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   3309篇
  免费   263篇
  国内免费   14篇
耳鼻咽喉   49篇
儿科学   94篇
妇产科学   93篇
基础医学   468篇
口腔科学   44篇
临床医学   311篇
内科学   774篇
皮肤病学   82篇
神经病学   381篇
特种医学   90篇
外科学   316篇
综合类   20篇
一般理论   1篇
预防医学   280篇
眼科学   91篇
药学   175篇
中国医学   5篇
肿瘤学   312篇
  2024年   5篇
  2023年   48篇
  2022年   89篇
  2021年   228篇
  2020年   95篇
  2019年   134篇
  2018年   150篇
  2017年   106篇
  2016年   104篇
  2015年   116篇
  2014年   169篇
  2013年   183篇
  2012年   273篇
  2011年   302篇
  2010年   143篇
  2009年   133篇
  2008年   212篇
  2007年   225篇
  2006年   201篇
  2005年   167篇
  2004年   146篇
  2003年   113篇
  2002年   110篇
  2001年   9篇
  2000年   6篇
  1999年   16篇
  1998年   14篇
  1997年   10篇
  1996年   12篇
  1995年   9篇
  1994年   8篇
  1993年   5篇
  1992年   3篇
  1991年   2篇
  1990年   3篇
  1989年   5篇
  1988年   4篇
  1986年   6篇
  1985年   3篇
  1984年   2篇
  1981年   3篇
  1980年   2篇
  1963年   1篇
  1946年   1篇
  1940年   1篇
  1938年   1篇
  1923年   1篇
  1911年   1篇
  1907年   1篇
  1905年   1篇
排序方式: 共有3586条查询结果,搜索用时 15 毫秒
11.
Sexual activity was evaluated in 51 women with hirsutism associated with increased levels of circulating androgens before and while on combined treatment with the antiandrogen cyproterone acetate (CA) and ethinyl estradiol (EE2) and compared to a reference group of 52 subjects. The percentage of unbound testosterone (T) was higher (p < 0.001), the coital frequency lower (p < 0.05), and the masturbation frequency higher (p< 0.04) in hirsute women. Mean frequency of total activity (coitus plus masturbation) was similar in the two groups. Treatment with combination of CA and EE2 resulted in a decline of unbound T (p< 0.001). There was no change of total sexual activity, but coital frequency increased (p < 0.05) and masturbation frequency declined (p < 0.04). It is concluded that raised levels of circulating androgens, as judged by free T concentration, are not of crucial importance in the expression of sexual behavior in hirsute women.  相似文献   
12.
Beckwith-Wiedemann syndrome (BWS) is a fetal overgrowth disorder involving the deregulation of a number of genes, including IGF2 and CDKN1C, in the imprinted gene cluster on chromosome 11p15.5. In sporadic BWS cases the majority of patients have epimutations in this region. Loss of imprinting of the IGF2 gene is frequently observed in BWS, as is reduced CDKN1C expression related to loss of maternal allele-specific methylation (LOM) of the differentially methylated region KvDMR1. The causes of epimutations are unknown, although recently an association with assisted reproductive technologies has been described. To date the only genetic mutations described in BWS are in the CDKN1C gene. In order to screen for other genetic predispositions to BWS, the conserved sequences between human and mouse differentially methylated regions (DMRs) of the IGF2 gene were analyzed for variants. Four single nucleotide polymorphisms (SNPs) were found in DMR0 (T123C, G358A, T382G and A402G) which occurred in three out of 16 possible haplotypes: TGTA, CATG and CAGA. DNA samples from a cohort of sporadic BWS patients and healthy controls were genotyped for the DMR0 SNPs. There was a significant increase in the frequency of the CAGA haplotype and a significant decrease in the frequency of the CATG haplotype in the patient cohort compared to controls. These associations were still significant in a BWS subgroup with KvDMR1 LOM, suggesting that the G allele at T382G SNP (CAGA haplotype) is associated with LOM at KvDMR1. This indicates either a genetic predisposition to LOM or interactions between genotype and epigenotype that impinge on the disease phenotype.  相似文献   
13.
Breast carcinoma is a genetically and phenotypically heterogeneous disease and is frequently associated with nonrandom chromosomal alterations. The aim of this study was to investigate the numerical aberrations of chromosome 20 in breast cancer. The observed chromosome-specific numerical abnormalities were evaluated along with the established clinicopathological parameters, the immunohistochemical expression of ER, PR, p53, c-erbB-2, Ki-67 and patients' survival. Nonisotopic in situ hybridization was applied to interphase cell nuclei on paraffin embedded tissue sections. Polysomy of chromosome 20 was the prevalent alteration in 45 of 50 (90%), monosomy in 2 of 50 (4%) and disomy in 3 of 50 (6%) cases. Invasive ductal carcinomas displayed a higher percentage of polysomy than lobular ones. A statistical significant association was demonstrated between Ki-67 immunohistochemical expression and polysomy of chromosome 20. Disomy was inversely correlated with Ki-67, while monosomy was suggestively associated with PR positive expression. Among the patients, those with the highest levels of polysomy showed the worst survival. In conclusion, the gain of chromosome 20 is the prevalent aberration in patients with breast carcinomas and may be useful prognostic marker in breast cancer.  相似文献   
14.
Restriction fragment length polymorphisms (RFLPs) at the apolipoprotein AI-CIII-AIV gene cluster and their association with coronary artery disease (CAD) and lipid levels were studied in a Northern Greek population. Ninety-five patients with CAD and fifty-four normal controls, angio-graphically proven, were included in this study. Using genomic hybridization techniques, three polymorphic restriction sites were identified at this locus: the PstI at the 3' end of the apoAI gene, the SacI at the 3' non-coding region of the apoCIII gene and the PvuII at the intergenic region between the apoCIII-AIV genes. The rare allele (P2) arising from the absence of the PstI restriction site was observed with a significantly higher frequency (p<0.01) in patients compared to normals (0.11 vs 0.02). In contrast, the rare allele for the SacI polymorphic site had a similar distribution among patients and controls (0.12 vs 0.16). The same was observed for the PvuII RFLP (0.04 vs 0.05). Correlation of lipid and apolipoprotein AI levels with the three RFLPs revealed no significant association, although apo AI and HDL were lower in patients with the P2 allele. Thus, in this Greek population, only the PstI polymorphism, among the polymorphic restriction sites examined, appears to be associated with CAD.  相似文献   
15.
DNA and FISH (fluorescence in situ hybridization) analysis were carried out in 12 patients with stigmata of Turner syndrome to determine whether the Supernumerary M arker C hromosome (SMC) found cytogenetically in each of these patients was derived from the Y chromosome. The presence of a Y chromosome in these patients may predispose them to develop gonadoblastoma. PCR-Southern blot analysis, followed by FISH, was used to detect the presence of Y chromosome material. The S ex determining R egion Y (SRY), T estis S pecific P rotein Y -encoded (TSPY) and Y -chromosome R NA R ecognition M otif (YRRM) genes, which map at Yp11.31, Yp11.1–11.2 and Yp11.2/Yq11.21–11.23, respectively, were selected as markers, because they span the whole Y chromosome, and more importantly, they are considered to be involved in the development of gonadoblastoma. It was shown that in 12 patients, all of whom had an SMC, the SMC of 11 was derived from the Y chromosome. Furthermore, the presence of the SRY, TSPY and YRRM gene sequences was determined and FISH analysis confirmed the Y origin of the SMCs. The methodology described in this report is a rapid, reliable and sensitive approach which may be easily applied to determine the Y origin of an SMC carried in Turner syndrome. The identification of an SMC is important for the clinical management and prognostic counseling of these patients with Turner syndrome.  相似文献   
16.
PURPOSE: It is unclear whether academic health centers are successfully addressing societal needs and expectations by preparing students with knowledge and skills in disease prevention and health promotion. The authors assessed whether students were exposed to key content in these areas and whether they felt this exposure was adequate. METHOD: All components of the first three years of the Case Western Reserve University (Case) curriculum were examined in 2001 to create a curricular map, using competencies in disease prevention and health promotion identified by the Association of Teachers of Preventive Medicine (ATPM) as a template to assess the scope of instruction. Case students' United States Medical Licensing Examination (USMLE) Step 2 subscores in preventive medicine and health maintenance from 1994 to 2000 and graduating seniors' assessment of the adequacy of their training were compared to national data from the Association of American Medical Colleges' 2000 Graduation Questionnaire (GQ). RESULTS: Most content areas identified by ATPM were present in the Case curriculum and were offered frequently in a variety of educational venues over the first three years. USMLE scores increased nationally and at Case from 1994 to 2000 and Case students' perception of training adequacy in preventive medicine and health promotion was comparable to national ratings from the 2000 GQ. CONCLUSIONS: Broad and frequent exposure to disease prevention and health promotion core competencies has value, but may not sufficiently prepare students to deliver health-promoting services confidently. Creative curricula highlighting prevention's relevance throughout clinical practice and incorporating formal opportunities to apply knowledge and build experience may result in greater success.  相似文献   
17.
Tissue inhibitor of metalloproteinase-1 (TIMP-1) has emerged as a multifunctional protein with the contrasting activities of inhibiting tissue-degrading enzymes and promoting cellular growth. In an attempt to elucidate the clinical significance of TIMP-1 in breast cancer, the expression of TIMP-1 mRNA was evaluated in 117 invasive breast carcinomas by mRNA in situ hybridization, in correlation with clinicopathological parameters, immunohistochemical prognostic factors (Ki-67, c-erb-B-2, bcl-2) and clinical outcome. TIMP-1 was detected in stromal cells in areas within the tumours and at the tumour margin. High TIMP-1 mRNA expression in the marginal portion of the tumours was significantly correlated with lymph node metastasis (p<0.05) and c-erbB-2 expression (p<0.05). On the other hand, increased TIMP-1 mRNA expression within the tumours showed a statistically significant correlation with ER detection (p<0.01). Multivariate analysis revealed worse survival for patients with high TIMP-1 mRNA expression in the marginal portion of the tumours; the subgroup of these patients co-expressing high levels of TIMP-1 mRNA within the tumours as well had even worse survival (p=0.042). In conclusion, our data support the multifunctional role of TIMP-1, particularly its growth-promoting activity, on the basis of its significant correlation with lymph node metastasis and adverse prognosis. In addition to the latter property, a probable association of TIMP-1 with tumour cell differentiation is suggested by its topographical correlation with ER detection.  相似文献   
18.
This report describes a case of lymphocytic hypophysitis in a 63-year-old man who presented with symptoms of a pituitary mass lesion associated with hypothyroidism and hypogonadism. Postoperative endocrinological testing demonstrated gonadotropic, thyrotropic, and corticotropic hypopituitarism, and the patient was commenced on replacement therapy with hydrocortisone and levothyroxine. Histological examination of the pituitary tissue obtained by transsphenoidal surgery revealed lymphocytic hypophysitis without evidence of a pituitary adenoma. The vast majority of patients with lymphocytic hypophysitis are women particularly during pregnancy and the puerperium. Until recently only four men were reported in the literature. The pathogenesis of lymphocytic hypophysitis is uncertain but autoimmune mechanisms are possibly involved.  相似文献   
19.
RAG1/GFP knockin mice were exploited to isolate and characterize fetal lymphoid progenitors. CD11b and IL-7Ralpha are expressed in a developmental stage-dependent fashion, revealing how substantial numbers of early lymphoid progenitors were discarded or neglected in previous studies. The myeloerythroid potential of fetal progenitors in clonal assays declined in synchrony with activation of the RAG1 locus but was not completely extinguished. Lymphoid differentiation corresponded to patterns of gene expression previously found for adult marrow, but no fraction of fetal liver was enriched with respect to B + T progenitors. Also, unlike adults, fetal lymphoid progenitors transiently expressed endothelial cell markers. These findings help to reconcile discrepancies in previous reports and suggest that the fetal immune system arises via unique mechanisms.  相似文献   
20.
The presence of Y chromosome sequences in Turner syndrome (TS) patients may predispose them to gonadoblastoma formation with an estimated risk of 15–25%. The aim of this study was to determine the presence and the incidence of cryptic Y chromosome material in the genome of TS patients. The methodology involved a combination of polymerase chain reaction (PCR) and nested PCR followed by Southern blot analysis of three genes—the sex determining region Y (SRY), testis specific protein Y encoded (TSPY) and RNA binding motif protein (RBM) (previously designated as YRRM) and nine additional STSs spanning all seven intervals of the Y chromosome. The methodology has a high sensitivity as it detects one 46, XY cell among 105 46, XX cells. Reliability was ensured by taking several precautions to avoid false positive results. We report the results of screening 50 TS patients and the identification of cryptic Y chromosome material in 12 (24%) of them. Karyotypes were divided in four groups: 5 (23.8%) patients out of the 21 TS patients which have the 45, X karyotype (group A) also have cryptic Y sequences; none (0%) of the 7 patients who have karyotypes with anomalies on one of the X chromosomes have Y mosaicism (group B); 1 (6.3%) of the 16 patients with a mosaic karyotype have Y material (group C); and 6 (100%) out of 6 patients with a supernumerary marker chromosome (SMC) have Y chromosome sequences (group D). Nine of the 12 patients positive for cryptic Y material were recalled for a repeat study. Following new DNA extraction, molecular analysis was repeated and, in conjunction with fluorescent in situ hybridization (FISH) analysis using the Y centromeric specific probe Yc-2, confirmed the initial positive DNA findings. This study used a reliable and sensitive methodology to identify the presence of Y chromosome material in TS patients thus providing not only a better estimate of a patient's risk in developing either gonadoblastoma or another form of gonadal tumor but also the overall incidence of cryptic Y mosaicism.  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