全文获取类型
收费全文 | 718篇 |
免费 | 26篇 |
国内免费 | 2篇 |
专业分类
林业 | 56篇 |
农学 | 21篇 |
基础科学 | 3篇 |
136篇 | |
综合类 | 98篇 |
农作物 | 79篇 |
水产渔业 | 37篇 |
畜牧兽医 | 260篇 |
园艺 | 14篇 |
植物保护 | 42篇 |
出版年
2022年 | 7篇 |
2021年 | 14篇 |
2020年 | 21篇 |
2019年 | 9篇 |
2018年 | 14篇 |
2017年 | 8篇 |
2016年 | 8篇 |
2015年 | 15篇 |
2014年 | 24篇 |
2013年 | 32篇 |
2012年 | 29篇 |
2011年 | 46篇 |
2010年 | 20篇 |
2009年 | 20篇 |
2008年 | 40篇 |
2007年 | 40篇 |
2006年 | 20篇 |
2005年 | 41篇 |
2004年 | 29篇 |
2003年 | 37篇 |
2002年 | 28篇 |
2001年 | 7篇 |
2000年 | 8篇 |
1999年 | 14篇 |
1998年 | 5篇 |
1997年 | 8篇 |
1995年 | 6篇 |
1994年 | 6篇 |
1993年 | 6篇 |
1992年 | 6篇 |
1991年 | 12篇 |
1990年 | 10篇 |
1989年 | 9篇 |
1988年 | 6篇 |
1987年 | 6篇 |
1986年 | 13篇 |
1985年 | 6篇 |
1984年 | 9篇 |
1980年 | 4篇 |
1979年 | 8篇 |
1978年 | 5篇 |
1975年 | 4篇 |
1974年 | 4篇 |
1969年 | 4篇 |
1966年 | 4篇 |
1962年 | 3篇 |
1961年 | 4篇 |
1960年 | 3篇 |
1955年 | 4篇 |
1913年 | 3篇 |
排序方式: 共有746条查询结果,搜索用时 250 毫秒
61.
El-Sayed NM Myler PJ Blandin G Berriman M Crabtree J Aggarwal G Caler E Renauld H Worthey EA Hertz-Fowler C Ghedin E Peacock C Bartholomeu DC Haas BJ Tran AN Wortman JR Alsmark UC Angiuoli S Anupama A Badger J Bringaud F Cadag E Carlton JM Cerqueira GC Creasy T Delcher AL Djikeng A Embley TM Hauser C Ivens AC Kummerfeld SK Pereira-Leal JB Nilsson D Peterson J Salzberg SL Shallom J Silva JC Sundaram J Westenberger S White O Melville SE Donelson JE Andersson B Stuart KD Hall N 《Science (New York, N.Y.)》2005,309(5733):404-409
A comparison of gene content and genome architecture of Trypanosoma brucei, Trypanosoma cruzi, and Leishmania major, three related pathogens with different life cycles and disease pathology, revealed a conserved core proteome of about 6200 genes in large syntenic polycistronic gene clusters. Many species-specific genes, especially large surface antigen families, occur at nonsyntenic chromosome-internal and subtelomeric regions. Retroelements, structural RNAs, and gene family expansion are often associated with syntenic discontinuities that-along with gene divergence, acquisition and loss, and rearrangement within the syntenic regions-have shaped the genomes of each parasite. Contrary to recent reports, our analyses reveal no evidence that these species are descended from an ancestor that contained a photosynthetic endosymbiont. 相似文献
62.
Energy redistribution, including the many phonon-assisted and electronically assisted energy-exchange processes at a gas-metal interface, can hamper vibrationally mediated selectivity in chemical reactions. We establish that these limitations do not prevent bond-selective control of a heterogeneously catalyzed reaction. State-resolved gas-surface scattering measurements show that the nu1 C-H stretch vibration in trideuteromethane (CHD3) selectively activates C-H bond cleavage on a Ni(111) surface. Isotope-resolved detection reveals a CD3:CHD2 product ratio > 30:1, which contrasts with the 1:3 ratio for an isoenergetic ensemble of CHD3 whose vibrations are statistically populated. Recent studies of vibrational energy redistribution in the gas and condensed phases suggest that other gas-surface reactions with similar vibrational energy flow dynamics might also be candidates for such bond-selective control. 相似文献
63.
64.
Winfree AT 《Science (New York, N.Y.)》2002,298(5602):2336-2337
65.
Kump LR Junium C Arthur MA Brasier A Fallick A Melezhik V Lepland A Crne AE Luo G 《Science (New York, N.Y.)》2011,334(6063):1694-1696
The stable isotope record of marine carbon indicates that the Proterozoic Eon began and ended with extreme fluctuations in the carbon cycle. In both the Paleoproterozoic [2500 to 1600 million years ago (Ma)] and Neoproterozoic (1000 to 542 Ma), extended intervals of anomalously high carbon isotope ratios (δ(13)C) indicate high rates of organic matter burial and release of oxygen to the atmosphere; in the Neoproterozoic, the high δ(13)C interval was punctuated by abrupt swings to low δ(13)C, indicating massive oxidation of organic matter. We report a Paleoproterozoic negative δ(13)C excursion that is similar in magnitude and apparent duration to the Neoproterozoic anomaly. This Shunga-Francevillian anomaly may reflect intense oxidative weathering of rocks as the result of the initial establishment of an oxygen-rich atmosphere. 相似文献
66.
Carla C. Eisemberg Mark Rose Benedict Yaru Arthur Georges 《Biological conservation》2011,144(9):2282-2288
Papua New Guinea has astonishing biological and cultural diversity which, coupled with a strong community reliance on the land and its biota for subsistence, add complexity to monitoring and conservation and in particular, the demonstration of declines in wildlife populations. Many species of concern are long-lived which provides additional challenges for conservation. We provide, for the first time, concrete evidence of a substantive decline in populations of the pig-nosed turtle (Carettochelys insculpta); an important source of protein for local communities. Our study combined matched village and market surveys separated by 30 years, trends in nesting female size, and assessment of levels and efficacy of harvest, each of which was an essential ingredient to making a definitive assessment of population trends. Opportunities for an effective response by local communities to these declines needs to consider both conservation and fisheries perspectives because local communities consider the turtle a food resource, whereas the broader global community views it as a high priority for conservation. Our study in the Kikori region is representative of harvest regimes in most rivers within the range of the species in Papua New Guinea, and provides lessons for conservation of many other wildlife species subject to harvest. 相似文献
67.
Christos G. Athanassiou Frank H. Arthur Nickolas G. Kavallieratos James E. Throne 《Journal of pest science》2011,84(1):61-67
Efficacy of the insecticides spinosad and methoprene, applied alone or in combination to wheat, was evaluated against six
stored-product insect species, Rhyzopertha dominica, Sitophilus oryzae, S. granarius, Cryptolestes ferrugineus, Oryzaephilus surinamensis, and Liposcelis bostrychophila. The concentrations of the insecticides were 0.1 and 0.5 ppm for spinosad and 1 and 5 ppm for methoprene. Parental mortality
of R. dominica was 100% on wheat treated with either rate of spinosad, with no progeny production in any combination treatment. Parental
mortality of S. oryzae did not exceed 62%, and progeny production was not reduced by any insecticide treatment. All S. granarius adults exposed on wheat treated with spinosad alone at 0.5 ppm were killed, but parental mortality was reduced when methoprene
was added. Progeny production was reduced in treatments containing spinosad. Mortality of adult C. ferrugineus was 97% or greater in treatments containing spinosad, but adult mortality of O. surinamensis and L. bostrychophila was not reduced by insecticide treatments. The specific combinations of spinosad and methoprene evaluated in our study would
have no benefit over spinosad used alone for control of any of the six species tested. 相似文献
68.
Phongpa-Ngan P Grider A Mulligan JH Aggrey SE Wicker L 《Journal of agricultural and food chemistry》2011,59(24):13181-13187
Chickens from a randomly bred genetic line were segregated into high and low growth rates and high and low water-holding capacities (WHCs). The objective of this study was to identify protein markers associated with slow and fast growth rates and low and high WHCs from water-soluble protein (WSP) and crude myofibrillar protein (CMP) extracts of chicken breast muscle. Proteins were fractionated using two-dimensional electrophoresis, and a total of 22 protein spots were selected, excised, and analyzed by in-gel tryptic digestion and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Proteins expressed in extracts from slow and fast growth rates and low and high WHCs included metabolic enzymes, such as creatine kinase, pyruvate kinase, triosephosphate isomerase, and ubiqitin; housekeeping proteins, such as heat shock protein; contractile proteins, such as myosin heavy chain; actin; and also MHC isoforms and actin isoforms. The mass spectra of 20 protein spots significantly matched (protein score >83; P < 0.05) an online database. In CMP, there were unique proteins that were present only in the fast-growth population: gi|118099530 , gi|20664362 , gi|71895043 , gi|114794125 , gi|297343122 , and gi|71895043 . This information identified protein markers associated with growth rate and water holding capacity. Some of those protein markers could be added to the chicken database. 相似文献
69.
Arthur J. Horowitz Ken R. Lum John R. Garbarino Gwendy E. M. Hall Claire Lemieux Charles R. Demas 《Water, air, and soil pollution》1996,90(1-2):281-294
The almost universally accepted operational definition for dissolved constituents is based on processing The almost universally accepted operational definition for dissolved constituents is based on processing whole-water samples through a 0.45-μm membrane filter. Results from field and laboratory experiments indicate that a number of factors associated with filtration, other than just pore size (e.g., diameter, manufacturer, volume of sample processed, amount of suspended sediment in the sample), can produce substantial variations in the ‘disolved’ concentrations of such elements as Fe, Al, Cu, Zn, Pb, Co, and Ni. These variations result from the inclusion/exclusion of colloidally-associated trace elements. Thus, 'dissolved' concentrations quantitated by analyzing filtrates generated by processing whole-water through similar pore-sized membrane filters may not be equal/comparable. As such, simple filtration through a 0.45-μm membrane filter may no longer represent an acceptable operational definition for dissolved chemical constituents. This conclusion may have important implications for environmental studies and regulatory agencies. 相似文献
70.
Waste site cover systems used to prevent rainfall from reaching the waste need to remain intact throughout the lifetime of the waste site. Monitoring of these covers is needed to ascertain the performance and to determine if any degradation has occurred. Researchers at Brookhaven National Laboratory have used gaseous perfluorocarbon tracers (PFTs) to monitor the integrity of caps and covers for waste disposal sites. Detection of the PFTs currently uses gas chromatography techniques developed at BNL. This paper presents a potential approach to this wide-area screening problem by replacing conventional gas chromatography analysis with laser-based, lidar (Light Detection and Ranging) detection of the PFTs. Lidar can be used to scan the surface of the cover system, looking for fugitive PFTs. If successful this would enable the departure from soil gas analysis and instead look for PFTs in the air just above the soil surface. The advantages of using a lidar platform are multi-fold and include the elimination of soil monitoring ports. Benchtop and pilot-scale indoor experiments using an a continuous wave, line-tunable infrared CO2 laser were used to detect PMCH (perfluoromethylcyclohexane, one of a group of PFTs used at BNL). Laboratory measurements of the absorption cross-section were the same order of magnitude compared to literature values for similar perfluorocarbon compounds. Initial benchtop, fixed cell length experiments were successful in detecting PMCH to levels of 10 ppb-m. To improve the lower limit of detection, a HgCdTe detector was purchased that was more specific to the lasing region of interest and hence had a higher sensitivity at this spectral region Using a pilot-scale lidar system in a 40m indoor hallway air concentrations of PMCH were then measured down to 1 ppb-m. These results are very promising and show great potential for monitoring the integrity of cover systems using lidar and PFTs. 相似文献