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   4009篇
  免费   291篇
  国内免费   37篇
耳鼻咽喉   42篇
儿科学   74篇
妇产科学   77篇
基础医学   559篇
口腔科学   67篇
临床医学   372篇
内科学   928篇
皮肤病学   82篇
神经病学   267篇
特种医学   129篇
外科学   552篇
综合类   73篇
一般理论   2篇
预防医学   319篇
眼科学   237篇
药学   285篇
中国医学   29篇
肿瘤学   243篇
  2024年   9篇
  2023年   52篇
  2022年   115篇
  2021年   206篇
  2020年   152篇
  2019年   189篇
  2018年   229篇
  2017年   151篇
  2016年   173篇
  2015年   160篇
  2014年   189篇
  2013年   257篇
  2012年   370篇
  2011年   361篇
  2010年   223篇
  2009年   178篇
  2008年   255篇
  2007年   244篇
  2006年   192篇
  2005年   133篇
  2004年   122篇
  2003年   104篇
  2002年   65篇
  2001年   16篇
  2000年   18篇
  1999年   15篇
  1998年   14篇
  1997年   9篇
  1996年   14篇
  1995年   8篇
  1994年   4篇
  1993年   4篇
  1992年   4篇
  1991年   7篇
  1990年   8篇
  1989年   7篇
  1987年   3篇
  1985年   3篇
  1984年   6篇
  1983年   5篇
  1982年   6篇
  1981年   5篇
  1980年   5篇
  1979年   8篇
  1978年   5篇
  1977年   7篇
  1976年   4篇
  1974年   4篇
  1973年   4篇
  1971年   4篇
排序方式: 共有4337条查询结果,搜索用时 46 毫秒
961.
Acute ischemia of the rectum is uncommon and usually occurs after aorto-iliac surgery. In this report, we present a case of acute ischemic proctosigmoiditis that developed from a brief episode of hypotension. An 85-year-old male presented to the emergency room with hypotension, mental confusion, and passage of maroon-colored stool. He was resuscitated and treated for presumed sepsis. Computerized tomography of the abdomen and pelvis displayed signs of acute inflammation of the distal colon and rectum. Endoscopic findings and microscopic examination of the rectal biopsy revealed changes consistent with acute ischemic proctosigmoiditis. An evaluation for infectious etiologies was negative. The patient's clinical condition improved over the next 24 h with supportive care. Involvement of the rectum is rare in ischemic colitis because of its abundant collateral blood supply. Acute ischemic proctosigmoiditis should be considered in the differential diagnosis of elderly patients with multiple co-morbidities presenting with hematochezia.  相似文献   
962.
OBJECTIVE: Juvenile rheumatoid arthritis (JRA) represents a heterogeneous group of disorders with a complex genetic component. A genome scan was performed to detect linkage to JRA in 121 families containing 247 affected children in North America (the JRA Affected Sibpair [ASP] Registry). METHODS: Genotype data collected for HLA-DR and 386 microsatellite markers were subjected to multipoint nonparametric linkage analysis. Following analysis of the entire set of families, additional analyses were performed after a priori stratification by disease onset type, age at onset, disease course, and selected HLA-DRB1 alleles. RESULTS: Linkage of JRA to the HLA region was confirmed (logarithm of odds [LOD] score 2.26). Additional evidence supporting linkage of JRA was observed at 1p36 (D1S214; LOD 1.65), 19p13 (D19S216; LOD 1.72), and 20q13 (D20S100; LOD 1.75). For early-onset polyarticular disease, evidence of linkage was found at chromosome 7q11 (D7S502; LOD 3.47). For pauciarticular disease, evidence supporting linkage was observed on chromosome 19p13 (D19S216; LOD 2.98), the same marker that supported linkage to the "JRA" phenotype. Other regions supporting linkage with JRA disease subtype included 20q13, 4q24, 12q24, and Xp11. Stratification of families based on the presence of the HLA-DR8 allele in affected siblings resulted in significant linkage observed at 2p25 (D2S162/D2S305; LOD 6.0). CONCLUSION: These data support the hypothesis that multiple genes, including at least 1 in the HLA region, influence susceptibility to JRA. These findings for JRA are consistent with findings for other autoimmune diseases and support the notion that common genetic regions contribute to an autoimmune phenotype.  相似文献   
963.

Objectives

Hyperglycemia with unknown mechanism plays a predictive role in determining the prognosis of multiple trauma patients. The exact time of blood sugar measurement and the role of blood sugar changes in the monitoring of these patients have not been well established.

Methods

This follow-up study was done on multiple trauma patients (> 18 years) with an Injury Severity Scores (ISS) > 16. These patients didn?t have any history of diabetes, underlying disease, or drug or alcohol use. Data collection was done by the questionnaire (checklist), and the patients were followed by the medical records. Cox regression was used to measure the effect of independent variables on the patients' hospital mortality.

Results

Of a total of 963 patients, 280 patients were enrolled. Of those, 202 were male (72.1%) and 78 were female (27.9%). Hospital mortality was 18 (6.4%). Cox regression analysis suggested that those who had high blood sugar 3 h after admission had higher hospital mortality (P = 0.04). Changes in blood sugar, ΔBS (BS 3 h after admission – BS on admission), in these patients was also significantly correlated with hospital mortality (P < 0.001). The multivariate model using the backward conditional method showed that ΔBS (P < 0.001), international normalized ration (INR) (P < 0.001), and heart rate (P = 0.036) were significantly correlated with hospital mortality.

Conclusions

In multiple trauma patients, blood sugar changes in the early hours of admission to the emergency department may help predict hospital mortality, but further studies are needed. Blood sugar monitoring in these patients during this time frame may be helpful in predicting these patients' outcomes. In addition, coagulopathy and tachycardia were significantly associated with hospital mortality.  相似文献   
964.
A BaCO3/BaSnO3/SnO2 nanocomposite has been prepared using a co-precipitation method without adding any additives. The prepared sample was characterized by using X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), Fourier-transform infrared (FT-IR) spectroscopy, energy dispersive X-ray spectroscopy (EDS) and Raman spectroscopy. Detailed studies on the dielectric and electrical behavior (dielectric constant, complex impedance Z*, ac conductivity, and relaxation mechanisms) of the nanocomposite have been performed using the nondestructive complex impedance spectroscopy technique within the temperature range 150–400 K. The dielectric constant of the sample as a function of temperature showed the typical characteristics of a relaxor. The maximum dielectric constant value was observed to depend on frequency. The non-monotonic relaxation behavior of the prepared nanocomposite was evidenced from the spectra of loss tan, tan(δ). The relaxation kinetics was modeled using a non-Arrhenius model.

A BaCO3/BaSnO3/SnO2 nanocomposite has been prepared using a co-precipitation method without adding any additives.  相似文献   
965.

Background

Work-related accidents result in human suffering and economic losses and are considered as a major health problem worldwide, especially in the economically developing world.

Objectives

To introduce seasonal autoregressive moving average (ARIMA) models for time series analysis of work-related accident data for workers insured by the Iranian Social Security Organization (ISSO) between 2000 and 2011.

Methods

In this retrospective study, all insured people experiencing at least one work-related accident during a 10-year period were included in the analyses. We used Box–Jenkins modeling to develop a time series model of the total number of accidents.

Results

There was an average of 1476 accidents per month (1476·05±458·77, mean±SD). The final ARIMA (p,d,q) (P,D,Q)s model for fitting to data was: ARIMA(1,1,1)×(0,1,1)12 consisting of the first ordering of the autoregressive, moving average and seasonal moving average parameters with 20·942 mean absolute percentage error (MAPE).

Conclusions

The final model showed that time series analysis of ARIMA models was useful for forecasting the number of work-related accidents in Iran. In addition, the forecasted number of work-related accidents for 2011 explained the stability of occurrence of these accidents in recent years, indicating a need for preventive occupational health and safety policies such as safety inspection.  相似文献   
966.
Background: Visceral leishmaniasis is systematic serous parasitic disease with public health importance. Zoonotic form of visceral leishmaniasis is wide spread in Mediterranean basin and South America regions. Direct agglutination test (DAT) is an accurate, reliable and non-expensive serological test for the diagnosis of visceral leishmaniasis in human and canines but the antigen preparation involves some limitations. This study aimed to compare the conventional production of DAT antigen with our modified DAT antigen and then assessed on human and dog pooled sera. Methods: Conventional DAT antigen has been prepared at the School of Public Health, Tehran University of Medical Sciences and some modifications were carried out on it, which named as modified DAT antigen. Three positive and one negative human and dog pooled serum were separately used for the comparison of modified DAT with conventional DAT antigen batches with one-month interval for a period of 9 months. Results: A good concordance was observed between modified DAT compared to conventional DAT antigens for the detection of visceral leishmaniasis on human (100%) and dog (94.4%) pooled sera, respectively. Conclusion: Since the modified DAT antigen could be reduced the preparation time from 3 days to several hours and a good degree of agreement was found between modified DAT and convention DAT antigen batches, it can be used as a simple and easy tool for screening and serodiagnosis of human and canine L. infantum infection.Key Words: Direct agglutination test, Antigen modification, Visceral leishmaniasis  相似文献   
967.

Background:

The number of malaria cases is declining worldwide; however, it remains as a serious health problem. Diagnosing unusual cases is the most important issue to manage the problem. This study designed to describe the number of falciparum and vivax malaria infected patients referred to Malaria Reference Laboratory in Tehran University of Medical Science from 2000 to 2012.

Methods:

A retrospective study was conducted based on the collected questionnaires from each patient referred to the laboratory. Diagnosing results and demographic information for positive cases were analyzed using SPSS software. Problematic cases were evaluated for any difficulties in diagnosis or in clinical signs. Scanning and molecular methods were performed whenever there was an atypical case referred to the laboratory. Some of the samples had various difficulties for diagnosing such as presence of fussed gametocytes and schizonts of Plasmodium falciparum in peripheral blood and CCHF like hemoragic disorders.

Results:

Plasmodium vivax caused a large proportion of the cases (76.1%) in contrast with P. falciparum that included smaller proportion (22.8%) and the rest (1.1) belonged to mixed infection. Most of the positive cases (69.6%) were belonged to Afghani people. Men (94.6%) showed more infection than women (5.4%), moreover the most infection (44.5%) was seen at a range of 21–30 yr.

Conclusion:

In the case of existing atypical issues to diagnose, it is needed to perform more precise microscopical examination beyond the current standard conditions. Sometimes molecular method is required to verify the exact agent of the disease.  相似文献   
968.
969.

Background:

Dense granules are immunodominant proteins for the standardization of immunodiagnostic procedures to detect neosporosis. In the presented study different fragment of a dense-granule protein was evaluated for serodiagnosis of Neospora caninum in cattle and water buffalo.

Methods:

NcGRA7, from N. caninum tachyzoites was amplified. PCR product and pMAL-c2X plasmid were digested with EcoR1 restriction enzyme and expressed in Escherichia coli to evaluate its competence for detection of anti- N. caninum antibodies with ELISA in comparison with commercial IDEXX ELISA. Furthermore, 230 sera of presumably healthy cattle and water buffaloes (108 cattle and 122 water buffaloes) were analyzed by both tests to determine the agreement of these two procedures.

Results:

Sensitivities and specificities of NcGRA7-based ELISA were 94.64% and 90.38% respectively using sera of cattle, but were 98.57% and 86.54% in the case of buffaloes respectively. A good correlation between the results of IDEXX ELISA and ELISA based on recombinant NcGRA7 for detecting N. caninum antibodies was appeared. Analyzing by Mc Nemar′s showed that NcGRA7-based ELISA has acceptable capability to differentiate the positive results in comparison with IDEXX ELISA.

Conclusion:

NcGRA7-based ELISA considering utilized new fragment of genomic DNA is a good tool for serodiagnosis of anti- N. caninum antibodies for screening and epidemiological purposes on cattle herd and water buffaloes as well.  相似文献   
970.
Objectives : We compared the long‐term outcomes of drug‐eluting stents (DES) versus bare‐metal stents (BMS) for treatment of bare‐metal in‐stent restenosis (ISR). Background : There are no randomized trials or observational studies directly comparing the safety and efficacy of DES versus BMS for treatment of bare‐metal ISR. Methods : We examined data on all patients who underwent percutaneous coronary intervention (PCI) for ISR at Cleveland Clinic between 05/1999 and 06/2007. We compared the efficacy and safety of DES to BMS for treating bare‐metal ISR. The primary end point was a composite of death, myocardial infarction (MI), or target lesion revascularization (TLR). The secondary endpoints were individual components of the primary endpoint. Results : Of the 931 patients identified over 8 years, 706 had bare‐metal ISR and met our study criteria. Of the 706 patients with bare‐metal ISR, 362 were treated with DES and 344 with BMS. There were 230 cumulative events for a median follow‐up of 3.2 years. After adjusting for 27 variables, DES were associated with lower primary endpoint compared to BMS for treatment of bare‐metal ISR (21% vs. 45%, adjusted hazard ratio [HR] 0.63; 95% confidence interval [CI], 0.42–0.95; P = 0.03). The individual secondary endpoint of death (8% vs. 24%, P = 0.005) favored DES, but MI (3% vs. 8%, P = 0.31), and TLR (13% vs. 20%, P = 0.23) failed to reach statistical significance. Conclusions : In our multivariate analysis of patients with bare‐metal ISR, DES use was associated with significantly lower death, MI, or TLR when compared to BMS. © 2010 Wiley‐Liss, Inc.  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