全文获取类型
收费全文 | 223篇 |
免费 | 12篇 |
专业分类
林业 | 36篇 |
农学 | 11篇 |
基础科学 | 6篇 |
48篇 | |
综合类 | 11篇 |
农作物 | 10篇 |
水产渔业 | 31篇 |
畜牧兽医 | 56篇 |
园艺 | 8篇 |
植物保护 | 18篇 |
出版年
2023年 | 2篇 |
2022年 | 4篇 |
2021年 | 9篇 |
2020年 | 9篇 |
2019年 | 16篇 |
2018年 | 18篇 |
2017年 | 11篇 |
2016年 | 12篇 |
2015年 | 7篇 |
2014年 | 15篇 |
2013年 | 11篇 |
2012年 | 12篇 |
2011年 | 18篇 |
2010年 | 8篇 |
2009年 | 9篇 |
2008年 | 8篇 |
2007年 | 7篇 |
2006年 | 7篇 |
2005年 | 12篇 |
2004年 | 1篇 |
2003年 | 4篇 |
2002年 | 2篇 |
2001年 | 1篇 |
2000年 | 3篇 |
1999年 | 4篇 |
1995年 | 1篇 |
1994年 | 2篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1990年 | 4篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1985年 | 2篇 |
1982年 | 3篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1977年 | 2篇 |
1970年 | 1篇 |
1969年 | 3篇 |
1962年 | 1篇 |
排序方式: 共有235条查询结果,搜索用时 15 毫秒
91.
Marlene Roellig Augusta Costa Matteo Garbarino Jan Hanspach Tibor Hartel Simon Jakobsson Regina Lindborg Sabine Mayr Tobias Plieninger Marek Sammul Anna Varga Joern Fischer 《Strength and Conditioning Journal》2018,71(5):526-535
Europe’s woodland and savanna rangelands, often part of silvopastoral systems known as wood-pastures, are deteriorating because of abandonment that leads to return to a forested state or lack of tree regeneration from overgrazing or tree and shrub removal. Despite numerous local studies, there has been no broader survey of the stand structure of European wood-pastures showing which systems are at risk of losing their semiopen character. This overview aims to 1) show some of the differences and similarities in wood-pastures from landscapes across Europe and 2) identify which of these wood-pastures are at risk of losing their semiopen character. We collated a dataset of 13 693 trees from 390 plots in wood-pastures from eight different European regions (western Estonia, eastern Greece, northern Germany, Hungary, northern Italy, southern Portugal, central Romania, and southern Sweden), including tree diameters at breast height, tree density, management type, and tree species composition. On the basis of their structural characteristics, we classified wood-pastures using principal component analysis (PCA) and cluster analysis. The PCA showed a gradient from dense wood-pastures with high levels of regeneration (e.g., in Estonia) to sparse wood-pastures with large trees but a lack of regeneration (e.g., in Romania). Along this gradient, we identified three main groups of wood-pastures: 1) sparse wood-pastures with mostly big trees; 2) dense wood-pastures composed of small trees, and 3) wood-pastures containing a wide range of tree ages. Our results show a large structural gradient in European wood-pastures, as well as regeneration problems varying in their severity, highlighting the importance of social-ecological context for wood-pasture conditions. To maintain the ecological and cultural integrity of European wood-pastures, we suggest 1) more comprehensively considering them in European policies such as the Common Agricultural Policy and EU Habitats Directive, while 2) taking into account their structural characteristics and social-ecological backgrounds. 相似文献
92.
Floortje Vodde Kalev Jõgiste Yasuhiro Kubota Timo Kuuluvainen Kajar Köster Aljona Lukjanova Marek Metslaid Toshiya Yoshida 《Journal of Forest Research》2011,16(3):155-167
We reviewed studies dealing with regeneration under variable conditions in boreal and hemiboreal forests as affected by different
microsite types by tree species functional groups. Generally, the importance of storm-induced microsites for regeneration
dynamics in boreal forests depends on several factors: (1) distribution and type of microsites (generated by storm characteristics
and stand conditions); (2) viable seed supply (stand history, species dispersal traits and status of surviving trees) and
their species’ life history strategy; (3) climatic and site conditions (pre-storm conditions and storm-induced changes); and
(4) delayed storm effects, such as retarded falling of trees, favoured vegetation growth, etc. Studies acknowledging the significance
of microsites were mostly related to intermediate or severe events, causing sufficient changes in resource levels and growth
conditions, and influencing extrinsic factors such as frost heaving, erosion and browsing. Also, the dispersal traits of available
tree species, including sprouting and response of surviving trees, such as canopy expansion, should be considered in evaluating
microsite importance in individual cases. In intermediate to severe windstorm events, pioneer species are generally profiting
most from the additional offer in microsites, requiring bare mineral soil and elevated locations for their establishment and
growth. Under gap dynamics, shade-tolerant species benefit from dead wood and elevated locations as these offer safe sites
in stands with abundant understorey vegetation. 相似文献
93.
Marek Kolenčík Hana Vojtková Martin Urík Mária Čaplovičová Jaromír Pištora Michael Cada Aneta Babičová Huan Feng Yu Qian Illa Ramakanth 《Water, air, and soil pollution》2017,228(6):224
Artificial adamite [Zn2(AsO4)(OH)] is a convenient structural model because it is isostructural with other rock-forming minerals in secondary ore deposits formed in cementation zones. Microbial activity in these zones accelerates mineral biogeochemical deterioration and metal release, and our results confirmed that Pseudomonas, Rhodococcus and Cupriavidus strains accelerate adamite leaching by 10 to 465 times compared to controls. Here, the Pseudomonas chlororaphis ZK-1 bacterial strain in a static 42-day cultivation proved more effective than Rhodococcus and Cupriavidus by leaching over 90% arsenic and 10% zinc from adamite in one-step in vitro. We evaluated adamite with the VESTA visualization system for electronic and structural analysis, and our results enhance understanding of zinc and arsenic biogeochemical cycles and mobilization, and highlight bacteria’s beneficial natural and biotechnological application in environmental geochemistry and biohydrometallurgy. 相似文献
94.
Findoráková Lenka Šestinová Oľga Matik Marek Hančuľák Jozef Bureš Radovan 《Journal of Soils and Sediments》2022,22(9):2448-2458
Journal of Soils and Sediments - To evaluate the ecological risk, physico-chemical properties, and the impact of anthropogenic sources on permanent eighteen samples of grass vegetation soils (PGVS)... 相似文献
95.
Otomar Linhart Marek Rodina Martin Flajshans Nicola Mavrodiev Jana Nebesarova David Gela Martin Kocour 《Aquaculture International》2006,14(1-2):9-25
The tench Tinca tinca is an interesting fish from the viewpoint of polyploidy and related atypical reproduction aspects. Triploid tench were produced
artificially. Studies of spermiation as well as of sperm motility and structure were performed on several triploid and diploid
males simultaneously with individual experimental crosses with diploid females to define their reproductive capacities. The
testes of triploids visually looked less developed in the most of cases with lower sperm production (0.05 cm3 sperm per male), GSI and weight of testes compared to diploids (0.58 cm3 sperm per male). Analysis of variance showed significant influence of ploidy level on the percentage of motile spermatozoa.
Triploidy did not change percentage of live spermatozoa and velocity of spermatozoa at the first time of sperm movement. The
study of sperm structure by scanning electron microscopy revealed that most sperm cells were of normal structure with some
anomalies. Sperm heads of triploid and diploid males were mostly round-shaped, 1.86±0.2 and 1.6±0.18 μm in diameter. The midpiece
of triploid spermatozoa was slightly narrower than that of diploid ones with typical cylindrical shape. Flow cytometry revealed
sperm cells of triploids to be largely aneuploid (1.47 n) with high mosaic DNA, oscillating from haploid DNA content (1.0 n)
to diploid DNA content (1.9 n). Experimental crosses between triploid males and diploid females revealed that these males
were capable to stimulate effective development with relatively high level of fertilization and hatching rates from 0 to 70%.
In conclusion, triploidization does not seem to guarantee sterility of tench. 相似文献
96.
A ratio of crop evapotranspiration (ETC) to reference evapotranspiration (ETO) determines a crop coefficient (KC) value, which is related to specific crop phenological development to improve transferability of the KC values. Development of KC can assist in predicting crop irrigation needs using meteorological data from weather stations. The objective of the research was conducted to determine growth-stage-specific KC and crop water use for maize (Zea Mays) and sorghum (Sorghum bicolor) at Texas AgriLife Research field in Uvalde, TX, USA from 2002 to 2008. Seven lysimeters, weighing about 14 Mg, consisted of undisturbed 1.5 m × 2.0 m × 2.2 m deep soil monoliths. Six lysimeters were located in the center of a 1-ha field beneath a linear-move sprinkler system equipped with low energy precision application (LEPA). A seventh lysimeter was established to measure reference grass ETO. Crop water requirements, KC determination, and comparison to existing FAO KC values were determined over a 3-year period for both maize and sorghum. Accumulated seasonal crop water use ranged between 441 and 641 mm for maize and between 491 and 533 mm for sorghum. The KC values determined during the growing seasons varied from 0.2 to 1.2 for maize and 0.2 to 1.0 for sorghum. Some of the values corresponded and some did not correspond to those from FAO-56 and from the Texas High Plains and elsewhere in other states. We assume that the development of regionally based and growth-stage-specific KC helps in irrigation management and provides precise water applications for this region. 相似文献
97.
The Bursaphelenchus genus (Nematoda: Parasitaphelenchidae) comprises mostly wood‐inhabiting nematodes that feed on various tree‐colonizing fungi. One species of the genus, B. xylophilus, has been proven as an agent causing pine wilt disease (PWD). However, involvement of other Bursaphelenchus species in the PWD remains enigmatic. In the current paper, comparative molecular analysis is performed based on nuclear ribosomal DNA (rDNA) of B. vallesianus, a species that was recently isolated from pine trees (Pinus sylvestris) exhibiting wilting and declining symptoms in the Czech Republic. Sequencing of the nuclear‐encoded ITS1–5·8S–ITS2 rDNA region confirmed previous taxonomic conclusions based on morphology. Evolutionary reconstructions resulted in a phylogenetic tree, where the Czech isolate of B. vallesianus occupied a common clade together with other species belonging to the so‐called B. sexdentati group. Unexpectedly, comprehensive analysis of the sequence data revealed a genetic variation distinguishing the Czech isolate of B. vallesianus from all other species of the B. sexdentati group. This dissimilarity consists of the presence of a four nucleotide exchange found in the 5·8S rRNA‐coding gene. The newly identified genetic variation appears to affect the 5·8S rRNA folding, as deduced from secondary structure models. Additionally, it is shown that for the first time, to the authors’ knowledge, both bursaphelenchid internal transcribed spacers (ITS1 and ITS2) fold into the multibranched closed loops. While the ITS2 closed loop is formed with help of canonical 5·8S‐28S rRNA pairing, the ITS1 forms the thermodynamically stable closed loop with no support of flanking rRNA sequences. The current information on bursaphelenchid ITS rDNA sequence diversity and structure is further discussed. 相似文献
98.
Jędrysek Mariusz O. Krąpiec Marek Skrzypek Grzegorz Kałużny Adam 《Water, air, and soil pollution》2003,145(1-4):359-375
Water, Air, &; Soil Pollution - Carbon isotope analyses of peat profiles from the Karkonosze Mts. (SW Poland) and tree-ring cellulose from Wis?a river valley in the Kraków region (S... 相似文献
99.
Marek Uliasz 《Water, air, and soil pollution》1988,40(1-2):33-49
A Fourier Amplitude Sensitivity Test (FAST) is applied to study uncertainty of the EMEP-W atmospheric model of long range transport of S in Europe. The FAST method requires frequency distribution of model parameters as input data and provides the following results: (i) mean value of the model output, (ii) variance of the model output which characterizes the parameter uncertainty of the model, and (iii) partial variances of the model output which are the measures of the model sensitivity to uncertainties in individual input parameters. A mathematical formulation of the FAST method and approximations used in its computer implementation is presented. The application requires an extension of the original method to evaluate the model output frequency distribution for different forms of prescribed frequency distributions for parameters. The computer program allows one to apply the FAST method for an arbitrary mathematical model with different options defined by the user. Some examples of uncertainty analysis of the EMEP model using real meteorological and emission data are described and compared with results obtained by the Monte-Carlo method. 相似文献
100.