全文获取类型
收费全文 | 3010篇 |
免费 | 284篇 |
专业分类
3294篇 |
出版年
2023年 | 15篇 |
2022年 | 56篇 |
2021年 | 99篇 |
2020年 | 61篇 |
2019年 | 82篇 |
2018年 | 95篇 |
2017年 | 75篇 |
2016年 | 107篇 |
2015年 | 176篇 |
2014年 | 169篇 |
2013年 | 233篇 |
2012年 | 228篇 |
2011年 | 221篇 |
2010年 | 141篇 |
2009年 | 106篇 |
2008年 | 153篇 |
2007年 | 140篇 |
2006年 | 103篇 |
2005年 | 127篇 |
2004年 | 110篇 |
2003年 | 88篇 |
2002年 | 83篇 |
2001年 | 42篇 |
2000年 | 42篇 |
1999年 | 38篇 |
1998年 | 31篇 |
1997年 | 35篇 |
1996年 | 34篇 |
1995年 | 27篇 |
1994年 | 21篇 |
1993年 | 24篇 |
1992年 | 41篇 |
1991年 | 35篇 |
1990年 | 28篇 |
1989年 | 22篇 |
1988年 | 14篇 |
1987年 | 15篇 |
1986年 | 26篇 |
1985年 | 15篇 |
1984年 | 11篇 |
1983年 | 8篇 |
1982年 | 11篇 |
1979年 | 13篇 |
1977年 | 12篇 |
1976年 | 7篇 |
1975年 | 9篇 |
1974年 | 7篇 |
1971年 | 5篇 |
1969年 | 6篇 |
1968年 | 8篇 |
排序方式: 共有3294条查询结果,搜索用时 15 毫秒
81.
Paola Luciani Cristiana Deledda Susanna Benvenuti Roberta Squecco Ilaria Cellai Benedetta Fibbi Ilaria Maddalena Marone Corinna Giuliani Giulia Modi Fabio Francini Gabriella Barbara Vannelli Alessandro Peri 《PloS one》2013,8(8)
Exendin-4 is a molecule currently used, in its synthetic form exenatide, for the treatment of type 2 diabetes mellitus. Exendin-4 binds and activates the Glucagon-Like Peptide-1 Receptor (GLP-1R), thus inducing insulin release. More recently, additional biological properties have been associated to molecules that belong to the GLP-1 family. For instance, Peptide YY and Vasoactive Intestinal Peptide have been found to affect cell adhesion and migration and our previous data have shown a considerable actin cytoskeleton rearrangement after exendin-4 treatment. However, no data are currently available on the effects of exendin-4 on tumor cell motility. The aim of this study was to investigate the effects of this molecule on cell adhesion, differentiation and migration in two neuroblastoma cell lines, SH-SY5Y and SK-N-AS. We first demonstrated, by Extra Cellular Matrix cell adhesion arrays, that exendin-4 increased cell adhesion, in particular on a vitronectin substrate. Subsequently, we found that this molecule induced a more differentiated phenotype, as assessed by i) the evaluation of neurite-like protrusions in 3D cell cultures, ii) the analysis of the expression of neuronal markers and iii) electrophysiological studies. Furthermore, we demonstrated that exendin-4 reduced cell migration and counteracted anchorage-independent growth in neuroblastoma cells. Overall, these data indicate for the first time that exendin-4 may have anti-tumoral properties. 相似文献
82.
Adriano Redler Giorgio Di Rocco Domenico Giannotti Francesca Frezzotti Maria Giulia Bernieri Simona Ceccarelli Sirio D’Amici Enrica Vescarelli Anna Paola Mitterhofer Antonio Angeloni Cinzia Marchese 《PloS one》2013,8(8)
Fibroblast growth factor receptor-2 (FGFR-2) plays an important role in tumorigenesis. In thyroid cancer it has been observed a FGFR-2 down-modulation, but the role of this receptor has not been yet clarified. Therefore, we decided to examine the expression of both FGFR-2 isoform, FGFR-2-IIIb and FGFR-2-IIIc, in different histological thyroid variants such as hyperplasia, follicular adenoma and papillary carcinoma. Immunohistochemistry and quantitative Real-Time PCR analyses were performed on samples of hyperplasia, follicular adenoma and papillary carcinoma, compared with normal thyroid tissue. Thyroid hyperplasia did not show statistically significant reduction in FGFR-2 protein and mRNA levels. Interestingly, in both follicular adenoma and papillary carcinoma samples we observed a strongly reduced expression of both FGFR-2 isoforms. We speculate that FGFR-2 down-modulation might be an early event in thyroid carcinogenesis. Furthermore, we suggest the potential use of FGFR-2 as an early marker for thyroid cancer diagnosis. 相似文献
83.
Andrea Picin Marco Peresani Christophe Falguères Giulia Gruppioni Jean-Jacques Bahain 《PloS one》2013,8(10)
The introduction of Levallois technology in Europe marked the transition from the Lower to the early Middle Paleolithic. This new method of flake production was accompanied by significant behavioral changes in hominin populations. The emergence of this technological advance is considered homogeneous in the European archaeological record at the Marine isotopic stage (MIS) 9/MIS 8 boundary. In this paper we report a series of combined electron spin resonance/U-series dates on mammal bones and teeth recovered from the lower units of San Bernardino Cave (Italy) and the technological analyses of the lithic assemblages. The San Bernardino Cave has yielded the earliest evidence of Levallois production on the Italian Peninsula recovered to date. In addition to our results and the review of the archaeological record, we describe the chronological and geographical differences between European territories and diversities in terms of technological developments. The belated emergence of Levallois technology in Italy compared to western Europe corresponds to the late Italian Neanderthal speciation event. The new radiometric dates and the technological analyses of San Bernardino Cave raise the issue of the different roles of glacial refugia in the peopling and the spread of innovative flaking strategies in Europe during the late Middle Pleistocene. 相似文献
84.
Oecologia - Fluctuations in the abundance of main prey species might shape animal communities, by inducing numerical responses and dietary shifts in predators. Whether numerical responses and... 相似文献
85.
Sara J. Schmuecker Drew A. Becker Michael J. Lanzone Bob Fogg Susan P. Romano Todd E. Katzner Tricia A. Miller 《The Journal of wildlife management》2020,84(8):1578-1589
Weather can shape movements of animals and alter their exposure to anthropogenic threats. Bald eagles (Haliaeetus leucocephalus) are increasingly at risk from collision with turbines used in onshore wind energy generation. In the midwestern United States, development of this energy source typically occurs in upland areas that bald eagles use only intermittently. Our objective was to determine the factors that cause wintering bald eagles to occupy riparian areas and riskier, upland areas. We tracked 20 bald eagles using telemetry in the Upper Midwest (MN, IA, MO, WI, IL, USA) during winter 2014–2015 and 2015–2016 and evaluated habitat use by eagles in response to variation in weather and time of year. Eagles used riparian areas more when wind speed and atmospheric pressure were low. Exclusive use of uplands was more frequent during weather systems with low pressure and high humidity and after long periods of cold weather. There was a non-linear response to time of year (measured by days before migration) in the frequency of exclusive use of uplands or riparian areas. Probability of exclusive use of either landscape was generally constant within 95 days prior to migration. The probability of use of riparian areas, however, was markedly less during dates >100 days before migration. Our results suggest that eagles are most likely to be exposed to wind energy developments located in upland areas during low pressure systems, after long periods of cold weather, and several months before the onset of spring migration. This information helps to better understand the factors influencing bald eagle habitat use in winter and will be useful to managers and developers wishing to establish effective strategies to avoid, minimize, and mitigate take, and to survey for mortalities at wind energy developments. © 2020 The Wildlife Society. 相似文献
86.
Gianluca
E.M. Boari Giulia Chiarini Silvia Bonetti Paolo Malerba Gianluca Bianco Cristina Faustini Federico Braglia-Orlandini Daniele Turini Vittoria Guarinoni Michele Saottini Sara Viola Giulia Ferrari-Toninelli Giancarlo Pasini Cristina Mascadri Bianca Bonzi Paolo Desenzani Claudia Tusi Eros Zanotti Matteo Nardin Damiano Rizzoni 《Bioscience reports》2020,40(12)
The aim of the present study was to simultaneously assess several potential predictors of outcome (co-morbidity, previous and in-hospital treatment, radiologic Brixia score) in patients with COVID-19.This retrospective cohort study included 258 consecutive patients with confirmed COVID-19 admitted to a medical ward at Montichiari Hospital, Brescia, Italy from February 28th to April 30rd, 2020. Patients had SARS-CoV-2 related pneumonia with respiratory failure, and were treated with hydroxychloroquine and lopinavir plus ritonavir. In some patients, additional treatment with tocilizumab, dexamethasone and enoxaparin was adopted. Outcomes (death or recovery) were assessed at the end of the discharge period or at the end of the follow-up (August 2020).During hospitalization, 59 patients died, while 6 died after discharge. The following variables were demonstrated to be associated with a worse prognosis: Radiologic Brixia score higher than 8, presence at baseline of hypertension, diabetes, chronic obstructive pulmonary disease, heart disease, cancer, previous treatment with ACE-inhibitors or anti-platelet drugs. Anticoagulant treatment during hospital admission with enoxaparin at a dose higher than 4000 U once daily was associated with a better prognosis.In conclusion, our study demonstrates that some co-morbidities and cardiovascular risk factors may affect prognosis. The radiologic Brixia score may be a useful tool to stratify the risk of death at baseline. Anticoagulant treatment with enoxaparin might be associated to a clinical benefit in terms of survival in patients with COVID-19. 相似文献
87.
Weiss Steven Grimm Jacqueline Gonçalves Duarte V. Secci-Petretto Giulia Englmaier Gernot K. Baimukanov Mirgaliy Froufe Elsa 《Hydrobiologia》2020,847(13):2823-2844
Hydrobiologia - A high number of grayling (Thymallus) species have been described from the Altai-Sayan mountain region, for which little to no genetic information is available. We investigated... 相似文献
88.
89.
90.
Kyle B. Vrtis Radoslaw P. Markiewicz Louis J. Romano David Rueda 《Nucleic acids research》2013,41(16):7843-7853
DNA polymerases must accurately replicate DNA to maintain genome integrity. Carcinogenic adducts, such as 2-aminofluorene (AF) and N-acetyl-2-aminofluorene (AAF), covalently bind DNA bases and promote mutagenesis near the adduct site. The mechanism by which carcinogenic adducts inhibit DNA synthesis and cause mutagenesis remains unclear. Here, we measure interactions between a DNA polymerase and carcinogenic DNA adducts in real-time by single-molecule fluorescence. We find the degree to which an adduct affects polymerase binding to the DNA depends on the adduct location with respect to the primer terminus, the adduct structure and the nucleotides present in the solution. Not only do the adducts influence the polymerase dwell time on the DNA but also its binding position and orientation. Finally, we have directly observed an adduct- and mismatch-induced intermediate state, which may be an obligatory step in the DNA polymerase proofreading mechanism. 相似文献