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   19581篇
  免费   1883篇
  国内免费   632篇
  2023年   116篇
  2022年   272篇
  2021年   471篇
  2020年   321篇
  2019年   412篇
  2018年   472篇
  2017年   350篇
  2016年   592篇
  2015年   965篇
  2014年   1057篇
  2013年   1253篇
  2012年   1452篇
  2011年   1430篇
  2010年   938篇
  2009年   739篇
  2008年   1009篇
  2007年   944篇
  2006年   891篇
  2005年   821篇
  2004年   750篇
  2003年   717篇
  2002年   643篇
  2001年   551篇
  2000年   484篇
  1999年   450篇
  1998年   218篇
  1997年   203篇
  1996年   187篇
  1995年   167篇
  1994年   151篇
  1993年   121篇
  1992年   245篇
  1991年   244篇
  1990年   203篇
  1989年   216篇
  1988年   189篇
  1987年   152篇
  1986年   144篇
  1985年   168篇
  1984年   123篇
  1983年   98篇
  1982年   90篇
  1981年   97篇
  1979年   109篇
  1978年   91篇
  1977年   71篇
  1976年   68篇
  1975年   88篇
  1974年   89篇
  1973年   81篇
排序方式: 共有10000条查询结果,搜索用时 453 毫秒
971.
Gang  Qun  Chang  Scott X.  Lin  Guigang  Zhao  Qiong  Mao  Bing  Zeng  De-Hui 《Plant and Soil》2019,436(1-2):109-122
Plant and Soil - Nitrogen (N) addition could affect litter decomposition through its direct effects on soil N availability and indirect effects on initial litter chemistry. The aim of this study...  相似文献   
972.
973.
Chang  Lijing  Mei  Gaofu  Hu  Yan  Deng  Jieqiong  Zhang  Tianzhen 《Plant molecular biology》2019,99(4-5):449-460
Plant Molecular Biology - This report reveals that the LMI1-like and KNOX1 genes coordinately control the leaf development and different combinations of those genes which produce diverse leaf...  相似文献   
974.
975.
Lin  Jiahui  Chang  Qun  Dai  Xueting  Liu  Dan  Jiang  Yuyin  Dai  Yalei 《Molecular and cellular biochemistry》2019,453(1-2):179-186
Molecular and Cellular Biochemistry - Mycoplasma pneumoniae pneumonia (MPP) is the most common respiratory infection in young children and its incidence has increased worldwide. In this study, high...  相似文献   
976.
Lab-scale membrane bioreactors (MBRs) were investigated at 12, 18, and 25?°C to identify the correlation between quorum sensing (QS) and biofouling at different temperatures. The lower the reactor temperature, the more severe the membrane biofouling measured in terms of the transmembrane pressure (TMP) during filtration. More extracellular polymeric substances (EPSs) that cause biofouling were produced at 18?°C than at 25?°C, particularly polysaccharides, closely associated with QS via the production of N-acyl homoserine lactone (AHL). However, at 12?°C, AHL production decreased, but the release of EPSs due to deflocculation increased the soluble EPS concentration. To confirm the temperature effect related to QS, bacteria producing AHL were isolated from MBR sludge and identified as Aeromonas sp., Leclercia sp., and Enterobacter sp. through a 16S rDNA sequencing analysis. Batch assays at 18 and 25?°C showed that there was a positive correlation between QS through AHL and biofilm formation in that temperature range.  相似文献   
977.
Molecular dynamics simulations (MDS) are employed to investigate the effects of interatomic interaction and nanostructure on wettability of water on a copper plate. In the nano scale, these simulation results showed that the contact angle gradually increases with the decreasing of the reaction parameters, which results in the decreasing of free energy on the solid-liquid interface. Therefore, it leads to that the hydrophilic material is turned into hydrophobic, which fits the results that the wettability is changed by low surface energy materials in macro scale. Furthermore, the contact angles on smooth and rough surfaces are 87° and 71.6°, respectively. That is to say that the hydrophilic will increase for hydrophilic material due to the existence of one-layer structure; it agrees with the experimental results in macro scale.  相似文献   
978.
Viral noncoding RNAs (Epstein–Barr virus-encoded RNAs, EBERs) are believed to play a critical role in the progression of lymphoma and nasopharyngeal carcinoma (NPC). However, the accurate mechanisms accounting for their oncogenic function have not been elucidated, especially in terms of interaction between tumor cells and mesenchymal cells. Here, we report that, in addition to NPC cells, EBERs are also found in endothelial cells in Epstein–Barr virus (EBV)-infected NPC parenchymal tissues, which implicates NPC-derived extracellular vesicles (EVs) in transmitting EBERs to endothelial cells. In support of this hypothesis, we first ascertained if EBERs could be transferred to endothelial cells via EVs isolated from NPC culture supernatant. Then, we clarified that EVs-derived EBERs could promote angiogenesis through stimulation of VCAM-1 expression. Finally, we explored the involvement of EBER recognition by TLR3 and RIG-I in NPC angiogenesis. Our observations collectively illustrate the significance and mechanism of EVs-derived EBERs in angiogenesis and underlie the interaction mechanisms between EBV-infected NPC cells and the tumor microenvironment.  相似文献   
979.
Chang  Yuansheng  He  Ping  Wang  Haibo  Li  Huifeng  Wang  Sen  Li  Linguang 《Plant Molecular Biology Reporter》2019,37(1-2):63-73

The Taiyi mountainous region of Shandong province in eastern China has an abundance of wild Malus species. We evaluated the genetic diversity of 88 Malus accessions (45 Asian apple cultivars, 10 American apple cultivars, 12 European apple cultivars, 19 Chinese wild apples, and two apple cultivars with unknown origins) based on single-nucleotide polymorphism (SNP) markers. A total of 38,364 SNPs were obtained with an average of 2256 SNPs per chromosome. The average of the polymorphism information content (PIC), gene diversity, and allele frequency for SNPs was 0.268, 0.306, and 0.364, respectively. A circular phylogenetic tree constructed based on SNP data revealed that the 88 Malus accessions could be divided into three groups. However, a population structure analysis suggested the 88 Malus accessions could be divided into four groups. A principal component analysis (PCA) revealed some population stratification. The first three PCs accounted for 41.62% of the population-wide SNP variation, with PC1 accounting for 33.9%. Moreover, the kinship values of the 88 Malus accessions ranged from 0 to 2.36, with 96.42% of the kinship values between 0 and 0.2. A phylogenetic tree and a PCA indicated the Chinese wild apples widely distributed among the cultivated apples had a diverse genetic background. Characterizing the genetic relationships between cultivated apples and Chinese wild apples is essential for increasing the genetic diversity of the germplasms used by apple breeders.

  相似文献   
980.
Repetitive exposure to ultraviolet radiation (UVR) results in continuous insults to the skin, including continuous loss of the capacities of epidermal stem cells (ESCs). Takeda G-protein-coupled receptor-5 (TGR5) participates in a variety of physiological activities, but its biological function in skin has not been reported. In this study, we report that TGR5 could be detected in ESCs and its expression was reduced after ultraviolet B (UV-B) irradiation. Treatment with the specific TGR5 agonist 3-(2-chlorophenyl)-N-(4-chlorophenyl)-N,5-dimethylisoxazole-4-carboxamide (GPBARA) prevented UV-B-induced oxidative stress by reducing 4-hydroxy-2-nonenal and increasing the level of glutathione. We also found that the presence of GPBARA improved UV-B irradiation-induced mitochondrial dysfunction by elevating mitochondrial membrane potential. Interestingly, our results indicate that GPBARA pretreatment suppressed UV-B irradiation-induced reduced cell viability, release of lactic dehydrogenase, and secretion of high mobility group box 1. Notably, GPBARA pretreatment inhibited UV-B irradiation-induced decrease in integrin β1 and Krt19, dependent on TGR5. Mechanistically, we found that the activation of TGR5 by GPBARA increased Wnt1, Wnt3a, Myc, and cyclin D1 in ESCs. Our data suggest a new function of TGR5 in regulating ESCs.  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