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   2581篇
  免费   118篇
  国内免费   229篇
林业   293篇
农学   316篇
基础科学   156篇
  421篇
综合类   817篇
农作物   144篇
水产渔业   79篇
畜牧兽医   475篇
园艺   103篇
植物保护   124篇
  2024年   7篇
  2023年   50篇
  2022年   88篇
  2021年   81篇
  2020年   95篇
  2019年   82篇
  2018年   70篇
  2017年   92篇
  2016年   79篇
  2015年   85篇
  2014年   97篇
  2013年   132篇
  2012年   177篇
  2011年   198篇
  2010年   185篇
  2009年   153篇
  2008年   154篇
  2007年   131篇
  2006年   92篇
  2005年   131篇
  2004年   67篇
  2003年   91篇
  2002年   98篇
  2001年   68篇
  2000年   64篇
  1999年   48篇
  1998年   43篇
  1997年   36篇
  1996年   37篇
  1995年   34篇
  1994年   21篇
  1993年   28篇
  1992年   21篇
  1991年   21篇
  1990年   22篇
  1989年   13篇
  1988年   7篇
  1987年   6篇
  1986年   5篇
  1985年   2篇
  1982年   1篇
  1981年   2篇
  1980年   3篇
  1978年   2篇
  1977年   1篇
  1974年   2篇
  1972年   1篇
  1962年   1篇
  1958年   1篇
  1956年   1篇
排序方式: 共有2928条查询结果,搜索用时 9 毫秒
991.
YU Shou-he  HONG An 《园艺学报》2013,29(3):481-487
AIM:To explore the relationship between macroautophagy and Runx2-induced osteogenic differentiation of C2C12 cells.METHODS:The cells of C2C12/Runx2Dox subline were used in the study, which expresses Runx2 in response to doxycycline (Dox). The cells were treated with Dox (10 mg/L) for 0 d, 1 d, 3 d, and 6 d, and the expression levels of LC3b, Beclin-1, p62, and LAMP-2 were detected at each time point using real-time qPCR. The LC3-I/LC3-II ratio was measured by Western blotting. The cells were treated with different concentrations of 3-methyladenine (3-MA) or rapamycin (Rap) for 14 days in the presence of Dox, and the alkaline phosphatase (ALP) activity was measured. The cells were treated with 3-MA (5 mmol/L) or Rap (10 μmol/L) for 1 d, 3 d, and 6 d in the presence of Dox, and the expression levels of ALP and osteocalcin (OC) were detected.RESULTS:The expression levels of LC3b and Beclin-1 were dramatically down-regulated during Runx2-induced osteogenic differentiation of C2C12 cells, and the levels of p62 and LAMP-2 were not changed during this process. The conversion of LC3-I into LC3-II was inhibited. The ALP activity was increased in 3-MA (5 mmol/L)-treated cells, but decreased in Rap (10 μmol/L)-treated cells. The expression levels of ALP and OC were up-regulated by 3-MA treatment and were down-regulated by Rap treatment.CONCLUSION:Runx2 induces osteogenic differentiation of C2C12 cells by inhibiting the formation of autophagosome through down-regulating LC3 and Beclin-1 as well as inhibiting the conversion of LC3-I to LC3-II.  相似文献   
992.
The spectroscopic properties of liposomal curcumin in pH 7.0 sodium phosphate buffer were studied at various curcumin concentrations and temperatures. At 25 °C, liposomal curcumin exhibited much higher values than free curcumin in absorption maximum, fluorescence maximum, and fluorescence anisotropy. When curcumin concentration was increased from 2 to 20 μM, the values of fluorescence anisotropy of liposomal curcumin decreased gradually, consistent with the reduction of phase transition temperature of liposome. This observation revealed that liposomal curcumin can disrupt the packing of phospholipid bilayer and give a loose and disordered structure. On the other hand, as the temperature was increased from 25 to 80 °C, the relative intensity of maximum absorption of liposomal curcumin showed a more pronounced decrease above the phase transition temperature than lower temperatures, suggesting a weaker curcumin protection from the liquid crystalline phase of phospholipid bilayer than the rigid gel phase. However, it was observed that the fluorescence anisotropy of liposomal curcumin had higher values as the temperature increased. This phenomenon was explained as the result of location change of curcumin toward the core of phospholipid bilayer, although the structure of the phospholipid bilayer tended to be looser at higher temperatures.  相似文献   
993.
On the basis of glycine-dimethyl phosphite synthesis of glyphosate, a new synthesis approach of glyphosate, without using triethylamine and the establishment of triethylamine recovery equipment, was designed in the laboratory. The environmental pollutants were reduced. The influences of reactant amount (mol), reaction temperature (°C), and reaction time (min) on the glyphosate yield and purity were investigated. The results showed that the glyphosate yield and purity could be 80.12 and 86.31 wt %, respectively, under the optimum scheme for glyphosate yield (glycine consumption, 0.1 mol; dimethyl phosphite consumption, 0.12 mol; condensation reaction temperature, 50 °C; hydrochloric acid consumption in hydrolysis reaction, 0.35 mol; temperature of acidification with hydrochloric acid, 10 °C; adjusting hydrolysis product pH value, 1.0; time of dropping esterifying liquid into hydrochloric acid in hydrolysis reaction, 80 min; hydrolysis reaction temperature, 120 °C; and vacuum distillation time, 90 min), and the glyphosate yield and purity could be 77.92 and 94.94 wt %, respectively, under the optimum scheme for glyphosate purity (glycine consumption, 0.1 mol; dimethyl phosphite consumption, 0.1 mol; condensation reaction temperature, 50 °C; hydrochloric acid consumption in hydrolysis reaction, 0.35 mol; temperature of acidification with hydrochloric acid, 10 °C; adjusting hydrolysis product pH value, 1.5; time of dropping esterifying liquid into hydrochloric acid in hydrolysis reaction, 60 min; hydrolysis reaction temperature, 110 °C; and vacuum distillation time, 90 min). The product structures under the two schemes were confirmed by means of FTIR (Fourier transform infrared spectroscopy) and (1)H NMR ((1)H nuclear magnetic resonance spectroscopy).  相似文献   
994.
不同氮磷钾施肥量对烤烟农艺性状及养分吸收的影响   总被引:6,自引:2,他引:4  
研究氮磷钾用量对烟草生长和叶片养分吸收的影响,大田试验结果表明,不同水平的N、P、K施肥量明显影响烟株的长势,影响程度N>K>P,综合考虑产量和上等烟比例,以施肥量N 112.5 kg/hm2、P2O5112.46 kg/hm2、K2O 269.84 kg/hm2的N2P2K2处理最好,某种元素不足或过量都会降低上等烟比例。施用适量的氮有利于烤烟中N和K的吸收,而过量50%的N3水平的氮使烟草钾含量降低了11%。磷浓度过高或过低都会降低N和K的积累。增施K肥有利于N和K的积累,其中钾含量最高增长幅度可达37%。随着氮用量增加,上等级烟氮肥农学利用率呈直线下降的趋势,而磷、钾农学利用率在一定氮磷钾用量范围内增加。  相似文献   
995.
为明确贵州烤烟棒孢霉叶斑病病原菌种类及生物学特性,本研究采用常规组织分离法对贵州省采集的烟叶进行病原菌分离与纯化,根据柯赫氏法则进行致病性测定,得到两个代表菌株YC1002和YC1104,通过形态学特征及ITS序列将其鉴定为多主棒孢霉(Corynespora cassiicola).生物学特性研究结果表明:病原菌在胡萝卜琼脂培养基(CA)上生长最快,在燕麦琼脂培养基(OA)上产孢量最多,最适生长温度为30℃,最适宜pH 6,菌丝致死温度为52℃ 10 min,光照对菌落生长影响不大.最适碳源为麦芽糖和可溶性淀粉,最适氮源为甘氨酸和苏氨酸.研究结果可为生产上烤烟棒孢霉叶斑病的有效防治提供一定的理论依据.  相似文献   
996.
安明珠  赵世伟  朱文露  韩博  文亦芾  周凯 《草学》2022,(1):30-36,47
为筛选适用于鸭茅物种的基因引物序列,开展相关系统发育学研究,通过搜集鸭茅近缘物种叶绿体基因引物,使用PCR扩增技术和琼脂糖凝胶电泳检测来筛选出目的基因片段,对目的基因进行BLAST序列比对.结果表明:试验搜集的35对引物中共能筛选出trnL-F 1、trnL-F 5、rpL162、rpL164、matK 6、matK ...  相似文献   
997.
Six new prenylated indole diketopiperazine alkaloids, asperthrins A–F (1–6), along with eight known analogues (7–14), were isolated from the marine-derived endophytic fungus Aspergillus sp. YJ191021. Their planar structures and absolute configurations were elucidated by HR-ESI-MS, 1D/2D NMR data, and time-dependent density functional theory (TDDFT)/ECD calculation. The isolated compounds were assayed for their inhibition against three agricultural pathogenic fungi, four fish pathogenic bacteria, and two agricultural pathogenic bacteria. Compound 1 exhibited moderate antifungal and antibacterial activities against Vibrio anguillarum, Xanthomonas oryzae pv. Oryzicola, and Rhizoctonia solani with minimal inhibitory concentration (MIC) values of 8, 12.5, and 25 μg/mL, respectively. Furthermore, 1 displayed notable anti-inflammatory activity with IC50 value of 1.46 ± 0.21 μM in Propionibacterium acnes induced human monocyte cell line (THP-1).  相似文献   
998.
玉米自交系表型性状与产量的灰色关联分析   总被引:2,自引:0,他引:2  
以257份玉米自交系为材料,采用灰色关联分析方法,对影响玉米自交系产量(单株粒重)的主要表型性状进行研究。结果表明:关联序排在前三位的是全生育期、散粉期与吐丝期,生育期是影响玉米自交系单株粒重最重要的因素,其他性状与单株粒重的密切程度依次减小;与产量相关的主要性状中,关联序排在前三位的是穗位、穗长、百粒重;总体排序为全生育期>散粉期>吐丝期>穗位>穗长>百粒重>全株叶数>株高>穗位叶面积>穗粗>出苗期>行粒数>行数;高产玉米自交系选育目标:尽量延长生育期,提高穗长及百粒重,其他性状适中,协调相关因素,提高产量。本试验利用大量有代表性的玉米自交系,明确了主要农艺性状对产量的贡献,为选育高产玉米自交系提供了理论参考依据。  相似文献   
999.
安喜平  赵凯  李嘉  吴燕  李树 《农业工程》2013,3(1):31-34
采用膜生物反应器(MBR)-高级氧化(AOPs)工艺对餐饮废水进行了深度处理试验研究。结果显示,经一级高级氧化预处理后进水COD平均值为1 370 mgL,MBR出水均值可达118 mgL,高级氧化深度处理出水为57 mgL,同时工艺对去除SS、色度等优势明显,出水均达到国家中水回用标准(GBT 19820-2002城市杂用水标准)。   相似文献   
1000.
试验旨在研究日粮添加不同水平微生态制剂对樱桃谷鸭生产性能的影响,确定最佳添加水平。选用1日龄樱桃谷鸭750只,随机分成5个组(试验Ⅰ、Ⅱ、Ⅲ、Ⅳ、Ⅴ组,Ⅴ组为对照组),每组设3个重复,每个重复50只。分别在基础日粮中添加500、1000、1500、2000和0 mg/kg微生态制剂,饲养至42日龄。结果表明,添加1000和1500 mg/kg的微生态制剂促生长效果显著高于对照组(P<0.05);添加1000 mg/kg微生态制剂的肉鸭全程料重比最佳;添加500 mg/kg的微生态制剂组对肉鸭增重不明显;添加2000 mg/kg的微生态制剂组优于对照组和500 mg/kg添加组,但差异不显著(P>0.05)。因此,日粮微生态制剂能促进樱桃谷肉鸭的增重、降低料重比,从而提高其生长性能、产肉性能及养殖效益,1000 mg/kg微生态制剂能取得最佳料重比和经济效益,1500 mg/kg微生态制剂能取得最佳产肉性能,由此可知,添加1000 mg/kg微生态制剂为最佳添加水平。  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