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   4684篇
  免费   397篇
  国内免费   331篇
  2024年   10篇
  2023年   34篇
  2022年   143篇
  2021年   248篇
  2020年   172篇
  2019年   194篇
  2018年   208篇
  2017年   139篇
  2016年   192篇
  2015年   302篇
  2014年   370篇
  2013年   356篇
  2012年   445篇
  2011年   391篇
  2010年   225篇
  2009年   233篇
  2008年   266篇
  2007年   208篇
  2006年   175篇
  2005年   146篇
  2004年   127篇
  2003年   125篇
  2002年   123篇
  2001年   86篇
  2000年   76篇
  1999年   61篇
  1998年   33篇
  1997年   44篇
  1996年   38篇
  1995年   47篇
  1994年   33篇
  1993年   25篇
  1992年   30篇
  1991年   23篇
  1990年   19篇
  1989年   16篇
  1988年   8篇
  1987年   8篇
  1986年   9篇
  1985年   4篇
  1984年   6篇
  1983年   5篇
  1982年   2篇
  1981年   1篇
  1980年   1篇
  1975年   1篇
  1973年   1篇
  1971年   1篇
  1970年   1篇
  1967年   1篇
排序方式: 共有5412条查询结果,搜索用时 93 毫秒
71.
Liu  Xia  Ruan  Zhi  Shao  Xing-cheng  Feng  Hong-xuan  Wu  Lei  Wang  Wei  Wang  Hong-min  Mu  Hong-yan  Zhang  Ru-jun  Zhao  Wei-min  Zhang  Hai-yan  Zhang  Nai-xia 《Neurochemical research》2021,46(3):686-698

28-O-caffeoyl betulin (B-CA) has been demonstrated to reduce the cerebral infarct volume caused by transient middle cerebral artery occlusion (MCAO) injury. B-CA is a novel derivative of naturally occurring caffeoyl triterpene with little information associated with its pharmacological target(s). To date no data is available regarding the effect of B-CA on brain metabolism. In the present study, a 1H-NMR-based metabolomics approach was applied to investigate the therapeutic effects of B-CA on brain metabolism following MCAO in rats. Global metabolic profiles of the cortex in acute period (9 h after focal ischemia onset) after MCAO were compared between the groups (sham; MCAO?+?vehicle; MCAO?+?B-CA). MCAO induced several changes in the ipsilateral cortex of ischemic rats, which consequently led to the neuronal damage featured with the downregulation of NAA, including energy metabolism dysfunctions, oxidative stress, and neurotransmitter metabolism. Treatment with B-CA showed statistically significant rescue effects on the ischemic cortex of MCAO rats. Specifically, treatment with B-CA ameliorated the energy metabolism dysfunctions (back-regulating the levels of succinate, lactate, BCAAs, and carnitine), oxidative stress (upregulating the level of glutathione), and neurotransmitter metabolism disturbances (back-regulating the levels of γ-aminobutyric acid and acetylcholine) associated with the progression of ischemic stroke. With the administration of B-CA, the levels of three phospholipid related metabolites (O-phosphocholine, O-phosphoethanolamine, sn-glycero-3-phosphocholine) and NAA improved significantly. Overall, our findings suggest that treatment with B-CA may provide neuroprotection by augmenting the metabolic changes observed in the cortex following MCAO in rats.

  相似文献   
72.
Sun  Xiaowen  Shao  Chuang  Chen  Ling  Jin  Xinmeng  Ni  Hong 《Journal of Plant Growth Regulation》2021,40(4):1674-1686

Phosphate-solubilizing bacteria (PSB) are important plant growth-promoting rhizobacteria that can increase soil fertility through the solubilization of insoluble inorganic phosphate and organophosphorus. In this study, a PSB, Burkholderia gladioli MEL01, was isolated and identified from rice–wheat rotation rhizosphere soil. MEL01 had an excellent phosphate-solubilizing capacity (reaching 107.69 mg/L) toward insoluble inorganic phosphate rock phosphate. HPLC analysis revealed that the mechanism of phosphate solubilization of MEL01 was probably due to secreted oxalic acid and gluconic acid transformation of phosphate from insoluble to soluble. MEL01 also exhibited 4030 U/L specific chitosanase activity when cultured with chitosan fermentation medium. Interestingly, the chitosan hydrolysis product chitooligosaccharide could significantly enhance the MEL01 phosphate-solubilizing capacity. Pot experiments showed that MEL01 chitosan medium fermentation liquor (MCMFL) could promote improvement of soil available phosphorus and pakchoi growth when supplemented with phosphate rock phosphate as the phosphate fertilizer. In addition, pot experiments demonstrated that MCMFL could also promote the growth of wheat, which could decrease the amount of compound fertilizer used. Microbial diversity analysis showed that the genera Pseudomonas, Burkholderia, Mycoplana, and Cellvibrio were enriched, which might participate in synergetic phosphate solubilization. Therefore, after fermentation with chitosan and fertilization with rock phosphates, MEL01 has potential as a phosphate biofertilizer in ecological agricultural production.

  相似文献   
73.
74.
ObjectivesSalivary gland regeneration is closely related to the parasympathetic nerve; however, the mechanism behind this relationship is still unclear. The aim of this study was to evaluate the relationship between the parasympathetic nerve and morphological differences during salivary gland regeneration.Materials and MethodsWe used a duct ligation/deligation‐induced submandibular gland regeneration model of Sprague‐Dawley (SD) rats. The regenerated submandibular gland with or without chorda lingual (CL) innervation was detected by haematoxylin–eosin staining, real‐time PCR (RT‐PCR), immunohistochemistry and Western blotting. We counted the number of Ki67‐positive cells to reveal the proliferation process that occurs during gland regeneration. Finally, we examined the expression of the following markers: aquaporin 5, cytokeratin 7, neural cell adhesion molecule (NCAM) and polysialyltransferases.ResultsIntact parasympathetic innervation promoted submandibular gland regeneration. The process of gland regeneration was significantly repressed by cutting off the CL nerve. During gland regeneration, Ki67‐positive cells were mainly found in the ductal structures. Moreover, the expression of NCAM and polysialyltransferases‐1 (PST) expression in the innervation group was significantly increased during early regeneration and decreased in the late stages. In the denervated submandibular glands, the expression of NCAM decreased during regeneration.ConclusionsOur findings revealed that the regeneration of submandibular glands with intact parasympathetic innervation was associated with duct cell proliferation and the increased expression of PST and NCAM.  相似文献   
75.
Zheng  Yang  Zhang  Qing  Ali  Ashaq  Li  Ke  Shao  Nan  Zhou  Xiaoli  Ye  Zhiqin  Chen  Xiaomin  Cao  Shanshan  Cui  Jing  Zhou  Juan  Wang  Dianbing  Hou  Baidong  Li  Min  Cui  Mengmeng  Deng  Lihua  Sun  Xinyi  Zhang  Qian  Yang  Qinfang  li  Yong  Wang  Hui  Lei  Yake  Yu  Bo  Cheng  Yegang  Tong  Xiaolin  Men  Dong  Zhang  Xian-En 《中国病毒学》2021,36(5):869-878
Virologica Sinica - Understanding the persistence of antibody in convalescent COVID-19 patients may help to answer the current major concerns such as the risk of reinfection, the protection period...  相似文献   
76.
为探究北盘江大峡谷流域内浮游生物群落组成及多样性情况,于2017年10月对该流域进行浮游生物调查及多样性分析.结果表明该流域内浮游植物共有7门40属61种、其中绿藻门、硅藻门和蓝藻门种类分别为21种、19种和12种,分别占到34.43%、31.15%和19.67%,浮游植物平均密度为4 298.33(375~9 500)ind./L,Shannon-Wiener藻类生物多样性指数均处于1和2之间;浮游动物3门12属21种,其中轮虫类、枝角类和桡足类种类分别为11种、5种和5种,各占到52.38%、23.81%和23.81%,浮游动物平均密度为436.11(55~1 437.5)ind./L,Shannon-Wiener生物多样性指数均处于1和2之间.本研究结果该地区水生生物资源积累了本底资料.  相似文献   
77.
本研究是利用公共基因芯片数据库筛选乳腺癌的预后基因,预测和探索这些基因在乳腺癌进展中的可能机制和临床价值.首先,我们筛选了公共基因芯片数据库(gene expression omnibus,GEO)GSE22820和癌症基因组图谱(the cancer genome atlas,TCGA)乳腺癌数据库的重叠差异表达基因,联合R语言分析乳腺癌组织与癌旁正常组织差异表达的基因;其次,基于STRING数据库及Cytoscape软件构建蛋白质相互作用网络图,分析并识别了中枢基因和前3个模块;之后进行了更多的功能分析,包括基因本体(gene ontology,GO)和京都基因与基因组百科全书(kyoto encyclopedia of genes and genomes,KEGG)通路分析以及基因集富集分析(gene set enrichment analysis,GSEA),以研究这些基因的作用以及潜在的潜在机制;最后进行了Kaplan-Meier分析和Cox比例风险分析,以阐明这些基因的诊断和预后效果.相关数据分析表明15个基因的表达水平与生存预后相关,高表达基因患者的总生存时间短于低表达患者(P<0.05);Cox比例风险分析表明UBE2T、ER-CC6L和RAD51这3个基因是预后生存的独立因素(P<0.05);GSEA分析表明在UBE2T、ERCC6L和RAD51基因中细胞周期、基础转录因子和卵母细胞减数分裂明显富集.最终,我们得出结论,这3种基因标志物的高表达是乳腺癌预后不良因素,可作为预测乳腺癌患者转移和预后的有效生物标志物.  相似文献   
78.
It has been demonstrated that neural precursor cell expressed developmentally downregulated protein (NEDD) plays crucial roles in tumorigenesis and may serve as potential biomarkers in cancer diagnosis and prognosis. However, few studies systematically investigated the expression of NEDD family members in acute myeloid leukaemia (AML). We systemically determined the expression of NEDD family members in AML and determined their clinical significance. We identified that NEDD9 expression was the only member among NEDD family which was significantly increased in AML. NEDD9 overexpression was more frequently classified as FAB-M4/M5 (= 0.008 and 0.013, respectively), hardly as FAB-M2/M3. Moreover, NEDD9 overexpression was significantly associated with complex karyotype and TP53 mutation. The significant association between NEDD9 overexpression and survival was also observed in whole-cohort AML and non-M3 AML patients. Notably, AML patients with NEDD9 overexpression may benefit from hematopoietic stem cell transplantation (HSCT), whereas those cases without NEDD9 overexpression did not. Finally, a total of 822 mRNAs and 31 microRNAs were found to be differentially expressed between two groups. Among the microRNAs, miR-381 was also identified as a microRNA that could direct target NEDD9. Taken together, our findings demonstrated that NEDD9 overexpression is associated with genetic abnormalities as well as prognosis and might act as a potential biomarker guiding the choice between HSCT and chemotherapy in patients with AML after achieving complete remission.  相似文献   
79.
Molecular Breeding - The stem color of young mung bean is a very useful tool in germplasm identification. Flowering time and plant height (PH) are known to be strongly correlated with crop adaption...  相似文献   
80.
The current study was undertaken to investigate anticancer activity of coumestrol phytoestrogen against human skin cancer. MTT assay was performed for cell viability assessment and clonogenic assay for cell colony formation assessment. Apoptosis was analysed by Annexin V/FITC staining, AO/EB staining and western blotting assays. Effects on the m-TOR/PI3K/AKT signalling pathway were investigated by western blotting. Results indicated that coumestrol induced significant toxicity in human skin cancer cells in contrast to mouse skin cancer cells. The proliferation rate in normal skin cells remained almost intact. Annexin V-FITC and AO/EB staining assays indicated coumestrol induced cytotoxicity in skin cancer cells is mediated through apoptosis stimulation. The apoptosis in skin cancer cells was mediated through caspase-activation. Cell migration and invasion was inhibited by coumestrol in human skin cancer cells via inhibition of MMP-2 and MMP-9 expressions. Moreover, m-TOR/PI3K/AKT signalling pathway in SKEM-5 cells was blocked by coumestrol.  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