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   58172篇
  免费   4879篇
  国内免费   5001篇
  68052篇
  2024年   162篇
  2023年   749篇
  2022年   1649篇
  2021年   2903篇
  2020年   1966篇
  2019年   2454篇
  2018年   2512篇
  2017年   1803篇
  2016年   2449篇
  2015年   3585篇
  2014年   4230篇
  2013年   4619篇
  2012年   5412篇
  2011年   4774篇
  2010年   3143篇
  2009年   2497篇
  2008年   3097篇
  2007年   2713篇
  2006年   2435篇
  2005年   2071篇
  2004年   1794篇
  2003年   1635篇
  2002年   1446篇
  2001年   1056篇
  2000年   907篇
  1999年   958篇
  1998年   554篇
  1997年   515篇
  1996年   468篇
  1995年   427篇
  1994年   441篇
  1993年   330篇
  1992年   394篇
  1991年   317篇
  1990年   274篇
  1989年   242篇
  1988年   174篇
  1987年   133篇
  1986年   132篇
  1985年   118篇
  1984年   93篇
  1983年   72篇
  1982年   58篇
  1981年   28篇
  1980年   19篇
  1979年   24篇
  1976年   13篇
  1975年   13篇
  1973年   21篇
  1958年   13篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
831.
龚明  尹昕  黄天宇  郑婷婷  唐利华  张赫男  汪滢 《菌物学报》2022,41(12):2074-2082
为了改进草菇低温保鲜方法,在15 ℃贮藏条件下,采用泛素化结合酶E2 (UBEV2)抑制剂对草菇子实体进行处理,并开展相关生理指标和基因表达检测。结果表明,使用100 μmol/L的UBEV2抑制剂L345-0044维持了草菇较好的品质,提高了草菇可溶性糖的含量。低温明显提升抑制剂处理下的碱性蛋白酶和中性蛋白酶活力,并证实了低温胁迫显著提高了抑制剂处理下的一种类型蛋白酶肽基赖氨酸金属内肽酶的表达。本研究证实了草菇可溶性糖和高活性的冷诱导金属内肽酶对于延长草菇的低温保鲜时间是必须的。  相似文献   
832.
崔静  徐明芳  章群  李瑶  曾晓舒  李莎 《生物多样性》2022,30(5):21485-144
角木叶鲽(Pleuronichthys cornutus)是东亚沿海重要的鲽形目经济鱼类, 为更好地保护和开发利用其种质资源, 有必要全面了解其遗传背景。本研究测定了中国和日本沿海7个群体200尾角木叶鲽线粒体控制区(CR) 5'端、细胞色素b (Cytb)和NADH脱氢酶第二亚基(ND2)基因序列, 比较不同标记在解析遗传多样性和种群结构上的可行性与有效性, 阐明中日沿海角木叶鲽群体间出现遗传分化的分子机制。CR序列分析发现中日沿海7个角木叶鲽群体遗传多样性表现出较高的单倍型多样性(Hd = 0.9699)和较低的核苷酸多样性(π = 0.0061); 各群体间无显著的遗传分化(FST = -0.0197-0.0184, P > 0.05); 单倍型网络未显示出明显的地理聚群和谱系结构; 分子方差分析(AMOVA)表明变异主要发生在群体内部(> 99.17%)。进一步通过CytbND2基因分别与CR序列对比分析, 结果表明群体遗传多样性均表现为高Hd (0.9683-0.9829)低π (0.0050-0.0063)模式, 仅有ND2基因分析FST值(FST = 0.0302, P < 0.05)显示了中国碣石(GDJS)和日本明石(JAP)群体间显著的低水平遗传分化现象。CRCytbND2的单倍型网络图均无明显的地理聚类和谱系结构, AMOVA分析也显示变异主要来源于群体内(> 98.39%)。种群历史动态分析结果显示, 角木叶鲽可能在第四纪中更新世晚期经历了群体扩张事件, 扩张时间分别为31.93-9.58万年前(CR)、27.53-22.02万年前(Cytb)和26.99-18.75万年前(ND2)。综上所述, 中日沿海的角木叶鲽具有较高遗传多样性, GDJS和JAP群体间存在低度分化; ND2基因比CRCytb序列更适于分析角木叶鲽种群遗传结构, 选择多个遗传标记可有效弥补单一标记分析遗传多样性的局限性; 推测冰期两大独立避难所的形成及GDJS和JAP群体距离相隔较远是其发生遗传分化的主要原因。研究结果为中日沿海角木叶鲽渔业资源的种质保护与可持续利用提供了理论依据。  相似文献   
833.
Callus induction,which results in fate transition in plant cells,is considered as the first and key step for plant regeneration.This process can be stimulated in different tissues by a callus-inducing medium(CIM),which contains a high concentration of phytohormone auxin.Although a few key regulators for callus induction have been identified,the multiple aspects of the regulatory mechanism driven by high levels of auxin still need further investigation.Here,we find that high auxin induces callus ...  相似文献   
834.
835.
836.
The current study was designed to explore the role and underlying mechanism of lncRNA taurine up-regulated gene 1 (TUG1) in cardiac hypertrophy. Mice were treated by transverse aortic constriction (TAC) surgery to induce cardiac hypertrophy, and cardiomyocytes were treated by phenylephrine (PE) to induce hypertrophic phenotype. Haematoxylin-eosin (HE), wheat germ agglutinin (WGA) and immunofluorescence (IF) were used to examine morphological alterations. Real-time PCR, Western blots and IF staining were used to detect the expression of RNAs and proteins. Luciferase assay and RNA pull-down assay were used to verify the interaction. It is revealed that TUG1 was up-regulated in the hearts of mice treated by TAC surgery and in PE-induced cardiomyocytes. Functionally, overexpression of TUG1 alleviated cardiac hypertrophy both in vivo and in vitro. Mechanically, TUG1 sponged and sequestered miR-34a to increase the Dickkopf 1 (DKK1) level, which eventually inhibited the activation of Wnt/β-catenin signalling. In conclusion, the current study reported the protective role and regulatory mechanism of TUG1 in cardiac hypertrophy and suggested that TUG1 may serve as a novel molecular target for treating cardiac hypertrophy.  相似文献   
837.
In this study, we investigated the effects of isorhamnetin on myocardial ischaemia reperfusion (I/R) injury in Langendorff-perfused rat hearts. Isorhamnetin treatment (5, 10 and 20 μg/mL) significantly alleviated cardiac morphological injury, reduced myocardial infarct size, decreased the levels of marker enzymes (LDH and CK) and improved the haemodynamic parameters, reflected by the elevated levels of the left ventricular developed pressure (LVDP), coronary flow (CF) and the maximum up/down velocity of left ventricular pressure (+dp/dtmax). Moreover, isorhamnetin reperfusion inhibited apoptosis of cardiomyocytes in the rats subjected to cardiac I/R in a dose-dependent manner concomitant with decreased protein expression of Bax and cleaved-caspase-3, as well as increased protein expression of Bcl-2. In addition, I/R-induced oxidative stress was manifestly mitigated by isorhamnetin treatment, as showed by the decreased malondialdehyde (MDA) level and increased antioxidant enzymes activities of superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GSH-Px). These results indicated that isorhamnetin exerts a protective effect against I/R-induced myocardial injury through the attenuation of apoptosis and oxidative stress.  相似文献   
838.
Lophialetidae is an extinct group of endemic Asiatic tapiroids that are widely distributed in the Eocene sediments of Asia. Schlosseria magister and Lophialetes expeditus are the most abundant species in this family. However, their dietary and ecological characteristics are largely unknown. For the first time, we reconstruct the palaeodiet and habitat of these two lophialetids using a combination of mesowear and stable carbon isotope analysis of fossil teeth excavated from the Erlian Basin, China. Mesowear analysis (n = 141) suggests that the dietary structure of S. magister and L. expeditus shifted from less to more abrasive diets from ~52 to ~42 Ma. Stable carbon isotope analysis (n = 137) suggests that the habitats of S. magister and L. expeditus became drier and/or more open through time. The dietary shifts of the two lophialetids are consistent with evident changes in habitat. The changes in the diet and habitat were probably related to global climate change during that time period. The gradual drop in global temperatures during the early–middle Eocene led to a drier and more open terrestrial ecosystem in the Erlian Basin, probably resulting in changes in floral composition of the environment inhabited by S. magister and L. expeditus. Hence, herbivores highly susceptible to vegetation modification had to develop new resource exploitation strategies to adapt to these changes. Schlosseria magister, considered to be the sister-group of L. expeditus and with a low level of ecological flexibility, was unable to adapt to the habitat changes finally becoming extinct at ~45 Ma.  相似文献   
839.
We found previously that KLF4 expression was up-regulated in cultured rat and human pulmonary artery smooth muscle cells (PASMCs) exposed to cigarette smoke (CS) extract and in pulmonary artery from rats with pulmonary hypertension induced by CS. Here, we aim to investigate whether CS-induced pulmonary hypertension (PH) is prevented and ameliorated by targeted pulmonary vascular gene knockdown of KLF4 via adeno-associated virus 1 (AAV1)-KLF4-shRNA in vivo in rat model. The preventive and therapeutic effects were observed according to the different time-point of AAV1-KLF4-shRNA intratracheal administration. We tested haemodynamic measurements of systemic and pulmonary circulations and observed the degree of pulmonary vascular remodelling. In the preventive experiment, KLF4 expression and some pulmonary circulation hemodynamic measurements such as right ventricular systolic pressure (RVSP), mean right ventricular pressure (mRVP), peak RV pressure rate of rise (dP/dt max) and right ventricle (RV) contractility index were increased significantly in the CS-induced PH model. While in the prevention group (AAV1-KLF4-shRNA group), RVSP, mRVP, dP/dt max and RV contractility index which are associated with systolic function of right ventricle decreased and the degree of pulmonary vascular remodelling relieved. In the therapeutic experiment, we observed a similar trend. Our findings emphasize the feasibility of sustained pulmonary vascular KLF4 gene knockdown using intratracheal delivery of AAV1 in an animal model of cigarette smoke-induced PH and determined gene transfer of KLF4-shRNA could prevent and ameliorate the progression of PH.  相似文献   
840.
This study aims to construct a robust prognostic model for adult adrenocortical carcinoma (ACC) by large-scale multiomics analysis and real-world data. The RPPA data, gene expression profiles and clinical information of adult ACC patients were obtained from The Cancer Proteome Atlas (TCPA), Gene Expression Omnibus (GEO) and The Cancer Genome Atlas (TCGA). Integrated prognosis-related proteins (IPRPs) model was constructed. Immunohistochemistry was used to validate the prognostic value of the IPRPs model in Fudan University Shanghai Cancer Center (FUSCC) cohort. 76 ACC cases from TCGA and 22 ACC cases from GSE10927 in NCBI’s GEO database with full data for clinical information and gene expression were utilized to validate the effectiveness of the IPRPs model. Higher FASN (P = .039), FIBRONECTIN (P < .001), TFRC (P < .001), TSC1 (P < .001) expression indicated significantly worse overall survival for adult ACC patients. Risk assessment suggested significantly a strong predictive capacity of IPRPs model for poor overall survival (P < .05). IPRPs model showed a little stronger ability for predicting prognosis than Ki-67 protein in FUSCC cohort (P = .003, HR = 3.947; P = .005, HR = 3.787). In external validation of IPRPs model using gene expression data, IPRPs model showed strong ability for predicting prognosis in TCGA cohort (P = .005, HR = 3.061) and it exhibited best ability for predicting prognosis in GSE10927 cohort (P = .0898, HR = 2.318). This research constructed IPRPs model for predicting adult ACC patients’ prognosis using proteomic data, gene expression data and real-world data and this prognostic model showed stronger predictive value than other biomarkers (Ki-67, Beta-catenin, etc) in multi-cohorts.  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