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   391篇
  免费   43篇
  国内免费   29篇
林业   36篇
农学   9篇
基础科学   2篇
  49篇
综合类   72篇
农作物   40篇
水产渔业   35篇
畜牧兽医   195篇
园艺   8篇
植物保护   17篇
  2024年   1篇
  2023年   6篇
  2022年   20篇
  2021年   16篇
  2020年   11篇
  2019年   30篇
  2018年   28篇
  2017年   45篇
  2016年   20篇
  2015年   17篇
  2014年   25篇
  2013年   37篇
  2012年   32篇
  2011年   12篇
  2010年   19篇
  2009年   20篇
  2008年   12篇
  2007年   24篇
  2006年   10篇
  2005年   13篇
  2004年   4篇
  2003年   11篇
  2002年   9篇
  2001年   5篇
  2000年   3篇
  1999年   3篇
  1998年   7篇
  1997年   4篇
  1996年   3篇
  1995年   2篇
  1994年   1篇
  1993年   4篇
  1992年   3篇
  1990年   2篇
  1989年   1篇
  1988年   1篇
  1986年   1篇
  1956年   1篇
排序方式: 共有463条查询结果,搜索用时 9 毫秒
1.
The present study was designed to examine the effects of cell-cycle synchronization protocols, such as confluent, roscovitine treatment and serum starvation, in bovine foetal fibroblasts on synchronization accuracy at G0/G1, viability, apoptosis, necrosis and ploidy for use as a nuclei donor. The cells in 5-10 passages were randomly allocated into three treated groups. Cells were cultured either in Dulbecco's modified Eagle's medium (DMEM) + 10% foetal bovine serum (FBS) until 90% confluent (group 1, confluent), in DMEM + 10% FBS + 30 microM roscovitine for 12 h (group 2, roscovitine), or in DMEM + 0.5% FBS for 5 days (group 3, serum starvation). Most of the cells (>80%) in all groups were arrested at the G0/G1 stage. Although the rates did not differ, cells in group 1 showed an increased cell population arrested at the G0/G1 phase. Significantly (p < 0.05) higher rates of apoptosis occurred in group 3 than in group 1 and 2 (10% vs 6% and 6%, respectively). No differences in chromosomal abnormality were observed among groups. However, by increasing the number of cell culture passages up to 15, significantly (p < 0.05) higher chromosomal abnormality was observed than in 5 and 10 passages (39% vs 28% and 23%, respectively) in group 1. The results clearly indicated that bovine foetal fibroblasts could be effectively synchronized at G0/G1 stages by all the three different treatments, confluent, roscovitine and serum starvation. However, cells in confluent showed reduced apoptosis and necrosis when they underwent 5-10 passages, exhibiting increased percentage of cells with stable chromosome diversity. Hence, cells in confluent merit further studies before they could be used as nuclear donors.  相似文献   
2.
3.
4.
为探究羊经布鲁菌病疫苗(S2株)免疫后的血清抗体长期动态消长规律,本试验于2012年9月-2015年9月选取阿拉善盟阿拉善左旗96只山羊、100只绵羊作为试验动物,经布鲁菌疫苗(S2株)100亿CFU、200亿CFU不同免疫剂量灌服,分别于免疫前和免疫后不同时间段采血分离血清,应用虎红平板凝集试验和试管凝集试验进行抗体监测。结果表明,绵羊组在一免后20d时,血清抗体阳性率达到最高峰,之后呈下降趋势,150d抗体阳性率降至0%,免疫后180d^360d,绵羊组抗体阳性率一直处于较低水平(0%~4%),二免和三免后不同时间段免疫抗体消长规律与首次免疫基本一致;山羊组抗体阳性率在免疫后20 d时,血清抗体阳性率达到最高峰,之后呈下降趋势,免疫后90 d^360 d,免疫抗体时高时低,起伏较大,无明显规律,二免和三免后不同时间段免疫抗体消长规律与首次免疫基本一致,结果同时表明,100亿CFU和200亿CFU两个免疫剂量组的抗体阳性率无明显差异。  相似文献   
5.
In recent few years, there have been some attempts to find a reliable indicator trait as a selection criterion against susceptibility to ascites syndrome (AS). Blood parameters were of great interest as they could be measured in live animals without implementing an ascites‐inducing challenge (AIC). In this work, the suitability of some blood parameters was evaluated for diagnosing AS‐susceptible chicks in later steps of the disease in trial 1 as well as their early predictive ability in trial 2. In the first trial, one hundred 1‐day‐old chicks from two pure broiler lines namely S1 and S2 and, in the second trial, 226 1‐day‐old chicks from line S2 were subjected to AIC. Saline drinking water (1200 mg/l) and lower‐than‐standard ambient temperatures were the implemented AICs in trials 1 and 2 respectively. The blood parameters including pH, partial pressure of O2 (pO2), partial pressure of CO2 (pCO2), bicarbonate ion concentration (BIC), percentage of haematocrit (HCT) and saturated haemoglobin (SaO2) were measured twice per each bird at days 28 and 35 in trial 1 and once in trial 2 at day 21. The results of the first trial revealed that in line S2 some of the blood parameters differed significantly between the ascitic and non‐ascitic groups following exposure to AIC. In this line, the incidence of AS was accompanied by a lower pO2, SaO2 and BIC, while with higher pCO2 and HCT values. In the second trial, however, although almost all of the parameters showed meaningful differences between the ascitic and non‐ascitic broilers, only mean difference of BIC parameter was statistically significant. The general conclusion of this study is that the blood parameters can somewhat have diagnostic ability in the condition in which the AIC is already present, whereas the results did not approve their usefulness as early predictors of AS.  相似文献   
6.
对浙江省夏秋蚕品种薪杭,白云,丰1和54A等进行了充血复壮改良,基本稳定后的复壮系与现行生产系进行了生产性能的比较试验。结果表明复壮系在各项性状都有一定的提高,其中龄期经过,各品种的复壮系与生产系之间差别不大,只有薪杭丙和白云丙稍有延长。全茧量和茧层量基本上复壮系都比生产系有所提高。生命率差异比较大,奠中薪杭的复壮系低下生产系,差异达到显著水平,白云复壮系略微低于白云甲,但高于白云乙,丰1的复壮系与生产系无明显差异,54A则是复壮系高于生产系。良卵数除薪杭丙比薪杭甲略低外,其他品种的复壮系都比生产系显著提高,有的甚至达到极显著水平。说明复壮系在生产性能上有较大的改良,有一定的推广应用价值。  相似文献   
7.
Self-sterility in cherry (Prunus avium L.) is one of the most important problems in commercial cherry orchards in Iran and many other countries. The main objective of this research was to determine self-fertility rate and blooming phenology of 25 commercial cherry (P. avium L.) cultivars in Iran. This study was conducted during 2006–2007.Results revealed that the stage of bud swell in all cultivars began late second decade of March, which lasts 8–11 days. In all cultivars the duration end bloom to petal fall stage took 5 days. Cherry cultivars were classified into three groups considering their overlapping pollination. The cultivars each group had a great overlapped pollination toward each other. The results also showed that there was a significant difference among cultivars in respect of the fruit set (P < 1%). The fruit set of open pollination treatment among the cultivars varied in range of 7.36–41.58%. However fruit set was not observed in isolated pollination (artificial and natural self-pollination). In open pollination, the cultivars were also classified into four groups, i.e. weak fertility (Moreau and Ferracida), mean fertility (Siah Mashhad, Napelon, Proteva, Haj usefy, Lambert, Roshun, Sefid Ghermeze Baghno, Arak, Belamarka, Siah Shabestar, Ghermeze Rezaeyeh, Abardeh, Soraty Lavisan and Victoria), good fertility (Peshrase Mashhad, Dovoumras Mashhad, Bing, Shesheiy Mashhad, Siah Ghazvin and Sefid Rezaeyeh), very good fertility (Zarde Daneshkadeh, Dirrase Italia and No. 1 karaj). All cultivars were found to need cross-pollination and included in self-sterile group.  相似文献   
8.
通过正交试验,对"珍珠"的工艺配方进行了研究,结果表明,胶液最佳配方为海藻酸钠∶明胶∶琼脂为3∶1∶2,奶油含量5%,蔗糖含量10%。氯化钙浓度3.0%,固化时间10min。得到的"珍珠"颗粒形状圆润,口感滑嫩,3个月内不发生溶解。  相似文献   
9.
Our understanding of the basis to immunoglobulin formation in cattle has benefited substantially from the application of molecular biology over the past decade. It is now established that both the lambda light chain and heavy chain repertoires are founded upon the frequent expression of single gene families and subgroups of segments which are of conserved sequence. It is likely that a functional kappa locus exists in the bovine genome but this isotype comprises as few as 5% of bovine light chains. Similarly, alternative but non-expressed V(H) gene families are present posing intriguing but unresolved questions about the regulation of immunoglobulin synthesis. The heavy chain frequently bears a third complementarity-determining region which is atypically long but the processes which expand this region of the reading frame and its contribution to the interaction with antigen remain matters of speculation. Opportunities exist to map the major immunoglobulin loci and to define the membership and sequence diversity of the gene families which dominate each repertoire. However, it is already evident that cattle cannot generate significant diversity from rearrangement and junctional imprecision alone. Elucidation of the mechanism(s), dynamics and tissue distribution of immunoglobulin diversification in cattle, thus, remain key challenges in this branch of veterinary immunology.  相似文献   
10.
采用免疫组织化学方法对不同日龄的长爪沙鼠颌下腺IgA的定位分布进行了研究。结果表明,长爪沙鼠的颌下腺由导管部和分泌部构成,分泌部主要由浆液腺构成,导管部包括闰管、纹管、颗粒曲管和小叶间导管等。DAB显色结果表明,IgA阳性细胞主要分布于浆液性腺泡、闰管、纹管、颗粒曲管和小叶间导管,并可分布于腺泡和腺管间结缔组织,IgA阳性产物的分布具有不均一性,无明显随年龄变化的规律性。阳性产物分布于胞质中,胞核呈阴性,对照组阴性。提示从浆细胞产生或循环而来的IgA先经结缔组织进入颌下腺组织,进而定位分布于浆液腺泡和各级导管,导管部有较多的IgA分布。  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