全文获取类型
收费全文 | 69419篇 |
免费 | 18723篇 |
国内免费 | 4871篇 |
出版年
2024年 | 138篇 |
2023年 | 714篇 |
2022年 | 1632篇 |
2021年 | 2819篇 |
2020年 | 3757篇 |
2019年 | 5585篇 |
2018年 | 5549篇 |
2017年 | 5352篇 |
2016年 | 5896篇 |
2015年 | 6759篇 |
2014年 | 6955篇 |
2013年 | 7567篇 |
2012年 | 6116篇 |
2011年 | 5313篇 |
2010年 | 5366篇 |
2009年 | 3695篇 |
2008年 | 3096篇 |
2007年 | 2337篇 |
2006年 | 2063篇 |
2005年 | 1853篇 |
2004年 | 1510篇 |
2003年 | 1281篇 |
2002年 | 1191篇 |
2001年 | 978篇 |
2000年 | 793篇 |
1999年 | 774篇 |
1998年 | 408篇 |
1997年 | 356篇 |
1996年 | 384篇 |
1995年 | 321篇 |
1994年 | 365篇 |
1993年 | 233篇 |
1992年 | 321篇 |
1991年 | 250篇 |
1990年 | 235篇 |
1989年 | 169篇 |
1988年 | 125篇 |
1987年 | 107篇 |
1986年 | 79篇 |
1985年 | 93篇 |
1984年 | 67篇 |
1983年 | 56篇 |
1982年 | 53篇 |
1981年 | 30篇 |
1980年 | 21篇 |
1979年 | 35篇 |
1978年 | 19篇 |
1976年 | 25篇 |
1975年 | 23篇 |
1973年 | 18篇 |
排序方式: 共有10000条查询结果,搜索用时 281 毫秒
41.
42.
Yihe Lu Bojie Fu Liding Chen Zhiyun Ouyang Jianying Xu 《Biodiversity and Conservation》2006,15(8):2813-2827
Resolving the conflicts between biodiversity conservation and socioeconomic development is a global pursuit for the long-run
prospects of the human species. Based on Wenchuan County, a typical county in southwestern China, a group of 20 indicators
quantifying regional biodiversity and socioeconomic development was established to classify and evaluate the county area spatially.
A fuzzy c-means clustering (FCM) algorithm was used as the classification method. Three indices including BD, DL and DR characterizing
the value of biodiversity, the level and rate of socioeconomic development of the delineated regions were formulated. The
results indicated that Wenchuan County was optimally classified into 4 types of regions (region I to IV). The area percentages
of the regions vary widely from 4.3 to 65.7%. The sequences of the regions on biodiversity, socioeconomic development level,
and socioeconomic development rate were, respectively, IV > II > III > I, I > III > II > IV and III >I >II >IV. The spatial
strategy on coordinating biodiversity conservation and regional development is to develop mainly from the east(I, II, III)
and to conserve mainly in the west(IV). Eco-industry, such as eco-tourism and eco-agriculture, need to be emphasized in the
process of regional development. The quantitative methods used here may have a wide applicability. 相似文献
43.
44.
45.
Wei Lu 《Evolution; international journal of organic evolution》2020,74(8):1879-1880
What determines the rate at which species adapt to new climatic conditions? Weaver et al. found that the evolution of short larval periods promotes climatic niche evolution in salamanders in the genus Desmognathus. 相似文献
46.
Late Quaternary climate change,relict populations and present‐day refugia in the northern Atacama Desert: a case study from Quebrada La Higuera (18° S)
下载免费PDF全文
![点击此处可从《Journal of Biogeography》网站下载免费的PDF全文](/ch/ext_images/free.gif)
47.
48.
49.
Fei Mi Ying Zhang Dan Yang Xiaozhao Tang Pengfei Wang Xiaoxia He Yunrun Zhang Jianyong Dong Yang Cao Chunli Liu Ke-Qin Zhang Jianping Xu 《PloS one》2016,11(2)
During the past 40 years, more than 400 Sudden Unexplained Deaths (SUDs) have occurred in Yunnan, southwestern China. Epidemiological and toxicological analyses suggested that a newly discovered mushroom called Trogia venenata was the leading culprit for SUDs. At present, relatively little is known about the genetics and natural history of this mushroom. In this study, we analyzed the sequence variation at four DNA fragments among 232 fruiting bodies of T. venenata collected from seven locations. Our ITS sequence analyses confirmed that all the isolates belonged to the same species. The widespread presence of sequence heterozygosity within many strains at each of three protein-coding genes suggested that the fruiting bodies were diploid, dikaryotic or heterokaryotic. Within individual geographic populations, we found significant deviations of genotype frequencies from Hardy-Weinberg expectations, with the overall observed heterozygosity lower than that expected under random mating, consistent with prevalent inbreeding within local populations. The geographic populations were overall genetically differentiated. Interestingly, while a positive correlation was found between population genetic distance and geographic distance, there was little correlation between genetic distance and barium concentration difference for the geographic populations. Our results suggest frequent inbreeding, geographic structuring, and limited gene flow among geographic populations of T. venenata from southwestern China. 相似文献
50.