全文获取类型
收费全文 | 9099篇 |
免费 | 699篇 |
专业分类
9798篇 |
出版年
2023年 | 68篇 |
2022年 | 114篇 |
2021年 | 212篇 |
2020年 | 153篇 |
2019年 | 174篇 |
2018年 | 280篇 |
2017年 | 234篇 |
2016年 | 341篇 |
2015年 | 442篇 |
2014年 | 431篇 |
2013年 | 658篇 |
2012年 | 860篇 |
2011年 | 818篇 |
2010年 | 440篇 |
2009年 | 396篇 |
2008年 | 622篇 |
2007年 | 589篇 |
2006年 | 551篇 |
2005年 | 444篇 |
2004年 | 376篇 |
2003年 | 345篇 |
2002年 | 288篇 |
2001年 | 88篇 |
2000年 | 87篇 |
1999年 | 62篇 |
1998年 | 42篇 |
1997年 | 39篇 |
1996年 | 30篇 |
1995年 | 30篇 |
1994年 | 29篇 |
1993年 | 32篇 |
1992年 | 29篇 |
1991年 | 19篇 |
1990年 | 19篇 |
1989年 | 20篇 |
1988年 | 23篇 |
1987年 | 17篇 |
1986年 | 12篇 |
1985年 | 18篇 |
1984年 | 22篇 |
1983年 | 24篇 |
1982年 | 27篇 |
1981年 | 22篇 |
1980年 | 13篇 |
1979年 | 16篇 |
1978年 | 17篇 |
1977年 | 12篇 |
1976年 | 22篇 |
1973年 | 15篇 |
1972年 | 11篇 |
排序方式: 共有9798条查询结果,搜索用时 15 毫秒
91.
Marta Coll Chiara Piroddi Camille Albouy Frida Ben Rais Lasram William W. L. Cheung Villy Christensen Vasiliki S. Karpouzi François Guilhaumon David Mouillot Michelle Paleczny Maria Lourdes Palomares Jeroen Steenbeek Pablo Trujillo Reg Watson Daniel Pauly 《Global Ecology and Biogeography》2012,21(4):465-480
Aim A large body of knowledge exists on individual anthropogenic threats that have an impact on marine biodiversity in the Mediterranean Sea, although we know little about how these threats accumulate and interact to affect marine species and ecosystems. In this context, we aimed to identify the main areas where the interaction between marine biodiversity and threats is more pronounced and to assess their spatial overlap with current marine protected areas in the Mediterranean. Location Mediterranean Sea. Methods We first identified areas of high biodiversity of marine mammals, marine turtles, seabirds, fishes and commercial or well‐documented invertebrates. We mapped potential areas of high threat where multiple threats are occurring simultaneously. Finally we quantified the areas of conservation concern for biodiversity by looking at the spatial overlap between high biodiversity and high cumulative threats, and we assessed the overlap with protected areas. Results Our results show that areas with high marine biodiversity in the Mediterranean Sea are mainly located along the central and north shores, with lower values in the south‐eastern regions. Areas of potential high cumulative threats are widespread in both the western and eastern basins, with fewer areas located in the south‐eastern region. The interaction between areas of high biodiversity and threats for invertebrates, fishes and large animals in general (including large fishes, marine mammals, marine turtles and seabirds) is concentrated in the coastal areas of Spain, Gulf of Lions, north‐eastern Ligurian Sea, Adriatic Sea, Aegean Sea, south‐eastern Turkey and regions surrounding the Nile Delta and north‐west African coasts. Areas of concern are larger for marine mammal and seabird species. Main conclusions These areas may represent good candidates for further research, management and protection activities, since there is only a maximum 2% overlap between existing marine protected areas (which cover 5% of the Mediterranean Sea) and our predicted areas of conservation concern for biodiversity. 相似文献
92.
Lara Saraiva Alanna Silva Reis Jeronimo Marteleto Nunes Rugani Agnes Ant?nia Sampaio Pereira Felipe Dutra Rêgo Ana Cristina Vianna Mariano da Rocha Lima Célia Maria Ferreira Gontijo José Dilermando Andrade Filho 《PloS one》2015,10(8)
Brazil is one of the most important endemic areas for leishmaniasis worldwide. Protected areas that are tourist attractions likely present an important risk of transmission of cutaneous leishmaniasis (CL). Furthermore, with the geographical expansion of visceral leishmaniasis (VL), several studies have recorded the occurrence of its vector, Lutzomyia longipalpis, and cases of human and canine VL in such tourist areas. The Parque Estadual do Sumidouro is an environmentally protected area located in the Brazilian Cerrado biome and in an important area endemic for leishmaniasis in the state of Minas Gerais. The purpose of this study was to monitor the sand fly fauna in areas of tourist activity in the park. Sampling was performed every month, from September 2011 to August 2013, using CDC light traps at six sites of differing environmental characteristics. Sampled specimens were identified following Galati (2003), and females were submitted to molecular techniques for the detection and identification of Leishmania DNA. A total of 4,675 sand fly specimens of 25 species belonging to nine genera were collected. The most abundant species were Micropygomyia quinquefer, Lutzomyia renei and Pintomyia pessoai, although only Pi. pessoai is implicated in the transmission of Leishmania braziliensis. The species accumulation curve reached saturation on the 16th sampling event. Species richness, diversity and evenness differed among the sampled areas. The seasonal curve was not determined by a single unique species, and no single species was the most abundant in all environments sampled. The main vector of Leishmania (Leishmania) infantum, Lutzomyia longipalpis, accounted for only 5.35% of the specimens collected. Proven or suspected vectors of Leishmania (Viannia) braziliensis were recorded, and one female of the cortellezzii complex tested positive for Le. braziliensis DNA. Even with a low infection rate (0.62%), these data indicate the circulation of the parasite and reinforce the need for entomological and epidemiological surveillance in the park and its surroundings. 相似文献
93.
Enrico Baldan Sebastiano Nigris Chiara Romualdi Stefano D’Alessandro Anna Clocchiatti Michela Zottini Piergiorgio Stevanato Andrea Squartini Barbara Baldan 《PloS one》2015,10(10)
We investigated the potential plant growth-promoting traits of 377 culturable endophytic bacteria, isolated from Vitis vinifera cv. Glera, as good biofertilizer candidates in vineyard management. Endophyte ability in promoting plant growth was assessed in vitro by testing ammonia production, phosphate solubilization, indole-3-acetic acid (IAA) and IAA-like molecule biosynthesis, siderophore and lytic enzyme secretion. Many of the isolates were able to mobilize phosphate (33%), release ammonium (39%), secrete siderophores (38%) and a limited part of them synthetized IAA and IAA-like molecules (5%). Effects of each of the 377 grapevine beneficial bacteria on Arabidopsis thaliana root development were also analyzed to discern plant growth-promoting abilities (PGP) of the different strains, that often exhibit more than one PGP trait. A supervised model-based clustering analysis highlighted six different classes of PGP effects on root architecture. A. thaliana DR5::GUS plantlets, inoculated with IAA-producing endophytes, resulted in altered root growth and enhanced auxin response. Overall, the results indicate that the Glera PGP endospheric culturable microbiome could contribute, by structural root changes, to obtain water and nutrients increasing plant adaptation and survival. From the complete cultivable collection, twelve promising endophytes mainly belonging to the Bacillus but also to Micrococcus and Pantoea genera, were selected for further investigations in the grapevine host plants towards future application in sustainable management of vineyards. 相似文献
94.
95.
96.
97.
Histone H4K20 tri‐methylation at late‐firing origins ensures timely heterochromatin replication 下载免费PDF全文
Charlotte Grimaud Paulina Prorok Christelle Cayrou Gunnar Schotta Alhassan F Abdelsamie Jérôme Déjardin Marcel Méchali Giuseppe Baldacci Claude Sardet Jean‐Charles Cadoret Aloys Schepers Eric Julien 《The EMBO journal》2017,36(18):2726-2741
Among other targets, the protein lysine methyltransferase PR‐Set7 induces histone H4 lysine 20 monomethylation (H4K20me1), which is the substrate for further methylation by the Suv4‐20h methyltransferase. Although these enzymes have been implicated in control of replication origins, the specific contribution of H4K20 methylation to DNA replication remains unclear. Here, we show that H4K20 mutation in mammalian cells, unlike in Drosophila, partially impairs S‐phase progression and protects from DNA re‐replication induced by stabilization of PR‐Set7. Using Epstein–Barr virus‐derived episomes, we further demonstrate that conversion of H4K20me1 to higher H4K20me2/3 states by Suv4‐20h is not sufficient to define an efficient origin per se, but rather serves as an enhancer for MCM2‐7 helicase loading and replication activation at defined origins. Consistent with this, we find that Suv4‐20h‐mediated H4K20 tri‐methylation (H4K20me3) is required to sustain the licensing and activity of a subset of ORCA/LRWD1‐associated origins, which ensure proper replication timing of late‐replicating heterochromatin domains. Altogether, these results reveal Suv4‐20h‐mediated H4K20 tri‐methylation as a critical determinant in the selection of active replication initiation sites in heterochromatin regions of mammalian genomes. 相似文献
98.
Bezerra EH Rocha BA Nagano CS Bezerra Gde A Moura TR Bezerra MJ Benevides RG Sampaio AH Assreuy AM Delatorre P Cavada BS 《Biochemical and biophysical research communications》2011,(4):566-570
Diocleinae lectins are highly homologous in their primary structure which features metal binding sites and a carbohydrate recognition domain (CRD). Differences in the biological activity of legume lectins have been widely investigated using hemagglutination inhibition assays, isothermal titration microcalorimetry and co-crystallization with mono- and oligosaccharides. Here we report a new lectin crystal structure (ConBr) extracted from seeds of Canavalia brasiliensis, predict dimannoside binding by docking, identify the α-aminobutyric acid (Abu) binding pocket and compare the CRD of ConBr to that of homologous lectins. Based on the hypothesis that the carbohydrate affinity of lectins depends on CRD configuration, the relationship between tridimensional structure and endothelial NO synthase activation was used to clarify differences in biological activity. Our study established a correlation between the position of CRD amino acid side chains and the stimulation of NO release from endothelium. 相似文献
99.
Graciela Gil-Romera Mercedes García Antón Juan A. Calleja 《Vegetation History and Archaeobotany》2008,17(6):653-666
New pollen results and radiocarbon dating from a valley mire in south-western Spain are presented. This is a region where
few palaeoecological records have been preserved and the sequence yields important new palaeobotanical evidence for the late
Holocene. The landscape is shown as having been largely open woodland, but more wooded than at present. The vegetation history
of the last four millennia in these montane territories of south-western Iberia is discussed in the light of anthropogenic
indicators, archaeological and documentary archives; fire incidence and climate change. Alnus is the predominant pollen type, although a decline is noted during the last couple of centuries. Its presence is connected
with local topography behaving as a phreatophyte, that is, a plant which obtains a significant amount of water from the zone
of saturated soil. A framework is also provided for the age and ecological dynamics of some major woodland taxa—Betula, Corylus, Ilex, evergreen and deciduous oaks, Ericaceae and Pinus. In addition, the natural status of several pollen taxa and local trends in biodiversity are discussed. We consider that
the results of our work will have important implications for the understanding of the vegetation history in a floristically
very rich area, with a noticeable diversity of woody taxa, and a relatively well preserved ecosystem structure. 相似文献
100.