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   35756篇
  免费   2786篇
  国内免费   360篇
耳鼻咽喉   391篇
儿科学   972篇
妇产科学   955篇
基础医学   4572篇
口腔科学   586篇
临床医学   3723篇
内科学   7624篇
皮肤病学   836篇
神经病学   2416篇
特种医学   1175篇
外科学   4885篇
综合类   1176篇
一般理论   32篇
预防医学   1966篇
眼科学   1588篇
药学   2731篇
中国医学   308篇
肿瘤学   2966篇
  2023年   266篇
  2022年   512篇
  2021年   961篇
  2020年   617篇
  2019年   783篇
  2018年   1000篇
  2017年   765篇
  2016年   872篇
  2015年   1046篇
  2014年   1379篇
  2013年   1642篇
  2012年   2344篇
  2011年   2458篇
  2010年   1408篇
  2009年   1244篇
  2008年   1918篇
  2007年   1999篇
  2006年   1996篇
  2005年   1925篇
  2004年   1702篇
  2003年   1583篇
  2002年   1414篇
  2001年   1122篇
  2000年   1051篇
  1999年   906篇
  1998年   369篇
  1997年   269篇
  1996年   246篇
  1995年   198篇
  1994年   190篇
  1993年   191篇
  1992年   452篇
  1991年   443篇
  1990年   422篇
  1989年   396篇
  1988年   348篇
  1987年   367篇
  1986年   320篇
  1985年   272篇
  1984年   204篇
  1983年   146篇
  1982年   95篇
  1981年   86篇
  1980年   89篇
  1979年   138篇
  1978年   89篇
  1977年   72篇
  1976年   78篇
  1975年   77篇
  1972年   69篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
Summary Human cytomegalovirus (HCMV) infection is an important cause of neonatal death. Using primers derived from sequences within the morphological transforming region II (mtrII), HCMV DNA was amplified by polymerase chain reaction (PCR) from fixed tissues of infants who had died of congenital HCMV infection. In one neonate, HCMV DNA with reduction in the expected size was detected in the liver, spleen, kidney, adrenal, und thyroid tissues by gel electrophoresis. Nucleotide sequencing of the PCR product revealed a 65bp frame-shift deletion within the 79 amino acid open reading frame (ORF) of themtrII. Based upon this observation, it is likely that viral genomic rearrangement involving themtrII may occur in some cases of congenital HCMV infection.  相似文献   
82.
83.
84.
BACKGROUND: Severe acute respiratory syndrome (SARS) became a worldwide outbreak with a mortality of 9.2%. This new human emergent infectious disease is dominated by severe lower respiratory illness and is aetiologically linked to a new coronavirus (SARS-CoV). METHODS: Pulmonary pathology and clinical correlates were investigated in seven patients who died of SARS in whom there was a strong epidemiological link. Investigations include a review of clinical features, morphological assessment, histochemical and immunohistochemical stainings, ultrastructural study, and virological investigations in postmortem tissue. RESULTS: Positive viral culture for coronavirus was detected in most premortem nasopharyngeal aspirate specimens (five of six) and postmortem lung tissues (two of seven). Viral particles, consistent with coronavirus, could be detected in lung pneumocytes in most of the patients. These features suggested that pneumocytes are probably the primary target of infection. The pathological features were dominated by diffuse alveolar damage, with the presence of multinucleated pneumocytes. Fibrogranulation tissue proliferation in small airways and airspaces (bronchiolitis obliterans organising pneumonia-like lesions) in subpleural locations was also seen in some patients. CONCLUSIONS: Viable SARS-CoV could be isolated from postmortem tissues. Postmortem examination allows tissue to be sampled for virological investigations and ultrastructural examination, and when coupled with the appropriate lung morphological changes, is valuable to confirm the diagnosis of SARS-CoV, particularly in clinically unapparent or suspicious but unconfirmed cases.  相似文献   
85.
Helicobacter pylori (HP) infection induces expression of IL-8 and IL-10 in benign gastric epithelium. This study compared the expression of cytokines in CD4+ and CD8+ lymphocyte subsets of peripheral blood lymphocytes (PBL), benign mucosal lymphocytes (ML), and tumor infiltrative lymphocytes (TIL) as well as in the benign and malignant epithelial cells of the same patient, with respect to the presence of HP infection, lymph node metastases, and tumor histologic type. The mRNA of the cytokines was measured by a semiquantitative RT-PCR method. The levels were ranked and compared using the Wilcoxon sign-ranked test. Compared with CD8+ ML, the CD8+ TIL expresses higher levels of IL-6 and IL-8 but lower level of IL-4 in patients with lymph node metastases. In patients with HP infection, expression of IL-8 and IL-10 was higher in the gastric carcinoma cells than in the benign epithelial cells while expression of IL-6 and IL-8 were higher in CD8+ TIL than CD8+ ML. Overexpression of IL-8 in HP associated gastric carcinomas suggested that they might have arisen from HP-infected epithelial cells.  相似文献   
86.
Postpartum haemorrhage accounts for nearly 28% of maternal mortality in developing countries. Syntometrine is an effective and commonly used oxytocic in preventing postpartum haemorrhage, but it requires a controlled storage environment and i.m. administration. Misoprostol is an orally active uterotonic agent. A total of 2058 patients having a singleton pregnancy, low risk for postpartum haemorrhage and vaginal delivery were randomized to receive either 1 ml syntometrine or 600 microgram misoprostol for the management of the third stage of labour. There were no significant differences between the two groups in the mean blood loss, the incidence of postpartum haemorrhage and the fall in haemoglobin concentration. The need for additional oxytocic injection was significantly higher in the misoprostol group [relative risk (RR) 1.62, 95% confidence interval (CI) 1.34-1.96], but that of manual removal of placenta was reduced (RR 0.29, 95% CI 0.09-0.87). Shivering and transient pyrexia were more common in the misoprostol group. Oral misoprostol might be used in the management of the third stage, especially in situations where the use of syntometrine is contraindicated and facilities for storage and parenteral administration of oxytocics are limited.  相似文献   
87.
Several studies have suggested that the regulator of G-protein signaling 4 (RGS4) may be a positional and functional candidate gene for schizophrenia. Three single nucleotide polymorphisms (SNP) located at the promoter region (SNP4 and SNP7) and the intron 1 (SNP18) of RGS4 have been verified in different ethnic groups. Positive results have been reported in these SNPs with different numbers of SNP combinatory haplotypes. In this study, these three SNP markers were genotyped in 218 schizophrenia pedigrees of Taiwan (864 individuals) for association analysis. Among these three SNPs, neither SNP4, SNP7, SNP18 has shown significant association with schizophrenia in single locus association analysis, nor any compositions of the three SNP haplotypes has shown significantly associations with the DSM-IV diagnosed schizophrenia. Our results fail to support the RGS4 as a candidate gene for schizophrenia when evaluated from these three SNP markers.  相似文献   
88.
Seasonal allergic conjunctivitis is one of the most common manifestations of allergic disease, affecting 15 % population in the United States annually. Short ragweed (RW) is a major cause of seasonal allergies. Immunostimulatory DNA sequences (ISS or CpG motifs) can inhibit an on-going Th2/allergic response and induce a de novo Th1 response. In this study, we investigated the ability of these ISS to modulate allergic responses in a RW-induced mouse model of seasonal allergic conjunctivitis. Systemic or mucosal administration of ISS oligonucleotide (ISS-ODN) after RW sensitization inhibited both the immediate hypersensitivity response and the late-phase cellular infiltration and induced a RW-specific Th1 response. ISS-ODN administration suppressed the rise of RW-specific IgE titers after repeated allergen challenge. Furthermore, ISS administration was more effective than dexamethasone in inhibiting the allergic response. Mechanistically, the ISS-induced immunomodulatory effects were abolished when mice were treated with anti-IL-12 neutralizing antibodies, suggesting a pivotal role for type 1 cytokines in the inhibition of both the immediate hypersensitivity and the late-phase cellular infiltration. Thus, ISS-ODN is a novel anti-inflammatory and immunomodulatory agent that significantly inhibits the allergic response and may provide an alternative to the current standard care of ocular allergy.  相似文献   
89.
Glutaric acidemia type I is caused by mutations of the glutaryl-CoA dehydrogenase (GCDH) gene resulting in loss of GCDH enzyme activity. Patients present with progressive dystonia and lesions in basal ganglia. Dietary treatment, when instituted from the early neonatal period, markedly reduces dystonia and morbidity. Early diagnosis and prenatal diagnosis will be facilitated by knowledge of locally prevalent GCDH mutations. Several common GCDH mutations have been found in different ethnic groups. GCDH mutations were studied in 5 Chinese glutaric acidemia type I families. We detected two novel recurrent mutations (A219T and IVS10-2A>C) which were found in two unrelated families. An asymptomatic carrier of IVS10-2A>C was also found on screening of 120 individuals. Other mutations were identified, including two other novel (R386G & IVS3+1G>A) and two known mutations (G178R & R355H). Fibroblasts from patients carrying the novel mutations were confirmed to be deficient for GCDH activity. This is the first report of GCDH mutations describing recurrent mutations in Chinese patients. The carrier rate of IVS10-2A>C may be particularly high in Chinese.  相似文献   
90.
Y F Chan  S H Yeung  T C Chow  L Ma 《Pathology》1989,21(2):134-137
A case of clear cell chondrosarcoma in a Chinese patient is described. The clear cells showed strongly positive S-100 protein immunoreactivity. Ultrastructurally 2 types of chondroid cells were demonstrated. One type appeared more primitive with abundant electron-lucent cytoplasm and sparse organelles. The other type of cell was more differentiated with presence of microvilli and numerous dilated cisternae of endoplasmic reticulum. Previous ultrastructural studies on these lesions were reviewed and compared with the present findings.  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