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   35518篇
  免费   2124篇
  国内免费   3601篇
林业   2424篇
农学   2250篇
基础科学   1799篇
  3686篇
综合类   16707篇
农作物   2499篇
水产渔业   1282篇
畜牧兽医   6260篇
园艺   2659篇
植物保护   1677篇
  2024年   247篇
  2023年   730篇
  2022年   1709篇
  2021年   1670篇
  2020年   1536篇
  2019年   1521篇
  2018年   1100篇
  2017年   1686篇
  2016年   1193篇
  2015年   1822篇
  2014年   1901篇
  2013年   2255篇
  2012年   3100篇
  2011年   3141篇
  2010年   2918篇
  2009年   2599篇
  2008年   2607篇
  2007年   2391篇
  2006年   1931篇
  2005年   1492篇
  2004年   929篇
  2003年   540篇
  2002年   641篇
  2001年   542篇
  2000年   504篇
  1999年   209篇
  1998年   49篇
  1997年   35篇
  1996年   33篇
  1995年   34篇
  1994年   32篇
  1993年   22篇
  1992年   31篇
  1991年   16篇
  1990年   11篇
  1989年   9篇
  1988年   6篇
  1987年   5篇
  1986年   3篇
  1981年   3篇
  1980年   1篇
  1973年   2篇
  1969年   1篇
  1965年   1篇
  1962年   11篇
  1956年   12篇
  1955年   6篇
  1938年   1篇
  1931年   1篇
  1928年   1篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
不同地下水位植物蒸腾耗水特性研究   总被引:20,自引:6,他引:20  
在甘肃省民勤治沙站利用非称量测渗仪研究了梭梭、柠条等 10种沙区植物的蒸腾耗水特征。结果表明 ,各种植物 5a的总蒸腾量由大到小排列为 :沙枣、花棒、沙木蓼、柠条、梭梭、白皮沙拐枣 ;随植物年龄增长 ,蒸腾系数有上升的趋势 ,而蒸散系数有下降的趋势 ;在民勤沙区 6~ 9月是主要蒸腾季节 ,该时段的蒸腾量占全年蒸腾量的80 %~ 90 % ;植物的蒸腾量随年龄的增长而迅速增加 ,但增长幅度随物种不同而异。一般生长快的植物增长快 ,生长慢的植物增长慢。  相似文献   
62.
AIM: To investigate the protective effect of onychin on the endothelial cells injured by oxidative stress. METHODS: The injured model was established by endothelial cells treated with menadione. The growth inhibitory rate of endothelial cell was determined by MTT assay; NO2-/NO3- concentration in the medium was determined by nitrate reductase assay; eNOS and caveolin-1 protein levels were determined by Western blot. RESULTS: Onychin significantly decreased the growth inhibitory rate of endothelial cells injured by menadione, increased NO2-/NO3- concentration in the medium and eNOS activity and up-regulated caveolin-1 expression. CONCLUSION: Onychin possesses a protective effect against endothelial cell injury induced by menadione via caveolin-1/eNOS pathway.  相似文献   
63.
AIM:To construct a recombinant adenovirus expression vector containing CTLA4Ig gene.METHODS:The CTLA4Ig gene derived from the plasmid PCDNA3.0/CTLA4Ig by using polymerase chain reaction (PCR) was inserted into the backward position of cytomegalovirus (CMV) immediate early promoter of the shuttle plasmid (pAdTrack-CMV). After being identified by endonuclease, PCR and sequencing, the recombinant shuttle plasmid pAdTrack-CTLA4Ig was co-transformed into E.coli. BJ5183 cells with the adeoviral backbone plasmid pAdEasyl-1 to obtain the homologous recombination. The adenovirus was generated in 293 cells. A series methods such as PCR and fluorescence microscope was employed to identify the generated recombinant adenovirus.RESULTS:Recombinant CTLA4Ig adenoviruses were constructed and the titer of virus was generally up to 1.65×1012 phaque forming units per liter (PFU/L).CONCLUSION:Success in constructing recombinant pAdTrack-CTLA4Ig will be the base of the further research on its expression in the mammalian cells, and be potenially used in the prevention of transplant rejection and autoimmunity diseases.  相似文献   
64.
AIM:To observe the dynamic changes of expression of PKCα, TGF-β1 and α-SMA in glomeruli of diabetic rats induced by the alloxon and to invesitigate their roles in the diabetic nephropathy(DN).METHODS:Rats were randomly divided into four groups: normal control group (group A), diabetic group of one week (group B), diabetic group of one month (group C), diabetic group of two months (group D). Immunohistochemistry and Western blotting were used to detect the expression of PKCα, TGF-β1 and α-SMA in renal tissue of all groups. Blood glucose, triglycerides, cholesterol, creatinine and urine protein were analysed by chemical methods. The morphological changes of renal tissue were checked through microscopy.RESULTS:The expression of PKCα and TGF-β1 in renal tissue of diabetic groups were increased comparing with those of nomal control group(P<0.05). The mesangial cells expressed α-SMA in two months group. Chronologically the expression of PKCα, TGF-β1 and α-SMA were positively correlative with each other and the impairment of kidney was also observed.CONCLUSIONS: During the DN process the expression of PKCα increased. PKCα raised GFR and the permeability of glomerular filtration membrane which enhanced urinary albumin excretion. PKCα also increased expression of TGF-β and therefore to induce the expression of α-SMA. The appearance of α-SMA was a marker of the phenotypic transform of renal cells.  相似文献   
65.
转Bt基因棉在安庆市大面积种植后害虫发生特点调查   总被引:6,自引:1,他引:6  
根据调查,转Bt基因棉大面积种植后,棉铃虫、红铃虫发生减轻;棉叶螨发生加重,为害时间延长;甜菜夜蛾、斜纹夜蛾发生面积扩大,为害程度加重。据此初步提出了当地转Bt基因棉害虫防治中应注意的问题和管理对策。  相似文献   
66.
AIM:To investigate the effect of Se-containing spirulina phycocyanin (Se-SPC) on liver injury of mice induced by carbon tetrachloride (CCl4). METHODS:The mouse model was conducted by intragastric feeding with 2% CCl4 oil for three times, meanwhile Se-SPC, spirulina phycocyanin (SPC) and Na2SeO3 were injected (ip) to various groups for 7 days. Then selenium (Se), glutathione peroxidase (GPx), superoxide dismutase (SOD), alanine aminotransferase (ALT), malondiaoldehyde (MDA) and nitric oxide (NO) levels in blood and liver were measured. RESULTS:The level of Se,GPx and SOD activities were obviously higher(P<0.05)but ALT activity,MDA and NO2-/NO3- levels were remarkably lower(P<0.05)in Se-SPC treated groups than those in CCl4 groups,and effects of high dose Se-SPC on Se,GPx,MDA and NO2-/NO3- were even more significant(P<0.01).Under the same dose of Se or protein,effects of all selected targets in Se-SPC groups were more efficient than those in SPC groups and inorganic-Se groups.Furthermore,Se levels had a positive correlation with GPx activity(r=01705),which had negative correlation with levels of MDA,NO2-/NO3- and ALT(r=-0.629,r=-0.336,r=-0.457,respectively), and positive correlations between ALT activity and MDA or NO2-/NO3- level were found (r=0.519,r=0.641). CONCLUSION:These results indicated that Se-SPC may attenuate liver injury of mice induced by CCl4 through its anti-inflammatory action and enhancing selenoenzyme expression.  相似文献   
67.
AIM: IL-12 acts upon Tlymphocytes and activates its receptor complexes of β1/β2,and so IL-12 can regulate TH1/TH2 balance. Our study is aimed at IL-12-inducing apoptosis of Tcells and expression and signal transduction of Fas/FasLduring Tcell apoptosis. METHODS: The apoptosis of Tcells was detected by Annexin Vstaining cytometry and the expression of Fas/FasLunder different inhibitors were detected by semi-quantitative PCR. RESULTS: IL-12 induced the human leukemic Tcell line(TIB-152) and the human lymphoma Tcell line(HTB-176) and the normal human Tcells to undergo apoptosis. The FasLexpression at 6 hours after treatment with IL-12 increased apparently, and reached the max at 24 hours, and FasLexpression induced by IL-12 was inhibited by PKCinhibitor. But IL-12 did not influence Fas expression. CONCLUSIONS: IL-12 can induce Tcells to undergo apoptosis which is characterized by early membrane changes, the inducing effect is correlated with the concentration of IL-12 and the maturation of Tcells. FasLparticipates in the progression of Tcell apoptosis as a apoptosis mediator, and the effect of IL-12 on FasLexpression may be related with PKCpathway.  相似文献   
68.
69.
香菇杂交新菌株1363号的选育研究   总被引:1,自引:0,他引:1  
采用单孢杂交的方法培育出香菇新菌株 136 3号。它具有产量高 ,质量好 ,遗传性状稳定 ,抗逆性状强等优点。  相似文献   
70.
甲基对硫磷人工抗原的合成与鉴定   总被引:23,自引:1,他引:23       下载免费PDF全文
根据甲基对硫磷的结构特征,分别从甲基对硫磷的硝基一端或磷酸酯基甲氧基一端引入一定长度的间隔臂和活性基团,设计并合成了4种结构的半抗原;针对各种半抗原所带活性基团的性质,通过多种方法制备了与不同的载体蛋白偶联的人工抗原。进行动物免疫后,得到了针对甲基对硫磷的高效价抗体。  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