全文获取类型
收费全文 | 733篇 |
免费 | 39篇 |
出版年
2023年 | 3篇 |
2022年 | 7篇 |
2021年 | 7篇 |
2020年 | 6篇 |
2019年 | 2篇 |
2018年 | 12篇 |
2017年 | 6篇 |
2016年 | 15篇 |
2015年 | 25篇 |
2014年 | 35篇 |
2013年 | 52篇 |
2012年 | 50篇 |
2011年 | 50篇 |
2010年 | 22篇 |
2009年 | 37篇 |
2008年 | 45篇 |
2007年 | 39篇 |
2006年 | 31篇 |
2005年 | 52篇 |
2004年 | 39篇 |
2003年 | 25篇 |
2002年 | 29篇 |
2001年 | 19篇 |
2000年 | 12篇 |
1999年 | 15篇 |
1998年 | 10篇 |
1997年 | 4篇 |
1996年 | 6篇 |
1995年 | 5篇 |
1994年 | 7篇 |
1993年 | 2篇 |
1992年 | 4篇 |
1991年 | 8篇 |
1990年 | 7篇 |
1989年 | 14篇 |
1988年 | 4篇 |
1987年 | 3篇 |
1986年 | 4篇 |
1985年 | 8篇 |
1984年 | 8篇 |
1983年 | 3篇 |
1982年 | 4篇 |
1980年 | 4篇 |
1979年 | 7篇 |
1977年 | 4篇 |
1975年 | 7篇 |
1974年 | 3篇 |
1972年 | 3篇 |
1971年 | 3篇 |
1969年 | 1篇 |
排序方式: 共有772条查询结果,搜索用时 672 毫秒
161.
162.
163.
164.
Three protected derivatives of 1,N(6)-ethenoadenine nucleosides, viz. 3-[5-O-(4,4'-dimethoxytrityl) of 7-formyl-(1) and 7-(1,2-diacetyloxypropyl)-2'-deoxyadenosine (2), and 3-[5-O-(4,4'-dimethoxytrityl)-2-O-(tert-butyldimethylsilyl)-7-(ethoxycarbonyl)adenosine (3), expected to allow introduction of formyletheno and carboxyethenoadenine adducts into oligonucleotides by the conventional phosphoramidite chemistry, have been synthesized. 相似文献
165.
Applying a framework for landscape planning under climate change for the conservation of biodiversity in the Finnish boreal forest
下载免费PDF全文
![点击此处可从《Global Change Biology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Adriano Mazziotta Maria Triviño Olli‐Pekka Tikkanen Jari Kouki Harri Strandman Mikko Mönkkönen 《Global Change Biology》2015,21(2):637-651
Conservation strategies are often established without consideration of the impact of climate change. However, this impact is expected to threaten species and ecosystem persistence and to have dramatic effects towards the end of the 21st century. Landscape suitability for species under climate change is determined by several interacting factors including dispersal and human land use. Designing effective conservation strategies at regional scales to improve landscape suitability requires measuring the vulnerabilities of specific regions to climate change and determining their conservation capacities. Although methods for defining vulnerability categories are available, methods for doing this in a systematic, cost‐effective way have not been identified. Here, we use an ecosystem model to define the potential resilience of the Finnish forest landscape by relating its current conservation capacity to its vulnerability to climate change. In applying this framework, we take into account the responses to climate change of a broad range of red‐listed species with different niche requirements. This framework allowed us to identify four categories in which representation in the landscape varies among three IPCC emission scenarios (B1, low; A1B, intermediate; A2, high emissions): (i) susceptible (B1 = 24.7%, A1B = 26.4%, A2 = 26.2%), the most intact forest landscapes vulnerable to climate change, requiring management for heterogeneity and resilience; (ii) resilient (B1 = 2.2%, A1B = 0.5%, A2 = 0.6%), intact areas with low vulnerability that represent potential climate refugia and require conservation capacity maintenance; (iii) resistant (B1 = 6.7%, A1B = 0.8%, A2 = 1.1%), landscapes with low current conservation capacity and low vulnerability that are suitable for restoration projects; (iv) sensitive (B1 = 66.4%, A1B = 72.3%, A2 = 72.0%), low conservation capacity landscapes that are vulnerable and for which alternative conservation measures are required depending on the intensity of climate change. Our results indicate that the Finnish landscape is likely to be dominated by a very high proportion of sensitive and susceptible forest patches, thereby increasing uncertainty for landscape managers in the choice of conservation strategies. 相似文献
166.
Models relating stem growth to crown length dynamics: application to loblolly pine and Norway spruce
Harry T. Valentine Annikki Mäkelä Edwin J. Green Ralph L. Amateis Harri Mäkinen Mark J. Ducey 《Trees - Structure and Function》2012,26(2):469-478
We derive and analyze a model that relates the growth rate of cross-sectional area (‘csa’) at any height on the central stem
of a tree to crown-length dynamics. The derivation is based, in part, on assumptions that (a) active csa on the central stem
relates allometrically to the length of crown above the cross section, and (b) inactive csa is proportional to active csa
within the crown. We also assume that the deactivation rate of csa beneath the crown is determined, in part, by the rate of
crown rise. Integration of the growth-rate model under an additional assumption—that total crown length is constant after
stand closure—provides a simple model of annual or periodic growth of total csa that can be fit to standard growth data. Three
implications of the assumptions and integration are notable: (1) total csa within the crown scales allometrically with stem
length above the cross section; (2) for a special case, total csa beneath the crown scales with stem length above the cross
section; more generally, csa scales with a linear combination of the stem and crown lengths; and (3) the stem beneath the
crown forms to approximate a frustum of a quadratic paraboloid. Basal area data from a loblolly pine (Pinus taeda L.) spacing trial show good agreement with (1) and (2), and with an empirical model developed from the special case of (2).
Data from the plots of a Norway spruce (Picea abies (L.) Karst.) thinning trial, where crown length remained approximately constant, show good agreement with (2) and the empirical
model. Prediction (3) is demonstrated by simulation. 相似文献
167.
Moose and vole browsing patterns in experimentally assembled pure and mixed forest stands 总被引:2,自引:0,他引:2
Plants growing in diverse communities are believed to exhibit associational resistance to herbivores, but this hypothesis has seldom been tested experimentally for vertebrate herbivores in forest ecosystems. We examined browsing patterns of the two principal mammalian herbivores of Finnish boreal forests, moose and voles, in young stands where tree species diversity and composition were experimentally manipulated. The stands were composed either of monocultures or different 2–5 species mixtures of Norway spruce, Scots pine, Siberian larch, silver birch, and black alder. Voles and moose showed contrasting responses to stand diversity and species composition. In accordance with the predictions of the associational resistance hypothesis, vole damage was higher in tree monocultures than in mixed stands, although stand diversity effects were statistically significant only at one of the three study areas. Voles also damaged more trees in coniferous than in deciduous stands. In contrast, moose browsing tended to increase with the number of tree species in a stand and with the presence of the preferred tree species, birch, in a mixture. The observed differences in vole and moose responses to stand diversity and species composition are likely to be due to different feeding specialisation, foraging patterns, and movement ability of these herbivores. Voles switched to trees only when the supply of a more preferred food (grasses and forbs) was depleted and restricted their feeding choice only to the most palatable tree species regardless of the number of tree species present per stand. In contrast, tree branches and foliage represented an important part of moose diet throughout the year; moose may be able to tolerate secondary plant metabolites of different tree species better than voles and may thus benefit from diet broadening when more tree species are available. Furthermore, the home range size and foraging ability of these two very differently sized herbivores may partly explain the observed differences in utilisation of different tree species. Finally, both moose and voles showed high spatial and temporal variation in their feeding; in particular, vole damage was more influenced by tree species diversity in areas and years with high vole densities. Thus, diversification of forest stands may have very different effects on mammalian browsing depending on the herbivores present, their densities, and the tree species used in reforestation. 相似文献
168.
Pääkkönen K Tossavainen H Permi P Rakkolainen H Rauvala H Raulo E Kilpeläinen I Güntert P 《Proteins》2006,64(3):665-672
F-spondin is a protein mainly associated with neuronal development. It attaches to the extracellular matrix and acts in the axon guidance of the developing nervous system. F-spondin consists of eight domains, six of which are TSR domains. The TSR domain family binds a wide range of targets. Here we present the NMR solution structures of TSR1 and TSR4. TSR domains have an unusual fold that is characterized by a long, nonglobular shape, consisting of two beta-strands and one irregular extended strand. Three disulfide bridges and stack of alternating tryptophan and arginine side-chains stabilize the structure. TSR1 and TSR4 structures are similar to each other and to the previously determined TSR domain X-ray structures from another protein, TSP, although TSR4 exhibits a mobile loop not seen in other structures. 相似文献
169.
Marcos Roberto de Oliveira Max William Soares Oliveira Rodrigo Lorenzi Ricardo Fagundes da Rocha José Cláudio Fonseca Moreira 《Cell biology and toxicology》2009,25(6):545-560
There is a growing body of evidence showing that vitamin A induces toxic effects in several experimental models and in human beings. In the present work, we have investigated the effects of short-term vitamin A supplementation on the adult rat liver redox status. We have found that vitamin A at therapeutic doses induces a hepatic oxidative insult. Furthermore, we have observed increased antioxidant enzyme activity in the liver of vitamin-A-treated rats. Additionally, some mitochondrial dysfunction was found since superoxide anion production was increased in vitamin-A-treated rat liver submitochondrial particles, which may be the result of impaired mitochondrial electron transfer chain activity, as assessed here. We have also isolated rat liver mitochondria and challenged it with 75 μM CaCl2, a non-oxidant agent that is able to induce mitochondrial oxidative stress indirectly. We have found that mitochondria isolated from vitamin-A-treated rat liver are more sensitive to CaCl2 than control mitochondria regarding the redox status. Importantly, vitamin A seems to alter mitochondrial redox status independently of the participation of the mitochondrial permeability transition pore, which is activated by Ca2+ ions since cyclosporin A did not prevent the oxidative insult elicited by Ca2+ addition. Overall, we show here that mitochondria are a target of vitamin-A-associated toxicity also in vivo. 相似文献
170.
Outi Heikkinen Perttu Permi Harri Koskela Olli Carpén Jari Ylänne Ilkka Kilpeläinen 《Journal of biomolecular NMR》2009,44(2):107-112
Myotilin is a 57 kDa actin-binding and -bundling protein that consists of a unique serine-rich amino-terminus, two Ig-domains
and a short carboxy-terminus with a PDZ-binding motif. Myotilin localizes in sarcomeric Z-discs, where it interacts with several
sarcomeric proteins. Point mutations in myotilin cause muscle disorders morphologically highlighted by sarcomeric disarray
and aggregation. The actin-binding and dimerization propensity of myotilin has been mapped to the Ig-domains. Here we present
high-resolution structure of the first Ig-domain of myotilin (MyoIg1) determined with solution state NMR spectroscopy. Nearly
complete chemical shift assignments of MyoIg1 were achieved despite several missing backbone 1H-15N-HSQC signals. The structure derived from distance and dihedral angle restraints using torsion angle dynamics was further
refined using molecular dynamics. The structure of MyoIg1 exhibits I-type Ig-fold. The absence of several backbone 1H-15N-HSQC signals can be explained by conformational exchange taking place at the hydrophobic core of the protein.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献