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   41505篇
  免费   3343篇
  国内免费   2396篇
  2024年   41篇
  2023年   417篇
  2022年   954篇
  2021年   1946篇
  2020年   1221篇
  2019年   1505篇
  2018年   1409篇
  2017年   1084篇
  2016年   1623篇
  2015年   2427篇
  2014年   2848篇
  2013年   3090篇
  2012年   3586篇
  2011年   3398篇
  2010年   1943篇
  2009年   1794篇
  2008年   2086篇
  2007年   1867篇
  2006年   1604篇
  2005年   1420篇
  2004年   1199篇
  2003年   1053篇
  2002年   905篇
  2001年   851篇
  2000年   740篇
  1999年   716篇
  1998年   435篇
  1997年   464篇
  1996年   441篇
  1995年   390篇
  1994年   378篇
  1993年   308篇
  1992年   441篇
  1991年   383篇
  1990年   331篇
  1989年   246篇
  1988年   236篇
  1987年   198篇
  1986年   141篇
  1985年   185篇
  1984年   121篇
  1983年   104篇
  1982年   80篇
  1981年   60篇
  1980年   55篇
  1979年   72篇
  1978年   66篇
  1977年   46篇
  1976年   48篇
  1973年   48篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
肺部微生物组存在于呼吸道和实质组织中,通过菌群紊乱、代谢产物、炎症反应、免疫反应、基因毒性等方面介导肺部损伤。随着肺部微生物组的深入研究,发现肺部微生物组的相关活动与慢性阻塞性肺疾病(chronic obstructive pulmonary disease, COPD)和肺癌息息相关,能够促使COPD向肺癌的转变。本文主要介绍了肺部微生物组稳态及其通过炎症反应导致COPD和肺癌,重点探讨了肺部微生物组如何通过炎症反应介导COPD转化为肺癌,以期为COPD和肺癌的临床预防、优化治疗以及新型药物设计提供新的理论依据。  相似文献   
992.
Faithful genome integrity maintenance plays an essential role in cell survival. Here, we identify the RNA demethylase ALKBH5 as a key regulator that protects cells from DNA damage and apoptosis during reactive oxygen species (ROS)-induced stress. We find that ROS significantly induces global mRNA N6-methyladenosine (m6A) levels by modulating ALKBH5 post-translational modifications (PTMs), leading to the rapid and efficient induction of thousands of genes involved in a variety of biological processes including DNA damage repair. Mechanistically, ROS promotes ALKBH5 SUMOylation through activating ERK/JNK signaling, leading to inhibition of ALKBH5 m6A demethylase activity by blocking substrate accessibility. Moreover, ERK/JNK/ALKBH5-PTMs/m6A axis is activated by ROS in hematopoietic stem/progenitor cells (HSPCs) in vivo in mice, suggesting a physiological role of this molecular pathway in the maintenance of genome stability in HSPCs. Together, our study uncovers a molecular mechanism involving ALKBH5 PTMs and increased mRNA m6A levels that protect genomic integrity of cells in response to ROS.  相似文献   
993.
Chai  Qian  Meng  Ziang  Lu  Dexue  Zhang  Ziying  Liu  Meili  Wu  Weihua 《Molecular and cellular biochemistry》2021,476(6):2479-2489
Molecular and Cellular Biochemistry - Cardiomyocyte death is an important pathogenic process in cardiac complications of diabetes. Diabetic patients often suffer glycemic variability. Pyroptosis is...  相似文献   
994.
Chen  Qiangtang  Wu  Yu  Yu  Yachun  Wei  Junxiang  Huang  Wen 《Molecular and cellular biochemistry》2021,476(5):2159-2170

HIV-1 transactivator protein (Tat) induces tight junction (TJ) dysfunction and amyloid-beta (Aβ) clearance dysfunction, contributing to the development and progression of HIV-1-associated neurocognitive disorder (HAND). The Rho/ROCK signaling pathway has protective effects on neurodegenerative disease. However, the underlying mechanisms of whether Rho/ROCK protects against HIV-1 Tat-caused dysfunction of TJ and neprilysin (NEP)/Aβ transfer receptor expression have not been elucidated. C57BL/6 mice were administered sterile saline (i.p., 100 μL) or Rho-kinase inhibitor hydroxyfasudil (HF) (i.p., 10 mg/kg) or HIV-1 Tat (i.v., 100 μg/kg) or HF 30 min before being exposed to HIV-1 Tat once a day for seven consecutive days. Evans Blue (EB) leakage was detected via spectrophotometer and brain slides in mouse brains. The protein and mRNA levels of zonula occludens-1 (ZO-1), occludin, NEP, receptor for advanced glycation end products (RAGE), and low-density lipoprotein receptor-related protein 1 (LRP1) in mouse brain microvessels were, respectively, analyzed by Western blotting and quantitative real-time polymerase chain reaction (qRT-PCR) analyses. Exposure of the mice to HIV-1 Tat increased the amount of EB leakage, EB fluorescence intensity, blood–brain barrier (BBB) permeability, as well as the RAGE protein and mRNA levels, and decreased the protein and mRNA levels of ZO-1, occludin, NEP, and LRP1 in mouse brain microvessels. However, these effects were weakened by Rho-kinase inhibitor HF. Taken together, these results provide information that the Rho/ROCK signaling pathway is involved in HIV-1 Tat-induced dysfunction of TJ and NEP/Aβ transfer receptor expression in the C57BL/6 mouse brain. These findings shed some light on potentiality of inhibiting Rho/Rock signaling pathway in handling HAND.

  相似文献   
995.
Wu  Ying  Jiang  Lisha  Zhang  Lingling  Liu  Xia  Yan  Lina  Luan  Ting  Rui  Can  Mao  Zhiyuan  Fan  Chong  Liu  Yu  Li  Ping  Zeng  Xin 《Mycopathologia》2021,186(2):177-188
Mycopathologia - Vulvovaginal candidiasis (VVC) caused by Candida spp. affects 70–75% of women at least once during their lives. We aim to elucidate the potential mechanism of VVC and...  相似文献   
996.
Liu  Xia  Ruan  Zhi  Shao  Xing-cheng  Feng  Hong-xuan  Wu  Lei  Wang  Wei  Wang  Hong-min  Mu  Hong-yan  Zhang  Ru-jun  Zhao  Wei-min  Zhang  Hai-yan  Zhang  Nai-xia 《Neurochemical research》2021,46(3):686-698

28-O-caffeoyl betulin (B-CA) has been demonstrated to reduce the cerebral infarct volume caused by transient middle cerebral artery occlusion (MCAO) injury. B-CA is a novel derivative of naturally occurring caffeoyl triterpene with little information associated with its pharmacological target(s). To date no data is available regarding the effect of B-CA on brain metabolism. In the present study, a 1H-NMR-based metabolomics approach was applied to investigate the therapeutic effects of B-CA on brain metabolism following MCAO in rats. Global metabolic profiles of the cortex in acute period (9 h after focal ischemia onset) after MCAO were compared between the groups (sham; MCAO?+?vehicle; MCAO?+?B-CA). MCAO induced several changes in the ipsilateral cortex of ischemic rats, which consequently led to the neuronal damage featured with the downregulation of NAA, including energy metabolism dysfunctions, oxidative stress, and neurotransmitter metabolism. Treatment with B-CA showed statistically significant rescue effects on the ischemic cortex of MCAO rats. Specifically, treatment with B-CA ameliorated the energy metabolism dysfunctions (back-regulating the levels of succinate, lactate, BCAAs, and carnitine), oxidative stress (upregulating the level of glutathione), and neurotransmitter metabolism disturbances (back-regulating the levels of γ-aminobutyric acid and acetylcholine) associated with the progression of ischemic stroke. With the administration of B-CA, the levels of three phospholipid related metabolites (O-phosphocholine, O-phosphoethanolamine, sn-glycero-3-phosphocholine) and NAA improved significantly. Overall, our findings suggest that treatment with B-CA may provide neuroprotection by augmenting the metabolic changes observed in the cortex following MCAO in rats.

  相似文献   
997.
Single-cell RNA sequencing enables us to characterize the cellular heterogeneity in single cell resolution with the help of cell type identification algorithms. However, the noise inherent in single-cell RNA-sequencing data severely disturbs the accuracy of cell clustering, marker identification and visualization. We propose that clustering based on feature density profiles can distinguish informative features from noise. We named such strategy as ‘entropy subspace’ separation and designed a cell clustering algorithm called ENtropy subspace separation-based Clustering for nOise REduction (ENCORE) by integrating the ‘entropy subspace’ separation strategy with a consensus clustering method. We demonstrate that ENCORE performs superiorly on cell clustering and generates high-resolution visualization across 12 standard datasets. More importantly, ENCORE enables identification of group markers with biological significance from a hard-to-separate dataset. With the advantages of effective feature selection, improved clustering, accurate marker identification and high-resolution visualization, we present ENCORE to the community as an important tool for scRNA-seq data analysis to study cellular heterogeneity and discover group markers.  相似文献   
998.
Chen  Yen-Chi  Wang  I-Jen  Cheng  Chih-Ching  Wu  Yu-Chiao  Bai  Chun-Hsuan  Yu  Kuo-Pin 《Aerobiologia》2021,37(2):243-252
Aerobiologia - The liquid impingers can be used for sampling of viral aerosols, such as COVID-19 virus, influenza, and measles. However, the lowest cutoff diameter of commercially available liquid...  相似文献   
999.
Wu  Xiao-Han  Fan  Ming-Zhi  Li  Xue-Feng  Piao  Xuan-Chun  Gao  Ri  Lian  Mei-Lan 《Journal of Plant Growth Regulation》2021,40(4):1440-1449
Journal of Plant Growth Regulation - The adventitious root (AR) culture of Panax ginseng C.A. Meyer is an alternative route for mass production of ginsenosides. During the AR culture of P. ginseng,...  相似文献   
1000.
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