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   265931篇
  免费   25500篇
  国内免费   20454篇
耳鼻咽喉   2040篇
儿科学   2323篇
妇产科学   3013篇
基础医学   32711篇
口腔科学   4301篇
临床医学   38282篇
内科学   38906篇
皮肤病学   2406篇
神经病学   15012篇
特种医学   9620篇
外国民族医学   198篇
外科学   25625篇
综合类   44467篇
现状与发展   74篇
一般理论   27篇
预防医学   15949篇
眼科学   8267篇
药学   28449篇
  304篇
中国医学   16020篇
肿瘤学   23891篇
  2024年   3249篇
  2023年   4491篇
  2022年   11411篇
  2021年   14112篇
  2020年   10969篇
  2019年   9390篇
  2018年   9730篇
  2017年   8617篇
  2016年   8169篇
  2015年   12206篇
  2014年   14965篇
  2013年   12547篇
  2012年   18784篇
  2011年   21533篇
  2010年   13036篇
  2009年   10058篇
  2008年   13333篇
  2007年   13363篇
  2006年   13595篇
  2005年   13848篇
  2004年   8203篇
  2003年   7603篇
  2002年   6380篇
  2001年   5700篇
  2000年   6425篇
  1999年   7176篇
  1998年   4742篇
  1997年   4758篇
  1996年   3680篇
  1995年   3518篇
  1994年   2902篇
  1993年   1965篇
  1992年   2214篇
  1991年   1842篇
  1990年   1570篇
  1989年   1333篇
  1988年   1134篇
  1987年   992篇
  1986年   749篇
  1985年   608篇
  1984年   350篇
  1983年   214篇
  1982年   115篇
  1981年   127篇
  1980年   86篇
  1979年   91篇
  1965年   1篇
  1962年   1篇
排序方式: 共有10000条查询结果,搜索用时 93 毫秒
951.
With the emergence of many antibiotic-resistant strains worldwide, antimicrobial peptides (AMPs) are being evaluated as promising alternatives to conventional antibiotics. P3, a novel hemoglobin peptide derived from bovine erythrocytes, exhibited modest antimicrobial activity in vitro. We evaluated the antimicrobial activities of P3 and an analog, JH-3, both in vitro and in vivo. The MICs of P3 and JH-3 ranged from 3.125 μg/ml to 50 μg/ml when a wide spectrum of bacteria was tested, including multidrug-resistant strains. P3 killed bacteria within 30 min by disrupting the bacterial cytoplasmic membrane and disturbing the intracellular calcium balance. Circular dichroism (CD) spectrometry showed that P3 assumed an α-helical conformation in bacterial lipid membranes, which was indispensable for antimicrobial activity. Importantly, the 50% lethal dose (LD50) of JH-3 was 180 mg/kg of mouse body weight after intraperitoneal (i.p.) injection, and no death was observed at any dose up to 240 mg/kg body weight following subcutaneous (s.c.) injection. Furthermore, JH-3 significantly decreased the bacterial count and rescued infected mice in a model of mouse bacteremia. In conclusion, P3 and an analog exhibited potent antimicrobial activities and relatively low toxicities in a mouse model, indicating that they may be useful for treating infections caused by drug-resistant bacteria.  相似文献   
952.
Two porcine Escherichia coli isolates harbored the cfr gene on conjugative plasmids of 38,405 bp (pGXEC6) and 41,646 bp (pGXEC3). In these two plasmids, the cfr gene was located within a 4,612-bp region containing a tnpA-IS26-cfr-IS26hyp element. Plasmid pGXEC3 was almost identical to pGXEC6 except for a 3,235-bp ISEcp1-blaCTX-M-14b insertion. The colocation of the multiresistance cfr gene with an extended-spectrum-β-lactamase gene on a conjugative plasmid may support the dissemination of these genes by coselection.  相似文献   
953.
Two compatible conversion factors for converting diameter measurements taken at different breast heights were derived for Pinus radiata using taper data from more than 3000 trees. The two breast heights used for conversion were 1.3 and 1.4 m above ground, as defined in Australia and New Zealand, two major radiata-growing countries in the world. The conversion factors were estimated through three alternative statistical methods including simple least squares regression, seemingly unrelated regression and errors-in-variables models. The three sets of estimates were almost identical and had similar conversion accuracy, although the second method was slightly better. The conversion factors were more accurate than overbark taper equations used for the same purpose. The factor was 0.9916 for converting diameter measured at 1.3 to that at 1.4 m above ground, and the inverse of this value, 1.0084, was for the vice versa. When calculating tree and stand volume and biomass using equations with diameter at a different breast height as a predictor to that of the input data, the bias, either over or under estimation, could be between 1.67% and 2.00% without conversion. These conversion factors will facilitate the sharing of data among radiata growing countries with different definitions of breast height, but more importantly it will help correct the bias in stand volume and biomass estimation caused by the seemingly negligible difference in breast height when software for forest resource management and decision support developed in one country is applied in another. Such bias when accumulated over a large management area may not be financially insignificant for an astute forest management agency.  相似文献   
954.
In this study, we tested the antimicrobial activity of three metal nanoparticles (NPs), ZnO, MgO, and CaO NPs, against Salmonella enterica serovar Enteritidis in liquid medium and on solid surfaces. Out of the three tested metal NPs, ZnO NPs exhibited the most significant antimicrobial effect both in liquid medium and when embedded on solid surfaces. Therefore, we focused on revealing the mechanisms of surface-associated ZnO biocidal activity. Using the global proteome approach, we report that a great majority (79%) of the altered proteins in biofilms formed by Salmonella enterica serovar Enteritidis were downregulated, whereas a much smaller fraction (21%) of proteins were upregulated. Intriguingly, all downregulated proteins were enzymes involved in a wide range of the central metabolic pathways, including translation; amino acid biosynthetic pathways; nucleobase, nucleoside, and nucleotide biosynthetic processes; ATP synthesis-coupled proton transport; the pentose phosphate shunt; and carboxylic acid metabolic processes, indicating that ZnO NPs exert a panmetabolic toxic effect on this prokaryotic organism. In addition to their panmetabolic toxicity, ZnO NPs induced profound changes in cell envelope morphology, imposing additional necrotic effects and triggering the envelope stress response of Salmonella serovar Enteritidis. The envelope stress response effect activated periplasmic chaperones and proteases, transenvelope complexes, and regulators, thereby facilitating protection of this prokaryotic organism against ZnO NPs.  相似文献   
955.
956.
957.
958.
959.
目的探讨手术改善非小细胞肺癌(NSCLC)合并脑转移患者的预后。方法对我院2005年3月—2013年5月切除NSCLC原发灶的62例患者进行分析,分析原发病灶的部位、手术方法、病理分型,脑转移灶的数量、治疗方式、治疗后的生存期等。结果本组男21例,女41例。全肺切除4例,肺叶、肺段或肺部分切除58例。腺癌47例(75.8%),鳞癌8例,混合型腺鳞癌7例。在处理脑转移瘤后再切除原发灶38例,先处理原发灶者24例。本组中位生存期18.7个月。其中1年生存率为75.9%;2年生存率为38.9%;3年生存率为16.7%。与同期未手术对照组比较1年生存率无差异,2、3年生存率比较差异有统计学意义(P<0.01)。结论积极处理肺部原发灶,结合头部放疗及全身化疗或基因靶向等综合治疗可延长生存期,提高此类患者预后。  相似文献   
960.
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