全文获取类型
收费全文 | 2521篇 |
免费 | 212篇 |
专业分类
林业 | 158篇 |
农学 | 74篇 |
基础科学 | 3篇 |
627篇 | |
综合类 | 175篇 |
农作物 | 66篇 |
水产渔业 | 366篇 |
畜牧兽医 | 1063篇 |
园艺 | 48篇 |
植物保护 | 153篇 |
出版年
2023年 | 21篇 |
2022年 | 18篇 |
2021年 | 34篇 |
2020年 | 42篇 |
2019年 | 31篇 |
2018年 | 94篇 |
2017年 | 88篇 |
2016年 | 95篇 |
2015年 | 69篇 |
2014年 | 87篇 |
2013年 | 211篇 |
2012年 | 159篇 |
2011年 | 170篇 |
2010年 | 107篇 |
2009年 | 49篇 |
2008年 | 126篇 |
2007年 | 127篇 |
2006年 | 129篇 |
2005年 | 134篇 |
2004年 | 132篇 |
2003年 | 124篇 |
2002年 | 127篇 |
2001年 | 81篇 |
2000年 | 79篇 |
1999年 | 49篇 |
1998年 | 25篇 |
1997年 | 21篇 |
1996年 | 25篇 |
1995年 | 41篇 |
1994年 | 25篇 |
1993年 | 27篇 |
1992年 | 24篇 |
1991年 | 17篇 |
1990年 | 10篇 |
1989年 | 10篇 |
1988年 | 9篇 |
1987年 | 6篇 |
1986年 | 4篇 |
1985年 | 7篇 |
1984年 | 12篇 |
1983年 | 12篇 |
1982年 | 4篇 |
1980年 | 8篇 |
1979年 | 5篇 |
1977年 | 8篇 |
1976年 | 7篇 |
1975年 | 5篇 |
1972年 | 3篇 |
1969年 | 6篇 |
1966年 | 4篇 |
排序方式: 共有2733条查询结果,搜索用时 15 毫秒
1.
2.
3.
4.
Summary Results from a cooperative breeding programme with timothy for the northern areas of Scandinavia are presented. The main aim of the programme was to identify genotypes for synthetic populations that are high yielding, adapted over the whole area and stable over years. A polycross comprising 12 genotypes from each of five sites within the region was formed. The subsequent 60 half-sib families and four reference varieties were then compared under sward conditions at the same sites. The trials lasted for three years and results for total dry matter yields are presented.Significant differences in yield between lines were found. There were also significant two and three factor interactions between lines, sites and years. A new two-step procedure is presented to select the genotypes to make up a synthetic variety. Firstly, a superiority measure (Q-value) is used to select a group of genotypes that are high yielding and stable over sites and years. Secondly, the GxE part of the Q-value is split into two terms. One measures adaptation to predictable environmental conditions. The other one measures stability to unpredictable changes in the environment. A plot of these two measures provides a tool for discarding unstable or poorly adapted genotypes. The statistical properties of the selection parameters are discussed. 相似文献
5.
6.
An in vivo experiment was conducted to evaluate the effects of tetracycline and zinc on pig colonization and transmission of methicillin-resistant Staphylococcus aureus (MRSA) sequence type (ST) 398. Eight piglets naturally colonized with MRSA ST398 and 8 MRSA-negative piglets of the same age and breed were assigned to three groups treated with tetracycline and zinc (Group 1), zinc (Group 2) or tetracycline alone (Group 3) and one non-treated group (Group 4), each containing two MRSA-positive and two MRSA-negative animals. Two additional non-treated control groups composed of only MRSA-positive (Group 5) and MRSA-negative (Group 6) animals were used to check for stability of MRSA carriage status. Nasal swabs and environmental wipes were collected on Days 0, 7, 14, and 21, and the occurrence of MRSA in each sample was quantified by bacteriological counts on Brilliance? MRSA agar. Significantly higher nasal MRSA counts were observed in the zinc-treated (p=0.015) and tetracycline-treated (p=0.008) animals compared to the non-treated animals. Environmental MRSA counts appeared to increase over time in Groups 1 and 2 but such an increase was not statistically significant. MRSA-negative animals housed with MRSA-positive animals became positive in all groups, whereas the carriage status of the animals in Groups 5 and 6 did not change. This study demonstrates that feed supplemented with tetracycline or zinc increases the numbers of MRSA ST398 in the nasal cavity of pigs. Transmission of MRSA from positive to negative animals housed within the same pen was not influenced by exposure to these agents. 相似文献
7.
Silvina Fernández A Henningsen E Larsen M Nansen P Grønvold J Søndergaard J 《Equine veterinary journal》1999,31(6):488-491
An experiment was carried out in 1997 to test the efficacy of an isolate of the microfungus Duddingtonia flagrans against free-living stages of horse strongyles under conditions in the field and to assess the eventual effect of the fungus on the normal degradation of faeces. Faecal pats were made from faeces of a naturally strongyle infected horse, which had been fed fungal material at a dose level of 106 fungal unit/kg bwt. Control pats without fungi were made from faeces collected from the same animal just before being fed fungi. Faecal cultures set up for both groups of faeces to monitor the activity of the fungus under laboratory conditions showed that the fungus significantly reduced the number of infective third-stage larvae (L3) by an average of 98.4%. Five faecal pats from each batch of faeces were deposited on pasture plots at 3 times during spring-summer. The herbage around each pat was sampled fortnightly to recover L3 transmitted from faeces. The results showed that the herbage infectivity around fungus-treated pats was reduced by 85.8-99.4%. The remaining faecal material at the end of each sampling period was collected, and the surviving L3 were extracted. Significantly fewer larvae were recovered from the fungus-treated pats. Analysis of wet and dry weight of the collected pats, as well as their organic matter content, were performed to compare the degradation of faeces of both groups. The results indicated that the presence of the fungus did not alter the degradation of the faeces. 相似文献
8.
Hjulsager CK Grau-Roma L Sibila M Enøe C Larsen L Segalés J 《Veterinary microbiology》2009,133(1-2):172-178
Several real-time PCR assays for quantification of PCV2 DNA (qPCR) have been described in the literature, and different in-house assays are being used by laboratories around the world. A general threshold of 10(7) copies of PCV2 per millilitre serum for postweaning multisystemic wasting syndrome (PMWS) diagnosis has been suggested. However, neither inter-laboratory nor inter-assay comparisons have been published so far. In the present study, two different qPCR probe assays used routinely in two laboratories were compared on DNA extracted from serum, nasal and rectal swabs. Results showed a significant linear association between the assays (p<0.0001), and a systematic difference of 1.4 log10 copies of PCV2 per millilitre of sample (p<0.0001). This difference indicated that the assay from laboratory 1 yielded a higher output than the one from laboratory 2. Results also showed that there was no linear association between the amount of PCV2 DNA and the amount of total DNA, neither in nasal (p=0.86) nor in rectal (p=0.78) swabs, suggesting that normalizing of PCV2 DNA load in swab samples to total DNA concentration is not suitable. The present exploratory study highlights the need for the performance of ring trials on qPCV2 protocols between laboratories. Meanwhile, the proposed thresholds for PMWS diagnosis should only be considered reliable for each particular laboratory and each particular assay. 相似文献
9.
10.
Kirsch P Jores J Wieler LH 《Berliner und Münchener tier?rztliche Wochenschrift》2004,117(3-4):116-129
Many bacterial virulence attributes, like toxins, adhesins, invasins, iron uptake systems, are encoded within specific regions of the bacterial genome. These in size varying regions are termed pathogenicity islands (PAIs) since they confer pathogenic properties to the respective micro-organism. Per definition PAIs are exclusively found in pathogenic strains and are often inserted near transfer-RNA genes. Nevertheless, non-pathogenic bacteria also possess foreign DNA elements that confer advantageous features, leading to improved fitness. These additional DNA elements as well as PAIs are termed genomic islands and were acquired during bacterial evolution. Significant G+C content deviation in pathogenicity islands with respect to the rest of the genome, the presence of direct repeat sequences at the flanking regions, the presence of integrase gene determinants as other mobility features,the particular insertion site (tRNA gene) as well as the observed genetic instability suggests that pathogenicity islands were acquired by horizontal gene transfer. PAIs are the fascinating proof of the plasticity of bacterial genomes. PAIs were originally described in human pathogenic Escherichia (E.) coli strains. In the meantime PAIs have been found in various pathogenic bacteria of humans, animals and even plants. The Locus of Enterocyte Effacement (LEE) is one particular widely distributed PAI of E coli. In addition, it also confers pathogenicity to the related species Citrobacter (C.) rodentium and Escherichia (E.) alvei. The LEE is an important virulence feature of several animal pathogens. It is an obligate PAI of all animal and human enteropathogenic E. coli (EPEC), and most enterohaemorrhegic E. coli (EHEC) also harbor the LEE. The LEE encodes a type III secretion system, an adhesion (intimin) that mediates the intimate contact between the bacterium and the epithelial cell, as well as various proteins which are secreted via the type III secretion system. The LEE encoded virulence features are responsible for the formation of so called attaching and effacing (AE) lesions in the intestinal epithelium. Due to its wide distribution in animal pathogens, LEE encoded antigens are suitable vaccine antigens. Acquisition and structure of the LEE pathogenicity island is the crucial point of numerous investigations. However, the evolution of the LEE, its origin and further spread in E. coli, are far from being resolved. 相似文献