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   17917篇
  免费   806篇
  国内免费   1777篇
林业   857篇
农学   1620篇
基础科学   372篇
  2513篇
综合类   6661篇
农作物   1185篇
水产渔业   769篇
畜牧兽医   4327篇
园艺   1386篇
植物保护   810篇
  2024年   51篇
  2023年   241篇
  2022年   416篇
  2021年   645篇
  2020年   597篇
  2019年   719篇
  2018年   480篇
  2017年   742篇
  2016年   902篇
  2015年   841篇
  2014年   933篇
  2013年   1084篇
  2012年   1358篇
  2011年   1439篇
  2010年   1268篇
  2009年   1269篇
  2008年   1090篇
  2007年   1202篇
  2006年   991篇
  2005年   693篇
  2004年   576篇
  2003年   451篇
  2002年   346篇
  2001年   282篇
  2000年   280篇
  1999年   246篇
  1998年   154篇
  1997年   163篇
  1996年   159篇
  1995年   135篇
  1994年   94篇
  1993年   101篇
  1992年   88篇
  1991年   79篇
  1990年   73篇
  1989年   70篇
  1988年   50篇
  1987年   40篇
  1986年   34篇
  1985年   30篇
  1984年   19篇
  1983年   11篇
  1982年   7篇
  1981年   6篇
  1980年   7篇
  1979年   5篇
  1978年   5篇
  1977年   6篇
  1962年   4篇
  1956年   9篇
排序方式: 共有10000条查询结果,搜索用时 312 毫秒
41.
通过对不同基因型黑杨无性系植株净光合速率日变化曲线与光合主体叶面积在时间和光强上进行累计积分来计算植株日CO2固定总量P。由于净光合速率日变化曲线不易准确测得,故以光响应曲线和光强的日变化来推测净光合速率日变化。对P值和生物量的相关性研究表明,二者的相关性很高。且认为可以用计算出的P值作为评估苗木生产潜势的指标之一,这为育种中生产力的早期选择提供了有力的证据。  相似文献   
42.
2型猪链球菌的血清学鉴定   总被引:41,自引:0,他引:41  
本试验首次证实了2型猪链球菌在我国的存在,采用玻片凝集、琼脂扩散及毛细管沉淀等3项试验,对1990年以来广东某猪场断奶仔猪暴发流行的败血症、脑膜炎及关节炎病猪中分离的15株链球菌进行了血清学鉴定。结果表明:15株链球菌均为2型猪链球菌;用高压法提取抗原进行沉淀反应,其结果比酸热法提取抗原具有简便、敏感、特异性强的特点。  相似文献   
43.
This review describes the discovery and identification of the pathogenesis-related proteins (PRs) from tobacco. In crude leaf extracts the PRs are distinguished from the proteins in uninfected plants by their solubility at pH 3, resistance to a range of proteases, and mobility in polyacrylamide gels upon electrophoresis (PAGE) in non-denaturing conditions. PAGE has been used as a qualitative and semi-quantitative assay for PRs, and their migration in gels made from different acrylamide concentrations has been used to identify charge and size isomers and electrophoretically identical PRs in different tobacco cultivars. The subunit composition and molecular weight (mol. wt) of the four PRs identified first in Xanthi-nc were determined by SDS-PAGE; staining the gels has shown that these same four proteins in Samsun NN did not contain carbohydrate, lipid or nucleic acid, nor were they isozymic forms of twenty five enzymes known to increase in activity following infection with TMV. Evidence suggests that most of the PRs in Xanthi-nc and Samsun NN are extracellular.The purification of several PRs from Xanthi-nc, Samsun NN and other tobaccos is described, as well as their mol. wt, subunit and amino acid composition. PRs 1a, b and c consist of a single polypeptide and have similar mol. wt and amino acid compositions. Antisera prepared against purified Xanthi-nc b1 protein have been used to determine serological relationships between PRs and form the basis of a very sensitive quantitative assay using ELISA. The regulation of synthesis of some PRs has been shown to involve translational control.  相似文献   
44.
应用种子蛋白电泳图谱对高羊茅品种进行鉴别与聚类研究   总被引:2,自引:2,他引:0  
利用种子贮藏蛋白进行二二烷其磺酸钠-聚丙烯酰胺凝脉电泳,对23个高羊茅品种进行了 分析。表明该方法成本低,效率高,重复性好,能有效地反应高羊茅品种的遗传差异和亲缘关系。电泳谱带聚类分析所得到的类群,能代表生产上,饲用,草坪用类型以及两种用途中的主要生态类型。  相似文献   
45.
INTRODUCTIONIntheworldoftoday,theglobalclimatechangeanditsinfluenceonecologyhavebe-comeaveryimportantproblem,towhichmanyscientists,governnentleadersandordinarypcoplepaycloseattentionI1-'].Inl979,theWorldClimateResearchProgram(WCP)waslaiddowninthefirstworldclimatemeeting.lnl99(),thesecondworldclimatemeetingwasconvcl1edinGencva,andalltl1eexpertsagreedthattheglobalwarmlngwillbeextremelyseriousdisasterthananynatUralcalamityever.Attl1eMectingof"WorldEnvironmentandDevelopment,"holdinBrazil…  相似文献   
46.
The position of plants withRhizoctonia solani sclerotia (black scurf) on progeny tubers was mapped for an experimental field at Haren where potatoes were grown continuously and in rotation with other crops for five successive years, and for another field at Borgercompagnie with a 12 frequency of potatoes during three potato crops. Initially, the distribution of plants with black scurf on both fields was rather dense and homogeneous. In the following years the distribution became heterogeneous and patchy. The local decline ofR. solani AG 3 (the common potato pathogen) in Haren was apparently caused by an unknown factor selectively suppressingR. solani AG 3, while simultaneouslyR. solani AG 5 increased in mass. This AG 5 type proved to be an inferior competitor of AG 3 on the potato plant in a laboratory experiment. The specificR. solani antagonistVerticillium biguttatum did not play a role. A similar factor could have reduced the formation of black scurf in the experimental field at Borgercompagnie, whereV. biguttatum was also too infrequent to account for the decline.R. solani AG 5 was not present here and could not indicate the presence of a selective factor against AG 3.  相似文献   
47.
Pleural effusions from 23 dogs and 25 cats hospitalized between November 1986 and April 1987 at the Veterinary Hospital of the University of Pennsylvania (VHUP) were classified as chylous (chylomicrons present) or nonchylous (chylomicrons absent) by the presence or absence, respectively, of a chylomicron band on lipoprotein electrophoresis gels of the effusions. Triglyceride concentrations, cholesterol concentrations, and cholesterol/triglyceride (C/T) ratios were compared between the chylous and nonchylous groups in each species. Cholesterol concentrations were not significantly different between chylous and nonchylous effusions in both dogs and cats. Cholesterol/triglyceride ratios of less than 1 were present in all dogs and cats with chylous effusions; however, 12% of dogs with nonchylous effusions and 50% of cats with nonchylous effusions also had a C/T ratio less than 1. Triglyceride concentrations accurately classified all effusions as chylous or nonchylous in both dogs and cats. Pleural effusions with triglyceride concentrations greater than l00 mg/dl were chylous in all cases, whereas, effusions with triglyceride concentrations less than l00 mg/dl were nonchylous in all cases.  相似文献   
48.
Type III procollagen peptide (P-3-P) is a serum marker for hepatic fibrosis in humans. The utility of a commercially available radioimmunoassay for P-3-P was evaluated in the dog. The specificity of the assay was assessed by polyacrylamide gel electrophoresis (PAGE) of canine serum and purified bovine P-3-P, followed by Western immunoblotting with rabbit aniti-P-3-P serum. The sensitivity was assessed by performing the radioimmunoassay on dilutions of sera from 22 dogs. Polyacrylamide gel electrophoresis of purified bovine P-3-P and sera from two dogs suspected of having elevated P-3-P concentrations revealed no homologous bands of staining. Western immunoblotting showed marked cross-reactivity of the high antisera concentrations with several components of the serum proteins, but none corresponding to the purified P-3-P. All tested sera from dogs had minimal competitive binding with radiolabeled P-3-P in the radioimmunoassay. Dilution curves of dog sera did not parallel either the standard curve or the dilution curve of a known test human serum. There were no statistically different P-3-P concentrations in any of the groups of dogs studied. It was concluded that currently available radioimmunoassay kits for the measurement of P-3-P in the human are not applicable in the dog. Seemingly, the structure or metabolism of canine P-3-P may vary significantly from that of the bovine or human, limiting the sensitivity and specificity of this assay in the dog.  相似文献   
49.
 外源Ca2 +能降低高温下黄瓜单核期花药的胞内Ca2 +水平并提高花粉萌发率, 而ABA的作用与此相反。外源Ca2 +和ABA处理能显著提高高温下黄瓜花药内源ABA的水平, 并产生新的蛋白质。以上结果表明, 高温下外源Ca2 +可影响黄瓜花药内ABA信号系统, 继而可能改变基因表达, 并获得耐热性;外源ABA亦能影响黄瓜花药内Ca2 +信号系统。  相似文献   
50.
蛋白质组学研究技术及其在果树学中的应用   总被引:7,自引:3,他引:7  
蛋白质组研究是当今生命科学发展的一个新的增长点,它能阐明基因组所表达的真正执行生命活动的全 部蛋白质的表达规律和生物功能。简要介绍了蛋白质组学产生的科学背景、研究方法和研究内容。蛋白质组学研究 方法主要有双向聚丙烯酰胺凝胶电泳(2D-PAGE)、质谱(Mass-spectrometric)技术、蛋白质芯片(Protein chips)技术、酵母 双杂交系统(Yeast two-hybrid system)、双向高效柱层析和生物信息学等。其应用的范围包括植物群体遗传学、在个体 水平上植物对生物和非生物环境的适应机制、植物的发育和组织器官的分化过程,以及不同亚细胞结构在生理生态 过程中的作用等诸多方面。同时展望了植物蛋白质组学研究前景以及蛋白质组学技术在果树学中的应用前景。  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