全文获取类型
收费全文 | 259篇 |
免费 | 2篇 |
国内免费 | 5篇 |
专业分类
系统科学 | 11篇 |
教育与普及 | 1篇 |
理论与方法论 | 1篇 |
现状及发展 | 52篇 |
研究方法 | 31篇 |
综合类 | 150篇 |
自然研究 | 20篇 |
出版年
2021年 | 1篇 |
2020年 | 2篇 |
2019年 | 1篇 |
2018年 | 4篇 |
2017年 | 4篇 |
2016年 | 2篇 |
2014年 | 6篇 |
2013年 | 5篇 |
2012年 | 14篇 |
2011年 | 39篇 |
2010年 | 3篇 |
2008年 | 14篇 |
2007年 | 20篇 |
2006年 | 17篇 |
2005年 | 31篇 |
2004年 | 18篇 |
2003年 | 16篇 |
2002年 | 19篇 |
2001年 | 3篇 |
2000年 | 2篇 |
1999年 | 2篇 |
1998年 | 1篇 |
1997年 | 1篇 |
1994年 | 2篇 |
1993年 | 3篇 |
1991年 | 2篇 |
1990年 | 2篇 |
1989年 | 1篇 |
1988年 | 3篇 |
1984年 | 2篇 |
1979年 | 3篇 |
1977年 | 2篇 |
1974年 | 1篇 |
1973年 | 2篇 |
1972年 | 3篇 |
1970年 | 1篇 |
1969年 | 3篇 |
1968年 | 2篇 |
1967年 | 1篇 |
1965年 | 1篇 |
1957年 | 2篇 |
1948年 | 1篇 |
1947年 | 2篇 |
1946年 | 1篇 |
1945年 | 1篇 |
排序方式: 共有266条查询结果,搜索用时 15 毫秒
61.
In neotropical forests, adults of many large scarab beetle species spend most of their time inside the floral chambers of heat-producing flowers, where they feed and mate throughout the night and rest during the following day, before briefly flying to another flower. Here we measure floral temperatures in Philodendron solimoesense (Araceae) in French Guiana and the respiration rates of Cyclocephala colasi beetles at floral and ambient temperatures, and show that the the beetles' extra energy requirements for activity are 2.0-4.8 times greater outside the flower than inside it. This finding indicates that heat produced by the flower constitutes an important energy reward to pollinators, allowing them to feed and mate at a fraction of the energy cost that would be required outside the flower. 相似文献
62.
63.
64.
65.
66.
Roger Spear 《Systemic Practice and Action Research》1993,6(2):139-153
Conventional OR/systems practice, it is argued in this paper, is based upon assumptions which make it unsuitable for guiding interventions in nontraditional organizations. Any methodology or method rests upon a social theory,upon craft knowledge, and upon a theory of how change can and should be brought about. Conventional OR/systems is not explicit about any of these matters. Reflecting on why conventional methods often fail to work with nontraditional organizations, however, enables us to get beneath the iceberg and unearth what is being taken for granted. It is then obvious that the nature of many organizations in the social economy requires a different type of practice. Soft OR/systems is a response to the failings of the traditional approach, but goes only some way toward meeting the criticisms. 相似文献
67.
Hans-J?rg Schek Heiko Schuldt Christoph Schuler Roger Weber 《Cellular and molecular life sciences : CMLS》1991,47(7):643-643
Science Policy News
United Kingdom: The Science and Engineering Research Council (SERC): A Report on Research in the United Kingdom, France and Germany (W) 相似文献68.
Albert Lee Stephanie L. Rayner Serene S. L. Gwee Alana De Luca Hamideh Shahheydari Vinod Sundaramoorthy Audrey Ragagnin Marco Morsch Rowan Radford Jasmin Galper Sarah Freckleton Bingyang Shi Adam K. Walker Emily K. Don Nicholas J. Cole Shu Yang Kelly L. Williams Justin J. Yerbury Ian P. Blair Julie D. Atkin Mark P. Molloy Roger S. Chung 《Cellular and molecular life sciences : CMLS》2018,75(2):335-354
Amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) are fatal neurodegenerative disorders that have common molecular and pathogenic characteristics, such as aberrant accumulation and ubiquitylation of TDP-43; however, the mechanisms that drive this process remain poorly understood. We have recently identified CCNF mutations in familial and sporadic ALS and FTD patients. CCNF encodes cyclin F, a component of an E3 ubiquitin–protein ligase (SCFcyclin F) complex that is responsible for ubiquitylating proteins for degradation by the ubiquitin–proteasome system. In this study, we examined the ALS/FTD-causing p.Ser621Gly (p.S621G) mutation in cyclin F and its effect upon downstream Lys48-specific ubiquitylation in transfected Neuro-2A and SH-SY5Y cells. Expression of mutant cyclin FS621G caused increased Lys48-specific ubiquitylation of proteins in neuronal cells compared to cyclin FWT. Proteomic analysis of immunoprecipitated Lys48-ubiquitylated proteins from mutant cyclin FS621G-expressing cells identified proteins that clustered within the autophagy pathway, including sequestosome-1 (p62/SQSTM1), heat shock proteins, and chaperonin complex components. Examination of autophagy markers p62, LC3, and lysosome-associated membrane protein 2 (Lamp2) in cells expressing mutant cyclin FS621G revealed defects in the autophagy pathway specifically resulting in impairment in autophagosomal–lysosome fusion. This finding highlights a potential mechanism by which cyclin F interacts with p62, the receptor responsible for transporting ubiquitylated substrates for autophagic degradation. These findings demonstrate that ALS/FTD-causing mutant cyclin FS621G disrupts Lys48-specific ubiquitylation, leading to accumulation of substrates and defects in the autophagic machinery. This study also demonstrates that a single missense mutation in cyclin F causes hyper-ubiquitylation of proteins that can indirectly impair the autophagy degradation pathway, which is implicated in ALS pathogenesis. 相似文献
69.
Simona Kavaliauskiene Carl-Martin Nymark Jonas Bergan Roger Simm Tuulia Sylvänne Helena Simolin Kim Ekroos Tore Skotland Kirsten Sandvig 《Cellular and molecular life sciences : CMLS》2014,71(6):1097-1116
Cell density is one of the extrinsic factors to which cells adapt their physiology when grown in culture. However, little is known about the molecular changes which occur during cell growth and how cellular responses are then modulated. In many cases, inhibitors, drugs or growth factors used for in vitro studies change the rate of cell proliferation, resulting in different cell densities in control and treated samples. Therefore, for a comprehensive data analysis, it is essential to understand the implications of cell density on the molecular level. In this study, we have investigated how lipid composition changes during cell growth, and the consequences it has for transport of Shiga toxin. By quantifying 308 individual lipid species from 17 different lipid classes, we have found that the levels and species distribution of several lipids change during cell growth, with the major changes observed for diacylglycerols, phosphatidic acids, cholesterol esters, and lysophosphatidylethanolamines. In addition, there is a reduced binding and retrograde transport of Shiga toxin in high density cells which lead to reduced intoxication by the toxin. In conclusion, our data provide novel information on how lipid composition changes during cell growth in culture, and how these changes can modulate intracellular trafficking. 相似文献
70.
Pujana MA Han JD Starita LM Stevens KN Tewari M Ahn JS Rennert G Moreno V Kirchhoff T Gold B Assmann V Elshamy WM Rual JF Levine D Rozek LS Gelman RS Gunsalus KC Greenberg RA Sobhian B Bertin N Venkatesan K Ayivi-Guedehoussou N Solé X Hernández P Lázaro C Nathanson KL Weber BL Cusick ME Hill DE Offit K Livingston DM Gruber SB Parvin JD Vidal M 《Nature genetics》2007,39(11):1338-1349
Many cancer-associated genes remain to be identified to clarify the underlying molecular mechanisms of cancer susceptibility and progression. Better understanding is also required of how mutations in cancer genes affect their products in the context of complex cellular networks. Here we have used a network modeling strategy to identify genes potentially associated with higher risk of breast cancer. Starting with four known genes encoding tumor suppressors of breast cancer, we combined gene expression profiling with functional genomic and proteomic (or 'omic') data from various species to generate a network containing 118 genes linked by 866 potential functional associations. This network shows higher connectivity than expected by chance, suggesting that its components function in biologically related pathways. One of the components of the network is HMMR, encoding a centrosome subunit, for which we demonstrate previously unknown functional associations with the breast cancer-associated gene BRCA1. Two case-control studies of incident breast cancer indicate that the HMMR locus is associated with higher risk of breast cancer in humans. Our network modeling strategy should be useful for the discovery of additional cancer-associated genes. 相似文献