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   626篇
  免费   38篇
林业   24篇
农学   17篇
基础科学   1篇
  110篇
综合类   55篇
农作物   28篇
水产渔业   32篇
畜牧兽医   280篇
园艺   11篇
植物保护   106篇
  2023年   9篇
  2022年   5篇
  2021年   17篇
  2020年   21篇
  2019年   23篇
  2018年   14篇
  2017年   13篇
  2016年   15篇
  2015年   15篇
  2014年   17篇
  2013年   33篇
  2012年   39篇
  2011年   41篇
  2010年   22篇
  2009年   23篇
  2008年   45篇
  2007年   28篇
  2006年   26篇
  2005年   34篇
  2004年   28篇
  2003年   26篇
  2002年   31篇
  2001年   17篇
  2000年   8篇
  1999年   11篇
  1998年   9篇
  1997年   7篇
  1996年   4篇
  1995年   4篇
  1994年   4篇
  1993年   4篇
  1992年   4篇
  1991年   4篇
  1990年   5篇
  1989年   8篇
  1988年   8篇
  1987年   2篇
  1986年   3篇
  1985年   4篇
  1984年   6篇
  1983年   4篇
  1982年   3篇
  1981年   2篇
  1979年   2篇
  1968年   2篇
  1965年   1篇
  1964年   2篇
  1962年   1篇
  1958年   1篇
  1930年   1篇
排序方式: 共有664条查询结果,搜索用时 203 毫秒
571.
To determine the factors affecting reproductive efficiency in a seasonal breeding artificial insemination (AI) programme in dairy herds in Uruguay, a field trial was conducted on three dairy farms. Lactating cows (n=328) intended to be bred at the following breeding period were selected. The trial started 1 week before the beginning of the breeding period and lasted 80 days or until first service. Milk samples were obtained biweekly for 12 weeks, starting 1 week prior to the breeding season to determine progesterone concentrations. Data indicated that 12.5% of the cows were anoestrus at the beginning of the season remaining in this condition throughout the trial. Most of the anoestrous animals were first-calf heifers. A varying number of cycling cows (8.5%) at each farm were never reported in heat. Oestrous detection rate for cows cycling, as determined by progesterone patterns, was evaluated in three periods of 21 days and resulted in an overall efficiency of 46.9%. Main factors affecting oestrous detection were farm, with an effect of parity (67.8%, mature cows and 33.2%, first-calf heifers) and no effect of days postpartum. Mean interval from the beginning of the breeding season to first breeding was 27.4 days, which was also affected by farm. Neither parity nor days postpartum affected this parameter.  相似文献   
572.
BALB/c mice are widely used in genetic, tumour and immunological studies. However, the mice demonstrate a lower reproduction rate, low fertility and small litters, because of their highly genetic homozygoisty. Based on in vitro fertilization (IVF), a routine technique for biomedical studies, it is worth to evaluate the effects to BALB/c mice on IVF efficiency. In order to test the genetic factor affecting the IVF efficiency of BALB/c, four reciprocal IVF tests of BALB/cByJ and FVB/NCrl mice were performed. The results showed that the average fertility of IVF sponsored by FVB/NCrl spermatozoa was 69.6%, but only 12.1% was obtained from BALB/cByJ strain. Effect of glucose contained in the culture medium to the IVF efficiency of BALB/cByJ was also evaluated. The results showed that the fertility of BALB/cByJ spermatozoa incubated with 0, 2.7, 5.5, 11.1 and 22.2 mm of glucose in the TYH medium were 6.8, 9.9, 13.9, 32.7 and 22.2%, respectively. It is showed that IVF efficiency of BALB/cByJ spermatozoa could be improved depending on the concentration of glucose in the IVF medium. According to the results, it is beleived that lower IVF of BALB/cByJ mice might be due to the genetic defect in spermatozoa and increasing glucose in the IVF medium which significantly affect the IVF efficiency of BALB/cByl via activating the spermatozoa.  相似文献   
573.
574.
575.
A natural hybrid of Vipera ammodytes × Vipera berus was presented having low body weight, seizures and generalized swelling of the cephalic region. Based on the history of the case and clinical examination, hemorrhagic stomatitis of traumatic origin was diagnosed. The snake was kept in a terrarium with wood chips as a substrate, and the material had induced trauma in the oral mucosa which was further complicated with Salmonella Arizonae and Morganella morganii co-infection, abscessation and osteomyelitis. To the best of the authors’ knowledge, this is the first reported case of bacterial infection in European snake hybrids and one of a few case reports in European snakes. Although wood chips are an inexpensive substrate, based on our findings, they should be avoided when keeping and breeding European vipers.  相似文献   
576.
577.
Mixtures of glycine, glucose, and starch were extrusion cooked using sodium hydroxide at 0, 3, and 6 g/L of extruder water feed, 18% moisture, and 120, 150, and 180 degrees C target die temperatures, giving extrudates with pH values of 5.6, 6.8, and 7.4. Freeze-dried equimolar solutions of glucose and glycine were heated either dry or after equilibration to approximately 13% moisture at 180 degrees C in a reaction-tube system designed to mimic the heating profile in an extruder. Volatile compounds were isolated onto Tenax and analyzed by gas chromatography-mass spectrometry. For the extrudates, total yields of volatiles increased with decreasing pH at 180 degrees C, reached a maximum at pH 6.8 at 150 degrees C, and increased with increasing pH at 120 degrees C. Amounts increased with temperature at all pH values. Pyrazines were the most abundant class for all sets of conditions (54-79% of total volatiles). Pyrroles, ketones, furans, oxazoles, and pyridines were also identified. Yields of volatiles from the reaction-tube samples increased by >60% in the moist system. Levels of individual classes also increased in the presence of moisture, except pyrazines, which decreased approximately 3.5-fold. Twenty-one of the compounds were common to the reaction-tube samples and the extrudates.  相似文献   
578.
Following sodium carbonate treatment, accumulation of scoparone (6,7-dimethoxycoumarin) but not scopoletin (6-methoxy-7-hydroxycoumarin) was found in the albedo of wounded fruit from different Citrus sp. and cultivars. Treating wounded mandarin fruit cv. Fairchild with 5% Na(2)CO(3) (SC) lead to a scoparone accumulation in the albedo of 310, 361, and 382 microg g(-1) fresh weight after 7, 10, and 15 days, respectively. Scoparone accumulation was associated with a decrease in decay severity. When oranges cv. Biondo comune wounded and treated with 5% SC were inoculated with Penicillium digitatum or Penicillium italicum conidia 3 days posttreatment, the decay percentage as compared to untreated wounds was reduced by 97.2 and 93.9%, respectively. Observations by scanning electron microscopy of wounded Citrus fruits treated at 20 degrees C with 2, 3, 4, or 5% (w/v) solutions of sodium carbonate showed structural modifications to the albedo as well as damage to 24-48 h old mycelia of P. digitatum, the cause of citrus green mold. Modifications were more evident in orange, lemon, and grapefruit as compared to mandarin fruit. The efficacy of the treatment was strictly related to the SC interaction with the albedo tissue that, in addition to structural changes, significantly increased tissue pH, affecting P. digitatum pathogenicity. The SC remaining as a film on unwounded flavedo had no effect in preventing contact infection by the Penicillia.  相似文献   
579.
580.
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