全文获取类型
收费全文 | 158篇 |
免费 | 5篇 |
专业分类
林业 | 3篇 |
20篇 | |
综合类 | 52篇 |
农作物 | 1篇 |
水产渔业 | 6篇 |
畜牧兽医 | 60篇 |
植物保护 | 21篇 |
出版年
2019年 | 2篇 |
2017年 | 2篇 |
2016年 | 1篇 |
2015年 | 3篇 |
2014年 | 8篇 |
2013年 | 2篇 |
2011年 | 3篇 |
2010年 | 6篇 |
2009年 | 4篇 |
2008年 | 7篇 |
2007年 | 4篇 |
2006年 | 4篇 |
2005年 | 8篇 |
2004年 | 2篇 |
2003年 | 6篇 |
2002年 | 5篇 |
2001年 | 4篇 |
2000年 | 3篇 |
1999年 | 3篇 |
1998年 | 7篇 |
1997年 | 2篇 |
1996年 | 4篇 |
1994年 | 1篇 |
1993年 | 6篇 |
1992年 | 3篇 |
1991年 | 2篇 |
1990年 | 4篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1987年 | 3篇 |
1986年 | 3篇 |
1985年 | 5篇 |
1984年 | 7篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1978年 | 3篇 |
1977年 | 2篇 |
1975年 | 2篇 |
1973年 | 4篇 |
1972年 | 4篇 |
1971年 | 2篇 |
1970年 | 3篇 |
1969年 | 1篇 |
1968年 | 2篇 |
1967年 | 2篇 |
1963年 | 1篇 |
1951年 | 1篇 |
1945年 | 1篇 |
排序方式: 共有163条查询结果,搜索用时 15 毫秒
41.
Subedi R Shneor R Monaghan P Anderson BD Aniol K Annand J Arrington J Benaoum H Benmokhtar F Boeglin W Chen JP Choi S Cisbani E Craver B Frullani S Garibaldi F Gilad S Gilman R Glamazdin O Hansen JO Higinbotham DW Holmstrom T Ibrahim H Igarashi R de Jager CW Jans E Jiang X Kaufman LJ Kelleher A Kolarkar A Kumbartzki G Lerose JJ Lindgren R Liyanage N Margaziotis DJ Markowitz P Marrone S Mazouz M Meekins D Michaels R Moffit B Perdrisat CF Piasetzky E Potokar M Punjabi V Qiang Y Reinhold J Ron G 《Science (New York, N.Y.)》2008,320(5882):1476-1478
The protons and neutrons in a nucleus can form strongly correlated nucleon pairs. Scattering experiments, in which a proton is knocked out of the nucleus with high-momentum transfer and high missing momentum, show that in carbon-12 the neutron-proton pairs are nearly 20 times as prevalent as proton-proton pairs and, by inference, neutron-neutron pairs. This difference between the types of pairs is due to the nature of the strong force and has implications for understanding cold dense nuclear systems such as neutron stars. 相似文献
42.
Partial skeletons of four species of extinct carnivores have been found in their dens excavated in the floodplain of an early Miocene ephemeral braided stream at Agate Fossil Beds National Monument, Nebraska. Bear dogs (Carnivora: Amphicyonidae) were the principal occupants; their den dimensions and body size are similar to those of living wolves and hyenas. Discovery of this predator community extends the record of denning behavior of large mammalian carnivores to the early Miocene, 20 million years ago. 相似文献
43.
Olcott AN Sessions AL Corsetti FA Kaufman AJ de Oliviera TF 《Science (New York, N.Y.)》2005,310(5747):471-474
Laterally extensive black shales were deposited on the S?o Francisco craton in southeastern Brazil during low-latitude Neoproterozoic glaciation approximately 740 to 700 million years ago. These rocks contain up to 3.0 weight % organic carbon, which we interpret as representing the preserved record of abundant marine primary productivity from glacial times. Extractable biomarkers reflect a complex and productive microbial ecosystem, including both phototrophic bacteria and eukaryotes, living in a stratified ocean with thin or absent sea ice, oxic surface waters, and euxinic conditions within the photic zone. Such an environment provides important constraints for parts of the "Snowball Earth" hypothesis. 相似文献
44.
Sodium chlorate (NaClO(3)) crystals are optically active although the molecules of the compound are not chiral. When crystallized from an aqueous solution while the solution is not stirred, statistically equal numbers of levo (L) and dextro (D) NaClO(3) crystals were found. When the solution was stirred, however, almost all of the NaClO(3) crystals (99.7 percent) in a particular sample had the same chirality, either levo or dextro. This result represents an experimental demonstration of chiral symmetry breaking or total spontaneous resolution on a macroscopic level brought about by autocatalysis and competition between L- and D-crystals. 相似文献
45.
46.
Hu FS Kaufman D Yoneji S Nelson D Shemesh A Huang Y Tian J Bond G Clegg B Brown T 《Science (New York, N.Y.)》2003,301(5641):1890-1893
High-resolution analyses of lake sediment from southwestern Alaska reveal cyclic variations in climate and ecosystems during the Holocene. These variations occurred with periodicities similar to those of solar activity and appear to be coherent with time series of the cosmogenic nuclides 14C and 10Be as well as North Atlantic drift ice. Our results imply that small variations in solar irradiance induced pronounced cyclic changes in northern high-latitude environments. They also provide evidence that centennial-scale shifts in the Holocene climate were similar between the subpolar regions of the North Atlantic and North Pacific, possibly because of Sun-ocean-climate linkages. 相似文献
47.
Boyce M Bryant KF Jousse C Long K Harding HP Scheuner D Kaufman RJ Ma D Coen DM Ron D Yuan J 《Science (New York, N.Y.)》2005,307(5711):935-939
Most protein phosphatases have little intrinsic substrate specificity, making selective pharmacological inhibition of specific dephosphorylation reactions a challenging problem. In a screen for small molecules that protect cells from endoplasmic reticulum (ER) stress, we identified salubrinal, a selective inhibitor of cellular complexes that dephosphorylate eukaryotic translation initiation factor 2 subunit alpha (eIF2alpha). Salubrinal also blocks eIF2alpha dephosphorylation mediated by a herpes simplex virus protein and inhibits viral replication. These results suggest that selective chemical inhibitors of eIF2alpha dephosphorylation may be useful in diseases involving ER stress or viral infection. More broadly, salubrinal demonstrates the feasibility of selective pharmacological targeting of cellular dephosphorylation events. 相似文献
48.
In its recent Jupiter flyby Pioneer 10 passed through a belt of intense particulate radiation. The radiation dose on the outer surface of the spacecraft was at least 4.9 x 10(5) rads from electrons plus 2.9 x 10(6) rads from protons, sufficient to cause significant microbial decontamination. The radiation dose inside Pioneer 10, approximately 2.8 x 10(5) rads, was less likely to cause microbial decontamination but would be lethal to man and to most multicellular biological organisms. 相似文献
49.
Kaufman AJ Johnston DT Farquhar J Masterson AL Lyons TW Bates S Anbar AD Arnold GL Garvin J Buick R 《Science (New York, N.Y.)》2007,317(5846):1900-1903
High-resolution geochemical analyses of organic-rich shale and carbonate through the 2500 million-year-old Mount McRae Shale in the Hamersley Basin of northwestern Australia record changes in both the oxidation state of the surface ocean and the atmospheric composition. The Mount McRae record of sulfur isotopes captures the widespread and possibly permanent activation of the oxidative sulfur cycle for perhaps the first time in Earth's history. The correlation of the time-series sulfur isotope signals in northwestern Australia with equivalent strata from South Africa suggests that changes in the exogenic sulfur cycle recorded in marine sediments were global in scope and were linked to atmospheric evolution. The data suggest that oxygenation of the surface ocean preceded pervasive and persistent atmospheric oxygenation by 50 million years or more. 相似文献
50.
A biologically based indicator of soil quality 总被引:3,自引:0,他引:3
Vladimir Yakovchenko Lawrence J. Sikora Donald D. Kaufman 《Biology and Fertility of Soils》1996,21(4):245-251
Soil quality indices are attempts to classify soil conditions and to compare these conditions to their historical use. From this information it may be possible to determine which uses of soils are better for the long-range goals of agriculture and society. With many factors involved in the profitable production of safe foodstuffs without significant degradation of the environment and soils, an indicator that represents a broad biological perspective of quality is appropriate. Among a group of biological indicators, the ratio of crop N uptake to mineralized N as determined by microbial respiration plus net mineralized N found over a growing season is an useful indicator of soil quality. An evaluation of the 12-year-old Farming Systems Trial at the Rodale Institute Research Center indicated that soils in plots that had been conventionally managed were of lower quality than soil treated with manure or planted with legume-cash grain crops. 相似文献