全文获取类型
收费全文 | 6674篇 |
免费 | 692篇 |
国内免费 | 84篇 |
专业分类
耳鼻咽喉 | 9篇 |
儿科学 | 364篇 |
妇产科学 | 262篇 |
基础医学 | 1003篇 |
口腔科学 | 157篇 |
临床医学 | 672篇 |
内科学 | 1275篇 |
皮肤病学 | 213篇 |
神经病学 | 538篇 |
特种医学 | 497篇 |
外科学 | 655篇 |
综合类 | 171篇 |
一般理论 | 5篇 |
预防医学 | 671篇 |
眼科学 | 158篇 |
药学 | 383篇 |
2篇 | |
中国医学 | 15篇 |
肿瘤学 | 400篇 |
出版年
2021年 | 71篇 |
2020年 | 43篇 |
2019年 | 74篇 |
2018年 | 102篇 |
2017年 | 86篇 |
2016年 | 91篇 |
2015年 | 96篇 |
2014年 | 132篇 |
2013年 | 177篇 |
2012年 | 223篇 |
2011年 | 216篇 |
2010年 | 208篇 |
2009年 | 191篇 |
2008年 | 234篇 |
2007年 | 308篇 |
2006年 | 277篇 |
2005年 | 227篇 |
2004年 | 205篇 |
2003年 | 194篇 |
2002年 | 225篇 |
2001年 | 214篇 |
2000年 | 211篇 |
1999年 | 197篇 |
1998年 | 194篇 |
1997年 | 200篇 |
1996年 | 185篇 |
1995年 | 148篇 |
1994年 | 159篇 |
1993年 | 152篇 |
1992年 | 154篇 |
1991年 | 147篇 |
1990年 | 156篇 |
1989年 | 168篇 |
1988年 | 140篇 |
1987年 | 150篇 |
1986年 | 149篇 |
1985年 | 145篇 |
1984年 | 113篇 |
1983年 | 91篇 |
1982年 | 78篇 |
1981年 | 65篇 |
1980年 | 75篇 |
1979年 | 71篇 |
1978年 | 60篇 |
1977年 | 64篇 |
1976年 | 69篇 |
1975年 | 58篇 |
1974年 | 53篇 |
1973年 | 52篇 |
1972年 | 45篇 |
排序方式: 共有7450条查询结果,搜索用时 15 毫秒
11.
The Stafford outbreak of Legionnaires' disease 总被引:1,自引:0,他引:1
M C O'Mahony R E Stanwell-Smith H E Tillett D Harper J G Hutchison I D Farrell D N Hutchinson J V Lee P J Dennis H V Duggal 《Epidemiology and infection》1990,104(3):361-380
A large outbreak of Legionnaires' disease was associated with Stafford District General Hospital. A total of 68 confirmed cases was treated in hospital and 22 of these patients died. A further 35 patients, 14 of whom were treated at home, were suspected cases of Legionnaires' disease. All these patients had visited the hospital during April 1985. Epidemiological investigations demonstrated that there had been a high risk of acquiring the disease in the out patient department (OPD), but no risk in other parts of the hospital. The epidemic strain of Legionella pneumophila, serogroup 1, subgroup Pontiac 1a was isolated from the cooling water system of one of the air conditioning plants. This plant served several departments of the hospital including the OPD. The water in the cooling tower and a chiller unit which cooled the air entering the OPD were contaminated with legionellae. Bacteriological and engineering investigations showed how the chiller unit could have been contaminated and how an aerosol containing legionellae could have been generated in the U-trap below the chiller unit. These results, together with the epidemiological evidence, suggest that the chiller unit was most likely to have been the major source of the outbreak. Nearly one third of hospital staff had legionella antibodies. These staff were likely to have worked in areas of the hospital ventilated by the contaminated air conditioning plant, but not necessarily the OPD. There was evidence that a small proportion of these staff had a mild legionellosis and that these 'influenza-like' illnesses had been spread over a 5-month period. A possible explanation of this finding is that small amounts of aerosol from cooling tower sources could have entered the air-intake and been distributed throughout the areas of the hospital served by this ventilation system. Legionellae, subsequently found to be of the epidemic strain, had been found in the cooling tower pond in November 1984 and thus it is possible that staff were exposed to low doses of contaminated aerosol over several months. Control measures are described, but it was later apparent that the outbreak had ended before these interventions were introduced. The investigations revealed faults in the design of the ventilation system. 相似文献
12.
13.
Rosa M. Razaboni M. Alba Greco Alice D. Harper William W. Shaw Donald L. Ballantyne 《Microsurgery》1981,3(2):65-71
Segments 15 mm in length were excised from the femoral veins of rats and preserved by refrigeration at 4 C in lactated Ringer's solution for periods up to 21 days. The findings show that veins can be preserved for up to seven days and successfully grafted to recipients. Although there was some success in preserving vein segments for more than seven days, a high rate of thrombosis occurred after implantation in the recipients. It is generally accepted that damaged endothelium causes thrombosis. The light and electron microscopic observations in this study, however, suggest that the condition of the endothelium may not be the only important factor in the patency of small vessels. A thickened and prominent elastic lamina may also play a role in keeping the lumen open. 相似文献
14.
15.
Clare E Herbert Martin A Ebert D Barclay David S Whittall David J Joseph Chris S Harper Nigel A Spry 《Medical Dosimetry》2003,28(1):27-30
A previously developed method for achieving patient relocation in fractionated stereotactic radiotherapy (attachment of an infrared fiducial system to a bite tray) relies on the integrity of a bite tray system that incorporates moulding to the patient's upper dentition. Reproducible and accurate patient positioning requires stability of the bite tray and mould during the full treatment process, both during the time the bite tray is inserted in the patient's mouth, and between separate bite tray insertions. The optimum construction method for a stable reproducible tray has not been sufficiently investigated. We undertook a study to identify factors which might influence the integrity of the hard palate bite tray system. Reprosil Fast Set Putty was used to construct 3 impression conditions; teeth only; teeth and alveolar sulcus; and teeth, alveolar sulcus, and the hard palate. Reproducibility was assessed by volunteers inserting the impressions multiple times and recording the locations of 8 standard reference points. Our results showed the optimal impression technique (i.e., the one that led to the smallest ranges in positional and rotational errors) was that which incorporated the teeth, alveolar sulcus, and hard palate. 相似文献
16.
17.
18.
Mutagenesis of aspartic acid-116 enhances the ribonucleolytic activity and angiogenic potency of angiogenin. 总被引:7,自引:5,他引:2 下载免费PDF全文
J W Harper B L Vallee 《Proceedings of the National Academy of Sciences of the United States of America》1988,85(19):7139-7143
Site-specific mutagenesis of the blood vessel-inducing protein angiogenin has been used to further explore both its homology to pancreatic ribonuclease and the functional roles of particular residues. Replacement of Asp-116 in angiogenin by either asparagine (D116N), alanine (D116A), or histidine (D116H) markedly enhances both its ribonucleolytic activity and angiogenic potency. Activity toward tRNA is 8-, 15-, and 18-fold greater than native angiogenin for D116N-, D116A-, and D116H-angiogenin, respectively. The enzymatic specificity of angiogenin, however, has been maintained. Thus, cleavage of 18S and 28S rRNA by the most active His-116 mutant yields the same pattern of polynucleotide products as from angiogenin, whereas there are only minor alterations in activity with cytidylyl(3',5')adenosine and uridylyl(3',5')-adenosine. Extensive biological assays on the chicken embryo chorioallantoic membrane demonstrate that D116H-angiogenin is one to two orders of magnitude more potent in inducing neovascularization than native angiogenin, which correlates well with enhanced enzymatic action. These results support the proposition that the enzymatic and angiogenic activities on angiogenin are interrelated. 相似文献
19.
20.