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   484篇
  免费   24篇
林业   37篇
农学   18篇
基础科学   2篇
  111篇
综合类   48篇
农作物   28篇
水产渔业   32篇
畜牧兽医   166篇
园艺   13篇
植物保护   53篇
  2023年   4篇
  2022年   8篇
  2021年   13篇
  2020年   13篇
  2019年   19篇
  2018年   18篇
  2017年   21篇
  2016年   14篇
  2015年   7篇
  2014年   17篇
  2013年   18篇
  2012年   26篇
  2011年   47篇
  2010年   21篇
  2009年   24篇
  2008年   34篇
  2007年   42篇
  2006年   25篇
  2005年   18篇
  2004年   28篇
  2003年   19篇
  2002年   19篇
  2001年   6篇
  2000年   4篇
  1999年   2篇
  1997年   2篇
  1996年   2篇
  1995年   4篇
  1994年   1篇
  1992年   4篇
  1991年   1篇
  1990年   3篇
  1989年   2篇
  1988年   2篇
  1987年   2篇
  1983年   1篇
  1981年   1篇
  1980年   1篇
  1978年   1篇
  1977年   1篇
  1976年   1篇
  1975年   1篇
  1974年   1篇
  1973年   2篇
  1972年   1篇
  1969年   1篇
  1951年   1篇
  1942年   1篇
  1941年   1篇
  1940年   1篇
排序方式: 共有508条查询结果,搜索用时 594 毫秒
71.
The usefulness of endoscopic examination for the diagnosis and treatment of chronic enteritis in dogs was determined in this study. It was demonstrated, based on a clinical case, that endoscopy is essential for IBD diagnosis in dogs. Endoscopy also helps to estimate the efficiency of the treatment strategy applied. Nonspecific clinical examination results as well as a predominating lack of deviation in laboratory parameters make endoscopy the basic examination technique in mild and moderately advanced forms of chronic enteritis in the dog.  相似文献   
72.
Salmonella enterica serovar Typhimurium (S. Typhimurium) is a facultative intracellular bacterium which can infect and colonize pigs. After contact with enterocytes and macrophages, S. Typhimurium induces production of cytokines thus triggering the innate immune response. In this study we evaluated the cytokine response of two porcine cell lines, IPI-2I and 3D4/31, of epithelial or macrophage origins, respectively, to the wild-type S. Typhimurium and its hilA and ssrA mutants. We observed that the 3D4/31 cell line essentially did not respond to S. Typhimurium infection when a medium with foetal calf serum was used. However when the 3D4 cell line was incubated overnight in the presence of porcine serum, it efficiently responded to the wild-type strain and the ssrA mutant but not to the noninvasive hilA mutant as measured by mRNA quantification of TNF-alpha, IL-8 and GM-CSF by the real-time RT-PCR. In IPI-2I, all the cytokines were also induced by the wild-type S. Typhimurium and the ssrA mutant although the induction of TNF-alpha was lower than that induced by the wild-type strain. The hilA mutant was unable to induce any of the cytokines tested. The ssrA mutant can therefore be considered as more suitable for further vaccine development as the stimulation of innate immune response is important for animal protection against a challenge with virulent strains.  相似文献   
73.
Quantification of the mycotoxin patulin by a stable isotope dilution assay.   总被引:1,自引:0,他引:1  
Two stable isotope dilution assays for the quantification of patulin [4-hydroxy-4H-furo[3,2-c]pyran-2(6H)-one] in foods were developed using (13)C-labeled patulin as the internal standard. One method was performed by means of LC/MS in negative electrospray ionization mode without derivatization; the other used HRGC/HRMS after trimethylsilylation of the patulin isotopomers. In comparison with previously reported methods based on high-performance liquid chromatography with UV detection, HRGC/HRMS of the derivatized samples showed better repeatability, higher recovery rates (96% at a spike level of 200 ng/L), and a 100 times lower detection limit (12 ng/L). In contrast, LC/MS showed a much lower performance as compared to HPLC/UV or HRGC/HRMS. Using HRGC/HRMS, the mycotoxin was quantified in many different fruit products and in molded wheat bread.  相似文献   
74.
The objective of the present study was to asses the effect of watertable level on N mineralization in a Histosol and a Humic Gleysol profile under natural meadows in Ljubljana marsh, Slovenia. The two soils differ significantly in organic matter content (27—40 % in Histosol and 14—20 % in Humic Gleysol) but not in C : N ratio (13—20) and pH (6.5—7.0). For each soil, the watertable was maintained at two levels (above or below 50 cm from the soil surface) for approximately one year. The four main plots, according to soil carbon content and watertable level were divided into 4 subplots, according to 4 fertilization treatments (unfertilized control, PK, PK + 50 kg N ha—1, PK + 3 × 50 kg N ha—1). Net N mineralization in unfertilized subplots was estimated from indices of N mineralization obtained by incubation of soil samples in the laboratory and by seasonal dynamics of mineral N content in the field. Annual uptake of N in herbage under the 4 fertilization treatments was also measured. Total mineral N content in topsoil was 20—80 % higher in Histosol than in Humic Gleysol. Similarly, aerobic N mineralization potentials along the entire soil profile (0—90 cm) were 20—130 % higher in Histosol than in Humic Gleysol. By contrast, anaerobic N mineralization potentials in subsoil were 10—60 % lower in Histosol than in Humic Gleysol. Both, aerobic and anaerobic N mineralization potentials strongly depended on watertable levels at sampling time. Seasonal dynamics of soil mineral N content as well as N mineralization potentials indicated that the N mineralization in the Histosol could be 10—40 % higher at low than at high watertable level. In the Humic Gleysol the N mineralization could be 10—100 % higher at high watertable level. Higher N availability in Histosol at low watertable and in Humic Gleysol at high watertable was also reflected in higher N uptake in herbage. These results indicate that N mineralization in Histosol and Humic Gleysol, was proportional to soil organic matter content, whereas in both soils, higher N mineralization rates can be expected at watertable levels between 40 and 60 cm below the soil surface, than at higher/lower watertable levels.  相似文献   
75.
76.
The life‐history traits and population dynamics of the black bullhead Ameiurus melas (Rafinesque) were studied monthly from August 2009 to December 2012 in Lake Sava in Belgrade (Serbia). This period included a mass mortality event in May 2011 and subsequent population recovery during 2012. Available evidence suggests the mass mortality was caused by European catfish virus that only affected the black bullhead. Changes in key life‐history traits and the recovery potential (increase in catch‐per‐unit‐effort, doubling of young‐of‐the‐year to adult ratio, earlier maturation and increased fecundity) following the mass mortality event suggest population resilience typical of a recurring boom‐bust pattern and demonstrate the species’ capacity to recover rapidly and re‐establish following disturbance. Repeated systematic mass removals of both juveniles and adults (using fyke nets) will be required if future fishery management measures aimed at limiting the population size are to be effective.  相似文献   
77.
This study aimed to determine the genetic variability of isolates of rotting of pineapple fruitlet core in Brazil on the states of Paraiba, Pernambuco and Rio Grande do Norte, based on phylogenetic analysis of the RPB2 gene, morphocultural markers and aggressiveness of the isolates. The phylogenetic reconstruction of maximum parsimony and bayesian inference of the isolates were performed. Twenty-seven phylogenetic lineages were characterized with morphocultural markers on potato dextrose agar and synthetic nutrient-poor agar. The aggressiveness of these lineages were characterized in leaves and fruits of pineapple ‘Pérola’ cultivar. The Phylogenetic reconstruction showed close relationship between isolates of this study and phylogenetic lineages of F. guttiforme, F. ananatum and F. oxysporum by analysis of RPB2 gene. Phylogenetic lineages of this study shared significant morphocultural markers similar to those described for this species. Overall, the lineages related with Fusarium oxysporum Species Complex were more aggressive to the fruits of the Fusarium lineages related with Fusarium fujikuroi Species Complex. It is possible that F. ananatum and F. guttiforme or other lineages closely related to these species or F. oxysporum are present in the fields causing pineapple rotting fruitlet core in fruits of pineapple ‘Pérola’ in Brazil. The used markers determined high genetic variability in isolates analyzed in leaves and pineapple fruit ‘Pérola’ in the states of Paraíba, Pernambuco and Rio Grande do Norte of Brazil and the pathogenic lineages analyzed were better adapted to the fruits than to the detached leaves in pineapple ‘Pérola’ analyzed.  相似文献   
78.
79.
In this report, we presented the profile of polyphenolic substances in flowers, leaves, stalk and roots of Fagopyrum tataricum estimated by using RP–UHPLC–ESI-MS equipment (reversed-phase ultra-high-performance liquid chromatography electrospray ionisation mass spectrometry). The neutral detergent fibre, acid detergent fibre, acid detergent lignin, cellulose and hemicellulose were also determined. Flowers, leaves, stalk and roots showed varying levels of dietary fibre and polyphenols. The highest content of neutral and acid detergent fibre were found in the roots (63.92 and 45.45% d.m., respectively) while the most rich in phenolic compounds were flowers (4.8 mg/1 g d.m.). Root and stalk contained the highest level of cellulose, 38.70 and 25.57% d.m., respectively. Among the investigated polyphenolic substances such as: 2,6-dihydroxybenzoic acid, 3,4-dihydroxybenzoic acid, 3,5-dihydroxybenzoic acid, 4-hydrobenzoic acid, caffeic acid, catechin, chlorogenic acid, fagopyrin, ferulic acid, myricetin, gallic acid, isovanilic acid, isovitexin, kaempferol, luteolin, p-coumaric acid, procyanidin B2, quercetin, quercetin 3-D galactoside, rutin, syringic acid and vitexin, we observed that the contents of rutin and chlorogenic acid were the highest. We found some correlation between dietary fibre fractions and individual phenolic substances. The levels of acid detergent fibre (ADF), cellulose and hemicellulose were negatively correlated with isovitexin, kaempferol, vitexin, fagopyrin, caffeic acid and procyanidin B2 content. In this investigation, two solvents (water and methanol) were estimated regarding their extraction efficiency of phenolic compounds. Taking these results into consideration, we recommend using methanol as the extractor to isolate chlorogenic acid, fagopyrin, kaempferol, procyanidin B2, quercetin, quercetin 3-D-galactoside, rutin, vitexin, and water for other investigated polyphenolic substances obtained from Fagopyrum tataricum.  相似文献   
80.
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