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   3623篇
  免费   274篇
  国内免费   110篇
耳鼻咽喉   11篇
儿科学   132篇
妇产科学   51篇
基础医学   461篇
口腔科学   79篇
临床医学   450篇
内科学   798篇
皮肤病学   33篇
神经病学   307篇
特种医学   164篇
外科学   449篇
综合类   147篇
预防医学   291篇
眼科学   27篇
药学   376篇
中国医学   6篇
肿瘤学   225篇
  2022年   32篇
  2021年   77篇
  2020年   34篇
  2019年   71篇
  2018年   65篇
  2017年   59篇
  2016年   73篇
  2015年   75篇
  2014年   89篇
  2013年   161篇
  2012年   206篇
  2011年   205篇
  2010年   125篇
  2009年   122篇
  2008年   169篇
  2007年   242篇
  2006年   167篇
  2005年   173篇
  2004年   167篇
  2003年   155篇
  2002年   122篇
  2001年   84篇
  2000年   80篇
  1999年   73篇
  1998年   76篇
  1997年   64篇
  1996年   65篇
  1995年   43篇
  1994年   42篇
  1993年   32篇
  1992年   47篇
  1991年   35篇
  1990年   67篇
  1989年   50篇
  1988年   59篇
  1987年   47篇
  1986年   35篇
  1985年   34篇
  1984年   24篇
  1982年   23篇
  1981年   29篇
  1980年   24篇
  1979年   41篇
  1978年   24篇
  1977年   24篇
  1976年   25篇
  1975年   23篇
  1973年   26篇
  1972年   28篇
  1971年   27篇
排序方式: 共有4007条查询结果,搜索用时 15 毫秒
51.
Basaloid squamous cell carcinoma (BSCC) is a rare form of cancer that arises primarily in the upper aerodigestive tract. Esophageal BSCC is extremely rare, accounting for less than 2% of primary esophageal malignancies. It is histopathologically distinct from squamous cell carcinoma and has an aggressive biological behavior with poor survival outcomes. There is no known association of Barrett’s esophagus with esophageal BSCC. Here, we report what we believe is the first such case of esophageal BSCC occurring in the setting of Barrett’s esophagus.  相似文献   
52.
Hypospadias trends in two US surveillance systems   总被引:6,自引:0,他引:6  
OBJECTIVE: Hypospadias is a common congenital anomaly, the cause of which is unknown. Unexplained increases in the rates of hypospadias occurred in five European countries in the 1970s and 1980s. We examined data from two birth defects surveillance systems in the United States for evidence of similar trends. METHODOLOGY: The Metropolitan Atlanta Congenital Defects Program (MACDP) provided birth prevalence rates from 1968 to 1993. The nationwide Birth Defects Monitoring Program (BDMP) provided rates from 1970 to 1993. MACDP data are population-based and could be categorized by the severity of the hypospadias. BDMP data allowed analysis of rate trends for the four census regions of the United States. RESULTS: Data from both surveillance systems showed an approximate doubling of hypospadias rates in the 1970s and 1980s. MACDP data showed that the rate of severe cases increased while the ratio of mild to severe cases decreased. BDMP data showed that hypospadias rates increased markedly in all four regions of the United States. CONCLUSIONS: The observed increases are unlikely to be attributable to increased sensitivity of the surveillance systems or the identification of more mild cases by physicians over time, because either trend would have increased rather than decreased the ratio of mild to severe cases. If real, these trends represent the largest number of cases and the first report of an increase in hypospadias rates outside of Europe. Additional investigation of a possible increase in hypospadias rates is warranted.  相似文献   
53.
Rogers  AE; Hafer  LJ; Iskander  YS; Yang  S 《Carcinogenesis》1998,19(7):1269-1273
Epidemiological studies suggest that tea may reduce cancer risk, and in laboratory rodents, chemopreventive effects of tea or purified extracts of tea have been demonstrated in lung, gastrointestinal tract and skin. There is some evidence of chemoprevention by tea in the mammary gland, but the data are not conclusive. In order to evaluate more fully the possible influence of black tea on 7,12-dimethylbenz[a]anthracene (DMBA)-induced mammary gland tumors in the female S-D (Sprague-Dawley) rat, three large studies were performed: experiment 1, tumorigenesis in rats fed AIN-76A diet and given 25 mg/kg DMBA and 1.25 or 2.5% whole tea extract or water to drink; experiment 2, tumorigenesis in rats given 15 mg/kg DMBA and the same diet and fluids as in experiment 1; experiment 3, tumorigenesis in rats fed control or HF (high fat, corn oil) diet and given 15 mg/kg DMBA and 2% tea or water to drink. Tea was given throughout the experiment; DMBA was given by gastric gavage at 8 weeks of age. There was no consistent effect of tea on tumorigenesis in rats fed AIN-76A diet; there was, however, evidence in experiment 3 of a reduction of tumorigenesis by tea in rats fed the HF diet. In experiment 3, rats fed the HF diet and given water showed the expected increase in tumor burden (number and weight) compared with rats fed control diet. However, rats fed the HF diet and given 2% tea showed no increase in tumor burden; their tumor burden was significantly lower than in rats fed the HF diet and given water (P < 0.01) and was not different from rats fed control diet and given water or tea. In addition, in experiment 3, the number of malignant tumors per tumor- bearing rat was increased by the HF diet in water-drinking rats (P < 0.01) but not in tea-drinking rats. Therefore, it appears that tea partially blocked the promotion of DMBA-induced mammary tumorigenesis by the HF diet.   相似文献   
54.
Cannabinoids have significant analgesic properties in animal models, particularly for chronic pain states, but there are few human studies. An endogenous cannabinoid system, with specific receptors and transmitters, has recently been discovered. This discovery has led pharmacologists to explore the potential of synthetic cannabinoids to selectively target chronic pain disorders without producing the side effects associated with cannabis. Well-controlled clinical trials on cannabinoids, and cannabinoid delivery systems, are now required.  相似文献   
55.
The nucleocapsid (N) protein of SARS-coronavirus (SARS-CoV) is the key protein for the formation of the helical nucleocapsid during virion assembly. This protein is believed to be more conserved than other proteins of the virus, such as spike and membrane glycoprotein. In this study, the N protein of SARS-CoV was expressed in Escherichia coli DHSalpha and identified with pooled sera from patients in the convalescence phase of SARS. A plasmid pCI-N, encoding the full-length N gene of SARS-CoV, was constructed. Expression of the N protein was observed in COS1 cells following transfection with pCI-N. The immune responses induced by intramuscular immunization with pCI-N were evaluated in a murine model. Serum anti-N immunoglobutins and splenocytes proliferative responses against N protein were observed in immunized BALB/c mice. The major immunoglobulin G subclass recognizing N protein was immunoglobulin G2a, and stimulated splenocytes secreted high levels of gamma interferon and IL-2 in response to N protein. More importantly, the immunized mice produced strong delayed-type hypersensitivity (DTH) and CD^8+ CTL responses to N protein.  相似文献   
56.
医学院学生及年轻医生应该在乡村及偏远地区的医院接受部分训练,此举有助于培养出更多适合在这些地区工作的医生。这是由爱丁堡皇家医学院组织的一项活动中提出的众多建议之一,该项目旨在考察苏格兰偏远地区医疗保健的可持续性问题。  相似文献   
57.
Interruption of the contrast column during inspiration can lead to non‐diagnostic CT pulmonary angiograms. The importance of this artefact will increase with more CT studies being performed for pulmonary embolism on multidetector row CT. We describe here an instance of such an artefact and discuss its aetiology.  相似文献   
58.
We report a case of an assisted pregnancy in an asymptomatic woman who was found to have an extrauterine mass on ultrasound and MRI. This complex mass had equivocal imaging features and was found to be a ruptured ovarian ectopic pregnancy at surgery. This case illustrates that vigilance is required regarding the possibility of coexisting ectopic and intrauterine pregnancy following assisted conception, even in entirely asymptomatic cases.  相似文献   
59.

Background

Asthma is an inflammatory condition characterized by airway hyperresponsiveness and chronic inflammation. The resolution of inflammation is an essential process to treat this condition. In this study we investigated the effect of Allium cepa L. extract (AcE) and quercetin (Qt) on cytokine and on smooth muscle contraction in vitro and its therapeutic potential in a murine model of asthma.

Methods

AcE was obtained by maceration of Allium cepa L. and it was standardized in terms of quercetin concentration using high performance liquid chromatography (HPLC). In vitro, using AcE 10, 100 or 1000 μg/ml or Qt 3.5, 7.5, 15 μg/ml, we measured the concentration of cytokines in spleen cell culture supernatants, and the ability to relax tracheal smooth muscle from A/J mice. In vivo, Blomia tropicalis (BT)-sensitized A/J mice were treated with AcE 100, 1000 mg/kg or 30 mg/kg Qt. We measured cell influx in bronchoalveolar lavage (BAL), eosinophil peroxidase (EPO) in lungs, serum levels of Bt-specific IgE, cytokines levels in BAL, and lung histology.

Results

We observed a reduction in the production of inflammatory cytokines, a relaxation of tracheal rings, and a reduction in total number of cells in BAL and EPO in lungs by treatment with AcE or Qt.

Conclusion

AcE and Qt have potential as antiasthmatic drugs, as they possess both immunomodulatory and bronchodilatory properties.  相似文献   
60.
为了寻找毒性低、增敏作用强的乏氧细胞放射增敏剂,设计并合成了一系列5-溴-,5-甲基-,和5-未取代的3-硝基-1,2,4-三唑-1-乙酰胺类化合物,用HeLaS3细胞进行了体外试验。结果表明5-溴取代衍生物的增敏作用强于相应的5-甲基-或5-未取代的硝基三唑衍生物,但是它们的毒性亦增大。修饰1位乙酰胺侧链也可以改变化合物的增敏作用和亲脂性。在所测定的化合物中TA-101[2-(3-硝基-1-三唑基)乙酰胺]由于有高的增敏作用和低亲脂性,可能是一个有希望的放射增敏剂。  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