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   17459篇
  免费   960篇
  国内免费   1219篇
林业   1744篇
农学   1351篇
基础科学   533篇
  1908篇
综合类   8240篇
农作物   932篇
水产渔业   701篇
畜牧兽医   2884篇
园艺   615篇
植物保护   730篇
  2024年   60篇
  2023年   224篇
  2022年   329篇
  2021年   387篇
  2020年   425篇
  2019年   452篇
  2018年   314篇
  2017年   510篇
  2016年   643篇
  2015年   594篇
  2014年   840篇
  2013年   838篇
  2012年   1261篇
  2011年   1334篇
  2010年   1043篇
  2009年   1166篇
  2008年   1110篇
  2007年   1210篇
  2006年   1067篇
  2005年   901篇
  2004年   694篇
  2003年   521篇
  2002年   488篇
  2001年   460篇
  2000年   398篇
  1999年   326篇
  1998年   255篇
  1997年   255篇
  1996年   238篇
  1995年   214篇
  1994年   207篇
  1993年   149篇
  1992年   143篇
  1991年   125篇
  1990年   109篇
  1989年   101篇
  1988年   53篇
  1987年   59篇
  1986年   36篇
  1985年   11篇
  1984年   16篇
  1983年   11篇
  1982年   7篇
  1981年   8篇
  1980年   9篇
  1979年   9篇
  1978年   4篇
  1977年   6篇
  1976年   7篇
  1956年   3篇
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
81.
AIM:To investigate expression and function of CD40 ligand by peripheral blood mononuclear cells (PBMCs) in patients with systemic lupus erythematosus (SLE).METHODS:Expression of CD40 ligand by PBMCs in patients with SLE and control were examined by flow cytometric analysis before and after stimulated by phytohemagglutinin(PHA)and depressed by Dexamethasone(Dex). The correlation between expression of CD40 ligand and SLE activity index(SLEDAI) was analysed in patients with SLE.RESULTS:The expression of CD40 ligand by PBMCs in patients with active SLE was higher than that in patients with inactive SLE and control. Though the expression of CD40 ligang by PBMCs could be stimulated by PHA in three groups, it was the highest in patients with active SLE. Dex depressed the expression of CD40 ligand by PBMCs significantly in patients with SLE, but not in control. There was high positive correlation between expression of CD40 ligand and SLEDAI in patients with active and inactive SLE.CONCLUSION:Increased expression of CD40L by PBMCs in patients with SLE may play an important role in pathogenesis of SLE.  相似文献   
82.
毒死蜱和甲氰菊酯对家蚕毒性与安全评价研究   总被引:24,自引:3,他引:24  
通过食下毒叶法和接触法测定了毒死蜱和甲氰菊酯对家蚕的毒性。结果表明:食下毒叶法对2龄起蚕的LC50(48h)分别为:毒死蜱2.3322mg/kg桑叶和甲氰菊酯0.1522mg/kg桑叶,其浸渍桑叶的药液浓度分别为4.6622mg/L和0.3044mg/L。接触法中毒死蜱和甲氰菊酯对2龄起蚕的LC50值(24h)分别为:6.32μg/cm2和0.92μg/cm2。毒死蜱和甲氰菊酯的毒性比都<1,对家蚕的毒性为高毒。  相似文献   
83.
甜菜夜蛾性信息素组分的鉴定及其田间试验   总被引:8,自引:0,他引:8  
采用气相色谱仪(GC)及气质联用仪(GC-MS)等技术对我国甜菜夜蛾性信息素组分的鉴定结果表明,雌蛾性信息素腺体中含有4种组分,分别为Z9,E12-14:Ac(A)、Z9-14:OH(B)、Z9-14:Ac(C)和Z9,E12-14:OH(D);田间和室内种群各组分的比例(A:B:C:D)分别为47:18:18:17和43:18:23:16,比例及滴度在两种群间未有显著差异;雄蛾田间引诱测定表明,组分A、B显示性信息素活性。几种不同配比的硅橡胶塞诱芯在田间均显示极高的诱蛾活性,以9:1的AB二元诱芯(剂量100μg)最高,其诱蛾量与黑光灯相当,两者呈显著的正相关性,表明该诱芯可替代黑光灯用于甜菜夜蛾的种群测报。利用性诱捕器进行田间种群监测显示,1999年浙江省慈溪市的甜菜夜蛾共发生6代,以第4、5代发生量最高。  相似文献   
84.
 小麦(Triticum aestivum)品种洛夫林10和叶锈菌小种366组成不亲和组合,小麦叶片发生过敏性坏死反应(HR)是小麦抵抗叶锈菌侵染的重要因素。在接种前给小麦叶片分别预注射微管解聚药物磺草硝(oryzalin)和微丝解聚药物细胞松弛素D (cytochalasin D,CD),结果表明2种药物注射使得寄主因叶锈菌侵染诱导的细胞过敏性坏死数目明显减少,并且注射药物的浓度越大,寄主细胞发生HR的数量越少。说明肌动蛋白和微管蛋白的聚合状态是诱发小麦叶片发生HR防卫反应所必需的,细胞骨架在小麦抵抗叶锈菌侵染过程中可能起着重要作用。  相似文献   
85.
培养条件对酸枣叶片不定梢再生率的影响   总被引:7,自引:0,他引:7  
以酸枣无菌苗叶片为外植体,选用基本培养基NN69和WPM,外源激素包括TDZ、IAA、IBA和NAA,暗培养时间为2、3、4周。采用正交实验设计方法,研究了基本培养基、外源激素及暗培养时间对叶片不定梢再生的影响。结果表明在附加TDZ1~3mg/L的WPM和NN69上都可诱导不定梢再生,但WPM比NN69更有效。暗培养时间对不定梢再生也有影响,暗培养3周比2、4周更有利于提高叶片的不定梢再生率。在附加TDZ1mg/L、IAA0.1mg/L的WPM培养基上,暗培养3周后转到光下培养,获得的不定梢再生率达87.5%。  相似文献   
86.
CPPU在柿试管繁殖中的应用   总被引:6,自引:0,他引:6  
艾鹏飞  罗正荣 《果树学报》2002,19(4):272-274
对CPPU和ZT在柿试管繁殖中的应用价值进行了比较研究,结果表明:CPPU是一种可代替ZT的特效细胞分裂素,添加有CPPU0.2mg/L的MS(1/2N)培养基能促进芽的增殖和生长,且用此培养基继代培养的试管苗生根能力也有所提高。  相似文献   
87.
AIM: To probe into the genetic susceptibility of HLA-DRB1 alleles to esophageal neoplasm in Hubei Han Chinese. METHODS: HLA-DRB1 gene polymorphism in 42 patients with esophageal neoplasm and 136 normal control subjects was studied by PCR and sequence. RESULTS: Allele frequency of HLA-DRB1 *0901 allele was significantly higher in esophageal cancer patients than those in normal controls(0.2500 vs 0.1397, P =0.028; the odds ratiO2.053; etiologic fraction 0.1282).There were no association between the rested HLA-DRB1 alleles with patients. CONCLUSION: Individuals carrying HLA-DRB1 *0901 may be susceptible to esophagealo carcinoma, its nucleotide sepuence approachs to the corresponded allele sequence(exoN2)published in GenBank.  相似文献   
88.
Seasonal distribution of phytoplasmas in Australian grapevines   总被引:1,自引:0,他引:1  
The distribution and persistence of phytoplasmas were determined in Australian grapevines. Phytoplasmas could be detected using the polymerase chain reaction (PCR) from shoots, cordons, trunks and roots throughout the year, and phytoplasmas appear to persistently infect Australian grapevines from year to year. Phytoplasmas were not always detected in samples from the same sampling area from one sampling period to the next. Phytoplasma detection by PCR was improved by sampling from shoots, cordons and trunks, especially during October (early spring). The diseases expressed by the 20 grapevines used in the distribution and persistence studies were monitored. Australian grapevine yellows disease (AGY) was expressed by 17/20 grapevines at some time during the study, whilst only 4/20 and 15/20 grapevines expressed restricted growth disease (RG) and late season leaf curl disease (LSLC), respectively. All grapevines with RG and LSLC also had AGY. The three diseases were persistently expressed in some grapevines and remission of disease was observed in others. The results of PCR detection in the same grapevines indicated that phytoplasmas were more frequently detected in AGY-affected grapevines that also expressed RG and LSLC compared with grapevines expressing AGY alone. Phytoplasmas were detected in symptomless plant material but less frequently compared with AGY-affected material.  相似文献   
89.
A rapid resistance/susceptibility test for Peronospora parasitica (downy mildew) was established by inoculating leaf-disks of four Brassica oleracea accessions. Several conditions were tested: disk disinfection or not, agar medium with or without nutrients and with 50 or 100 ppm of benzimidazole. Using disinfected disks placed on agar (no nutrient and benzimidazole at 50 or 100 ppm), the responses of leaf-disks to four isolates were similar to those obtained using the classical cotyledon test, whereas undesired contaminations occurred in all other conditions. The possible effect of the particular leaf used for obtaining the disks was also studied. In each incompatible interaction tested, disks were resistant whatever the leaf used. In compatible interactions, susceptible phenotypes were observed on disks derived from the six lowest leaves, but disks from upper leaves were resistant. The genetic basis of resistance in a F1 hybrid broccoli was assessed, by testing six isolates on an F2 population derived from this hybrid. The cotyledon test only allows inoculation of two isolates per seedling, whereas many isolates can be tested on each plant by using leaf-disks. The segregation of the resistance to each of the six isolates was analysed: two dominant genes (tightly linked) control resistance to all isolates (one to five isolates; the other to only one isolate).  相似文献   
90.
内蒙河套灌区盐碱低产田建立有机质富积层改土培肥效果   总被引:1,自引:0,他引:1  
通过连续四年在内蒙古河套灌区低产盐碱地定点、定位试验与定时测土分析,明确了土壤耕层增施有机物料建立有机质富积层,能够改善土壤理化性状,尤其是能降低土壤表层含盐量,提高作物保苗率和显著增加作物产出量。  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