全文获取类型
收费全文 | 64254篇 |
免费 | 18244篇 |
国内免费 | 4454篇 |
出版年
2024年 | 92篇 |
2023年 | 526篇 |
2022年 | 1205篇 |
2021年 | 2533篇 |
2020年 | 3555篇 |
2019年 | 5434篇 |
2018年 | 5367篇 |
2017年 | 5229篇 |
2016年 | 5666篇 |
2015年 | 6355篇 |
2014年 | 6529篇 |
2013年 | 7049篇 |
2012年 | 5407篇 |
2011年 | 4850篇 |
2010年 | 5074篇 |
2009年 | 3668篇 |
2008年 | 2885篇 |
2007年 | 2158篇 |
2006年 | 1909篇 |
2005年 | 1722篇 |
2004年 | 1476篇 |
2003年 | 1367篇 |
2002年 | 1194篇 |
2001年 | 954篇 |
2000年 | 795篇 |
1999年 | 685篇 |
1998年 | 387篇 |
1997年 | 378篇 |
1996年 | 289篇 |
1995年 | 282篇 |
1994年 | 246篇 |
1993年 | 203篇 |
1992年 | 253篇 |
1991年 | 192篇 |
1990年 | 187篇 |
1989年 | 146篇 |
1988年 | 121篇 |
1987年 | 109篇 |
1986年 | 81篇 |
1985年 | 87篇 |
1984年 | 51篇 |
1983年 | 57篇 |
1982年 | 34篇 |
1981年 | 19篇 |
1980年 | 17篇 |
1979年 | 12篇 |
1978年 | 10篇 |
1977年 | 10篇 |
1969年 | 9篇 |
1965年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 15 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.
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
![点击此处可从《Journal of Biogeography》网站下载免费的PDF全文](/ch/ext_images/free.gif)
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.
Suspension culture of Ajuga lobata D. Don cells provides a method of synthesis of the phytoecdysteroid 20-hydroxyecdysone (20E) which can regulate the molting process of larvae. We characterized the culture conditions to optimize 20E production. Growth of A. lobata D. Don cells fits the logistic equation curve with a growth cycle of 19 days. Medium conductivity was negatively correlated with dry cell weight and 20E accumulation, thus could be used to determine the optimal time for cell harvest. Continuous subculture reduced 20E synthesis, but supplementing medium with 20E precursors mevalonic (MVA), α-Pinene, and nitric oxide (NO) can significantly promote cell growth and influence 20E accumulation. Combination of α-Pinene, MVA, and SNP significantly elevated 20E accumulation, thus may synergistically enhance 20E synthesis in A. lobata D. Don. The optimal concentrations of α-Pinene, MVA, and NO donor SNP in suspension culture were 50 μL L?1, 10 mg L?1, and 80 μmol L?1. 相似文献