全文获取类型
收费全文 | 298篇 |
免费 | 25篇 |
国内免费 | 36篇 |
专业分类
系统科学 | 25篇 |
丛书文集 | 3篇 |
理论与方法论 | 2篇 |
现状及发展 | 78篇 |
研究方法 | 29篇 |
综合类 | 216篇 |
自然研究 | 6篇 |
出版年
2022年 | 4篇 |
2021年 | 8篇 |
2020年 | 8篇 |
2019年 | 7篇 |
2018年 | 10篇 |
2017年 | 12篇 |
2016年 | 11篇 |
2015年 | 9篇 |
2014年 | 11篇 |
2013年 | 17篇 |
2012年 | 20篇 |
2011年 | 32篇 |
2010年 | 6篇 |
2009年 | 10篇 |
2008年 | 18篇 |
2007年 | 16篇 |
2006年 | 17篇 |
2005年 | 10篇 |
2004年 | 8篇 |
2003年 | 14篇 |
2002年 | 8篇 |
2001年 | 6篇 |
2000年 | 10篇 |
1999年 | 2篇 |
1996年 | 4篇 |
1993年 | 2篇 |
1990年 | 5篇 |
1989年 | 6篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1986年 | 3篇 |
1985年 | 3篇 |
1984年 | 3篇 |
1983年 | 4篇 |
1982年 | 4篇 |
1980年 | 5篇 |
1979年 | 7篇 |
1978年 | 2篇 |
1976年 | 4篇 |
1975年 | 3篇 |
1974年 | 2篇 |
1971年 | 3篇 |
1969年 | 5篇 |
1968年 | 3篇 |
1967年 | 1篇 |
1966年 | 3篇 |
1965年 | 1篇 |
1964年 | 1篇 |
1962年 | 1篇 |
1960年 | 1篇 |
排序方式: 共有359条查询结果,搜索用时 15 毫秒
1.
外加电磁场对火焰结构及燃料燃烧特性的影响 总被引:1,自引:0,他引:1
燃料在电、磁场作用下的燃烧是一个新的跨学科性质的研究课题.它涉及磁流体发电、空间技术中电磁燃烧技术的应用以及能源与动力工程中能量转换与效率.本文从实验和理论两个方面,扼要地报导了碳氢燃料在外加磁场、电场影响下的火焰结构及其燃烧特性.把近年来我研究小组的主要研究结果汇总发表. 相似文献
2.
C. Baroni Urbani G. S. Boyan A. Blarer J. Billen T. M. Musthak Ali 《Cellular and molecular life sciences : CMLS》1994,50(1):63-71
The Indian antHarpegnathos saltator may be unique among insects in using its jumping capacity not only as an escape mechanism but also as a normal means of locomotion, and for catching its prey in flight. High-speed cinematography used to analyse the various phases of the jump suggests thatHarpegnathos employs a novel jumping mechanism to mediate these behaviours: namely the synchronous activation of its middle and hindlegs. Electrophysiological recordings from muscles or nerves in pairs of middle and hindlegs show remarkably synchronous activity during fictive jumping, supporting the synchronous activation hypothesis.Harpegnathos is not the only ant to jump, and a cladistic analysis suggests that jumping behaviour evolved independently three times during ant evolutionary history. 相似文献
3.
D. V. Amin R. B. Doctor A. O. Girdhar U. H. Shah 《Cellular and molecular life sciences : CMLS》1980,36(12):1410-1411
Summary Prostaglandin (PG) release was measured from the isolated perfused rabbit heart. The effects of -adrenergic stimulation and blockade suggest that PG synthesis is regulated in part by adrenergic mechanisms. 相似文献
4.
纳吉波 《东南大学学报(自然科学版)》1996,26(4):150-154
发展中国家的历史文化名城保护纳吉波②(东南大学建筑系,南京210018)由于各国文化背景和经济建设状况不同,对历史文化遗产的保护在时间和深度上都存在差异.发达国家对历史文化遗产的保护较早,特别是保护那些保留了整个地区文物建筑及历史风貌的城镇,从而形... 相似文献
5.
Improvement of microstructure and corrosion properties of friction stir welded AA5754 by adding Zn interlayer 下载免费PDF全文
This study investigated the effect of Zn foil layers on the microstructure and corrosion characteristics of friction stir welded aluminum alloy 5754. Samples of various joints were prepared by applying different rotational and welding speeds, and their microstructures were evaluated via a metallographic technique and scanning electron microscopy equipped with energy-dispersive X-ray spectroscopy elemental analysis. The anticorrosion behavior of joints in the absence and presence of a Zn interlayer was studied by cyclic potentiodynamic polarization test in 3.5wt% NaCl aqueous solution, and sound welds were obtained in the presence of the Zn interlayer foil. The results revealed that the joint made at a rotational speed of 800 r/min and traveling speed of 15 mm/min achieved a chemical composition identical to that of aluminum alloy 7xxx series, and as such, it showed the best resistance to corrosion. 相似文献
6.
The effect of deep cryogenic treatment on the mechanical properties of 80CrMo12 5 tool steel was investigated. Moreover, the effects of stabilization (holding at room temperature for some periods before deep cryogenic treatment) and tempering before deep cryogenic treatment were studied. The results show that deep cryogenic treatment can eliminate the retained austenite, making a better carbide distribution and a higher carbide amount. As a result, a remarkable improvement in wear resistance of cryogenically treated specimens is observed. Moreover, the ultimate tensile strength increases, and the toughness of the sample decreases. It is also found that both stabilization and tempering before deep cryogenic treatment decrease the wear resistance, hardness, and carbides homogeneity compared to the deep cryogenically treated samples. It is concluded that deep cryogenic treatment should be performed without any delay on samples after quenching to reach the highest wear resistance and hardness. 相似文献
7.
S. Ali Ghafari Oskoei Ghyslaine McClure Department of Civil Engineering Applied Mechanics McGill University Montréal Québec HA K Canada 《清华大学学报》2008,13(Z1):53-57
At present, high-speed computing capabilities and advanced nonlinear dynamic finite element procedures enable detailed dynamic analysis of cable structures. Although deterministic approaches require considerable analysis time and effort in relation to modeling, running, and data processing, they seem to be the only alternative to obtain high accuracy. Detailed dynamic analysis of cable roof networks is sophisticated and requires advanced modeling expertise. This paper presents a comparison between detailed nonlinear dynamic analysis and a simplified frequency domain approach to estimate the maximum probable response of weakly nonlinear cable roofs. The approach can be considered as alternative to detailed time-domain analysis in the preliminary design phase, or can be used to validate results obtained from more elaborated numerical models. The proposed method is illustrated with two examples of cable net roofs that were also analysed in the time domain. 相似文献
8.
RNA polymerase is poised for activation across the genome 总被引:2,自引:0,他引:2
Muse GW Gilchrist DA Nechaev S Shah R Parker JS Grissom SF Zeitlinger J Adelman K 《Nature genetics》2007,39(12):1507-1511
9.
10.
Rasmussen SG DeVree BT Zou Y Kruse AC Chung KY Kobilka TS Thian FS Chae PS Pardon E Calinski D Mathiesen JM Shah ST Lyons JA Caffrey M Gellman SH Steyaert J Skiniotis G Weis WI Sunahara RK Kobilka BK 《Nature》2011,477(7366):549-555
G protein-coupled receptors (GPCRs) are responsible for the majority of cellular responses to hormones and neurotransmitters as well as the senses of sight, olfaction and taste. The paradigm of GPCR signalling is the activation of a heterotrimeric GTP binding protein (G protein) by an agonist-occupied receptor. The β(2) adrenergic receptor (β(2)AR) activation of Gs, the stimulatory G protein for adenylyl cyclase, has long been a model system for GPCR signalling. Here we present the crystal structure of the active state ternary complex composed of agonist-occupied monomeric β(2)AR and nucleotide-free Gs heterotrimer. The principal interactions between the β(2)AR and Gs involve the amino- and carboxy-terminal α-helices of Gs, with conformational changes propagating to the nucleotide-binding pocket. The largest conformational changes in the β(2)AR include a 14 ? outward movement at the cytoplasmic end of transmembrane segment 6 (TM6) and an α-helical extension of the cytoplasmic end of TM5. The most surprising observation is a major displacement of the α-helical domain of Gαs relative to the Ras-like GTPase domain. This crystal structure represents the first high-resolution view of transmembrane signalling by a GPCR. 相似文献