全文获取类型
收费全文 | 69693篇 |
免费 | 6890篇 |
国内免费 | 108篇 |
专业分类
耳鼻咽喉 | 508篇 |
儿科学 | 2149篇 |
妇产科学 | 1477篇 |
基础医学 | 9494篇 |
口腔科学 | 1468篇 |
临床医学 | 9415篇 |
内科学 | 13189篇 |
皮肤病学 | 1179篇 |
神经病学 | 6158篇 |
特种医学 | 2265篇 |
外国民族医学 | 1篇 |
外科学 | 8519篇 |
综合类 | 1359篇 |
一般理论 | 66篇 |
预防医学 | 8559篇 |
眼科学 | 1235篇 |
药学 | 5277篇 |
中国医学 | 96篇 |
肿瘤学 | 4277篇 |
出版年
2022年 | 518篇 |
2021年 | 1346篇 |
2020年 | 915篇 |
2019年 | 1378篇 |
2018年 | 1610篇 |
2017年 | 1171篇 |
2016年 | 1273篇 |
2015年 | 1390篇 |
2014年 | 1940篇 |
2013年 | 2820篇 |
2012年 | 4153篇 |
2011年 | 4246篇 |
2010年 | 2313篇 |
2009年 | 2133篇 |
2008年 | 3645篇 |
2007年 | 3838篇 |
2006年 | 3642篇 |
2005年 | 3432篇 |
2004年 | 3134篇 |
2003年 | 2890篇 |
2002年 | 2836篇 |
2001年 | 1656篇 |
2000年 | 1578篇 |
1999年 | 1596篇 |
1998年 | 794篇 |
1997年 | 629篇 |
1996年 | 595篇 |
1995年 | 583篇 |
1994年 | 526篇 |
1993年 | 559篇 |
1992年 | 1254篇 |
1991年 | 1164篇 |
1990年 | 1104篇 |
1989年 | 1066篇 |
1988年 | 982篇 |
1987年 | 982篇 |
1986年 | 998篇 |
1985年 | 914篇 |
1984年 | 799篇 |
1983年 | 647篇 |
1982年 | 451篇 |
1981年 | 367篇 |
1979年 | 599篇 |
1978年 | 491篇 |
1977年 | 379篇 |
1976年 | 393篇 |
1974年 | 440篇 |
1973年 | 407篇 |
1972年 | 390篇 |
1969年 | 358篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
921.
Kumanyika SK Adams-Campbell L Van Horn B Ten Have TR Treu JA Askov E Williams J Achterberg C Zaghloul S Monsegu D Bright M Stoy DB Malone-Jackson M Mooney D Deiling S Caulfield J 《Journal of the American Dietetic Association》1999,99(11):1380-1391
OBJECTIVE: To evaluate a cardiovascular nutrition education package designed for African-American adults with a wide range of literacy skills. DESIGN: Comparison of a self-help group and a full-instruction group; each group received nutrition counseling and clinical monitoring every 4 months. SUBJECTS: Three hundred thirty African-American adults, aged 40 to 70 years, with elevated cholesterol level or high blood pressure were randomly assigned to the self-help or full-instruction group; 255 completed the 12-month follow-up. INTERVENTIONS: Counseling to reduce intake of dietary fat, cholesterol, and sodium was based on Cardiovascular Dietary Education System (CARDES) materials, which included food-picture cards, a nutrition guide (self-help and full-instruction group), a video and audiotape series, and 4 classes (full-instruction group only). MAIN OUTCOME MEASURES: Changes in lipid levels and blood pressure after 12 months. STATISTICAL ANALYSES PERFORMED: Primary analyses consisted of repeated-measures analysis of variance to examine effects of time and randomization group on outcomes. RESULTS: Total cholesterol and low-density lipoprotein cholesterol level decreased by 7% to 8% in the self-help and full-instruction groups of men and women (P < .01). The ratio of total cholesterol to high-density lipoprotein cholesterol (HDL-C) decreased in both groups of women and in the men in the full-instruction group (P < .01). In full-instruction and self-help participants with elevated blood pressure at baseline, systolic blood pressure decreased by 7 to 11 mm Hg and diastolic blood pressure decreased by 4 to 7 mm Hg (P < .01). Outcomes did not differ by literacy scores but were positively related to the reported initial frequency of using CARDES materials. APPLICATIONS/CONCLUSIONS: These results suggest that periodic nutrition counseling based on CARDES materials used for home study can enhance management of lipid levels and blood pressure in African-American outpatients. 相似文献
922.
Maternal second trimester serum tumor necrosis factor-alpha-soluble receptor p55 (sTNFp55) and subsequent risk of preeclampsia 总被引:1,自引:0,他引:1
Williams MA Farrand A Mittendorf R Sorensen TK Zingheim RW O'Reilly GC King IB Zebelman AM Luthy DA 《American journal of epidemiology》1999,149(4):323-329
Preeclampsia is characterized by diffuse vascular endothelial dysfunction. Tumor necrosis factor-alpha (TNF-alpha), which plays a key role in the cytokine network responsible for immunoregulation, is also known to contribute to endothelial dysfunction and other metabolic disturbances noted in preeclampsia. Results from cross-sectional studies and one longitudinal study indicate that TNF-alpha (or its soluble receptor, sTNFp55) is increased in the peripheral circulation and amniotic fluid of women with preeclampsia as compared with normotensive women. Between December 1993 and August 1994, prediagnostic sTNFp55 concentrations (a marker of excessive TNF-alpha release) were measured in 35 women with preeclampsia and 222 normotensive women to determine whether elevations precede the clinical manifestation of the disorder. Logistic regression procedures were used to calculate maximum likelihood estimates of odds ratios and 95% confidence intervals. Mean second trimester (15-22 weeks' gestation) serum sTNFp55 concentrations, measured by enzyme-linked immunosorbent assay, were 14.4% higher in preeclamptic women than in normotensive controls (716.6 pg/ml (standard deviation 193.6) vs. 626.4 pg/ml (standard deviation 158.0); p = 0.003). The relative risk of preeclampsia increased across successively higher quintiles of sTNFp55 (odds ratios were 1.0, 1.3, 2.1, and 3.7, with the lowest quintile used as the referent; p for trend = 0.007). After adjustment for maternal age, adiposity, and parity, the relative risk between extreme quintiles was 3.3 (95% confidence interval 0.8-13.4). These findings indicate that the level of TNF-alpha in maternal circulation is increased prior to the clinical manifestation of the disorder, and they are consistent with the hypothesized role of cytokines in mediating endothelial dysfunction and the pathogenesis of preeclampsia. Further work is needed to identify modifiable risk factors for the excessive synthesis and release of TNF-alpha in pregnancy, and to assess whether lowering of TNF-alpha concentrations in pregnancy alters the incidence and severity of preeclampsia. 相似文献
923.
Giesy JP Kannan K Kubitz JA Williams LL Zabik MJ 《Archives of environmental contamination and toxicology》1999,36(4):432-446
Concentrations of polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs) were measured in dorsal muscle and eggs of coho salmon, lake trout, and chinook
salmon collected from Lakes Superior, Michigan, and Huron (Michigan waters). Absolute and relative concentrations of PCDDs
and PCDFs varied among sampling locations (inter- and intralake) and fish species. Fish collected from Bay City (Saginaw Bay)
contained the greatest concentrations of PCDDs and PCDFs both in muscle and eggs. Among the three fish species, chinook salmon
accumulated greater concentrations than did coho salmon or lake trout. Concentrations of PCDFs were greater than those of
PCDDs in all fishes. OCDF and TCDF were the predominant congeners of PCDF, whereas OCDD and TCDD concentrations predominated
in PCDDs. Homolog compositions of PCDDs and PCDFs suggested the existence of multiple local sources in various locations.
Concentrations of PCDDs and PCDFs in eggs of fishes were significantly correlated with those in muscle.
Received: 2 May 1998/Accepted: 20 December 1998 相似文献
924.
Effects of Mercury on Health and First-Year Survival of Free-Ranging Great Egrets (Ardea albus) from Southern Florida 总被引:1,自引:0,他引:1
M. S. Sepúlveda G. E. Williams Jr. P. C. Frederick M. G. Spalding 《Archives of environmental contamination and toxicology》1999,37(3):369-376
The objectives of this study were to determine whether elevated mercury (Hg) concentrations have a negative impact on the
health and survival of nestling and juvenile free-ranging great egrets (Ardea albus) from southern Florida. During 1994, when health and survival was monitored in a cohort of young birds with naturally variable
concentrations of Hg, packed cell volume was positively correlated with blood Hg concentrations, and high Hg concentration
in blood was not related to the probability of surviving during the first 10.5 months of life. During 1995, 70 first-hatched
great egret chicks were included in a Hg field-dosing experiment to compare the effects of elevated Hg on health and survival.
Birds were dosed while in the nest orally every 2.5 days for 15 days with 0.5 mg of methyl mercury chloride (MeHgCl) for an
estimated intake of 1.54 mg MeHgCl/kg food intake. These birds were compared with controls, which received an estimated 0.41
mg MeHgCl/kg food. No differences were observed in health parameters or in the probability of surviving during the first 8
months of age between egrets that were dosed with Hg and those that were not. A likely explanation for the lack of any effects
on health and survival between both groups could be that chicks at this age were eliminating most of the dietary Hg through
the production of new feathers.
Received: 10 November 1998/Accepted: 8 April 1999 相似文献
925.
926.
927.
K G Jackson A Zampelas J M Knapper C C Culverwell J Wright B J Gould C M Williams 《The British journal of nutrition》1999,81(1):51-57
The extent and duration of postprandial lipaemia have been linked to risk of CHD but the influence of dietary variables on, and the relative contributions of, exogenous (chylomicron) and endogenous (VLDL) triacylglycerols to the total lipaemic response have not been comprehensively evaluated. In the present study the triacylglycerol, apolipoprotein (apo) B-48 and retinyl ester (RE) responses to three test meals of varying monounsaturated (MUFA) and saturated fatty acid (SFA) content were measured in the triacylglycerol-rich lipoprotein (TRL) fraction of plasma (rho = 1.006 g/ml) for 9 h after meal consumption. Fifteen healthy normolipidaemic young men consumed, on separate occasions, three test meals which were identical apart from their MUFA and SFA contents. Expressed as a percentage of total energy the MUFA/SFA contents of the meals were: (1) 12%/17%; (2) 17%/12% and (3) 24%/5%. The contribution of the intestinally-derived lipoproteins (chylomicrons) to the lipaemic response was investigated by determining the time to reach peak concentration and the total and incremental areas under the time response curves (AUC and incremental AUC) for RE, apoB-48 and triacylglycerol in the TRL fraction. No significant differences in these measurements were observed for the three meals. However, visual comparison of the postprandial responses to the three meals suggested that as meal MUFA content increased there was a tendency for the triacylglycerol, apoB-48 and RE responses to become biphasic as opposed to the typical monophasic response seen with the 12% MUFA/17% SFA meal. Comparison of the apoB-48 and RE responses for the three test meals confirmed other workers' findings of delayed entry of RE relative to apoB-48 in TRL. The value of the two markers in investigating dietary fat absorption and metabolism is discussed. 相似文献
928.
Lee CM Boileau AC Boileau TW Williams AW Swanson KS Heintz KA Erdman JW 《The Journal of nutrition》1999,129(12):2271-2277
Foods containing provitamin A carotenoids are the primary source of vitamin A in many countries, despite the poor bioavailability of carotenoids. In addition, epidemiologic studies suggest that dietary intake of carotenoids influences the risk for certain types of cancer, cardiovascular disease and other chronic diseases. Although it would be ideal to use humans directly to answer critical questions regarding carotenoid absorption, metabolism and effects on disease progression, appropriate animal models offer many advantages. This paper will review recent progress in the development of animal models with which to study this class of nutrients. Each potential model has strengths and weaknesses. Like humans, gerbils, ferrets and preruminant calves all absorb beta-carotene (betaC) intact, but only gerbils and calves convert betaC to vitamin A with efficiency similar to that of humans. Mice and rats efficiently convert betaC to vitamin A but absorb carotenoids intact only when they are provided in the diet at supraphysiologic levels. Mice, rats and ferrets can be used to study cancer, whereas primates and gerbils are probably more appropriate for studies on biomarkers of heart disease. No one animal model completely mimics human absorption and metabolism of carotenoids; thus the best model must be chosen with consideration of the specific application being studied, characteristics of the model, and the available funding and facilities. 相似文献
929.
930.
Levin JL O'Sullivan MF Corn CJ Williams MG Dodson RF 《Occupational and environmental medicine》1999,56(9):602-605
OBJECTIVES: To present a case of asbestosis and small cell lung cancer caused by asbestos in a clutch refabricator. METHODS: Exposed surfaces of used clutches similar to those refabricated in the worker's workplace were rinsed, and the filtrate analysed by analytical transmission electron microscopy. Tissue samples were also analysed by this technique. RESULTS: Numerous chrysotile fibres of respirable dimensions and sufficient length to form ferruginous bodies (FBs) were detected from rinsed filtrates of the clutch. Bronchoalveolar lavage fluid contained many FBs, characteristic of asbestos bodies. Necropsy lung tissue showed grade 4 asbestosis and a small cell carcinoma in the right pulmonary hilum. Tissue analysis by light and analytical electron microscopy showed tissue burdens of coated and uncoated asbestos fibres greatly exceeding reported environmental concentrations (3810 FBs/g dry weight and 2,080,000 structures > or = 0.5 micron/g dry weight respectively). 72% Of the cores were identified as chrysotile. CONCLUSIONS: Clutch refabrication may lead to exposure to asbestos of sufficient magnitude to cause asbestosis and lung cancer.
相似文献