全文获取类型
收费全文 | 348篇 |
免费 | 1篇 |
国内免费 | 2篇 |
专业分类
系统科学 | 5篇 |
丛书文集 | 1篇 |
教育与普及 | 1篇 |
现状及发展 | 71篇 |
研究方法 | 34篇 |
综合类 | 227篇 |
自然研究 | 12篇 |
出版年
2018年 | 3篇 |
2017年 | 3篇 |
2016年 | 1篇 |
2015年 | 2篇 |
2014年 | 3篇 |
2013年 | 2篇 |
2012年 | 25篇 |
2011年 | 44篇 |
2010年 | 15篇 |
2009年 | 4篇 |
2008年 | 11篇 |
2007年 | 15篇 |
2006年 | 24篇 |
2005年 | 10篇 |
2004年 | 10篇 |
2003年 | 6篇 |
2002年 | 7篇 |
2001年 | 10篇 |
2000年 | 11篇 |
1999年 | 7篇 |
1997年 | 1篇 |
1996年 | 3篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1992年 | 11篇 |
1991年 | 4篇 |
1990年 | 7篇 |
1989年 | 6篇 |
1987年 | 10篇 |
1986年 | 5篇 |
1985年 | 4篇 |
1984年 | 4篇 |
1983年 | 3篇 |
1982年 | 4篇 |
1981年 | 4篇 |
1980年 | 3篇 |
1979年 | 9篇 |
1978年 | 4篇 |
1977年 | 1篇 |
1976年 | 5篇 |
1975年 | 2篇 |
1974年 | 4篇 |
1973年 | 7篇 |
1971年 | 4篇 |
1970年 | 9篇 |
1969年 | 3篇 |
1968年 | 5篇 |
1967年 | 7篇 |
1966年 | 1篇 |
1965年 | 5篇 |
排序方式: 共有351条查询结果,搜索用时 15 毫秒
231.
The per locus of Drosophila has been implicated in the control of behavioural rhythms. In fruitfly embryos and larvae per is expressed in salivary glands. Per mutations have striking effects on intercellular communication in salivary glands: gap junction channels are modulated so that their conductance varies inversely with the period of behavioural rhythms in the mutants. A similar effect on junctional communication in the nervous system may explain how per influences behavioural rhythms. 相似文献
232.
Constitutive synthesis of interleukin-3 by leukaemia cell line WEHI-3B is due to retroviral insertion near the gene 总被引:3,自引:0,他引:3
Interleukin-3 (multi-CSF) is a multilineage haematopoietic growth regulator that initiates the proliferation and differentiation of multipotential stem cells. Complementary DNA clones encoding interleukin-3 (IL-3) have recently been isolated and the structure of the IL-3 gene determined. IL-3 is produced by T lymphocytes or T lymphomas only after stimulation with antigens, mitogens or chemical activators such as phorbol esters. The myelomonocytic leukaemia line WEHI-3B also produces IL-3 but its production is constitutive and the WEHI-3B cells do not appear to produce significant levels of any of the other lymphokines normally secreted by T lymphocytes after stimulation. It has been proposed that the genetic change leading to the constitutive expression of IL-3 may have been a key event in the development of this leukaemia. We report here that the constitutive synthesis of IL-3 by the WEHI-3B cell line is due to the insertion of an endogenous retrovirus-like element close to the 5' end of the gene. The insertion, an intracisternal A particle (IAP) genome, is positioned with its 5' long terminal repeat (LTR) close to the promoter region of the IL-3 gene, resulting in constitutive synthesis of IL-3. 相似文献
233.
234.
A. M. Young 《Cellular and molecular life sciences : CMLS》1985,41(6):760-762
Summary Stingless bees (Trigona jaty) routinely visit the flowers ofTheobroma cacao (Sterculiaceae) in the Atlantic lowlands of Costa Rica. The bees collect pollen and behave as pollen thieves in flowers well exposed to direct sunlight in cacao plantations, and avoid flowers in heavy shade. Pollination rates are maximized, however, in heavy shade due to the high abundance of the small-bodied pollinating midges (Ceratopogonidae and Cecidomyiidae) found in such places. Pollen-thieving by stingless bees, therefore, may only impact on fruit set in cacao trees in direct sunlight, with only minimal to no impact in areas of cacao where natural pollinator activity is high.This research was funded by grants from The American Cocoa Research Institute of the United States of America. I thank T. Noeske for statistical assistance. 相似文献
235.
本文导出一次击中和二次击中相叠加的响应函数,作为描述各种γ辐射剂量计响应的基本方程,引入特征剂量D_0和一次击中因子R,并阐明了辐射剂量响应的线性、超线性和亚线性与这两个参量的关系。模型计算与实验结果相符合。 相似文献
236.
237.
Acetate and other carboxylic acids as precursors of ethylene 总被引:2,自引:0,他引:2
238.
239.
240.
Suttinart Noothongkaew Jin Kyu Han Young Bum Lee Orathai Thumthan Ki-Seok An 《自然科学进展(英文版)》2017,27(6):641-646
This work reports the Au nanoparticles (NPs) deposited on TiO2 nanotubes (NTs) which were successfully
synthesized by a simple two-step anodization method. This fabrication process is notable for a simple and inexpensive
method for obtaining pure TiO2 NTs and Au NPs deposited TiO2 NTs. The prepared samples were
characterized by field emission scanning electron microscope (FESEM), X-ray diffraction (XRD), X-ray photoelectron
spectroscopy (XPS), and I-V curve. We found that the size of Au NPs can be controlled by changing the
bias voltage during the deposition. The photodetectors of Au NPs/TiO2 devices showed good wavelength selectivity
with high photocurrent as compared to pure TiO2 NTs devices. Subsequently, Au NPs deposited on TiO2
NTs at bias voltage of 70 V was potentially used in fabrication of UV photodetector. At this applied voltage, a
high density of Au NPs was uniformly deposited on TiO2 NTs. As a result, it enables a high photocurrent and
great responsivity in UV region. It is suggested that the Au NPs deposited TiO2 NTs device shows good promise
for UV photodetectors with possibility to fine-tune properties in both UV and visible regions and is worthy of
further investigation. 相似文献