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   11259篇
  免费   735篇
  国内免费   48篇
耳鼻咽喉   140篇
儿科学   303篇
妇产科学   227篇
基础医学   1564篇
口腔科学   1268篇
临床医学   734篇
内科学   2180篇
皮肤病学   273篇
神经病学   634篇
特种医学   421篇
外科学   1249篇
综合类   187篇
一般理论   3篇
预防医学   1110篇
眼科学   311篇
药学   796篇
中国医学   166篇
肿瘤学   476篇
  2023年   98篇
  2022年   224篇
  2021年   467篇
  2020年   295篇
  2019年   382篇
  2018年   468篇
  2017年   286篇
  2016年   356篇
  2015年   440篇
  2014年   561篇
  2013年   634篇
  2012年   948篇
  2011年   953篇
  2010年   521篇
  2009年   444篇
  2008年   619篇
  2007年   612篇
  2006年   538篇
  2005年   427篇
  2004年   432篇
  2003年   319篇
  2002年   242篇
  2001年   176篇
  2000年   151篇
  1999年   163篇
  1998年   122篇
  1997年   105篇
  1996年   89篇
  1995年   61篇
  1994年   46篇
  1993年   42篇
  1992年   51篇
  1991年   57篇
  1990年   58篇
  1989年   71篇
  1988年   71篇
  1987年   70篇
  1986年   56篇
  1985年   47篇
  1984年   32篇
  1983年   29篇
  1982年   22篇
  1981年   24篇
  1980年   23篇
  1977年   14篇
  1976年   18篇
  1975年   21篇
  1974年   14篇
  1973年   18篇
  1969年   14篇
排序方式: 共有10000条查询结果,搜索用时 171 毫秒
991.
992.
993.
BACKGROUND: The Knops blood group system consists of antigens encoded by exon 29 of complement receptor 1 (CR1) gene. To better elucidate the complexity of Knops group system, the frequency of six single-nucleotide polymorphisms (SNPs) in three Brazilian populations is determined. STUDY DESIGN AND METHODS: A total of 118 individuals descendant from Europe, Asia, and Africa were studied. The genomic fragment of CR1 was amplified by polymerase chain reaction, and the SNPs and haplotypes were determined after DNA sequence analysis. RESULTS: Among the six polymorphisms characterized, one of them was described for the first time. The analysis of allele frequency showed that these six SNPs did not differ between the European and Asian groups. The African group presented a higher frequency of alleles McC(b), Sl2, and KAM+. The six polymorphisms gave origin to 12 haplotypes that were defined for the first time. The haplotypes 1 (4646A, Kn(a), McC(a), Sl1, Sl4, KAM+), 2 (4646A, Kn(a), McC(a), Sl1, KAM-), and 3 (4646A, Kn(a), McC(a), Sl2, Sl4, KAM-) are the most frequent in all populations. The H2 presents similar frequency in all populations; however, whereas the H1 presented a higher prevalence in the European and Asian groups, in the African group H3 was present in a higher prevalence. CONCLUSIONS: In this study, a new SNP substituting serine for asparagine at amino acid 1540 was identified. Moreover 12 haplotypes were identified. The differences in haplotype frequencies strongly suggest that the H1 and H2 might be the ancestral one while the H3 may have originated in Africa and may have fixed there by positive selection.  相似文献   
994.
Spouses of combat veterans with PTSD have greater psychological and marital distress than spouses of veterans without PTSD; however, few studies have examined how variables related to the spouses (e.g., cognitions) may play a role in their own distress. The current study examined spouses’ perceptions of combat veterans’ PTSD symptom severity in 465 spouses of veterans from the National Vietnam Veterans Readjustment Study. Spouses’ perceptions of veterans’ symptom severity were positively associated with spouses’ psychological and marital distress; furthermore, spouses’ perceptions fully mediated the effects of veterans’ self-reported PTSD severity on spouses’ distress. Additionally, for spouses who provided complete data with regard to their perceptions of veterans’ PTSD, distress was highest when they perceived high levels of symptoms but veterans reported low levels. These results highlight the importance of interpersonal perceptions in intimate relationships and provide preliminary groundwork for future research on cognitions in spouses of combat veterans with PTSD.  相似文献   
995.
Bone strength is the result of its material composition and structural design, particularly bone mass distribution. The purpose of this study was to analyze femoral neck bone mass distribution by Ward's area location and its relationship with physical activity (PA) and body composition in children 8 and 9 years of age. The proximal femur shape was defined by geometric morphometric analysis in 88 participants (48 boys and 40 girls). Using dual‐energy X‐ray absorptiometry (DXA) images, 18 landmarks were digitized to define the proximal femur shape and to identify Ward's area position. Body weight, lean and fat mass, and bone mineral were assessed by DXA, PA by accelerometry, and bone age by the Tanner‐Whitehouse III method. Warps analysis with Thin‐Plate Spline software showed that the first axis explained 63% of proximal femur shape variation in boys and 58% in girls. Most of this variation was associated with differences in Ward's area location, from the central zone to the superior aspect of the femoral neck in both genders. Regression analysis demonstrated that body composition explained 4% to 7% of the proximal femur shape variation in girls. In boys, body composition variables explained a similar amount of variance, but moderate plus vigorous PA (MVPA) also accounted for 6% of proximal femur shape variation. In conclusion, proximal femur shape variation in children ages 8 and 9 was due mainly to differences in Ward's area position determined, in part, by body composition in both genders and by MVPA in boys. These variables were positively associated with a central Ward's area and thus with a more balanced femoral neck bone mass distribution. © 2010 American Society for Bone and Mineral Research.  相似文献   
996.
The purpose of this study was to assess the results of therapy with mycophenolate mofetil (MMF) in children with idiopathic nephrotic syndrome (INS) who were both steroid- and cyclophosphamide-resistant. Treatment lasted a minimum of 6 months, and follow-up data were collected over a 2-year period. The children were divided into two groups: Group 1 (n?=?34) comprised patients who had received cyclosporine A (CsA) before the initiation of MMF therapy; Group 2 (n?=?18) comprised patients who received only MMF. Among the 34 patients of Group 1, complete and partial remission were achieved in seven (20.6%) and 13 patients (38.6%), respectively; there was no response in 14 patients (41.2%). Among the 18 patients in Group 2, complete and partial remission occurred in five (27.8%) and six (33.3%) patients, respectively; there was no response in seven patients (38.9%). Eight patients developed chronic kidney disease. The main side-effects were gastrointestinal complaints (n?=?11, 21%), recurring severe infections (n?=?1, 1.9%), and mild thrombocytopenia/leucopenia (n?=?1, 1.9%). MMF proved to be therapeutically effective in 59.5% of the cases. These beneficial effects need to be confirmed in studies with a long-term follow-up after discontinuation of the treatment. Our statistical analysis of the results of therapy with MMF did not reveal any significant difference between its use alone or following CsA administration.  相似文献   
997.
998.
999.

Background

Kidney transplantation is widely recognized as the best treatment in patients who require renal replacement therapy. Although considered a clinical and surgical triumph, it is also a source of frustration because of lack of donor organs and the growth of waiting lists. Strategies need to be developed to increase the supply of organs. One measure is use of expanded criteria for donation.

Objective

To evaluate the effect of donor age on cadaver graft survival.

Materials and Methods

We reviewed the medical records for 454 patients who underwent kidney transplantation with cadaver donors from April 1987 to December 2003.

Results

Donor age had a significant effect on kidney transplant survival. Survival of grafts from donors aged 16 to 40 years (mean, 143.30 months) was significantly greater compared with that of grafts from donors older than 40 years (66.46 months) (P = .005). The HLA matching and cold ischemia time did not significantly affect transplant survival (P = .98 and P = .16, respectively).

Conclusions

Kidneys from cadaver donors older than 40 years significantly compromised graft survival, generating a negative effect via early return of recipients to waiting lists and increasing the rate of repeat transplantation, risk of death, and unnecessary costs.  相似文献   
1000.
Epidemiological analyses of injury patterns and mechanisms help to identify the expertise military surgeons need in a combat setting and accordingly help to adjust infrastructure and training requirements. Therefore, a MEDLINE search (1949–2009), World Wide Web search (keywords “combat, casualties, war, military, wounded and neurosurgery”) and an analysis of deaths among allied war casualties in Afghanistan and Iraq were performed. Up to 10th December 2009 there had been 4,688 allied military deaths in Iraq and 1,538 in Afghanistan. Of these 22% died in non-hostile action, 33% in direct combat situations and the majority of 45% in indirect combat actions. The leading causes of injury were explosive devices (70%) and gunshot wounds. Chest or abdominal injuries (40%) and traumatic brain injuries (35%) were the main causes of death for soldiers killed in action. The case fatality rate in Iraq is approximately half that of the Vietnam War, whereas the killed-in-action rate in Afghanistan (18.7%) is similar to the Vietnam War (20%); however, the amputation rate is twice as high in modern conflicts. Approximately 8–15% of the fatal injuries seem to be potentially survivable. Military surgeons must have an excellent expertise in a wide variety of surgical specialties. Life saving emergency care, especially in the fields of thoracic, visceral and vascular surgery as well as practical skills in the fields of neurosurgery and oral and maxillofacial surgery are required. Additionally, it is of vital importance to ensure the availability of sufficient tactical and strategic medical evacuation capabilities for the wounded.  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