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排序方式: 共有1451条查询结果,搜索用时 15 毫秒
991.
992.
Evolution of the protein repertoire 总被引:2,自引:0,他引:2
993.
Precision Agriculture - As part of a precision agricultural approach, drones have increasingly been employed within agriculture for more than a decade and are shown to provide many benefits.... 相似文献
994.
McGillicuddy DJ Anderson LA Bates NR Bibby T Buesseler KO Carlson CA Davis CS Ewart C Falkowski PG Goldthwait SA Hansell DA Jenkins WJ Johnson R Kosnyrev VK Ledwell JR Li QP Siegel DA Steinberg DK 《Science (New York, N.Y.)》2007,316(5827):1021-1026
Episodic eddy-driven upwelling may supply a significant fraction of the nutrients required to sustain primary productivity of the subtropical ocean. New observations in the northwest Atlantic reveal that, although plankton blooms occur in both cyclones and mode-water eddies, the biological responses differ. Mode-water eddies can generate extraordinary diatom biomass and primary production at depth, relative to the time series near Bermuda. These blooms are sustained by eddy/wind interactions, which amplify the eddy-induced upwelling. In contrast, eddy/wind interactions dampen eddy-induced upwelling in cyclones. Carbon export inferred from oxygen anomalies in eddy cores is one to three times as much as annual new production for the region. 相似文献
995.
Blewett DT Chabot NL Denevi BW Ernst CM Head JW Izenberg NR Murchie SL Solomon SC Nittler LR McCoy TJ Xiao Z Baker DM Fassett CI Braden SE Oberst J Scholten F Preusker F Hurwitz DM 《Science (New York, N.Y.)》2011,333(6051):1856-1859
High-resolution images of Mercury's surface from orbit reveal that many bright deposits within impact craters exhibit fresh-appearing, irregular, shallow, rimless depressions. The depressions, or hollows, range from tens of meters to a few kilometers across, and many have high-reflectance interiors and halos. The host rocks, which are associated with crater central peaks, peak rings, floors, and walls, are interpreted to have been excavated from depth by the crater-forming process. The most likely formation mechanisms for the hollows involve recent loss of volatiles through some combination of sublimation, space weathering, outgassing, or pyroclastic volcanism. These features support the inference that Mercury's interior contains higher abundances of volatile materials than predicted by most scenarios for the formation of the solar system's innermost planet. 相似文献
996.
Raftopoulou M Etienne-Manneville S Self A Nicholls S Hall A 《Science (New York, N.Y.)》2004,303(5661):1179-1181
PTEN is a tumor suppressor protein that dephosphorylates phosphatidylinositol 3,4,5 trisphosphate and antagonizes the phosphatidylinositol-3 kinase signaling pathway. We show here that PTEN can also inhibit cell migration through its C2 domain, independent of its lipid phosphatase activity. This activity depends on the protein phosphatase activity of PTEN and on dephosphorylation at a single residue, threonine(383). The ability of PTEN to control cell migration through its C2 domain is likely to be an important feature of its tumor suppressor activity. 相似文献
997.
The response of vegetation on the Andean flank in western Amazonia to Pleistocene climate change 总被引:1,自引:0,他引:1
Cárdenas ML Gosling WD Sherlock SC Poole I Pennington RT Mothes P 《Science (New York, N.Y.)》2011,331(6020):1055-1058
A reconstruction of past environmental change from Ecuador reveals the response of lower montane forest on the Andean flank in western Amazonia to glacial-interglacial global climate change. Radiometric dating of volcanic ash indicates that deposition occurred ~324,000 to 193,000 years ago during parts of Marine Isotope Stages 9, 7, and 6. Fossil pollen and wood preserved within organic sediments suggest that the composition of the forest altered radically in response to glacial-interglacial climate change. The presence of Podocarpus macrofossils ~1000 meters below the lower limit of their modern distribution indicates a relative cooling of at least 5°C during glacials and persistence of wet conditions. Interglacial deposits contain thermophilic palms suggesting warm and wet climates. Hence, global temperature change can radically alter vegetation communities and biodiversity in this region. 相似文献
998.
Lu K Heng X Garyu L Monti S Garcia EL Kharytonchyk S Dorjsuren B Kulandaivel G Jones S Hiremath A Divakaruni SS LaCotti C Barton S Tummillo D Hosic A Edme K Albrecht S Telesnitsky A Summers MF 《Science (New York, N.Y.)》2011,334(6053):242-245
The 5'-leader of the HIV-1 genome regulates multiple functions during viral replication via mechanisms that have yet to be established. We developed a nuclear magnetic resonance approach that enabled direct detection of structural elements within the intact leader (712-nucleotide dimer) that are critical for genome packaging. Residues spanning the gag start codon (AUG) form a hairpin in the monomeric leader and base pair with residues of the unique-5' region (U5) in the dimer. U5:AUG formation promotes dimerization by displacing and exposing a dimer-promoting hairpin and enhances binding by the nucleocapsid (NC) protein, which is the cognate domain of the viral Gag polyprotein that directs packaging. Our findings support a packaging mechanism in which translation, dimerization, NC binding, and packaging are regulated by a common RNA structural switch. 相似文献
999.
1000.
Mayrose I Zhan SH Rothfels CJ Magnuson-Ford K Barker MS Rieseberg LH Otto SP 《Science (New York, N.Y.)》2011,333(6047):1257
Polyploidy, the doubling of genomic content, is a widespread feature, especially among plants, yet its macroevolutionary impacts are contentious. Traditionally, polyploidy has been considered an evolutionary dead end, whereas recent genomic studies suggest that polyploidy has been a key driver of macroevolutionary success. We examined the consequences of polyploidy on the time scale of genera across a diverse set of vascular plants, encompassing hundreds of inferred polyploidization events. Likelihood-based analyses indicate that polyploids generally exhibit lower speciation rates and higher extinction rates than diploids, providing the first quantitative corroboration of the dead-end hypothesis. The increased speciation rates of diploids can, in part, be ascribed to their capacity to speciate via polyploidy. Only particularly fit lineages of polyploids may persist to enjoy longer-term evolutionary success. 相似文献