全文获取类型
收费全文 | 297篇 |
免费 | 18篇 |
专业分类
林业 | 34篇 |
农学 | 9篇 |
57篇 | |
综合类 | 56篇 |
农作物 | 13篇 |
水产渔业 | 21篇 |
畜牧兽医 | 84篇 |
园艺 | 8篇 |
植物保护 | 33篇 |
出版年
2023年 | 1篇 |
2022年 | 10篇 |
2021年 | 12篇 |
2020年 | 21篇 |
2019年 | 11篇 |
2018年 | 7篇 |
2017年 | 18篇 |
2016年 | 8篇 |
2015年 | 13篇 |
2014年 | 16篇 |
2013年 | 11篇 |
2012年 | 31篇 |
2011年 | 34篇 |
2010年 | 23篇 |
2009年 | 7篇 |
2008年 | 22篇 |
2007年 | 12篇 |
2006年 | 11篇 |
2005年 | 10篇 |
2004年 | 8篇 |
2003年 | 11篇 |
2002年 | 4篇 |
2001年 | 1篇 |
2000年 | 4篇 |
1991年 | 2篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1975年 | 1篇 |
1973年 | 1篇 |
1959年 | 1篇 |
1952年 | 1篇 |
1950年 | 1篇 |
排序方式: 共有315条查询结果,搜索用时 31 毫秒
41.
Johannes Stoffels Sebastian Mader Joachim Hill Willy Werner Godehard Ontrup 《European Journal of Forest Research》2012,131(4):1071-1089
Due to high variation in forest communities, forest structure and the fragmentation of the forested area in Central Europe, satellite-based forest inventory methods have to meet particularly high-quality requirements. This study presents an innovative method to combine official forest inventory information at stand level with multidate satellite imagery using a spatially adaptive classification approach for producing wall-to-wall forest cover maps of important tree species and management classes across multiple ownership regions in a heterogeneous low mountain range in Germany. The classification approach was applied to a 5,200-km2 area (about 2,080?km2 of forest land, mostly mixed forests) located in the Eifel mountain range in Central Europe. In comparison with conventional classifiers, our results demonstrate a significant increase in classification accuracy in the order of 12%. The method was tested with ASTER images but holds the potential to be used for regular state forest inventories based on standard and novel earth observation data supplied for instance from the SPOT-5 and RapidEye sensors. 相似文献
42.
The objective of the present research was to determine the effect of increasing and decreasing natural photoperiods on selected parameters of boar ejaculates. The study material consisted of 17 boars: six Polish Large White (PLW) breed, five Polish Landrace (PL) breed, and six Duroc×Pietrain (D×P) crossbreed, all aged between 8 and 12 months at the beginning of the research. Analyses were conducted on 612 ejaculates, which were collected in two experimental periods: an increasing photoperiod (IP) (January–June) and a decreasing photoperiod (DP) (July–December). A statistically proven impact of photoperiod on the volume of semen was observed in all the studied breeds (P=0.004). During the decreasing photoperiod the mean volume of semen was 261.16±75.20 ml and this was almost 17 ml higher than that for the increasing period. For boars involved in the experiment, day length also had a significant impact on the total number of motile spermatozoa (P=0.037). In the increasing photoperiod the mean number was 3.26×109 lower. A decreasing photoperiod has a positive affect on both boars and the parameters of the collected ejaculates, which were observed in the higher number of insemination doses per ejaculate. Between the different breeds, the reactions of boars to photoperiod differed and the most significant influence of photoperiod on semen parameters was noted among D×P breed boars. Least susceptible to changes in day length were PLW breed boars. 相似文献
43.
Martin J Schmidt Antje Wigger Sebastian Jawinski Tanja Golla Martin Kramer 《Veterinary radiology & ultrasound》2008,49(5):472-476
Ultrasonographic evaluation of the spine, especially of the spinal cord, has been rarely reported in dogs. The atlanto-occipital junction provides a small acoustic window through which examination of the craniocervical transition can be performed. Normal sonographic findings of this region in 10 normal brachycephalic dogs are presented and compared with sonographic findings from 25 Cavalier King Charles Spaniels with the caudal occipital malformation syndrome. Sonographic findings were compared with magnetic resonance imaging findings to determine the extent of cerebellar herniation and syringohydromyelia. Cerebellar displacement into the foramen magnum was clearly identified sonographically; however, syringohydromyelia was not discernable due to bone overlay. 相似文献
44.
Sebastian Gasparis Maciej Kała Mateusz Przyborowski Leszek A. Łyżnik Wacław Orczyk Anna Nadolska-Orczyk 《Plant methods》2018,14(1):111
Background
Genome editing of monocot plants can be accomplished by using the components of the CRISPR/Cas9 (clustered regularly interspaced short palindromic repeat/CRISPR associated Cas9) technology specifically optimized for these types of plants. Here, we present the development of RNA-guided Cas9 system for simplex and multiplex genome editing in barley.Results
We developed a set of customizable RNA-guided Cas9 binary vectors and sgRNA modules for simplex and multiplex editing in barley. To facilitate the design of RNA-guided Cas9 constructs, the pBract derived binary vectors were adapted to Gateway cloning and only one restriction enzyme was required for construction of the sgRNA. We designed a synthetic, codon optimized Cas9 gene containing the N terminal SV40 nuclear localization signal and the UBQ10 Arabidopsis 1st intron. Two different sgRNAs were constructed for simplex editing and one polycistronic tRNA-gRNA construct (PTG) for multiplex editing using an endogenous tRNA processing system. The RNA-guided Cas9 constructs were validated in transgenic barley plants produced by Agrobacterium-mediated transformation. The highest mutation rate was observed in simplex editing of the cytokinin oxidase/dehydrogenase HvCKX1 gene, where mutations at the hvckx1 locus were detected in 88% of the screened T0 plants. We also proved the efficacy of the PTG construct in the multiplex editing of two CKX genes by obtaining 9 plants (21% of all edited plants) with mutations induced in both HvCKX1 and HvCKX3. Analysis of the T1 lines revealed that mutations in the HvCKX1 gene were transmitted to the next generation of plants. Among 220 screened T1 plants we identified 85 heterozygous and 28 homozygous mutants, most of them bearing frameshift mutations in the HvCKX1 gene. We also observed independent segregation of mutations and the Cas9-sgRNA T-DNA insert in several T1 plants. Moreover, the knockout mutations of the Nud gene generated phenotype mutants with naked grains, and the phenotypic changes were identifiable in T0 plants.Conclusions
We demonstrated the effectiveness of an optimized RNA-guided Cas9 system that can be used for generating homozygous knockout mutants in the progeny of transgenic barely plants. This is also the first report of successful multiplex editing in barley using a tRNA processing system.45.
Daub Matthias Hakl Ulrike Molendijk Leendert PG Schomaker Corrie Been Thomas H van Beers Thea G Jivishova Sevda Jivishov Emil Keusgen Michael Bluemel Roman Fischer Daniel Grundler Florian MW Reuther Marie Cappel Sabrina Bauer Harald Lang Christian Watrin Cliff den Nijs Loes JMF Van Bruggen Anne-Sophie Karssen Gerrit Kiewnick Sebastian Büchler Urs Roth Irma Frey Jürg 《植物病害和植物保护杂志》2015,122(4):189-193
Journal of Plant Diseases and Protection - 相似文献
46.
47.
Josef Kohler Brigitte A. Knapp Sebastian Waldhuber Fuensanta Caravaca Antonio Roldán Heribert Insam 《Journal of Soils and Sediments》2010,10(8):1585-1597
Purpose
In this study, we investigated the effects of elevated atmospheric CO2, drought, and inoculation with a plant-growth-promoting rhizobacterium (PGPR) or an arbuscular mycorrhizal (AM) fungus on microbial community composition and functional diversity in the rhizosphere of Lactuca sativa L. cv. Tafalla. 相似文献48.
Chun-Sheng Wang Ji Zeng Sebastian Hein Zhi-Gang Zhao Jun-Jie Guo 《Scandinavian Journal of Forest Research》2017,32(8):679-687
Both crown and branch characteristics greatly affect tree growth and timber quality, and their development is closely related to planting density (PD). Here crown and branch attributes of Betula alnoides were investigated in a 14-year-old experimental plantation in southern China with five planting densities ranging from 500 to 3333 stems per hectare (sph). The results showed that high PD significantly reduced crown and branch sizes. The ratios of crown diameter to stem diameter at breast height at the stand level and for dominant and co-dominant trees were almost constant regardless of PD. PD also had no significant influence on the number and angle of branches, and only planting with the highest density significantly increased branch density and mortality. Insertion angle (IA) of dead branches was greater than that of live branches and these differences were significant at the two low planting densities (833 and 500?sph). Linear mixed models revealed that branch diameter (BD) was negatively correlated with its relative height in the crown and IA. The binary-logistic regression model indicated that branch status (live or dead) was codetermined by BD and PD. These findings can help farmers cultivate high-quality wood of B. alnoides and obtain a higher economic return. 相似文献
49.
Maike?Krauss Hans-Martin?KrauseEmail author Simone?Spangler Ellen?Kandeler Sebastian?Behrens Andreas?Kappler Paul?M?der Andreas?Gattinger 《Biology and Fertility of Soils》2017,53(1):49-59
Since the development of effective N2O mitigation options is a key challenge for future agricultural practice, we studied the interactive effect of tillage systems on fertilizer-derived N2O emissions and the abundance of microbial communities involved in N2O production and reduction. Soil samples from 0–10 cm and 10–20 cm depth of reduced tillage and ploughed plots were incubated with dairy slurry (SL) and manure compost (MC) in comparison with calcium ammonium nitrate (CAN) and an unfertilized control (ZERO) for 42 days. N2O and CO2 fluxes, ammonium, nitrate, dissolved organic C, and functional gene abundances (16S rRNA gene, nirK, nirS, nosZ, bacterial and archaeal amoA) were regularly monitored. Averaged across all soil samples, N2O emissions decreased in the order CAN and SL (CAN?=?748.8?±?206.3, SL?=?489.4?±?107.2 μg kg?1) followed by MC (284.2?±?67.3 μg kg?1) and ZERO (29.1?±?5.9 μg kg?1). Highest cumulative N2O emissions were found in 10–20 cm of the reduced tilled soil in CAN and SL. N2O fluxes were assigned to ammonium as source in CAN and SL and correlated positively to bacterial amoA abundances. Additionally, nosZ abundances correlated negatively to N2O fluxes in the organic fertilizer treatments. Soils showed a gradient in soil organic C, 16S rRNA, nirK, and nosZ with greater amounts in the 0–10 than 10–20 cm layer. Abundances of bacterial and archaeal amoA were higher in reduced tilled soil compared to ploughed soils. The study highlights that tillage system induced biophysicochemical stratification impacts net N2O emissions within the soil profile according to N and C species added during fertilization. 相似文献