全文获取类型
收费全文 | 6748篇 |
免费 | 439篇 |
国内免费 | 1篇 |
出版年
2023年 | 62篇 |
2022年 | 72篇 |
2021年 | 167篇 |
2020年 | 155篇 |
2019年 | 151篇 |
2018年 | 197篇 |
2017年 | 199篇 |
2016年 | 247篇 |
2015年 | 378篇 |
2014年 | 389篇 |
2013年 | 515篇 |
2012年 | 587篇 |
2011年 | 578篇 |
2010年 | 365篇 |
2009年 | 284篇 |
2008年 | 384篇 |
2007年 | 372篇 |
2006年 | 301篇 |
2005年 | 302篇 |
2004年 | 287篇 |
2003年 | 226篇 |
2002年 | 216篇 |
2001年 | 56篇 |
2000年 | 46篇 |
1999年 | 42篇 |
1998年 | 78篇 |
1997年 | 50篇 |
1996年 | 34篇 |
1995年 | 32篇 |
1994年 | 34篇 |
1993年 | 30篇 |
1992年 | 21篇 |
1991年 | 18篇 |
1990年 | 26篇 |
1989年 | 14篇 |
1988年 | 15篇 |
1987年 | 21篇 |
1986年 | 19篇 |
1985年 | 32篇 |
1984年 | 20篇 |
1983年 | 13篇 |
1982年 | 17篇 |
1981年 | 12篇 |
1980年 | 17篇 |
1979年 | 14篇 |
1977年 | 7篇 |
1976年 | 7篇 |
1973年 | 9篇 |
1972年 | 7篇 |
1968年 | 11篇 |
排序方式: 共有7188条查询结果,搜索用时 218 毫秒
81.
82.
83.
James I. Kirkland Luis Alcalá Mark A. Loewen Eduardo Espílez Luis Mampel Jelle P. Wiersma 《PloS one》2013,8(12)
Nodosaurids are poorly known from the Lower Cretaceous of Europe. Two associated ankylosaur skeletons excavated from the lower Albian carbonaceous member of the Escucha Formation near Ariño in northeastern Teruel, Spain reveal nearly all the diagnostic recognized character that define nodosaurid ankylosaurs. These new specimens comprise a new genus and species of nodosaurid ankylosaur and represent the single most complete taxon of ankylosaur from the Cretaceous of Europe. These two specimens were examined and compared to all other known ankylosaurs. Comparisons of these specimens document that Europelta carbonensis n. gen., n. sp. is a nodosaur and is the sister taxon to the Late Cretaceous nodosaurids Anoplosaurus, Hungarosaurus, and Struthiosaurus, defining a monophyletic clade of European nodosaurids– the Struthiosaurinae. 相似文献
84.
Nicolas Tromas Zofia E. Taranu Mathieu Castelli Juliana S. M. Pimentel Daniel A. Pereira Romane Marcoz B. Jesse Shapiro Alessandra Giani 《Environmental microbiology》2020,22(4):1238-1250
Understanding how ecological traits have changed over evolutionary time is a fundamental question in biology. Specifically, the extent to which more closely related organisms share similar ecological preferences due to phylogenetic conservation – or if they are forced apart by competition – is still debated. Here, we explored the co-occurrence patterns of freshwater cyanobacteria at the sub-genus level to investigate whether more closely related taxa share more similar niches and to what extent these niches were defined by abiotic or biotic variables. We used deep 16S rRNA gene amplicon sequencing and measured several abiotic environmental parameters (nutrients, temperature, etc.) in water samples collected over time and space in Furnas Reservoir, Brazil. We found that relatively more closely related Synechococcus (in the continuous range of 93%–100% nucleotide identity in 16S) had an increased tendency to co-occur with one another (i.e. had similar realized niches). This tendency could not be easily explained by shared preferences for measured abiotic niche dimensions. Thus, commonly measured abiotic parameters might not be sufficient to characterize, nor to predict community assembly or dynamics. Rather, co-occurrence between Synechococcus and the surrounding community (whether or not they represent true biological interactions) may be a more sensitive measure of realized niches. Overall, our results suggest that realized niches are phylogenetically conserved, at least at the sub-genus level and at the resolution of the 16S marker. Determining how these results generalize to other genera and at finer genetic resolution merits further investigation. 相似文献
85.
86.
Eduardo Henrique Bredda Aneirson Francisco Da Silva Messias Borges Silva 《Preparative biochemistry & biotechnology》2020,50(4):379-389
AbstractFor a feasible microalgae biodiesel, increasing lipid productivity is a key parameter. An important cultivation parameter is light wavelength (λ). It can affect microalgal growth, lipid yield, and fatty acid composition. In the current study, the mixture design was used as an alternative to model the influence of the λ on the Dunaliella salina lipid productivity. The illumination was considered to be the mixture of different λ (the light colors blue, red, and green). All experiments were performed with and without sodium acetate (4?g/L), as carbon source, allowing the identification of the impact of the cultivation regimen (autotrophic or mixotrophic). Without sodium acetate, the highest lipid productivity was obtained using blue and red light. The use of mixotrophic cultivations significantly enhanced the results. The optimum obtained result was mixotrophic cultivation under 65% blue and 35% green light, resulting in biomass productivity of 105.06 mgL?1day?1, a lipid productivity of 53.47 mgL?1day?1, and lipid content of 50.89%. The main fatty acids of the oil obtained in this cultivation were oleic acid (36.52%) and palmitic acid (18.31%). 相似文献
87.
Funck Graciele Daiana de Lima Marques Juliana da Silva Dannenberg Guilherme dos Santos Cruxen Claudio Eduardo Sehn Carla Pohl Prigol Marina Silva Márcia Rósula Poetini da Silva Wladimir Padilha Fiorentini Ângela Maria 《Probiotics and antimicrobial proteins》2020,12(1):91-101
Probiotics and Antimicrobial Proteins - This study aimed to characterize, evaluate toxicity and optimize the conditions for the growth and production of bacteriocin-like substances by Lactobacillus... 相似文献
88.
Ailec Ho‐Plagaro Concepcin Santiago‐Fernandez Cristina Rodríguez‐Díaz Carlos Lopez‐Gmez Sara Garcia‐Serrano Francisca Rodríguez‐Pacheco Sergio Valdes Alberto Rodríguez‐Caete Guillermo Alcaín‐Martínez Natalia Ruiz‐Santana Luis Vzquez‐Pedreo Eduardo García‐Fuentes 《Obesity (Silver Spring, Md.)》2020,28(9):1708-1717
89.
Cesar B. Ramírez-López Rita Beltrán-Sánchez Alistair Hernández-Izquierdo José Luis SalvadorHernández Eduardo Salcedo-Pérez Rosa E. del Río Mauro M. Martínez Pacheco 《Phyton》2021,90(3):907-920
This study scrutinized the possibility of finding toxicant or deterrent plant metabolites against the dry wood termite Incisitermes marginipennis (Latreille). Plant deterrent agents act as repellents or antifeedants to prevent
wood decay and increase its useful life. The potential of the tree Caesalpinia coriaria (Fabaceae) as a biological
source of molecules with deterrent effects against the dry wood termite was assessed by a phytochemical fractionation guided by repellence and antifeedant activities. The gas chromatography-mass spectrometry analysis of the
leaf essential oil showed geraniol to be one of the major components and its repellent and antifeedant effects were
determined. Geraniol had only an antifeedant effect without affecting the body weight or survival of the dry wood
termite. Unlike the leaf essential oil, geraniol did not exhibit a repellency effect. An in-silico approach of the activity of acetylcholinesterase in interaction with geraniol resulted in an affinity energy of −7.5 Kcal/mol. Geraniol
interacted with the amino acid tyrosine 324 located in the enzyme’s active site while citronellol (negative control)
interacted with tryptophan 83 located adjacent to the active site. These deterring terpenes have not been implemented for the preservation and restoration of wood products exposed to the attack of the dry wood termite.
However, they are an important natural control alternative. 相似文献
90.
Choosing what scientific project to pursue is the most important decision that scientists at all levels continually face. Time devoted to a project can further desirable knowledge and advance a career or cost years in lost opportunity. Knowing what to consider before embarking on a specific scientific journey, as well as when to drop a project and change course, offers a way of practicing science that keeps us mindful of what is relevant at a given time and place while preserving our freedom to explore the most exciting findings. This article explores both the pressures that restrict this delicate decision-making process and the processes that scientists can apply to overcome those pressures. Above all else, as it turns out, we must still love the pursuit of knowledge for its own sake – and this love directly impacts our results. 相似文献