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   648篇
  免费   124篇
  国内免费   58篇
林业   12篇
农学   6篇
  5篇
综合类   135篇
农作物   10篇
水产渔业   565篇
畜牧兽医   35篇
园艺   1篇
植物保护   61篇
  2024年   5篇
  2023年   17篇
  2022年   11篇
  2021年   16篇
  2020年   38篇
  2019年   26篇
  2018年   20篇
  2017年   47篇
  2016年   37篇
  2015年   37篇
  2014年   40篇
  2013年   47篇
  2012年   36篇
  2011年   32篇
  2010年   26篇
  2009年   39篇
  2008年   33篇
  2007年   39篇
  2006年   32篇
  2005年   32篇
  2004年   18篇
  2003年   24篇
  2002年   20篇
  2001年   31篇
  2000年   22篇
  1999年   21篇
  1998年   10篇
  1997年   10篇
  1996年   13篇
  1995年   10篇
  1994年   10篇
  1993年   8篇
  1992年   9篇
  1991年   4篇
  1990年   5篇
  1988年   3篇
  1987年   2篇
排序方式: 共有830条查询结果,搜索用时 31 毫秒
741.
家蚕血液中胰凝乳蛋白酶抑制剂研究--品种间的多态型   总被引:1,自引:0,他引:1  
采用聚丙烯酰胺凝胶电泳和胰凝乳蛋白酶抑制剂(CI)活性染色,对9个家蚕品种血液中CI种类的分布进行了调整。结果:在碱性电泳条件下可检测出12种以上的CI,品种间CI分布存在多态型,根据结果筛选出作为分离纯化家蚕胰凝乳蛋白酶抑制剂的理想品种材料。  相似文献   
742.
743.
744.
We used an up‐to‐date, a high accuracy CO2 manipulation system to investigate the sensitivity of organisms to CO2 acidification, rearing marine calcifiers under elevated CO2 in running water. We evaluated the effects of elevated partial pressures of carbon dioxide (pCO2) in seawater on larvae of the commercially important marine gastropod Ezo abalone Haliotis discus hannai. In larval Ezo abalone, no effect of exposure to <1100 μatm pCO2 seawater was observed in fertilization, malformation, or mortality rates until 15 h after fertilization. However, compared to control larvae in seawater (450 or 500 μatm pCO2), the fertilization rate and the hatching rate (15 h after fertilization) decreased with increased pCO2 exposure (1650 and 2150 μatm pCO2) and the malformation rate increased significantly, with the larval shell length being smaller 75 h after hatching. These results suggest that ocean acidification will potentially impact the marine population of Ezo abalone as a human food source in the future.  相似文献   
745.
A primary cDNA expression library with a titer of 5.0 × 105 PFU mL-1 was constructed from mRNA extracted from larval Haemaphysalis qinghaiensis ticks in order to identify certain genes,which would then be used as candidate molecules for development of effective vaccines to control this parasite.Totally 11 positive clones,which designated as HqL01-11,were obtained by immunoscreening of the library using a polyclonal antibody generated in rabbit with larval tick protein extract.Results of sequence analysis from BLASTN searching revealed that 6 of them had no significant homology with the adult H.qinghaiensis ticks’ known genes,4 of them had no significant homology with all genes deposited in GenBank database.HqL07,HqL08,HqL09,and HqL11 were deposited to GenBank database,and accession numbers were EF605263,EF605264,EF605265,and EF605266,respectively.Subsequently,HqL07 and HqL09 were expressed in vitro and the molecular weights of the corresponding expressed products were 60 and 70 kDa,respectively.Western blot analyses showed that HqL07 and HqL09 had immunogenicity.This study laid the foundation for future production of genetically engineered vaccines for the immunological control of H.qinghaiensis.  相似文献   
746.
Total lipid and fatty acid compositions were determined during embryogenesis and larval development in Eurasian perch (Perca fluviatilis). During embryonic development, perch did not catabolize lipids and fatty acids as an energy source. However, during larval development, there was an exponential relationship between the decrease in total lipids and the duration of starving (r 2=0.9957) and feeding (r 2=1). The duration of the starving period (10 days post hatching) was shorter than the feeding period (35 days post hatching). In both starved and fed larvae, there is an apparent preference in utilization of polyunsaturated fatty acids followed by monounsaturated fatty acids. Saturated fatty acids were utilized by neither fed perch larvae nor by starved perch larvae. In starved larvae, palmitoleic 16:1(n-7) and oleic 18:1(n-9) acids were the preferentially monounsaturated fatty acids catabolized and their contribution as energy source from total fatty acids catabolized over the first week was 37.6%. In fed larvae, these 2 nutrients were also the most monounsaturated fatty acids utilized as energy source and possibly also as precursors for others monounsaturated fatty acids biosynthesis. During the same period and among (n-6) polyunsaturated fatty acids, starved perch utilized less linoleic 18:2(n-6) and arachidonic 20:4(n-6) acids than fed larvae despite the fact that the starved perch were in more unfavorable nutritional conditions. In the case of (n-3) fatty acids, starved larvae utilized more linolenic acid 18:3(n-3) and less eicosapentaenoic 20:5(n-3) acid and docosahexaenoic 22:6(n-3) acid than fed perch. Starved larvae probably spared 20:5(n-3) and 22:6(n-3) for physiological functions.  相似文献   
747.
The larval development of the southern African endemic sparid Spondyliosoma emarginatum is described and illustrated from specimens collected in Algoa Bay and the Swartkops, Sundays and Swartvlei estuaries of the Cape Province. S. emarginatum has demersal eggs. Preflexion larvae are moderately elongate (BD = 18–23% BL) with body depth increasing to 31 % BL in postflexion stages. The head is rounded and the snout blunt but becomes more elongate in postflexion stages. There are short spines on the preoperculum. Flexion occurs at about 6 mm BL and postflexion larvae are characterized by distinct medio-lateral pigmentation. Osteological development is described from a series of cleared and stained specimens. All fins have the adult complement of spines and rays by 12 mm BL. The larvae of S. emarginatum are compared with those of the European S. canthurus and other southern African sparids.  相似文献   
748.
薯蓣零余子的原基起源于叶腋表层1~3层细胞。初期,原基细细胞团分化为内外两部分组织:外侧为薄壁组织及紧邻其内的囊状初生加厚分生组织,内侧为薄壁组织。初生加厚分生组织主要向内衍生细胞,它们分化为薄壁组织和散生其中的有限外韧维管束。零余子的外形多样,常呈块状,无节,基部有1~3个不定芽。从零余子原基外起源、幼期与叶芽间存在过渡型、有限外韧维管束和散生中柱等特点分析,表明其形态本质为茎;从零余子的芽为内起源、无顶端分生组织、主要靠初生加厚分生组织增大体积分析,则它又属于一种特殊的变态茎。  相似文献   
749.
大眼鳜幼鱼的发育和生长   总被引:3,自引:0,他引:3  
2000年4月2005年4月从嘉陵江合川江段收集大眼鳜亲鱼,通过人工催情获得受精卵,经孵化对其胚后发育和仔稚鱼的生长进行了研究.结果表明:大眼鳜仔稚鱼发育可分为卵黄囊期仔鱼、晚期仔鱼、稚鱼期3个阶段;初孵仔鱼全长4.6-5.2 mm,肌节数32-35对;在水温26.5-29.5℃条件下,历时45-50 d完成仔稚鱼外部形态变化和内脏器官建成;仔稚鱼期全长与日龄呈直线增长关系,拟合的回归方程为L=1.235 9T+1.312 1(R2=0.965 3),全长与肛后长的比值介于1.63~2.44之间.  相似文献   
750.
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