全文获取类型
收费全文 | 6825篇 |
免费 | 483篇 |
国内免费 | 1篇 |
专业分类
7309篇 |
出版年
2024年 | 6篇 |
2023年 | 40篇 |
2022年 | 115篇 |
2021年 | 181篇 |
2020年 | 138篇 |
2019年 | 163篇 |
2018年 | 209篇 |
2017年 | 160篇 |
2016年 | 281篇 |
2015年 | 449篇 |
2014年 | 437篇 |
2013年 | 571篇 |
2012年 | 650篇 |
2011年 | 623篇 |
2010年 | 340篇 |
2009年 | 310篇 |
2008年 | 389篇 |
2007年 | 369篇 |
2006年 | 333篇 |
2005年 | 301篇 |
2004年 | 257篇 |
2003年 | 211篇 |
2002年 | 234篇 |
2001年 | 41篇 |
2000年 | 28篇 |
1999年 | 40篇 |
1998年 | 53篇 |
1997年 | 28篇 |
1996年 | 34篇 |
1995年 | 23篇 |
1994年 | 28篇 |
1993年 | 22篇 |
1992年 | 27篇 |
1991年 | 16篇 |
1990年 | 15篇 |
1989年 | 14篇 |
1988年 | 12篇 |
1987年 | 13篇 |
1985年 | 9篇 |
1984年 | 13篇 |
1983年 | 6篇 |
1982年 | 11篇 |
1981年 | 8篇 |
1980年 | 13篇 |
1979年 | 9篇 |
1978年 | 6篇 |
1977年 | 11篇 |
1976年 | 5篇 |
1974年 | 6篇 |
1973年 | 14篇 |
排序方式: 共有7309条查询结果,搜索用时 15 毫秒
91.
Biodegradation kinetic constants and sorption coefficients of micropollutants in membrane bioreactors 总被引:1,自引:0,他引:1
Eduardo Fernandez-Fontaina Ines Pinho Marta Carballa Francisco Omil Juan M. Lema 《Biodegradation》2013,24(2):165-177
In order to elucidate the capability of biomass developed in membrane bioreactors (MBR) to degrade and sorb emerging micropollutants, biodegradation (kbiol) and sorption (ksor) kinetic constants as well as solid–liquid partition coefficients (Kd) of 13 selected pharmaceutical and personal care products (PPCPs) were determined with MBR heterotrophic biomass adding a pulse (100 ppb of each compound) and following the liquid and solid phase concentrations over time. The results obtained were compared to literature data referring to conventional activated sludge (CAS) systems. Two experiments were performed: one in the MBR itself and the second one in a batch reactor with the same type and concentration of biomass as in the MBR. Overall, both biodegradation and sorption coefficients were in the same range as previously reported by other studies in CAS systems, indicating that MBR biomass does not show better capabilities for the biological degradation and/or sorption of PPCPs compared to the biomass developed in CAS reactors. Therefore, the higher PPCPs removal efficiencies found in MBRs are explained by the high biomass concentrations obtained at the long sludge retention times at which this type of reactors are usually operated. 相似文献
92.
Julien Foucaud Céline Moreno Marta Pascual Enrico L. Rezende Luis E. Castañeda Patricia Gibert Frederic Mery 《Ecology and evolution》2016,6(6):1725-1736
The success of invasive species is tightly linked to their fitness in a putatively novel environment. While quantitative components of fitness have been studied extensively in the context of invasive species, fewer studies have looked at qualitative components of fitness, such as behavioral plasticity, and their interaction with quantitative components, despite intuitive benefits over the course of an invasion. In particular, learning is a form of behavioral plasticity that makes it possible to finely tune behavior according to environmental conditions. Learning can be crucial for survival and reproduction of introduced organisms in novel areas, for example, for detecting new predators, or finding mates or oviposition sites. Here we explored how oviposition performance evolved in relation to both fecundity and learning during an invasion, using native and introduced Drosophila subobscura populations performing an ecologically relevant task. Our results indicated that, under comparable conditions, invasive populations performed better during our oviposition task than did native populations. This was because invasive populations had higher fecundity, together with similar cognitive performance when compared to native populations, and that there was no interaction between learning and fecundity. Unexpectedly, our study did not reveal an allocation trade‐off (i.e., a negative relationship) between learning and fecundity. On the contrary, the pattern we observed was more consistent with an acquisition trade‐off, meaning that fecundity could be limited by availability of resources, unlike cognitive ability. This pattern might be the consequence of escaping natural enemies and/or competitors during the introduction. The apparent lack of evolution of learning may indicate that the introduced population did not face novel cognitive challenges in the new environment (i.e., cognitive “pre‐adaptation”). Alternatively, the evolution of learning may have been transient and therefore not detected. 相似文献
93.
Szoszkiewicz Krzysztof Jusik Szymon Lewin Iga Czerniawska-Kusza Izabela Kupiec Jerzy Mirosław Szostak Marta 《Hydrobiologia》2018,808(1):327-342
Hydrobiologia - The aim of the study was to compare the patterns of development of macrophytes and macroinvertebrates in different types of reference mountain rivers. The study is based on... 相似文献
94.
Environmental context and magnitude of disturbance influence trait‐mediated community responses to wastewater in streams
下载免费PDF全文
![点击此处可从《Ecology and evolution》网站下载免费的PDF全文](/ch/ext_images/free.gif)
95.
Chandana Basu Mallick Florin Mircea Iliescu M?rt M?ls Sarah Hill Rakesh Tamang Gyaneshwer Chaubey Rie Goto Simon Y. W. Ho Irene Gallego Romero Federica Crivellaro Georgi Hudjashov Niraj Rai Mait Metspalu C. G. Nicholas Mascie-Taylor Ramasamy Pitchappan Lalji Singh Marta Mirazon-Lahr Kumarasamy Thangaraj Richard Villems Toomas Kivisild 《PLoS genetics》2013,9(11)
Skin pigmentation is one of the most variable phenotypic traits in humans. A non-synonymous substitution (rs1426654) in the third exon of SLC24A5 accounts for lighter skin in Europeans but not in East Asians. A previous genome-wide association study carried out in a heterogeneous sample of UK immigrants of South Asian descent suggested that this gene also contributes significantly to skin pigmentation variation among South Asians. In the present study, we have quantitatively assessed skin pigmentation for a largely homogeneous cohort of 1228 individuals from the Southern region of the Indian subcontinent. Our data confirm significant association of rs1426654 SNP with skin pigmentation, explaining about 27% of total phenotypic variation in the cohort studied. Our extensive survey of the polymorphism in 1573 individuals from 54 ethnic populations across the Indian subcontinent reveals wide presence of the derived-A allele, although the frequencies vary substantially among populations. We also show that the geospatial pattern of this allele is complex, but most importantly, reflects strong influence of language, geography and demographic history of the populations. Sequencing 11.74 kb of SLC24A5 in 95 individuals worldwide reveals that the rs1426654-A alleles in South Asian and West Eurasian populations are monophyletic and occur on the background of a common haplotype that is characterized by low genetic diversity. We date the coalescence of the light skin associated allele at 22–28 KYA. Both our sequence and genome-wide genotype data confirm that this gene has been a target for positive selection among Europeans. However, the latter also shows additional evidence of selection in populations of the Middle East, Central Asia, Pakistan and North India but not in South India. 相似文献
96.
Stefania Raimondo Ornella Urzì Serena Meraviglia Marta Di Simone Anna Maria Corsale Nima Rabienezhad Ganji Antonio Palumbo Piccionello Giulia Polito Elena Lo Presti Francesco Dieli Alice Conigliaro Riccardo Alessandro 《Journal of cellular and molecular medicine》2022,26(15):4195
Chronic inflammation is associated with the occurrence of several diseases. However, the side effects of anti‐inflammatory drugs prompt the identification of new therapeutic strategies. Plant‐derived extracellular vesicles (PDEVs) are gaining increasing interest in the scientific community for their biological properties. We isolated PDEVs from the juice of Citrus limon L. (LEVs) and characterized their flavonoid, limonoid and lipid contents through reversed‐phase high‐performance liquid chromatography coupled to electrospray ionization quadrupole time‐of‐flight mass spectrometry (RP‐HPLC–ESI‐Q‐TOF‐MS). To investigate whether LEVs have a protective role on the inflammatory process, murine and primary human macrophages were pre‐treated with LEVs for 24 h and then were stimulated with lipopolysaccharide (LPS). We found that pre‐treatment with LEVs decreased gene and protein expression of pro‐inflammatory cytokines, such as IL‐6, IL1‐β and TNF‐α, and reduced the nuclear translocation and phosphorylation of NF‐κB in LPS‐stimulated murine macrophages. The inhibition of NF‐κB activation was associated with the reduction in ERK1‐2 phosphorylation. Furthermore, the ability of LEVs to decrease pro‐inflammatory cytokines and increase anti‐inflammatory molecules was confirmed ex vivo in human primary T lymphocytes. In conclusion, we demonstrated that LEVs exert anti‐inflammatory effects both in vitro and ex vivo by inhibiting the ERK1‐2/NF‐κB signalling pathway. 相似文献
97.
The ability of Escherichia coli with different receptor specificities to interact with meconium was studied. E. coli strains expressing P-fimbriae, specific for Gal alpha 1-4Gal beta-containing receptors, were agglutinated by meconium at high titres. This reaction was inhibited by globotetraosylceramide. The attachment of P-fimbriated E. coli to human colonic epithelial cells of the HT-29 cell line was inhibited by meconium. Some type 1 fimbriated strains were agglutinated by meconium, but the agglutination was rarely blocked by methyl alpha-D-mannoside. The attachment by type 1 fimbriated strains to HT-29 cells was reduced by meconium only in some cases. These results suggest that meconium interacts with the P-fimbriae of E. coli, in a way that may influence bacterial colonization of the neonatal intestine. 相似文献
98.
Marta Marchetti Delphine Capela Renaud Poincloux Nacer Benmeradi Marie-Christine Auriac Aurélie Le Ru Isabelle Maridonneau-Parini Jacques Batut Catherine Masson-Boivin 《PloS one》2013,8(2)
Rhizobia are symbiotic soil bacteria able to intracellularly colonize legume nodule cells and form nitrogen-fixing symbiosomes therein. How the plant cell cytoskeleton reorganizes in response to rhizobium colonization has remained poorly understood especially because of the lack of an in vitro infection assay. Here, we report on the use of the heterologous HeLa cell model to experimentally tackle this question. We observed that the model rhizobium Sinorhizobium meliloti, and other rhizobia as well, were able to trigger a major reorganization of actin cytoskeleton of cultured HeLa cells in vitro. Cell deformation was associated with an inhibition of the three major small RhoGTPases Cdc42, RhoA and Rac1. Bacterial entry, cytoskeleton rearrangements and modulation of RhoGTPase activity required an intact S. meliloti biosynthetic pathway for queuosine, a hypermodifed nucleoside regulating protein translation through tRNA, and possibly mRNA, modification. We showed that an intact bacterial queuosine biosynthetic pathway was also required for effective nitrogen-fixing symbiosis of S. meliloti with its host plant Medicago truncatula, thus indicating that one or several key symbiotic functions of S. meliloti are under queuosine control. We discuss whether the symbiotic defect of que mutants may originate, at least in part, from an altered capacity to modify plant cell actin cytoskeleton. 相似文献
99.
100.
Marta Castro Lizet Sánchez Dennis Pérez Carlos Sebrango Ziv Shkedy Patrick Van der Stuyft 《PloS one》2013,8(12)
The reemergence of dengue as an important public health problem reflects the difficulties in sustaining vertically organized, effective, control programs and the need for community-based strategies for Aedes aegypti control that result in behavioral change. We aimed to disentangle the relationships between underlying determinants of dengue related practices. We conducted a cross-sectional study in 780 households in La Lisa, Havana, Cuba. A questionnaire and an observation guide were administrated to collect information on variables related to economic status, knowledge on dengue, risk perception and practices associated with Aedes aegypti breading sites. To test a conceptual model that hypothesized direct relationships among all these constructs, we first used Exploratory Factor Analysis with Principal Component Analysis to establish the relationship between observed variables and the underlying latent variables. Subsequently, we tested whether the observed data supported the conceptual model through Confirmatory Factor Analysis. Exploratory Factor Analysis indicated that the items measured could be reduced into five factors with an eigenvalue >1.0: Knowledge on dengue, Intradomiciliar risk practices, Peridomiciliar risk practices, Risk perception and Economic status. The proportion of the total variance in the data explained by these five factors was 74.3%. The Confirmatory Factor Analysis model differed from our hypothesized conceptual model. Only Knowledge on dengue had a significant, direct, positive, effect on Practices. There was also a direct association of Economic status with Knowledge on dengue, but not with Risk perception and Practices. Clarifying the relationship between direct and indirect determinants of dengue related practices contributes to a better understanding of the potential effect of Information Education and Communication on practices and on the reduction of Aedes aegypti breeding sites and provides inputs for designing a community based strategy for dengue control. 相似文献