全文获取类型
收费全文 | 18714篇 |
免费 | 1701篇 |
国内免费 | 12篇 |
出版年
2023年 | 90篇 |
2022年 | 222篇 |
2021年 | 422篇 |
2020年 | 219篇 |
2019年 | 267篇 |
2018年 | 356篇 |
2017年 | 290篇 |
2016年 | 497篇 |
2015年 | 767篇 |
2014年 | 838篇 |
2013年 | 1019篇 |
2012年 | 1333篇 |
2011年 | 1330篇 |
2010年 | 839篇 |
2009年 | 774篇 |
2008年 | 1107篇 |
2007年 | 1056篇 |
2006年 | 1027篇 |
2005年 | 931篇 |
2004年 | 888篇 |
2003年 | 840篇 |
2002年 | 766篇 |
2001年 | 305篇 |
2000年 | 234篇 |
1999年 | 295篇 |
1998年 | 230篇 |
1997年 | 166篇 |
1996年 | 172篇 |
1995年 | 127篇 |
1994年 | 136篇 |
1993年 | 145篇 |
1992年 | 175篇 |
1991年 | 183篇 |
1990年 | 147篇 |
1989年 | 163篇 |
1988年 | 135篇 |
1987年 | 112篇 |
1986年 | 113篇 |
1985年 | 135篇 |
1984年 | 124篇 |
1983年 | 106篇 |
1982年 | 85篇 |
1981年 | 108篇 |
1980年 | 78篇 |
1979年 | 79篇 |
1978年 | 72篇 |
1977年 | 75篇 |
1974年 | 71篇 |
1973年 | 68篇 |
1972年 | 64篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
12.
13.
Pinealectomy or radical sham pinealectomy were performed on adult golden-mantled ground squirrels,Spermophilus (=Citellus) lateralis, approximately 1 month prior to the date of normal winter emergence. The first hibernatory period and subsequent active season were not different in either of the operated groups from intact animals. However, although the initiation of the second hibernatory period was not affected in the pinealectomized animals, this group failed to show the progressive increase in the length of heterothermic bouts that is characteristic of normal hibernation. Also, terminal arousal occurred approximately 6 weeks earlier in the second year after pinealectomy. Male squirrels showed a corresponding time compression in their annual gonadal cycle, as was assessed by testicular state.These results suggest that the pineal gland of the golden-mantled ground squirrel is involved in the expression of the annual hibernatory cycle. In the absence of the pineal gland the adult of this species is unable to sustain the normal depth and duration of hibernation in the second over-wintering period following pinealectomy.We have carried out additional experiments with young, laboratory-bornS. lateralis and with field-caught, adultS. richardsonii. The results of these studies also are described in this paper.Presented at the Ninth International Congress of Biometeorology, 23 Sept – 1 Oct 1981, Osnabrück and Hohenheim, FRG. 相似文献
14.
Three acetotrophicMethanosarcina species, which included marine, nonmarine, and thermophilic strains, were grown on acetate in a 10-liter pH auxostat. Specific growth rates and molar growth yields were constant throughout growth. Cell yields were up to 18-fold greater than previously reported. These properties of the pH auxostat indicate that it is a preferred culture method for the biochemical study of methanogenesis from acetate. 相似文献
15.
One hundred and forty-four isolates of dairy origin were identified using a number of commercially available test kits. Agreement between these kits was acceptable for assignment of isolates to genera, but there was some variation between the kits for the identification of the isolates at specific level. The reasons for these variations are discussed. In terms of cost, ease of performance and accuracy, the identification systems manufactured by Roche Products Ltd (viz. the Oxi/Ferm tube and the Enterotube) are considered to be the best suited to the routine identification of dairy micro-organisms. 相似文献
16.
17.
Laura W. Pomeroy Jacob M. Aaronson Samuel Handelman Jori Hardman Kevin Kawalec Thomas Bitterman Ward C. Wheeler 《Cladistics : the international journal of the Willi Hennig Society》2012,28(5):483-488
We have reported previously on use of a web‐based application, Supramap ( http://supramap.org ) for the study of biogeographic, genotypic, and phenotypic evolution. Using Supramap we have developed maps of the spread of drug‐resistant influenza and host shifts in H1N1 and H5N1 influenza and coronaviruses such as SARS. Here we report on another zoonotic pathogen, H7 influenza, and provide an update on the implementation of Supramap as a web service. We find that the emergence of pathogenic strains of H7 is labile with many transitions from high to low pathogenicity, and from low to high pathogenicity. We use Supramap to put these events in a temporal and geospatial context. We identify several lineages of H7 influenza with biomarkers of high pathogenicity in regions that have not been reported in the scientific literature. The original implementation of Supramap was built with tightly coupled client and server software. Now we have decoupled the components to provide a modular web service for POY ( http://poyws.org ) that can be consumed by a data provider to create a novel application. To demonstrate the web service, we have produced an application, Geogenes ( http://geogenes.org ). Unlike in Supramap, in which the user is required to create and upload data files, in Geogenes the user works from a graphical interface to query an underlying dataset. Geogenes demonstrates how the web service can provide underlying processing for any sequence and metadata database. © The Willi Hennig Society 2012. 相似文献
18.
19.
20.
Kevin J. Beiler Suzanne W. Simard Valerie LeMay Daniel M. Durall 《Molecular ecology》2012,21(24):6163-6174
Understanding ectomycorrhizal fungal (EMF) community structure is limited by a lack of taxonomic resolution and autecological information. Rhizopogon vesiculosus and Rhizopogon vinicolor (Basidiomycota) are morphologically and genetically related species. They are dominant members of interior Douglas‐fir (Pseudotsuga menziesii var. glauca) EMF communities, but mechanisms leading to their coexistence are unknown. We investigated the microsite associations and foraging strategy of individual R. vesiculosus and R. vinicolor genets. Mycelia spatial patterns, pervasiveness and root colonization patterns of fungal genets were compared between Rhizopogon species and between xeric and mesic soil moisture regimes. Rhizopogon spp. mycelia were systematically excavated from the soil and identified using microsatellite DNA markers. Rhizopogon vesiculosus mycelia occurred at greater depth, were more spatially pervasive, and colonized more tree roots than R. vinicolor mycelia. Both species were frequently encountered in organic layers and between the interface of organic and mineral horizons. They were particularly abundant within microsites associated with soil moisture retention. The occurrence of R. vesiculosus shifted in the presence of R. vinicolor towards mineral soil horizons, where R. vinicolor was mostly absent. This suggests that competition and foraging strategy may contribute towards the vertical partitioning observed between these species. Rhizopogon vesiculosus and R. vinicolor mycelia systems occurred at greater mean depths and were more pervasive in mesic plots compared with xeric plots. The spatial continuity and number of trees colonized by genets of each species did not significantly differ between soil moisture regimes. 相似文献