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   289篇
  免费   28篇
林业   3篇
农学   3篇
  26篇
综合类   69篇
农作物   4篇
水产渔业   8篇
畜牧兽医   193篇
园艺   2篇
植物保护   9篇
  2021年   3篇
  2020年   4篇
  2019年   3篇
  2018年   4篇
  2017年   6篇
  2016年   4篇
  2015年   3篇
  2014年   9篇
  2013年   20篇
  2012年   3篇
  2011年   7篇
  2010年   3篇
  2008年   4篇
  2007年   4篇
  2006年   5篇
  2005年   7篇
  2004年   5篇
  2003年   4篇
  2002年   4篇
  2001年   4篇
  2000年   7篇
  1999年   7篇
  1998年   16篇
  1997年   4篇
  1996年   8篇
  1995年   12篇
  1994年   5篇
  1993年   7篇
  1992年   5篇
  1991年   4篇
  1990年   6篇
  1989年   16篇
  1988年   8篇
  1986年   5篇
  1985年   5篇
  1984年   4篇
  1976年   4篇
  1974年   9篇
  1973年   8篇
  1972年   6篇
  1971年   4篇
  1970年   8篇
  1966年   5篇
  1965年   3篇
  1945年   2篇
  1940年   2篇
  1915年   2篇
  1910年   2篇
  1909年   4篇
  1905年   2篇
排序方式: 共有317条查询结果,搜索用时 31 毫秒
71.
72.
Abstract. Inputs of acidity to the ground arise through two distinct routes: wet deposition which includes all acidity deposited in rain and snow and dry deposition, the direct sorption of SO2, NO2 or HNO3 gases by vegetation or soil surfaces. The acidity from dry deposition of SO2 and NO2 is created during the oxidation of deposited SO2 and NO2 to SO24 and NO3 respectively. The areas of Britain experiencing the largest wet deposition of acidity are the high rainfall areas of the west and north, in particular the west central highlands of Scotland, Galloway and Cumbria where inputs exceed 1 kp H+ ha−1 annually. Wet deposited acidity in the east coast regions of Britain is in the range 0.3–0.6 kg H+ ha−1 a−1. Monitoring data for rainfall acidity at rural sites throughout northern Britain show a decline in deposited acidity of about 50% during the last six years. Dry deposition is largest in the industrial midlands and southeast England and in the central lowlands of Scotland, where concentrations of SO2 are largest. In these regions the dry deposition of SO2 following oxidation may lead to acid inputs approaching 3 kg H+ ha−1 a−1 and greatly exceeding wet deposition.  相似文献   
73.
74.
The association of various prognostic factors with remission and survival after the excision of lung tumors was evaluated in 76 dogs. Overall, the median survival time of treated dogs was 120 days; 72% had tumor that underwent remission (median duration of remission, 120 days). Dogs with tumors that underwent remission had significantly (P = 0.001) increased survival time (median, 330 days vs 28 days for dogs with tumors that did not undergo remission). The finding of normal-sized lymph nodes at the time of therapeutic thoracotomy was significantly (P = 0.001) correlated with increased remission probability (85.4% remission rate vs 43.6% in dogs with large lymph nodes). Use of various diagnostic methods to find normal regional lymph nodes before surgery indicated that such finding was significantly (P less than or equal to 0.01) correlated with increased remission duration (median remission duration, 365 days, vs 60 days for tumors in dogs with large lymph nodes), and the finding of normal lymph nodes at the time of surgery was significantly (P less than or equal to 0.01) correlated with increased survival time (median, 345 days, vs 60 days for dogs with large lymph nodes).  相似文献   
75.
76.
77.
78.
79.
Abstract— The paper reviews the humanitarian, clinical and public relations roles of the practising veterinary surgeon when dealing with an accident case.
Résumé— L'article examine les rôles humanitaire, clinique et de propagande du praticien vétérin-aire lorsque celui-ci a affaire à un accident.
Zusammenfassung— Dieser Vortrag handelt von der menschenfreundlichen und klinischen Rolle des praktischen Tierarztes und von seiner Beziehung zur Öffentlichkeit, wenn er ein bei einem Unfall verletztes Tier behandelt.  相似文献   
80.
Oleoresin flow is an important factor in the resistance of pines to attack by southern pine beetle, Dendroctonus frontalis Zimm., and its associated fungi. Abiotic factors, such as nutrient supply and water relations, have the potential to modify this plant-insect-fungus interaction; however, little is known of the effects of inoculation with beetle-associated fungi on oleoresin flow. We observed that constitutive and induced resin yield in loblolly pine, Pinus taeda L., were affected by either fungal inoculation (with the southern pine beetle-associated fungus Ophiostoma minus (Hedgcock) H. & P. Sydow) or silvicultural treatment. The effects of mass wounding (400 wounds m(-2)) and mass wounding and inoculation with O. minus were assessed by comparison with untreated (control) trees. The treatments were applied to trees in a 2 x 2 factorial combination of fertilizer and irrigation treatments. Fertilization did not significantly affect constitutive resin yield. Even as long as 105 days post-treatment, however, mass-inoculated trees produced higher induced resin yields than control or wounded-only trees, indicating a localized induced response to fungal inoculation. We noted no systemic induction of host defenses against fungal colonization. Although beetles attacking previously attacked trees face a greater resinous response from their host than beetles attacking trees that had not been previously attacked, the effect of an earlier attack may not last more than one flight season. Despite mass inoculations, O. minus did not kill the host trees, suggesting that this fungus is not a virulent plant pathogen.  相似文献   
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