
2021年 | 18篇 |
2020年 | 11篇 |
2019年 | 19篇 |
2018年 | 25篇 |
2017年 | 19篇 |
2016年 | 20篇 |
2015年 | 34篇 |
2014年 | 50篇 |
2013年 | 43篇 |
2012年 | 63篇 |
2011年 | 57篇 |
2010年 | 43篇 |
2009年 | 44篇 |
2008年 | 57篇 |
2007年 | 37篇 |
2006年 | 39篇 |
2005年 | 32篇 |
2004年 | 33篇 |
2003年 | 21篇 |
2002年 | 21篇 |
2001年 | 31篇 |
2000年 | 16篇 |
1999年 | 19篇 |
1998年 | 9篇 |
1997年 | 4篇 |
1996年 | 4篇 |
1995年 | 9篇 |
1994年 | 7篇 |
1993年 | 9篇 |
1992年 | 6篇 |
1991年 | 9篇 |
1990年 | 12篇 |
1989年 | 7篇 |
1988年 | 11篇 |
1987年 | 7篇 |
1986年 | 7篇 |
1985年 | 4篇 |
1983年 | 7篇 |
1982年 | 7篇 |
1981年 | 4篇 |
1980年 | 3篇 |
1979年 | 5篇 |
1978年 | 5篇 |
1977年 | 3篇 |
1976年 | 3篇 |
1974年 | 4篇 |
1972年 | 3篇 |
1971年 | 3篇 |
1968年 | 2篇 |
1961年 | 2篇 |
排序方式: 共有918条查询结果,搜索用时 15 毫秒
21.
Andy R. Griffiths Miles R. Silman William Farfn Rios Kenneth J. Feeley Karina García Cabrera Patrick Meir Norma Salinas Kyle G. Dexter 《Biotropica》2021,53(1):38-50
Understanding how evolutionary constraints shape the elevational distributions of tree lineages provides valuable insight into the future of tropical montane forests under global change. With narrow elevational ranges, high taxonomic turnover, frequent habitat specialization, and exceptional levels of endemism, tropical montane forests and trees are predicted to be highly sensitive to environmental change. Using plot census data from a gradient traversing > 3,000 m in elevation on the Amazonian flank of the Peruvian Andes, we employ phylogenetic approaches to assess the influence of evolutionary heritage on distribution trends of trees at the genus‐level. We find that closely related lineages tend to occur at similar mean elevations, with sister genera pairs occurring a mean 254 m in elevation closer to each other than the mean elevational difference between non‐sister genera pairs. We also demonstrate phylogenetic clustering both above and below 1,750 m a.s.l, corresponding roughly to the cloud‐base ecotone. Belying these general trends, some lineages occur across many different elevations. However, these highly plastic lineages are not phylogenetically clustered. Overall, our findings suggest that tropical montane forests are home to unique tree lineage diversity, constrained by their evolutionary heritage and vulnerable to substantial losses under environmental changes, such as rising temperatures or an upward shift of the cloud‐base. 相似文献
22.
G. Cabrera Walsh Y. Magalí Dalto Federico M. Mattioli Raymond I. Carruthers Lars W. Anderson 《BioControl》2013,58(1):133-147
Egeria densa (Hydrocharitaceae) is a submerged macrophyte from South America that is a weed in several countries. It crowds out native plants and hinders water use, causing economic and environmental damage. The leafminer fly Hydrellia sp. 1 (Diptera: Ephydridae), was found feeding in E. densa throughout its Argentine distribution, and is currently the only known specialist herbivore of E. densa. It was reared in the laboratory and tested on 25 plant species. This herbivore can cause heavy defoliation in the laboratory and in the field. Hydrellia sp. 1 was found only on E. densa, but in the laboratory it also developed on two other Hydrocharitaceae species in the same family; Egeria naias, and Elodea callitrichoides. Significant oviposition and feeding were only observed on its primary natural host, and to a lesser degree on E. naias. Field studies indicate Hydrellia sp. 1 is present in the field year round, unless the host plant is prostrate for long periods, or covered by floating macrophytes. These results indicate Hydrellia sp. 1 may be a suitable biocontrol candidate for E. densa. 相似文献
23.
Emilio García García María-Ángeles Vázquez López Rafael Galera Martínez Irene Alias Manuel Martín González Antonio Bonillo Perales José Eugenio Cabrera Sevilla Icíar García Escobar Sara Gómez Bueno Encarnación López Ruzafa Francisco-Javier Muñoz Vico Patricia Oliva Pérez María Ortiz Pérez Juan Poveda González Marisa Rodríguez Lucenilla Firma-Isabel Rodríguez Sánchez Ana Ruiz Sánchez Lucía Ruiz Tudela Sara Torrico 《Endocrinología y nutrición》2013,60(3):121-126
ObjectivesTo estimate the prevalence of obesity and overweight in children and adolescents in our city and to investigate the associated factors.Subjects and methodsA cross-sectional study of 1317 children and adolescents aged 2-16 years. Multistage probability sampling was used to select three groups of subjects: 411 aged 12 to 16 years, 504 aged 6 to 12 years, and 402 aged 2 to 6 years. Body mass index was calculated, and obesity and overweight were diagnosed using the threshold levels of the International Obesity Task Force for children and adolescents. Parents were asked about eating habits, health, social, and demographic aspects. Results are given as percentages (95% confidence interval). The relationship between obesity and overweight and the different variables was studied using multiple logistic regression. The adjusted odds ratio (OR) was calculated.ResultsAmong children and adolescentes aged 2-16 years, 9.5% (8.0%-11.0%) were obese and 22.4% (23.3%-24.6%) were overweight. Of subjects aged 12-16 years, 8.5% (5.9%-11.2%) were obese and 20.5% (16.7%-24.3%) were overweight. In the groups aged 6-12 years and 2-6 years, rates of obesity and overweight were 11.6% (8.9% -14.3%) and 31.0% (27.0-35.0) and 8.0% (5.4%-10.6%) and 13.6% (10.3%-16.9%) respectively. Obesity or overweight was associated to age (OR 1.21; P< 0.001), maternal obesity (OR 10.99; P= 0.008), a birthweight higher than 4 kg (OR 2.91; p 0.002), and formula feeding (OR 1.82; P= 0.005).ConclusionObesity and overweight in children and adolescents are highly prevalent problems in our city. 相似文献
24.
Pereira Isabela Tiemy Spangenberg Lucia Cabrera Guillermo Dallagiovanna Bruno 《Molecular and cellular biochemistry》2020,466(1-2):35-44
Molecular and Cellular Biochemistry - In stress conditions, as neoplastic transformation, amino acids serve not only as nutrients to maintain the cell survival but also as mediators of several... 相似文献
25.
Tadeo Ramirez-Parada Domingo Cabrera Zoe Diaz-Martin Luke Browne Jordan Karubian 《Biotropica》2020,52(5):845-856
Many tropical plant species show wide intra-population variation in reproductive timing, resulting in the protracted presence of flowering and fruiting individuals. Various eco-evolutionary drivers have been proposed as ultimate causes for asynchronous phenology, yet little is known about the proximate factors that control reproductive onset among individuals or that influence the proportion of trees producing new inflorescences within a population. We employed a nine-year phenological record from 178 individuals of the hyperdominant, asynchronously flowering canopy palm, Oenocarpus bataua (Arecaceae)¸ to assess whether resource-related variables influence individual- and population-level flowering phenology. Among individuals, access to sunlight increased rates of inflorescence production, while the presence of resource sinks related to current investment in reproduction—developing infructescences—reduced the probability of producing new inflorescences. At the population level, climate anomalies induced by El Niño Southern Oscillation (ENSO) affected the proportion of the population producing inflorescences through time. Moreover, the effects of ENSO anomalies on flowering patterns depended on the prevalence of developing infructescences in the population, with stronger effects in periods of low developing-infructescence frequency. Taken together, these results suggest that resource-related variables can drive phenological differences among individuals and mediate population-level responses to larger-scale variables, such as climate anomalies. Consequently, a greater focus on the role of resource levels as endogenous cues for reproduction might help explain the frequent aseasonal phenological patterns observed among tropical plants, particularly those showing high intra-population asynchrony. 相似文献
26.
Roniel Cabrera Miguel Ararat Yiling Xu Todd Brusko Clive Wasserfall Mark A. Atkinson Lung Ji Chang Chen Liu David R. Nelson 《Cancer immunology, immunotherapy : CII》2013,62(4):737-746
Hepatocellular carcinoma (HCC) is a difficult to treat cancer characterized by poor tumor immunity with only one approved systemic drug, sorafenib. If novel combination treatments are to be developed with immunological agents, the effects of sorafenib on tumor immunity are important to understand. In this study, we investigate the impact of sorafenib on the CD4+CD25? effector T cells (Teff) and CD4+CD25+ regulatory T cells (Tregs) from patients with HCC. We isolated Teff and Treg from peripheral mononuclear cells of HCC patients to determine immune reactivity by thymidine incorporation, ELISA and flow cytometry. Teff cultured alone or with Treg were supplemented with different concentrations of sorafenib. The effects of sorafenib on Teff responses were dose-dependent. Pharmacologic doses of sorafenib decreased Teff activation by down regulating CD25 surface expression. In contrast, sub-pharmacologic concentrations of sorafenib resulted in Teff activation. These low doses of sorafenib in the Teff cultures led to a significant increase in Teff proliferation, IL2 secretion and up-regulation of CD25 expression on the cell surface. In addition, low doses of sorafenib in the suppression Teff/Treg cocultures restored Teff responses by eliminating Treg suppression. The loss of Treg suppressive function correlated with an increase in IL2 and IL6 secretion. Our findings show that sub-pharmacologic doses of sorafenib impact subsets of T cells differently, selectively increasing Teff activation while blocking Treg function. In conclusion, this study describes novel immune activating properties of low doses of sorafenib by promoting immune responsiveness in patients with HCC. 相似文献
27.
Arun T. John Peter Jens Lachmann Meenakshi Rana Madeleine Bunge Margarita Cabrera Christian Ungermann 《The Journal of cell biology》2013,201(1):97-111
Membrane microcompartments of the early endosomes serve as a sorting and signaling platform, where receptors are either recycled back to the plasma membrane or forwarded to the lysosome for destruction. In metazoan cells, three complexes, termed BLOC-1 to -3, mediate protein sorting from the early endosome to lysosomes and lysosome-related organelles. We now demonstrate that BLOC-1 is an endosomal Rab-GAP (GTPase-activating protein) adapter complex in yeast. The yeast BLOC-1 consisted of six subunits, which localized interdependently to the endosomes in a Rab5/Vps21-dependent manner. In the absence of BLOC-1 subunits, the balance between recycling and degradation of selected cargoes was impaired. Additionally, our data show that BLOC-1 is both a Vps21 effector and an adapter for its GAP Msb3. BLOC-1 and Msb3 interacted in vivo, and both mutants resulted in a redistribution of active Vps21 to the vacuole surface. We thus conclude that BLOC-1 controls the lifetime of active Rab5/Vps21 and thus endosomal maturation along the endocytic pathway. 相似文献
28.
Apeksha A. Gulvady Henry P. Ciolino Robert M. Cabrera Christopher A. Jolly 《The Journal of nutritional biochemistry》2013,24(9):1625-1633
Obesity is associated with an increased risk of infectious diseases. It has been shown to have deleterious effects on cell-mediated immunity, including reducing thymocyte numbers and altering responses of thymocytes to pathogens. In the current study, we examined the efficacy of the antiobesity phytochemical resveratrol in preventing the deleterious effects of a high-fat diet on thymic anatomy and function. Compared to C57Bl/6 male mice fed a low-fat diet, mice on a high-fat diet had a significant increase in thymic weight and lipid content, and a disrupted anatomy, including a reduction of the medullary compartment and absence of a corticomedullary junction. There were a decrease in thymic cellularity and mature T-cell output, and a disrupted T-cell maturation, as evidenced by increased double-negative and decreased single- and double-positive thymocytes. Mice that had been fed resveratrol along with a high-fat diet had a dose-dependent reversal in all these parameters. Western blots from thymi showed that obese mice had lower levels of the key stimulators of lipid metabolism, phospho-5′ adenosine monophosphate-activated protein kinase and its downstream target, carnitine palmitoyl transferase-1; this was restored to normal levels in resveratrol-fed mice. Resveratrol also reversed an increase in glycerol-3-phosphate acyltransferase-1, the enzyme that catalyzes the first step in triglycerol synthesis. Taken together, these results indicate that resveratrol is a potent inhibitor of the deleterious effects of diet-induced obesity on thymic anatomy and function, and this may hold promise in preventing obesity-related deficits in cell-mediated immunity. 相似文献
29.
Jose Alfonso Cabrera Roy D. Menjivar Abd el‐Fattah A. Dababat Richard A. Sikora 《Journal of Phytopathology》2013,161(2):65-69
In 1979, the anthelmintic activity of abamectin, a mixture of avermectins B1a and B1b, was first reported. Since then, multiple articles have investigated avermectins' degradation and its efficacy against a wide variety of pests under different conditions and using different modes of application. However, there is a gap in the literature of analysing abamectin properties and its performance as a non‐fumigant nematicide when applied liquid or granular vs. new avenues of application based on seed and seedling treatment. Therefore, this article reviewed literature to discuss the mode of action, environmental aspects, the nematicidal effectiveness of treatment forms and the range of activity to address these topics. 相似文献
30.
Juan P. de-Torres Jose M. Marín Víctor Pinto-Plata Miguel Divo Pablo Sanchez-Salcedo Jorge Zagaceta Javier J. Zulueta Juan Berto Carlos Cabrera Bartolome R. Celli Ciro Casanova 《PloS one》2016,11(4)
BackgroundThe Global Initiative for Obstructive Lung Diseases (GOLD) defines COPD as a disease that is usually progressive. GOLD also provides a spirometric classification of airflow limitation. However, little is known about the long-term changes of patients in different GOLD grades.ObjectiveExplore the proportion and characteristics of COPD patients that change their spirometric GOLD grade over long-term follow-up.MethodsPatients alive for at least 8 years since recruitment and those who died with at least 4 years of repeated spirometric measurements were selected from the BODE cohort database. We purposely included the group of non survivors to avoid a “survival selection” bias. The proportion of patients that had a change (improvement or worsening) in their spirometric GOLD grading was calculated and their characteristics compared with those that remained in the same grade.ResultsA total of 318 patients were included in the survivor and 217 in the non-survivor groups. Nine percent of survivors and 11% of non survivors had an improvement of at least one GOLD grade. Seventy one percent of survivors and non-survivors remained in the same GOLD grade. Those that improved had a greater degree of airway obstruction at baseline.ConclusionsIn this selected population of COPD patients, a high proportion of patients remained in the same spirometric GOLD grade or improved in a long-term follow-up. These findings suggest that once diagnosed, COPD is usually a non-progressive disease. 相似文献