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   43379篇
  免费   2089篇
  国内免费   193篇
耳鼻咽喉   716篇
儿科学   731篇
妇产科学   793篇
基础医学   5775篇
口腔科学   1293篇
临床医学   3036篇
内科学   10061篇
皮肤病学   640篇
神经病学   3549篇
特种医学   1564篇
外科学   7238篇
综合类   194篇
一般理论   3篇
预防医学   1670篇
眼科学   717篇
药学   3721篇
中国医学   83篇
肿瘤学   3877篇
  2023年   209篇
  2022年   447篇
  2021年   781篇
  2020年   392篇
  2019年   548篇
  2018年   674篇
  2017年   523篇
  2016年   634篇
  2015年   666篇
  2014年   878篇
  2013年   1171篇
  2012年   1860篇
  2011年   2022篇
  2010年   1184篇
  2009年   998篇
  2008年   1892篇
  2007年   2096篇
  2006年   2024篇
  2005年   1984篇
  2004年   1892篇
  2003年   1899篇
  2002年   1869篇
  2001年   1628篇
  2000年   1786篇
  1999年   1518篇
  1998年   493篇
  1997年   403篇
  1996年   372篇
  1995年   313篇
  1994年   286篇
  1993年   257篇
  1992年   1115篇
  1991年   921篇
  1990年   902篇
  1989年   939篇
  1988年   833篇
  1987年   830篇
  1986年   784篇
  1985年   770篇
  1984年   527篇
  1983年   422篇
  1982年   220篇
  1979年   484篇
  1978年   274篇
  1977年   251篇
  1975年   207篇
  1974年   223篇
  1971年   230篇
  1969年   230篇
  1968年   216篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
The conversion of cellulose into valuable chemicals has attracted much attention, due to the concern about depletion of fossil fuels. The hydrolysis of cellulose is a key step in this conversion, for which Brønsted acidic ionic liquids (BAILs) have been considered promising acid catalysts. In this study, using BAILs with various structures, their acidic catalytic activity for cellulose hydrolysis assisted by microwave irradiation was assessed using the Hammett acidity function (H0) and theoretical calculations. The glucose yields exceeded 10% when the H0 values of the BAIL aqueous solutions were below 1.5. The highest glucose yield was about 36% in 1-(1-octyl-3-imidazolio)propane-3-sulfonate (Oimps)/sulfuric acid (H2SO4) aqueous solution. A long alkyl side chain on the imidazolium cation, which increased the hydrophobicity of the BAILs, enhanced the glucose yield.

Using Brønsted acidic ionic liquids with various structures, their acidic catalytic activity for cellulose hydrolysis assisted by microwave irradiation was assessed using the Hammett acidity function (H0) and theoretical calculations.  相似文献   
992.
993.
We have investigated the dose rate effects on cell damage caused by photon-beam irradiation. During a relatively long dose-delivery time with a low dose rate, lesions created in cells may undergo some reactions, such as DNA repair. In order to investigate these reactions quantitatively, we adopted the microdosimetric–kinetic (MK) model and deduced a cell surviving fraction (SF) formula for continuous irradiation. This model enabled us to estimate the SF from dose and dose rate. The parameters in the MK model were determined so as to generate the SF, and we attempted to evaluate the dose rate effects on the SF. To deduce the cell-specific parameters in the SF formula, including the dose rate, we performed a split-dose experiment and a single-dose experiment with a constant dose-delivery time (10 min) (to retain the condition for equivalent behavior of cell lesions) by means of a clonogenic assay. Then, using the MK model parameters, the SFs were reproduced for a variety of dose rates (1.0, 0.31, 0.18, 0.025 and 0.0031 Gy/min) and were compared with reported experimental data. The SF curves predicted by the MK model agreed well with the experimental data, suggesting that the dose rate effects appear in the kinetics of cell lesions during the dose-delivery time. From fitting the analysis of the model formula to the experimental data, it was shown that the MK model could illustrate the characteristics of log-SF in a rectilinear form at a high dose range with a relatively low dose rate.  相似文献   
994.
X-ray radiotherapy activates tumor antigen-specific T-cell responses, and increases in the serum levels of high mobility group box 1 (HMGB1) induced by X-ray irradiation play a pivotal role in activating anti-tumor immunity. Here, we examined whether carbon-ion beams, as well as X-rays, can induce HMGB1 release from human cancer cell lines. The study examined five human cancer cell lines: TE2, KYSE70, A549, NCI-H460 and WiDr. The proportion of cells surviving X- or carbon-ion beam irradiation was assessed in a clonogenic assay. The D10, the dose at which 10% of cells survive, was calculated using a linear–quadratic model. HMGB1 levels in the culture supernatants were assessed by an ELISA. The D10 dose for X-rays in TE2, KYSE70, A549, NCI-H460 and WiDr cells was 2.1, 6.7, 8.0, 4.8 and 7.1 Gy, respectively, whereas that for carbon-ion beams was 0.9, 2.5, 2.7, 1.8 and 3.5 Gy, respectively. X-rays and carbon-ion beams significantly increased HMGB1 levels in the culture supernatants of A549, NCI-H460 and WiDr cells at 72 h post-irradiation with a D10 dose. Furthermore, irradiation with X-rays or carbon-ion beams significantly increased HMGB1 levels in the culture supernatants of all five cell lines at 96 h post-irradiation. There was no significant difference in the amount of HMGB1 induced by X-rays and carbon-ion beams at any time-point (except at 96 h for NCI-H460 cells); thus we conclude that comparable levels of HMGB1 were detected after irradiation with iso-survival doses of X-rays and carbon-ion beams.  相似文献   
995.

Background

Sudden bath-related deaths occur frequently in Japan, particularly among elderly people. However, the precise mechanism of bath-related death remains uncertain, and effective prevention strategies have not been established.

Methods

Cases of bath-related deaths (n = 3289) were selected from all cases handled by the Tokyo Medical Examiner’s Office from 2009 to 2011 (N = 41 336). The ages and occurrence dates were examined, and major autopsy findings, including toxicological analysis, were evaluated for the autopsied cases (n = 550).

Results

Most cases occurred in individuals older than 60 years of age during winter. Analysis of autopsy findings revealed water inhalation signs in many cases (n = 435, 79.1%). Circulatory system diseases constituted more than half of the pathological findings regarding factors that may have contributed significantly to death (n = 300, 54.5%), and cardiac lesions were the most common pathological finding (n = 250, 45.5%). However, approximately one-third of the cases exhibited no remarkable pathological findings (n = 198, 36.0%). A quarter of all cases involved blood ethanol levels that exceeded 0.5 mg/mL (n = 140).

Conclusions

The results suggested that drowning plays an important role in the final process of bath-related death. Circulatory system diseases may be the primary underlying pathology; however, there were variations in the medical histories and pathologies of cases of bath-related death. From a preventive perspective, family members should pay attention to elderly people with circulatory system diseases during bathing, particularly in winter. Additionally, the notion that ill or inebriated individuals should not take baths should be reinforced.Key words: bath-related death, sudden death, forensic autopsy, medical examiner  相似文献   
996.
997.

Introduction

This was the first exploratory randomized controlled study to compare the efficacy and safety of a preserved tafluprost/timolol fixed combination (TAF/TIM) with a preserved latanoprost/timolol fixed combination (LAT/TIM).

Methods

This prospective, randomized, open-label study was conducted in Japanese patients with primary open-angle glaucoma, including normal-tension glaucoma or ocular hypertension. Following a 4-week LAT/TIM run-in period, eligible patients entered a 12-week treatment period, during which they received either LAT/TIM or TAF/TIM. The efficacy endpoint was the change in intraocular pressure (IOP) from baseline to week 12 and the safety endpoints included the changes from baseline to week 12 in superficial punctate keratopathy (SPK) score, tear breakup time (TBUT), and hyperemia score, as well as adverse events (AEs). At week 6, ocular symptoms were evaluated using a questionnaire.

Results

In total, 131 patients provided informed consent. Of these, 115 completed the run-in period and were assigned to receive TAF/TIM (n?=?60) or LAT/TIM (n?=?55). At week 12, there were no significant differences between the TAF/TIM and LAT/TIM groups in the change from baseline in trough IOP and IOP at 4–6 h after instillation. There were no significant differences between the two groups in the change from baseline to week 12 in SPK score, TBUT, and hyperemia score. However, only in the TAF/TIM group, the total SPK score and the inferior cornea SPK score were significantly lower at week 12 compared with baseline. Eye irritation and eye pain were significantly decreased in the TAF/TIM group compared with the LAT/TIM group. Two treatment-related AEs were reported in the TAF/TIM group (3.3%) and none in the LAT/TIM group, while no serious AEs were reported in either group.

Conclusion

TAF/TIM is as effective as LAT/TIM in terms of IOP-reducing effect, with fewer ocular symptoms. TAF/TIM was associated with a significant improvement in SPK scores.

Trial Registration

UMIN Clinical Trials Registry Identifier, UMIN000023862.

Funding

Santen Pharmaceutical Co., Ltd., Osaka, Japan.
  相似文献   
998.
Purpose: Swallowing dysfunction has been reported in Duchenne muscular dystrophy (DMD), but has not been studied in Becker muscular dystrophy (BMD). The aims of this study were to report the characteristics of swallowing dysfunction in BMD compared with DMD.

Materials and methods: The study participants were 18 patients with BMD and 18 patients with DMD. All the patients were examined using videofluorography during swallowing of 5?mL of fluid. The penetration–aspiration scale (P–A scale) and the videofluorographic dysphagia scale (VDS) were used to evaluate dysphagia.

Results: Swinyard functional ability stage was not significantly different between the BMD and DMD groups. Rate of aspiration, P–A scale score, and total VDS score did not differ across groups, but the VDS item score for laryngeal elevation was lower in the BMD group than in the DMD group (median scores 4.5 and 9, respectively; p?r?=?0.78, p?Conclusion: Patients with BMD have swallowing problems similar to those observed in patients with DMD when matched according to physical functional status. These patients should be evaluated and followed-up for the duration of their disease.

  • Implications for rehabiliation
  • Dysphagia is one of the most critical problems in patients with progressive neuromuscular disease but dysphagia in patients with Becker muscular dystrophy (BMD) was not well known.

  • Eighteen patients with BMD and 18 patients with Duchenne muscular dystrophy were examined with videofluorography.

  • Patients with BMD have swallowing problems similar to those observed in patients with DMD.

  相似文献   
999.
1000.
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