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   29602篇
  免费   2885篇
  国内免费   2450篇
  2024年   78篇
  2023年   542篇
  2022年   569篇
  2021年   852篇
  2020年   1197篇
  2019年   1335篇
  2018年   1180篇
  2017年   1106篇
  2016年   1276篇
  2015年   1335篇
  2014年   1701篇
  2013年   2406篇
  2012年   1423篇
  2011年   1671篇
  2010年   1166篇
  2009年   1617篇
  2008年   1655篇
  2007年   1664篇
  2006年   1509篇
  2005年   1316篇
  2004年   1124篇
  2003年   1061篇
  2002年   1016篇
  2001年   800篇
  2000年   734篇
  1999年   572篇
  1998年   572篇
  1997年   481篇
  1996年   399篇
  1995年   425篇
  1994年   335篇
  1993年   283篇
  1992年   287篇
  1991年   197篇
  1990年   217篇
  1989年   177篇
  1988年   85篇
  1987年   88篇
  1986年   74篇
  1985年   59篇
  1984年   70篇
  1983年   44篇
  1982年   52篇
  1981年   34篇
  1980年   33篇
  1979年   40篇
  1978年   20篇
  1977年   15篇
  1976年   13篇
  1973年   9篇
排序方式: 共有10000条查询结果,搜索用时 800 毫秒
961.
Ten alberti-group species of the genus Metaphycus Mercet from China are reviewed. Six species Metaphycus dorsalis sp. n., Metaphycus chinensis sp. n., Metaphycus wui sp. n., Metaphycus stylatus sp. n., Metaphycus fusiscapus sp. n. and Metaphycus fusiformis sp. n. are described as new to science. Four known species from China are redescribed. A key to the females of the Chinese species is given and photomicrographs are provided to illustrate morphological characters of these species. All specimens unless otherwise specified are deposited in the National Zoological Museum of China Institute of Zoology Chinese Academy of Sciences Beijing.  相似文献   
962.
963.
The first overview on the Auchenorrhyncha fauna of peat bogs of the Austrian Bohemian Forest is presented. Seven oligotrophic peat bog sites were studied in 2011 by suction sampler (“G-Vac”) and 93 Auchenorrhyncha species (with 7465 adult specimens) were recorded. Eleven species (about 18 % of the individuals) are tyrphobiontic or tyrphophilous. The relative species abundance plot is not very steep; the six most abundant species represent 50 % of the individuals. The most common species is Conomelus anceps (17 % of the individuals). Compared to the whole Austrian Auchenorrhyncha fauna, the fauna of peat bogs comprises distinctly more univoltine species and more species hibernating in nymphal stage. Densities of adult Auchenorrhyncha in peat bogs are low in spring (about 10–60 individuals per m²) and high in July, with up to 180 (±50) individuals per m². Disturbed peat bogs have higher species numbers and higher Auchenorrhyncha densities in total, but lower numbers and densities in peat bog specialists.  相似文献   
964.
Seven new species of the genus Lobrathium Mulsant & Rey from China are described and illustrated: Lobrathium anatinum Li & Li, sp. n. (Guangxi), Lobrathium diaoluoense Li & Li, sp. n. (Hainan), Lobrathium dufui Li & Li, sp. n. (Hubei), Lobrathium lirunyui Li & Li, sp. n. (Guizhou), Lobrathium pengi Li & Li, sp. n. (Guangxi), Lobrathium quyuani Li & Li, sp. n. (Hubei) and Lobrathium uncinatum Li & Li, sp. n. (Qinghai). A recent key to the species of mainland China is modified to accommodate the new species. New locality data are provided for eleven species.  相似文献   
965.
Thirteen species of Pyrrhalta Joannis, 1865 with black elytron are reviewed. A key to species, photographs of aedeagus and habitus are provided. Pyrrhalta qianana sp. n. is described from Guizhou, China. Pyrrhalta martensi Medvedev & Sprecher-Uebersax, 1999 is newly recorded from China (Tibet).  相似文献   
966.
The arboreal, Neotropical lizard Plica plica (Linnaeus, 1758) has been long considered a widespread species with a distribution east of the Andes. A preliminary examination of 101 specimens from about 28 locations mostly north of the Amazon suggests that Plica plica is a cryptic species complex with taxa that can be distinguished on the basis of the number of scale rows at mid-body; the arrangement, shape and ornamentation of scales on the snout; the number of lamellae on the fourth toe; the number of subocular plates; as well as other commonly used external morphological traits. The allopatric species discussed here are concordant with northern South American geography. Plica plica (Linnaeus, 1758) is associated with the Guiana Shield (Suriname, Guyana and Venezuela). A second species, P. caribeana sp. n. is associated with the Caribbean Coastal Range of Venezuela including Trinidad and Tobago. A third, distinctive species, P. rayi sp. n. is associated with the middle Orinoco at the eastern edge of the Guiana Shield. Two other species, P. kathleenae sp. n. and P. medemi sp. n., each based upon a single specimen, one from the Sierra Acarai Mountains of Guyana, and the other from southern Meta, Colombia are described. In addition to morphological analyses, we sequenced 12S and 16S rDNA gene fragments from one Plica plica from Trinidad to assess its relationship and taxonomy to other mainland Plica cf. plica. The results suggest Plica caribeana sp. n. likely diverged prior to the separation of Trinidad from northern Venezuela. Isolation in the Caribbean Coastal Range during its rapid uplift in the late Miocene, combined with a marine incursion into northern Venezuela may have contributed to their genetic divergence from other populations.  相似文献   
967.
A recent molecular phylogeny of the Arid clade of the genus Hemidactylus revealed that the recently described H. saba and two unnamed Hemidactylus species from Sinai, Saudi Arabia and Yemen form a well-supported monophyletic group within the Arabian radiation of the genus. The name ‘Hemidactylus saba species group’ is suggested for this clade. According to the results of morphological comparisons and the molecular analyses using two mitochondrial (12S and cytb) and four nuclear (cmos, mc1r, rag1, rag2) genes, the name Hemidactylus granosus Heyden, 1827 is resurrected from the synonymy of H. turcicus for the Sinai and Saudi Arabian species. The third species of this group from Yemen is described formally as a new species H. ulii sp. n. The phylogenetic relationships of the members of ‘Hemidactylus saba species group’ are evaluated and the distribution and ecology of individual species are discussed.  相似文献   
968.
Recent studies indicate that the discriminatory power of the core DNA barcodes (rbcLa + matK) for land plants may have been overestimated since their performance have been tested only on few closely related species. In this study we focused mainly on how the addition of complementary barcodes (nrITS and trnH-psbA) to the core barcodes will affect the performance of the core barcodes in discriminating closely related species from family to section levels. In general, we found that the core barcodes performed poorly compared to the various combinations tested. Using multiple criteria, we finally advocated for the use of the core + trnH-psbA as potential DNA barcode for the family Combretaceae at least in southern Africa. Our results also indicate that the success of DNA barcoding in discriminating closely related species may be related to evolutionary and possibly the biogeographic histories of the taxonomic group tested.  相似文献   
969.
In this contribution the results of a zoogeographical analysis, carried out on the 123 endemic leaf beetle species (Coleoptera: Chrysomelidae) occurring in Italy and its immediately adjacent regions, are reported. To assess the level of faunistic similarity among the different geographic regions studied, a cluster analysis was performed, based on the endemic component. This was done by calculating the Baroni Urbani & Buser’s similarity index (BUB). Finally, a parsimony analysis of endemicity (PAE) was used to identify the most important areas of endemism in Italy.  相似文献   
970.
The mygalomorph neotropical genus Fufius Simon, 1888 comprises ten species, distributed from Guatemala in Central America to southeastern Brazil, in South America. Most of the species were described from northern South America, in the Amazonian region. Only F. funebris Vellard, 1924 and F. lucasae Guadanucci & Indicatti, 2004 are known from regions more to the south of the continent. Herein we describe three new Brazilian species, Fufius minusculus sp. n. and F. jalapensis sp. n. from the state of Tocantins, and F. candango sp. n. from Distrito Federal. The female of F. lucasae is described for first time and the male and female of F. funebris are redescribed based on specimens collected at the type locality.  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