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   252篇
  免费   54篇
  国内免费   123篇
  2024年   2篇
  2023年   9篇
  2022年   9篇
  2021年   7篇
  2020年   16篇
  2019年   11篇
  2018年   17篇
  2017年   19篇
  2016年   13篇
  2015年   19篇
  2014年   20篇
  2013年   38篇
  2012年   14篇
  2011年   14篇
  2010年   22篇
  2009年   10篇
  2008年   13篇
  2007年   18篇
  2006年   12篇
  2005年   10篇
  2004年   20篇
  2003年   11篇
  2002年   16篇
  2001年   13篇
  2000年   11篇
  1999年   10篇
  1998年   11篇
  1997年   12篇
  1996年   4篇
  1995年   3篇
  1994年   5篇
  1993年   3篇
  1992年   2篇
  1991年   2篇
  1990年   1篇
  1989年   2篇
  1988年   3篇
  1987年   1篇
  1986年   1篇
  1984年   2篇
  1983年   2篇
  1982年   1篇
排序方式: 共有429条查询结果,搜索用时 169 毫秒
411.
Afenestrata koreana n. sp. collected from roots of bamboo (Phyllostachys pubescens) in Gyeongnam Province in the southern part of the Korean peninsula is described and illustrated. Its primary differentiating characteristics are a globose to subspherical body in adults with a prominent neck and terminal cone, thick cuticle, terminal vulva, and deep vagina. Fenestra, bullae, and underbridge are absent. The anus is on the immediate posterior side of the cone. Superficial small tubercules cover all the terminal cone area. The new species differs markedly from the other two known species in the genus, specifically in having three incisures in the lateral field of juveniles and a shorter stylet length in juveniles and adults. The male is unknown.  相似文献   
412.
《植物生态学报》2014,38(3):289
克隆植物不同年龄分株间可以通过生理整合作用相互传递资源, 实现资源共享。施肥可以改变林地资源状况, 进而可能影响分株间的整合作用及不同年龄分株间的生长关系。该文采用标准主轴(SMA)估计法和多元回归分析, 对不同施肥管理下大型克隆植物毛竹(Phyllostachys edulis)种群不同年龄分株(1年生分株、3年生分株和5年生分株)间的胸径(DBH)关系进行了研究, 探讨毛竹不同年龄分株DBH大小关系对施肥的响应。结果表明: 连续5年施肥有效地增加了毛竹1年生分株的DBH, 而施肥1年处理下, 1年生分株DBH与3年生分株和5年生分株平均DBH差异不显著(p > 0.05)。1年生分株与3年生分株和5年生分株DBH之间的SMA斜率为0.88-1.10, 均与1.00不存在显著差异(p > 0.05), 表现为等速生长关系。施肥1年和连续施肥5年没有改变不同年龄分株DBH之间的SMA斜率, 但连续5年施肥导致SMA的y轴截距显著增大(p < 0.001), 即在3年生分株和5年生分株DBH相同的情况下, 连续5年施肥使1年生分株具有更大的DBH增长量。采用多元线性逐步回归分析发现, 毛竹1年生分株的DBH大小在很大程度上受3年生分株DBH大小的影响, 而连续5年施肥可增强5年生分株对1年生分株DBH大小的影响。  相似文献   
413.
Hairy (Dryobates villosus) and downy (Dryobates pubescens) woodpeckers occur in high densities in residential areas of the eastern United States. In many areas of their range, they cause damage to wooden structures through foraging, excavation of nesting cavities, and drumming behaviors, causing requests for allowable take permits. Both species hold year-round territories, which could make them vulnerable to local extirpation with excess take. To meet the requirements of the Migratory Bird Treaty act, the United States Fish and Wildlife Service (USFWS) requested scientifically informed evaluation of take to minimize population effects as part of its approach to reduce human–wildlife conflict. We used a prescribed take approach, which uses data from population, demographic, and management parameter estimates to determine the allowable take from Louisiana to Minnesota and all states east. Furthermore, we used 2 different methods of estimating growth rates to control for demographic uncertainties. The resulting estimates provide take at the state and USFWS regional scales to improve stakeholder choices when setting allowable take. Current authorized take (2016–2018) is below the take that could be sustained by current populations, and current rates of take are not likely to cause population-level effects. These results were largely consistent across methodologies for calculating the rate of growth for both species. Take still needs to be managed to prevent local extirpation of these resident species. Allowable take estimates should be periodically updated to reflect changing management and population needs for both species.  相似文献   
414.
两色绿刺蛾生物学特性及发生规律   总被引:3,自引:2,他引:1  
两色绿刺蛾在福建闽西北1a发生2代,以老熟幼虫在土壤中结茧越冬。该虫1a有2次发生高峰期,分别在6月上、中旬和9月下旬至10月上旬。以第1代发生量大,危害严重。该虫发生与竹林结构、竹立量、坡向、坡位均有关系。林间调查表明:该虫第2代的天敌寄生率高。天敌是抑制种群数量增长的重要因素之一。  相似文献   
415.
416.
为寻找当归及其混淆品独活、欧当归的紫外吸收光谱鉴别特征,采用紫外谱线组法对三者在不同极性溶剂中的紫外吸收光谱图进行比较。结果表明,当归和独活在四种极性溶剂中均存在明显差异,而当归和欧当归仅在无水乙醇和蒸馏水溶剂中鉴别差异显著。紫外谱线组法可以鉴别当归及其混淆品独活、欧当归。  相似文献   
417.
Abstract: Seedlings of mountain birch ( Betula pubescens ssp. czerepanovii ), a subarctic tree, mainly survive and establish in early-successional patches with low vegetation cover. In particular, during the first years after seed germination, a rapid seedling growth rate is important for winter survival. Seedling growth rate is controlled by plant nitrogen (N) concentration. On a year-round perspective, the N concentration is influenced by N uptake rate during both summer and winter and by N loss during autumn. The aim of the present study was to evaluate the effects of autumn N loss and winter N uptake for seedling growth during summer. The study used young seedlings growing in situ in northern Sweden. Since the growth rate of whole plants cannot be measured in situ, it was estimated using a simple, empirical seedling growth model. The model was based on data from controlled experiments and validated using growth data from a field study. The field study included sequential seedling harvests which were carried out at two sites differing in altitude, from autumn 1994 until autumn 1996. The seedling growth model was used to simulate the effects on growth rate of autumn N losses and winter N uptake. It was found that a decrease in the amount of N lost in autumn and an increase in the amount of N taken up during winter could enhance the growth rate of mountain birch seedlings by the same order of magnitude as an increase in growing season soil temperature by 1 to 2 K.  相似文献   
418.
419.
姜培坤  徐秋芳 《生态学杂志》2001,20(6):25-28,40
有关土层厚度、土壤有机质、土壤有效P、土壤水解N含量以及土壤质地等理化性质影响毛竹(Phyllostachys pubescens)粗生长的研究已有报道[1,2 ] 。但迄今为止 ,毛竹林地土壤生物学性质的系统研究尚少见报道 ,有关土壤生物学性质与毛竹粗生长关系方面的研究更是空白。作者在浙江省安吉县生长状况不同的毛竹林中设置了 2 3块标准地 ,采集土壤样品、测定毛竹眉径 ,以寻找土壤生物学性质与毛竹粗生长之间的关系。1 样地与方法1 1 样地概况样地设在浙江省安吉港口乡 ,该处年平均气温15℃ ,极端最高温 39.2℃ ,极端最低…  相似文献   
420.
Earwigs are usually considered pest predators in orchards. Because of its worldwide distribution, most research on earwigs focuses on the European earwig Forficula auricularia Linnaeus (Insecta: Dermaptera: Forficulidae). However, very little is known of this species in Mediterranean citrus orchards. Earwigs and aphids were collected monthly during 5 years (2006–2010) from citrus canopies. Two species of earwigs were found: F. auricularia and Forficula pubescens Gené (=Guanchia pubescens), with the latter seldom cited in the literature. The goals of this study were (i) to document the abundance of these two earwig species in Mediterranean citrus canopies; (ii) to determine whether they are positively or negatively associated with each other, or randomly distributed; (iii) to measure the interannual variation of the abundance of both species during a 5‐year period and (iv) to evaluate the potential role of earwigs as pest predators in citrus canopies. As compared to colder regions, F. auricularia active period in citrus canopies in our study site lasted longer. Both species co‐occurred randomly in canopies. In 2006, both species showed approximately the same abundance, but in 2010, F. pubescens abundance in canopies was 28 times greater than that of F. auricularia. The potential role of earwigs as pest predators is higher in the Mediterranean than in other colder regions, because of the longer active period. F. auricularia is a sedentary generalist predator, already present in citrus canopies at the onset of most pest outbreaks, while F. pubescens arrived later to the canopies, but most likely was abundant enough to contribute in the control of citrus pests.  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