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   12693篇
  免费   922篇
  国内免费   68篇
耳鼻咽喉   282篇
儿科学   247篇
妇产科学   212篇
基础医学   1919篇
口腔科学   292篇
临床医学   1212篇
内科学   2745篇
皮肤病学   310篇
神经病学   1214篇
特种医学   789篇
外国民族医学   3篇
外科学   1719篇
综合类   141篇
一般理论   4篇
预防医学   814篇
眼科学   95篇
药学   885篇
中国医学   11篇
肿瘤学   789篇
  2023年   49篇
  2022年   123篇
  2021年   248篇
  2020年   128篇
  2019年   204篇
  2018年   251篇
  2017年   209篇
  2016年   281篇
  2015年   369篇
  2014年   407篇
  2013年   529篇
  2012年   865篇
  2011年   910篇
  2010年   497篇
  2009年   479篇
  2008年   838篇
  2007年   884篇
  2006年   800篇
  2005年   825篇
  2004年   795篇
  2003年   773篇
  2002年   688篇
  2001年   154篇
  2000年   122篇
  1999年   166篇
  1998年   156篇
  1997年   171篇
  1996年   125篇
  1995年   116篇
  1994年   101篇
  1993年   102篇
  1992年   80篇
  1991年   76篇
  1990年   63篇
  1989年   80篇
  1988年   54篇
  1987年   56篇
  1986年   62篇
  1985年   49篇
  1984年   64篇
  1983年   57篇
  1982年   73篇
  1981年   56篇
  1980年   59篇
  1979年   46篇
  1978年   35篇
  1977年   35篇
  1975年   40篇
  1974年   34篇
  1972年   31篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
22.

Background  

A substance use screening instrument was used to determine factors predictive of drinking during pregnancy. Alcohol consumption during pregnancy can lead to negative birth outcomes.  相似文献   
23.
We sought whether microdamage could rise in postmenopausal osteoporotic women on long-term bisphosphonates, as suggested by recent animal studies. We found few microcracks in iliac bone biopsies, despite a marked reduction in bone turnover. INTRODUCTION: Animal studies suggest that bisphosphonates (BPs) could increase microdamage frequency in a dose-dependent manner, caused by excessively suppressed bone turnover. However, there is limited data in humans receiving BP therapeutic doses for >3 yr. MATERIALS AND METHODS: We measured microcrack frequency and histomorphometry parameters on transiliac bone biopsies in 50 postmenopausal osteoporotic women (mean age = 68 yr) who had received BP therapy (3 on intravenous pamidronate, 37 on oral alendronate, and 10 on oral risedronate) for at least 3 yr (mean treatment duration = 6.5 yr). We compared these results with transiliac bone biopsies obtained from 12 cadavers. We used bulk staining with green calcein as a fluorochrome. The microcracks were quantified in three 100-microm-thick sections using optic microscopy and were confirmed by laser confocal microscopy. Microcrack frequency (number of microcracks/mm2 of bone tissue) was compared between treated women and controls using nonparametric tests. We also explored predictors of microcrack frequency, including age, duration of BP therapy, and activation frequency. RESULTS: Among treated women, cancellous bone microcrack frequency was low (mean, 0.13 microcracks/mm2) and did not differ significantly from that observed in controls (0.05 microcracks/mm2; p = 0.59). Of note, 54% of the treated women and 58% of the controls had no observable microcracks. There was no association between microcrack frequency and the duration of BP therapy (for microcracks/mm2 and duration, Spearman r = 0.04, p = 0.80) and between patients' ages and the number of microcracks (Spearman r = -0.09, p = 0.61). Although bone remodeling parameters were suppressed in treated women, we found no relationship between microcrack density and activation frequency (Spearman r = -0.003, p = 0.99). Also, microcrack frequency was not increased in women with prevalent vertebral fracture compared with those without fractures. CONCLUSIONS: Among postmenopausal osteoporotic women on long-term BPs, microcrack frequency in the iliac bone is low, despite a marked reduction of bone turnover.  相似文献   
24.
BACKGROUND: Reactive oxygen species play a major role in the development of endothelial dysfunction. It is as yet unspecified whether increased oxidative stress contributes to endothelial dysfunction of the renal vasculature in patients with type 2 diabetes. METHODS: Renal haemodynamics were studied in 20 patients with type 2 diabetes and arterial hypertension (age 62 +/- 5 years) and 20 non-diabetic hypertensive patients at baseline and following infusions of the nitric oxide synthase inhibitor, N(G)-monomethyl-L-arginine (L-NMMA; 4.25 mg/kg); the substrate of nitric oxide synthase, L-arginine (100 mg/kg); and the antioxidant, vitamin C (3 g, co-infused with L-arginine 100 mg/kg). RESULTS: The response of renal plasma flow (RPF) to L-NMMA (-54 +/- 62 and -45 +/- 42 ml/min/1.73 m(2); P = NS) and L-arginine (+46 +/- 36 and +49 +/- 25 ml/min/1.73 m(2); P = NS) was not different between diabetic and non-diabetic patients. In contrast, vitamin C induced a more pronounced increase in RPF in diabetic than in non-diabetic patients when co-infused with L-arginine (+71+/-47 and +43+/-33 ml/min/1.73 m(2); P<0.05). CONCLUSIONS: The difference in the response of renal perfusion to an antioxidant suggests increased formation of reactive oxygen species and thereby reduced nitric oxide bioavailability in the renal vasculature of patients with type 2 diabetes.  相似文献   
25.
26.
27.
The excitatory responses of neurones in the anterior cingulate cortex of the rat to iontophoretically applied substance P (SP) are reduced by noradrenaline (NA) applied iontophoretically or released from noradrenergic pathways. In order to determine the receptor involved in this inhibitory effect we have studied the effects of a number of receptor-specific adrenergic agonists and antagonists on responses of cingulate neurones to SP in rats anaesthetized with chloral hydrate. Low iontophoretic currents (0-15 nA) of NA, adrenaline and the beta-agonist, clenbuterol, all strongly reduced responses to SP. Isoprenaline was also effective but less consistently so, although problems were experienced with its iontophoretic release from micropipettes. The alpha 1-agonists, phenylephrine and methoxamine were also able to reduce responses to SP. However, this reduction required higher iontophoretic currents (15-60 nA) and was associated with depressant effects on baseline firing rate. The alpha 2-agonist clonidine was only weakly active at high currents and this too was associated with depression of baseline firing. Similar weak effects were noted with dopamine. The inhibitory effects of NA on SP responses were convincingly blocked or reversed by the beta-antagonist, practolol, but not by the alpha 1-antagonist, prazosin. The reduction of SP responses by phenylephrine was also blocked by practolol but unaffected by prazosin. Finally, reduction of SP excitations by activation of the coeruleocortical pathway was also blocked by practolol applied iontophoretically to the cortical cells. These results are consistent with the hypothesis that the effect of NA on SP responsiveness in the cingulate cortex is mediated by beta-adrenoreceptors.  相似文献   
28.
We report the case of a newborn with macrosomia, extensive subcutaneous fat necrosis and symptomatic hypercalcemia. Low doses of prednisone were efficient, while dietary intervention, hyperhydratation and furosemide were not. Treatment of hypercalcemia in this specific neonatal condition are discussed.  相似文献   
29.
30.
Long-term effects of cochlear implants in children.   总被引:5,自引:0,他引:5  
OBJECTIVE: Since 1987, when the use of multichannel cochlear implants was initiated in children, candidacy has expanded; many thousands of children have received these devices, and results have revealed a wide range of performance. However, few long-term studies exist on a large population of these children. There have been concerns expressed that cochlear implant function might degrade over time, that devices and electrodes might migrate and extrude in the growing child, or that there might even be a deleterious effect of long-term stimulation of the cochlear nerve. The purpose of this study was to explore the long-term effects of implantation as a function of performance over time, reimplantation, and educational factors. STUDY DESIGN AND SETTING: We studied 81 children who received implants at a major academic medical center and were followed for 5 to 13 years. RESULTS: Results revealed significant gains in speech perception, use of oral language, and ability to function in a mainstream environment. There was no decrease in performance over time and no significant incidence of device or electrode migration or extrusion, and device failure did not cause a deterioration in long-term outcome. CONCLUSIONS: Multichannel cochlear implants in children provide perception, linguistic, and educational advantages, which are not adversely affected by long-term electrical stimulation.  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