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   35702篇
  免费   3066篇
  国内免费   1940篇
耳鼻咽喉   578篇
儿科学   508篇
妇产科学   819篇
基础医学   4179篇
口腔科学   564篇
临床医学   4246篇
内科学   6249篇
皮肤病学   813篇
神经病学   1919篇
特种医学   1198篇
外国民族医学   17篇
外科学   3618篇
综合类   4303篇
现状与发展   4篇
一般理论   7篇
预防医学   2333篇
眼科学   795篇
药学   3710篇
  23篇
中国医学   1658篇
肿瘤学   3167篇
  2024年   83篇
  2023年   485篇
  2022年   1150篇
  2021年   1528篇
  2020年   1118篇
  2019年   1168篇
  2018年   1284篇
  2017年   1094篇
  2016年   1046篇
  2015年   1549篇
  2014年   1900篇
  2013年   1893篇
  2012年   2663篇
  2011年   2805篇
  2010年   1792篇
  2009年   1332篇
  2008年   1930篇
  2007年   1896篇
  2006年   1869篇
  2005年   1837篇
  2004年   1330篇
  2003年   1270篇
  2002年   1097篇
  2001年   910篇
  2000年   827篇
  1999年   752篇
  1998年   465篇
  1997年   419篇
  1996年   336篇
  1995年   308篇
  1994年   279篇
  1993年   205篇
  1992年   342篇
  1991年   287篇
  1990年   225篇
  1989年   177篇
  1988年   202篇
  1987年   159篇
  1986年   123篇
  1985年   117篇
  1984年   84篇
  1983年   44篇
  1982年   25篇
  1981年   35篇
  1980年   21篇
  1979年   32篇
  1978年   24篇
  1977年   19篇
  1975年   18篇
  1973年   24篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
61.
三氧化二锑诱导急性早幼粒细胞白血病细胞凋亡的研究   总被引:2,自引:0,他引:2  
目的 研究锑剂三氧化二锑(Sb2O3)对早幼粒细胞白血病细胞株NB4凋亡的诱导作用,以寻求早幼粒细胞白血病治疗的新方法。方法 采用细胞生长曲线,形态学及硝基四氮唑蓝(NBT)还原试验,判定NB4细胞的生长,分化及功能。采用细胞周期分析和DNA电泳研究细胞凋亡。结果 Sb2O3能诱导早幼粒白血病细胞凋亡,且具有时间,剂量依赖性。结论 Sb2O3能有效地诱导早幼粒白血病细胞凋亡,提示锑剂诱导细胞半亡的疗法,有望成为临床治疗早幼粒细胞白血病的新方法。  相似文献   
62.
The S glycoprotein of transmissible gastroenteritis virus (TGEV) has been shown to contain four major antigenic sites (A, B, C, and D). Site A is the main inducer of neutralizing antibodies and has been previously subdivided into the three subsites Aa, Ab, and Ac. The residues that contribute to these sites were localized by sequence analysis of 21 mutants that escaped neutralization or binding by TGEV-specific monoclonal antibodies (MAbs), and by epitope scanning (PEPSCAN). Site A contains the residues 538, 591, and 543, which are essential in the formation of subsites Aa, Ab, and Ac, respectively. In addition, mar mutant 1B.H6 with residue 586 changed had partially altered both subsite Aa and Ab, indicating that these subsites overlap in residue 586; i.e. this residue also is part of site A. The peptide 537-MKSGYGQPIA-547 represents, at least partially, subsite Ac which is highly conserved among coronaviruses. This site is relevant for diagnosis and could be of interest for protection. Other residues contribute to site B (residues 97 and 144), site C (residues 50 and 51), and site D (residue 385). The location of site D is in agreement with PEPSCAN results. Site C can be represented by the peptide 48-P-P/S-N-S-D/E-52 but is not exposed on the surface of native virus. Its accessibility can be modulated by treatment at pH greater than 11 (at 4 degrees) and temperatures greater than 45 degrees. Sites A and B are fully dependent on glycosylation for proper folding, while sites C and D are fully or partially independent of glycosylation, respectively. Once the S glycoprotein has been assembled into the virion, the carbohydrate moiety is not essential for the antigenic sites.  相似文献   
63.
应用放射配体结合分析,测定40例正常晚期妊娠妇女及40例妊高征妇女外周血淋巴细胞β_2-肾上腺素能受体(β_2-AR)结合量,并测定两组妇女分娩的新生儿体重。结果为:1.正常晚期妊娠妇女外周淋巴细胞β_2-AR结合量明显降低,妊高征妇女β_2-AR结合量降低更显著;2.妊高征孕妇组的新生儿出生体重明显低于正常妊娠组的新生儿体重;3.孕妇β_2-AR结合量与新生儿出生体重呈明显正相关,提示好高征与机体β_2-AR结合量下降有关,β_2-AR改变影响胎儿生长发育。  相似文献   
64.
Polymerase chain reaction and nucleotide sequence analysis were performed to amplify and determine the V3 loop sequences of human immunodeficiency virus type 1 (HIV-1) from ten seropositive patients at National Cheng Kung University Hospital, Tainan. The nucleotide sequences and the deduced amino acid (a. a.) sequences of these V3 regions were compared with those of known HIV-1 prototypes. The V3 loop a. a. sequences detected in eight individuals belong to subtype B which predominates in North America and Europe, whereas two individuals were infected with HIV-1 subtype E which is mainly found in the heterosexual populations of Thailand. Sequence analysis of these variant HIV-1 strains revealed a number of interesting features and a phylogenetic tree was also constructed according to the V3 loop nucleotide sequences of these variant strains and HIV-1 isolates from other parts of the world. Furthermore, our results suggest that the north vs south geographical separation in terms of HIV-1 epidemiology in Taiwan is insignificant.  相似文献   
65.
Cell cycle “checkpoints” help to ensure the integrity of normal cellular functions prior to replicative DNA synthesis and/or cell division. Cell kinetic abnormalities, particularly arrests at the G1/S and G2/M cell cycle checkpoints, are induced following exposure to ionizing radiationin vitro. Following irradiation, cellular signaling pathways may lead to G1 arrest and/or apoptosis at the G1/S cell cycle transition point. Transfection of cyclin D1, a G1/S cyclin, into a rat embryo cells (REC) results in cellular populations that overexpress cyclin D1, are transformed morphologically, demonstrate an increased incidence of apoptosis, and are tumorigenic in immune-deficient mice. Despite such phenotypic changes, transfected cell populations maintain the itegrity of the G1 checkpoint following ionizing radiation. The transfected cells overexpressing Cyclin D1 have a statistically significant increase in the incidence of apoptosis as compared to parental REC strains or mock-transfected REC. The work provides further evidence of Cyclin D1 playing a critical role in maintaining the integrity of the G1/S checkpoint, via the activation of apoptotic pathways following exposure to ionizing radiationin vitro.  相似文献   
66.
Wu WC  Wang Y  Su CK  Chai CY 《Neuroscience letters》2001,302(2-3):121-124
The potential neuroprotective effects of the novel nitro-derivate of aspirin (NCX4016) on permanent focal cerebral ischemia in spontaneously hypertensive rats (SHRs) was investigated. Reference compounds were acetylsalicilic acid (ASA) and FK506 (tacrolimus). Ten minutes after surgery, SHRs were randomly divided into four groups of ten, pharmacologically treated and sacrificed 24 h after treatment. Brains were removed and processed to measure infarct volume, 70 kDa heat shock protein (hsp70), glial fibrillary acidic protein (GFAP) and vimentin (Vim) immunoreactivity (IR), and apoptosis using terminal deoxynucleotidyl transferase (TdT)-mediated dUTP-digoxigenin nick end-labeling (TUNEL) assay. NCX-4016 significantly reduced total infarct volume compared to ASA (-20%, P < 0.05), FK506 (-18%, P < 0.05) and vehicle treatment (-20%, P < 0.05). Experimental groups did not differ in hsp70-IR and GFAP-IR. Conversely, hyperplastic astrocytes, measured by Vim-IR, were significantly lower in NCX-4016 than in the vehicle group (-36%, P<0.01). TUNEL assay indicated a significantly lower degree of apoptosis in NCX-4016 group than vehicle in both the homolateral (-27%, P < 0.01) and contralateral hemisphere (-29%, P < 0.05). These findings indicate that NO release associated with aspirin confers neuroprotective effects against ischemic injury.  相似文献   
67.
Elevation of the intracellular free Ca(2+) concentration regulates many functional responses in airway smooth muscle, including contraction, proliferation, adhesion, and cell survival. This increase in calcium can be achieved by a release from internal stores (sarcoplasmic reticulum) and/or entry across the cell membrane from the extracellular environment. The molecular identity of this calcium influx pathway in human airway smooth muscle (HASM) remains unclear. Functional studies using Fluo 4-loaded HASM suggest the presence of a histamine H(1) receptor-activated Ca(2+) entry pathway with characteristics similar to those seen with transient receptor potential (TRP) family homologs. Using a range of molecular and cell biological approaches we defined the expression pattern of transient receptor potential classics (TRPC) homologs in airway cells and tissue. Here we show that HASM and human bronchial epithelial cells both express TRPC1, -4, and -6, with HASM also expressing TRPC3 at the mRNA level. Identification of TRPC6 protein by western blot and confocal microscopy indicated that the protein is localized in specific cell types, suggesting that it plays an important role in regulating key functions in airway cells. These data demonstrate the expression of a range of TRPC homologs in the airway and the presence of a functional Ca(2+) entry pathway with characteristics typical of TRPC family members. TRPC homologs may provide an important novel target for the treatment of airway disease.  相似文献   
68.
领导干部心理健康量表的初步编制   总被引:1,自引:0,他引:1  
目的编制一套适用于领导干部群体的心理健康量表。方法通过文献研究、个案分析、问卷调查等,确立测验结构并编制成预测量表,通过对127位被试施测结果进行条目分析等形成正式量表,并进行因子分析等考察量表的信度和效度。结果编制成一个含3个量表:心理症状量表、自我概念量表、外界适应量表,共计93个项目的测评系统。项目与其所在量表的题总相关系数在0.445~0.855之间(P<0.001),各条目决断值(CR值)均具有显著性;对自我概念量表和外界适应量表探索性因素分析分别提取4个和3个公因子,累计解释总变异量分别为54.842%,48.365%,因子载荷在0.427~0.814和0.434~0.796之间;各量表的Cronbach'sα系数分别为0.775,0.860,0.952。结论初步研究显示量表的信效度均达到心理学测量标准,具有较好的信效度。  相似文献   
69.
Typhoid fever, a systemic disease caused by Salmonella typhi, is classically characterized by fever and abdominal symptoms. Although now considered uncommon, it seems to have re-emerged in Taiwan in recent years. We conducted a retrospective study of the clinical characteristics and microbiologic findings in 24 confirmed cases of typhoid fever treated over a 7-year period at a medical center in northern Taiwan. There were 11 males and 13 females, including 15 adults (over 18 years in age) and 9 children. Their mean age was 24.7 years (range, 9 months to 58 years). Twelve patients had recently returned from abroad, mostly from Southeast Asia. The most common complaints were fever (24/24), diarrhea (18/24), abdominal pain (10/24), and cough (10/24). The average duration of fever before diagnosis was 14.1 days, with a maximum of 30 days. Relative bradycardia was noted in 6 patients. Leukopenia was noted in 2 patients. S. typhi was isolated from blood culture in 20 cases, from stool culture in 3 cases, and from bone marrow culture in 1 case. Widal test was only positive initially in 7/18 cases. Fever of unknown origin was the most common initial diagnosis. Typhoid or enteric fever was impressed initially in only 2 cases. Almost all isolates of S. typhi were susceptible to antibiotics currently used for typhoid fever, with only 1 isolate resistant to chloramphenicol. All patients survived after antibiotic treatment. Only 1 patient developed recurrence after a 10-day course of ceftriaxone. In conclusion, the diagnosis of typhoid fever is often challenging due to non-specific symptoms and lack of an immediate confirmatory test. It is important to include this disease in the differential diagnosis of febrile patients with abdominal symptoms.  相似文献   
70.
艾滋病的致病因子为人免疫缺陷病毒。该病毒的蛋白酶在病毒复制和成熟中具有决定性的意义。由于目前国内外尚未获得艾滋病病毒蛋白酶高效表达的重组子及简便的活性检测系统,限制了它的研究与应用。本文将用PCR技术修饰的HIVPr基因克隆入原核高效表达载体pTTQ18的EcoRⅠ和HindⅢ酶切位点之间,并用豆芽核酸酶将EcoRⅠ的粘端削平,构建了读框正确的表达载体,IPTG诱导表明,该重组子在大肠杆菌中获得了高表达,激光扫描结果表明:重组的HIVPr占细菌总蛋白8.9%以上。  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