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   1139083篇
  免费   74547篇
  国内免费   1758篇
耳鼻咽喉   14802篇
儿科学   37415篇
妇产科学   28762篇
基础医学   181745篇
口腔科学   30563篇
临床医学   102579篇
内科学   215132篇
皮肤病学   25738篇
神经病学   79438篇
特种医学   42232篇
外国民族医学   126篇
外科学   169578篇
综合类   21625篇
现状与发展   3篇
一般理论   251篇
预防医学   83240篇
眼科学   26410篇
药学   86688篇
  4篇
中国医学   3244篇
肿瘤学   65813篇
  2021年   8655篇
  2018年   12563篇
  2017年   9481篇
  2016年   10734篇
  2015年   11991篇
  2014年   16221篇
  2013年   24321篇
  2012年   33555篇
  2011年   35984篇
  2010年   21031篇
  2009年   19475篇
  2008年   33173篇
  2007年   36021篇
  2006年   35941篇
  2005年   33939篇
  2004年   33050篇
  2003年   31639篇
  2002年   30702篇
  2001年   54898篇
  2000年   55789篇
  1999年   46150篇
  1998年   12256篇
  1997年   10364篇
  1996年   10649篇
  1995年   10032篇
  1994年   9172篇
  1992年   34738篇
  1991年   35355篇
  1990年   34689篇
  1989年   34324篇
  1988年   31288篇
  1987年   30664篇
  1986年   28908篇
  1985年   27372篇
  1984年   20213篇
  1983年   17184篇
  1982年   9365篇
  1979年   18807篇
  1978年   13255篇
  1977年   10941篇
  1976年   10947篇
  1975年   12544篇
  1974年   14483篇
  1973年   13941篇
  1972年   13012篇
  1971年   12311篇
  1970年   11765篇
  1969年   10881篇
  1968年   10123篇
  1967年   9024篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
161.
ABSTRACT

Introduction: Steroid hormones are responsible for specific changes in the endometrium during the menstrual cycle, when they are sequentially secreted and, because of this, in the early days sequential combined oral contraceptive regimens were utilized. The same basic concept has been utilized with multi-phasic regimens, in order to produce endometrial pictures mimicking the normal cycle.

Areas covered: The Endometrial effects of progestins and estrogens; combined monophasic high- (50 μg), medium- (30 μg), low- (20 μg), ultralow- (15 μg) estrogen content; sequential regimens; multiphasic combinations; treatment schedules.

Cervical effects of combined high-dose and sequential combinations, including evidence for an increase in malignant lesions.

Expert opinion: Overall, combined oral contraceptives (COCs) inhibit normal proliferative changes and the endometrium becomes thin, narrow, with widely spaced glands and pre-decidual changes in the stroma. During the first few cycles the progestin induces a coexistence of proliferative and secretory features; with time, the picture changes because the progestin induces a down-regulation of estrogen receptors, resulting in tortuous glands similar to those in the secretory phase, but characterized by a quiescent, atrophic glandular epithelium.

In the cervical epithelium, under the influence of high-dose COCs, endocervical glands became hypersecretory and in some instances, distinctive type of atypical polypoid endocervical hyperplasia is found.  相似文献   
162.
163.

Background

Inflammation and infections have been associated with prostate cancer progression. We assessed whether elevated serum cytokines or T. vaginalis seropositivity at the time of diagnosis was associated with higher grade or lethal prostate cancer.

Patients and Methods

Men with localized or metastatic prostate cancer were included in this study. Cytokine serum levels including interleukin (IL)-1α, IL-1β, IL-2, IL-6, IL-8, monocyte chemotactic protein 1 (CCL-2), tumor necrosis factor α, and growth-regulated oncogene α (CXCL-1) using a multiplex enzyme-linked immunosorbent assay and T. vaginalis serology were measured in blood samples at diagnosis.

Results

A total of 324 patients were identified at time of localized disease and 118 at time of metastatic disease. Of the 189 patients with localized disease and clinical follow-up data (median, 73 months), 28 developed lethal disease. There was no association between circulating cytokine levels above median concentrations nor T. vaginalis seropositivity and risk of intermediate- to high-risk or lethal prostate cancer.

Conclusion

Higher levels of serum cytokine levels and T. vaginalis seropositivity at diagnosis are not associated with high-grade or lethal prostate cancer and do not aid risk stratification of localized prostate cancer.  相似文献   
164.
165.

Background

Intramedullary nailing is considered a “gold standard” for treatment of tibial shaft fractures. However, some types of fractures are typically considered as “difficult for nailing”. This group includes the periarticular fractures, fractures of both bones at the same level, comminuted and segmental fractures of the tibia. Fixator-assisted nailing (FAN) is an effective method treatment of these types of fractures. The main requirements for the ideal reduction device are an ease of its installation and an ability of multiplanar fracture reduction. Fixator-assisted nailing (FAN) with the use of two perpendicular to each other monolateral tubular frames perfectly meets these requirements. In this study we present this new surgical technique and the analysis of first 30 cases.

Methods

A prospective analysis was conducted for 30 patients with “difficult for nailing” tibial fractures treated with fixator-assisted nailing in our institution between September 1st, 2017, and March 1st, 2018. The duration of surgery and its different stages, the time of fluoroscopy, difficulties encountered during surgery, were analyzed. Clinical and radiological methods were used to evaluated reduction quality.

Results

In all 30 cases the acceptable reduction was achieved. The mean duration of the surgical procedure was 73.7?±?3?min. The mean duration of fluoroscopy 85.9?±?4.8?s. In 7 cases we faced with technical difficulties, which were successfully addressed.

Conclusion

The described technique of FAN is an effective method for the treatment of “difficult for nailing” tibial fractures. Future multi-centered studies with a larger number of patients are needed to validate our results.  相似文献   
166.
Objective: To determine serotonin system abnormalities related to major depression or previous suicidal behavior.

Methods: [11C]WAY100635, [18F]altanserin and positron emission tomography were used to compare 5-HT1A and 5-HT2A binding in MDD patients divided into eight past suicide attempters (>4yrs prior to scanning) and eight lifetime non-attempters, and both groups were compared to eight healthy volunteers.

Results: The two receptor types differed in binding pattern across brain regions from each other, but there were no differences in binding between healthy volunteers and the two depressed groups or between depressed suicide attempters and non-attempters. No effects of depression severity or lifetime aggression were observed for either receptor.

Conclusion: Limitations of this study include small sample size and absence of high lethality suicide attempts in the depressed attempter group. No trait-like binding correlations with past suicide attempt or current depression were observed. Given the heterogeneity of nonfatal suicidal behavior, a larger sample study emphasizing higher lethality suicide attempts may find the serotonin biological phenotype seen in suicide decedents.  相似文献   

167.
168.
Chronic spontaneous urticaria (CSU) pathogenesis shows a complex and still unclear interplay between immunoglobulin (Ig)G- and IgE-mediated autoimmunity, leading to mast cell and basophil degranulation and wheal formation. The objective of this study was to evaluate at the same time IgE- and IgG-reactivity to well recognized and recently reported autoantigens in CSU patients, and to assess the effects of such reactivity on response to the anti-IgE monoclonal antibody omalizumab. Twenty CSU patients underwent omalizumab treatment. Urticaria activity score 7 (UAS7) was recorded at baseline and at different drug administration time-points for categorizing early-, late- or non-responders. At baseline, sera from the 20 patients and from 20 controls were tested for IgE and IgG autoantibodies to high- and low-affinity IgE receptors (FcεRI and FcεRII), tissue factor (TF) and thyroglobulin (TG) by immunoenzymatic methods. Antibody levels were compared with those of controls and analysed according to response. Eighteen patients were omalizumab responders (11 early and seven late), while two were non-responders. More than 50% of patients had contemporary IgE and IgG to at least to one of the four different autoantigens. Late responders showed higher levels of both anti-TF IgE and IgG than early responders (P = 0·011 and P = 0·035, respectively). Twenty-five per cent of patients had levels of anti-FcεRI IgE, exceeding the upper normal limit, suggesting that it could be a novel auto-allergen in CSU. In CSU, there is an autoimmune milieu characterized by the co-existence of IgE and IgG autoantibodies to the same antigen/allergen, particularly in late responders to omalizumab, possibly explaining the slower response.  相似文献   
169.
170.
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