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   78842篇
  免费   6538篇
  国内免费   4873篇
  90253篇
  2024年   138篇
  2023年   901篇
  2022年   2075篇
  2021年   3602篇
  2020年   2326篇
  2019年   2838篇
  2018年   2868篇
  2017年   2029篇
  2016年   2872篇
  2015年   4585篇
  2014年   5294篇
  2013年   5961篇
  2012年   6897篇
  2011年   6352篇
  2010年   3817篇
  2009年   3372篇
  2008年   4112篇
  2007年   3652篇
  2006年   3171篇
  2005年   2679篇
  2004年   2276篇
  2003年   1972篇
  2002年   1730篇
  2001年   1559篇
  2000年   1565篇
  1999年   1447篇
  1998年   847篇
  1997年   797篇
  1996年   808篇
  1995年   736篇
  1994年   687篇
  1993年   530篇
  1992年   818篇
  1991年   657篇
  1990年   601篇
  1989年   531篇
  1988年   421篇
  1987年   362篇
  1986年   336篇
  1985年   299篇
  1984年   221篇
  1983年   199篇
  1982年   112篇
  1981年   118篇
  1980年   86篇
  1979年   147篇
  1978年   84篇
  1977年   95篇
  1975年   111篇
  1974年   116篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
981.
Hierarchical Cu2S microspheres wrapped by reduced graphene oxide (RGO) nanosheets are prepared via a one‐step solvothermal process. The amount of graphene oxide used in the synthesis process has a remarkable effect on the features of Cu2S microspheres. Compared to Pt and Cu2S electrodes, RGO‐Cu2S electrodes show better electrocatalytic activity, greater stability, lower charge‐transfer resistance, and higher exchange current density. As expected, RGO‐Cu2S electrodes exhibit superior performance when functioning as counter electrodes in CdS/CdSe quantum dot‐sensitized solar cells (QDSSCs) using a polysulfide electrolyte. A power conversion efficiency up to 3.85% is achieved for the QDSSC employing an optimized RGO‐Cu2S counter electrode, which is higher than those of the QDSSCs featuring Pt (2.14%) and Cu2S (3.39%) counter electrodes.  相似文献   
982.
983.

Pursuing the rural idyll for retirement is especially a popular age-old dream for Taiwan people. Farming for health is an emerging trend, which drivers to initiate a green care service based on a combination of agriculture resources and traditional care. The purposes of this study were to assess the feasibility of green care in rural communities and to propose implementation strategies for varied rural area types in Taiwan. This study was conducted with two stags. A feasibility study comprising two aspects of political and environmental feasibilities was assessed in the first stage. The political feasibility was assessed based on social demand and government policies. Accordingly, three alternative models for senior green care participation were proposed, including green occupational therapy (for residents), rural long-stay tourism (for tourists), and agricultural working holiday (for volunteers). The environmental feasibility assessment was conducted in 102 rural communities in northern Taiwan. Five indexes, including the natural environment, rural resources, public facilities, senior care, and community capacity, were used to evaluate the potential of communities for developing green care. The results showed that green care implementing active aging in place in rural areas is feasible. Seventeen communities with plentiful or unique rural resources and high-quality community capacity were recommended as potential communities. In the second stage, a multiple case study was conducted in three communities representing different alternative models of green care. The community leader interviews, on-site investigations, vision forum, and operation workshop were adopted to propose the implementation strategies of green care for three communities, respectively, including human resource, volunteer or tourist management, revenue distribution, and marketing.

  相似文献   
984.
Li  Jiang-Fan  He  Lei  Deng  Yong-Qiang  Qi  Shu-Hui  Chen  Yue-Hong  Zhang  Xiao-Lu  Hu  Shi-Xiong  Fan  Rui-Wen  Zhao  Guang-Yu  Qin  Cheng-Feng 《中国病毒学》2021,36(6):1484-1491
Virologica Sinica - The sudden emergence of severe acute respiratory syndrome coronavirus (SARS-CoV) has caused global panic in 2003, and the risk of SARS-CoV outbreak still exists. However, no...  相似文献   
985.
Ma  Jun  Chen  Yiyun  Wu  Wei  Chen  Zhongzhou 《中国病毒学》2021,36(5):1104-1112
Virologica Sinica - SARS-CoV-2 has become a global pandemic threatening human health and safety. It is urgent to find effective therapeutic agents and targets with the continuous emergence of novel...  相似文献   
986.
Duan  Luning  Han  Shichen  Wang  Ke  Jiang  Peihong  Gu  Yunsong  Chen  Lin  Mu  Junyi  Ye  Xingguo  Li  Yaxuan  Yan  Yueming  Li  Xiaohui 《Plant molecular biology》2020,102(1-2):225-237
Key message

The specific and high-level expression of 1Ax1 is determined by different promoter regions. HMW-GS synthesis occurs in aleurone layer cells. Heterologous proteins can be stored in protein bodies.

Abstract

High-molecular-weight glutenin subunit (HMW-GS) is highly expressed in the endosperm of wheat and relative species, where their expression level and allelic variation affect the bread-making quality and nutrient quality of flour. However, the mechanism regulating HMW-GS expression remains elusive. In this study, we analyzed the distribution of cis-acting elements in the 2659-bp promoter region of the HMW-GS gene 1Ax1, which can be divided into five element-enriched regions. Fragments derived from progressive 5′ deletions were used to drive GUS gene expression in transgenic wheat, which was confirmed in aleurone layer cells, inner starchy endosperm cells, starchy endosperm transfer cells, and aleurone transfer cells by histochemical staining. The promoter region ranging from ??297 to ??1 was responsible for tissue-specific expression, while fragments from ??1724 to ??618 and from ??618 to ??297 were responsible for high-level expression. Under the control of the 1Ax1 promoter, heterologous protein could be stored in the form of protein bodies in inner starchy endosperm cells, even without a special location signal. Our findings not only deepen our understanding of glutenin expression regulation, trafficking, and accumulation but also provide a strategy for the utilization of wheat endosperm as a bioreactor for the production of nutrients and metabolic products.

  相似文献   
987.
Sun  Fan  Yang  WanChun  Du  ChaoLing  Chen  YangXi  FU  TianYi  Shi  DaNing 《Plasmonics (Norwell, Mass.)》2020,15(4):949-955
Plasmonics - Both the excitation wavelength and aspect ratio AR are key parameters controlling the refractive index sensitivity performances of plasmonic sensors of individual Au nanoplate dimmers....  相似文献   
988.
The International Journal of Life Cycle Assessment - Low carbon footprint agriculture has received increasing attention in the effect of reducing greenhouse gas emissions and mitigating climate...  相似文献   
989.
Xiao  Na  Zhang  Jun  Chen  Chao  Wan  Yanfang  Wang  Ning  Yang  Jing 《Mammalian genome》2019,30(9-10):276-288
Mammalian Genome - Increasing evidence shows that miRNAs play pivotal roles in cardiovascular diseases, including heart failure (HF). The aim of this study was to investigate the role of miR-129-5p...  相似文献   
990.
[背景]闽楠是珍贵用材树种.阐明闽楠根际土壤微生物特征,对科学经营闽楠人工林有指导作用.[目的]明确闽楠人工林恢复过程中根际土壤丛枝菌根群落随林龄的变化特征.[方法]采用高通量Illumina MiSeq测序的方法,评估不同林龄闽楠幼林根际土壤丛枝菌根真菌(Arbuscular Mycorrhiza Fungi,AMF...  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