首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   189篇
  免费   7篇
林业   40篇
农学   3篇
基础科学   1篇
  42篇
综合类   28篇
农作物   8篇
水产渔业   11篇
畜牧兽医   38篇
园艺   5篇
植物保护   20篇
  2022年   1篇
  2021年   10篇
  2020年   1篇
  2019年   3篇
  2018年   2篇
  2017年   4篇
  2016年   10篇
  2015年   1篇
  2014年   4篇
  2013年   12篇
  2012年   6篇
  2011年   15篇
  2010年   7篇
  2009年   5篇
  2008年   12篇
  2007年   16篇
  2006年   5篇
  2005年   7篇
  2004年   7篇
  2003年   5篇
  2002年   7篇
  2001年   5篇
  2000年   5篇
  1999年   1篇
  1998年   2篇
  1997年   1篇
  1996年   1篇
  1995年   5篇
  1991年   3篇
  1990年   1篇
  1989年   2篇
  1987年   3篇
  1983年   1篇
  1982年   3篇
  1979年   2篇
  1975年   3篇
  1973年   1篇
  1972年   1篇
  1969年   1篇
  1967年   3篇
  1966年   1篇
  1958年   1篇
  1957年   1篇
  1956年   1篇
  1955年   2篇
  1954年   1篇
  1953年   1篇
  1942年   1篇
  1936年   1篇
  1913年   1篇
排序方式: 共有196条查询结果,搜索用时 31 毫秒
1.
2.
Cutaneous leiomyosarcomas are malignant mesenchymal tumors of smooth muscle origin and are reported occasionally in avian species. A 14-y-old male laboratory White Carneau pigeon (Columba livia) was presented for surgical excision of a cervical soft tissue mass. Ultrasonography with color flow Doppler imaging revealed multiple cavitations of mixed echogenicity within the mass and vascularization. Histologically, the dermis and subcutis were expanded by a densely cellular multinodular mass comprised of fusiform cells forming haphazardly arranged broad streams and short interwoven bundles, often surrounding blood vessels and variably sized cavitations. Neoplastic cells were strongly immunopositive for desmin and α–smooth muscle actin, and negative for pancytokeratin, S100, and von Willebrand factor. Based on histopathology and IHC findings, the cutaneous mass was diagnosed as leiomyosarcoma (LMS). The pigeon died 312 d post-operatively. Postmortem examination revealed masses infiltrating the left and right pulmonary airways and one hepatic nodule, but no regrowth at the surgical site. Histologic and IHC evaluation of the pulmonary and hepatic masses were consistent with LMS, representing metastatic foci from the primary cutaneous LMS. Our case highlights the malignant behavior and histomorphologic features of cutaneous LMS in an avian species.  相似文献   
3.
Infectious bronchitis (IB) disease progression in vaccinated chickens after challenge was evaluated in a single commercial line of layer chickens presenting two different major histocompatibility complex (MHC) B complex genotypes. MHC B genotypes were determined by DNA sequence-based typing of BF2 alleles. In total, 33 B2/B15 and 47 B2/B21 chickens were vaccinated with an Ark-type IB virus (IBV) attenuated vaccine and challenged with Ark-type IBV field isolate AL/4614/98 14 days later. Additional chickens of both genotypes served as unvaccinated/challenged and unvaccinated/nonchallenged controls. Clinical signs, histopathologic analysis, detection of IBV genomes in tears, and IBV-specific immunoglobulin A (IgA) in tears were used to evaluate disease progression and immune response. The incidence of IBV respiratory signs was significantly higher in B2/21 than in B2/B15 MHC genotype birds. However, neither the severity and duration of respiratory signs nor the severity and incidence of histologic lesions differed significantly with MHC genotype. The levels of IBV-specific IgA in tears of vaccinated and challenged chickens did not differ significantly between MHC genotypes. IBV genomes were present in the tears of vaccinated and challenged birds, and the incidence of detectable IBV genomes did not vary significantly with MHC B genotype. From an applied perspective, these results indicate that vaccinated commercial outbred chickens with these MHC genotypes are equally resistant to IBV.  相似文献   
4.
A total of 32 select line (SL) and 32 control line (CL) Duroc pigs were used in two trials to determine the effect of dietary amino acid contents during the grower (G) phase and selection for lean growth efficiency on growth performance, carcass traits, and meat quality. In each trial, pigs weighing 20 kg were assigned to 16 pens with two gilts or two castrated males per pen, and pens were randomly assigned within the genetic line to corn-soybean meal G diets formulated to contain 5.0, 7.0, 9.0, or 11.0 g lysine/kg. After 50 kg, all pigs were fed common finisher 1 (F1) and finisher 2 (F2) diets. Pigs were allowed ad libitum access to feed and water. After the initial statistical analyses, the data sets from the two trials were combined. During the G phase, pigs consumed less feed [linear (Ln), P < 0.001] and more lysine (Ln, P < 0.001), grew faster (Ln, P < 0.05) but utilized feed more and lysine less efficiently (Ln, P < 0.001) for weight gain as the amino acid content of G diets increased. Increasing dietary amino acids resulted in less ultrasound backfat (Ln, P < 0.001) and more serum urea nitrogen [Ln, P < 0.001; quadratic (Qd), P < 0.01] at the end of the G phase. Pigs grew more slowly during the F1 (Ln, P < 0.01 and Qd, P = 0.05) and F2 (Ln, P = 0.07) phases and utilized feed and lysine less efficiently (Ln, P < 0.05) for weight gain during the F1 phase as the amino acid content of G diets increased. The grower diet had no effect on overall weight gain and feed efficiency, carcass traits, or meat quality scores. The efficiency of lysine utilization for overall weight gain (Ln, P < 0.001) and lean accretion (Ln, P < 0.05) improved as the amino acid content of G diets decreased. The SL pigs grew faster (P < 0.05) and had less (P < 0.001) ultrasound backfat throughout the study compared with the CL pigs. The SL pigs had less 10th rib backfat (P < 0.001) and tended to have larger longissimus muscle area (P = 0.09) than the CL pigs, which were reflected in greater rate (P < 0.001) and efficiency (P < 0.05) of lean accretion. Marbling (P < 0.05) and meat color (P = 0.07) scores were lower in the SL pigs. No grower diet x genotype interactions were observed in response criteria of interest. The results indicate that pigs subjected to dietary amino acid restrictions during the G phase (as low as 5.0 g lysine/kg) compensated completely in terms of growth rate and body composition regardless of the genotype. Compensatory growth can have a positive impact not only on the overall efficiency of pig production but also on the environment by reducing excretion of unused nutrients.  相似文献   
5.
6.
7.
8.
Three rapid agglutination assays for the identification of Staphylococcus aureus Monostaph (Bionor A/S, Skien, Norway), Staphyslide-Test (BioMerieux, Lyon, France) and Staph-Rapid-Test (Roche, Basel, Switzerland), were compared. A total of 104 Gram-positive, catalase positive cocci were tested: Nineteen Staphylococcus reference strains comprising 15 spp. (4 strains were coagulase positive), and 7 Micrococcus reference strains comprising 4 spp.; 22 food isolates comprising 13 S. aureus, 8 coagulase positive Staphylococcus spp., and 1 Micrococcus sp.; 56 animal isolates comprising 11 S. aureus, 9 S. hyicus subsp. hyicus, 2 S. intermedius, 15 coagulase positive and 19 coagulase negative Staphylococcus spp. Totally 54 strains were coagulase positive. Considering agglutination of a coagulase positive strain as a correct identification, Monostaph, Staph-Rapid-Test, and Staphyslide-Test correctly identified 52 (96.3%), 47 (87.0%) and 48 (89.0%) of the coagulase positive staphylococci, respectively. Monostaph, Staph-Rapid-Test and Staphyslide-Test showed 1 (2.0%), 4 (8.0%) and 4 (8.0%) false positive reactions respectively. Monostaph, Staph-Rapid-Test and Staphyslide-Test gave 0 (0.0%), 6 (5.8%) and 7 (6.7%) non-interpretable reactions, respectively. Monostaph may be a good alternative to the tube-coagulase test for rapid and reliable identification of coagulase positive staphylococci from both food and veterinary sources. However, false negative reactions may occur with coagulase positive strains of S. hyicus subsp. hyicus and S. intermedius.  相似文献   
9.
Feed samples checked for the mycotoxins zearalenone and ochratoxin A from the harvest 1987 were positive at a markedly higher percentage (37.5%) compared to previous years, which is explained by the especially unfavourable harvesting conditions of 1987. In certain herd problems affecting the digestive or respiratory tract, mycotoxins could be detected with a much higher frequency (64.7% and 50.0% respectively). The mean level detected in feed samples by thin layer chromatography ranged within 30.3 ppb for zearalenone and within 58.3 ppb for ochratoxin A. In most cases there was a history of infertility. Considering the clinical situation, which is presented comparatively in herds with positive mycotoxin results, the possible involvement of mycotoxins in the disease, even at very low concentrations, is pointed out. In this context, zearalenone is incriminated of being an indicator of a multitoxic process besides its own direct effects. According to own experiences low levels of zearalenone in the range of 20-50 ppb in the feed have to be considered hazardous. If changing of pig feed in cases of herd problems will be recommended, a level of less than 10 ppb of zearalenone, especially in sow and piglet rations, should not be exceeded. Same may be valid to ochratoxin A.  相似文献   
10.
Forest biodiversity is highly linked with the occurrence of certain forest development phases (fdp) within the forest life cycle. Generally, the disintegration phase provides the highest biodiversity. The objective of the study was to test different existing forest life cycle assessment approaches aiming at developing a common reliable fdp assessment method. We tested and compared three approaches to record fdp in beech, mixed beech and spruce forests, in managed and unmanaged forests, and in four different plot sizes ranging from 125 to 2000 m2. The main results of the fdp comparison are as follows:
(1)
In approximately two thirds of the cases the three considered methods did not yield a corresponding fdp record.
(2)
Generally, the larger the plot sizes, the larger the average fdp deviation in forest reserves.
(3)
The fdp deviation is stronger in beech or spruce dominated forest reserves than in mixed beech forest reserves.
(4)
Plots of 500 m2 show most distinct numbers of microhabitats corresponding to the fdp sequence within the forest life cycle.
(5)
Furthermore, the managed forests mostly show lower fdp deviation than the forest reserves.
One approach resulted in the most differentiated portrayal of the studied forest structures compared to the other two as shown by the facts that, (a) the studied forests are seen to be divided up into more fdp than when applying the other two methods, and that (b) the dominant fdp changed depending on the forest community and plot size reflecting different growth conditions and probabilities to meet large dimensioned trees during records, respectively, and (c) considering the distribution of microhabitats which are crucial for xylobiontic (saproxylic) organisms, this approach resulted in the assumed biodiversity patterns with increasing microhabitat numbers up to the disintegration phase thus it was used as a basis for the creation of an optimized fdp assessment method as a tool for common and standardized use in forest ecology and biodiversity research.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号