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   20240篇
  免费   2273篇
  国内免费   1535篇
林业   1494篇
农学   773篇
基础科学   1064篇
  2096篇
综合类   10746篇
农作物   1757篇
水产渔业   901篇
畜牧兽医   2777篇
园艺   1574篇
植物保护   866篇
  2025年   7篇
  2024年   495篇
  2023年   512篇
  2022年   1025篇
  2021年   934篇
  2020年   880篇
  2019年   857篇
  2018年   556篇
  2017年   965篇
  2016年   674篇
  2015年   964篇
  2014年   1124篇
  2013年   1318篇
  2012年   1652篇
  2011年   1713篇
  2010年   1624篇
  2009年   1486篇
  2008年   1454篇
  2007年   1368篇
  2006年   1248篇
  2005年   950篇
  2004年   610篇
  2003年   350篇
  2002年   358篇
  2001年   383篇
  2000年   338篇
  1999年   120篇
  1998年   14篇
  1997年   9篇
  1996年   7篇
  1995年   9篇
  1994年   8篇
  1993年   3篇
  1992年   7篇
  1991年   3篇
  1990年   3篇
  1989年   1篇
  1988年   2篇
  1986年   1篇
  1981年   3篇
  1965年   1篇
  1962年   3篇
  1956年   5篇
  1955年   4篇
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
41.
为探讨孕穗期叶面喷素对小麦穗粒数和粒重的调控效应,于2014-2015年在河南农业大学科教示范园区进行试验,以半冬性品种豫麦49-198为供试材料,在小麦拔节后25d(4月6号),以清水为对照,叶面分别喷施硼砂(B)、6苄基腺嘌呤(6-BA)、6-BA+B、奇善宝(QSB)、双增1号(CPD),对不同喷素条件下小花败育速率和籽粒灌浆进程及其成熟后小麦穗部性状进行观察和分析。结果表明,与对照相比,不同喷素处理均能降低小花的败育速率,显著增加小麦不同部位的小穗粒数和粒重。对小麦各部位小穗粒数的促进效果,以CPD处理对小麦下、中部小穗粒数提高幅度最大,分别较对照增加了1.95个和4.85个;对不同部位小穗粒重的促进效果,也以CPD处理效果最佳,使小麦下、中和上部小穗粒重分别较对照提高了11.97%、5.87%和9.32%。  相似文献   
42.
为探究实现水稻广谱持久抗性育种,以及水稻病害的有效防治,本研究利用文献中报道的与抗稻瘟病及白叶枯病相关的43个功能基因相关标记,研究了76个中国籼型(Oryza sativa ssp.indica)三系杂交水稻骨干亲本的遗传多样性。结果显示,36个标记具有多态性,多态性位点百分率(P)81.81%,共检测到87个等位基因位点;其中有效等位基因(Ne)61.96个,占71.22%,Nei’s遗传多样性指数(He)变幅为0.358~0.974,平均值0.629。76份材料间的遗传相似系数(Gs)变幅为0.341~0.925,平均值0.550。采用UPGMA法进行聚类分析,在遗传相似系数0.624处分为保持系和恢复系两类。保持系和恢复系间的遗传分化系数(Fst)为0.158,呈高度遗传分化,Nei遗传距离(D)0.201。结果显示,功能基因相关标记具有较高的DNA多态性检测效率,用于类群划分和种质资源的多样性分析等方面更具准确性和可靠性;中国三系杂交稻骨干亲本在43个功能基因位点的亲缘关系较近,遗传基础狭窄,同源性较高。但保持系群和恢复群系间在这些功能基因位点的遗传差异较大,遗传分化程度较高。研究结果提示,所研究材料在DNA水平存在丰富的杂种优势利用空间,特别随着更多更细的功能基因位点的发掘,为水稻分子辅助抗性选育以及病害防治提供了有效的实现途径。  相似文献   
43.
职技高师类院校数学实验课程教学改革探索   总被引:2,自引:0,他引:2  
对职技高师类院校数学实验课实施情况进行调查分析,针对在教与学两方面存在的问题,提出了优化数学实验课程教学内容与改革教学模式的理念,从新的视角对高校数学实验内容进行模块化方面提出了改革措施,并给出了数学实验课程的建设目标。  相似文献   
44.
AIM: To study the effect of ClC-3 gene over-expression on thyroid structure and function in mice.METHODS: Three-months-old FVB mice were used to study the difference of thyroid structure and function between wild-type (WT) mouse and ClC-3 transgene mice. The expression and distribution of ClC-3 in the thyroid of mice were determined by the methods of qPCR, Western blot and immunofluorescence. Behavioral monitoring was performed on the daily activities of mice. Serum concentrations of total triiodothyronine (TT3), total thyroxine (TT4) and thyrotropin (TSH) were measured by ELISA.RESULTS: Compared with the WT group, the expression of ClC-3 in the thyroid of ClC-3 transgene group was significantly increased (P<0.05). The thyroid gland showed obvious hyperplasia and the folliculi glandulae thyreoideae was significantly bigger in ClC-3 transgene mice (P<0.05). The weight loss was increased in ClC-3 transgene mice (P<0.05). The expression of TT3 and TT4 were significantly higher than that of WT group (P<0.05), but the change of TSH was not obvious.CONCLUSION: ClC-3 over-expression results in thyroid hyperplasia and thyroid hormone secretion. This study suggests that ClC-3 is likely to be involved in the synthesis of thyroid hormones.  相似文献   
45.
珠海淇澳岛红树林群落空气负离子浓度特征研究   总被引:4,自引:0,他引:4  
对珠海淇澳岛红树林群落空气负离子浓度特征进行研究。结果表明:无瓣海桑群落空气负离子浓度昼间变 化为“V冶型特征,秋茄和水黄皮群落内的空气负离子浓度的昼间变化表现出双峰曲线的变化特征。空气负离子的 年变化特征表现为夏、秋高于冬、春,且夏季最高,春季最低。红树林群落空气负离子浓度与相对湿度呈显著正相 关。在释放负离子能力方面,秋茄群落释放空气负离子的能力要优于水黄皮和无瓣海桑群落。红树林内一年四季 的空气质量等级均在A 级或B 级,表现出优良的空气质量。   相似文献   
46.
对张家口市奶牛场进行了奶牛乳腺炎调查并对25头患有急性乳腺炎奶牛的64个乳区64份乳样进行细菌分离与鉴定,共分离葡萄球菌、链球菌、沙门氏菌、棒状杆菌、大肠杆菌、酵母菌6种致病菌,其中,酵母菌最多,占32.81%,葡萄球菌和链球菌之和占40.63%.  相似文献   
47.
AIM: To investigate the effects of BARF1 down-regulation on EBV-positive gastric carcinoma cell apoptosis, and the molecular mechanisms by BARF1 silencing-mediated apoptosis. METHODS: After NUGC3 and SNU719 cells were transfected with NCsiRNA and siRNA, respectively, the protein levels of BARF1, Bcl-2, Bax, cytochrome C, caspase 3 and capase 9 were detected by Western blot, and the mRNA expression of BARF1, Bcl-2 and Bax was determined by RT-PCR. The cell viability was measured by the method of Trypan blue exclusion and the cell apoptosis was analyzed by flow cytometry analysis with Annexin V-FITC/PI staining. The expression of the apoptosis-related proteins in the cells transfected with siRNA and NCsiRNA was examined by human apoptosis antibody arrays. Mitochondrial membrane potential was determined by flow cytometry. The interaction between Apaf-1 and caspase 9 was confirmed by immunoprecipitation. RESULTS: Compared with untreated and NCsiRNA groups, BARF1 gene silencing significantly inhibited the cell viability, induced apoptosis, and reduced the mitochondrial membrane potential in the NUGC3 and SNU719 cells transfected with siRNA. BARF1 gene silencing up-regulated the expression of pro-apoptotic proteins and down-regulated the expression of anti-apoptotic proteins, and the Bcl-2/Bax ratio was significantly decreased. In BARF1 gene silencing cells, the caspase inhibitor z-VAD-fmk inhibited BARF1 silencing-mediated apoptosis, and significantly increased the levels of cleaved caspase 3 and caspase 9. The concentration of cytochrome C significantly increased as compared with NCsiRNA group, and Apaf-1 interacted with caspase 9 in the cytoplasm. CONCLUSION: BARF1 silencing induces apoptosis via the mitochondrial pathway through regulating the expression of Bcl-2 and Bax proteins in a caspase-dependent manner in the NUGC3 and SNU719 cells.  相似文献   
48.
不同性诱剂对甜菜夜蛾雄蛾诱捕效果的研究   总被引:3,自引:1,他引:3  
通过大田试验,对3种甜菜夜蛾性诱剂的诱捕效率、持效期等性能进行了测定,并分析比较了它们在不同时间段的性能差异。结果表明,三者之间存在着明显差异,在1~31 d内,诱芯A与诱芯B的平均诱捕量相近,极显著高于诱芯C的平均诱捕量,三者的持效期差异亦然;而诱芯B与诱芯C的最高诱捕量相仿,均明显低于诱芯A。但在1~10 d内,诱芯A和诱芯C的平均诱捕量相近,均极显著高于诱芯B。  相似文献   
49.
AIM: To detect the effects of NK cells on the etiology of severe pre-eclampsia. METHODS: The peripheral blood and umbilical blood from severe pre-eclamptic patients and normal late pregnant women were collected. NK cells were seperated in percoll and counted by SAP. The proliferating ability of NK cells was measured by MTT and killing power of NK cells was determined by [51Cr] releasing test. The immunohistochemistry method was used to detect the quantity of NK cells and the expression of HLA-G in placenta of them. RESULTS: (1) Compared with that in normal late pregnant women, the counts of the NK cells in peripheral blood, umbilical blood and decidua of severe pre-eclamptic patients were significantly higher (all P<0.05). (2) Compared with that in normal late pregnant women, proliferating and killing ability of NK cells in peripheral blood and umbilical blood of severe pre-eclamptic patients were significantly higher. (3) The expression of HLA-G protein in placenta of severe pre-eclampsia group was lower than that in normal group (P<0.05). CONCLUSION: The quantity of NK cells in severe pre-eclamptic patients is increased with stronger biologic function. They may be related with the pathogenesis of severe pre-eclampsia.  相似文献   
50.
研究周氏啮小蜂防治美国白蛾林间释放技术,结果表明:对于蜂茧,其对美国白蛾的寄生率最大可达到68%,放蜂20~25 d后离放蜂点100 m以内,周氏啮小蜂的寄生率可达20%以上,有一定的控制效果。  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