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   66367篇
  免费   2276篇
  国内免费   1942篇
  2023年   507篇
  2022年   646篇
  2021年   1840篇
  2020年   924篇
  2019年   1210篇
  2018年   951篇
  2017年   740篇
  2016年   1313篇
  2015年   3166篇
  2014年   6407篇
  2013年   5634篇
  2012年   4722篇
  2011年   5400篇
  2010年   3833篇
  2009年   3348篇
  2008年   3448篇
  2007年   3765篇
  2006年   2462篇
  2005年   2083篇
  2004年   1318篇
  2003年   1062篇
  2002年   941篇
  2001年   707篇
  2000年   654篇
  1999年   635篇
  1998年   535篇
  1997年   470篇
  1996年   528篇
  1995年   603篇
  1994年   565篇
  1993年   581篇
  1992年   543篇
  1991年   547篇
  1990年   461篇
  1989年   458篇
  1988年   449篇
  1987年   375篇
  1986年   336篇
  1985年   546篇
  1984年   848篇
  1983年   550篇
  1982年   715篇
  1981年   714篇
  1980年   513篇
  1979年   529篇
  1978年   326篇
  1977年   340篇
  1976年   308篇
  1974年   225篇
  1973年   230篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
The planthopper genus Neodurium Fennah is reviewed and Neodurium fennahi Chang & Chen, sp. n. (Hemiptera: Fulgoromorpha: Issidae) from China (Yunnan), is described and illustrated. A checklist of the species of Neodurium is given and a key provided for their separation. The female genitalia of Neodurium species are described for the first time.  相似文献   
992.
993.
Seven new species of oribatid mites of the genus Galumna are described from litter and soil materials of Sumatra, Indonesia. A new subgenus, Galumna (Atypicogalumna) subgen. n., is proposed; it differs from all galumnid genera and subgenera by the simultaneous presence of porose areas and sacculi on the notogaster (vs. either porose areas or sacculi present). Galumna (Galumna) calva Starý, 1997 is recorded for the first time in the Oriental region, and Galumna (Galumna) sabahna Mahunka, 1995 is recorded for the first time in the Indonesian fauna.  相似文献   
994.
995.
The genus Liancalus Loew is revised for the Nearctic Region. Seven species are documented from this region including two new species: Liancalus genualis Loew, Liancalus hydrophilus Aldrich, Liancalus limbatus Van Duzee, Liancalus pterodactyl sp. n., Liancalus querulus Osten Sacken, Liancalus similis Aldrich, and Liancalus sonorus sp. n. Lectotypes are designated for the following species: Liancalus genualis, Liancalus hydrophilus, Liancalus querulus, and Liancalus similis. The species are illustrated, a key to males and females is provided, and their distributions mapped. Adults of Liancalus are some of the largest species of Dolichopodidae and commonly occur on waterfalls and vertical seeps.  相似文献   
996.
There are four species of Gymnetron in China recorded to date including Gymnetron miyoshii Miyoshi, 1922, Gymnetron villosipenne Roelofs, 1875, Gymnetron auliense Reitter, 1907 and Gymnetron vittipenne Marseul, 1876, of which the last two are new country records. The pre-imaginal stages including eggs, mature larvae and pupae of Gymnetron miyoshii, Gymnetron auliense and Gymnetron vittipenne are described and illustrated. In addition, their diagnostic characters (larvae and pupae) are discussed and differentiated, and notes on some of their biological parameters are provided. Potential ecological impacts between Gymnetron weevils and their host Veronica spp. also are provided.  相似文献   
997.
Alain Migeon 《ZooKeys》2015,(489):15-24
The family Tetranychidae (spider mites) currently comprises 1,275 species and represents one of the most important agricultural pest families among the Acari with approximately one hundred pest species, ten of which considered major pests. The dataset presented in this document includes all the identified spider mites composing the Jean Gutierrez Collection hosted at the CBGP (Montferrier-sur-Lez, France), gathered from 1963 to 1999 during his career at the Institut de Recherche pour le Développement (IRD). It consists of 5,262 specimens corresponding to 1,564 occurrences (combination species/host plant/date/location) of 175 species. Most specimens were collected in Madagascar and other islands of the Western Indian Ocean, New Caledonia and other islands of the South Pacific and Papuasia. The dataset constitutes today the most important one available on Tetranychidae worldwide.  相似文献   
998.
The genus Hisonotus was resurrected as a member of the tribe Otothyrini (actually subfamily Otothyrinae). However, phylogenetic studies based on morphological and molecular data showed that Hisonotus is not monophyletic and independent lineages can be identified, such as the group composed of the species Hisonotus insperatus, Hisonotus luteofrenatus, Hisonotus oliveirai, Hisonotus paresi and Hisonotus piracanjuba, a lineage unrelated to that containing the type species of the genus Hisonotus (Hisonotus notatus). Herein, based in molecular and morphological data, a new genus is described to accommodate the lineage mentioned above, into which are also added three new species. This new genus can be distinguished from other genera of Otothyrinae by the following combination of characters: (1) a pair of rostral plates at the tip of the snout; (2) two large pre-nasal plates just posterior to the rostral plates; (3) a supra-opercular plate that receives the laterosensory canal from the compound pterotic before the preopercle; (4) a well developed membrane at anal opening in females; and (5) a V-shaped spinelet. A key to species of Curculionichthys is provided.  相似文献   
999.
In this paper new mitochondrial COI sequences of Common Barn Owl Tyto alba (Scopoli, 1769) and Short-eared Owl Asio flammeus (Pontoppidan, 1763) from southern Chile are reported and compared with sequences from other parts of the World. The intraspecific genetic divergence (mean p-distance) was 4.6 to 5.5% for the Common Barn Owl in comparison with specimens from northern Europe and Australasia and 3.1% for the Short-eared Owl with respect to samples from north America, northern Europe and northern Asia. Phylogenetic analyses revealed three distinctive groups for the Common Barn Owl: (i) South America (Chile and Argentina) plus Central and North America, (ii) northern Europe and (iii) Australasia, and two distinctive groups for the Short-eared Owl: (i) South America (Chile and Argentina) and (ii) north America plus northern Europe and northern Asia. The level of genetic divergence observed in both species exceeds the upper limit of intraspecific comparisons reported previously for Strigiformes. Therefore, this suggests that further research is needed to assess the taxonomic status, particularly for the Chilean populations that, to date, have been identified as belonging to these species through traditional taxonomy.  相似文献   
1000.
Radomir Jasku?a 《ZooKeys》2015,(482):35-53
The tiger beetle fauna of the Maghreb region is one of the richest in the Palaearctic, including 22 species and 5 subspecies and 19% of all Palaearctic species of Cicindelinae. Assembled to their chorotypes, the Maghreb tiger beetles fall into eight different groups that include Maghreb endemics (26% of fauna), Mediterranean (7%), West Mediterranean (40%), North African (4%), Mediterranean-Westturanian (4%), West Palaearctic (4%), Afrotropico-Indo-Mediterranean (4%), and Saharian (11%) species. The Mediterranean Sclerophyl and Atlas Steppe are the Maghreb biogeographical provinces with the highest species richness, while the Sahara Desert has the lowest Cicindelinae diversity. Twenty-five cicindelid species and subspecies (93% of Maghreb fauna) are restricted to only one or two habitat types in lowland areas. Only Calomera littoralis littoralis and Lophyra flexuosa flexuosa are recognized as eurytopic species and occur in three types of habitat. The highest tiger beetle diversity characterizes salt marshes and river banks (in both cases 11 species and subspecies or 41% of Maghreb fauna). Approximately 85% of all Maghreb tiger beetle species and subspecies are found in habitats potentially endangered by human activity.  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