全文获取类型
收费全文 | 864篇 |
免费 | 72篇 |
出版年
2023年 | 2篇 |
2022年 | 3篇 |
2021年 | 25篇 |
2020年 | 11篇 |
2019年 | 15篇 |
2018年 | 21篇 |
2017年 | 17篇 |
2016年 | 32篇 |
2015年 | 48篇 |
2014年 | 58篇 |
2013年 | 61篇 |
2012年 | 97篇 |
2011年 | 66篇 |
2010年 | 45篇 |
2009年 | 48篇 |
2008年 | 52篇 |
2007年 | 50篇 |
2006年 | 49篇 |
2005年 | 34篇 |
2004年 | 41篇 |
2003年 | 31篇 |
2002年 | 26篇 |
2001年 | 12篇 |
2000年 | 4篇 |
1999年 | 16篇 |
1998年 | 7篇 |
1997年 | 9篇 |
1996年 | 6篇 |
1995年 | 4篇 |
1994年 | 2篇 |
1993年 | 3篇 |
1992年 | 4篇 |
1991年 | 4篇 |
1990年 | 5篇 |
1989年 | 2篇 |
1988年 | 5篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1985年 | 4篇 |
1984年 | 2篇 |
1983年 | 4篇 |
1982年 | 1篇 |
1976年 | 1篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1972年 | 3篇 |
1971年 | 1篇 |
排序方式: 共有936条查询结果,搜索用时 31 毫秒
141.
Francesco G Salerno Riccardo Pellegrino Gianluca Trocchio Antonio Spanevello Vito Brusasco Emanuele Crimi 《Journal of applied physiology》2005,98(3):817-821
The effects of breathing depth in attenuating induced bronchoconstriction were studied in 12 healthy subjects. On four separate, randomized occasions, the depth of a series of five breaths taken soon (approximately 1 min) after methacholine (MCh) inhalation was varied from spontaneous tidal volume to lung volumes terminating at approximately 80, approximately 90, and 100% of total lung capacity (TLC). Partial forced expiratory flow at 40% of control forced vital capacity (V(part)) and residual volume (RV) were measured at control and again at 2, 7, and 11 min after MCh. The decrease in V(part) and the increase in RV were significantly less when the depth of the five-breath series was progressively increased (P < 0.001), with a linear relationship. The attenuating effects of deep breaths of any amplitude were significantly greater on RV than V(part) (P < 0.01) and lasted as long as 11 min, despite a slight decrease with time when the end-inspiratory lung volume was 100% of TLC. In conclusion, in healthy subjects exposed to MCh, a series of breaths of different depth up to TLC caused a progressive and sustained attenuation of bronchoconstriction. The effects of the depth of the five-breath series were more evident on the RV than on V(part), likely due to the different mechanisms that regulate airway closure and expiratory flow limitation. 相似文献
142.
Mariella Baratti Emanuele Goti Giuseppe Messana 《Journal of experimental marine biology and ecology》2005,315(2):225-234
Sphaeroma terebrans Bate 1866 is a marine isopod belonging to the large family Sphaeromatidae, which normally colonises the aerial roots of the mangrove genus Rhizophora in tropical and subtropical areas. S. terebrans is part of a group of species whose complete life cycle occurs within the same mangrove wood. In this paper, we provide clear evidence of significant genetic differentiation among geographic populations of the taxon S. terebrans. The consistently low internal variation and the large interpopulation distances indicate that almost all the mitochondrial variation (cytochrome oxidase I) in S. terebrans is apportioned among populations rather than within them. The mean haplotype diversity (h) is 0.71%, and the mean nucleotide diversity (π) is 0.34%. The Minimum Spanning Tree (MST) reveals a complex pattern: three principal haplotype groups corresponding to the geographic locations investigated are distributed in a network. This suggests an ancient evolutionary history and very restricted gene flow between populations. The large genetic distances between the populations of S. terebrans could suggest that this taxon is not a single species but a species complex whose taxonomic status must be revaluated. 相似文献
143.
144.
145.
We tested the hypothesis that elevations of inflammatory markers such as C-reactive protein (CRP) and interleukin-6 (IL-6)
could be associated with the presence of aggressive behavior in domestic dogs. Serum concentrations of CRP and IL-6 were determined
by ELISA in eighteen adult male German Shepherd dogs showing no clinical signs but aggression. Eighteen healthy male dogs
with a negative history of behavioral and neurological disorders were used as controls. Compared with normal dogs, those with
aggression had significantly higher levels of CRP (P < 0.05) and IL-6 (P < 0.01) after adjustment for age, body weight, creatinine, blood urea nitrogen, total protein, total bilirubin and cholesterol.
Our pilot data suggest for the first time that an activation of systemic inflammatory processes may contribute to the pathophysiology
of aggression in domestic dogs. Further investigations are needed regarding the impact of our findings on treatment strategies. 相似文献
146.
147.
148.
Gianluca Piovesan Emanuele Presutti Saba Franco Biondi Alfredo Alessandrini Alfredo Di Filippo Bartolomeo Schirone 《Plant Ecology》2009,205(1):23-46
Understanding the ecological mechanisms that allow a species to transition from an occasional understory component to the
dominant type in the forest canopy is essential for predicting future shifts in the distribution of species. We investigated
this issue with regard to yew, also because mature yew trees have been reported to inhibit self-regeneration and seedling
survival, prompting concerns for the long-term preservation of the species. Our objectives were (a) to quantify spatial patterns
of yew (Taxus baccata L.) populations near the southern limit of the species’ ecological distribution, (b) to determine the relationships between
yew presence and topographic gradients, and (c) to answer the question of how yew regeneration is affected by such patterns
and relationships. We analyzed three extensive yew populations (90–165 ha, including 3–12 thousand established individuals)
that mostly occupy the understory of beech forests located in protected areas of the central Apennines (Italy). Overall, the
realized niche of yew (either as established trees, saplings, or seedlings) followed the expected bell-shaped curve of a species
response to an environmental gradient. Yew was mainly found at 1,000–1,600 m elevation on mesic exposures (north and west)
and intermediate slopes (30–60%). Geostatistical analysis revealed that yew occurred in patches, as shown by variogram ranges
of 40–110 m for yew tree basal area and regeneration abundance. Yew regeneration over the landscape was directly related to
basal area of yew trees. At local scales (~10 m), presence of established trees favored regeneration in relatively less developed
stands, whereas high density of mature yews suppressed regeneration. Healthy yew populations in beech forests had a minimum
size of 0.5–3 ha. As yew density increased within these patches, regeneration dropped, so that yew conservation cannot be
limited to presently occurring populations, despite the longevity and potential for vegetative reproduction of the species.
Disturbance from grazing and wildfire was also found to impact yew survival. Long-term existence of yew in the Italian Apennines
depends on maintaining and expanding old-growth beech forests that incorporate yew patches, and have a minimum continuous
cover equivalent to a relatively undisturbed regime (10–50 ha). 相似文献
149.
Emanuele Kuhn Giovani Sebben Bellicanta Vivian Helena Pellizari 《Environmental microbiology》2009,11(3):669-673
Alkane monooxygenases (Alk) are the key enzymes for alkane degradation. In order to understand the dispersion and diversity of alk genes in Antarctic marine environments, this study analysed by clone libraries the presence and diversity of alk genes ( alkB and alkM ) in sediments from Admiralty Bay, King George Island, Peninsula Antarctica. The results show a differential distribution of alk genes between the sites, and the predominant presence of new alk genes, mainly in the pristine site. Sequences presented 53.10–69.60% nucleotide identity and 50.90–73.40% amino acid identity to alkB genes described in Silicibacter pomeroyi , Gordonia sp., Prauserella rugosa , Nocardioides sp., Rhodococcus sp., Nocardia farcinica , Pseudomonas putida , Acidisphaera sp., Alcanivorax borkumensis , and alkM described in Acinetobacter sp. This is the first time that the gene alkM was detected and described in Antarctic marine environments. The presence of a range of previously undescribed alk genes indicates the need for further studies in this environment. 相似文献
150.