全文获取类型
收费全文 | 13215篇 |
免费 | 31篇 |
国内免费 | 55篇 |
专业分类
系统科学 | 67篇 |
丛书文集 | 80篇 |
教育与普及 | 36篇 |
理论与方法论 | 69篇 |
现状及发展 | 5330篇 |
研究方法 | 784篇 |
综合类 | 6723篇 |
自然研究 | 212篇 |
出版年
2013年 | 118篇 |
2012年 | 280篇 |
2011年 | 513篇 |
2010年 | 120篇 |
2009年 | 65篇 |
2008年 | 292篇 |
2007年 | 321篇 |
2006年 | 316篇 |
2005年 | 338篇 |
2004年 | 310篇 |
2003年 | 304篇 |
2002年 | 316篇 |
2001年 | 397篇 |
2000年 | 387篇 |
1999年 | 268篇 |
1992年 | 235篇 |
1991年 | 187篇 |
1990年 | 214篇 |
1989年 | 199篇 |
1988年 | 210篇 |
1987年 | 214篇 |
1986年 | 165篇 |
1985年 | 253篇 |
1984年 | 172篇 |
1983年 | 154篇 |
1982年 | 168篇 |
1981年 | 136篇 |
1980年 | 177篇 |
1979年 | 391篇 |
1978年 | 294篇 |
1977年 | 290篇 |
1976年 | 251篇 |
1975年 | 290篇 |
1974年 | 313篇 |
1973年 | 313篇 |
1972年 | 349篇 |
1971年 | 353篇 |
1970年 | 439篇 |
1969年 | 371篇 |
1968年 | 389篇 |
1967年 | 357篇 |
1966年 | 324篇 |
1965年 | 206篇 |
1959年 | 108篇 |
1958年 | 204篇 |
1957年 | 137篇 |
1956年 | 122篇 |
1955年 | 105篇 |
1954年 | 81篇 |
1948年 | 83篇 |
排序方式: 共有10000条查询结果,搜索用时 109 毫秒
1.
从“十四五”保护与发展的生态关系角度,探讨了生态保护与绿色发展的十大生态关系,阐述了生态保护和绿色发展中的一系列有关生态关系的生态智慧及生态技术,并对长江、黄河等流域的生态保护和修复提出了相关建议。 相似文献
2.
ABSTRACTVideofilms of a foraging flying gurnard (Dactylopterus volitans) were collected at Itaipu, Niterói, RJ, Brazil. Analysis revealed details of the use of anterior parts of the pectoral fins which act as digging ‘hands’ to access infaunal prey items that are subsequently captured by oral suction feeding. Each pectoral fin has two distinct sections articulated separately on the pectoral girdle. The digging ‘anterior pectoral fin’ mainly consists of segmented and flexible fin rays but has an anterior robust unsegmented ray that provides an edge to the ‘hand’, allowing penetration of the substratum. The huge ‘posterior pectoral fins’ are supported by unsegmented rays. Most digging episodes involved one ‘hand’ and consisted of 1–7 cycles of movement with frequencies 1.15–3.74 cycles s?1. During a cycle, the ‘hand’ is moved forwards and medially above the substratum, then is twisted medially and simultaneously depressed so that the anterior unsegmented ray impacts and enters the substratum. The hand is then drawn backwards and laterally to disturb the substratum. To prevent upward pitching of the head during digging, the ‘posterior pectoral fins’ are both moved anteriorly and laterally to shift the centre of gravity forwards while the caudal and ?second dorsal fins continue to provide propulsive force. 相似文献
3.
4.
Aristotle Said “Happiness is a State of Activity” — Predicting Mood Through Body Sensing with Smartwatches 总被引:1,自引:1,他引:0
Peter A. Gloor Andrea Fronzetti Colladon Francesca Grippa Pascal Budner Joscha Eirich 《系统科学与系统工程学报(英文版)》2018,27(5):586-612
We measure and predict states of Activation and Happiness using a body sensing application connected to smartwatches. Through the sensors of commercially available smartwatches we collect individual mood states and correlate them with body sensing data such as acceleration, heart rate, light level data, and location, through the GPS sensor built into the smartphone connected to the smartwatch. We polled users on the smartwatch for seven weeks four times per day asking for their mood state. We found that both Happiness and Activation are negatively correlated with heart beats and with the levels of light. People tend to be happier when they are moving more intensely and are feeling less activated during weekends. We also found that people with a lower Conscientiousness and Neuroticism and higher Agreeableness tend to be happy more frequently. In addition, more Activation can be predicted by lower Openness to experience and higher Agreeableness and Conscientiousness. Lastly, we find that tracking people’s geographical coordinates might play an important role in predicting Happiness and Activation. The methodology we propose is a first step towards building an automated mood tracking system, to be used for better teamwork and in combination with social network analysis studies. 相似文献
5.
Danielle Kamato Muhamad Ashraf Rostam Rebekah Bernard Terrence J. Piva Nitin Mantri Daniel Guidone Wenhua Zheng Narin Osman Peter J. Little 《Cellular and molecular life sciences : CMLS》2015,72(4):799-808
G protein-coupled receptor (GPCR) signalling is mediated through transactivation-independent signalling pathways or the transactivation of protein tyrosine kinase receptors and the recently reported activation of the serine/threonine kinase receptors, most notably the transforming growth factor-β receptor family. Since the original observation of GPCR transactivation of protein tyrosine kinase receptors, there has been considerable work on the mechanism of transactivation and several pathways are prominent. These pathways include the “triple membrane bypass” pathway and the generation of reactive oxygen species. The recent recognition of GPCR transactivation of serine/threonine kinase receptors enormously broadens the GPCR signalling paradigm. It may be predicted that the transactivation of serine/threonine kinase receptors would have mechanistic similarities with transactivation of tyrosine kinase pathways; however, initial studies suggest that these two transactivation pathways are mechanistically distinct. Important questions are the relative importance of tyrosine and serine/threonine transactivation pathways, the contribution of transactivation to overall GPCR signalling, mechanisms of transactivation and the range of cell types in which this phenomenon occurs. The ultimate significance of transactivation-dependent signalling remains to be defined but it appears to be prominent and if so will represent a new cell signalling frontier. 相似文献
6.
Ten-day treatment with nicotine (5, 25 or 50 micrograms/ml drinking water) dose-dependently intensified gastric ulceration induced by cold-restraint, and emptying rate. Stomach contractions produced by graded doses of bethanechol i.v. were elevated further by nicotine treatment. It is suggested that chronic nicotine administration produces hypersensitivity of the gastric muscarinic receptors; stomach hypermotility contributes to the ulcer-worsening action of the alkaloid. 相似文献
7.
8.
9.
10.