全文获取类型
收费全文 | 1529篇 |
免费 | 143篇 |
国内免费 | 3篇 |
出版年
2024年 | 1篇 |
2023年 | 5篇 |
2022年 | 11篇 |
2021年 | 22篇 |
2020年 | 10篇 |
2019年 | 17篇 |
2018年 | 32篇 |
2017年 | 18篇 |
2016年 | 23篇 |
2015年 | 63篇 |
2014年 | 79篇 |
2013年 | 77篇 |
2012年 | 116篇 |
2011年 | 113篇 |
2010年 | 73篇 |
2009年 | 87篇 |
2008年 | 99篇 |
2007年 | 109篇 |
2006年 | 106篇 |
2005年 | 105篇 |
2004年 | 105篇 |
2003年 | 111篇 |
2002年 | 95篇 |
2001年 | 13篇 |
2000年 | 12篇 |
1999年 | 15篇 |
1998年 | 19篇 |
1997年 | 21篇 |
1996年 | 20篇 |
1995年 | 8篇 |
1994年 | 8篇 |
1993年 | 9篇 |
1992年 | 14篇 |
1991年 | 8篇 |
1990年 | 9篇 |
1989年 | 5篇 |
1988年 | 3篇 |
1987年 | 3篇 |
1986年 | 6篇 |
1985年 | 2篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1981年 | 3篇 |
1980年 | 3篇 |
1977年 | 2篇 |
1976年 | 4篇 |
1974年 | 2篇 |
1973年 | 1篇 |
1972年 | 1篇 |
排序方式: 共有1675条查询结果,搜索用时 15 毫秒
961.
The study of behavioral laterality in humans and nonhumans can contribute to our understanding of brain evolution and functional similarities across species. Few studies have focused on cetaceans. This report exams lateralized behaviors in two captive bottlenose dolphins (Tursiops truncatus). Observations were made by videotaping through a 90 × 150 cm underwater one-way Plexiglass mirror. Directional bias in swimming, “barrel-roll” maneuvers, and circular head movements was assessed for each subject. There was a strong clockwise bias in swimming direction and direction of “barrel-rolls,” but not circular head movements. The clockwise bias in swimming direction and “barrel-roll” maneuvers may be consistent with a rightward turning bias. Zoo Biol 16:173–177, 1997. © 1997 Wiley-Liss, Inc. 相似文献
962.
Jorge C. G. Blanco Lori M. Cullen Arash Kamali Fatoumata Y. D. Sylla Marina S. Boukhvalova Trudy G. Morrison 《PLoS pathogens》2021,17(12)
Maternal anti-respiratory syncytial virus (RSV) antibodies acquired by the fetus through the placenta protect neonates from RSV disease through the first weeks of life. In the cotton rat model of RSV infections, we previously reported that immunization of dams during pregnancy with virus-like particles assembled with mutation stabilized pre-fusion F protein as well as the wild type G protein resulted in robust protection of their offspring from RSV challenge. Here we describe the durability of those protective responses in dams, the durability of protection in offspring, and the transfer of that protection to offspring of two consecutive pregnancies without a second boost immunization. We report that four weeks after birth, offspring of the first pregnancy were significantly protected from RSV replication in both lungs and nasal tissues after RSV challenge, but protection was reduced in pups at 6 weeks after birth. However, the overall protection of offspring of the second pregnancy was considerably reduced, even at four weeks of age. This drop in protection occurred even though the levels of total anti-pre-F IgG and neutralizing antibody titers in dams remained at similar, high levels before and after the second pregnancy. The results are consistent with an evolution of antibody properties in dams to populations less efficiently transferred to offspring or the less efficient transfer of antibodies in elderly dams. 相似文献
963.
964.
Robert G. McMurray Joanne S. Harrell Shibing Deng Chyrise B. Bradley Lori M. Cox Shrikant I. Bangdiwala 《Obesity (Silver Spring, Md.)》2000,8(2):130-139
Objective: This study examined the effects of physical activity, television viewing, video game play, socioeconomic status (SES), and ethnicity on body mass index (BMI). Research Methods and Procedures: The sample was 2389 adolescents, 10 to 16 years of age (12.7 ± 1.0 years); 1240 (52%) females and 1149 (48%) males; 77% white and 23% African American; from rural (77%) and urban (23%) settings. BMI and skinfolds were directly assessed. All other data were obtained from questionnaires. Results: Watching television on non‐school days was related to being overweight (p < 0.005). However, when BMI analyses were adjusted for ethnicity and SES, there were no significant effects of television viewing on BMI (p > 0.061). Increased hours of video game play enhanced the risk of being overweight for both genders when analyses were adjusted for ethnicity and SES (p < 0.019). In males, participation in as little as one high‐intensity physical activity 3 to 5 days a week decreased the ethnic‐ and SES‐adjusted relative risk of being overweight (RR = 0.646; CI: 0.427 to 0.977). For females, the ethnic‐ and SES‐adjusted relative risk for being overweight was not significantly altered by physical activity. The logistic analyses further indicated the influence of low SES and African American ethnicity overshadowed any direct effect of television or videos. Discussion: Because weight status of male adolescents appears to be more related to exercise habits than to television or video game habits, increased participation in high‐intensity exercise appears to be important. For females, neither videos nor exercise habits appear to be related to risk of being overweight. However, ethnicity and SES may be important factors that can influence body weight status, while television viewing may be of some importance. Thus, programs to reduce obesity in female adolescent should focus their efforts in lower SES communities. 相似文献
965.
966.
967.
Novel cationic antimicrobial peptides typified by structures such as KKKKKKAAXAAWAAXAA-NH2, where X = Phe/Trp, and several of their analogues display high activity against a variety of bacteria but exhibit no hemolytic activity even at high dose levels in mammalian erythrocytes. To elucidate their mechanism of action and source of selectivity for bacterial membranes, phospholipid mixtures mimicking the compositions of natural bacterial membranes (containing anionic lipids) and mammalian membranes (containing zwitterionic lipids + cholesterol) were challenged with the peptides. We found that peptides readily inserted into bacterial lipid mixtures, although no insertion was detected in model "mammalian" membranes. The depth of peptide insertion into model bacterial membranes was estimated by Trp fluorescence quenching using doxyl groups variably positioned along the phospholipid acyl chains. Peptide antimicrobial activity generally increased with increasing depth of peptide insertion. The overall results, in conjunction with molecular modeling, support an initial electrostatic interaction step in which bacterial membranes attract and bind peptide dimers onto the bacterial surface, followed by the "sinking" of the hydrophobic core segment to a peptide sequence-dependent depth of approximately 2.5-8 A into the membrane, largely parallel to the membrane surface. Antimicrobial activity was likely enhanced by the fact that the peptide sequences contain AXXXA sequence motifs, which promote their dimerization, and possibly higher oligomerization, as assessed by SDS-polyacrylamide gel analysis and fluorescence resonance energy transfer experiments. The high selectivity of these peptides for nonmammalian membranes, combined with their activity toward a wide spectrum of Gram-negative and Gram-positive bacteria and yeast, while retaining water solubility, represent significant advantages of this class of peptides. 相似文献
968.
Under static growth conditions, hyperpiliated, nontwitching pilT and pilU mutants of Pseudomonas aeruginosa formed dense biofilms, showing that adhesion, not twitching motility, is necessary for biofilm initiation. Under flow conditions, the pilT mutant formed mushroom-like structures larger than those of the wild type but the pilU mutant was defective in biofilm formation. Therefore, twitching motility affects the development of biofilm structure, possibly through modulation of detachment. 相似文献
969.
970.
Meningococcal genetic variation mechanisms viewed through comparative analysis of serogroup C strain FAM18 下载免费PDF全文
Bentley SD Vernikos GS Snyder LA Churcher C Arrowsmith C Chillingworth T Cronin A Davis PH Holroyd NE Jagels K Maddison M Moule S Rabbinowitsch E Sharp S Unwin L Whitehead S Quail MA Achtman M Barrell B Saunders NJ Parkhill J 《PLoS genetics》2007,3(2):e23
The bacterium Neisseria meningitidis is commonly found harmlessly colonising the mucosal surfaces of the human nasopharynx. Occasionally strains can invade host tissues causing septicaemia and meningitis, making the bacterium a major cause of morbidity and mortality in both the developed and developing world. The species is known to be diverse in many ways, as a product of its natural transformability and of a range of recombination and mutation-based systems. Previous work on pathogenic Neisseria has identified several mechanisms for the generation of diversity of surface structures, including phase variation based on slippage-like mechanisms and sequence conversion of expressed genes using information from silent loci. Comparison of the genome sequences of two N. meningitidis strains, serogroup B MC58 and serogroup A Z2491, suggested further mechanisms of variation, including C-terminal exchange in specific genes and enhanced localised recombination and variation related to repeat arrays. We have sequenced the genome of N. meningitidis strain FAM18, a representative of the ST-11/ET-37 complex, providing the first genome sequence for the disease-causing serogroup C meningococci; it has 1,976 predicted genes, of which 60 do not have orthologues in the previously sequenced serogroup A or B strains. Through genome comparison with Z2491 and MC58 we have further characterised specific mechanisms of genetic variation in N. meningitidis, describing specialised loci for generation of cell surface protein variants and measuring the association between noncoding repeat arrays and sequence variation in flanking genes. Here we provide a detailed view of novel genetic diversification mechanisms in N. meningitidis. Our analysis provides evidence for the hypothesis that the noncoding repeat arrays in neisserial genomes (neisserial intergenic mosaic elements) provide a crucial mechanism for the generation of surface antigen variants. Such variation will have an impact on the interaction with the host tissues, and understanding these mechanisms is important to aid our understanding of the intimate and complex relationship between the human nasopharynx and the meningococcus. 相似文献