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   1007篇
  免费   32篇
  国内免费   1篇
林业   53篇
农学   20篇
基础科学   15篇
  186篇
综合类   127篇
农作物   44篇
水产渔业   73篇
畜牧兽医   415篇
园艺   26篇
植物保护   81篇
  2024年   3篇
  2023年   5篇
  2022年   11篇
  2021年   13篇
  2020年   14篇
  2019年   18篇
  2018年   18篇
  2017年   13篇
  2016年   11篇
  2015年   14篇
  2014年   13篇
  2013年   50篇
  2012年   63篇
  2011年   76篇
  2010年   54篇
  2009年   45篇
  2008年   66篇
  2007年   64篇
  2006年   70篇
  2005年   59篇
  2004年   54篇
  2003年   64篇
  2002年   65篇
  2001年   8篇
  2000年   10篇
  1999年   11篇
  1998年   13篇
  1997年   7篇
  1996年   10篇
  1995年   9篇
  1994年   3篇
  1993年   9篇
  1992年   3篇
  1991年   5篇
  1990年   4篇
  1989年   4篇
  1988年   10篇
  1987年   8篇
  1986年   9篇
  1985年   9篇
  1984年   8篇
  1983年   7篇
  1982年   6篇
  1981年   2篇
  1980年   4篇
  1979年   2篇
  1978年   3篇
  1976年   2篇
  1975年   6篇
  1967年   2篇
排序方式: 共有1040条查询结果,搜索用时 31 毫秒
991.
Ancient grains are becoming an increasingly abundant carbohydrate source in the pet food market as a result of their popularity and novelty in the human market. Thus, it is imperative to evaluate the characteristics of these ingredients in vivo. Ten adult intact female beagles were used in a replicated 5 × 5 Latin square design. Five dietary treatments were evaluated containing either: rice (CON), amaranth (AM), white proso millet (WPM), quinoa (QU), or oat groats (OG). All diets were formulated to include 40% of the test grain and to be isonitrogenous, isocaloric, and nutritionally complete and balanced for adult dogs at maintenance. The objectives were 1) to evaluate the effects of the novel carbohydrate sources on total apparent total tract digestibility (ATTD), fecal microbiota, and fermentative end-product concentrations and 2) to evaluate the effects of novel carbohydrate sources on the postprandial glycemic and insulinemic responses in healthy adult dogs. All diets were well accepted by the dogs and fecal scores remained within the ideal range for all treatments. In terms of ATTD, all diets were well digested by the dogs; WPM had the highest digestibility of dry and organic matter in contrast with dogs fed the other treatments (P < 0.05). Additionally, ATTD of total dietary fiber was highest for WPM (72.6%) in contrast with QU (63.5%) and CON (50.8%) but did not differ from AM (65.7%) and OG (66.6%). Dogs fed AM or OG had greater (P < 0.05) fecal concentrations of total short-chain fatty acids, as well as propionate and butyrate concentrations, than CON. Ancient grain inclusion appears to beneficially shift fecal microbial populations, with increases in relative abundances of butyrogenic bacteria (i.e., members of the Lachnospiraceae family) observed for OG and reductions in Fusobacteriaceae for both AM and OG when compared with CON. Postprandial glycemic and insulinemic responses did not differ among treatments. Together, these data suggest that ancient grains can be included up to 40% of the diet while eliciting beneficial effects on the overall host health without detrimentally affecting nutrient digestibility.  相似文献   
992.
Objectives: To compare the mean number of cycles to failure under axial compression of equine proximal interphalangeal (PIP) joint arthrodesis constructs created by 2 parallel transarticular Acutrak Plus screws (AP‐TS) or 2 parallel transarticular 5.5 mm cortical screws inserted in lag fashion (AO‐TLS). Study Design: Paired in vitro biomechanical testing of 2 methods of stabilizing cadaveric adult equine forelimb PIP joints. Sample Population: Cadaveric adult equine forelimbs (n=5 pairs). Methods: For each forelimb pair, 1 PIP joint was stabilized with AP‐TS and 1 with AP‐TLS. The 5 construct pairs were tested for cyclic fatigue under axial compression. Mean number of cycles to failure for each fixation method were compared by a paired t‐test within each group with statistical significance set at P<.05. Results: The mean number of cycles to failure under axial compression for AO‐TLS fixation and AP‐TS fixation were 57,723±8488 and 35,322±4698, respectively. Conclusion: The AO‐TLS was superior to the AP‐TS in resisting cyclic fatigue under axial compression.  相似文献   
993.
Porcine postweaning Escherichia coli enteritis is a cause of significant morbidity and mortality in pigs worldwide, and effective prevention remains an unsolved problem. This study examined the correlation between susceptibility of pigs to experimental infection with an E. coli F18 strain and the porcine intestinal F18 receptor genotypes. Thirty-one pigs classified as either belonging to the susceptible or the resistant genotype were inoculated with cultures of an E. coli O138:F18 isolated from a pig with postweaning diarrhoea. Susceptibility to colonisation and diarrhoea was assessed by clinical observations, faecal shedding of the challenge strain, histopathology and microscopic adhesion tests. Ten of 14 (71.4%) genetically susceptible pigs and one of 17 (5.9%) resistant pigs developed diarrhoea attributable to the challenge strain. There was no difference in susceptibility between homozygotic and heterozygotic susceptible pigs. Faecal shedding of the challenge strain correlated with the genetic receptor profile. Twenty pigs examined immunohistochemically revealed focal to extensive small intestinal mucosal colonisation by E. coli O138:F18 in nine of 10 susceptible and three of 10 resistant pigs. Results of in vitro adhesion assays performed with F18 cells on enterocyte preparations from 24 pigs, showed complete concordance with the F18 genotypes. In conclusion, this study showed a high correlation between the porcine intestinal F18 receptor genotypes and susceptibility to disease. However, pigs of the resistant F18 receptor genotype were not entirely protected against intestinal colonisation by E. coli F18.  相似文献   
994.
995.
996.
在含粗小麦粉的生长育成期猪日粮中添加植酸酶的效果   总被引:2,自引:2,他引:2  
试验采用 5 4头杂交猪 (初始体重为 2 8.4± 0 .98kg)来评估在含粗小麦粉的生长育成日粮中添加植酸酶的效果。试验猪被随机分成 2组 :对照组和试验组。试验组日粮除了以每千克 5 0 0单位的植酸酶取代相应的无机磷以外 ,其它成分与对照组日粮相同。试验期分 3个日粮阶段 ,采用 Cr2 O3 为外源指示剂来测定营养成分的消化率 ,每 2周测定 1次猪的体重和采食量并计算饲料效率。在第 2和第 3个日粮阶段分别为 7d的 2个采样期中 ,每天随机采取猪的粪样并按栏混合 ,然后对粪样的干重以及 Ca、P、Cu、Zn的含量分别进行测定。试验结果表明 ,试验组和对照组之间无论是平均日增重还是平均日采食量均没有显著差异。 5~ 8周间对照组的料肉比高于试验组 ( P<0 .0 5 ) ,但在其它各阶段均无显著差异。干物质消化率在第 2日粮阶段中无显著差别 ,但在第 3阶段中试验组高于对照组 ( P<0 .0 1 )。 Ca的消化率也同样是在第 2阶段中 2组相似 ,但在第 3阶段中试验组高于对照组 ( P<0 .0 1 )。磷 ( P)的消化率则无论在第 2阶段 ( P<0 .0 5 )还是第 3阶段 ( P<0 .0 1 ) ,均是试验组高于对照组。试验结果表明 ,在含粗小麦粉的生长育成猪日粮中添加植酸酶可以达到同直接添加无机磷一样的效果。添加植酸酶可以促进含粗小麦粉日粮中钙  相似文献   
997.
BACKGROUND: Cosyntropin (adrenocorticotropic hormone [ACTH]) stimulation tests are used to evaluate adrenal function. Low-dose ACTH stimulation tests are the most accurate method for diagnosing relative adrenal insufficiency in critically ill humans but have not been evaluated in foals. HYPOTHESIS: Peak serum cortisol concentrations in healthy foals will not be significantly different after intravenous administration of 1, 10, 100, and 250 microg of cosyntropin. ANIMALS: 14 healthy neonatal foals, 3-4 days of age. METHODS: A randomized cross-over model was used in which cosyntropin (1, 10, 100, or 250 microg) was administered intravenously on days 3 and 4 of life. Blood samples were collected before and 30, 60, 90, 120, and 150 minutes after administration of cosyntropin for determination of serum cortisol concentration. RESULTS: Serum cortisol concentrations did not significantly increase after administration of 1 microg of cosyntropin. Cortisol concentration peaked 30 minutes after administration of 10 microg of cosyntropin and 90 minutes after 100 and 250 microg of cosyntropin. There was no relationship between cosyntropin dose and serum cortisol concentration at 30 minutes. Compared with the 10-microg dose, 100 and 250 microg of cosyntropin induced significantly greater cortisol concentrations at 90 minutes, at which point the 10-microg cosyntropin-dose cortisol values were indistinguishable from baseline. There was no significant difference in the area under the cortisol concentration curve between the 100- and 250-microg doses. No effect of day of testing or foal weight on peak cortisol concentration was detected. CONCLUSIONS AND CLINICAL IMPORTANCE: The results of this study suggest that 10- and 100-microg doses of cosyntropin would be appropriate for evaluating adrenal function in neonatal foals.  相似文献   
998.
前言  近年来,许多猪场为了提高母猪的生产率(增加每头母猪的年产仔数)、改善母猪断奶时的体况以及改善改善断奶仔猪的性能(减少仔猪接触母猪病原体的机会),实行了仔猪21日龄断奶的做法.然而,如此早期进行断奶,仔猪的营养和管理都很成问题,因为这时它们的消化系统和免疫系统都还没有成熟.……  相似文献   
999.
    
The objective of this project was to report the effects of season and age on conception rate amongst Italian Mediterranean Buffalo subjected to an Ovsynch/Resynch (O/R) reproductive management protocol. The study utilized nulliparous (heifers), primiparous buffalo cows (PBC) and multiparous buffalo cows (MBC). The primiparous and multiparous groups were subjected to the synchronization protocol throughout the entire year, but heifers were synchronized and inseminated only during the spring/summer seasons. The conception rate obtained following the OvSynch oestrus synchronization protocol, applied during spring, was 68.4% for heifers, 83.3% for PBC and 67.7% for MBC. The overall total conception rates following the complete O/R protocol were 84.27%, 94.4% and 79%. Conception rates achieved during summer were heifers 52%, PBC 47.2% and MBC 49%, whilst overall conception rates following the full O/R protocol were 72%, 69.8% and 58.2% respectively. In the autumn seasons, PBC conceived 58.9% and MBC 52.1% following initial Ovsynch, which improved to total overall conception rates of 87.5% and 78.7% following the full O/R protocol. Similarly, in the winter season, PBC experienced a conception rate of 47.5% following Ovsynch and 72.5% after a follow-up Resynch. MBC experienced 60.0% and 74.4% conception following Ovsynch and full O/R, respectively, during winter. Total conception rates during all seasons were quite acceptable following the O/R protocol. There was a significant decrease from spring to summer in conception rate for all parity groups, but heifers were not a severely affected as older buffalo cows. This finding agrees with that of other investigators indicating that heifer fertility is not as negatively impacted by long photoperiod and higher ambient temperature as that of older animals. The O/R protocol as utilized in this study is an effective means of reproductive management for dairy buffalo cows and is effective for improving fertility during out-of-season breeding.  相似文献   
1000.
Wild waterfowl and their habitats are the main reservoirs of influenza A virus (IAV) mainly during the breeding season and prior to migration. This study describes the molecular characterization of an IAV isolated from 240 water samples of a small wetland during non-breeding season of migratory wild ducks in the State of Mexico, Mexico. The results showed that the virus belongs to the H4N2 subtype and each of its eight segments of the viral genome has similarity to IAV isolated from ducks in North America. This study suggests that IAV can be isolated from small wetland during non-breeding season of migrating waterfowl.  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