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   914篇
  免费   64篇
  国内免费   109篇
  2024年   1篇
  2023年   29篇
  2022年   53篇
  2021年   26篇
  2020年   35篇
  2019年   42篇
  2018年   29篇
  2017年   32篇
  2016年   50篇
  2015年   70篇
  2014年   101篇
  2013年   131篇
  2012年   63篇
  2011年   79篇
  2010年   34篇
  2009年   19篇
  2008年   31篇
  2007年   33篇
  2006年   22篇
  2005年   18篇
  2004年   20篇
  2003年   13篇
  2002年   19篇
  2001年   11篇
  2000年   11篇
  1999年   11篇
  1998年   9篇
  1997年   7篇
  1996年   4篇
  1995年   4篇
  1994年   6篇
  1993年   29篇
  1992年   7篇
  1991年   3篇
  1990年   7篇
  1989年   4篇
  1988年   2篇
  1987年   1篇
  1986年   3篇
  1985年   1篇
  1984年   2篇
  1983年   2篇
  1982年   7篇
  1979年   1篇
  1977年   2篇
  1973年   3篇
排序方式: 共有1087条查询结果,搜索用时 15 毫秒
961.
962.
Liosarcophaga (s. str.) bartaki sp. n. is described from Turkey based on four males collected at three locations in Western Turkey. A morphological study of the genitalia using light and scanning electron microscopy has been carried out. An original key to the 10 species of Liosarcophaga occurring in Turkey is given.

http://www.zoobank.org/urn:urn:lsid:zoobank.org:pub:117C58FC-E957-4A7B-AB4C-B6DB35357763  相似文献   

963.
A new species of paedomorphic gobioid, Schindleria elongata, from the Red Sea, is described on the basis of five specimens. The new species is characterized by its lack of body pigmentation; the body depth at pectoral‐fin origin 4–5% of standard length (LS) and at anal‐fin origin 5–7% LS; the predorsal length 66–70% LS; pre‐anal length 66–71% LS; dorsal‐fin rays 13 or 14; anal‐fin rays 10 or 11; first dorsal‐fin ray at myomere 20 or 21; first anal‐fin ray below second to fourth dorsal‐fin rays; myomeres 19 or 20 + 13 or 14 = 33 or 34 total; premaxillae and dentaries with small teeth; gas bladder located posteriorly at 56–60% LS; males with a rod‐like, flexible urogenital papilla lacking lobes, projections or accessory papillae, with distal half tapering to a broad, angular point and usually posteriorly directed. A key to the species of Schindleriidae is presented.  相似文献   
964.
It is widely assumed that phenotypic traits can influence rates of speciation and extinction, and several statistical approaches have been used to test for correlations between character states and lineage diversification. Recent work suggests that model‐based tests of state‐dependent speciation and extinction are sensitive to model inadequacy and phylogenetic pseudoreplication. We describe a simple nonparametric statistical test (“FiSSE”) to assess the effects of a binary character on lineage diversification rates. The method involves computing a test statistic that compares the distributions of branch lengths for lineages with and without a character state of interest. The value of the test statistic is compared to a null distribution generated by simulating character histories on the observed phylogeny. Our tests show that FiSSE can reliably infer trait‐dependent speciation on phylogenies of several hundred tips. The method has low power to detect trait‐dependent extinction but can infer state‐dependent differences in speciation even when net diversification rates are constant. We assemble a range of macroevolutionary scenarios that are problematic for likelihood‐based methods, and we find that FiSSE does not show similarly elevated false positive rates. We suggest that nonparametric statistical approaches, such as FiSSE, provide an important complement to formal process‐based models for trait‐dependent diversification.  相似文献   
965.
In the present study, we determined the critical stages and the key factors of mortality for Planococcus citri (Hemiptera: Pseudococcidae) in Brazilian coffee plantations using a life table to understand the role of natural biological control on its population. Predators, parasitoids, rainfall, sunlight, physiological disturbances and fungal diseases were collectively responsible for 98.79% in the total mortality of P. citri. Predators belonging to the Chrysopidae, Syrphidae, Dolichopodidae and Coccinellidae families were the most important mortality factors in the early developmental stages of P. citri (i.e. eggs and 1st and 2nd instar nymphs), whereas predators belonging to the Coccinellidae and Chrysopidae families were the most important mortality factors for the last instars (i.e. 3rd instars and adults) for P. citri. The generalist predators Harmonia axyridis, Chrysoperla genanigra and Chrysoperla externa were the key mortality factors for P. citri. The third nymph stage was considered the critical life stage (i.e. the life stage that most influences population size). Our results show that generalist predators and climatic factors are important sources of natural mortality of P. citri governing the population dynamics of this pest in the field.  相似文献   
966.
The genus Codrus Panzer, 1803 is recorded for the first time from South Korea. A new species and three newly recorded species are described: C. tripotini Lee and Park sp. nov., C. ciliatus Townes, 1981, C. nebriae (Watanabe, 1954) and C. niger Panzer, 1803. Additionally, C. ciliatus Townes is newly added to Chinese fauna. A key to the South Korean Codrus, diagnostic characteristics and photographs are provided.  相似文献   
967.
燕山地区地处太行山生物多样性保护优先区,紧邻人口密集的京津冀城市群,拥有很高的鸟类物种多样性.为探讨燕山地区的鸟类生境状况与保护效益,本研究以当地40种国家重点保护鸟类为指示物种,利用物种分布模型和Marxan系统保护规划模型进行了保护空缺分析与保护策略优化.研究发现,在燕山地区的鸟类生境中,森林的面积最大(6 537...  相似文献   
968.
Multivariate analysis of leaf radian measurements was used to investigate variation in leaf shape among 34 Asian species of the Uvaria group, a large palaeotropical group of climbing Annonaceae characterized by imbricate petals and stellate hairs. Raw data were normalized by conversion into 15 ratio characters and using the log10 transformation. All species surveyed showed a unique leaf-shape 'bauplan'. The ratio character with the greatest discriminating power in both the Principal Components Analysis and Discriminant Analysis (DA) results was a measure of the shape of the leaf base. Ratio characters with the highest factor loadings for principal components 1 and 2 clearly separated the sampled taxa when plotted against one another and provided support for the retention of several taxa as distinct species or varieties. Classification of cases into taxa using DA yielded a correct classification rate of only 52% for the ratio-transformed data; however, division of taxa in the dataset into smaller subgroups defined by discrete morphological characters significantly increased the accuracy of case identification to between 67 and 100% of cases correctly classified, depending on the group. Case identification using DA on log10-transformed data was higher than for the ratio values in the entire dataset (61.7%) and the larger subgroups. However, the rate of correct case assignment was lower in the smaller groups than for the ratio data.  © 2003 The Linnean Society of London, Botanical Journal of the Linnean Society , 2003, 143 , 231–242.  相似文献   
969.
970.
《Journal of Asia》2022,25(1):101820
Flower fly species of the genus Monoceromyia Shannon (Diptera: Syrphidae) in India are reviewed and two new species, M. flavoscutata Sankararaman, Anooj and Mengual, sp. nov. and M. nigra Sankararaman, Anooj and Mengual, sp. nov., are described from Tamil Nadu and Arunachal Pradesh (India), respectively. A new synonym is proposed: M. multipunctata (Hull, 1941) is synonymised under M. polistoides (Brunetti, 1923). Moreover, lectotypes are designated for Ceria patricia Brunetti, 1923 and Ceria tredecimpunctata Brunetti, 1923. An identification key to the Indian Monoceromyia species is also provided.  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