全文获取类型
收费全文 | 3074篇 |
免费 | 299篇 |
国内免费 | 2篇 |
出版年
2023年 | 22篇 |
2022年 | 41篇 |
2021年 | 81篇 |
2020年 | 61篇 |
2019年 | 89篇 |
2018年 | 82篇 |
2017年 | 93篇 |
2016年 | 113篇 |
2015年 | 169篇 |
2014年 | 164篇 |
2013年 | 231篇 |
2012年 | 241篇 |
2011年 | 244篇 |
2010年 | 121篇 |
2009年 | 114篇 |
2008年 | 178篇 |
2007年 | 145篇 |
2006年 | 147篇 |
2005年 | 138篇 |
2004年 | 126篇 |
2003年 | 124篇 |
2002年 | 113篇 |
2001年 | 60篇 |
2000年 | 46篇 |
1999年 | 63篇 |
1998年 | 42篇 |
1997年 | 30篇 |
1996年 | 22篇 |
1995年 | 12篇 |
1994年 | 18篇 |
1993年 | 16篇 |
1992年 | 19篇 |
1991年 | 15篇 |
1990年 | 20篇 |
1989年 | 12篇 |
1988年 | 18篇 |
1987年 | 10篇 |
1986年 | 11篇 |
1985年 | 6篇 |
1984年 | 8篇 |
1983年 | 9篇 |
1982年 | 13篇 |
1981年 | 12篇 |
1980年 | 5篇 |
1977年 | 6篇 |
1976年 | 8篇 |
1975年 | 6篇 |
1974年 | 13篇 |
1973年 | 4篇 |
1972年 | 7篇 |
排序方式: 共有3375条查询结果,搜索用时 203 毫秒
61.
Abstract The first unambiguous documentation of hybridism in the genus Doronicum (Senecioneae – Asteraceae) is reported. All our morphological, karyological and molecular data concur to indicate that Doronicum × minutilloi Peruzzi hybr. nov. (2n = 60) is a hybrid growing in Monti Aurunci (Central Italy), originated from the spontaneous crossing D. orientale Hoffm. (2n = 60) × D. columnae Ten. (2n = 60). This new hybrid shows a slightly higher morphological, karyotypic and ribotypic affinity with D. columnae, but shares a trnL-trnF IGS haplotype with D. orientale, and co-occurs with the latter species only; it has reduced fertility and a high potential for vegetative propagation through rhizome fragmentation. Our results led us to suspect in fieri homoploid hybrid speciation. 相似文献
62.
Jason J. Kolbe Brian R. Lavin Russell L. Burke Lorenzo Rugiero Massimo Capula Luca Luiselli 《Biological invasions》2013,15(4):775-783
Tests of invasion success often require comparisons between introduced and native populations, but determining the native-range sources for introduced populations can be difficult. Molecular markers can help clarify the geographic extent of native-range sources, helping to identify which populations are appropriate for comparative studies. The Italian Wall Lizard (Podarcis siculus) was introduced multiple times to the United States with extant populations in California, Kansas, New Jersey, and New York. We used phylogeographic analysis of mtDNA sequences (cytb gene) for individuals sampled from these introduced populations and across the native range to identify the number of independent introductions and the location of the source populations. Haplotypes sampled from introduced populations were nested within three geographically distinct, well-supported clades that together encompassed a large portion of the native range. Combining these phylogeographic results with documentation of the introductions revealed putative sources: California individuals are derived from Sicily; Kansas and New York populations are from Tuscany near Florence; and the New Jersey population is likely from the Adriatic coastal region, but a more specific locality is not possible. The pet trade dominates the invasion pathway for P. siculus introductions to the US. The genetically and geographically diverse sampling of its native range may be driven by the desire for phenotypic variety in the pet trade, a hypothesis that needs future testing. 相似文献
63.
Elodie Lainey Alice Wolfromm Abdul Qader Sukkurwala Jean-Baptiste Micol Pierre Fenaux Lorenzo Galluzzi Oliver Kepp Guido Kroemer 《Cell cycle (Georgetown, Tex.)》2013,12(18):2978-2991
By means of an unbiased, automated fluorescence microscopy-based screen, we identified the epidermal growth factor receptor (EGFR) inhibitors erlotinib and gefitinib as potent enhancers of the differentiation of HL-60 acute myeloid leukemia (AML) cells exposed to suboptimal concentrations of vitamin A (all-trans retinoic acid, ATRA) or vitamin D (1α,25-hydroxycholecalciferol, VD). Erlotinib and gefitinib alone did not promote differentiation, yet stimulated the acquisition of morphological and biochemical maturation markers (including the expression of CD11b and CD14 as well as increased NADPH oxidase activity) when combined with either ATRA or VD. Moreover, the combination of erlotinib and ATRA or VD synergistically induced all the processes that are normally linked to terminal hematopoietic differentiation, namely, a delayed proliferation arrest in the G0/G1 phase of the cell cycle, cellular senescence, and apoptosis. Erlotinib potently inhibited the (auto)phosphorylation of mitogen-activated protein kinase 14 (MAPK14, best known as p38MAPK) and SRC family kinases (SFKs). If combined with the administration of ATRA or VD, the inhibition of p38MAPK or SFKs with specific pharmacological agents mimicked the pro-differentiation activity of erlotinib. These data were obtained with 2 distinct AML cell lines (HL-60 and MOLM-13 cells) and could be confirmed on primary leukemic blasts isolated from the circulation of AML patients. Altogether, these findings point to a new regimen for the treatment of AML, in which naturally occurring pro-differentiation agents (ATRA or VD) may be combined with EGFR inhibitors. 相似文献
64.
65.
66.
Giulio Bernardi Emiliano Ricciardi Lorenzo Sani Anna Gaglianese Alessandra Papasogli Riccardo Ceccarelli Ferdinando Franzoni Fabio Galetta Gino Santoro Rainer Goebel Pietro Pietrini 《PloS one》2013,8(10)
The present study was designed to investigate the brain functional architecture that subserves visuo-spatial and motor processing in highly skilled individuals. By using functional magnetic resonance imaging (fMRI), we measured brain activity while eleven Formula racing-car drivers and eleven ‘naïve’ volunteers performed a motor reaction and a visuo-spatial task. Tasks were set at a relatively low level of difficulty such to ensure a similar performance in the two groups and thus avoid any potential confounding effects on brain activity due to discrepancies in task execution. The brain functional organization was analyzed in terms of regional brain response, inter-regional interactions and blood oxygen level dependent (BOLD) signal variability. While performance levels were equal in the two groups, as compared to naïve drivers, professional drivers showed a smaller volume recruitment of task-related regions, stronger connections among task-related areas, and an increased information integration as reflected by a higher signal temporal variability. In conclusion, our results demonstrate that, as compared to naïve subjects, the brain functional architecture sustaining visuo-motor processing in professional racing-car drivers, trained to perform at the highest levels under extremely demanding conditions, undergoes both ‘quantitative’ and ‘qualitative’ modifications that are evident even when the brain is engaged in relatively simple, non-demanding tasks. These results provide novel evidence in favor of an increased ‘neural efficiency’ in the brain of highly skilled individuals. 相似文献
67.
68.
James E. Polston Carolyn E. Pritchett Jonathan M. Tomasko Ann M. Rogers Lorenzo Leggio Panayotis K. Thanos Nora D. Volkow Andras Hajnal 《PloS one》2013,8(12)
Roux-en-Y gastric bypass surgery (RYGB) is an effective treatment for severe obesity. Clinical studies however have reported susceptibility to increased alcohol use after RYGB, and preclinical studies have shown increased alcohol intake in obese rats after RYGB. This could reflect a direct enhancement of alcohol’s rewarding effects in the brain or an indirect effect due to increased alcohol absorption after RGYB. To rule out the contribution that changes in alcohol absorption have on its rewarding effects, here we assessed the effects of RYGB on intravenously (IV) administered ethanol (1%). For this purpose, high fat (60% kcal from fat) diet-induced obese male Sprague Dawley rats were tested ∼2 months after RYGB or sham surgery (SHAM) using both fixed and progressive ratio schedules of reinforcement to evaluate if RGYB modified the reinforcing effects of IV ethanol. Compared to SHAM, RYGB rats made significantly more active spout responses to earn IV ethanol during the fixed ratio schedule, and achieved higher breakpoints during the progressive ratio schedule. Although additional studies are needed, our results provide preliminary evidence that RYGB increases the rewarding effects of alcohol independent of its effects on alcohol absorption. 相似文献
69.
Graziano Oldani Stephanie Lacotte Lorenzo Orci Philippe Morel Gilles Mentha Christian Toso 《Journal of visualized experiments : JoVE》2013,(75)
Orthotopic rat liver transplantation is a popular model, which has been shown in a recent JoVE paper with the use of the "quick-linker" device. This technique allows for easier venous cuff-anatomoses after a reasonable learning curve. The device is composed of two handles, which are carved out from scalpel blades, one approximator, which is obtained by modifying Kocher''s forceps, and cuffs designed from fine-bore polyethylene tubing. The whole process can be performed at a low-cost using common laboratory material. The present report provides a step-by-step protocol for the design of the required pieces and includes stencils. 相似文献
70.
Berta Alquezar Maria J. Rodrigo Joanna Lado Lorenzo Zacarías 《Tree Genetics & Genomes》2013,9(5):1257-1269
Accumulation of lycopene in citrus fruits is an unusual feature restricted to selected mutants. Grapefruit (Citrus paradisi Macf.) is the Citrus specie with greater number of red-fleshed mutants, but the molecular bases of this alteration are not fully understood. To gain knowledge into the mechanisms implicated in this alteration, we conducted a comparative analysis of carotenoid profile and of the expression of genes related to carotenoid biosynthesis and catabolism in flavedo and pulp of two grapefruit cultivars with marked differences in colouration: the white Marsh and the red Star Ruby. Mature green fruit of Marsh accumulated chloroplastic carotenoids, while mature tissues lacked carotenoids. However, accumulation of downstream products such as abscisic acid (ABA) and expression of its biosynthetic genes, 9-cis-epoxycarotenoid dioxygenase (NCED1 and NCED2), increased after the onset of colouration. In contrast, red grapefruit accumulated lycopene, phytoene and phytofluene, while ABA content and NCED gene expression were lower than in Marsh, suggesting a blockage in the carotenoid biosynthetic pathway. Expression analysis of three genes of the isoprenoid pathway and nine of the carotenoid biosynthetic pathway revealed virtually no differences in flavedo and pulp between both genotypes, except for the chromoplast-specific lycopene cyclase 2 (β-LCY2) which was lower in the pulp of the red grapefruit. The proportion in the expression of the allele with high (β-LCY2a) and low (β-LCY2b) activity was also similar in the pulp of both genotypes. Therefore, results suggest that reduced expression of β-LCY2 appears to be responsible of lycopene accumulation in the red Star Ruby grapefruit. 相似文献