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   5126篇
  免费   518篇
  国内免费   661篇
  6305篇
  2024年   17篇
  2023年   79篇
  2022年   208篇
  2021年   334篇
  2020年   255篇
  2019年   326篇
  2018年   209篇
  2017年   188篇
  2016年   253篇
  2015年   375篇
  2014年   386篇
  2013年   437篇
  2012年   492篇
  2011年   459篇
  2010年   280篇
  2009年   267篇
  2008年   287篇
  2007年   198篇
  2006年   195篇
  2005年   170篇
  2004年   136篇
  2003年   126篇
  2002年   128篇
  2001年   89篇
  2000年   76篇
  1999年   53篇
  1998年   41篇
  1997年   37篇
  1996年   25篇
  1995年   24篇
  1994年   21篇
  1993年   18篇
  1992年   25篇
  1991年   16篇
  1990年   15篇
  1989年   11篇
  1988年   12篇
  1987年   5篇
  1986年   8篇
  1985年   6篇
  1983年   4篇
  1982年   2篇
  1981年   1篇
  1980年   3篇
  1979年   2篇
  1974年   1篇
  1970年   1篇
  1969年   1篇
  1935年   1篇
  1934年   1篇
排序方式: 共有6305条查询结果,搜索用时 15 毫秒
991.
The objective of this study was to explore the potential role of G-protein-coupled receptor kinase 2 (GRK2) in the progression of cannabinoid 2 receptor (CB2) agonist-induced analgesic effects of bone cancer pain. Female Sprague–Dawley rats, weighing 160–180 g, were utilized to establish a model of bone cancer pain induced by intra-tibia inoculation of Walker 256 mammary gland carcinoma cells. JWH-015, a selective CB2 agonist, was injected intrathecally or intraperitoneally on postoperative day 10. Bone cancer-induced pain behaviors—mechanical allodynia and ambulatory pain—were assessed on postoperative days ?1 (baseline), 4, 7, and 10 and at post-treatment hours 2, 6, 24, 48, and 72. The expressions of spinal CB2 and GRK2 protein were detected by Western Blotting on postoperative days ?1 (baseline), 4, 7, and 10 and at post-treatment hours 6, 24, and 72. The procedure produced prolonged mechanical allodynia, ambulatory pain, and different changes in spinal CB2 and GRK2 expression levels. Intrathecal or intraperitoneal administration of JWH-015 alleviated the induced mechanical allodynia and ambulatory pain, and inhibited the downregulation of spinal GRK2 expression. These effects were in a time-dependent manner and reversed by pretreatment of CB2 selective antagonist AM630. The results affirmed CB2 receptor agonists might serve as new treatment targets for bone cancer pain. Moreover, spinal GRK2 was an important regulator of CB2 receptor agonist-analgesia pathway.  相似文献   
992.
Diverse species of rodents and shrews, which are abundant worldwide, harbor a variety of viruses;some of these are closely related to human viruses and possess zoonotic potential. Previously studies have demonstrated that the mammarenavirus and hantavirus carried by rodents or shrews could cause diseases in human population. To determine the distribution of zoonotic viruses in Shenzhen city, the major city in southern China with a high population density, we analyzed 225 rodents(Rattus norvegicus and Rattus flavipectus) and 196 shrews(Suncus murinus) from urban and rural districts for the presence of mammarenavirus, hantavirus, and hepatitis E virus(HEV) by RT-PCR targeting the conserved regions. The infection rates for mammarenavirus, hantaviruses,and HEV in rodents and shrews were 3.56%, 6.89%, and 1.66%, respectively. Partial genome fragment analysis indicated that mammarenavirus and hantavirus strains had more than 90% and 99% nucleic acid identity with Cardamones virus and Seoul virus, respectively, which cause diseases in humans. Although the present HEV strains identified are typically found worldwide,phylogenetic analysis demonstrated a divergence of 16%. To our knowledge, the present work is the first report of the prevalence of mammarenavirus, hantaviruses, and rat HEV strains in rodents and shrews from Shenzhen city, China. Our findings highlight the zoonotic potential of rodent-and shrew-borne mammarenavirus and hantavirus, and the biodiversity of rat HEV isolates in Shenzhen city. The present work suggests that utilization of good hygiene habits is important to minimize the risk of zoonosis.  相似文献   
993.
Bocaparvovirus (BOV) is a genetically diverse group of DNA viruses and a possible cause of respiratory, enteric, and neurological diseases in humans and animals. Here, two highly divergent BOVs (tentatively named as Himalayan marmot BOV, HMBOV1 and HMBOV2) were identified in the livers and feces of wild Himalayan marmots in China, by viral metagenomic analysis. Five of 300 liver samples from Himalayan marmots were positive for HMBOV1 and five of 99 fecal samples from these animals for HMBOV2. Their nearly complete genome sequences are 4,672 and 4,887 nucleotides long, respectively, with a standard genomic organization and containing protein-coding motifs typical for BOVs. Based on their NS1, NP1, and VP1, HMBOV1 and HMBOV2 are most closely related to porcine BOV SX/1-2 (approximately 77.0%/50.0%, 50.0%/53.0%, and 79.0%/54.0% amino acid identity, respectively). Phylogenetic analysis of these three proteins showed that HMBOV1 and HMBOV2 formed two distinctly independent branches in BOVs. According to these results, HMBOV1 and HMBOV2 are two different novel species in the Bocaparvovirus genus. Their identification expands our knowledge of the genetic diversity and evolution of BOVs. Further studies are needed to investigate their potential pathogenicity and their impact on Himalayan marmots and humans.  相似文献   
994.
Although we now routinely sequence human genomes, we can confidently identify only a fraction of the sequence variants that have a functional impact. Here, we developed a deep mutational scanning framework that produces exhaustive maps for human missense variants by combining random codon mutagenesis and multiplexed functional variation assays with computational imputation and refinement. We applied this framework to four proteins corresponding to six human genes: UBE2I (encoding SUMO E2 conjugase), SUMO1 (small ubiquitin‐like modifier), TPK1 (thiamin pyrophosphokinase), and CALM1/2/3 (three genes encoding the protein calmodulin). The resulting maps recapitulate known protein features and confidently identify pathogenic variation. Assays potentially amenable to deep mutational scanning are already available for 57% of human disease genes, suggesting that DMS could ultimately map functional variation for all human disease genes.  相似文献   
995.
Acute inflammatory diseases are the leading causes of mortality in intensive care units. Myeloid differentiation 2 (MD‐2) is required for recognizing lipopolysaccharide (LPS) by toll‐like receptor 4 (TLR4), and represents an attractive therapeutic target for LPS‐induced inflammatory diseases. In this study, we report a chalcone derivative, L2H21, as a new MD2 inhibitor, which could inhibit LPS‐induced inflammation both in vitro and in vivo. We identify that L2H21 as a direct inhibitor of MD‐2 by binding to Arg90 and Tyr102 residues in MD‐2 hydrophobic pocket using a series of biochemical experiments, including surface plasmon response, molecular docking and amino acid mutation. L2H21 dose dependently inhibited LPS‐induced inflammatory cytokine expression in primary macrophages. In mice with LPS intratracheal instillation, L2H21 significantly decreased LPS‐induced pulmonary oedema, pathological changes in lung tissue, protein concentration increase in bronchoalveolar lavage fluid, inflammatory cells infiltration and inflammatory gene expression, accompanied with the decrease in pulmonary TLR4/MD‐2 complex. Meanwhile, administration with L2H21 protects mice from LPS‐induced mortality at a degree of 100%. Taken together, this study identifies a new MD2 inhibitor L2H21 as a promising candidate for the treatment of acute lung injury (ALI) and sepsis, and validates that inhibition of MD‐2 is a potential therapeutic strategy for ALI.  相似文献   
996.
Carbenoxolone (CBX) is a clinically prescribed drug for the treatment of digestive ulcer and inflammation. It is also a widely used pharmacological inhibitor of several channels in basic research. Given that the overactivity of several channels, including those inhibitable by CBX, underlies bladder dysfunction, we tested the potential therapeutic application and mechanism of CBX in the treatment of voiding dysfunction. In a mouse model of cystitis induced by cyclophosphamide (CYP), CBX administration prevented the CYP‐elicited increase in bladder weight, oedema, haemorrhage, and urothelial injury. CBX also greatly improved micturition pattern, as manifested by the apparently decreased micturition frequency and increased micturition volume. Western blot results showed that CBX suppressed CYP‐induced increase in protein carbonyls, COX‐2, and iNOS. Further analysis using cultured urothelial cells revealed that acrolein, the major metabolite of CYP, caused protein oxidation, p38 activation, and urothelial injury. These effects of acrolein were reproduced by TRPV4 agonists and significantly prevented by antioxidant NAC, p38 inhibitor SB203580, TRPV4 antagonist RN‐1734, and CBX. Further studies showed that CBX potently suppressed TRPV4 agonist‐initiated calcium influx and subsequent cell injury. CBX attenuated CYP‐induced cystitis in vivo and reduced acrolein‐induced cell injury in vitro, through mechanisms involving inhibition of TRPV4 channels and attenuation of the channel‐mediated oxidative stress. CBX might be a promising agent for the treatment of bladder dysfunction.  相似文献   
997.
Three new sesquiterpenoids, salplebeones A – C ( 1  –  3 ), were isolated from the ethanol‐soluble extract of the aerial part of Salvia plebeia R. Br . Their structures were established by detailed analysis of NMR and MS spectra. Salplebeone A was an eudesmane lactone, while salplebeones B and C were rare eudesmane sesquiterpenoids, containing 12,8‐lactam groups. Antiproliferative activities of salplebeones A – C to myeloid leukemia cell lines were evaluated.  相似文献   
998.
The plant SWEET family is a sugar transporter family that plays a significant role in plant development. Here, seven loquat SWEET family members were identified by RNA-seq. These were designated as EjSWEET1, EjSWEET2a, EjSWEET2b, EjSWEET2c, EjSWEET4, EjSWEET15, and EjSWEET17. Phylogenetic and predictive functional annotation analyses suggest that the loquat SWEETs are classified as having sucrose, glucose and fructose transportation features. The in vivo responses of loquat SWEETs to exogenous sugar or NaCl was investigated by applying high concentrations of sugar or salt to 7-month-old loquat seedlings cultured in a nutrient medium. The results showed that most loquat SWEET genes can respond to exogenous applications of sucrose, glucose, fructose and salt. The response of EjSWEET1 to exogenous fructose was faster than the others, indicating that EjSWEET1 is more sensitive to exogenous fructose compared with other loquat SWEETs. EjSWEET15 can be induced by sucrose, but is suppressed by glucose. This indicates its possible role in sucrose transporting. The response of loquat SWEETs to NaCl showed broadly similar patterns compared to sugars. However, after a longer time of NaCl treatment, most loquat SWEETs are upregulated, especially EjSWEET15. This indicates its long-term response to high salinity.  相似文献   
999.
Half‐Heusler (HH) alloys are among the best promising thermoelectric (TE) materials applicable for the middle‐to‐high temperature power generation. Despite of the large thermoelectric power factor and decent figure‐of‐merit ZT (≈1), their broad applications and enhancement on TE performance are limited by the high intrinsic lattice thermal conductivity (κL) due to insufficiencies of phonon scattering mechanisms, and the fewer powerful strategies associated with the microstructural engineering for HH materials. This study reports a bottom‐up nanostructure synthesis approach for these HH materials based on the displacement reaction between metal chlorides/bromides and magnesium (or lithium), followed by vacuum‐assisted spark plasma sintering process. The samples are featured with dense dislocation arrays at the grain boundaries, leading to a minimum κL of ≈1 W m?1 K?1 at 900 K and one of the highest ZT (≈1) and predicted η (≈11%) for n‐type Hf0.25Zr0.75NiSn0.97Sb0.03. Further manipulation on the dislocation defects at the grain boundaries of p‐type Nb0.8Ti0.2FeSb leads to enhanced maximum power factor of 47 × 10?4 W m?1 K?2 and the predicted η of ≈7.5%. Moreover, vanadium substitution in FeNb0.56V0.24Ti0.2Sb significantly promotes the η to ≈11%. This strategy can be extended to a broad range of advanced alloys and compounds for improved properties.  相似文献   
1000.
Shan  Yibo  Wang  Yao  Li  Jianfeng  Shi  Hongcan  Fan  Yiwei  Yang  Junfeng  Ren  Weidong  Yu  Xi 《Bioprocess and biosystems engineering》2017,40(12):1813-1823
Bioprocess and Biosystems Engineering - The goals of our study were to evaluate the biomechanical properties and cellular biocompatibility of 3D printed tracheal graft fabricated by...  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