全文获取类型
收费全文 | 4822篇 |
免费 | 472篇 |
国内免费 | 2篇 |
专业分类
5296篇 |
出版年
2021年 | 48篇 |
2019年 | 46篇 |
2018年 | 50篇 |
2017年 | 65篇 |
2016年 | 81篇 |
2015年 | 144篇 |
2014年 | 154篇 |
2013年 | 205篇 |
2012年 | 270篇 |
2011年 | 253篇 |
2010年 | 174篇 |
2009年 | 145篇 |
2008年 | 216篇 |
2007年 | 221篇 |
2006年 | 193篇 |
2005年 | 229篇 |
2004年 | 198篇 |
2003年 | 185篇 |
2002年 | 170篇 |
2001年 | 132篇 |
2000年 | 130篇 |
1999年 | 109篇 |
1998年 | 70篇 |
1997年 | 63篇 |
1996年 | 72篇 |
1995年 | 62篇 |
1994年 | 53篇 |
1993年 | 50篇 |
1992年 | 81篇 |
1991年 | 83篇 |
1990年 | 78篇 |
1989年 | 68篇 |
1988年 | 58篇 |
1987年 | 44篇 |
1986年 | 49篇 |
1985年 | 61篇 |
1984年 | 46篇 |
1983年 | 48篇 |
1982年 | 39篇 |
1981年 | 45篇 |
1980年 | 33篇 |
1979年 | 44篇 |
1978年 | 36篇 |
1977年 | 45篇 |
1976年 | 49篇 |
1975年 | 36篇 |
1974年 | 47篇 |
1973年 | 35篇 |
1972年 | 36篇 |
1970年 | 37篇 |
排序方式: 共有5296条查询结果,搜索用时 15 毫秒
951.
Marco daCosta DiBonaventura Yong Yuan Benedicte Lescrauwaet Gilbert L’Italien Gordon G. Liu Isao Kamae Josephine A. Mauskopf 《PloS one》2014,9(1)
Background
The World Health Organization has called for global and regional assessments of the burden of hepatitis C (HCV) along with country-specific patient profiles to better inform healthcare policy. The present investigated the characteristics and burden of patients reporting a diagnosis of HCV infection in the US, France, Germany, Italy, Spain, the UK, urban China, and Japan using a consistent methodology of patient-reported surveys.Methods
The 2010 5EU (N = 57,805), 2009 US (N = 75,000), 2008/2009 Japan (N = 37,683), and 2009/2010 urban China (N = 33,261) waves of the National Health and Wellness Survey were used as the data source. Within each country, patients with a self-reported diagnosis of HCV were compared with those who did not report a diagnosis of HCV on sociodemographics, health behaviors, comorbidities, and health outcomes (e.g., Short Form-12v2). The effect of HCV was examined using regression analysis applying sampling weights.Results
The prevalence of HCV ranged from 0.26% (China) to 1.42% (Italy). Patients in Japan and Italy (61.60 and 61.02 years, respectively) were the oldest, while patients in the US were the most likely to be obese (39.31%) and have concomitant anxiety (38.43%) and depression (46.05%) compared with other countries. Pooling countries and adjusting for sociodemographics, health behaviors, and comorbidities, HCV was associated with significantly lower physical component summary scores (b = −2.51) and health utilities (b = −0.04) and greater overall work impairment (b = 8.79), physician visits (b = 2.91), and emergency department visits (b = 0.30) (all p<.05). The effects on health status were strongest in the US and UK while the effects on healthcare resource use were strongest in Japan.Conclusions
HCV was associated with a significant humanistic and economic burden. These results suggest that the manifestation of the HCV burden, and the profile of the patients themselves, varied dramatically by country. Successful disease management should be cognizant of region-specific unmet needs. 相似文献952.
Many populations of migratory songbirds are declining or shifting in distribution. This is likely due to environmental changes that alter factors such as food availability that may have an impact on survival and/or breeding success. We tested the impact of experimentally supplemented food on the breeding success over three years of northern wheatears (Oenanthe oenanthe), a species in decline over much of Europe. The number of offspring fledged over the season was higher for food-supplemented birds than for control birds. The mechanisms for this effect were that food supplementation advanced breeding date, which, together with increased resources, allowed further breeding attempts. While food supplementation did not increase the clutch size, hatching success or number of chicks fledged per breeding attempt, it did increase chick size in one year of the study. The increased breeding success was greater for males than females; males could attempt to rear simultaneous broods with multiple females as well as attempting second broods, whereas females could only increase their breeding effort via second broods. Multiple brooding is rare in the study population, but this study demonstrates the potential for changes in food availability to affect wheatear breeding productivity, primarily via phenotypic flexibility in the number of breeding attempts. Our results have implications for our understanding of how wheatears may respond to natural changes in food availability due to climate changes or changes in habitat management. 相似文献
953.
Mathilde C. Paul Marius Gilbert Stéphanie Desvaux Harena Rasamoelina Andriamanivo Marisa Peyre Nguyen Viet Khong Weerapong Thanapongtharm Véronique Chevalier 《PloS one》2014,9(7)
Outbreaks of highly pathogenic avian influenza have occurred and have been studied in a variety of ecological systems. However, differences in the spatial resolution, geographical extent, units of analysis and risk factors examined in these studies prevent their quantitative comparison. This study aimed to develop a high-resolution, comparative study of a common set of agro-environmental determinants of avian influenza viruses (AIV) in domestic poultry in four different environments: (1) lower-Northern Thailand, where H5N1 circulated in 2004–2005, (2) the Red River Delta in Vietnam, where H5N1 is circulating widely, (3) the Vietnam highlands, where sporadic H5N1 outbreaks have occurred, and (4) the Lake Alaotra region in Madagascar, which features remarkable similarities with Asian agro-ecosystems and where low pathogenic avian influenza viruses have been found. We analyzed H5N1 outbreak data in Thailand in parallel with serological data collected on the H5 subtype in Vietnam and on low pathogenic AIV in Madagascar. Several agro-environmental covariates were examined: poultry densities, landscape dominated by rice cultivation, proximity to a water body or major road, and human population density. Relationships between covariates and AIV circulation were explored using spatial generalized linear models. We found that AIV prevalence was negatively associated with distance to the closest water body in the Red River Delta, Vietnam highlands and Madagascar. We also found a positive association between AIV and duck density in the Vietnam highlands and Thailand, and with rice landscapes in Thailand and Madagascar. Our findings confirm the important role of wetlands-rice-ducks ecosystems in the epidemiology of AI in diverse settings. Variables influencing circulation of the H5 subtype in Southeast Asia played a similar role for low pathogenic AIV in Madagascar, indicating that this area may be at risk if a highly virulent strain is introduced. 相似文献
954.
955.
Jonathan E. Ulmer Eric Morssing Vilén Ramesh Babu Namburi Alhosna Benjdia Julie Beneteau Annie Malleron David Bonnaffé Pierre-Alexandre Driguez Karine Descroix Gilbert Lassalle Christine Le Narvor Corine Sandstr?m Dorothe Spillmann Olivier Berteau 《The Journal of biological chemistry》2014,289(35):24289-24303
Despite the importance of the microbiota in human physiology, the molecular bases that govern the interactions between these commensal bacteria and their host remain poorly understood. We recently reported that sulfatases play a key role in the adaptation of a major human commensal bacterium, Bacteroides thetaiotaomicron, to its host (Benjdia, A., Martens, E. C., Gordon, J. I., and Berteau, O. (2011) J. Biol. Chem. 286, 25973–25982). We hypothesized that sulfatases are instrumental for this bacterium, and related Bacteroides species, to metabolize highly sulfated glycans (i.e. mucins and glycosaminoglycans (GAGs)) and to colonize the intestinal mucosal layer. Based on our previous study, we investigated 10 sulfatase genes induced in the presence of host glycans. Biochemical characterization of these potential sulfatases allowed the identification of GAG-specific sulfatases selective for the type of saccharide residue and the attachment position of the sulfate group. Although some GAG-specific bacterial sulfatase activities have been described in the literature, we report here for the first time the identity and the biochemical characterization of four GAG-specific sulfatases. Furthermore, contrary to the current paradigm, we discovered that B. thetaiotaomicron possesses an authentic GAG endosulfatase that is active at the polymer level. This type of sulfatase is the first one to be identified in a bacterium. Our study thus demonstrates that bacteria have evolved more sophisticated and diverse GAG sulfatases than anticipated and establishes how B. thetaiotaomicron, and other major human commensal bacteria, can metabolize and potentially tailor complex host glycans. 相似文献
956.
Susannah Gilbert Tony Chen Ian D. Hutchinson Dan ChoiClifford Voigt Russell F. WarrenSuzanne A. Maher 《Journal of biomechanics》2014
Despite significant advances in scaffold design, manufacture, and development, it remains unclear what forces these scaffolds must withstand when implanted into the heavily loaded environment of the knee joint. The objective of this study was to fully quantify the dynamic contact mechanics across the tibial plateau of the human knee joint during gait and stair climbing. Our model consisted of a modified Stanmore knee simulator (to apply multi-directional dynamic forces), a two-camera motion capture system (to record joint kinematics), an electronic sensor (to record contact stresses on the tibial plateau), and a suite of post-processing algorithms. During gait, peak contact stresses on the medial plateau occurred in areas of cartilage–cartilage contact; while during stair climb, peak contact stresses were located in the posterior aspect of the plateau, under the meniscus. On the lateral plateau, during gait and in early stair-climb, peak contact stresses occurred under the meniscus, while in late stair-climb, peak contact stresses were experienced in the zone of cartilage–cartilage contact. At 45% of the gait cycle, and 20% and 48% of the stair-climb cycle, peak stresses were simultaneously experienced on both the medial and lateral compartment, suggesting that these phases of loading warrant particular consideration in any simulation intended to evaluate scaffold performance. Our study suggests that in order to design a scaffold capable of restoring ‘normal’ contact mechanics to the injured knees, the mechanics of the intended site of implantation should be taken into account in any pre-clinical testing regime. 相似文献
957.
Joana Pereira Warren E. Johnson Stephen J. O’Brien Erich D. Jarvis Guojie Zhang M. Thomas P. Gilbert Vitor Vasconcelos Agostinho Antunes 《PloS one》2014,9(12)
The Hedgehog (Hh) gene family codes for a class of secreted proteins composed of two active domains that act as signalling molecules during embryo development, namely for the development of the nervous and skeletal systems and the formation of the testis cord. While only one Hh gene is found typically in invertebrate genomes, most vertebrates species have three (Sonic hedgehog – Shh; Indian hedgehog – Ihh; and Desert hedgehog – Dhh), each with different expression patterns and functions, which likely helped promote the increasing complexity of vertebrates and their successful diversification. In this study, we used comparative genomic and adaptive evolutionary analyses to characterize the evolution of the Hh genes in vertebrates following the two major whole genome duplication (WGD) events. To overcome the lack of Hh-coding sequences on avian publicly available databases, we used an extensive dataset of 45 avian and three non-avian reptilian genomes to show that birds have all three Hh paralogs. We find suggestions that following the WGD events, vertebrate Hh paralogous genes evolved independently within similar linkage groups and under different evolutionary rates, especially within the catalytic domain. The structural regions around the ion-binding site were identified to be under positive selection in the signaling domain. These findings contrast with those observed in invertebrates, where different lineages that experienced gene duplication retained similar selective constraints in the Hh orthologs. Our results provide new insights on the evolutionary history of the Hh gene family, the functional roles of these paralogs in vertebrate species, and on the location of mutational hotspots. 相似文献
958.
Antony Croxatto Guy Prod'hom Christian Durussel Gilbert Greub 《Journal of visualized experiments : JoVE》2014,(92)
Bloodstream infections and sepsis are a major cause of morbidity and mortality. The successful outcome of patients suffering from bacteremia depends on a rapid identification of the infectious agent to guide optimal antibiotic treatment. The analysis of Gram stains from positive blood culture can be rapidly conducted and already significantly impact the antibiotic regimen. However, the accurate identification of the infectious agent is still required to establish the optimal targeted treatment. We present here a simple and fast bacterial pellet preparation from a positive blood culture that can be used as a sample for several essential downstream applications such as identification by MALDI-TOF MS, antibiotic susceptibility testing (AST) by disc diffusion assay or automated AST systems and by automated PCR-based diagnostic testing. The performance of these different identification and AST systems applied directly on the blood culture bacterial pellets is very similar to the performance normally obtained from isolated colonies grown on agar plates. Compared to conventional approaches, the rapid acquisition of a bacterial pellet significantly reduces the time to report both identification and AST. Thus, following blood culture positivity, identification by MALDI-TOF can be reported within less than 1 hr whereas results of AST by automated AST systems or disc diffusion assays within 8 to 18 hr, respectively. Similarly, the results of a rapid PCR-based assay can be communicated to the clinicians less than 2 hr following the report of a bacteremia. Together, these results demonstrate that the rapid preparation of a blood culture bacterial pellet has a significant impact on the identification and AST turnaround time and thus on the successful outcome of patients suffering from bloodstream infections. 相似文献
959.
Dawn Field Peter Sterk Renzo Kottmann J. Wim De Smet Linda Amaral-Zettler Guy Cochrane James R. Cole Neil Davies Peter Dawyndt George M. Garrity Jack A. Gilbert Frank Oliver Gl?ckner Lynette Hirschman Hans-Peter Klenk Rob Knight Nikos Kyrpides Folker Meyer Ilene Karsch-Mizrachi Norman Morrison Robert Robbins Inigo San Gil Susanna Sansone Lynn Schriml Tatiana Tatusova Dave Ussery Pelin Yilmaz Owen White John Wooley Gregory Caporaso 《Standards in genomic sciences》2014,9(3):599-601
960.
Proteoid Root Development of Phosphorus Deficient Lupin is Mimicked by Auxin and Phosphonate 总被引:17,自引:4,他引:13
Gilbert Glena A.; Knight J. Diane; Vance Carroll P.; Allan Deborah L. 《Annals of botany》2000,85(6):921-928
White lupin (Lupinus albus L.) develops proteoid (cluster) rootsin response to phosphorus deficiency. Proteoid roots are composedof tight clusters of rootlets that initiate from the pericycleopposite protoxylem poles and emerge from every protoxylem polewithin the proteoid root axis. Auxins are required for lateralroot development, but little is known of their role in proteoidroot formation. Proteoid root numbers were dramatically increasedin P-sufficient (+P) plants by application of the syntheticauxin, naphthalene acetic acid (NAA), to leaves, and were reducedin P-deficient (-P) plants by the presence of auxin transportinhibitors [2,3,5-triiodobenzoic acid (TIBA) and naphthylphthalamicacid (NPA)]. While ethylene concentrations in the root zonewere 1.5-fold higher in -P plants, there was no effect on proteoidroot numbers of the ethylene inhibitors aminoethoxyvinvylglycine(AVG) and silver thiosulphate. Phosphonate, which interfereswith plant perception of internal P concentration, dramaticallyincreased the number of proteoid root segments in +P plants.Activities of phosphoenolpyruvate carboxylase (PEPC), malatedehydrogenase (MDH) and exuded acid phosphatase in proteoidroot segments were not different from +P controls when NAA wasapplied to +P lupin plants, but increased to levels comparableto -P plants in the phosphonate treatment. Addition of TIBAor NPA to -P plants reduced PEPC and MDH activity of -P proteoidroots to levels found in +P or -P normal root tissues, but didnot affect acid phosphatase in root exudates. These resultssuggest that auxin transport from the shoot plays a role inthe formation of proteoid roots during P deficiency. Auxin-stimulatedproteoid root formation is necessary, but not sufficient, tosignal the up-regulation of PEPC and MDH in proteoid root segments.In contrast, phosphonate applied to P-sufficient white lupinelicits the full suite of coordinated responses to P deficiencyCopyright2000 Annals of Botany Company Lupinus albus L., white lupin, proteoid roots, auxin, ethylene, phosphonate, phosphorus deficiency 相似文献