全文获取类型
收费全文 | 8938篇 |
免费 | 876篇 |
国内免费 | 38篇 |
专业分类
耳鼻咽喉 | 76篇 |
儿科学 | 223篇 |
妇产科学 | 170篇 |
基础医学 | 1361篇 |
口腔科学 | 185篇 |
临床医学 | 980篇 |
内科学 | 2036篇 |
皮肤病学 | 119篇 |
神经病学 | 741篇 |
特种医学 | 416篇 |
外科学 | 1194篇 |
综合类 | 196篇 |
一般理论 | 7篇 |
预防医学 | 861篇 |
眼科学 | 91篇 |
药学 | 657篇 |
1篇 | |
中国医学 | 4篇 |
肿瘤学 | 534篇 |
出版年
2021年 | 128篇 |
2019年 | 109篇 |
2018年 | 119篇 |
2016年 | 78篇 |
2015年 | 114篇 |
2014年 | 159篇 |
2013年 | 216篇 |
2012年 | 335篇 |
2011年 | 398篇 |
2010年 | 200篇 |
2009年 | 191篇 |
2008年 | 316篇 |
2007年 | 307篇 |
2006年 | 324篇 |
2005年 | 350篇 |
2004年 | 313篇 |
2003年 | 310篇 |
2002年 | 270篇 |
2001年 | 308篇 |
2000年 | 283篇 |
1999年 | 264篇 |
1998年 | 162篇 |
1997年 | 109篇 |
1996年 | 118篇 |
1995年 | 103篇 |
1994年 | 106篇 |
1993年 | 110篇 |
1992年 | 234篇 |
1991年 | 220篇 |
1990年 | 224篇 |
1989年 | 201篇 |
1988年 | 205篇 |
1987年 | 212篇 |
1986年 | 223篇 |
1985年 | 200篇 |
1984年 | 145篇 |
1983年 | 164篇 |
1982年 | 106篇 |
1981年 | 111篇 |
1980年 | 88篇 |
1979年 | 145篇 |
1978年 | 142篇 |
1977年 | 111篇 |
1976年 | 110篇 |
1975年 | 105篇 |
1974年 | 118篇 |
1973年 | 107篇 |
1970年 | 79篇 |
1969年 | 74篇 |
1968年 | 73篇 |
排序方式: 共有9852条查询结果,搜索用时 765 毫秒
21.
J M Mason D A Grande M Barcia R Grant R G Pergolizzi A S Breitbart 《Gene therapy》1998,5(8):1098-1104
A commonly encountered problem in orthopedics is bone and cartilage tissue injury which heals incompletely or without full structural integrity. This necessitates development of improved methods for treatment of injuries which are not amenable to treatment using current therapies. An already large and growing number of growth factors which play significant roles in bone remodeling and repair have been identified in the past few years. It is well established that bone morphogenic proteins induce the production of new bone and cartilage. An efficient method of delivery of these growth factors by conventional pharmacological means has yet to be elucidated. We wished to evaluate the use of retroviral vector-mediated gene transfer to deliver genes of therapeutic relevance for bone and cartilage repair. To determine the feasibility of using amphotropically packaged retroviral vectors to transduce primary rabbit mesenchymal stem cells of periosteal origin, primary periosteal cells were isolated from New Zealand white rabbits, transduced in vitro with a retroviral vector bearing both the nuclear localized lacZ marker gene and the neo(r) gene, and selected in G418. We used a convenient model for analysis of in vivo stability of these cells which were seeded on to polymer scaffold grafts and implanted into rabbit femoral osteochondral defects. The nuclear localized beta-galactosidase protein was expressed in essentially 100% of selected cells in vitro and was observed in the experimental explants from animals after both 4 and 8 weeks in vivo, while cells transduced with a retroviral vector bearing only the neo(r) gene in negative control explants showed no blue staining. We extended our study by delivering a gene of therapeutic relevance, human bone morphogenic protein 7 (hBMP-7), to primary periosteal cells via retroviral vector. The hBMP-7 gene was cloned from human kidney 293 cell total RNA by RT-PCR into a retroviral vector under control of the CMV enhancer/promoter. Hydroxyapatite secretion, presumably caused by overexpression of hBMP-7, was observed on the surface of the transduced and selected periosteal cells, however, this level of expression was toxic to both PA317 producer and primary periosteal cells. Subsequently, the strong CMV enhancer/promoter driving the hBMP-7 gene was replaced in the retroviral vector by a weaker enhancer/promoter from the rat beta-actin gene. Nontoxic levels of expression of hBMP-7 were confirmed at both the RNA and protein levels in PA317 producer and primary periosteal cell lines and cell supernatants. This work demonstrates the feasibility of using a gene therapy approach in attempts to promote bone and cartilage tissue repair using gene-modified periosteal cells on grafts. 相似文献
22.
23.
While health promotion practitioners are engaging increasingly in research,
there has been little examination of the practical dilemmas they may face
in negotiating and collaborating with academics and community members in
action research projects. This paper analyses how the practice of health
promotion can interact with action research, and considers issues that
arise for organizationally based health promotion practitioners and
professional researchers. The first section charts types of action research
along three dimensions (power, goals/values, resources). The second section
examines some of the issues and practical dilemmas which arise in
negotiating and researching collaborative projects in community health
promotion. The discussion includes the differing perspectives of:
practitioners (managerial and frontline), community members and academic
researchers. The final section outlines a hybrid model of action research,
developed in our work with community members, organizationally based health
promoters and academy-based researchers. It combines the reflective
practice of practice-based action research with the community participation
and control of participatory research. The model is called community
reflective action research. 相似文献
24.
25.
26.
27.
Effects of two extracellular matrices on morphologic and biochemical properties of human type II cells in vitro 总被引:1,自引:0,他引:1
Previous observations have suggested that differentiated functions of adult rat type II alveolar cells are affected in part by cell-matrix interactions. We examined several aspects of differentiated adult human type II cells cultured on either bovine corneal endothelial cell extracellular matrix (BCECM) or matrix derived from the Englebreth-Holm-Swarm tumor (EHS). Compared to cells cultured on BCECM, adult human type II cells grown on EHS assumed a more cuboidal shape, had a more defined apical-basal polarity, and appeared to contain a greater number of lamellar bodies and neutral lipid inclusions. These cells also incorporated a greater percentage of [14C]acetate into saturated phosphatidylcholine (SPC) than did their counterparts grown on BCECM. In contrast, the relative incorporation of [14C]acetate into phosphatidylglycerol (PG) was lower in cells grown on EHS than cells cultured on BCECM. The histochemical stain for alkaline phosphatase was useful in identification of human type II cells. Alkaline phosphatase expression was elevated in cells cultured on EHS compared to those cultured on BCECM. These results suggest that maintenance of a differentiated morphology, lipid synthesis, and expression of alkaline phosphatase activity by primary cultures of adult human type II cells are also influenced by cell-matrix interactions. All markers of differentiated function of type II cells except synthesis of PG are better maintained on EHS than on BCECM. Under the conditions of these experiments, synthesis of SPC and PG appears to be independently regulated. 相似文献
28.
J C Mason K S Ordelheide G M Grames T V Thrasher R D Harris R H Bui M C Mackett 《Transplantation》1987,44(4):588-591
29.
30.