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   15910篇
  免费   1399篇
  国内免费   1373篇
  18682篇
  2024年   47篇
  2023年   232篇
  2022年   485篇
  2021年   778篇
  2020年   642篇
  2019年   730篇
  2018年   712篇
  2017年   520篇
  2016年   691篇
  2015年   1040篇
  2014年   1250篇
  2013年   1276篇
  2012年   1473篇
  2011年   1315篇
  2010年   900篇
  2009年   739篇
  2008年   788篇
  2007年   706篇
  2006年   691篇
  2005年   559篇
  2004年   489篇
  2003年   519篇
  2002年   399篇
  2001年   248篇
  2000年   211篇
  1999年   207篇
  1998年   141篇
  1997年   112篇
  1996年   117篇
  1995年   109篇
  1994年   93篇
  1993年   57篇
  1992年   78篇
  1991年   64篇
  1990年   60篇
  1989年   44篇
  1988年   28篇
  1987年   24篇
  1986年   34篇
  1985年   25篇
  1984年   13篇
  1983年   7篇
  1982年   8篇
  1981年   5篇
  1980年   3篇
  1979年   3篇
  1976年   2篇
  1970年   1篇
  1962年   2篇
  1950年   1篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Low frequency magnetic fields have previously been shown to affect cell functions. In this article, the effects of 20 mT, 50 Hz sinusoidal magnetic field on cell proliferation, ion concentration, and osmolarity in two human cancer cell lines (HL-60 and SK-Hep-1) were investigated. Inhibition of cell growth was observed. On the other hand, the exposure also increased the Na+, K+ ion concentration and osmolarity in cell supernatant compared to the control group. To our knowledge, this is the first study on cancer cells where magnetic fields affect osmolarity in cell supernatant. In addition, a model of cells exposed to the oscillating magnetic field is described as well as the characteristics of ions in and out of cells. The experimental data appears to be consistent with the theoretical analysis. The results are also discussed in terms of the relationships among cell growth, ion concentration, and osmolarity. Magnetic field inhibitions of cell growth in vitro may relate to changes in cell ion concentration and osmolarity.  相似文献   
102.
A new acylated secoiridoidal glucoside, named gentiorigenoside A (1 ), was isolated from the root of Gentiana rigescens (Gentianaceae) , together with eight known compounds, gentiopicroside ( 2) , 6′- O-β- D-glucopyranosyl gentiopicroside (3) , loganic acid (4 ) , 6′- O-β- D-glucopyranosyl loganic acid ( 5), sweroside ( 6 ), 2′-( o, m-dihydoxybenzyl) -sweroside (7), swertiamarin (8) and secologanoside (9) . heir structures were elucidated on the basis of detailed spectroscopic analysis. Iridoidal glucosides 3, 5 and 9 were isolated for the first time from the title plant.  相似文献   
103.
Extracellular domains of the transmembrane glycoprotein, neuropilin-1 (Np1), specifically bind an array of factors and co-receptors including class-3 semaphorins (Sema3a), vascular endothelial growth factor (VEGF), hepatocyte growth factor, platelet-derived growth factor BB, transforming growth factor-β 1 (TGF-β1), and fibroblast growth factor2 (FGF2). Np1 may have a role in immune response, tumor cell growth, and angiogenesis, but its relative expression in comparison to its co-primary receptors, VEGF and Sema3a, is not known. In this study we determined the mRNA expression of Np1 and its co-receptors, VEGF and Sema3a, and the ratio of VEGF/Sema3a in different human and rodent cell lines. Expression of Np1, VEGF and Sema3a is very low in cells derived from normal tissues, but these proteins are highly expressed in tumor-derived cells. Furthermore, the ratio of VEGF/Sema3a is highly variable in different tumor cells. The elevated mRNA expression of Np1 and its putative receptors in tumor cells suggests a role for these proteins in tumor cell migration and angiogenesis. As different tumor cells exhibit varying VEGF/Sema3a ratios, it appears that cancer cells show differential response to angiogenic factors. These results bring to light the individual variation among the cancer-related genes, Np1, VEGF, and Sema3a, and provide an important impetus for the possible personalized therapeutic approaches for cancer patients.  相似文献   
104.
Dong S  Pang K  Bai X  Yu X  Hao P 《Current microbiology》2011,62(4):1133-1138
To determine the species of the yeast-like symbionts (YLS) in the brown planthoppers (BPH), Nilaparvata lugens, YLS were first isolated and purified by ultracentrifugation from the fat bodies of BPH, and then 18S rDNA and internal transcribed spacer (ITS)–5.8S rDNA sequences of YLS were amplified with the different general primers for fungi. The results showed that the two different 18S and ITS–5.8S rDNA sequences of YLS were obtained. One 2291-bp DNA sequence, which contained 18S and ITS–5.8S rDNA, showed the high similarity to Cryptococcus and was named Cryp-Like symbiotes. Another 1248-bp DNA sequence, which contained a part of 18S and ITS–5.8S rDNA, showed the high similarity to Pichia guilliermondii and was named Pichia-Like symbiotes. It was further proved that Cryp- and Pichia-Like symbiotes existed in BPH through nested PCR with specific primers for two symbiotes and in situ hybridization analysis using digoxigenin-labeled probes. Our results showed that BPH harbored more than one species of eukaryotic YLS, which suggested that diversity of fungal endosymbiotes may be occurred in planthoppers, just like bacterial endosymbiotes.  相似文献   
105.
A bacterial isolate was recovered from a soil sample collected in Jeollabuk-do Province, South Korea, and subjected to polyphasic taxonomic assessment. Cells of the isolate, designated strain S1-2-1-2-1T, were observed to be rod-shaped, pink in color, and Gram-stain negative. The strain was able to grow at temperature range from 10 to 30 °C, with an optimum of 25 °C, and growth occurred at pH 6–8. Comparative 16S rRNA gene sequence analysis showed that strain S1-2-1-2-1T belongs to the genus Hymenobacter, with closely related type strains being Hymenobacter daeguensis 16F3Y-2T (95.8% similarity), Hymenobacter rubidus DG7BT (95.8%), Hymenobacter soli PBT (95.7%), Hymenobacter terrenus MIMtkLc17T (95.6%), Hymenobacter terrae DG7AT (95.3%), and Hymenobacter saemangeumensis GSR0100T (95.2%). The genomic DNA G+C content of strain S1-2-1-2-1T was 63.0 mol%. The main polar lipid of this strain was phosphatidylethanolamine, the predominant respiratory quinone was menaquinone-7, and the major fatty acids were C15:0 iso (27.3%), summed feature 3 (C16:1 ω7c/C16:1 ω6c) (16.5%), C15:0 anteiso (15.3%), and C16:0 (14.7%), supporting the affiliation of this strain with the genus Hymenobacter. The results of this polyphasic analysis allowed for the genotypic and phenotypic differentiation of strain S1-2-1-2-1T from recognized Hymenobacter species. On the basis of its phenotypic properties, genotypic distinctiveness, and chemotaxonomic features, strain S1-2-1-2-1T is considered to represent a novel species of the genus Hymenobacter, for which the name Hymenobacter agri sp. nov. is proposed. The type strain is S1-2-1-2-1T (=KCTC 52739T?=?JCM 32194T).  相似文献   
106.
Lithium metal anodes are steadily gaining more attention, as their superior specific capacities and low redox voltage can significantly increase the energy density of rechargeable batteries far beyond those of current Li‐ion batteries. Nonetheless, the relevant technology is still in a premature research stage mainly due to the uncontrolled growth of Li dendrites that ceaselessly cause unwanted side reactions with electrolyte. In order to circumvent this shortcoming, herein, an ionic liquid additive, namely, 1‐dodecyl‐1‐methylpyrrolidinium (Pyr1(12)+) bis(fluorosulfonyl)imide (FSI?), for conventional electrolyte solutions is reported. The Pyr1(12)+ cation with a long aliphatic chain mitigates dendrite growth via the combined effects of electrostatic shielding and lithiophobicity, whereas the FSI? anion can induce the formation of rigid solid–electrolyte interphase layers. The synergy between the cation and anion significantly improves cycling performance in asymmetric and symmetric control cells and a full cell paired with an LiFePO4 cathode. The present study provides a useful insight into the molecular engineering of electrolyte components by manipulating the charge and structures of the involved molecules.  相似文献   
107.
Necroptosis is a unique programmed death mechanism of necrotic cells. However, its role and specific mechanism in cancer remain unclear, and a systematic pan‐cancer analysis of necroptosis is yet to be conducted. Thus, we performed a specific pan‐cancer analysis using The Cancer Genome Atlas and Genotype‐Tissue Expression databases to analyse necroptosis expression in terms of cancer prognosis, DNA methylation status, tumour mutative burden, microsatellite instability, immune cell infiltration in different types of cancer and molecular mechanisms. For the first time, we explored the correlation between necroptosis and immunotherapy prognosis. Thus, our study provides a relatively comprehensive understanding of the carcinogenicity of necroptosis in different types of cancer. It is suggested that necroptosis can be used to evaluate the sensitivity of different patients to immunotherapy and may become a potential target for tumour immunotherapy.  相似文献   
108.
Pan Y  Chu T  Dong S  Hao Y  Ren X  Wang J  Wang W  Li C  Zhang Z  Zhou Y 《Molecular biology reports》2012,39(9):8581-8594
The study was designed to investigate feasibility of tissue culture in vitro utilizing static culture method. Annulus fibrosus cells obtained from spine of rabbits were cultured. Results showed that fibrous tissue infiltration could be detected in shallow layer. With extended time, tissue infiltration depth increased, but there were still a large amount of holes in central part. Fibrous tissue infiltration was detected in the control side products and inner infiltration wasn't obvious. Hydroxyproline content of the control side products gradually increased with extended culture time. Hydroxyproline content of the control side products in the third and fourth month was significantly higher than that in the first month, but lower than those of the experimental side products and normal annulus fibrosus cells. DNA content of the control side products in the third and fourth month was significantly increased compared to the first month. DNA content of the control side products at each phase point was significantly lower than that of the experimental side and normal annulus fibrosus cells. Furthermore, there was lower expression levels of the type I, II collagen mRNA and protein in the experimental side scaffolds compared to the control side product. This study demonstrates the successful formation of Intervertebral disc Anulus Fibrosus in vitro by static culture method.  相似文献   
109.
Dong YN  Mao MH  Wang XM  Han JS 《生理学报》1998,50(6):663-670
西方采用放射配体结合实验研究了100HZ电针耐受发生发展过程中大鼠脑和脊髓K受体结构特性的变化。大鼠每天给予100HZ电针1次,连续7d。分别在电针的第1、3、5、7天取不同脑区进行观察。  相似文献   
110.
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