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   2841篇
  免费   204篇
  国内免费   11篇
耳鼻咽喉   21篇
儿科学   104篇
妇产科学   112篇
基础医学   424篇
口腔科学   89篇
临床医学   347篇
内科学   552篇
皮肤病学   117篇
神经病学   227篇
特种医学   42篇
外科学   198篇
综合类   52篇
一般理论   4篇
预防医学   225篇
眼科学   72篇
药学   230篇
中国医学   50篇
肿瘤学   190篇
  2024年   8篇
  2023年   53篇
  2022年   169篇
  2021年   223篇
  2020年   164篇
  2019年   189篇
  2018年   188篇
  2017年   107篇
  2016年   140篇
  2015年   116篇
  2014年   157篇
  2013年   188篇
  2012年   249篇
  2011年   236篇
  2010年   118篇
  2009年   83篇
  2008年   116篇
  2007年   106篇
  2006年   89篇
  2005年   93篇
  2004年   61篇
  2003年   32篇
  2002年   33篇
  2001年   4篇
  1999年   6篇
  1998年   3篇
  1997年   4篇
  1996年   2篇
  1995年   4篇
  1994年   3篇
  1993年   5篇
  1992年   5篇
  1991年   4篇
  1990年   5篇
  1989年   5篇
  1988年   8篇
  1987年   13篇
  1986年   6篇
  1985年   12篇
  1984年   6篇
  1983年   3篇
  1982年   2篇
  1980年   4篇
  1979年   8篇
  1977年   3篇
  1976年   4篇
  1973年   3篇
  1972年   2篇
  1970年   3篇
  1936年   1篇
排序方式: 共有3056条查询结果,搜索用时 19 毫秒
121.
Objective: Helicobacter pylori is associated with many pregnancy adverse effects such as preeclampsia (PE). We performed this systematic review and meta-analysis study to assess the possible association between H. pylori infection and PE and this is the first meta-analysis to clarify this issue.

Methods: PubMed, ISI (Web of Science), SCOPUS, and Google Scholar databases were searched (up to April 2017) to identify the relevant studies. The Meta-analysis of Observational Studies in Epidemiology and Preferred Reporting Items for Systematic Reviews and Meta-Analyses Protocols guidelines were used to do this study. Pooled odds ratio (OR) and 95% confidence intervals (CI) were estimated using a random-effects meta-analysis model. Heterogeneity was assessed with the χ2-based Q-test and I2 statistic.

Results: A total of eight studies including 889 participants (460 preeclamptic women and 429 controls) met the eligibility criteria. A positive association was found between H. pylori infection and PE (OR: 3.35; 95% CI: 2.21–5.10). Heterogeneity was acceptable (χ2?=?13.39; I2?=?47.7, 95% CI: 0–77). In subgroup analysis, cytotoxin-associated antigen A seropositivity was a substantial risk factor for PE when immunoblotting methods (OR: 11.12; 95% CI: 5.34–23.16; χ2?=?6.42; I2?=?53.3, 95% CI: 0–85) were used, whereas it was not potential risk factor for PE when ELISA was used as a detecting method (OR: 1.11; 95% CI: 0.6–2.06; χ2?=?1.83; I2?=?0, 95% CI: 0–90).

Conclusions: This study indicated that women with H. pylori infection, especially those infected with Cag A positive strains are more likely to have PE compared with the uninfected women.  相似文献   
122.

Objectives

Gynaecological cancer is common. It is highly amenable to effective treatment, but thrombosis remains a common complication. There is controversy about whether microparticles (MPs), particularly tissue factor (TF) positive MPs, are increased in patients with malignancy and/or thrombosis. We therefore set out to investigate the relationship between MPs of different cellular origins, in patients with gynaecological malignancy. We hypothesised that patients with gynaecological malignancy have increased numbers of MPs. We measured MPs released by different cell types in these patients, and correlated the results with measures of haemostatic activation.

Methods

We measured the number of platelet-derived MPs (PMPs), endothelial cell-derived MPs (EMPs), leucocyte-derived MPs (LMPs), TF+ve MPs and annexin V (AV) binding MPs in fresh plasma by flow cytometry in patients with gynaecological malignancy and a control group. We also measured D-dimers, prothrombin fragments 1 and 2 (PF1&2) and thrombin–antithrombin (TAT) complexes as indirect markers of haemostatic activation.

Results

The number of MPs (from all cell types) was similar in the two patient groups, with no significant differences. The number of circulating TF+ve MPs was also similar between the two groups. D-dimers (p < 0.001) and PF1&2 (p = 0.009) were significantly higher in the malignant group reflecting haemostatic activation, but there was no correlation between the level of D-dimers, PF1&2 and TAT and MP numbers.

Conclusion

Using fresh samples, MPs were not significantly increased in patients with gynaecological malignancy. There was, however, evidence of haemostatic activation in the patients with malignancy, but no correlation between the number of MPs and haemostatic activation.  相似文献   
123.
Several factors including demographic, reproductive, lifestyle, psychological and social factors can affect incidence and severity of primary dysmenorrhea. This study aimed to systematically review the psychological risk factors associated with primary dysmenorrhea. Embase, ISI web of knowledge, ProQuest, Science Direct, Scopus and PubMed central were searched using keywords related to risk factors and primary dysmenorrhea. Observational studies, published in English after 2000, focusing solely on psychological factors affecting primary dysmenorrhea were included. The search process retrieved 11,928 potential related articles. Thirty three articles met inclusion criteria and were assessed for final synthesis. The STROBE checklist was used to quality assessment of studies. Results of study showed that few studies had investigated relationship between dysmenorrhea and most psychological disorders. Most studies have investigated the relationship between dysmenorrhea and depression, anxiety, stress, alcohol abuse and somatic disorders. So, further studies are needed to investigate relation between most psychological disorders with primary dysmenorrhea. Significant relationship between some mental health components such as depression, anxiety and stress with primary dysmenorrhea shows the importance of psychological assessment before the choice of therapeutic methods. Also, the feasibility of designing and evaluating the effectiveness of the use of psychotherapy interventions for the treatment of primary dysmenorrhea as alternative therapies can be considered.  相似文献   
124.

Objective

Ovarian hyperstimulation syndrome (OHSS) is a major complication of assisted reproductive technologies (ART). Polycystic ovary syndrome (PCOS) is a risk factor for OHSS. The aim of this randomized clinical trial (RCT) was to study the effect of low-dose aspirin (LDA) on the development of OHSS and ART outcomes in PCOS during ART.

Materials and methods

This double-blinded placebo controlled RCT was performed on 232 PCOS infertile women in their first ART cycles during 2010–2016. LDA and placebo capsules were prepared, packed and specified by code numbers in similar shapes. One package was given to every woman and asked to take one capsule/day since the 21st day of her cycle prior to the gonadotropin stimulation. Gonadotropin releasing hormone agonist long protocol and triggering by human chorionic gonadotropin were used. Development of moderate to severe OHSS and their ART outcomes were documented then the codes were broken and data analyzed. Chi-square and Mann–Whitney U tests were used for the statistical analyses.

Results

Eighteen cases that did not follow the study design were excluded. 214 cycles remained for the final analyses with 109 cases in LDA and 105 in the placebo group. Rate of the moderate to severe OHSS in LDA group was 34.9% compared to 30.5% in placebo group (P = 0.494). Fertilization rate was 71.8% vs 65.1% (P = <0.001) and the mean number of grade III embryos were 3.28 ± 3.53 vs 1.46 ± 1.42 (P = 0.014) in LDA and placebo groups, respectively. The mean number of the oocytes in different grades, total and frozen embryos also implantation and clinical pregnancy rates were not different between the groups.

Conclusion

Moderate to Severe OHSS was not decreased but fertilization rate and the mean number of poor quality embryos were increased in LDA arm.

Registration number

IRCT 201105216541N1.  相似文献   
125.

Research question

Telomeres are non-coding, repetitive DNA sequences (TTAGGG repeats) that play an important role in maintaining genome integrity. Unlike in somatic cells, telomere length in spermatozoa increases with male age and is considered as a molecular marker of sperm quality. The aetiology of failed fertilization following intracytoplasmic sperm injection (ICSI) is multifactorial; perhaps one of the reasons for this failure in these individuals is shortened sperm telomere length. This study therefore aimed to assess sperm telomere length in addition to DNA damage, lipid peroxidation and protamine deficiency in infertile men with previously failed/low fertilization post-ICSI.

Design

Semen samples were obtained from infertile men with previous failed/low fertilization rates (n?=?10). Chromatin integrity (chromomycin A3 staining and TUNEL assay), lipid peroxidation (BODIPY probe) and telomere length (real-time PCR) for semen samples from these men were compared with samples obtained from fertile individuals (n = 10).

Results

The results showed significantly higher mean values for sperm DNA damage, lipid peroxidation and reduced telomere length in spermatozoa of infertile men with previous failed/low fertilization compared with fertile individuals (P < 0.05).

Conclusions

Failed/low fertilization rates could be related to oxidative stress resulting in short telomere length, and also increased sperm chromatin damage and lipid peroxidation. From literature sources, shortened telomere length may lead to detachment of chromosomes from the nuclear membrane, the consequences of which are defects in the process of spermatogenesis, pronuclei formation, and delayed or arrested cell cycle post-ICSI.  相似文献   
126.
127.
Sputum and serum from patients with active pulmonary tuberculosis (TB), healthy purified protein derivative-positive adults, and patients with bacterial pneumonia were collected to simultaneously assess local immunity in the lungs and peripheral blood. To determine whether cytokine profiles in sputum from TB patients and control subjects were a reflection of its cellular composition, cytospin slides were prepared in parallel and assessed for the presence of relative proportions of epithelial cells, neutrophils, macrophages, and T cells. Gamma interferon (IFN-γ) in sputum from TB patients was markedly elevated over levels for both control groups. With anti-TB therapy, IFN-γ levels in sputum from TB patients decreased rapidly and by week 4 of treatment were comparable to those in sputum from controls. Further, IFN-γ levels in sputum closely followed mycobacterial clearance. Although detected at fourfold-lower levels, IFN-γ immunoreactivities in serum followed kinetics in sputum. TNF-α, interleukin 8 (IL-8) and IL-6 also were readily detected in sputum from TB patients at baseline and responded to anti-TB therapy. In contrast to IFN-γ, however, TNF-α and IL-8 levels also were elevated in sputum from pneumonia controls. These data indicate that sputum cytokines correlate with disease activity during active TB of the lung and may serve as potential early markers for sputum conversion and response to anti-TB therapy.  相似文献   
128.
129.
Linear poly(ethylene glycol) (PEG)‐block‐poly(N‐isopropylacrylamide) (PNIPAM) and star‐like three‐arm PEG‐star‐(PNIPAM)2 copolymers having one PEG and two PNIPAM blocks are synthesized by atom transfer radical polymerization (ATRP). Single crystals of these block copolymers are grown from amyl acetate and toluene dilute solutions. To recognize PNIPAM and PEG thicknesses, small angle X‐ray scattering (SAXS) is applied. V‐type brushes behave differently from linear brushes because doubly grafted PNIPAM blocks from a common point onto PEG substrate exert a higher osmotic pressure, leading to a thinner crystal. In addition to three ordinary regimes, a fourth or extremely stretched regime is detected for V‐type PNIPAM brushes. Although in PEG5000star‐(PNIPAM)2 single crystals with overall PNIPAM molecular weight of 37 000 g/mol, each PNIPAM arm is shorter than PNIPAM grafts in linear PEG5000block‐PNIPAM26000 single crystals, their switching point from second to third regime is significantly lower (22 vs 33 °C). The V‐type configuration of PNIPAM brushes cause them to be entered into the extremely stretched or fourth regime, which has not been previously detected for coily brushes. The boundary between third and fourth regimes for PEG5000star‐(PNIPAM)2 single crystals is verified at 31.5 and 23.5 °C in amyl acetate and toluene, respectively.  相似文献   
130.
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