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   49014篇
  免费   17162篇
  国内免费   2747篇
  2024年   67篇
  2023年   329篇
  2022年   863篇
  2021年   1742篇
  2020年   3016篇
  2019年   4766篇
  2018年   4811篇
  2017年   4844篇
  2016年   5096篇
  2015年   5373篇
  2014年   5445篇
  2013年   5846篇
  2012年   3881篇
  2011年   3415篇
  2010年   4259篇
  2009年   2870篇
  2008年   1878篇
  2007年   1343篇
  2006年   1176篇
  2005年   1119篇
  2004年   1031篇
  2003年   1013篇
  2002年   909篇
  2001年   752篇
  2000年   620篇
  1999年   488篇
  1998年   227篇
  1997年   211篇
  1996年   180篇
  1995年   156篇
  1994年   141篇
  1993年   114篇
  1992年   129篇
  1991年   103篇
  1990年   99篇
  1989年   104篇
  1988年   68篇
  1987年   53篇
  1986年   30篇
  1985年   48篇
  1984年   31篇
  1983年   40篇
  1982年   33篇
  1981年   21篇
  1980年   20篇
  1979年   26篇
  1978年   23篇
  1977年   13篇
  1976年   16篇
  1973年   19篇
排序方式: 共有10000条查询结果,搜索用时 109 毫秒
941.
942.
943.
Asparagus (Asparagus officinalis L) is an economically important crop, rich in nutrients, and is also conducive to solving ecological and environmental problems. Plants may acquire benefits from root-associated endophytic bacteria. However, the composition of the endophytic bacterial community associated with the roots of asparagus is poorly elucidated. In this study, the nine root samples of asparagus from three different varieties including Asparagus officinalis var. Grande (GLD), A. officinalis var. Jinglvlu3 (JL3) and A. officinalis var. Jingzilu2 (JZL) were investigated by high-throughput sequencing technology of the 16S rDNA V5-V7 hypervariable region of endophytic bacteria. A total of 16 phyla, 29 classes, 90 orders, 171 families, and 312 genera were identified. Endophytic bacteria diversity and bacteria structure was different among the three varieties and was influenced by rhizosphere soil properties and varieties. In the GLD variety, the main phyla were Proteobacteria, Actinobacteria, and Firmicutes. The main phylum in JL3 and JZL varieties was Proteobacteria. The observations showed that GLD had the highest diversity of endophytes as indicated by the Shannon index (GLD > JZL > JL3). The order of the endophytes richness was GLD > JL3 > JZL. The PCA and PCoA analysis revealed the microbial communities were different between three different asparagus varieties, and the microbial composition of GLD and JZL was more similar. This report provides an important reference for the study of endophytic microorganisms of asparagus. Supplementary informationThe online version contains supplementary material available at (10.1007/s12088-021-00926-6) contains supplementary material, which is available to authorized users.  相似文献   
944.
945.
946.
947.
Artificial materials that can simultaneously mimic the relative permittivity and conductivity of various human tissues are usually used in medical applications. However, the method of precisely designing these materials with designated values of both relative permittivity and conductivity at 3 T MRI resonance frequency is lacking. In this study, a reliable method is established to determine the compositions of artificial dielectric materials with designated relative permittivity and conductivity at 128 MHz. Sixty dielectric materials were produced using oil, sodium chloride, gelatin, and deionized water as the main raw materials. The dielectric properties of these dielectric materials were measured using the open‐ended coaxial line method at 128 MHz. Nonlinear least‐squares Marquardt–Levenberg algorithm was used to obtain the formula, establishing the relationship between the compositions of the dielectric materials and their dielectric properties at 128 MHz. The dielectric properties of the blood, gall bladder, muscle, skin, lung, and bone at 128 MHz were selected to verify the reliability of the obtained formula. For the obtained formula, the coefficient of determination and the expanded uncertainties with a coverage factor of k = 2 were 0.991% and 4.9% for relative permittivity and 0.992% and 6.4% for conductivity. For the obtained artificial materials measured using the open‐ended coaxial line method, the maximal difference of relative permittivity and conductivity were 1.0 and 0.02 S/m, respectively, with respect to the designated values. In conclusion, the compositions of tissue‐mimicking material can be quickly determined after the establishment of the formulas with the expanded uncertainties of less than 10%. Bioelectromagnetics. 2021;42:86–94. © 2020 Bioelectromagnetics Society.  相似文献   
948.
949.
Su  Xin  Cheng  Ye  Zhang  Guoming  Wang  Bin 《Molecular biology reports》2021,48(7):5675-5687

Due to the technological advances, it has been well-established that obesity is strongly correlated with various health problems. Among these problems, dyslipidemia is one of the most important concomitant symptoms under obese status which is the main driving force behind the pathological progression of cardio-metabolic disorder diseases. Importantly, the type of dyslipidemia, arising from concerted action of obesity, has been identified as “metabolic related dyslipidemia”, which is characterized by increased circulating levels of Low density lipoprotein cholesterol (LDL-C), Triglycerides (TG) accompanied by lower circulating levels of High density lipoprotein cholesterol (HDL-C). On the other hand, the metabolic related dyslipidemia is being verified as a vital link between obesity and hypertension, diabetes mellitus, and Cardiovascular disease (CVD). In this review, we summarized the current understanding of metabolic related dyslipidemia and the potential mechanisms which lead to the pathogenesis of obesity. Meanwhile, we also summarized the emerging results which focused on several novel lipid bio-markers in metabolic related dyslipidemia, such as pro-protein convertase subtilisin/kexin type 9 (PCSK9) and sphingosine-1-phosphate (S1P), and their potential use as biomarkers of metabolic related dyslipidemia.

  相似文献   
950.
Hao  Yu-Qin  Liu  Ke-Wei  Zhang  Xin  Kang  Shu-Xia  Zhang  Kun  Han  Wurihan  Li  Li  Li  Zhe-Hai 《Molecular and cellular biochemistry》2021,476(3):1455-1465
Molecular and Cellular Biochemistry - Melanoma ranks second in aggressive tumors, and the occurrence of metastasis in melanoma results in a persistent drop in the survival rate of patients....  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