全文获取类型
收费全文 | 76099篇 |
免费 | 19031篇 |
国内免费 | 4631篇 |
出版年
2024年 | 62篇 |
2023年 | 622篇 |
2022年 | 1130篇 |
2021年 | 2893篇 |
2020年 | 3746篇 |
2019年 | 5635篇 |
2018年 | 5614篇 |
2017年 | 5397篇 |
2016年 | 6006篇 |
2015年 | 7022篇 |
2014年 | 7239篇 |
2013年 | 7813篇 |
2012年 | 6443篇 |
2011年 | 5821篇 |
2010年 | 5606篇 |
2009年 | 4122篇 |
2008年 | 3513篇 |
2007年 | 2836篇 |
2006年 | 2489篇 |
2005年 | 2183篇 |
2004年 | 1886篇 |
2003年 | 1687篇 |
2002年 | 1554篇 |
2001年 | 1165篇 |
2000年 | 1068篇 |
1999年 | 977篇 |
1998年 | 508篇 |
1997年 | 486篇 |
1996年 | 411篇 |
1995年 | 361篇 |
1994年 | 361篇 |
1993年 | 251篇 |
1992年 | 381篇 |
1991年 | 319篇 |
1990年 | 298篇 |
1989年 | 216篇 |
1988年 | 189篇 |
1987年 | 195篇 |
1986年 | 161篇 |
1985年 | 165篇 |
1984年 | 97篇 |
1983年 | 101篇 |
1982年 | 72篇 |
1981年 | 53篇 |
1980年 | 53篇 |
1979年 | 65篇 |
1978年 | 53篇 |
1977年 | 55篇 |
1975年 | 46篇 |
1974年 | 53篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
41.
42.
43.
44.
Yang Su-Rong Sun Huan-Xin Hu Zhen-Zhen Wang Si-Heng Sun Hui Xue Yin-Jia Ye Chen-Bo 《Sleep and biological rhythms》2017,15(1):57-65
Sleep and Biological Rhythms - Chronic sleep deprivation (SD) is an overwhelming problem in young students. Firstly, we investigated whether different levels of pre-training SD had effects on... 相似文献
45.
To clarify the mechanisms of Nosema ceranae parasitism, we deep-sequenced both honey bee host and parasite mRNAs throughout a complete 6-day infection cycle. By time-series analysis, 1122 parasite genes were significantly differently expressed during the reproduction cycle, clustering into 4 expression patterns. We found reactive mitochondrial oxygen species modulator 1 of the host to be significantly down regulated during the entire infection period. Our data support the hypothesis that apoptosis of honey bee cells was suppressed during infection. We further analyzed genome-wide genetic diversity of this parasite by comparing samples collected from the same site in 2007 and 2013. The number of SNP positions per gene and the proportion of non-synonymous substitutions per gene were significantly reduced over this time period, suggesting purifying selection on the parasite genome and supporting the hypothesis that a subset of N. ceranae strains might be dominating infection. 相似文献
46.
Late Quaternary climate change,relict populations and present‐day refugia in the northern Atacama Desert: a case study from Quebrada La Higuera (18° S) 下载免费PDF全文
47.
In species in which boron (B) mobility is limited, B deficiency only occurs in growing plant organs. As a consequence of the highly localized patterns of plant growth and the general immobility of B it has been extremely difficult to determine the primary function of B in plants. In species in which B is phloem mobile, the removal of B from the growth medium results in the depletion of B present in mature leaves. Thus, it is possible to develop mature leaves with increasingly severe levels of B depletion, thereby overcoming the complications of experiments based on growing tissues. Utilizing this approach we demonstrate here that B depletion of mature plum (Prunus salicina) leaves did not result in any discernible change in leaf appearance, membrane integrity or photosynthetic capacity even though B concentrations were reduced to 6-8 µg/g dwt, which is less than 30% of the reported tissue B requirement. Boron depletion, however, results in a severe disruption of plant growth and metabolism in young growing tissues. This experimental evidence and theoretical considerations suggest that the primary and possibly sole function of B, is as a structural component of growing tissues. 相似文献
48.
49.
N. Rocks C. Estrella G. Paulissen F. Quesada‐Calvo C. Gilles M. M. Guéders C. Crahay J.‐M. Foidart P. Gosset A. Noel D. D. Cataldo 《Cell proliferation》2008,41(6):988-1001
Abstract. Objectives: The ADAMs (a disintegrin and metalloproteinase) enzymes compose a family of membrane‐bound proteins characterized by their multi‐domain structure and ADAM‐12 expression is elevated in human non‐small cell lung cancers. The aim of this study was to investigate the roles played by ADAM‐12 in critical steps of bronchial cell transformation during carcinogenesis. Materials and methods: To assess the role of ADAM‐12 in tumorigenicity, BEAS‐2B cells were transfected with a plasmid encoding human full‐length ADAM‐12 cDNA, and then the effects of ADAM‐12 overexpression on cell behaviour were explored. Treatment of clones with heparin‐binding epidermal growth factor (EGF)‐like growth factor (HB‐EGF) neutralizing antibodies as well as an EGFR inhibitor allowed the dissection of mechanisms regulating cell proliferation and apoptosis. Results: Overexpression of ADAM‐12 in BEAS‐2B cells promoted cell proliferation. ADAM‐12 overexpressing clones produced higher quantities of HB‐EGF in their culture medium which may rely on membrane‐bound HB‐EGF shedding by ADAM‐12. Targeting HB‐EGF activity with a neutralizing antibody abrogated enhanced cell proliferation in the ADAM‐12 overexpressing clones. In sharp contrast, targeting of amphiregulin, EGF or transforming growth factor‐α failed to influence cell proliferation; moreover, ADAM‐12 transfectants were resistant to etoposide‐induced apoptosis and the use of a neutralizing antibody against HB‐EGF activity restored rates of apoptosis to be similar to controls.Conclusions: ADAM‐12 contributes to enhancing HB‐EGF shedding from plasma membranes leading to increased cell proliferation and reduced apoptosis in this bronchial epithelial cell line. 相似文献
50.
Christopher A. Fraker Camillo Ricordi Luca Inverardi Juan Domínguez‐Bendala 《Biology of the cell / under the auspices of the European Cell Biology Organization》2009,101(8):431-440
Beyond its role as an electron acceptor in aerobic respiration, oxygen is also a key effector of many developmental events. The oxygen‐sensing machinery and the very fabric of cell identity and function have been shown to be deeply intertwined. Here we take a first look at how oxygen might lie at the crossroads of at least two of the major molecular pathways that shape pancreatic development. Based on recent evidence and a thorough review of the literature, we present a theoretical model whereby evolving oxygen tensions might choreograph to a large extent the sequence of molecular events resulting in the development of the organ. In particular, we propose that lower oxygenation prior to the expansion of the vasculature may favour HIF (hypoxia inducible factor)‐mediated activation of Notch and repression of Wnt/β‐catenin signalling, limiting endocrine cell differentiation. With the development of vasculature and improved oxygen delivery to the developing organ, HIF‐mediated support for Notch signalling may decline while the β‐catenin‐directed Wnt signalling is favoured, which would support endocrine cell differentiation and perhaps exocrine cell proliferation/differentiation. 相似文献