全文获取类型
收费全文 | 342篇 |
免费 | 5篇 |
国内免费 | 6篇 |
专业分类
系统科学 | 25篇 |
丛书文集 | 3篇 |
教育与普及 | 1篇 |
理论与方法论 | 2篇 |
现状及发展 | 72篇 |
研究方法 | 27篇 |
综合类 | 196篇 |
自然研究 | 27篇 |
出版年
2020年 | 2篇 |
2019年 | 2篇 |
2018年 | 11篇 |
2017年 | 17篇 |
2016年 | 6篇 |
2015年 | 6篇 |
2014年 | 6篇 |
2013年 | 10篇 |
2012年 | 16篇 |
2011年 | 22篇 |
2010年 | 3篇 |
2009年 | 8篇 |
2008年 | 8篇 |
2007年 | 8篇 |
2006年 | 13篇 |
2005年 | 11篇 |
2004年 | 10篇 |
2003年 | 25篇 |
2002年 | 36篇 |
2001年 | 29篇 |
2000年 | 18篇 |
1999年 | 19篇 |
1996年 | 1篇 |
1993年 | 1篇 |
1992年 | 2篇 |
1991年 | 3篇 |
1990年 | 3篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1986年 | 2篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 3篇 |
1978年 | 4篇 |
1977年 | 1篇 |
1976年 | 3篇 |
1975年 | 1篇 |
1974年 | 5篇 |
1973年 | 2篇 |
1972年 | 1篇 |
1971年 | 1篇 |
1970年 | 4篇 |
1968年 | 4篇 |
1967年 | 1篇 |
1965年 | 10篇 |
1963年 | 2篇 |
1961年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有353条查询结果,搜索用时 18 毫秒
141.
Optimizing the success of random searches. 总被引:3,自引:0,他引:3
G M Viswanathan S V Buldyrev S Havlin M G da Luz E P Raposo H E Stanley 《Nature》1999,401(6756):911-914
We address the general question of what is the best statistical strategy to adapt in order to search efficiently for randomly located objects ('target sites'). It is often assumed in foraging theory that the flight lengths of a forager have a characteristic scale: from this assumption gaussian, Rayleigh and other classical distributions with well-defined variances have arisen. However, such theories cannot explain the long-tailed power-law distributions of flight lengths or flight times that are observed experimentally. Here we study how the search efficiency depends on the probability distribution of flight lengths taken by a forager that can detect target sites only in its limited vicinity. We show that, when the target sites are sparse and can be visited any number of times, an inverse square power-law distribution of flight lengths, corresponding to Lévy flight motion, is an optimal strategy. We test the theory by analysing experimental foraging data on selected insect, mammal and bird species, and find that they are consistent with the predicted inverse square power-law distributions. 相似文献
142.
143.
Höglinger GU Melhem NM Dickson DW Sleiman PM Wang LS Klei L Rademakers R de Silva R Litvan I Riley DE van Swieten JC Heutink P Wszolek ZK Uitti RJ Vandrovcova J Hurtig HI Gross RG Maetzler W Goldwurm S Tolosa E Borroni B Pastor P;PSP Genetics Study Group Cantwell LB Han MR Dillman A van der Brug MP Gibbs JR Cookson MR Hernandez DG Singleton AB Farrer MJ Yu CE Golbe LI Revesz T Hardy J Lees AJ Devlin B Hakonarson H Müller U Schellenberg GD 《Nature genetics》2011,43(7):699-705
Progressive supranuclear palsy (PSP) is a movement disorder with prominent tau neuropathology. Brain diseases with abnormal tau deposits are called tauopathies, the most common of which is Alzheimer's disease. Environmental causes of tauopathies include repetitive head trauma associated with some sports. To identify common genetic variation contributing to risk for tauopathies, we carried out a genome-wide association study of 1,114 individuals with PSP (cases) and 3,247 controls (stage 1) followed by a second stage in which we genotyped 1,051 cases and 3,560 controls for the stage 1 SNPs that yielded P ≤ 10(-3). We found significant previously unidentified signals (P < 5 × 10(-8)) associated with PSP risk at STX6, EIF2AK3 and MOBP. We confirmed two independent variants in MAPT affecting risk for PSP, one of which influences MAPT brain expression. The genes implicated encode proteins for vesicle-membrane fusion at the Golgi-endosomal interface, for the endoplasmic reticulum unfolded protein response and for a myelin structural component. 相似文献
144.
Fernando da Silva Carvalho-Filho Tiago Henrique Auko Cecília Waichert 《Journal of Natural History》2015,49(33-34):2035-2044
We describe, for the first time, the nesting behaviour of an Eragenia spider wasp, Eragenia congrua, based on field observations in the Brazilian Amazon. This species was observed nesting in holes at the base of the trunk of a Jacaranda copaia tree and provisioning nests with both amputated and non-amputated species of undetermined Corinna sp. (Corinnidae) spiders. The spiders are carried forward and grasped at the base of the chelicerae. Nesting is gregarious with females nesting in the same small area on successive days. 相似文献
145.
146.
Tatiane Archanjo de Sales Erik Daemon Juliane Floriano Santos Lopes 《Journal of Natural History》2016,50(15-16):971-974
This study aimed to identify the feeding habit of Pheidole radoszkowskii Mayr on Rattus norvegicus (Berkenhout) carcasses, as well as whether its presence limits the occurrence of flies. Pheidole radoszkowskii exhibited more necrophagous than predatory behaviour. Its abundance was inversely proportional to that of flies, confirming that this ant species may cause lesions in carcasses and its presence limits the occurrence of flies. This work clarifies the behaviour of an ant species often encountered on carcasses. 相似文献
147.
Cátia Emiliana Paes Marcella Bernardo Renato da Silva Lima Fabiano Leal 《Systemic Practice and Action Research》2017,30(4):377-393
One of the problems facing public education institutions in Brazil is the question of the correct handling and treatment of waste electrical and electronic equipment (WEEE). Being that these institutions are part of the public sector, they should adhere to Decree no. 99,658/1990 for the disposal of their goods. However, this decree is not completely in accordance with the Brazilian National Solid Waste Policy (PNRS), especially when considering the regulations for disposal of public goods. Thus, these institutions have no WEEE management model which encompasses not only the Decree but also the PNRS. An example of this situation can be found at the Federal University of Itajubá (UNIFEI) in Minas Gerais, Brazil. Due to the lack of such a management model, the university warehouse is at full capacity and unable to receive additional electronic equipment. Therefore, the objective of this study is to create a management model for WEEE to be used at public education institutions using the guidelines set forth in both the Decree and the PNRS. An action research investigation was performed at UNIFEI which relied upon two improvement and learning cycles to deal with all the WEEE found at the university. The first was undertaken at the university warehouse and the second at other sectors within the institution. In addition to the practical results obtained by properly disposing of 474 WEEE products, this study showed that action research is an adequate management tool for public institutions looking to deal with problems of this nature, being that these institutions are almost always subject to bureaucratic controls with respect to their public property, and expected to follow rigorous legislation that is often times controversial. 相似文献
148.
A. Gomes da Costa 《Cellular and molecular life sciences : CMLS》1978,34(1):82-83
Summary Filamentous bodies have been identified in the glomerular cells of human kidney biopsies. These structures have a close morphological resemblance to ciliary rootlets, although the cells of the glomerular tuft only occasionally bear cilia. Their significance could be, as for cilia, of a cellular disdifferentiation of a pathological cellular proliferation. 相似文献
149.
The fixative action of uranyl acetate in electron microscopy 总被引:3,自引:0,他引:3
M. T. Silva F. Carvalho Guerra M. M. Magalhães 《Cellular and molecular life sciences : CMLS》1968,24(10):1074-1074
Resumen La utilización del acetato de uranilo después del osmio durante la fijación, reduce la cantidad de fosfolípidos extraídos durante la deshidratación de los tejidos, lo que demuestra sus propiedades de fijador químico. 相似文献
150.
A. da Costa e Silva Z. P. Albuquerque 《Cellular and molecular life sciences : CMLS》1978,34(11):1465-1466
Summary A significant diminution in liver arginase activity of chronic renal failure uremic rats is described, thus implying that the experimental finding of an increased urea production is not due to a depressed arginase activity.This work was supported by the Conselho Nacional de Desenvolvimento Cientifico e Tecnologico do Brasil's Grants. —Acknowledgments. We are indebted to Mr D'Arrochela Lobo for technical assistance, Mr Celso Chiarin for the statistical review and Dr C.E. Tosta and Dr Linda Caldas for helpful advice. 相似文献