全文获取类型
收费全文 | 18424篇 |
免费 | 1575篇 |
国内免费 | 38篇 |
学科分类
医药卫生 | 20037篇 |
出版年
2021年 | 213篇 |
2019年 | 207篇 |
2018年 | 260篇 |
2017年 | 180篇 |
2016年 | 216篇 |
2015年 | 235篇 |
2014年 | 333篇 |
2013年 | 497篇 |
2012年 | 726篇 |
2011年 | 743篇 |
2010年 | 403篇 |
2009年 | 413篇 |
2008年 | 733篇 |
2007年 | 738篇 |
2006年 | 727篇 |
2005年 | 756篇 |
2004年 | 668篇 |
2003年 | 663篇 |
2002年 | 671篇 |
2001年 | 640篇 |
2000年 | 721篇 |
1999年 | 578篇 |
1998年 | 245篇 |
1997年 | 209篇 |
1996年 | 184篇 |
1995年 | 199篇 |
1994年 | 175篇 |
1993年 | 173篇 |
1992年 | 496篇 |
1991年 | 499篇 |
1990年 | 445篇 |
1989年 | 454篇 |
1988年 | 414篇 |
1987年 | 433篇 |
1986年 | 411篇 |
1985年 | 393篇 |
1984年 | 356篇 |
1983年 | 249篇 |
1982年 | 159篇 |
1981年 | 159篇 |
1980年 | 194篇 |
1979年 | 270篇 |
1978年 | 219篇 |
1977年 | 172篇 |
1976年 | 184篇 |
1975年 | 174篇 |
1974年 | 215篇 |
1973年 | 202篇 |
1972年 | 169篇 |
1971年 | 165篇 |
排序方式: 共有10000条查询结果,搜索用时 515 毫秒
71.
D A Schwartz L A Newsum R M Heifetz 《Scandinavian journal of work, environment & health》1986,12(1):51-54
The general birth outcome and prevalence of specific birth defects was investigated within an agricultural community through the review of birth records in a major hospital in Imperial County, California. Of all singleton births (N = 2 463) occurring within a four-year period, 990 or 40.2% involved offspring with one or both parent(s) who were agricultural workers. The progeny of agricultural and nonagricultural workers were similar with regard to sex ratios, prevalence of low birth-weight infants, stillbirth rate, minor and major malformation rates, and prevalence of neonatal deaths. Limb reduction defects, however, occurred more frequently among offspring of agricultural workers (5.05 per 1 000 total births versus 2.19 per 1 000 total births, rate ratio = 2.3). Furthermore, the prevalence of limb reduction defects among agricultural workers was 3- to 14-fold higher than available United States rates (0.36-1.65 per 1 000 total births). Findings from our study suggest that agricultural communities and, in particular, agricultural workers may be at excess risk of producing a child with a limb reduction defect. 相似文献
72.
Using 600 clinical specimens, we compared the concordance of four methods for carcinoembryonic antigen: the Roche RIA (I); the Roche EIA (II); Hybritech EIA (III); and Abbott EIA (IV). EDTA-treated plasma was used for Methods I and II and serum for Methods III and IV. However, no significant difference was found between results for serum and plasma in Method II. The normal reference interval (in micrograms/L) was I (222 specimens), 1.94 +/- 1.54; II (57 specimens), 0.8 +/- 0.5; III (100 specimens), 2.94 +/- 2.47; and IV (614 specimens), less than 5.0. The precision of all four methods was acceptable. Concordance among all of the methods exceeded 90%. 相似文献
73.
74.
75.
M Medina-Ramón J P Zock M Kogevinas J Sunyer X Basaga?a J Schwartz P S Burge V Moore J M Antó 《The European respiratory journal》2006,27(6):1196-1203
Symptoms of obstructive lung disease in domestic cleaners have been related to the use of bleach and other irritant cleaning products. The short-term effects of cleaning exposures on respiratory symptoms and peak expiratory flow (PEF) were investigated in domestic cleaners with respiratory disorders. In a panel study, 43 female domestic cleaners with a recent history of asthma and/or chronic bronchitis completed a 2-week diary, collecting information on respiratory symptoms, PEF and cleaning exposures. Mixed regression models were used to assess daily changes in symptoms and PEF associated with specific cleaning exposures. The probability of having work-related asthma was individually assessed by a computerised diagnostic system and an occupational asthma expert. Lower respiratory tract symptoms were more common on working days and were predominantly associated with exposure to diluted bleach, degreasing sprays/atomisers and air fresheners. Associations with upper respiratory tract symptoms and PEF were less apparent. Eleven (30%) subjects scored positively for work-related asthma. It is concluded that exposure to certain irritant cleaning products aggravates lower respiratory tract symptoms in female domestic cleaners with asthma or chronic bronchitis. 相似文献
76.
Objective. To determine if patients treated at hospitals under different levels of financial strain from the Balanced Budget Act (BBA) of 1997 had differential changes in 30-day mortality, and whether vulnerable patient populations such as the uninsured were disproportionately affected.
Data Source. Hospital discharge data from all general acute care hospitals in Pennsylvania from 1997 to 2001.
Study Design. A multivariate regression analysis was performed retrospectively on 30-day mortality rates, using hospital discharge data, hospital financial data, and death certificate information from Pennsylvania.
Data Collection. We used 370,017 hospital episodes with one of four conditions identified by the Agency for Healthcare Research and Quality as inpatient quality indicators were extracted.
Principal Findings. The average magnitude of Medicare payment reduction on overall net revenues was estimated at 1.8 percent for hospitals with low BBA impact and 3.6 percent for hospitals with a high impact in 1998, worsening to 2 and 4.8 percent, respectively, by 2001. Operating margins decreased significantly over the time period for all hospitals ( p <.05). While unadjusted mortality rates demonstrated a disproportionate rise in mortality for patients from high impact hospitals from 1997 to 2000, adjusted analyses show no consistent, significant difference in the rate of change in mortality between high-impact and low-impact hospitals ( p =.04–.94). Similarly, uninsured patients did not experience greater increases in mortality in high-impact hospitals relative to low-impact hospitals.
Conclusions. An analysis of hospitalizations in the Commonwealth of Pennsylvania did not find an adverse impact of increased financial strain from the BBA on patient mortality either among all patients or among the uninsured. 相似文献
Data Source. Hospital discharge data from all general acute care hospitals in Pennsylvania from 1997 to 2001.
Study Design. A multivariate regression analysis was performed retrospectively on 30-day mortality rates, using hospital discharge data, hospital financial data, and death certificate information from Pennsylvania.
Data Collection. We used 370,017 hospital episodes with one of four conditions identified by the Agency for Healthcare Research and Quality as inpatient quality indicators were extracted.
Principal Findings. The average magnitude of Medicare payment reduction on overall net revenues was estimated at 1.8 percent for hospitals with low BBA impact and 3.6 percent for hospitals with a high impact in 1998, worsening to 2 and 4.8 percent, respectively, by 2001. Operating margins decreased significantly over the time period for all hospitals ( p <.05). While unadjusted mortality rates demonstrated a disproportionate rise in mortality for patients from high impact hospitals from 1997 to 2000, adjusted analyses show no consistent, significant difference in the rate of change in mortality between high-impact and low-impact hospitals ( p =.04–.94). Similarly, uninsured patients did not experience greater increases in mortality in high-impact hospitals relative to low-impact hospitals.
Conclusions. An analysis of hospitalizations in the Commonwealth of Pennsylvania did not find an adverse impact of increased financial strain from the BBA on patient mortality either among all patients or among the uninsured. 相似文献
77.
78.
David D. Dean Zvi Schwartz Ofelia E. Muniz Ruben Gomez Larry D. Swain David S. Howell Barbara D. Boyan 《Calcified tissue international》1992,50(4):342-349
Summary This study examined the presence of extracellular matrix processing enzymes in matrix vesicles produced by rat costochondral resting zone and growth zone chondrocytes in culture. Optimum procedures for the extraction of each enzyme activity were determined. Enzyme activity associated with chondrocyte plasma membrane microsomes was used for comparison. There was a differential distribution of the enzyme activities related to the cartilage zone from which the cells were isolated. Acid and neutral metalloproteinase (TIMP), plasminogen activator, and betaglucuronidase were highest in the growth zone chondrocyte (GC) membrane fractions when compared with matrix vesicles and plasma membranes isolated from resting zone chondrocyte (RC) cultures. There was a threefold enrichment of total and active acid metalloproteinase in GC matrix vesicles, whereas no enrichment in enzyme activity was observed in RC matrix vesicles. Total and active neutral metalloproteinase were similarly enriched twofold in GC matrix vesicles. TIMP, plasminogen activator, and betaglucuronidase activities were highest in the plasma membranes of both cell types. No collagenase, lysozyme, or hyaluronidase activity was found in any of the membrane fractions. The data indicate that matrix vesicles are selectively enriched in enzymes which degrade proteoglycans. The highest concentrations of these enzymes are found in matrix vesicles produced by growth zone chondrocytes, suggesting that this may be a mechanism by which the more differentiated cell modulates the matrix for calcification. 相似文献
79.
Strategies for screening blood for human immunodeficiency virus antibody. Use of a decision support system 总被引:1,自引:0,他引:1
A decision analytic model was used to examine alternative strategies to screen donated blood for human immunodeficiency virus (HIV) using data from the literature and from 1987 blood-screening programs in areas with high and low prevalence of HIV. Sensitivity analyses incorporated uncertainties about HIV infection and test performance. Current screening strategies are estimated to allow 20.5 infected units per million donated units to be transfused at a cost of $16,850 per HIV-positive unit detected in high-prevalence areas and 4.7 infected units per million donated units to be transfused at a cost of $32,275 per HIV-positive unit detected in low prevalence areas, with nine false-positive notifications of uninfected patients per million units screened and 14.9 discarded, noninfected units per HIV-positive unit in low-prevalence areas. Testing donated blood for HIV can be improved by individualizing screening strategies for areas with different prevalences of HIV. Efforts to further reduce transfusion-associated HIV should focus on improved test performance in early stages of infection, reduction of unnecessary transfusions, donor recruitment in lower-risk groups, and public health measures to reduce HIV infection among the general population. 相似文献
80.