全文获取类型
收费全文 | 2853篇 |
免费 | 205篇 |
国内免费 | 1篇 |
专业分类
3059篇 |
出版年
2023年 | 31篇 |
2022年 | 51篇 |
2021年 | 72篇 |
2020年 | 56篇 |
2019年 | 74篇 |
2018年 | 113篇 |
2017年 | 90篇 |
2016年 | 117篇 |
2015年 | 142篇 |
2014年 | 140篇 |
2013年 | 194篇 |
2012年 | 230篇 |
2011年 | 220篇 |
2010年 | 150篇 |
2009年 | 105篇 |
2008年 | 161篇 |
2007年 | 161篇 |
2006年 | 168篇 |
2005年 | 119篇 |
2004年 | 102篇 |
2003年 | 103篇 |
2002年 | 81篇 |
2001年 | 48篇 |
2000年 | 23篇 |
1999年 | 21篇 |
1998年 | 19篇 |
1997年 | 9篇 |
1996年 | 13篇 |
1995年 | 13篇 |
1994年 | 18篇 |
1993年 | 11篇 |
1992年 | 9篇 |
1991年 | 14篇 |
1990年 | 12篇 |
1989年 | 10篇 |
1988年 | 15篇 |
1987年 | 9篇 |
1986年 | 10篇 |
1985年 | 6篇 |
1984年 | 8篇 |
1983年 | 9篇 |
1982年 | 6篇 |
1981年 | 8篇 |
1979年 | 8篇 |
1975年 | 8篇 |
1974年 | 6篇 |
1972年 | 7篇 |
1970年 | 6篇 |
1969年 | 6篇 |
1968年 | 6篇 |
排序方式: 共有3059条查询结果,搜索用时 15 毫秒
31.
Ale Bu
ek Menglin Wang Jan obotník Simon Hellemans David Sillam-Dusss Nobuaki Mizumoto Petr Stiblík Crystal Clitheroe Tomer Lu Juan Jos Gonzlez Plaza Alma Mohagan Jean-Jacques Rafanomezantsoa Brian Fisher Michael S. Engel Yves Roisin Theodore A. Evans Rudolf Scheffrahn Thomas Bourguignon 《Molecular biology and evolution》2022,39(5)
Termites are major decomposers in terrestrial ecosystems and the second most diverse lineage of social insects. The Kalotermitidae form the second-largest termite family and are distributed across tropical and subtropical ecosystems, where they typically live in small colonies confined to single wood items inhabited by individuals with no foraging abilities. How the Kalotermitidae have acquired their global distribution patterns remains unresolved. Similarly, it is unclear whether foraging is ancestral to Kalotermitidae or was secondarily acquired in a few species. These questions can be addressed in a phylogenetic framework. We inferred time-calibrated phylogenetic trees of Kalotermitidae using mitochondrial genomes of ∼120 species, about 27% of kalotermitid diversity, including representatives of 21 of the 23 kalotermitid genera. Our mitochondrial genome phylogenetic trees were corroborated by phylogenies inferred from nuclear ultraconserved elements derived from a subset of 28 species. We found that extant kalotermitids shared a common ancestor 84 Ma (75–93 Ma 95% highest posterior density), indicating that a few disjunctions among early-diverging kalotermitid lineages may predate Gondwana breakup. However, most of the ∼40 disjunctions among biogeographic realms were dated at <50 Ma, indicating that transoceanic dispersals, and more recently human-mediated dispersals, have been the major drivers of the global distribution of Kalotermitidae. Our phylogeny also revealed that the capacity to forage is often found in early-diverging kalotermitid lineages, implying the ancestors of Kalotermitidae were able to forage among multiple wood pieces. Our phylogenetic estimates provide a platform for critical taxonomic revision and future comparative analyses of Kalotermitidae. 相似文献
32.
33.
Hans J. De Boeck Juliette M. G. Bloor Rien Aerts Michael Bahn Claus Beier Bridget A. Emmett Marc Estiarte Jos M. Grünzweig Aud H. Halbritter Petr Holub Anke Jentsch Karel Klem Juergen Kreyling Gyrgy Krel‐Dulay Klaus Steenberg Larsen Alexandru Milcu Jacques Roy Bjarni D. Sigurdsson Melinda D. Smith Marcelo Sternberg Vigdis Vandvik Thomas Wohlgemuth Ivan Nijs Alan K. Knapp 《Global Change Biology》2020,26(2):e6-e7
34.
Vojtch Vejvoda Ondej Kaplan Karel Bezouka Petr Pompach Miroslav ulc Maria Cantarella Oldich Benada Bronislava Uhnkov Anna Ringelov Sabine Lutz-Wahl Lutz Fischer Vladimír Ken Ludmila Martínkov 《Journal of Molecular Catalysis .B, Enzymatic》2008,50(2-4):99-106
An intracellular nitrilase was purified from a Fusarium solani O1 culture, in which the enzyme (up to 3000 U L−1) was induced by 2-cyanopyridine. SDS-PAGE revealed one major band corresponding to a molecular weight of approximately 40 kDa. Peptide mass fingerprinting suggested a high similarity of the protein with the putative nitrilase from Gibberella moniliformis. Electron microscopy revealed that the enzyme molecules associated into extended rods. The enzyme showed high specific activities towards benzonitrile (156 U mg−1) and 4-cyanopyridine (203 U mg−1). Other aromatic nitriles (3-chlorobenzonitrile, 3-hydroxybenzonitrile) also served as good substrates for the enzyme. The rates of hydrolysis of aliphatic nitriles (methacrylonitrile, propionitrile, butyronitrile, valeronitrile) were 14–26% of that of benzonitrile. The nitrilase was active within pH 5–10 and at up to 50 °C with optima at pH 8.0 and 40–45 °C. Its activity was strongly inhibited by Hg2+ and Ag+ ions. More than half of the enzyme activity was preserved at up to 50% of n-hexane or n-heptane or at up to 15% of xylene or ethanol. Operational stability of the enzyme was examined by the conversion of 45 mM 4-cyanopyridine in a continuous and stirred ultrafiltration-membrane reactor. The nitrilase half-life was 277 and 10.5 h at 35 and 45 °C, respectively. 相似文献
35.
36.
Fungal laccases - occurrence and properties 总被引:8,自引:0,他引:8
Baldrian P 《FEMS microbiology reviews》2006,30(2):215-242
Laccases of fungi attract considerable attention due to their possible involvement in the transformation of a wide variety of phenolic compounds including the polymeric lignin and humic substances. So far, more than a 100 enzymes have been purified from fungal cultures and characterized in terms of their biochemical and catalytic properties. Most ligninolytic fungal species produce constitutively at least one laccase isoenzyme and laccases are also dominant among ligninolytic enzymes in the soil environment. The fact that they only require molecular oxygen for catalysis makes them suitable for biotechnological applications for the transformation or immobilization of xenobiotic compounds. 相似文献
37.
The PIN-FORMED (PIN) protein family of auxin transporters 总被引:4,自引:0,他引:4
38.
Transgelin is a protein reported to be a marker of several cancers. However, previous studies have shown both up‐ and down‐regulation of transgelin in tumors when compared with non‐tumor tissues and the mechanisms whereby transgelin may affect the development of cancer remain largely unknown. Transgelin is especially abundant in smooth muscle cells and is associated with actin stress fibers. These contractile structures participate in cell motility, adhesion, and the maintenance of cell morphology. Here, the role of transgelin in breast cancer is focused on. Initially, the effects of transgelin on cell migration of the breast cancer cell lines, BT 549 and PMC 42, is studied. Interestingly, transgelin silencing increased the migration of PMC 42 cells, but decreased the migration of BT 549 cells. To clarify these contradictory results, the changes in protein abundances after transgelin silencing in these two cell lines are analyzed using quantitative proteomics. The results confirmed the role of transgelin in the migration of BT 549 cells and suggest the involvement of transgelin in apoptosis and small molecule biochemistry in PMC 42 cells. The context‐dependent function of transgelin reflects the different molecular backgrounds of these cell lines, which differ in karyotypes, mutation statuses, and proteome profiles. 相似文献
39.
The biogeography of naturalization in alien plants 总被引:9,自引:0,他引:9
Aim This paper reviews the main geographical determinants of naturalization in plants.
Location Global.
Methods Comparative studies of large data sets of alien floras are the main source of information on global patterns of naturalization.
Results Temperate mainland regions are more invaded than tropical mainland regions but there seems to be no difference in invasibility of temperate and tropical islands. Islands are more invaded than the mainland. The number of naturalized species in temperate regions decreases with latitude and their geographical ranges increase with latitude. The number of naturalized species on islands increases with temperature. Naturalized species contribute to floristic homogenization, but the phenomenon is scale-dependent.
Main conclusions Some robust patterns are evident from currently available data, but further research is needed on several aspects to advance our understanding of the biogeography of naturalization of alien plants. For example, measures of propagule pressure are needed to determine the invasibility of communities/ecosystems/regions. The patterns discussed in this paper are derived largely from numbers and proportions of naturalized species, and little is known about the proportion of introduced species that become naturalized. Further insights on naturalization rates, i.e. the proportion of aliens that successfully naturalize within regions, and on geographical and other determinants of its variation would provide us with better understanding of the invasion process. Comparative studies, and resulting generalizations, are almost exclusively based on numbers of species, but alien species differ in their impact on native biodiversity and ecosystem processes. 相似文献
Location Global.
Methods Comparative studies of large data sets of alien floras are the main source of information on global patterns of naturalization.
Results Temperate mainland regions are more invaded than tropical mainland regions but there seems to be no difference in invasibility of temperate and tropical islands. Islands are more invaded than the mainland. The number of naturalized species in temperate regions decreases with latitude and their geographical ranges increase with latitude. The number of naturalized species on islands increases with temperature. Naturalized species contribute to floristic homogenization, but the phenomenon is scale-dependent.
Main conclusions Some robust patterns are evident from currently available data, but further research is needed on several aspects to advance our understanding of the biogeography of naturalization of alien plants. For example, measures of propagule pressure are needed to determine the invasibility of communities/ecosystems/regions. The patterns discussed in this paper are derived largely from numbers and proportions of naturalized species, and little is known about the proportion of introduced species that become naturalized. Further insights on naturalization rates, i.e. the proportion of aliens that successfully naturalize within regions, and on geographical and other determinants of its variation would provide us with better understanding of the invasion process. Comparative studies, and resulting generalizations, are almost exclusively based on numbers of species, but alien species differ in their impact on native biodiversity and ecosystem processes. 相似文献
40.
Yulia Frank David Banks Marat Avakian Dmitry Antsiferov Petr Kadychagov Olga Karnachuk 《Geomicrobiology journal》2016,33(5):387-400
The dominant microbial components of fluids from wells in pristine and water-injected, high-temperature, Western Siberian oil fields, were analyzed by PCR-DGGE. Particular emphasis was placed on sulphate-reducing organisms, due to their ecological and industrial importance. Bacterial phylotypes obtained from the non-water-injected Stolbovoye oil field were more diverse than those from the Samotlor field, which is subject to secondary oil recovery by reinjection of recycled production water. The majority of phylotypes from both sites were related to Firmicutes. The low similarity to their closest relatives indicates unique bacterial communities in deep underground production waters and crude oil. Archaeal phylotypes detected only in the Samotlor samples were represented by Methanosarcinales and Methanobacteriales. 相似文献