全文获取类型
收费全文 | 153599篇 |
免费 | 9961篇 |
国内免费 | 21篇 |
专业分类
163581篇 |
出版年
2023年 | 901篇 |
2022年 | 934篇 |
2021年 | 2020篇 |
2020年 | 1803篇 |
2019年 | 1931篇 |
2018年 | 4056篇 |
2017年 | 3652篇 |
2016年 | 4997篇 |
2015年 | 6594篇 |
2014年 | 6800篇 |
2013年 | 9168篇 |
2012年 | 11023篇 |
2011年 | 10148篇 |
2010年 | 6361篇 |
2009年 | 4912篇 |
2008年 | 8105篇 |
2007年 | 7678篇 |
2006年 | 7500篇 |
2005年 | 6431篇 |
2004年 | 6327篇 |
2003年 | 5860篇 |
2002年 | 5369篇 |
2001年 | 3873篇 |
2000年 | 3918篇 |
1999年 | 2808篇 |
1998年 | 1319篇 |
1997年 | 943篇 |
1996年 | 987篇 |
1995年 | 910篇 |
1994年 | 806篇 |
1993年 | 738篇 |
1992年 | 1489篇 |
1991年 | 1345篇 |
1990年 | 1278篇 |
1989年 | 1311篇 |
1988年 | 1112篇 |
1987年 | 1090篇 |
1986年 | 1012篇 |
1985年 | 1078篇 |
1984年 | 986篇 |
1983年 | 788篇 |
1982年 | 695篇 |
1979年 | 875篇 |
1978年 | 676篇 |
1975年 | 741篇 |
1974年 | 821篇 |
1973年 | 787篇 |
1972年 | 693篇 |
1969年 | 704篇 |
1968年 | 670篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
82.
Hermógenes Fernández-Marín David R. Nash Sarah Higginbotham Catalina Estrada Jelle S. van Zweden Patrizia d'Ettorre William T. Wcislo Jacobus J. Boomsma 《Proceedings. Biological sciences / The Royal Society》2015,282(1807)
Fungus-farming ant colonies vary four to five orders of magnitude in size. They employ compounds from actinomycete bacteria and exocrine glands as antimicrobial agents. Atta colonies have millions of ants and are particularly relevant for understanding hygienic strategies as they have abandoned their ancestors'' prime dependence on antibiotic-based biological control in favour of using metapleural gland (MG) chemical secretions. Atta MGs are unique in synthesizing large quantities of phenylacetic acid (PAA), a known but little investigated antimicrobial agent. We show that particularly the smallest workers greatly reduce germination rates of Escovopsis and Metarhizium spores after actively applying PAA to experimental infection targets in garden fragments and transferring the spores to the ants'' infrabuccal cavities. In vitro assays further indicated that Escovopsis strains isolated from evolutionarily derived leaf-cutting ants are less sensitive to PAA than strains from phylogenetically more basal fungus-farming ants, consistent with the dynamics of an evolutionary arms race between virulence and control for Escovopsis, but not Metarhizium. Atta ants form larger colonies with more extreme caste differentiation relative to other attines, in societies characterized by an almost complete absence of reproductive conflicts. We hypothesize that these changes are associated with unique evolutionary innovations in chemical pest management that appear robust against selection pressure for resistance by specialized mycopathogens. 相似文献
83.
84.
Léniz A. Portillo M. P. Fernández-Quintela Alfredo Macarulla M. T. Sarasua-Miranda A. del Hoyo M. Díez-López I. 《Journal of physiology and biochemistry》2019,75(3):311-319
Journal of Physiology and Biochemistry - Infants born small for gestational age (SGA) are at increased risk of perinatal morbidity, persistent short stature, and metabolic alterations in later... 相似文献
85.
Conclusion Since the EPG method is increasingly utilized in the investigation of plant-Homoptera interactions, this software has been developed to enable fast processing of abundant data. The objective seems to have been achieved and, with a little practice, a 2-hour experiment may be analysed in about 10–15 minutes. Mac-Stylet is stand-alone shareware, freely distributed to all persons interested (request to G. Febvay, email: febvay@jouy.inra.fr). 相似文献
86.
D. Padilla F. Acosta J. A. García F. Real Jose R. Vivas 《Archives of microbiology》2009,191(3):191-198
Hafnia alvei, a Gram negative bacillus related to the Enterobacteriaceae family, is considered an opportunistic pathogen of several animal species and humans. In this communication, we describe
fimbrial-like structures from different strains of H. alvei that cannot be easily ascribed to any of the previously reported fimbrial types in this species (type I or type III). Polymerase
chain reaction (PCR) and immunofluorescence assays were carried out to study fimbriae and flagella in H. alvei strains isolated from different sources. No correlation between the results obtained by PCR and those obtained by phenotypic
methods were found, and the antibodies used gave cross or different recognition patterns of the surface structures present
in these strains. We report as well that strain and growth temperature influence fimbriation and expression of flagella in
human and animal isolates of H. alvei. This study also indicates that the absence of fimbriae have a significant positive influence on the initial adhesion of
H. alvei to human epithelial cells. 相似文献
87.
E. Cortés A.A. Kirk J.A. Goolsby P.J. Moran A.E. Racelis M.A. Marcos-García 《Biocontrol Science and Technology》2011,21(11):1369-1373
Arundo donax L. (Poaceae) is native to Mediterranean Europe and invasive in the Rio Grande Basin of North America. Rhizomes from nine sites in France and Spain infested with a candidate control agent, the armoured scale Rhizaspidiotus donacis (Hemiptera: Diaspididae) weighed 50% less than those from nine sites without scale. 相似文献
88.
Late Quaternary climate change,relict populations and present‐day refugia in the northern Atacama Desert: a case study from Quebrada La Higuera (18° S) 下载免费PDF全文
89.
90.
Gwenvael Le Dréau Murielle Saade Irene Gutiérrez-Vallejo Elisa Martí 《The Journal of cell biology》2014,204(4):591-605
The different modes of stem cell division are tightly regulated to balance growth and differentiation during organ development and homeostasis. However, the mechanisms controlling such events are not fully understood. We have developed markers that provide the single cell resolution necessary to identify the three modes of division occurring in a developing nervous system: self-expanding, self-renewing, and self-consuming. Characterizing these three modes of division during interneuron generation in the developing chick spinal cord, we demonstrated that they correlate to different levels of activity of the canonical bone morphogenetic protein effectors SMAD1/5. Functional in vivo experiments showed that the premature neuronal differentiation and changes in cell cycle parameters caused by SMAD1/5 inhibition were preceded by a reduction of self-expanding divisions in favor of self-consuming divisions. Conversely, SMAD1/5 gain of function promoted self-expanding divisions. Together, these results lead us to propose that the strength of SMAD1/5 activity dictates the mode of stem cell division during spinal interneuron generation. 相似文献