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   2622篇
  免费   128篇
  国内免费   4篇
耳鼻咽喉   22篇
儿科学   151篇
妇产科学   115篇
基础医学   316篇
口腔科学   99篇
临床医学   300篇
内科学   482篇
皮肤病学   35篇
神经病学   236篇
特种医学   37篇
外科学   216篇
综合类   8篇
预防医学   291篇
眼科学   49篇
药学   212篇
中国医学   3篇
肿瘤学   182篇
  2023年   12篇
  2022年   16篇
  2021年   30篇
  2020年   26篇
  2019年   46篇
  2018年   49篇
  2017年   33篇
  2016年   55篇
  2015年   67篇
  2014年   82篇
  2013年   131篇
  2012年   171篇
  2011年   169篇
  2010年   109篇
  2009年   102篇
  2008年   166篇
  2007年   198篇
  2006年   181篇
  2005年   169篇
  2004年   142篇
  2003年   157篇
  2002年   130篇
  2001年   24篇
  2000年   25篇
  1999年   34篇
  1998年   30篇
  1997年   30篇
  1996年   35篇
  1995年   27篇
  1994年   25篇
  1993年   25篇
  1992年   17篇
  1991年   23篇
  1990年   15篇
  1989年   18篇
  1988年   14篇
  1987年   13篇
  1986年   12篇
  1985年   9篇
  1984年   9篇
  1983年   11篇
  1982年   10篇
  1981年   16篇
  1980年   11篇
  1979年   11篇
  1978年   9篇
  1975年   7篇
  1974年   6篇
  1972年   6篇
  1967年   6篇
排序方式: 共有2754条查询结果,搜索用时 15 毫秒
81.
BACKGROUND: Alternatively activated macrophages expressing the CD163 and CD206 surface receptors are the dominant immune-cell type found in the placenta. The placental number and distribution of macrophages is altered in pre-eclampsia, and the generalised inflammatory reaction associated with pre-eclampsia might lead to shedding of soluble CD163 into the circulation. METHODS: Serum samples from 18 women with pre-eclampsia and 90 normal pregnancies were obtained from a longitudinal study of 955 pregnant women at Randers County Hospital, Denmark. sCD163 and Neopterin were measured by ELISA on samples collected in weeks 18, 28, 32, and 38 of pregnancy. RESULTS: sCD163 levels in pregnancy (2-3 mg/l) were similar to previously measured levels in non-pregnant women, and did not increase from week 18 to 38. There was a tendency towards higher sCD163 in week 38 in pre-eclamptic women compared to healthy women. Neopterin increased throughout pregnancy in both healthy (from median 5.4 to 6.7 nmol/l, p<0.0001) and pre-eclamptic women (from 5.0 to 8.0 nmol/l, p<0.0001), but there were no differences between groups at any time-point. sCD163 correlated to neopterin in both the control (r=0.25, p<0.0001) and in the pre-eclampsia group (r=0.32, p=0.011). C-reactive protein was higher in pre-eclampsia than in healthy pregnancies by week 38 (159 versus 91 nmol/l, p=0.0189). CONCLUSIONS: The macrophage serum-markers sCD163 and neopterin are not pre-symptomatic nor prognostic markers for pre-eclampsia.  相似文献   
82.
AIM: To compare self-reported emotional and behavioural problems among Greek and Finnish adolescents. METHODS: Youth Self-Report scores were analysed for 3373 Greek adolescents aged 18 years and 7039 Finnish adolescents aged 15-16 years from the general population in both countries. The impact of country, gender, place of residence, socioeconomic status (SES) and family stability on the scores was evaluated. RESULTS: Only country and gender yielded small to medium effect on the scores. Greek boys scored significantly higher than Finns on 10 of the 11 YSR syndromes, particularly on the anxious/depressed scale. Greek girls scored significantly lower than Finnish girls on the somatic complaints and delinquent behaviour scales. In general, girls scored higher than boys on both internalising and externalising problems. The gender by country interaction revealed that Finnish girls reported more externalising problems. CONCLUSION: The main differences marked in this comparison were the higher level of anxiety and depression in Greeks than Finns and the higher level of externalising problems in Finnish girls than boys. Cultural standards could play an important role in explaining these differences. Overall, it seems that only a small number of differences exist between a northern and southern European region.  相似文献   
83.
The obstructive sleep apnea-hypopnea syndrome occurs more frequently and with higher apnea-hypopnea indices in men than in women. To investigate the gender differences we extended our respiratory analyses during sleep to cover not only periodic obstruction (apnea and hypopnea) but also nonperiodic partial upper airway obstruction during sleep and their associations with increasing age or body mass index (BMI). The clinical sleep recordings with the static-charge-sensitive bed (SCSB) and oximeter were reviewed in 233 age and BMI-matched men-women pairs. Periodic obstruction increased with increasing BMI only in men. Nonperiodic partial obstruction increased with moderate to morbid obesity in women and men after the age of 65 years. Our findings suggest that while partial upper airway obstruction increases with increasing age and BMI in both genders, men have a gender specific BMI dependent predisposition for periodic obstruction (obstructive sleep apnea). The apnea-hypopnea index is likely to underestimate the impact of sleep-disordered breathing, particularly in elderly patients.  相似文献   
84.
Graphene and graphene oxide receive much attention these years, because they add attractive properties to a wide range of applications and products. Several studies have shown toxicological effects of other carbon‐based nanomaterials such as carbon black nanoparticles and carbon nanotubes in vitro and in vivo. Here, we report in‐depth physicochemical characterization of three commercial graphene materials, one graphene oxide (GO) and two reduced graphene oxides (rGO) and assess cytotoxicity and genotoxicity in the murine lung epithelial cell line FE1. The studied GO and rGO mainly consisted of 2–3 graphene layers with lateral sizes of 1–2 µm. GO had almost equimolar content of C, O, and H while the two rGO materials had lower contents of oxygen with C/O and C/H ratios of 8 and 12.8, respectively. All materials had low levels of endotoxin and low levels of inorganic impurities, which were mainly sulphur, manganese, and silicon. GO generated more ROS than the two rGO materials, but none of the graphene materials influenced cytotoxicity in terms of cell viability and cell proliferation after 24 hr. Furthermore, no genotoxicity was observed using the alkaline comet assay following 3 or 24 hr of exposure. We demonstrate that chemically pure, few‐layered GO and rGO with comparable lateral size (> 1 µm) do not induce significant cytotoxicity or genotoxicity in FE1 cells at relatively high doses (5–200 µg/ml). Environ. Mol. Mutagen. 57:469–482, 2016. © 2016 The Authors. Environmental and Molecular Mutagenesis Published by Wiley Periodicals, Inc.  相似文献   
85.
86.
Organ transplant recipients infected with parvovirus B19 frequently develop persistent viremia associated with chronic anemia and pure red cell aplasia. In this study, a male renal transplant recipient who had been infected with parvovirus B19/genotype 2 after renal transplantation at the age of 34 years is described. The patient was repeatedly treated with high dose intravenous immunoglobulin (IVIG) that resulted in the resolvement of symptoms but not in virus eradication. During an observation period of 33 months after transplantation three phases associated with high parvovirus B19 viremia were observed. Both the first and the second viremic phases were combined with severe anemia. Parvovirus B19 specific IgM-antibodies were initially detected at the beginning of the second phase in continually rising concentrations. Initially eradication of the virus by immunoglobulin therapy was reported after the first viremic phase [Liefeldt et al. (2002): Nephrol Dial Transplant 17:1840-1842]. Retrospectively this statement has to be corrected. It was based on the use of a qualitative PCR assay specific for parvovirus B19 genotype 1 associated with reduced sensitivity for detection of genotype 2. After sequence analysis of the viral DNA and adjustment of a real-time PCR assay (TaqMan) for quantitative detection of all three B19 virus genotypes analysis of consecutive serum samples allowed the demonstration of long lasting phases with reduced viral loads following IVIG-treatment. These results demonstrate that IVIG treatment of parvovirus B19-triggered anemia in transplant recipients offers an opportunity to resolve symptoms, but does not guarantee eradication of the virus. Since reactivation of parvovirus B19 infection can result in high virus load associated with the recurrence of symptoms repeated screening for viral DNA is recommended using the TaqMan system established for quantitative detection of all three genotypes of parvovirus B19.  相似文献   
87.
Histological investigations of a new hydroxyapatite-collagen composite material were carried out to evaluate its possible suitability as a bone substitute. The three-dimensional scaffolds made from biomimetically mineralized collagen exhibit an interconnecting pore structure and elastic mechanical properties. They were implanted into the subcutaneous tissue and bone defects made in the femur of rats and harvested with the surrounding tissue at 1, 2, 4, 8, and 12 weeks after surgery. The materials implanted in the subcutaneous tissue were covered by fibrous connective tissue with a slight inflammatory response, and many foreign-body giant cells were observed on the surface of the scaffolds. Most of the material implanted in the subcutaneous tissue was resorbed at 8 weeks by phagocytosis. In the bone defects, new bone formation was observed on the surface of the material at 1 week. New bone increased with time, and osteoclasts were seen on the surface of the scaffolds at 2 weeks. Resorption and replacement by new bone of many parts of the materials implanted in the femur were observed by 12 weeks. These responses occurred faster than those of other hydroxyapatite-collagen composites. The results suggested that the new biomimetically mineralized collagen scaffolds were suitable as an implant material for bone-tissue reconstruction.  相似文献   
88.

Background  

A small region of about 70 kb on human chromosome 19q13.3 encompasses 4 genes of which 3, ERCC1, ERCC2, and PPP1R13L (aka RAI) are related to DNA repair and cell survival, and one, CD3EAP, aka ASE1, may be related to cell proliferation. The whole region seems related to the cellular response to external damaging agents and markers in it are associated with risk of several cancers.  相似文献   
89.
Folding and assembly of MHC molecules in mammals occurs in the endoplasmic reticulum (ER), but has not been studied in teleosts. Calnexin (CNX) is an ER chaperone that associates with glycoproteins bearing a monoglucosylated N-linked oligosaccharide side chain. Here we report the first identification and characterization of a full-length CNX cDNA clone in a teleost, and the association of the CNX chaperone with MHC class II in a channel catfish T cell line. The 1.8 kb CNX clone encodes a protein of 607 amino acids that is 72% identical to the consensus sequence of mammalian CNXs. The association of CNX with class II is of particular interest because the native MHC class II alpha chain of Ictalurus punctatus does not bear any N-linked oligosaccharide consensus glycosylation sequences. Thus the assembly of class II molecules in the catfish probably proceeds via different steps than occurs in mammals.  相似文献   
90.
The aim of this study was to identify significant prognostic factors by using unrelated genomically HLA-A, -B and -DRB1-identical donors. Such data could help to choose the best donor. We studied 136 consecutive patients with hematologic malignancies and a median age of 32 years (range, 0-55 years) who received hematopoietic stem cell transplantation. Bone marrow grafts were given to 83 and peripheral blood stem cells to 53 patients. The cumulative incidence of grade II to IV acute graft-versus-host disease (GVHD) was 30% and of chronic GVHD was 54%. At 5 years, the overall transplant-related mortality (TRM) was 34%, and patient survival was 50%. In Cox multivariate analysis, 32 potential risk factors were analyzed. Monoclonal antibody OKT-3 during conditioning was correlated with grade II to IV acute GVHD, chronic GVHD, and TRM. HLA-DP mismatch was associated with poor TRM and poor survival. Cytomegalovirus-seropositive patients with a seronegative donor had a decreased leukemia-free survival. Five-year TRM was 14% with no risk factor, 38% with 1 risk factor, and 87% with 2 risk factors. The 5-year survival was 72%, 48%, and 30% with 0, 1, and 2 risk factors, respectively. We concluded that unrelated hematopoietic stem cell transplantation may be improved if an optimal donor and immunosuppression are chosen.  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