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   2714篇
  免费   268篇
  国内免费   15篇
耳鼻咽喉   28篇
儿科学   46篇
妇产科学   51篇
基础医学   407篇
口腔科学   71篇
临床医学   358篇
内科学   525篇
皮肤病学   39篇
神经病学   242篇
特种医学   147篇
外科学   314篇
综合类   69篇
一般理论   1篇
预防医学   250篇
眼科学   71篇
药学   190篇
中国医学   1篇
肿瘤学   187篇
  2021年   41篇
  2020年   18篇
  2019年   40篇
  2018年   61篇
  2017年   37篇
  2016年   30篇
  2015年   54篇
  2014年   50篇
  2013年   79篇
  2012年   124篇
  2011年   103篇
  2010年   75篇
  2009年   91篇
  2008年   122篇
  2007年   100篇
  2006年   97篇
  2005年   106篇
  2004年   113篇
  2003年   91篇
  2002年   82篇
  2001年   91篇
  2000年   81篇
  1999年   81篇
  1998年   53篇
  1997年   56篇
  1996年   42篇
  1995年   47篇
  1994年   24篇
  1993年   27篇
  1992年   64篇
  1991年   67篇
  1990年   60篇
  1989年   74篇
  1988年   56篇
  1987年   45篇
  1986年   59篇
  1985年   67篇
  1984年   47篇
  1983年   44篇
  1982年   34篇
  1981年   18篇
  1980年   25篇
  1979年   34篇
  1978年   28篇
  1976年   18篇
  1975年   28篇
  1973年   24篇
  1972年   17篇
  1971年   17篇
  1969年   21篇
排序方式: 共有2997条查询结果,搜索用时 15 毫秒
21.
22.
A case of arterial dissection of the right coronary artery secondary to angioplasty guidewire manipulation is presented. No balloon inflation was performed. The histologic appearance of the involved arterial segment was similar to that found in the left anterior descending coronary artery, which had undergone successful balloon dilatation. Both arteries demonstrated medial disruption and fibrointimal proliferation. The pathologic features of angioplasty-induced vascular injury may occur with or without balloon inflation.  相似文献   
23.
We investigated whether the severity of septic shock is determined by virulence factors associated with or the levels of endotoxemia produced by two Escherichia coli strains. Canines were challenged intraperitoneally with an E. coli strain (O6:H1:K2) that has virulence factors associated with human disease or with an equal dose of a nonvirulent strain (O86:H8) that lacks these factors. Both strains were administered in viable, heat-killed, and purified endotoxin forms. Median survival times with the virulent strain compared with the nonvirulent strain were shorter with viable bacteria (5 x 10(10) CFU/kg) (144 h versus > 672 h; Wilcoxon, P = 0.03), longer with heat-killed bacteria (5 x 10(9) CFU/kg) ( > 676 h versus 26 h; P = 0.03), and similar with purified endotoxin (15 mg/kg) (28 h versus 48 h; P = 0.71). However, whether the challenge contained viable bacteria, heat-killed bacteria, or purified endotoxin, the virulent strain produced less endotoxemia (P = 0.001). Hence, the changing outcomes with differing forms of the two strains cannot be attributed solely to endotoxin levels. The viable virulent strain caused less endotoxemia but more harm, and this does not appear to be explained by a more potent endotoxin or other heat-stable component. This study suggests that circulating endotoxin levels per se are less important in the outcome of septic shock than virulence factors associated with E. coli strains. Furthermore, the data call into question the significance of the endotoxin concentration in the blood in predicting the severity of shock and the lethality of gram-negative infections.  相似文献   
24.
Eight cesarean-derived goat kids were inoculated with caprine arthritis-encephalitis virus (CAEV), and proliferative responses of their peripheral blood mononuclear cells to mitogens and CAEV antigen were monitored for 9 months. Antibody specific for CAEV was measured by an enzyme-linked immunosorbent assay. Five cesarean-derived noninfected goats were tested simultaneously. Significant differences between the infected and control mononuclear cell proliferation reactions to CAEV began 14 days post-inoculation and continued in a fluctuant manner until 134 days post-inoculation. The magnitude of the proliferative reaction steadily increased in infected goats until the end of the experiment at 271 days post-inoculation. Responses to mitogens were not significantly different between infected and control goats. Virus-inoculated goats produced CAEV-specific antibody that reached a maximum level between 49 and 77 days post-inoculation and then declined to lower levels through 271 days post-inoculation. The virus-inoculated goats developed mild but characteristic clinical evidence of caprine arthritis-encephalitis, and CAEV was reisolated from four goats at 286 days post-inoculation. The five control goats developed neither an anti-CAEV immune response nor clinical disease, and CAEV could not be reisolated from them.  相似文献   
25.
A sample of 1150 unemployed 17 year-olds, containing blacks and whites, males and females, was obtained from 11 urban regions in England. Social support was measured in respect of five different forms of help from others. Measures were also obtained of psychological distress, perceived pressure from others to obtain a job, employment commitment, contact with other young people, and contact with other unemployed young people. Two forms of social support (having someone to turn to for help with money, and having someone to suggest interesting things to do) were significantly associated with measures of distress, as were perceived pressure to obtain a job and employment commitment, but not contact with other unemployed young people. The association between distress and having someone to turn to for help with money was greater for those perceiving pressure from others to obtain a job than those not perceiving pressure. Also, the association between distress and having someone to turn to when feeling low was greater for those with a high employment commitment than for those with a low one. Other associations between support and distress were found to be affected by sex and ethnic differences in the sample. The results are discussed in the light of a stress-buffering model of social support; and the need to disaggregate social support into its component parts is emphasized.  相似文献   
26.
Administration of supraphysiological doses of testosterone to normal men causes inhibition of spermatogenesis, but while most become azoospermic, 30-55% maintain a low rate of spermatogenesis. We have investigated whether there are differences in endogenous androgen production, of testicular and adrenal origin, which may be related to the degree of suppression of spermatogenesis. Thirty-three healthy Caucasian men were given weekly i.m. injections of 200 mg testosterone oenanthate (TE), 18 became azoospermic, while 15 remained oligozoospermic. Urinary excretion of epitestosterone, a specific testicular product, was reduced to <10% of pretreatment values, with no differences between the groups. Similar results were obtained for other markers of testicular steroidogenesis. Urinary and plasma adrenal androgens were also reduced during TE treatment: a statistically significant decrease in both (P < 0.001 and P < 0.05 respectively) was seen in the azoospermic but not oligozoospermic responders. These results suggest that testicular steroidogenesis is decreased to <10% by the administration of supraphysiological doses of exogenous testosterone. Differences in the degree of ongoing steroidogenesis in the testis do not appear to account for incomplete suppression of spermatogenesis, thus differences in androgen metabolism may underlie this heterogeneous response. A small but significant reduction in secretion of adrenal androgens was also detectable, the relevance of which is unclear.   相似文献   
27.
Neoplasms of histiocytes and dendritic cells are rare, and their phenotypic and biological definition is incomplete. Seeking to identify antigens detectable in paraffin-embedded sections that might allow a more complete, rational immunophenotypic classification of histiocytic/dendritic cell neoplasms, the International Lymphoma Study Group (ILSG) stained 61 tumours of suspected histiocytic/dendritic cell type with a panel of 15 antibodies including those reactive with histiocytes (CD68, lysozyme (LYS)), Langerhans cells (CD1a), follicular dendritic cells (FDC: CD21, CD35) and S100 protein. This analysis revealed that 57 cases (93%) fit into four major immunophenotypic groups (one histiocytic and three dendritic cell types) utilizing six markers: CD68, LYS, CD1a, S100, CD21, and CD35. The four (7%) unclassified cases were further classifiable into the above four groups using additional morphological and ultrastructural features. The four groups then included: (i) histiocytic sarcoma (n=18) with the following phenotype: CD68 (100%), LYS (94%), CD1a (0%), S100 (33%), CD21/35 (0%). The median age was 46 years. Presentation was predominantly extranodal (72%) with high mortality (58% dead of disease (DOD)). Three had systemic involvement consistent with 'malignant histiocytosis'; (ii) Langerhans cell tumour (LCT) (n=26) which expressed: CD68 (96%), LYS (42%), CD1a (100%), S100 (100%), CD21/35 (0%). There were two morphological variants: cytologically typical (n=17) designated LCT; and cytologically malignant (n=9) designated Langerhans cell sarcoma (LCS). The LCS were often not easily recognized morphologically as LC-derived, but were diagnosed based on CD1a staining. LCT and LCS differed in median age (33 versus 41 years), male:female ratio (3.7:1 versus 1:2), and death rate (31% versus 50% DOD). Four LCT patients had systemic involvement typical of Letterer-Siwe disease; (iii) follicular dendritic cell tumour/sarcoma (FDCT) (n=13) which expressed: CD68 (54%), LYS (8%), CD1a (0%), S100 (16%), FDC markers CD21/35 (100%), EMA (40%). These patients were adults (median age 65 years) with predominantly localized nodal disease (75%) and low mortality (9% DOD); (iv) interdigitating dendritic cell tumour/sarcoma (IDCT) (n=4) which expressed: CD68 (50%), LYS (25%), CD1a (0%), S100 (100%), CD21/35 (0%). The patients were adults (median 71 years) with localized nodal disease (75%) without mortality (0% DOD). In conclusion, definitive immunophenotypic classification of histiocytic and accessory cell neoplasms into four categories was possible in 93% of the cases using six antigens detected in paraffin-embedded sections. Exceptional cases (7%) were resolvable when added morphological and ultrastructural features were considered. We propose a classification combining immunophenotype and morphology with five categories, including Langerhans cell sarcoma. This simplified scheme is practical for everyday diagnostic use and should provide a framework for additional investigation of these unusual neoplasms.  相似文献   
28.
A locus for autosomal dominant anterior polar cataract on chromosome 17p   总被引:6,自引:3,他引:6  
Inherited cataract is a clinically and genetically heterogeneous disease. Here we report the identification of a new locus for an autosomal dominant anterior polar cataract on the short arm of chromosome 17. To map this new locus we performed genetic linkage analysis with microsatellite markers in a four-generation pedigree. After exclusion of seven candidate loci for cataract, we obtained significant positive LOD scores for markers D17S849 (Z = 4.01 / theta = 0.05) and D17S796 (Z = 4.17 / theta = 0.05). Multipoint analysis gave a maximum LOD score of 5.2 (theta max = 0.06) between these two markers. From haplotype analysis, the cataract locus lies in the 13 cM interval between markers D17S849 and D17S796. This study provides the first genetic mapping of an autosomal dominant anterior polar cataract.   相似文献   
29.
We prospectively studied the ability of acrosome reaction (AR)inducibility to predict fertilization success in a group of232 infertile patients presenting sequentially for in-vitrofertilization (IVF). The median percentage of eggs fertilizedfor the overall patient population was 25% (interquartile range5–58%), with one to 29 oocytes available for insemination(median, five oocytes). The median percentage of eggs fertilizedat IVF increased as the percentage of spermatozoa able to undergoAR became greater: spermatozoa with a failed AR (5%) fertilizedonly 12% of eggs, while spermatozoa with AR values>9% fertilized50% of eggs. The assay had a specificity of 0.75, a sensitivityof 0.55 and an odds ratio of 2.9; thus, AR-positive patientsare 2.9 times more likely to achieve fertilization than patientswith a failed AR. Receiver operator characteristic (ROC) curveswere constructed for AR, sperm concentration and percentageof normal forms in semen. All three parameters proved to bepotentially useful in predicting the occurrence of fertilization,although AR and morphology appeared to be better than spermconcentration by ROC analysis. Patients were divided into fourclearly defined subgroups according to their traditional semencharacteristics, including morphology. The median percentageof eggs fertilized decreased as traditional semen characteristicsdeteriorated, from a median of 46% for patients with excellentsperm concentration, motility and morphology, to a median of29% for patients with suboptimal semen quality and a medianof 0% for patients with severely impaired semen. Within eachpatient subgroup, the median percentage of eggs fertilized was3-to 4-fold higher for individuals with a positive AR than forthose with a failed AR, indicating that AR has a greater effecton fertilization rate than traditional semen parameters includingmorphology. We now recognize that some men with good semen characteristicshave an unexpectedly poor AR and a markedly reduced fertilizationrate, while other men with poor traditional semen characteristicsunexpectedly retain AR and perform relatively well at IVF. Bycontrast to AR, morphology seemed to have little effect on fertilizationsuccess (two-way analysis of variance not significant). Thewife's age and oocyte quality were evenly distributed amongthe different patient subgroups, indicating that differencesin fertilization rate could not be attributed to either parameter.Our data indicate that AR has a much higher predictive valuefor IVF success than traditional semen parameters includingmorphology. We propose that AR assessment is a clinically usefuldiagnostic tool in determining a patient's likelihood of achievingfertilization at IVF.  相似文献   
30.
K L Banks  T C McGuire 《Immunology》1975,28(3):581-588
Surface receptors on peripheral blood neutrophils and monocytes from normal and immunodeficient horses have been studied. Sheep erythrocytes (SRBC) coated with IgG, IgM, and complement but not IgG(T), readily bound to normal equine monocytes and neutrophils. More than 4000 molecules of IgG were required to sensitize each SRBC for adherence to monocytes, and more than 12,000 molecules were required for adherence to neutrophils. Young horses with a severe combined immunodeficiency had an almost total absence of lymphocytes, but normal numbers of monocytes and neutrophils. The number of receptors for immunoglobulin, complement, and phytolectin on monocytes and neutrophils from immunodeficient animals were similar to those on the cells of normal horses. Although the precursor cells of lymphocytes of horses with combined immunodeficiency appear to be defective, no defect in the other cellular products of the bone marrow were apparent.  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