首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   1200篇
  免费   63篇
林业   24篇
农学   24篇
基础科学   7篇
  86篇
综合类   259篇
农作物   45篇
水产渔业   43篇
畜牧兽医   677篇
园艺   22篇
植物保护   76篇
  2021年   9篇
  2017年   11篇
  2016年   12篇
  2015年   11篇
  2014年   12篇
  2013年   29篇
  2012年   34篇
  2011年   47篇
  2010年   19篇
  2009年   18篇
  2008年   32篇
  2007年   26篇
  2006年   36篇
  2005年   38篇
  2004年   22篇
  2003年   28篇
  2002年   28篇
  2001年   32篇
  2000年   32篇
  1999年   31篇
  1998年   15篇
  1995年   13篇
  1994年   13篇
  1993年   12篇
  1992年   36篇
  1991年   29篇
  1990年   25篇
  1989年   35篇
  1988年   30篇
  1987年   36篇
  1986年   33篇
  1985年   29篇
  1984年   14篇
  1983年   10篇
  1982年   10篇
  1981年   10篇
  1980年   9篇
  1979年   15篇
  1978年   13篇
  1976年   15篇
  1975年   20篇
  1974年   31篇
  1973年   24篇
  1972年   22篇
  1971年   20篇
  1970年   20篇
  1969年   16篇
  1968年   14篇
  1967年   13篇
  1966年   16篇
排序方式: 共有1263条查询结果,搜索用时 15 毫秒
61.
Acid neutralizing capacities (ANC) of sediments from McCloud Lake, Florida and seven other lakes in Wisconsin and Florida were as high as 10 meq 100 g?1 over the pH range 4.5 to 5.5 in well-mixed batch experiments. Exchange of Ca2+ and Mg2+ accounted for over 50% of the neutralizing capacity; Al solubilization and sulfate adsorption were unimportant in neutralizing H+ additions. ANC was correlated with sediment volatile solids content. Sulfate reduction occurred in microcosms that simulated lake-water interactions and subsurface seepage;in situ pore water profiles and a whole-lake mass balance confirm the occurrence of this process in McCloud Lake. Sediment neutralization is important for lakes that receive most of their water from precipitation and thus are particularly susceptible to acidification.  相似文献   
62.
Following an oil spill at Sullom Voe Oil Terminal, Shetland, at least 13 otters died. Post-mortems on five corpses showed that they had died of haemorrhagic gastroenteropathy, associated with ingested oil. The primary cause of oil ingestion seems to have been grooming of the fur. A survey of the polluted coasts revealed that otters were still present throughout most of the area.  相似文献   
63.
Reserve corridors in production forestry landscapes are frequently concentrated in riparian areas. This study describes the numerical response of ground-dwelling beetles to increasing distance from streams, with the aim of evaluating the effectiveness of such a bias in reserve allocation. Patterns in abundance and diversity of epigaeic beetles were quantified at four first order streams in wet eucalypt forest in Tasmania, Australia. The depth and pattern of beetles’ riparian response varied between streams. Commonly trapped beetles were less abundant near to three of the four streams, and the numerical response model differed in each case. Species richness of common beetles was also lower near one of the streams. Pooled abundance and richness of rare species did not vary in response to the riparian-upslope transition. No riparian or upslope specialist species were identified among the most commonly collected species. Compared to upslope habitat, the riparian-upslope transition encompassed greater variability in species composition without actually increasing overall richness. The study findings demonstrate the need for ecosystem-specific data to optimize reserve placement, since the results were not predicted from general vegetation patterns, ecological theory, or the widely held assumption that riparian areas support greater abundance and diversity of organisms than adjacent upslope areas. Reserves encompassing more upslope habitat are recommended to complement those located in riparian areas.  相似文献   
64.
Cataclysmic flooding is a geomorphological process of planetary significance. Landforms of flood origin resulted from late Pleistocene ice-dammed lake failures in the Altay Mountains of south-central Siberia. Peak paleoflows, which exceeded 18 x 10(6) cubic meters per second, are comparable to the largest known terrestrial discharges of freshwater and show a hydrological scaling relation to floods generated by catastrophic dam failures. These seem to have been Earth's greatest floods, based on a variety of reconstructed paleohydraulic parameters.  相似文献   
65.
66.
67.
68.
69.
70.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号