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   8779篇
  免费   838篇
  国内免费   38篇
耳鼻咽喉   365篇
儿科学   596篇
妇产科学   388篇
基础医学   653篇
口腔科学   563篇
临床医学   825篇
内科学   1764篇
皮肤病学   238篇
神经病学   647篇
特种医学   427篇
外科学   1795篇
综合类   95篇
一般理论   1篇
预防医学   317篇
眼科学   289篇
药学   387篇
中国医学   25篇
肿瘤学   280篇
  2024年   22篇
  2023年   218篇
  2022年   139篇
  2021年   315篇
  2020年   232篇
  2019年   268篇
  2018年   620篇
  2017年   497篇
  2016年   614篇
  2015年   470篇
  2014年   730篇
  2013年   927篇
  2012年   746篇
  2011年   757篇
  2010年   651篇
  2009年   373篇
  2008年   243篇
  2007年   220篇
  2006年   207篇
  2005年   133篇
  2004年   75篇
  2003年   70篇
  2002年   79篇
  2001年   97篇
  2000年   66篇
  1999年   63篇
  1998年   130篇
  1997年   99篇
  1996年   102篇
  1995年   65篇
  1994年   78篇
  1993年   41篇
  1992年   14篇
  1991年   21篇
  1990年   13篇
  1989年   32篇
  1988年   29篇
  1987年   30篇
  1986年   26篇
  1985年   24篇
  1984年   12篇
  1983年   9篇
  1982年   20篇
  1981年   15篇
  1980年   16篇
  1979年   5篇
  1978年   6篇
  1977年   9篇
  1976年   13篇
  1975年   9篇
排序方式: 共有9655条查询结果,搜索用时 15 毫秒
71.
A pulmonary arteriovenous fistula is an abnormal connection between pulmonary arteries and veins. Patients with Rendu–Osler–Weber syndrome may present with this vascular malformation, which is a typical finding of the disease. Approximately 5–15% of Rendu–Osler–Weber syndrome patients have pulmonary arteriovenous malformations (AVM) and there is usually a family history of AVM in these patients. The malformations are usually located in the lower lobes. In this paper, I describe a 49‐year‐old male patient with dyspnoea, cough, haemoptysis and epistaxis. Physical examination showed nasal telangiectasias, cyanosis of the lips and nails, and a systolic bruit over the left lung. Chest X‐ray revealed a 5‐cm mass in the left lower lobe and after magnetic resonance examination, together with 3‐D magnetic resonance angiography, it was demonstrated to be a pulmonary arteriovenous fistula. The history of a niece with a similiar history of suspected pulmonary arteriovenous fistula led me to consider the possibility of Rendu–Osler–Weber syndrome presenting with a pulmonary arteriovenous fistula.  相似文献   
72.
Di(ethylhexyl)phthalate (DEHP), the most widely used plasticizer, was investigated to determine whether an oxidative stress process was one of the underlying mechanisms for its testicular toxicity potential. To evaluate the effects of selenium (Se), status on the toxicity of DEHP was further objective of this study, as Se is known to play a critical role in testis and in the modulation of intracellular redox equilibrium. Se deficiency was produced in 3‐weeks‐old Sprague–Dawley rats feeding them ≤0.05 mg Se /kg diet for 5 weeks, and Se‐supplementation group was on 1 mg Se/kg diet. DEHP‐treated groups received 1000 mg/kg dose by gavage during the last 10 days of the feeding period. Activities of antioxidant selenoenzymes [glutathione peroxidase 1 (GPx1), glutathione peroxidase 4 (GPx4), thioredoxin reductase (TrxR)], catalase (CAT), superoxide dismutase (SOD), and glutathione S‐transferase (GST); concentrations of reduced glutathione (GSH), oxidized glutathione (GSSG), and thus the GSH/GSSG redox ratio; and thiobarbituric acid reactive substance (TBARS) levels were measured. DEHP was found to induce oxidative stress in rat testis, as evidenced by significant decrease in GSH/GSSG redox ratio (>10‐fold) and marked increase in TBARS levels, and its effects were more pronounced in Se‐deficient rats with ~18.5‐fold decrease in GSH/GSSG redox ratio and a significant decrease in GPx4 activity, whereas Se supplementation was protective by providing substantial elevation of redox ratio and reducing the lipid peroxidation. These findings emphasized the critical role of Se as an effective redox regulator and the importance of Se status in protecting testicular tissue from the oxidant stressor activity of DEHP. © 2011 Wiley Periodicals, Inc. Environ Toxicol 29: 98–107, 2014.  相似文献   
73.
Introduction: In etiology of Alzheimer’s disease (AD), involvement of amyloid β (Aβ) plaque accumulation and oxidative stress in the brain have important roles. Several nanoparticles such as titanium dioxide, silica dioxide, silver and zinc oxide have been experimentally using for treatment of neurological disease. In the last decade, there has been a great interest on combination of antioxidant bioactive compounds such as selenium (Se) and flavonoids with the oxidant nanoparticles in AD. We evaluated the most current data available on the physiological effects of oxidant and antioxidant nanoparticles.

Areas covered: Oxidative nanoparticles decreased the activities of reactive oxygen species (ROS) scavenging enzymes such as glutathione peroxidase (GSH-Px), superoxide dismutase (SOD) and catalase in the brain of rats and mice. However, Se-rich nanoparticles in small size (5–15 nm) depleted Aβ formation through decreasing ROS production. Reports on low levels of Se in blood and tissue samples and the low activities of GSH-Px, catalase and SOD enzymes in AD patients and animal models support the proposed crucial role of oxidative stress in the pathogenesis of AD.

Expert commentary: In conclusion, present literature suggests that Se-rich nanoparticles appeared to be a potential therapeutic compound for the treatment of AD.  相似文献   
74.
Aim: To evaluate the effect of the platelet indices on the stage of diabetic retinopathy (DR) and diabetic macular edema (DME). Methods: In this retrospective study, the mean platelet valume (MPV), Plateletcrit (PCT), platelet (PLT), and platelet distribution width (PDW) of 199 diabetic patients and 76 healthy subjects were enrolled. The participants were divided into four groups. The first group was healthy control; the second group consisted of diabetic patients without DR; the third group was nonproliferative DR (NPDR); and the fourth group was proliferative DR (PDR). Results: Significant differences were found only in MPV and PCT values between patients with diabetes and healthy participants (8.6±0.96 fL vs 8.32±0.9 fL, P=0.011, 0.216± 0.58 vs 0.202±0.52, P=0.038). Comparing the groups, a statistically significant difference in MPV values was found between groups 4 and 1 (8.91±.7 fL vs 8.32±0.9 fL P=0.001) and between groups 4 and 3 (8.91±.7 fL vs 8.42±0.9 fL P=0.014). The MPV values of patients with DME were significantly higher than those of diabetic patients without DME (8.87±0.80 fL vs 8.45±0.97 fL). Conclusion: High MPV values may be an important risk factor for the development of PDR and DME in patients with diabetic retinopathy.  相似文献   
75.
76.
17β-hydroxysteroid dehydrogenase type 3 deficiency is a rare cause of 46 XY disorders of sexual development. Mutations in the HSD17B3 gene result in reduced activity of the 17β-HSD3 enzyme, decreasing the conversion of androstenedione to testosterone. In this report, two cases, admitted with different clinical findings in the neonatal and adolescent periods and were decided to be raised in different genders are presented. The first case who had complete female external genitalia presented on the third postnatal day with the complaint of swelling in the groin. He was decided to be raised as a male and was treated successfully with parenteral testosterone in order to increase phallus size before surgical correction of the external genitalia. The second case was an adolescent girl who presented due to pubertal virilisation and primary amenorrhoea and chose female gender. Molecular genetic analyses of the HSD17B3 gene revealed two different previously reported homozygous variants. We emphasise that patients with 17β-hydroxysteroid dehydrogenase type 3 deficiency can present with heterogeneous clinical findings in different age groups. Early diagnosis is important to prevent future gender confusion and related problems.  相似文献   
77.

Background

Ginger (Zingiber officinale) is a well known and extensively used antioxidant in traditional remedies. In this study, we aimed to investigate the effects of ginger powder on ovarian folliculogenesis and implantation in rats.

Methods

There were two study groups. In the 5-day treatment group (one estrous cycle), 100 mg ginger powder, 200 mg ginger powder or distilled water was given for 5 days to the three subgroups each containing seven rats. In the 10-day treatment group, same doses were given for 10 days (two estrous cycle) to the three subgroups each containing seven rats. At the end of the 5th and 10th days, ovarian volumes, ovarian weights, primordial follicles, antral follicles, atretic follicles, and corpus luteum counts were assessed. To evaluate the angiogenic effects of ginger, vascular endothelial growth factor (VEGF) and for the antioxidant effects of ginger endothelial nitric oxide synthase (eNOS) were examined in the ovaries and in the endometrium immunohistochemically.

Results

In the 5-day treatment group, antral follicle count and ovarian stromal VEGF were significantly high in the 100 mg ginger subgroup in comparison to the control group (p < 0.05). In the 10-day treatment group, endometrial VEGF and ovarian stromal eNOS were significantly high in the 100 mg ginger subgroup in comparison to the control group (p < 0.05). There was no statistically significant difference at 200 mg ginger dose both in 5-day and 10-day treatment groups.

Conclusion

The increases in the antral follicle count and ovarian stromal VEGF in the 100 mg/5-day treatment subgroup indicate that ginger have positive effects on folliculogenesis in short term with low dose. Additionally, ginger may enhance implantation in rats in long term with low dose.  相似文献   
78.
BACKGROUND: The primary goal of ultrasonography (US) in the evaluation of a thyroid nodule is to determine its malignancy, although the diagnosis of a malignant nodule on the basis of US alone is nearly impossible. The aim of this prospective study was to evaluate the predictive value of sonographic features in the preoperative diagnosis of malignant thyroid nodules, and to determine the important features of sonography. METHODS: This prospective study included 550 consecutive patients with , thyroid nodules. Nodules were divided into two groups on the basis of pathological diagnosis: group 1 consisted of 1,633 nodules with a benign pathology, and group 2 consisted of 293 nodules with a malignant pathology. RESULTS: Microcalcifications, blurred nodular margins, and solid and hypoechoic appearance were more common in malignant nodules compared to benign nodules (89.1% versus 5%; 64.5% versus 4.7%; 81.6% versus 30.6% ; and 62.5% versus 43.1%, respectively; p < 0.001). There was a positive correlation between the detection of malignant thyroid nodules and microcalcification (rs = 0.791, p = 0.0001), blurred nodular margin (rs = 0.625, p = 0.0001), solid appearance (rs = 0.376, p = 0.0001), and hypoechoic appearance (rs = 0.141, p = 0.0001). Microcalcifications, blurred nodular margins, and solid and hypoechoic appearance were independent determinants of malignancy upon US examination of thyroid nodules (OR: 159, OR: 37, OR: 9.9, and OR: 2.2, respectively). CONCLUSION: Although we did not identify a single feature indicative of malignancy in the sonographic examination of nodules, microcalcification and blurred margin were the strongest correlates for malignancy.  相似文献   
79.
ObjectiveTo compare the amounts of any clinically detectable gas passage into the urinary bag in laparoscopic and open surgeries.MethodsSeventy-nine women were allocated into two surgical groups; Group 1: carbon dioxide (CO2) laparoscopy (n=37) and Group 2: gasless laparoscopy or laparotomy (n=42). All patients had urinary catheter during the surgeries. After checking the tightness of the connection of the urinary catheter and bag operations were performed. At the end of each surgery the urine volumes were recorded. The bags were immersed into a water containing container with a volume scale. The volume rise of the container was recorded. The valve of the outlet of the bag was turned on under the water and any leakage of air bubbles was observed. The final volume of the container was recorded once again while the bag was still in the water. The two groups were compared by using the Student's t or Mann Whitney U tests.ResultsWe did not observe and hence measure any gas accumulation in the urine bags of both groups. The women's ages, total intraoperative urine volume, urine production rate and total operative times of the groups were not significantly different. The mean operative time was (82.98±62.14) min in open surgeries and (73.46±52.74) minutes in CO2 laparoscopic surgeries. The difference between the groups was not significant (P=0.468).ConclusionsAny gas accumulation in the urine bag during CO2 laparoscopic surgery should raise the suspicion of urinary tract injury. Urinary catheterization helps to diagnose the unnoticed bladder injuries.  相似文献   
80.
Objectives: Left ventricular (LV) systolic synchrony, defined as simultaneous peak contractions of corresponding cardiac segments, is well documented to be impaired in hypertension but its effect on LV function is not clear. The aim of this study was to assess the impacts of LV systolic dyssynchrony on LV function in newly diagnosed hypertensives. Methods: Forty-eight newly diagnosed hypertensive patients and 33 controls were enrolled. All study population underwent a comprehensive echocardiographic evaluation including tissue synchrony imaging. The time to regional peak systolic tissue velocity (Ts) in LV by 12 segmental models was measured and two parameters of systolic dyssynchrony were computed. Results: Baseline demographic characteristics were similar in both study groups. Dyssynchrony parameters prolonged in newly diagnosed hypertensive patients compared to controls: the standard deviation (SD) of 12 LV segments Ts (40.2 ± 21 vs. 26.2 ± 13.4, P = 0.003); the maximal difference in Ts between any 2 of 12 LV segments (123.3 ± 61.5 vs. 79.8 ± 37.9, P = 0.001). In multivariable analysis, Ts-SD-12 was found to be an independent predictor for systolic function (β=-0.29, P = 0.008). But, both diastolic and global functions were not independently related to Ts-SD-12. Conclusion: LV synchronization is impaired in newly diagnosed hypertensive patients. LV dyssynchrony is one of the independent predictors of systolic function in hypertensive patients.  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