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   78篇
  免费   1篇
林业   3篇
农学   3篇
基础科学   4篇
  11篇
综合类   5篇
农作物   4篇
水产渔业   1篇
畜牧兽医   34篇
园艺   7篇
植物保护   7篇
  2021年   1篇
  2019年   1篇
  2018年   2篇
  2017年   2篇
  2016年   1篇
  2015年   4篇
  2014年   2篇
  2013年   6篇
  2012年   7篇
  2011年   4篇
  2010年   4篇
  2009年   2篇
  2008年   10篇
  2007年   1篇
  2006年   6篇
  2005年   3篇
  2004年   1篇
  2003年   3篇
  2002年   2篇
  2001年   1篇
  2000年   1篇
  1999年   4篇
  1993年   1篇
  1989年   1篇
  1986年   1篇
  1984年   1篇
  1983年   1篇
  1982年   1篇
  1981年   1篇
  1972年   2篇
  1970年   1篇
  1967年   1篇
排序方式: 共有79条查询结果,搜索用时 15 毫秒
1.
Alkynes can be selectively hydrogenated into alkenes on solid palladium catalysts. This process requires a strong modification of the near-surface region of palladium, in which carbon (from fragmented feed molecules) occupies interstitial lattice sites. In situ x-ray photoelectron spectroscopic measurements under reaction conditions indicated that much less carbon was dissolved in palladium during unselective, total hydrogenation. Additional studies of hydrogen content using in situ prompt gamma activation analysis, which allowed us to follow the hydrogen content of palladium during catalysis, indicated that unselective hydrogenation proceeds on hydrogen-saturated beta-hydride, whereas selective hydrogenation was only possible after decoupling bulk properties from the surface events. Thus, the population of subsurface sites of palladium, by either hydrogen or carbon, governs the hydrogenation events on the surface.  相似文献   
2.
Oestrogen is an important regulator of reproduction and growth. The key enzyme of oestrogen biosynthesis, aromatase cytochrome P450, is encoded by the Cyp19 gene. In order to generate genetic markers for the sheep Cyp19 gene, two novel single nucleotide polymorphisms (SNPs), one located in promoter 2 (P2), the other one in intron 9 (I9), were identified by a comparative sequencing approach. The allele distributions of both SNPs were investigated by means of Polymerase chain reaction‐restriction fragment length polymorphism analysis (PCR‐RFLP) in five economically relevant sheep breeds (British Milk Sheep, Carranzana, Latxa Black Face, Latxa White Face, Merino) and three ancient Hungarian breeds kept as gene reserves (Cikta, Racka, Tsigai). In British Milk Sheep, only the intronic SNP was present whereas in Merino, Cikta, Racka, Tsigai, Carranzana, Latxa Black Face and Latxa White Face, both SNPs could be found. This indicates that the newly identified SNPs can be used as markers for the Cyp19 locus in various sheep breeds.  相似文献   
3.
The spectrum of water vapor is of fundamental importance for a variety of processes, including the absorption and retention of sunlight in Earth's atmosphere. Therefore, there has long been an urgent need for a robust and accurate predictive model for this spectrum. In our work on the high-resolution spectrum of water, we report first-principles calculations that approach experimental accuracy. To achieve this, we performed exceptionally large electronic structure calculations and considered a variety of effects, including quantum electrodynamics, which have routinely been neglected in studies of small many-electron molecules. The high accuracy of the resulting ab initio procedure is demonstrated for the main isotopomers of water.  相似文献   
4.
Lymphatic vessels develop from specialized endothelial cells in preexisting blood vessels, but the molecular signals that regulate this separation are unknown. Here we identify a failure to separate emerging lymphatic vessels from blood vessels in mice lacking the hematopoietic signaling protein SLP-76 or Syk. Blood-lymphatic connections lead to embryonic hemorrhage and arteriovenous shunting. Expression of slp-76 could not be detected in endothelial cells, and blood-filled lymphatics also arose in wild-type mice reconstituted with SLP-76-deficient bone marrow. These studies reveal a hematopoietic signaling pathway required for separation of the two major vascular networks in mammals.  相似文献   
5.
6.
Little information is known about infection, replication and transmission of porcine circovirus type 2 (PCV2) in species other than swine. Two sets of animal experiments were carried out to investigate the susceptibility of mice to PCV2 and to study their possible role in maintaining and transmitting the virus. In the first experiment 14 mice were inoculated with PCV2 by the intraperitoneal route with 5 x 10(2) TCID50 of the PCV2-ROM strain (Cadar et al., 2007). In a second experiment 24 mice were divided into two groups (A and B); mice in Group A (n = 18) were inoculated orally with 1 x 10(5) TCID50 PCV2-ROM and mice in Group B (n = 6) were left uninoculated until day 12 post inoculation (p.i.), when they were mixed with Group A. The animals were sacrificed at intervals for postmortem investigation and virus genome detection by polymerase chain reaction (PCR). The PCR results indicated that PCV2 could replicate in mice infected intraperitoneally or by the oral route, and that the virus can be transmitted directly from mouse to mouse.  相似文献   
7.
Ten guinea pigs with an ovarian cyst had clinical signs of anorexia, alopecia, or depression. Ultrasonographic features of the 2- to 3-cm diameter fluid-filled cysts included compartmentalization and connection to the ovary. In two animals, a unilateral cyst was present, and in two others, the cysts were bilateral. Diagnosis of the disease by plain radiography is difficult because of the similar opacity of ovarian cysts, abdominal neoplasms, and trichobezoars.  相似文献   
8.
9.
Horseradish (Armoracia rusticana) is a popular vegetable, spice and medicinal plant. We aimed to collect data about its cultivation, ethnomedicinal and culinary applications in a horseradish-producing region in Hungary and 32 villages in Romania. Horseradish roots are used in ethnomedicine for sore throat, asthma, cough and flu in both areas, alone or in combination with e.g. honey. In Transylvania, additional applications included digestive problems, pleuritis, and rheuma in various forms. The leaf and the grated root is for toothache and fever. Some applications were novel, others matched earlier records from these areas and those of other European countries. In ethnoveterinary practice, the root is used against roaring of horses in all regions. It is traditionally consumed in a soup in Hungary, as pickles, and the leaf in Transylvania. The root samples of the region of interest showed typical chemical pattern of horseradish roots, as shown by GC–MS: allyl isothiocyanate and 2-phenylethyl isothiocyanate were present in high amounts. The presented ethnomedicinal data are supported by a growing body of scientific evidence—pharmacological data available on the isothiocyanates. Data on antimicrobial activity support use in gastritis (Helicobacter pylori) and dental caries, while data on efficacy in inflammatory conditions justify the applications in diseases asthma and respiratory system infections. Our study presented scientific evidence-supported ethnomedicinal data on horseradish rich in bioactive isothiocyanates.  相似文献   
10.
A polymorphic site of the growth hormone gene (AluI polymorphism) that results in an amino acid change at position 127 of the protein chain (leucine, L to valine, V) has been linked to differences in circulating metabolites and metabolic hormones of calves and bulls and to milk yield traits of lactating cows. Our objective was to investigate the interrelationship of this polymorphism with plasma concentrations of β-hydroxybutyrate, insulin, IGF-I and leptin in postpartum dairy cows. Blood samples were taken from clinically healthy, spring-calving, group-fed Holstein-Friesian cows (n = 257; 7 large-scale farms) 4–13 days after calving. Of all herds, 100 cows had plasma β-hydroxybutyrate levels above 1.2 mmol/l and 157 cows were normoketonemic. The proportion of valine carriers and LL cows was not different within groups of normo- and hyperketonemic animals. Genotype was not associated with plasma β-hydroxybutyrate, insulin, IGF-I and leptin levels either in all of the herds or in the two with the highest proportion of the valine allele carriers (n = 28, 72%). We found significantly lower insulin, IGF-I and leptin concentrations in the presence of hyperketonemia compared to normoketonemic cows. There were strong negative correlations between BHB and the other blood parameters, while insulin, IGF-I and leptin were positively related to each other. In conclusion, in the first two weeks after calving we could not demonstrate any effect of AluI polymorphism on plasma concentrations of β-hydroxybutyrate and metabolic hormones studied. Hyperketonemia was associated with a significant decrease in insulin, IGF-I and leptin blood levels. We infer that cows homozygous for the leucine allele or carrying the valine allele may have a similar endocrine and metabolic response to the challenge of increased nutrient demand early postpartum and that the presence of hyperketonemia is mainly linked to the hormonal and metabolic changes occurring at the onset of lactation.  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