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   321篇
  免费   9篇
  国内免费   3篇
  2015年   5篇
  2014年   3篇
  2013年   11篇
  2012年   5篇
  2011年   15篇
  2010年   15篇
  2009年   13篇
  2008年   7篇
  2007年   10篇
  2006年   11篇
  2005年   4篇
  2003年   4篇
  2002年   5篇
  2000年   6篇
  1999年   3篇
  1998年   8篇
  1997年   4篇
  1996年   5篇
  1995年   5篇
  1994年   4篇
  1993年   3篇
  1992年   5篇
  1989年   3篇
  1984年   4篇
  1983年   2篇
  1980年   2篇
  1978年   3篇
  1977年   2篇
  1976年   2篇
  1975年   5篇
  1974年   2篇
  1972年   7篇
  1971年   4篇
  1970年   2篇
  1968年   2篇
  1967年   2篇
  1960年   2篇
  1959年   6篇
  1958年   16篇
  1957年   14篇
  1956年   10篇
  1955年   16篇
  1954年   12篇
  1953年   8篇
  1952年   15篇
  1951年   8篇
  1950年   5篇
  1949年   6篇
  1948年   8篇
  1946年   3篇
排序方式: 共有333条查询结果,搜索用时 421 毫秒
11.
12.
13.
ABSTRACT Bait-delivered pharmaceuticals, increasingly used to manage populations of wild boar (Sus scrofa) and feral pigs, may be ingested by nontarget species. Species-specificity could be achieved through a delivery system. We designed the BOSTM (Boar-Operated-System) as a device to deliver baits to wild pigs. The BOSTM consists of a metal pole onto which a round perforated base is attached. A metal cone with a wide rim slides up and down the pole and fully encloses the base onto which the baits are placed. We conducted a pilot, captive trial and found that captive wild boar fed from the BOSTM either directly, by lifting the cone, or indirectly, by feeding once another animal had lifted the cone. Thus, we tested whether free-living wild boar fed from the BOSTM and whether the BOSTM could prevent bait uptake by nontarget species. We observed that free-living wild boar fed regularly from the BOSTM and that the device successfully prevented bait uptake by nontarget species. The BOSTM should be trialed more extensively to confirm its effectiveness and species-specificity to distribute pharmaceuticals to wild suids. If successful, the BOSTM could be used to deliver vaccines in disease control programs as well as contraceptives to manage overabundant populations of wild suids.  相似文献   
14.
The braconid subfamily Euphorinae is a large, cosmopolitan group of endoparasitoid wasps. The majority of species attack adult hosts, a strategy that is rare among parasitic wasps, but there are also many species that attack nymphs and larval stages. Euphorine hosts may belong to a variety of insect orders (Coleoptera, Hemiptera, Hymenoptera, Neuroptera, Psocoptera, Orthoptera and Lepidoptera) although most euphorine tribes are confined to Coleoptera. Here we investigate the phylogenetic relationships of the Euphorinae based on molecular data (3 kb of nucleotide data from four markers: 18S, 28S, CAD and COI) and propose a higher‐level classification based upon the resulting phylogeny. We also infer the evolution of host associations and discuss the diversification of the Euphorinae. Results from both Bayesian inference and maximum‐likelihood analysis show that the subfamily, as previously circumscribed, is paraphyletic. We propose that the subfamily be expanded to include the tribes Meteorini and Planitorini (Mannokeraia + Planitorus), so that it corresponds to a clade that is strongly supported as monophyletic in our analyses. Based on our results, a revised higher classification of the Euphorinae is proposed, in which 52 extant genera and 14 tribes are recognized. We reinstate the genus Microctonus belonging to the tribe Perilitini, and synonymize Ussuraridelus with Holdawayella, Sinuatophorus with Eucosmophorus. Furthermore, we propose the following tribal rearrangements: Spathicopis and Stenothremma are transferred to Perilitini; Tuberidelus, Eucosmophorus and Plynops to Cosmophorini; Ecclitura to Dinocampini; Chrysopophthorus, Holdawayella and Wesmaelia to Helorimorphini; Proclithroporus and Heia to Townesilitini. The monotypic tribe Cryptoxilonini is synonymized with Cosmophorini. The genera Pygostolus and Litostolus are placed in a separate tribe, Pygostolini, previously recognized as a subtribe among the Centistini. Parsimony‐based ancestral state reconstructions suggest that the ancestor of Euphorinae was a parasitoid of lepidopteran larvae, and that a host shift to larval Coleoptera occurred only in one clade of the Meteorini, some members of which secondarily shifted back to larval lepidopteran hosts. In the remainder of the subfamily, there was an initial shift from larval to adult coleopterans, followed by subsequent shifts to adults or larvae of Hemiptera, Hymenoptera, Neuroptera, Orthoptera and Psocoptera.  相似文献   
15.
Leaf photosynthetic CO2 responses can provide insight into how major nutrients, such as phosphorus (P), constrain leaf CO2 assimilation rates (Anet). However, triose‐phosphate limitations are rarely employed in the classic photosynthesis model and it is uncertain as to what extent these limitations occur in field situations. In contrast to predictions from biochemical theory of photosynthesis, we found consistent evidence in the field of lower Anet in high [CO2] and low [O2] than at ambient [O2]. For 10 species of trees and shrubs across a range of soil P availability in Australia, none of them showed a positive response of Anet at saturating [CO2] (i.e. Amax) to 2 kPa O2. Three species showed >20% reductions in Amax in low [O2], a phenomenon potentially explained by orthophosphate (Pi) savings during photorespiration. These species, with largest photosynthetic capacity and Pi > 2 mmol P m?2, rely the most on additional Pi made available from photorespiration rather than species growing in P‐impoverished soils. The results suggest that rarely used adjustments to a biochemical photosynthesis model are useful for predicting Amax and give insight into the biochemical limitations of photosynthesis rates at a range of leaf P concentrations. Phosphate limitations to photosynthetic capacity are likely more common in the field than previously considered.  相似文献   
16.
17.
18.
19.
20.
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