全文获取类型
收费全文 | 4332篇 |
免费 | 339篇 |
国内免费 | 19篇 |
专业分类
耳鼻咽喉 | 26篇 |
儿科学 | 148篇 |
妇产科学 | 210篇 |
基础医学 | 624篇 |
口腔科学 | 124篇 |
临床医学 | 507篇 |
内科学 | 709篇 |
皮肤病学 | 45篇 |
神经病学 | 339篇 |
特种医学 | 141篇 |
外科学 | 585篇 |
综合类 | 89篇 |
一般理论 | 1篇 |
预防医学 | 423篇 |
眼科学 | 117篇 |
药学 | 275篇 |
中国医学 | 9篇 |
肿瘤学 | 318篇 |
出版年
2021年 | 58篇 |
2020年 | 42篇 |
2019年 | 57篇 |
2018年 | 63篇 |
2017年 | 38篇 |
2016年 | 54篇 |
2015年 | 47篇 |
2014年 | 76篇 |
2013年 | 158篇 |
2012年 | 186篇 |
2011年 | 171篇 |
2010年 | 120篇 |
2009年 | 115篇 |
2008年 | 170篇 |
2007年 | 179篇 |
2006年 | 164篇 |
2005年 | 151篇 |
2004年 | 157篇 |
2003年 | 143篇 |
2002年 | 125篇 |
2001年 | 122篇 |
2000年 | 125篇 |
1999年 | 97篇 |
1998年 | 58篇 |
1997年 | 49篇 |
1996年 | 56篇 |
1995年 | 55篇 |
1994年 | 50篇 |
1993年 | 40篇 |
1992年 | 124篇 |
1991年 | 109篇 |
1990年 | 117篇 |
1989年 | 102篇 |
1988年 | 98篇 |
1987年 | 114篇 |
1986年 | 67篇 |
1985年 | 107篇 |
1984年 | 77篇 |
1983年 | 77篇 |
1982年 | 46篇 |
1981年 | 44篇 |
1980年 | 54篇 |
1979年 | 87篇 |
1978年 | 57篇 |
1977年 | 38篇 |
1976年 | 32篇 |
1975年 | 32篇 |
1972年 | 38篇 |
1970年 | 45篇 |
1967年 | 36篇 |
排序方式: 共有4690条查询结果,搜索用时 15 毫秒
171.
L. Samuel C. H. Basch D. Ethan R. Hammond K. Chiazzese 《Journal of community health》2014,39(4):775-782
Americans’ consumption of sodium, fat, and saturated fat exceed federally recommended limits for these nutrients and has been identified as a preventable leading cause of hypertension and cardiovascular disease. More than 40 % of the Bronx population comprises African–Americans, who have increased risk and earlier onset of hypertension and are also genetically predisposed to salt-sensitive hypertension. This study analyzed nutrition information for packaged foods advertised in Bronx-based supermarket circulars. Federally recommended limits for sodium, saturated fat and total fat contents were used to identify foods that were high in these nutrients. The proportion of these products with respect to the total number of packaged foods was calculated. More than a third (35 %) and almost a quarter (24 %) of the 898 advertised packaged foods were high in saturated fat and sodium respectively. Such foods predominantly included processed meat and fish products, fast foods, meals, entrees and side dishes. Dairy and egg products were the greatest contributors of high saturated fat. Pork and beef products, fast foods, meals, entrees and side dishes had the highest median values for sodium, total fat and saturated fat content. The high proportion of packaged foods that are high in sodium and/or saturated fat promoted through supermarket circulars highlights the need for nutrition education among consumers as well as collaborative public health measures by the food industry, community and government agencies to reduce the amounts of sodium and saturated fat in these products and limit the promotion of foods that are high in these nutrients. 相似文献
172.
Retention of motor adaptation is evident in savings, where initial learning improves subsequent learning, and anterograde interference, where initial learning impairs subsequent learning. Previously, we proposed that use‐dependent movement biases induced by movement repetition contribute to anterograde interference, but not to savings. Here, we evaluate this proposal by limiting or extending movement repetition while stimulating the motor cortex (M1) with anodal transcranial direct current stimulation (tDCS), a brain stimulation technique known to increase use‐dependent plasticity when applied during movement repetition. Participants first adapted to a counterclockwise rotation of visual feedback imposed either abruptly (extended repetition) or gradually (limited repetition) in a first block (A1), during which either sham or anodal tDCS (2 mA) was applied over M1. Anterograde interference was then assessed in a second block (B) with a clockwise rotation, and savings in a third block (A2) with a counterclockwise rotation. Anodal M1 tDCS elicited more anterograde interference than sham stimulation with extended but not with limited movement repetition. Conversely, anodal M1 tDCS did not affect savings with either limited or extended repetition of the adapted movement. Crucially, the effect of anodal M1 tDCS on anterograde interference did not require large errors evoked by an abrupt perturbation schedule, as anodal M1 tDCS combined with extended movement repetition within a gradual perturbation schedule similarly increased anterograde interference but not savings. These findings demonstrate that use‐dependent plasticity contributes to anterograde interference but not to savings. 相似文献
173.
Spread of X inactivation on chromosome 15 is associated with a more severe phenotype in a girl with an unbalanced t(X; 15) translocation
下载免费PDF全文
![点击此处可从《American journal of medical genetics. Part A》网站下载免费的PDF全文](/ch/ext_images/free.gif)
174.
B-cell growth factor receptor expression and B-cell growth factor response of leukemic B cell precursors and B lineage lymphoid progenitor cells 总被引:8,自引:1,他引:8
Uckun FM; Fauci AS; Heerema NA; Song CW; Mehta SR; Gajl-Peczalska K; Chandan M; Ambrus JL 《Blood》1987,70(4):1020-1034
The purpose of this study was to analyze the expression of B cell growth factor (BCGF) receptors and to elucidate the biologic effects of biochemically purified natural BCGF at the B cell precursor stage of human B lineage lymphoid differentiation. The specific binding of radioiodinated high-mol-wt BCGF (125I-HMW-BCGF) and low-molecular-wt BCGF (125I-LMW-BCGF) to fresh marrow blasts from B cell precursor acute lymphoblastic leukemia (ALL) patients was initially investigated. The estimated number of radioiodinated BCGF molecules bound per blast ranged from undetectable to 24.3 X 10(3) for HMW-BCGF, and from 11.5 X 10(3) to 457.8 X 10(3) for LMW-BCGF. In 3H-TdR incorporation assays, 75% of cases showed a significant response to LMW-BCGF with a median stimulation index of 9.3. By comparison, only 33% of cases showed a significant response to HMW-BCGF with a median stimulation index of 2.4. Subsequently, B cell precursor colony assays were performed to assess and compare the biologic effects of BCGF on leukemic B lineage lymphoid progenitor cells. Among 28 cases studied, 57% responded to both HMW-BCGF and LMW-BCGF, 21% responded only to LMW-BCGF, and the remaining cases showed no proliferative response to either growth factor. The response patterns of virtually pure populations of FACS- sorted leukemic B cell precursors were essentially identical to the proliferative responses of unsorted leukemic B-cell precursors. Synergistic effects between HMW-BCGF and LMW-BCGF were observed in 80% of the cases that responded to both. The numbers of cell-bound radioiodinated BCGF molecules, the stimulation indices, as well as the number of B cell precursor colonies in BCGF-stimulated cultures showed a marked interpatient variation. Patients with structural chromosomal abnormalities (SCAs) involving 12p11-13 or patients with a Philadelphia chromosome showed a greater HMW-BCGF response at the level of leukemic progenitor cells than did other patients (P = .02). The LMW-BCGF response was significantly greater for patients with SCA than for patients without SCA (P = .04). The response of leukemic progenitor cells to HMW-BCGF or LMW-BCGF did not correlate with sex, age, disease status, FAB morphology, WBC at diagnosis, or immunophenotype. To our knowledge, this study represents the first detailed analyses of BCGF receptor expression and BCGF effects in B cell precursor ALL. The data presented provide direct evidence for the expression of functional receptors for both HMW-BCGF and LMW-BCGF in B cell precursor ALL. 相似文献
175.
The use of 7-amino actinomycin D in identifying apoptosis: simplicity of use and broad spectrum of application compared with other techniques 总被引:9,自引:5,他引:9
Philpott NJ; Turner AJ; Scopes J; Westby M; Marsh JC; Gordon-Smith EC; Dalgleish AG; Gibson FM 《Blood》1996,87(6):2244-2251
The detection and quantitation of apoptotic cells is becoming increasingly important in the investigation of the role of apoptosis in cellular proliferation and differentiation. The pathogenesis of hematologic disorders such as aplastic anemia and the development of neoplasia are believed to involve dysregulation of apoptosis. To quantitate accurately the proportion of apoptosis cells within different cell types of a heterogeneous cell population such as blood or bone marrow, a method is required that combines the analysis of large numbers of cells with concurrent immunophenotyping of cell surface antigens. In this study, we have evaluated such a method using the fluorescent DNA binding agent, 7-amino actinomycin D (7AAD), to stain three diverse human cell lines, induced to undergo apoptosis by three different stimuli. Flow cytometric analysis defines three populations on the basis of 7AAD fluorescence and forward light scatter. We have shown by cell sorting and subsequent morphological assessment and terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end labeling that the populations defined by 7AAD represent live, apoptotic, and late-apoptotic/dead cells. This method is quick, simple, reproducible, and cheap and will be a valuable tool in the investigation of the role of apoptosis in normal physiology and in disease states. 相似文献
176.
177.
178.
179.
The ts mutant F1 of vesicular stomatitis virus, New Jersey serotype, directs the synthesis of undermethylated 5'-terminal cap structures in vitro. In order to determine the relationship between the ts and hypomethylation phenotypes, a spontaneous revertant rev(ts)F1 of the ts phenotype was analyzed. The revertant retained the hypomethylation phenotype. The four cap structures (GpppA, 7mGpppA, GpppAm, and 7mGpppAm) synthesized in mutant and revertant-directed reactions in the presence of low as well as high concentrations of AdoMet were resolved by HPLC. Quantitation of the data and analysis of cap substrate to product ratios revealed that despite apparent similarities between the two hypomethylation phenotypes, the functional lesions in F1 and rev(ts)F1 were different. F1 displayed an AdoMet concentration-dependent alteration in the GpppA----GpppAm reaction and an AdoMet concentration-independent alteration in the GpppA----7mGpppA reaction. In contrast, rev(ts)F1 displayed AdoMet concentration-dependent alterations in the reactions GpppA----7mGpppA and GpppAm----7mGpppAm. 相似文献