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   4201篇
  免费   211篇
  国内免费   20篇
耳鼻咽喉   96篇
儿科学   100篇
妇产科学   55篇
基础医学   662篇
口腔科学   59篇
临床医学   296篇
内科学   1128篇
皮肤病学   55篇
神经病学   257篇
特种医学   201篇
外科学   696篇
综合类   15篇
预防医学   114篇
眼科学   48篇
药学   205篇
中国医学   5篇
肿瘤学   440篇
  2023年   24篇
  2022年   51篇
  2021年   84篇
  2020年   49篇
  2019年   61篇
  2018年   87篇
  2017年   62篇
  2016年   86篇
  2015年   84篇
  2014年   116篇
  2013年   165篇
  2012年   218篇
  2011年   259篇
  2010年   132篇
  2009年   123篇
  2008年   220篇
  2007年   241篇
  2006年   250篇
  2005年   252篇
  2004年   228篇
  2003年   234篇
  2002年   224篇
  2001年   112篇
  2000年   89篇
  1999年   96篇
  1998年   74篇
  1997年   56篇
  1996年   45篇
  1995年   44篇
  1994年   36篇
  1993年   39篇
  1992年   63篇
  1991年   55篇
  1990年   69篇
  1989年   48篇
  1988年   48篇
  1987年   46篇
  1986年   42篇
  1985年   43篇
  1984年   18篇
  1983年   18篇
  1982年   12篇
  1981年   15篇
  1979年   13篇
  1978年   10篇
  1976年   8篇
  1974年   11篇
  1971年   7篇
  1967年   9篇
  1966年   8篇
排序方式: 共有4432条查询结果,搜索用时 0 毫秒
101.
102.
Holoprosencephaly (HPE) is a rare brain abnormality characterized by an incomplete cleavage of the primitive prosencephalon of forebrain during early embryogenesis. To determine the clinical characteristics and outcome of fetuses with HPE, we retrospectively analyzed nine patients who were prenatally diagnosed as fetal HPE by ultrasounds. The mean diagnostic weeks were 20 weeks of gestation. Two cases died within one day after birth. The chromosomal examinations were performed in seven cases (trisomy 18: n = 2; trisomy 13: n = 2; 45,XX,der(18)t(18;21)(p10;p10)mat: n = 1; normal karyotype: n = 2). In our HPE cases, most cases had serious facial anomalies and poor prognosis. Our data suggested that the early prenatal diagnosis of HPE allowed time for parental counseling and delivery planning.  相似文献   
103.
104.
Development and validation of a salmon prolactin radioimmunoassay   总被引:1,自引:0,他引:1  
A highly specific radioimmunoassay (RIA) for the measurement of prolactin (PRL) in the plasma and pituitary of salmonid fishes was developed using a rabbit antiserum to chinook salmon (Oncorhynchus tschawytscha) PRL. The PRLs purified from chinook salmon and chum salmon (O. keta) pituitaries showed exactly the same competitive inhibition curves in the RIA, regardless of iodination of either hormone. The displacement curves for pituitary extracts and plasma from several salmonids, including chum, coho, and amago salmon, rainbow trout, and Japanese charr, were parallel to the salmon PRL standard, whereas those from the eel, goldfish, carp, and tilapia showed negligible cross-reactivity. Negligible cross-reactivity was also seen with plasma from hypophysectomized rainbow trout or coho salmon. None of the mammalian PRL or growth hormone (GH) preparations, bullfrog PRL, or presumptive chum salmon "gonadotropin" and eel "PRL" cross-reacted in the PRL RIA. Presumptive chum salmon GH showed less than 0.05% cross-reactivity. The RIA sensitivity was less than 0.1 ng of the salmon PRL standard per milliliter. The immunoreactive plasma PRL levels in mature chum salmon were below 1 ng/ml in seawater. The plasma PRL in females increased to about 8 ng/ml 1 day after transfer to fresh water, and high levels (2-4 ng/ml) were maintained during 3-7 days after the transfer. In contrast, when males were transferred to fresh water, an increase in plasma PRL was seen only 1 day after the transfer. A significant decrease in plasma osmolality was observed in both males and females after transfer to fresh water. No change was observed either in plasma PRL or osmolality, when fish were transferred from seawater to seawater.  相似文献   
105.
Hepatocyte growth factor (HGF) is a potent mitogen for vascular endothelial cells (EC); however, signal transduction pathways for HGF-stimulated EC growth remain unclear. In the present study we investigated the role of Src family kinases and nitric oxide (NO) in HGF-stimulated EC growth. Human umbilical vein endothelial cells (HUVEC) were stimulated with HGF and NO was measured by an NOx analyzing HPLC system. Activation of ERK1/2 and p38 MAPK was assessed by Western blot. NO production in HUVEC increased 1.8-fold by HGF. A Src family kinases inhibitor PP1 inhibited HGF-stimulated NO production by 71%. HUVEC growth increased 1.9-fold in cell number by HGF. PP1 and Nitro-L-arginine methylester (L-NAME) inhibited HGF-stimulated HUVEC growth by 51 and by 71%. ERK1/2 and p38 MAPK were phosphorylated by HGF and a MEK inhibitor PD98059 and a p38 MAPK inhibitor SB203580 inhibited HGF-stimulated HUVEC growth by 66% and by 58%; however, HGF-induced phosphorylation of ERK1/2 and p38 MAPK was not inhibited by L-NAME, indicating that NO is not an upstream activator of ERK1/2 and p38 MAPK. These findings demonstrated that Src family kinases regulate HGF-stimulated NO production in HUVEC and that HGF stimulates HUVEC growth through NO-dependent and NO-independent pathways.  相似文献   
106.
[Purpose] This study aimed to use a thermograph to observe temperature changes caused by different distances between an ultrasound transducer and bone during 1 MHz and 3 MHz continuous ultrasound emission on a phantom. [Materials and Methods] We observed the distribution of temperature elevations on a phantom consisting of pig ribs and tissue-mimicking material. One megahertz and 3 MHz ultrasound were delivered at 2.0 W/cm2 for 5 minutes. To record the temperature changes on the phantom, we took a screenshot of the thermograph with a digital camera every 20 seconds. [Results] With 1 MHz ultrasound at the distances of 2 and 3 cm, the temperature elevation near the bone was higher than that near the transducer. However, with 3 MHz ultrasound, the temperature elevation was higher near the transducer rather than near the bone. At this point, we consider that there is a possibility of heat injury to internal organs in spite of there being no elevation of skin temperature. [Conclusion] When performing ultrasonic therapy, not only should the frequency be taken into consideration, but also the influence of the absorption coefficient and the reflection of the tissue. We visually confirmed the thermal ultrasound effect by thermography. Special attention to the temperature elevation of the internal organs is necessary to avoid injuries.Key words: Ultrasound, Thermal effect, Thermography  相似文献   
107.
We have reported that tumor necrosis factor (TNF)-alpha in skeletal muscle is one of the determinants of insulin resistance and that the renin-angiotensin system may be related to the regulation of TNF-a in skeletal muscle. Recent studies have suggested the involvement of cyclic adenosine monophosphate (cAMP) in the regulation of TNF-a in vascular smooth muscle cells or monocytes. The aim of this study was to determine the relationship between cAMP and TNF-a in skeletal muscle in connection with the renin-angiotensin system. Six-week-old male Sprague-Dawley rats were fed either normal rat chow or fructose-rich chow for 6 weeks. For the last 2 weeks of a 6-week period, the rats were treated with a vehicle or with an angiotensin II type 1 receptor antagonist (olmesartan medoxomil, 0.1 mg/kg/day). TNF-alpha levels in the soleus muscle were significantly higher and cAMP levels in the soleus muscle were significantly lower in fructose-fed rats than in control rats. Olmesartan increased cAMP and reduced TNF-a simultaneously in fructose-fed rats. There was a significant negative correlation between levels of cAMP and TNF-alpha. Moreover, a cAMP analogue reduced TNF-a levels in the soleus muscle. These results indicate that the increase in TNF-alpha via suppression of cAMP may affect the induction of insulin resistance. In addition, the facts that olmesartan increased cAMP and decreased TNF-alpha suggest that a part of the TNF-alpha regulation by angiotensin II might consist of modulation of cAMP through Gi protein activation in skeletal muscle.  相似文献   
108.
The effects of ethanol on gastric vasculature in isolated vascularly perfused rabbit stomach was investigated. The isolated stomach was perfused with Krebs-Henseleit solution containing 3% dextran bubbled with 95% O2 and 5% CO2 at a rate of 12 ml/min. After mixture and perfusion of 10 mM to 400 mM of ethanol, perfusion pressure and endothelin-1 concentration in effluent from gastric vasculature were measured. Perfusion pressure and endothelin-1 concentration in effluent increased in a dose-dependent manner with increasing ethanol concentrations. In conclusion, the data suggest that ethanol may stimulate the release of endothelin from gastric vasculature and may cause gastric ischemia due to vasoconstriction resulting in acute gastric mucosal injury.  相似文献   
109.
In patients in whom dynamic coronary obstruction plays a predominant role in the pathogenesis of angina pectoris, dilatation of large coronary arteries and relief of coronary spasm account for the main mechanism of action of antianginal drugs. In this study, the acute vasodilating effects of nicorandil, a newly developed antianginal drug, were assessed in 10 patients who had spontaneous and ergonovine-evoked coronary spasms. The prompt, complete relief of both spontaneous and evoked coronary spasms was obtained in all of 10 patients with nicorandil. The coronary spasmolytic effect of nicorandil in the present series is thus considered to be beneficial to the treatment of coronary spasm.  相似文献   
110.
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