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   13466篇
  免费   1023篇
  国内免费   58篇
耳鼻咽喉   202篇
儿科学   378篇
妇产科学   249篇
基础医学   1883篇
口腔科学   1222篇
临床医学   1161篇
内科学   2982篇
皮肤病学   357篇
神经病学   916篇
特种医学   521篇
外国民族医学   1篇
外科学   1569篇
综合类   101篇
一般理论   6篇
预防医学   1324篇
眼科学   203篇
药学   882篇
中国医学   87篇
肿瘤学   503篇
  2023年   111篇
  2022年   290篇
  2021年   462篇
  2020年   322篇
  2019年   436篇
  2018年   515篇
  2017年   384篇
  2016年   417篇
  2015年   430篇
  2014年   588篇
  2013年   736篇
  2012年   994篇
  2011年   1053篇
  2010年   646篇
  2009年   521篇
  2008年   714篇
  2007年   768篇
  2006年   605篇
  2005年   582篇
  2004年   474篇
  2003年   397篇
  2002年   374篇
  2001年   296篇
  2000年   285篇
  1999年   213篇
  1998年   135篇
  1997年   117篇
  1996年   114篇
  1995年   103篇
  1994年   76篇
  1993年   78篇
  1992年   104篇
  1991年   103篇
  1990年   108篇
  1989年   75篇
  1988年   87篇
  1987年   94篇
  1986年   75篇
  1985年   64篇
  1984年   69篇
  1983年   59篇
  1982年   39篇
  1981年   34篇
  1980年   29篇
  1979年   34篇
  1978年   30篇
  1977年   29篇
  1976年   26篇
  1967年   25篇
  1966年   23篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
Biochemical markers of nutritional status (albumin, transthyretin, insulin-like growth factor-I and zinc) were measured in slowly growing two- to five-year-old, low-income Parisian children whose weight-for-height or height-for-age z scores (WHZ or HAZ) were between — 1 and — 2 SD of the NCHS median. The results were compared to controls who were matched for age, sex, and ethnic origin with WHZ and HAZ between — 1 and + 2 SD. Mean serum levels of transthyretin, albumin and insulin-like growth factor-I and mean plasma zinc concentrations were significantly lower in the growth-impaired children than in the controls ( p = 0.002, p = 0.006, p = 0.015, and p = 0.035, respectively). While the height-retarded children had low mean serum insulin-like growth factor-I values, the weight-retarded subjects had decreased levels of albumin, transthyretin and zinc when compared to controls. Lower mean levels of nutritional markers in healthy, slowly growing children suggest that inadequate dietary intakes of zinc, protein and/or energy may result in marginal delays in weight and height gains.  相似文献   
62.
Evidence for superantigenic activity during murine malaria infection   总被引:2,自引:0,他引:2  
TCR V beta usage was examined in C57BL/6 mice infected with Plasmodium yoelii. In addition to a polyclonal T cell activation, already described, a superantigenic-like activity was observed during the acute infection. This superantigenic activity induces a preferential deletion without prior expansion of CD4+ and CD8+ T cells bearing the TCR V beta 9 segment. The superantigen could be released by the parasite at different stages of its development since the deletion of V beta 9+ T cells was observed in blood and lymph nodes of mice infected either with sporozoites or with erythrocytic stages. Injection of sporozoite or parasitized erythrocytes to newborn mice led to a deletion and anergy of peripheral V beta 9+ T cells, without affecting thymic T cell populations. These observations suggest that the superantigen is released at very low concentrations during parasite development. The role of such parasite superantigenic activity in infectivity can be underlined by the observation that congenic BALB.D2 Mis1a mice lacking V beta 9 T cells are more susceptible to infection by P. yoelii.   相似文献   
63.
If 24-hour esophageal pH monitoring is to be a useful diagnostic tool, it must reliably discriminate gastroesophageal reflux patients despite daily variations in distal esophageal acid exposure. To address this issue, we studied 53 subjects (14 healthy normals, 14 esophagitis patients, and 25 patients with atypical symptoms) with two ambulatory pH tests performed within 10 days of each other. Intrasubject reproducibility of 12 pH parameters to discriminate the presence of abnormal acid reflux was determined. As a group, the parameters of percent time with pH<4 (total, upright, recumbent) were most reproducible (80%). Therefore, a subject was defined as having gastroesophageal reflux disease if at least one of these three values were abnormal. Intrasubject reproducibility for the diagnosis of reflux disease was 89% for the entire sample. Among subsets, the reproducibility was 93% for the normals and esophagitis patients and 84% for the atypical symptom patients. Total percent time with pH<4 was the single most discriminate pH parameter (85%) and nearly equaled that of the three combined parameters (89%). The intrasubject variability of this parameter was determined by the mean ±2sd of the relative differences between the two test results for all 53 subjects. Total percent time with pH<4 may vary between tests by a factor of 3.2-fold or less (218% higher to 69% lower). We conclude: (1) ambulatory 24-hr esophageal monitoring is a reproducible test for the diagnosis of gastroesophageal reflux disease; and (2) the large intrastudy variability in 24-hr total acid exposure may limit this test's usefulness as a measurement of therapeutic improvement.Supported, in part, by Public Health Services Grant AM 34200-01A1 from NIADDIK.  相似文献   
64.
A group of destructive changes occurring in jaws in patients with maxillary complete dentures and mandibular removable partial dentures (bilaterally) has been described in the literature as the combination syndrome. However, this condition is not clinically observed in all patients. The aim of this study was to establish the prevalence index on signs of combination syndrome and to verify whether these changes also occurred in patients rehabilitated with a mandibular removable partial denture (unilaterally). Sample was composed of 44 patients, completely edentulous in the maxilla. Thirty-two patients had a Kennedy Class I removable partial denture and 12 a Kennedy Class II. Three major alterations were observed in 20.5% of the studied population. Nevertheless, these changes were present only in 25% of patients with Kennedy Class I removable partial denture. Based on the findings of this study, it can be concluded that patients with Kennedy Class II removable partial denture do not have similar signs that lead to the combination syndrome’s condition.  相似文献   
65.
Because of its numerous etiologies, foot dermatitis can be difficult to diagnose despite of thorough history and physical examination. The differential diagnoses are challenging and include allergic contact dermatitis, dyshidrosis, juvenile plantar dermatosis, atopic dermatitis, lichen planus.
Methods:  In the Cutaneous Allergology Unit of the Department of Dermatovenereology of Pedro Hispano Hospital, between 1999 and 2003, 804 patients were observed with suspicion of contact dermatitis. In 9,3% there was a history of recurrent foot dermatitis. All these patients were patch tested with GPEDC standard and shoe series and shoe fragments.
Results:  Twenty‐five patients revealed shoe contact dermatitis with positive reactions to the series tested, with an average age of 40 years. The dermatitis involved the dorsal aspect of the foot in 20 patients and the volar aspect in 8, the lateral aspects in 4, typically sparing the instep and flexural creases of the toes. The most common allergen were para‐tertiary‐butylphenol formaldehyde resin – PTBFR (12 patients‐48%), mercapto mix (7 patients‐28%), potassium dichromate (24%), mercaptobenzothiazole (24%).
Conclusions:  The most common causes of shoe contact dermatitis were glues, followed by rubber components and chromated leather. As in other studies the most common allergen in shoe dermatitis in Portugal is PTBFR in neoprene adhesives. Rubber components (accelerators) were the second more frequent allergen in this study, probably a direct result of improved fixation of chrome and a change in footwear style and chrome sensitivity explains leather allergy. Other causes of foot contact dermatitis are iatrogenic complication, clothing (socks), cosmetics, adhesive tape and professional etiology.  相似文献   
66.
In a prospective, randomized study of insemination with donor semen, intracervical insemination by straw was compared with insemination using a cervical cap with an intracervical reservoir. A total of 91 patients completed 486 treatment cycles. There were no significant differences in age, parity, indication for insemination by donor, or method of cycle monitoring between women who became pregnant and those who did not conceive with either insemination method. In 236 standard intracervical insemination cycles, 14 patients became pregnant (5.9% per cycle), whereas 38 patients conceived in 250 cervical cap cycles (15.2% per cycle). Both the crude pregnancy rates and the cumulative pregnancy rates calculated by the Kaplan-Meier life-table method were significantly different (chi(2)-test, P < 0.001, and log-rank test, P < 0.005 respectively). Pregnancy rates in artificial insemination with cryopreserved donor semen may be improved by the use of a cervical cap when compared to cervical insemination by straw. The use of the cervical cap may prolong the exposure of the spermatozoa to the cervical mucus and prevent the backflow of semen into the vagina.   相似文献   
67.
Kaplan  PA; Reiskin  AB; Tu  HK 《Radiology》1987,163(1):217-220
Arthrograms of the temporomandibular joint were obtained in 20 symptomatic joints that had previous reconstructive arthroplasty with disk repositioning because of internal derangements. Preoperative arthrograms were available for comparison in 18 joints. Symptoms resulting in a postoperative arthrogram included pain, limited ability to open the mouth, and clicking of the joints. Postoperative arthrographic findings included limited anterior translation of the condyle (90%), irregularity in outline of the intraarticular contrast agent (60%), a conical configuration of the posterior recess (25%), decreased size of the joint (28%), anterior displacement of the meniscus (25%), and perforated meniscus (15%). Many of these findings may have resulted from fibrosis and scarring, which may be a response to intraarticular bleeding. The mechanism by which the fibrosis causes the postsurgical arthrographic features is discussed.  相似文献   
68.
Protoplasts of the pathogenic plant fungus, Crinipellis perniciosa, were transformed to hygromycin B resistance using the pAN7-1 plasmid, which contains the Escherichia coli hph gene under the control of Aspergillus nidulans regulatory sequences. The pAN7-1 plasmid was introduced by PEG/CaCl(2) treatment. Transformation frequencies of 1.6-2.5 transformants/microg of DNA were achieved. About 54% of the transformants were abortive and 40 analyzed transformants were mitotically stable and showed different hygromycin B resistance levels. The presence of the hph gene was checked by PCR in five transformants and the integration of multiple plasmid copies into different genome sites was observed by Southern analysis. This is the first report of a C. perniciosa transformation system and represents an important step for further research into genetic manipulation of this fungal plant pathogen.  相似文献   
69.
Much is known about specific antibodies and their titers in patients with tuberculosis. However, little is known about the avidity of these antibodies or whether changes in avidity occur during the progression of the disease or during treatment. The aims of this study were to determine the avidity of antibodies to Mycobacterium tuberculosis in patients with pulmonary tuberculosis, to explore the value of avidity determination for the diagnosis of tuberculosis, and to study changes in levels of antibodies and their avidity during treatment. Antibody avidity was measured by an enzyme-linked immunosorbent assay with thiocyanate elution. Avidity indices and serum levels of immunoglobulin G to M. tuberculosis were determined for 22 patients with pulmonary tuberculosis before and during treatment and for 24 patients with other pulmonary diseases. Antibody levels and avidity were both significantly higher in untreated tuberculosis patients than in the controls. Avidity determination had more diagnostic potential than determination of the antibody levels. Tuberculosis patients with a long duration of symptoms had higher antibody avidity than those with a recent onset of symptoms, indicating affinity maturation of specific antibodies during active disease. In the early phase of treatment, a decrease in antibody avidity was observed for 73% of all tuberculosis patients, accompanied by an initial increase in antibody levels in 36% of these patients. These phenomena could be explained by an intense stimulation of the humoral response by antigens released from killed bacteria, reflecting early bactericidal activity of antituberculous drugs leading to the production of low-affinity antibodies against these released antigens.  相似文献   
70.
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