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   8264篇
  免费   583篇
  国内免费   23篇
耳鼻咽喉   73篇
儿科学   240篇
妇产科学   203篇
基础医学   1217篇
口腔科学   75篇
临床医学   1259篇
内科学   1622篇
皮肤病学   115篇
神经病学   828篇
特种医学   266篇
外科学   701篇
综合类   81篇
一般理论   8篇
预防医学   991篇
眼科学   117篇
药学   485篇
中国医学   15篇
肿瘤学   574篇
  2023年   70篇
  2022年   116篇
  2021年   221篇
  2020年   126篇
  2019年   213篇
  2018年   238篇
  2017年   178篇
  2016年   197篇
  2015年   228篇
  2014年   268篇
  2013年   373篇
  2012年   588篇
  2011年   544篇
  2010年   309篇
  2009年   279篇
  2008年   472篇
  2007年   521篇
  2006年   431篇
  2005年   473篇
  2004年   453篇
  2003年   453篇
  2002年   378篇
  2001年   98篇
  2000年   88篇
  1999年   102篇
  1998年   83篇
  1997年   68篇
  1996年   61篇
  1995年   72篇
  1994年   42篇
  1993年   55篇
  1992年   48篇
  1991年   52篇
  1990年   62篇
  1989年   39篇
  1988年   44篇
  1987年   46篇
  1986年   50篇
  1985年   48篇
  1984年   52篇
  1983年   41篇
  1982年   42篇
  1981年   28篇
  1980年   30篇
  1979年   25篇
  1978年   28篇
  1976年   35篇
  1974年   29篇
  1973年   31篇
  1971年   29篇
排序方式: 共有8870条查询结果,搜索用时 0 毫秒
61.
62.
63.
64.
1. In the hog-cholera group the mutation from smooth (A) to granular (B) type occurs and a mutant with a moist, opaque colony formation was noted. 2. The B mutant when obtained pure remains a B type without reversion in the stock cultures. 3. The B mutant can be made to assume some of the A characters by rapid successive transplanting in bouillon. 4. The B mutant can usually be found in older transplants of A. 5. The two types may be distinguished by certain cultural characters, by slightly different agglutination reactions, and by different degrees of virulence.  相似文献   
65.
Increases in snack consumption associated with Westernized lifestyles provide an opportunity to introduce nutritious foods into poor diets. We describe two 10-wk-long open label, single group assignment human studies that measured the effects of two snack prototypes containing fiber preparations from two sustainable and scalable sources; the byproducts remaining after isolation of protein from the endosperm of peas and the vesicular pulp remaining after processing oranges for the manufacture of juices. The normal diets of study participants were supplemented with either a pea- or orange fiber-containing snack. We focused our analysis on quantifying the abundances of genes encoding carbohydrate-active enzymes (CAZymes) (glycoside hydrolases and polysaccharide lyases) in the fecal microbiome, mass spectrometric measurements of glycan structures (glycosidic linkages) in feces, plus aptamer-based assessment of levels of 1,300 plasma proteins reflecting a broad range of physiological functions. Computational methods for feature selection identified treatment-discriminatory changes in CAZyme genes that correlated with alterations in levels of fiber-associated glycosidic linkages; these changes in turn correlated with levels of plasma proteins representing diverse biological functions, including transforming growth factor type β/bone morphogenetic protein-mediated fibrosis, vascular endothelial growth factor-related angiogenesis, P38/MAPK-associated immune cell signaling, and obesity-associated hormonal regulators. The approach used represents a way to connect changes in consumer microbiomes produced by specific fiber types with host responses in the context of varying background diets.

Advances in our understanding of the role of the gut microbiome in regulating many aspects of human physiology hold the promise of evolving our view of human nutrition by establishing mechanistic connections between the foods we consume and how they affect health status. One manifestation of this effort is a series of studies, performed on well-phenotyped cohorts, that seek to relate features of gut microbial community composition (organisms, genes), dietary practices, and pre- and postprandial cardiometabolic responses to test meals (14). A key question raised by these initiatives relates to the nature of the “bioactive” components of foods. Specifically, what are the nutrients utilized by various gut community members or microbiome-encoded metabolic pathways? What products are produced by biotransformation of these nutrients? How are these products linked to specific host physiologic (or pathophysiologic) processes?Plant-derived dietary fibers represent a “poster child” for these efforts and illustrate the formidable challenges faced. The health benefits of dietary fibers are widely known, as is their inadequate representation in Western diets. However, natural fibers are structurally complex and highly diverse. They contain numerous, typically undefined polysaccharide structures and largely unspecified protein, lipid, and small molecule constituents. Their composition varies as a function of their origin (food staple and cultivar), the different methods employed to recover them from these sources, as well as the different techniques used to incorporate them into processed foods with acceptable organoleptic properties (5). Moreover, analyzing the host effects of metabolism of different fibers is confounded by the fact that there is substantial intra- and interpersonal variation in microbiome configuration (6, 7).Snacking is becoming an ever more dominant feature of daily life worldwide and thus provides an opportunity to introduce nutritious ingredients, such as fibers, into diets. However, obtaining structure-activity relationships for specific fiber types and their corresponding targets in the gut community is foundational for designing snack foods that evoke and/or reinforce microbiome responses that are beneficial to the host.Degradation of dietary polysaccharides is a function primarily performed by bacterial carbohydrate-active enzymes (CAZymes). The gut microbiome harbors tens of thousands of CAZyme genes belonging to at least 136 glycoside hydrolase (GH) and 29 polysaccharide lyase (PL) families [extrapolated and updated from El Kaoutari et al. (8)]. In contrast, the human genome only contains 98 GH and no PL genes (9), of which <20% contribute to the processing of dietary glycans.In the current study, we test the effects of dietary supplementation with two snack food prototypes, one containing pea fiber and the other orange fiber, in two pilot studies of overweight and obese individuals consuming their normal, unrestricted diets. Our strategy was to focus on fiber-associated changes in the abundances of microbial GH and PL genes to determine whether responses to the pea or orange fiber prototypes in the gut microbiome and host are decipherable against a background of varying dietary practices and starting microbiome configurations. Higher order singular value decomposition (10) was utilized as a feature selection tool to identify treatment-discriminating changes in GH and PL gene representation. Mass spectrometric assays of the levels of fecal glycan structures (glycosidic linkages) were subsequently performed and the results were correlated with changes in the abundances of treatment-discriminating GH and PL genes with known or predicted substrate specificities. Our analysis concluded by measuring changes in levels of 1,305 plasma proteins in each study participant as a function of fiber treatment and applying computational tools to identify links between these microbiome and plasma proteome changes in response to fiber consumption. Our results provide an approach, using pilot human studies, for selecting specific fiber preparations, plus informative microbiome and host biomarkers, that can be advanced to proof-of-concept clinical trials which assess their capacity for precise manipulation of microbiome and host features.  相似文献   
66.
Increased postmenopausal bone turnover leads to bone loss and fragility fracture risk. In the absence of osteoporosis, risk preventive measures, particularly those modifying nutritional lifestyle, are appropriate. We tested the hypothesis that milk supplementation affects bone turnover related to biochemical markers in a direction that, in the long term, may be expected to reduce postmenopausal bone loss. Thirty healthy postmenopausal women aged 59.3 (SD 3.3) years were enrolled in a prospective crossover trial of 16 weeks. After a 4-week period of adaptation with diet providing 600 mg calcium plus 300 mg ingested as 250 ml semi-skimmed milk, participants were maintained during 6 weeks under the same 600 mg calcium diet and randomized to receive either 500 ml semi-skimmed milk, thus providing a total of 1200 mg calcium, or no milk supplement. In the next 6 weeks they were switched to the alternative regimen. At the end of the each period, i.e. after 4, 10 and 16 weeks, blood and urinary samples were collected. The changes in blood variables between the periods of 6 weeks without and with milk supplementation were: for parathyroid hormone, -3.2 pg/ml (P=0.0054); for crosslinked telopeptide of type I collagen, -624 pg/ml (P<0.0001); for propeptide of type I procollagen, -5.5 ng/ml (P=0.0092); for osteocalcin, -2.8 ng/ml (P=0.0014). In conclusion, a 6-week period of milk supplementation induced a decrease in several biochemical variables compatible with diminished bone turnover mediated by reduction in parathyroid hormone secretion. This nutritional approach to postmenopausal alteration in bone metabolism may be a valuable measure in the primary prevention of osteoporosis.  相似文献   
67.
68.
Obesity has now emerged as 1 of the most serious public health problems facing American Indian (AI) children and adolescents. However, little is known about what factors contribute to the early development of obesity in AI children. This study explored the relationships between maternal prepregnancy BMI, feeding practices, and growth in AI infants. The findings of this study highlight the need for nurse midwives and pediatric nurse practitioners to increase AI mothers’ awareness about their feeding practices, exclusive breastfeeding, and timing for solid food introduction.  相似文献   
69.
70.
Health insurance coverage and the means by which it is paid have been topics of intense interest in recent years, but in the United States, creation of a uniform system for provision of medical care has been debated for nearly a century. During the Great Depression, before large group insurance plans, workers who formerly had been able to adequately support their families found themselves without employment or in low income jobs that barely put food on the table and a roof over their heads. Medical care was a luxury they could not afford. Health professionals suffered the effects of the economy too. Published in Public Health Nursing in 1936, this paper reflects a time period when the ravages of the Great Depression were manifest. California had received an influx of poor, migrant workers from other states hoping to provide for their families as pickers, canners, and manual laborers. The author, Marion E. Russell, described a 1935 health insurance proposal to cover all state residents. Selected excerpts illustrate differences in philosophy still evident in current considerations of national health care reform, particularly as related to mandated coverage. Russell worked in the State Relief Administration in San Francisco.  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