全文获取类型
收费全文 | 1479篇 |
免费 | 184篇 |
国内免费 | 75篇 |
专业分类
耳鼻咽喉 | 5篇 |
儿科学 | 23篇 |
妇产科学 | 9篇 |
基础医学 | 169篇 |
口腔科学 | 43篇 |
临床医学 | 222篇 |
内科学 | 354篇 |
皮肤病学 | 48篇 |
神经病学 | 83篇 |
特种医学 | 112篇 |
外科学 | 122篇 |
综合类 | 89篇 |
预防医学 | 112篇 |
眼科学 | 8篇 |
药学 | 166篇 |
中国医学 | 1篇 |
肿瘤学 | 172篇 |
出版年
2021年 | 18篇 |
2020年 | 9篇 |
2019年 | 19篇 |
2018年 | 23篇 |
2017年 | 19篇 |
2016年 | 27篇 |
2015年 | 20篇 |
2014年 | 24篇 |
2013年 | 61篇 |
2012年 | 64篇 |
2011年 | 59篇 |
2010年 | 56篇 |
2009年 | 50篇 |
2008年 | 41篇 |
2007年 | 106篇 |
2006年 | 70篇 |
2005年 | 60篇 |
2004年 | 57篇 |
2003年 | 54篇 |
2002年 | 56篇 |
2001年 | 48篇 |
2000年 | 58篇 |
1999年 | 43篇 |
1998年 | 32篇 |
1997年 | 36篇 |
1996年 | 35篇 |
1995年 | 37篇 |
1994年 | 15篇 |
1993年 | 29篇 |
1992年 | 29篇 |
1991年 | 30篇 |
1990年 | 25篇 |
1989年 | 38篇 |
1988年 | 27篇 |
1987年 | 28篇 |
1986年 | 30篇 |
1985年 | 31篇 |
1984年 | 15篇 |
1983年 | 23篇 |
1982年 | 21篇 |
1981年 | 15篇 |
1980年 | 14篇 |
1979年 | 10篇 |
1978年 | 17篇 |
1977年 | 11篇 |
1976年 | 12篇 |
1975年 | 19篇 |
1974年 | 11篇 |
1973年 | 9篇 |
1971年 | 8篇 |
排序方式: 共有1738条查询结果,搜索用时 15 毫秒
21.
22.
The evolution of baboon endogenous type C virus: related sequences in the DNA of distant species 总被引:9,自引:0,他引:9
The cellular DNA of species distantly related to the baboon have been tested for the presence of sequences related to baboon endogenous type C virus. Hybrids between viral cDNA and cellular DNA were detected using very low stringency hydroxyapatite conditions. The results confirm and extend the observation that the related sequences are more conserved in African primates than in non-African primates. Our data suggest that this result is due to unusual conservation of viral sequences in the African primates. Our assay is sufficiently sensitive to detect distantly related sequences in mouse type C viruses and in other primate endogenous viruses, including both the type C virus isolated from macaques (MAC-1) and the type D virus isolated from langurs (LAD-1). However, using baboon viral cDNA, we cannot distinguish human DNA from the DNA of several non-primate mammalian species. 相似文献
23.
R Leventhal H Bonner E J Soulsby A D Schreiber 《Clinical and experimental immunology》1978,32(1):69-76
The role of complement in the histopathology of primary and challenge re-infection by Ascaris suum was assessed. Guinea-pigs deficient in C4 or depleted of the terminal components C3 to C9 by cobra venom factor (CVF) were employed. Pathological changes in the livers of complement-deficient guinea-pigs differed slightly from controls. The most striking findings were in the lungs of CVF-treated infected animals, where marked eosinophilic abscesses were observed following either a primary or repeat infection with Ascaris suum. Additionally, greater numbers of larvae were harvested from the lungs of both CVF-treated and C4-deficient infected guinea-pigs as compared with controls. Serum C4 levels varied over the first 7 days after primary infection, declining in several of the normal and CVF-treated animals, but remaining stable in others. The C4 levels remained unchanged in re-infected animals. The C3 to C9 levels remained within the normal range in both primary and re-infected guinea-pigs. The data suggests that complement is involved in the host responses to infection with Ascaris suum. In the absence of complement (C3 to C9), enhanced pulmonary eosinophilic infiltration and eosinophilic granuloma formation occur in both primary and re-infected animals. 相似文献
24.
25.
RAJVIR BHALWAR HS SANDHU RC AHUJA GK SINGH RP MISRA 《Medical Journal Armed Forces India》1994,50(3):175-180
A population based hybrid design combining element of cohort and cross-sectional approach was used to develop a simple clinical algorithm to predict individual probability of developing hypertension (systolic BP > 140 mm Hg and/or diastolic BP > 90 mmHg). 3615 soldiers initially normotensive at the time of induction into high altitude, were studied by systematic random sampling. Multiple logistic regression analysis showed a high significant association between hypertension and age, body mass index (BMI), tobacco smoking and alcohol consumption. Using the constant/coefficient values obtained from the logistic model and the receiver operating characteristics (ROC) curve analysis, the following predictive rule was developed – To the age in years, add (BMIx 3.86); also add 5.53 if he is a smoker; and add 19.81 if he consumes alcohol. If the total exceeds 142, the individual is at high risk of developing hypertension. This algorithm carries a sensitivity of 68.2% and specificity of 78.5%.KEY WORDS: Hypertension, High altitude 相似文献
26.
M G Marin J Van Lieu A Yee E Bonner S Glied 《Journal of occupational and environmental medicine / American College of Occupational and Environmental Medicine》1999,41(9):754-760
We performed a cost-effectiveness analysis of a post-exposure chemoprophylaxis program for health care workers who sustained exposures to blood. We analyzed a program of (1) treatment with zidovudine alone versus no treatment and (2) treatment with three-drug therapy versus no treatment. Assuming that 35% of exposures were to HIV-positive sources, the zidovudine regimen prevented 53 HIV seroconversions per 100,000 exposures, at a societal cost of $2.0 million per case of HIV prevented. The cost per quality-adjusted life year saved was $175,222. A three-drug chemoprophylactic therapy program (postulating 100% effectiveness and 35% source HIV positivity), prevented 66 seroconversions per 100,000 exposures, at a cost of $2.1 million per case of HIV prevented and $190,392 per quality-adjusted life year saved. Treating sources known to be HIV-positive and treating severe exposures were the most cost-effective strategies. 相似文献
27.
The prevalence of microalbuminuria was assessed in 50 patients of non-insulin dependent diabetes mellitus. The mean age of patients was 52.1 ± 11.6 years and the duration of diabetes was 8.3 ± 6.8 years. Twenty (40%) patients had microalbuminuria. Microalbuminuria was more common in patients with a longer duration of diabetes (more than 5 years), a poor glycaemic control, and higher systolic blood pressure.KEY WORDS: Microalbuminuria, Diabetes mellitus, Diabetic nephropathy, Chronic renal failure 相似文献
28.
Recent investigations have emphasized the role of activated granulocytes in mediating vascular endothelial injury in the pathogenesis of shock lung. In vitro studies have indicated that tight adherence of the neutrophil to the endothelium is crucial for the development of cellular injury. Fibronectin is critical to cell-to- substratum and cell-to-cell interactions. Since fibronectin resides in plasma, on endothelial cell surfaces and is secreted into cell matrices, the adhesive properties of fibronectin must be modulated, lest universal cell agglomeration occur, yet be enhanced when cell attachment is appropriate. In these studies, treatment of fibronectin- coated surfaces with neutrophil release products increased the adhesion of activated neutrophils. Similarly, endothelial cells treated with neutrophil release products become a more adherent substrate for neutrophils. This enhanced adherence generated by treatment of fibronectin with neutrophil supernatants is inhibitable by heat and the lysosomal proteinase inhibitor, pepstatin-A. Neutrophil release products cause proteolytic fragmentation of fibronectin and enhanced fibronectin immunofluorescence on endothelial cells. In addition, neutrophils are more injurious to endothelial cells that have been pretreated with neutrophil release products. Neutrophils may enhance their own adherence to endothelial cells by altering fibronectin, and this altered, or "inflamed," fibronectin may serve as an amplifier of inflammation. 相似文献
29.
Interstitial pulmonary macrophages produce platelet-derived growth factor that stimulates rat lung fibroblast proliferation in vitro. 总被引:2,自引:0,他引:2
A R Brody J C Bonner L H Overby A Badgett V Kalter R K Kumar R A Bennett 《Journal of leukocyte biology》1992,51(6):640-648
Alveolar macrophages from humans and several animal species produce factors in vitro that modulate fibroblast growth and have been proposed as mediators of interstitial pulmonary fibrosis. Pulmonary interstitial macrophages (IMs) have not been studied previously in this regard. Pulmonary IMs were isolated from prelavaged rat lungs by enzymatic digestion of tissue and subsequent differential adherence of cells to culture dishes. The ability of IMs to release modulators of fibroblast growth into the culture medium was assessed by measuring [3H]thymidine incorporation into DNA and/or nuclear labeling of early-passage rat lung fibroblasts exposed to medium conditioned by IMs. The percentages of nuclei labeled in fibroblast cultures exposed to interstitial macrophage-conditioned medium (IMCM) alone did not significantly differ from that observed in controls, but fibroblasts exposed to IMCM supplemented with 2% platelet-poor plasma showed a 2.6-fold increase in labeling, indicating that IMCM contains predominantly "competence" growth factor activity. Similar results were obtained using purified human platelet-derived growth factor (PDGF). The level of growth factor activity released by IMs increased in cells that had phagocytized iron spheres during the culture period. In addition, fractionation of IMCM by high-performance liquid chromatography demonstrated most of the growth factor activity at a relative molecular mass of about 35 kd. Subsequent quantitative analysis of the fractions by an enzyme immunoassay for PDGF demonstrated that IMCM contains a homologue of human PDGF. These results show that IMs are capable of producing a PDGF-like growth factor for autologous fibroblasts and that release of this factor is enhanced by exposure to an insoluble inorganic particle. Because PDGF is a potent growth factor for fibroblasts and is released by IMs, it is essential to ask in future studies whether this or similar macrophage products play a significant role in mediating fibroblast proliferation in vivo. 相似文献
30.
Bingham D Bonner PT Cox R Edwards AA Gardin I Haines JW Harrison JD 《International journal of radiation biology》2000,76(9):1223-1231
PURPOSE: To assess the ability of the Auger-emitting nuclide, zinc-65 (65Zn), relative to gamma-irradiation, to cause chromosomal aberrations in cultured rat prostate cells. MATERIALS AND METHODS: Rat prostate adenocarcinoma cells in culture were exposed to doses of 1, 2, 3 or 5 Gy of external gamma-irradiation for 24h or incubated with 0.7, 1.5, 1.8 or 2.8 MBq of 65Zn for 24 h. The uptake by and clearance from cells of 65Zn was measured. Metaphase spreads prepared from washed cells were scored for chromatid- and chromosome-type aberrations. RESULTS: Following exposure to 65Zn or gamma-irradiation, chromatid-type damage was more commonly observed than chromosome-type aberrations. The relationship between induced chromatid damage and gamma dose (to 3 Gy) was best fitted by a second-order polynomial function, while the activity response relationship for chromatid damage caused by 65Zn appeared to be best fitted by a straight line. Measurements of the uptake of 65Zn by cells showed that average concentrations within cells were about 100 times the concentration in the culture medium. Assuming uniform distribution of 65Zn within cells, with 36% in the nucleus, the dose was estimated as 0.70 Gy per MBq added 65Zn, with Auger electrons contributing most (93%) of the dose. Assuming that 20% of cellular zinc was localized in the nucleus, based on previous measurements, the dose to the nucleus was calculated as 0.44 Gy per MBq added 65Zn. RBE values for chromatid damage induced by 65Zn compared to gamma-radiation range from about 1 to 3 based on a uniform dose throughout the cell and from about 2 to 5 based on 20% of 65Zn in the cell nucleus. CONCLUSION: The observed radiotoxicity of 65Zn is consistent with its behaviour as an Auger-emitting radionuclide that is localized to some extent in the nucleus. 相似文献