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   4987篇
  免费   633篇
  国内免费   739篇
  2024年   14篇
  2023年   116篇
  2022年   213篇
  2021年   337篇
  2020年   283篇
  2019年   317篇
  2018年   299篇
  2017年   202篇
  2016年   250篇
  2015年   395篇
  2014年   458篇
  2013年   408篇
  2012年   511篇
  2011年   412篇
  2010年   278篇
  2009年   208篇
  2008年   283篇
  2007年   215篇
  2006年   173篇
  2005年   127篇
  2004年   93篇
  2003年   98篇
  2002年   63篇
  2001年   64篇
  2000年   42篇
  1999年   46篇
  1998年   29篇
  1997年   24篇
  1996年   24篇
  1995年   26篇
  1994年   20篇
  1993年   15篇
  1992年   28篇
  1991年   20篇
  1990年   15篇
  1989年   20篇
  1988年   11篇
  1987年   19篇
  1986年   11篇
  1985年   17篇
  1984年   10篇
  1983年   12篇
  1982年   10篇
  1981年   9篇
  1978年   9篇
  1977年   10篇
  1974年   9篇
  1973年   11篇
  1971年   12篇
  1970年   8篇
排序方式: 共有6359条查询结果,搜索用时 15 毫秒
81.
82.
冯思远  赵文武  华廷  王涵 《生态学报》2021,41(20):7955-7964
“SDGs加速行动”是国际组织、政府部门、私营机构和其他利益攸关方为加快落实2030年可持续发展议程采取的全球行动。2019年联合国可持续发展目标峰会后,政府、国际组织、私营部门等提出了214项SDGs加速行动。2019年爆发的新型冠状病毒肺炎(Corona Virus Disease 2019,COVID-19)对实现可持续发展目标带来了系列影响,后疫情时代如何推动全球SDGs加速行动的实施成为重要的问题。对可持续发展评估报告(2019)和可持续发展目标加速行动等政策文件进行信息提取,建立加速行动匹配性指数模型和各国应对新冠疫情的恢复力指数模型,根据匹配性-恢复力分类体系将各国按照17项可持续发展目标分为9类,为推动后疫情时代全球可持续发展目标加速行动提供支撑。研究发现:(1)现有可持续发展目标加速行动的实施与区域需求不匹配,且这种不匹配的情况在COVID-19爆发前已经出现;(2)加速行动的实施受限于现有可持续发展水平和国家经济基础,区域关注的可持续发展目标与其自然地理位置和社会发展水平有着密切的关系,多边组织机构和其他利益攸关方需要在发展中国家大力推动可持续发展加速行动;(3)下一步实施加速行动需要加强国际间的合作,根据分类框架和可持续发展目标的关联关系,分重点推进加速行动的实施,完善可持续发展指标监测体系,分类设立后疫情时代不同时期的阶段目标,分阶段循序渐进,定期反馈追踪,以在2030年促进17项可持续目标的实现。  相似文献   
83.
作为活体营养专性寄生真菌,条形柄锈菌(小麦条锈病)在侵染过程中通过形成吸器向寄主细胞释放效应蛋白,干扰寄主的防卫反应,促进其侵染与致病。因此,条形柄锈菌效应蛋白的鉴定与功能研究对揭示其毒性机理具有重要意义。本实验室前期完成了条形柄锈菌CYR31生理小种吸器转录组分析,从中鉴定得到一个吸器特异诱导表达分泌蛋白Hasp68,利用农杆菌侵染在烟草细胞中瞬时表达该基因,能够抑制小鼠促细胞凋亡蛋白Bax诱导的细胞程序性死亡,鉴定为条形柄锈菌候选效应蛋白。Hasp68基因全长318bp,编码105_aa,N-端包含20_aa的信号肽,无保守结构域。BlastX分析表明Hasp68为条形柄锈菌特有效应蛋白,在其他真菌中无同源蛋白,且在条形柄锈菌16个菌系中呈较低的序列多态性,表明其在条形柄锈菌的进化过程中相对保守。借助荧光假单胞菌EtHAn的三型分泌系统,在小麦细胞中过表达Hasp68能够抑制由非致病细菌引起的PTI(PAMP-triggered immunity)相关胼胝质的积累;同时,也能抑制小麦与无毒条形柄锈菌互作中ETI(effector-triggered immunity)相关的活性氧爆发和过敏性坏死反应,表明效应蛋白Hasp68具有抑制寄主免疫反应的功能。利用酵母双杂交系统筛选Hasp68在小麦中的互作蛋白,发现其与组织蛋白酶B(cathepsin B)TaCTSB互作,双分子荧光技术进一步验证二者在烟草细胞中共表达存在互作,初步揭示了效应蛋白Hasp68的互作靶标。  相似文献   
84.
This work investigated the polar (PC: protein, amino acid and metabolite) and non‐polar (NPC: fatty acid) compounds and bioactivity characteristics of the EBN harvested from the state of Johor in Malaysia. The electrophoretic gels exhibited 15 protein bands (16–173 kD) with unique protein profile. Amino acids analysis by AccQ?Tag method revealed 18 types of amino acids in EBN. Metabolite profiling was performed using High‐Performance Liquid Chromatography coupled with Quadrupole Time‐of‐Flight Mass Spectrometer (HPLC‐QTOF/MS) technique and a total of 54 compounds belonging to different groups were detected and identified. These findings help to uncover the relation of therapeutic activity of EBN. The EBN was further extracted with AcOEt and BuOH. The AcOEt extract was fractionated into three fractions (F1?F3), and the high triglyceride content in F2 was verified by gC‐FID. The three groups of fatty acids discovered in EBN are 48.43 % of poly‐unsaturated (PUFA), 25.35 % of saturated fatty acids (SFA) and 24.74 % of mono‐unsaturated fat (MUFA). This is the first time to report results ofEBN, BuOH, and AcOEt extracts and of fraction F2 (TEBN) on their analysis for their antioxidant activities by DPPH, ABTS and catalase assay and for their paraoxonase and anti‐tyrosinase activities. The results showed that TEBN exhibited the significant bioactivity in all assays. These findings suggest that TEBN is a good source for natural bioactive compounds in promoting body vigor. Current work widened the content of EBN especially on the triglyceride and also marked the content of specific location (Johor, Malaysia) of EBN origin.  相似文献   
85.
86.
Fibroblast growth factor receptor‐like 1 (FGFRL1), a member of the FGFR family, has been demonstrated to play important roles in various cancers. However, the role of FGFRL1 in small‐cell lung cancer (SCLC) remains unclear. Our study aimed to investigate the role of FGFRL1 in chemoresistance of SCLC and elucidate the possible molecular mechanism. We found that FGFRL1 levels are significantly up‐regulated in multidrug‐resistant SCLC cells (H69AR and H446DDP) compared with the sensitive parental cells (H69 and H446). In addition, clinical samples showed that FGFRL1 was overexpressed in SCLC tissues, and high FGFRL1 expression was associated with the clinical stage, chemotherapy response and survival time of SCLC patients. Knockdown of FGFRL1 in chemoresistant SCLC cells increased chemosensitivity by increasing cell apoptosis and cell cycle arrest, whereas overexpression of FGFRL1 in chemosensitive SCLC cells produced the opposite results. Mechanistic investigations showed that FGFRL1 interacts with ENO1, and FGFRL1 was found to regulate the expression of ENO1 and its downstream signalling pathway (the PI3K/Akt pathway) in SCLC cells. In brief, our study demonstrated that FGFRL1 modulates chemoresistance of SCLC by regulating the ENO1‐PI3K/Akt pathway. FGFRL1 may be a predictor and a potential therapeutic target for chemoresistance in SCLC.  相似文献   
87.
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   
88.
Three dimeric cassane diterpenoids, caesalpanins A–C, were isolated from the seeds of Caesalpinia sappan L., as well as three known compounds. Their structures were determined via analysis of 1D‐, 2D‐NMR, and HR‐ESI‐MS data. Caesalpanins A and B were the second and third compounds that presented a nitrogen‐containing cassane diterpenoid dimer linked through one ether bond between C‐19 and C‐20′. Caesalpanin B exhibited moderate cytotoxic activity against MCF‐7 cell lines with IC50 value of 29.98 μm . Caesalpanins A and B had weak inhibitory effects against LPS‐induced nitric oxide (NO) production in RAW 264.7 macrophages at 50 μm with inhibitory rate of 36.01 % and 32.93 %, respectively.  相似文献   
89.
The electrochemical nitrogen reduction reaction (NRR) process usually suffers extremely low Faradaic efficiency and ammonia yields due to sluggish N?N dissociation. Herein, single‐atomic ruthenium modified Mo2CTX MXene nanosheets as an efficient electrocatalyst for nitrogen fixation at ambient conditions are reported. The catalyst achieves a Faradaic efficiency of 25.77% and ammonia yield rate of 40.57 µg h?1 mg?1 at ‐0.3 V versus the reversible hydrogen electrode in 0.5 m K2SO4 solution. Operando X‐ray absorption spectroscopy studies and density functional theory calculations reveal that single‐atomic Ru anchored on MXene nanosheets act as important electron back‐donation centers for N2 activation, which can not only promote nitrogen adsorption and activation behavior of the catalyst, but also lower the thermodynamic energy barrier of the first hydrogenation step. This work opens up a promising avenue to manipulate catalytic performance of electrocatalysts utilizing an atomic‐level engineering strategy.  相似文献   
90.
As performance of halide perovskite devices progresses, the device structure becomes more complex with more layers. Molecular interfacial structures between different layers play an increasingly important role in determining the overall performance in a halide perovskite device. However, current understanding of such interfacial structures at a molecular level nondestructively is limited, partially due to a lack of appropriate analytical tools to probe buried interfacial molecular structures in situ. Here, sum frequency generation (SFG) vibrational spectroscopy, a state‐of‐the‐art nonlinear interface sensitive spectroscopy, is introduced to the halide perovskite research community and is presented as a powerful tool to understand molecule behavior at buried halide perovskite interfaces in situ. It is found that interfacial molecular orientations revealed by SFG can be directly correlated to halide perovskite device performance. Here how SFG can examine molecular structures (e.g., orientations) at the perovskite/hole transporting layer and perovskite/electron transporting layer interfaces is discussed. This will promote the use of SFG to investigate molecular structures of buried interfaces in various halide perovskite materials and devices in situ nondestructively with a sub‐monolayer interface sensitivity. Such research will help to elucidate structure–function relationships of buried interfaces, aiding in the rational design/development of halide perovskite materials/devices with improved performance.  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