全文获取类型
收费全文 | 9706篇 |
免费 | 813篇 |
国内免费 | 770篇 |
专业分类
11289篇 |
出版年
2024年 | 25篇 |
2023年 | 127篇 |
2022年 | 149篇 |
2021年 | 283篇 |
2020年 | 294篇 |
2019年 | 359篇 |
2018年 | 342篇 |
2017年 | 338篇 |
2016年 | 327篇 |
2015年 | 351篇 |
2014年 | 442篇 |
2013年 | 645篇 |
2012年 | 389篇 |
2011年 | 398篇 |
2010年 | 354篇 |
2009年 | 431篇 |
2008年 | 463篇 |
2007年 | 463篇 |
2006年 | 355篇 |
2005年 | 364篇 |
2004年 | 383篇 |
2003年 | 285篇 |
2002年 | 318篇 |
2001年 | 272篇 |
2000年 | 280篇 |
1999年 | 239篇 |
1998年 | 231篇 |
1997年 | 185篇 |
1996年 | 183篇 |
1995年 | 184篇 |
1994年 | 163篇 |
1993年 | 179篇 |
1992年 | 162篇 |
1991年 | 138篇 |
1990年 | 114篇 |
1989年 | 88篇 |
1988年 | 91篇 |
1987年 | 98篇 |
1986年 | 72篇 |
1985年 | 92篇 |
1984年 | 94篇 |
1983年 | 65篇 |
1982年 | 82篇 |
1981年 | 66篇 |
1980年 | 61篇 |
1979年 | 48篇 |
1978年 | 49篇 |
1977年 | 44篇 |
1976年 | 44篇 |
1975年 | 29篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Peter S. Cranston 《水生昆虫》2013,35(2):103-114
A new dipteran species, Parapsectra wagneri sp. n. (Chironomidae), is described from emergence traps on Breitenbach, Schlitz, Germany. It differs in antennal ratio and characteristics of the genitalia from the three known species. 相似文献
102.
A new high-elevation scorpion species of the genus Scorpiops is described from the Indian state of Himachal Pradesh. Scorpiops spitiensis sp. nov. is the second highest-elevation scorpion species in Asia and the first one from India occurring at elevations above 4200 m. The new species closely resembles Scorpiops petersii, but it can be distinguished from it based on a suit of characters, one of which is the presence of 16 trichobothria on the external aspect of the patella, which is unique to the new species. 相似文献
103.
104.
105.
106.
自1982年以来,作者在长江中下游进行类寄生虫区系调查时,收集了一定数量的粘孢子虫标本。在鉴定这些标本时发现,寄生在赤眼鳟Squaliobarbus curriculus(Richardson)和黄Hypseleotris swinhonis(Gnther)的两种粘孢子虫,均系科学上的新物种。现报道如下。所有度量大小均以μm为单位。模式标本保存在中国科学院水生生物研究所鱼病学研究室。1宜都足孢虫新种 Podospora yiduensis sp.nov.(图) 寄生:赤眼蹲Squaliobarbus … 相似文献
107.
108.
Changwei Bi Na Lu Zhen Huang Junyuan Chen Chunpeng He Zuhong Lu 《Ecology and evolution》2020,10(15):8210-8224
Global climatic fluctuations governed the ancestral demographic histories of species and contributed to place the current population status into a more extensive ecological and evolutionary context. Genetic variations will leave unambiguous signatures in the patterns of intraspecific genetic variation in extant species since the genome of each individual is an imperfect mosaic of the ancestral genomes. Here, we report the genome sequences of 20 Branchiostoma individuals by whole‐genome resequencing strategy. We detected over 140 million genomic variations for each Branchiostoma individual. In particular, we applied the pairwise sequentially Markovian coalescent (PSMC) method to estimate the trajectories of changes in the effective population size (Ne) of Branchiostoma population during the Pleistocene. We evaluated the threshold of sequencing depth for proper inference of demographic histories using PSMC was ≥25×. The PSMC results highlight the role of historical global climatic fluctuations in the long‐term population dynamics of Branchiostoma. The inferred ancestral Ne of the Branchiostoma belcheri populations from Zhanjiang and Xiamen (China) seawaters was different in amplitude before the first (mutation rate = 3 × 10?9) or third glaciation (mutation rate = 9 × 10?9) of the Pleistocene, indicating that the two populations most probably started to evolve in isolation in their respective seas after the first or third glaciation of the Pleistocene. A pronounced population bottleneck coinciding with the last glacial maximum was observed in all Branchiostoma individuals, followed by a population expansion occurred during the late Pleistocene. Species that have experienced long‐term declines may be especially vulnerable to recent anthropogenic activities. Recently, the industrial pollution and the exploitation of sea sand have destroyed the harmonious living environment of amphioxus species. In the future, we need to protect the habitat of Branchiostoma and make full use of these detected genetic variations to facilitate the functional study of Branchiostoma for adaptation to local environments. 相似文献
109.
报道了木何兰小石藓(Weissia muhlenbergiana)为中国新记录种,提供了该种详细的特征描述和显微照片以及孢子电镜扫描照片,同时比较了该种与属内近似种类的异同。 相似文献
110.
Francisco J. Román‐Dañobeytia Samuel I. Levy‐Tacher James Aronson Ricardo Ribeiro Rodrigues Jorge Castellanos‐Albores 《Restoration Ecology》2012,20(3):378-386
The rainforest of Mexico has been degraded and severely fragmented, and urgently require restoration. However, the practice of restoration has been limited by the lack of species‐specific data on survival and growth responses to local environmental variation. This study explores the differential performance of 14 wet tropical early‐, mid‐ or late‐successional tree species that were grown in two abandoned pastures with contrasting land‐use histories. After 18 months, seedling survival and growth of at least 7 of the 14 tree species studied were significantly higher in the site with a much longer history of land use (site 2). Saplings of the three early‐successional species showed exceptional growth rates. However, differences in performance were noted in relation to the differential soil properties between the experimental sites. Mid‐successional species generally showed slow growth rates but high seedling survival, whereas late‐successional species exhibited poor seedling survival at both the study sites. Stepwise linear regressions revealed that the species integrated response index combining survivorship and growth measurements, was influenced mostly by differences in soil pH between the two abandoned pastures. Our results suggest that local environmental variation among abandoned pastures of contrasting land‐use histories influences sapling survival and growth. Furthermore, the similarity of responses among species with the same successional status allowed us to make some preliminary site and species‐specific silvicultural recommendations. Future field experiments should extend the number of species and the range of environmental conditions to identify site “generalists” or more narrowly adapted species, that we would call “sensitive.” 相似文献