全文获取类型
收费全文 | 1463篇 |
免费 | 139篇 |
国内免费 | 3篇 |
专业分类
林业 | 96篇 |
农学 | 35篇 |
基础科学 | 7篇 |
179篇 | |
综合类 | 312篇 |
农作物 | 51篇 |
水产渔业 | 192篇 |
畜牧兽医 | 591篇 |
园艺 | 59篇 |
植物保护 | 83篇 |
出版年
2024年 | 3篇 |
2023年 | 26篇 |
2022年 | 28篇 |
2021年 | 45篇 |
2020年 | 62篇 |
2019年 | 72篇 |
2018年 | 65篇 |
2017年 | 57篇 |
2016年 | 62篇 |
2015年 | 40篇 |
2014年 | 56篇 |
2013年 | 76篇 |
2012年 | 102篇 |
2011年 | 157篇 |
2010年 | 81篇 |
2009年 | 49篇 |
2008年 | 99篇 |
2007年 | 84篇 |
2006年 | 70篇 |
2005年 | 63篇 |
2004年 | 72篇 |
2003年 | 62篇 |
2002年 | 51篇 |
2001年 | 11篇 |
2000年 | 8篇 |
1999年 | 6篇 |
1998年 | 5篇 |
1997年 | 6篇 |
1996年 | 9篇 |
1995年 | 8篇 |
1994年 | 7篇 |
1993年 | 6篇 |
1992年 | 7篇 |
1991年 | 5篇 |
1990年 | 2篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1984年 | 2篇 |
1959年 | 3篇 |
1956年 | 3篇 |
1955年 | 2篇 |
1921年 | 2篇 |
1917年 | 2篇 |
1916年 | 2篇 |
1914年 | 1篇 |
1913年 | 2篇 |
1909年 | 1篇 |
1906年 | 1篇 |
1903年 | 1篇 |
1902年 | 1篇 |
排序方式: 共有1605条查询结果,搜索用时 31 毫秒
991.
Tocheri MW Orr CM Larson SG Sutikna T Jatmiko Saptomo EW Due RA Djubiantono T Morwood MJ Jungers WL 《Science (New York, N.Y.)》2007,317(5845):1743-1745
Whether the Late Pleistocene hominin fossils from Flores, Indonesia, represent a new species, Homo floresiensis, or pathological modern humans has been debated. Analysis of three wrist bones from the holotype specimen (LB1) shows that it retains wrist morphology that is primitive for the African ape-human clade. In contrast, Neandertals and modern humans share derived wrist morphology that forms during embryogenesis, which diminishes the probability that pathology could result in the normal primitive state. This evidence indicates that LB1 is not a modern human with an undiagnosed pathology or growth defect; rather, it represents a species descended from a hominin ancestor that branched off before the origin of the clade that includes modern humans, Neandertals, and their last common ancestor. 相似文献
992.
Levine JA Lanningham-Foster LM McCrady SK Krizan AC Olson LR Kane PH Jensen MD Clark MM 《Science (New York, N.Y.)》2005,307(5709):584-586
Obesity occurs when energy intake exceeds energy expenditure. Humans expend energy through purposeful exercise and through changes in posture and movement that are associated with the routines of daily life [called nonexercise activity thermogenesis (NEAT)]. To examine NEAT's role in obesity, we recruited 10 lean and 10 mildly obese sedentary volunteers and measured their body postures and movements every half-second for 10 days. Obese individuals were seated, on average, 2 hours longer per day than lean individuals. Posture allocation did not change when the obese individuals lost weight or when lean individuals gained weight, suggesting that it is biologically determined. If obese individuals adopted the NEAT-enhanced behaviors of their lean counterparts, they might expend an additional 350 calories (kcal) per day. 相似文献
993.
Khakoo SI Thio CL Martin MP Brooks CR Gao X Astemborski J Cheng J Goedert JJ Vlahov D Hilgartner M Cox S Little AM Alexander GJ Cramp ME O'Brien SJ Rosenberg WM Thomas DL Carrington M 《Science (New York, N.Y.)》2004,305(5685):872-874
Natural killer (NK) cells provide a central defense against viral infection by using inhibitory and activation receptors for major histocompatibility complex class I molecules as a means of controlling their activity. We show that genes encoding the inhibitory NK cell receptor KIR2DL3 and its human leukocyte antigen C group 1 (HLA-C1) ligand directly influence resolution of hepatitis C virus (HCV) infection. This effect was observed in Caucasians and African Americans with expected low infectious doses of HCV but not in those with high-dose exposure, in whom the innate immune response is likely overwhelmed. The data strongly suggest that inhibitory NK cell interactions are important in determining antiviral immunity and that diminished inhibitory responses confer protection against HCV. 相似文献
994.
Ghedin E Wang S Spiro D Caler E Zhao Q Crabtree J Allen JE Delcher AL Guiliano DB Miranda-Saavedra D Angiuoli SV Creasy T Amedeo P Haas B El-Sayed NM Wortman JR Feldblyum T Tallon L Schatz M Shumway M Koo H Salzberg SL Schobel S Pertea M Pop M White O Barton GJ Carlow CK Crawford MJ Daub J Dimmic MW Estes CF Foster JM Ganatra M Gregory WF Johnson NM Jin J Komuniecki R Korf I Kumar S Laney S Li BW Li W Lindblom TH Lustigman S Ma D Maina CV Martin DM McCarter JP McReynolds L Mitreva M Nutman TB 《Science (New York, N.Y.)》2007,317(5845):1756-1760
Parasitic nematodes that cause elephantiasis and river blindness threaten hundreds of millions of people in the developing world. We have sequenced the approximately 90 megabase (Mb) genome of the human filarial parasite Brugia malayi and predict approximately 11,500 protein coding genes in 71 Mb of robustly assembled sequence. Comparative analysis with the free-living, model nematode Caenorhabditis elegans revealed that, despite these genes having maintained little conservation of local synteny during approximately 350 million years of evolution, they largely remain in linkage on chromosomal units. More than 100 conserved operons were identified. Analysis of the predicted proteome provides evidence for adaptations of B. malayi to niches in its human and vector hosts and insights into the molecular basis of a mutualistic relationship with its Wolbachia endosymbiont. These findings offer a foundation for rational drug design. 相似文献
995.
996.
Simionescu A Allen SW Mantz A Werner N Takei Y Morris RG Fabian AC Sanders JS Nulsen PE George MR Taylor GB 《Science (New York, N.Y.)》2011,331(6024):1576-1579
Studies of the diffuse x-ray-emitting gas in galaxy clusters have provided powerful constraints on cosmological parameters and insights into plasma astrophysics. However, measurements of the faint cluster outskirts have become possible only recently. Using data from the Suzaku x-ray telescope, we determined an accurate, spatially resolved census of the gas, metals, and dark matter out to the edge of the Perseus Cluster. Contrary to previous results, our measurements of the cluster baryon fraction are consistent with the expected universal value at half of the virial radius. The apparent baryon fraction exceeds the cosmic mean at larger radii, suggesting a clumpy distribution of the gas, which is important for understanding the ongoing growth of clusters from the surrounding cosmic web. 相似文献
997.
Sadequr Rahman Anthony Bird Ahmed Regina Zhongyi Li Jean Philippe Ral Steve McMaugh David Topping Matthew Morell 《Journal of Cereal Science》2007,46(3):251
Some of the starch consumed by humans is not digested in the small intestine. Such starch, known as resistant starch, is fermented in the large intestine and leads to the production of short chain fatty acids. Increased consumption of resistant starch is associated with improved cardio-vascular health. A high proportion of amylose in the starch consumed is correlated with increased resistant starch but other unknown aspects of starch structure may also influence the digestibility of starch. Detailed investigation of the starch biosynthetic pathway has revealed that reducing the activity of specific isoforms of branching enzymes and starch synthases can lead to increased amylose. Methods to alter the expression of and detect mutations in targeted genes involved are discussed. 相似文献
998.
Nikolai Kondratev Martin J. Middleditch Matthew Denton-Giles Rosie E. Bradshaw Murray P. Cox Paul P. Dijkwel 《Plant pathology》2022,71(2):437-445
Ciborinia camelliae (Sclerotiniaceae) is a host- and organ-specific fungal pathogen that causes rapid browning and flower drop on ornamental plants of the genus Camellia. To determine the nature of its necrotrophic factors, we tested whether proteins secreted by C. camelliae can damage host-plant tissues. Fungal culture filtrate caused necrogenic activity, abolished by heat or protease treatments, thus indicating that the secreted necrogenic agents are probably proteinaceous in nature. Mass spectrometry-based proteomics was used to detect and identify secreted proteins of C. camelliae. Proteins secreted in culture media (in vitro) and in petal apoplast (in planta) had similar functional distributions, and key identified proteins included homologs to known virulence factors of the closely related Sclerotiniaceae fungus Botrytis cinerea, including endopolygalacturonases, cerato-platanin family proteins, and necrosis- and ethylene-inducing peptides. The main class of secreted proteins were carbohydrate-active enzymes, a characteristic signature of necrotrophic plant pathogens. Both fungal culture filtrate and apoplastic washes of infected petals induced necrosis when infiltrated into host and nonhost plants. This suggests that while some of the secreted proteins might contribute to virulence of C. camelliae, and can cause necrosis similar to secreted proteins of broad-host Sclerotiniaceae pathogens, they do not have a role in determining its host specificity. 相似文献
999.
Carbohydrate recognition is biologically important but intrinsically challenging, for both nature and host-guest chemists. Saccharides are complex, subtly variable, and camouflaged by hydroxyl groups that hinder discrimination between substrate and water. We have developed a rational strategy for the biomimetic recognition of carbohydrates with all-equatorial stereochemistry (beta-glucose, analogs, and homologs) and have now applied it to disaccharides such as cellobiose. Our synthetic receptor showed good affinities, not unlike those of some lectins (carbohydrate-binding proteins). Binding was demonstrated by nuclear magnetic resonance, induced circular dichroism, fluorescence spectroscopy, and calorimetry, all methods giving self-consistent results. Selectivity for the target substrates was exceptional; minor changes to disaccharide structure (for instance, cellobiose to lactose) caused almost complete suppression of complex formation. 相似文献
1000.
Oxley DR Smith KB Alford JR Hibbing MV Miller JL Scalora M Hatemi PK Hibbing JR 《Science (New York, N.Y.)》2008,321(5896):1667-1670
Although political views have been thought to arise largely from individuals' experiences, recent research suggests that they may have a biological basis. We present evidence that variations in political attitudes correlate with physiological traits. In a group of 46 adult participants with strong political beliefs, individuals with measurably lower physical sensitivities to sudden noises and threatening visual images were more likely to support foreign aid, liberal immigration policies, pacifism, and gun control, whereas individuals displaying measurably higher physiological reactions to those same stimuli were more likely to favor defense spending, capital punishment, patriotism, and the Iraq War. Thus, the degree to which individuals are physiologically responsive to threat appears to indicate the degree to which they advocate policies that protect the existing social structure from both external (outgroup) and internal (norm-violator) threats. 相似文献