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   1516篇
  免费   79篇
  国内免费   6篇
耳鼻咽喉   22篇
儿科学   41篇
妇产科学   10篇
基础医学   190篇
口腔科学   22篇
临床医学   172篇
内科学   317篇
皮肤病学   18篇
神经病学   83篇
特种医学   97篇
外科学   198篇
综合类   6篇
一般理论   2篇
预防医学   220篇
眼科学   6篇
药学   103篇
肿瘤学   94篇
  2023年   9篇
  2022年   16篇
  2021年   26篇
  2020年   20篇
  2019年   20篇
  2018年   19篇
  2017年   26篇
  2016年   36篇
  2015年   29篇
  2014年   60篇
  2013年   54篇
  2012年   83篇
  2011年   101篇
  2010年   51篇
  2009年   52篇
  2008年   94篇
  2007年   117篇
  2006年   89篇
  2005年   89篇
  2004年   84篇
  2003年   83篇
  2002年   80篇
  2001年   30篇
  2000年   30篇
  1999年   24篇
  1998年   22篇
  1997年   16篇
  1996年   12篇
  1995年   13篇
  1994年   10篇
  1993年   8篇
  1992年   10篇
  1991年   13篇
  1988年   8篇
  1987年   6篇
  1986年   8篇
  1985年   7篇
  1984年   7篇
  1983年   9篇
  1982年   8篇
  1981年   8篇
  1980年   8篇
  1979年   13篇
  1978年   8篇
  1976年   9篇
  1975年   12篇
  1974年   9篇
  1973年   6篇
  1970年   6篇
  1969年   11篇
排序方式: 共有1601条查询结果,搜索用时 15 毫秒
1.
Low-trauma fractures of elderly people are a major public health burden worldwide, and as the number and mean age of older adults in the population continue to increase, the number of fractures is also likely to increase. Epidemiologically, however, an additional concern is that, for unknown reasons, the age-standardized incidence (average individual risk) of fracture has also risen in many populations during the recent decades. Possible reasons for this rise include a birth cohort effect, deterioration in the average bone strength by time, and increased average risk of (serious) falls. Literature provides evidence that the rise is not due to a birth cohort effect, whereas no study shows whether bone fragility has increased during this relatively short period of time. This osteoporosis hypothesis could, however, be tested if researchers would now repeat the population measurements of bone mass and density that were made in the late 1980s and the 1990s. If such studies proved that women's and men's age-standardized mean values of bone mass and density have declined over time, the osteoporosis hypothesis would receive scientific support. The third explanation is based on the hypothesis that the number and/or severity of falls has risen in elderly populations during the recent decades. Although no study has directly tested this hypothesis, a great deal of indirect epidemiologic evidence supports this contention. For example, the age-standardized incidence of fall-induced severe head injuries, bruises and contusions, and joint distortions and dislocations has increased among elderly people similarly to the low-trauma fractures. The fall hypothesis could also be tested in the coming years because the 1990s saw many research teams reporting age- and sex-specific incidences of falling for elderly populations, and the same could be done now to provide data comparing the current incidence rates of falls with the earlier ones.  相似文献   
2.
To evaluate the effect of weight loss on substrate oxidation, energy expenditure, and insulin sensitivity we studied 12 obese subjects (body mass index 33.4 +/- 1.1) before and after 6 wk of a very-low-calorie diet (VLCD) with euglycemic insulin clamp in combination with indirect calorimetry. Body weight decreased from 105.3 +/- 4.6 to 94.1 +/- 4.0 kg (P less than 0.001) and fat mass from 47.2 +/- 3.6 to 37.7 +/- 3.0 kg (P less than 0.001). Total glucose disposal during insulin clamp increased from 30.4 +/- 4.3 to 38.4 +/- 4.4 mumol.kg lean body mass (LBM)-1.min-1 (P less than 0.05), insulin-stimulated glucose oxidation from 14.3 +/- 4.6 to 19.1 +/- 1.4 mumol.kg LBM-1.min-1 (P less than 0.05), and non-oxidative glucose metabolism from 16.0 +/- 3.8 to 19.3 +/- 3.6 mumol.kg LBM-1.min-1 (NS). Lipid oxidation decreased in the basal state (P less than 0.05) and during the insulin clamp (P less than 0.01). The basal rate of energy expenditure decreased from 99.1 +/- 4.6 to 88.5 +/- 2.7 kJ.kg LBM-1.min-1 (P less than 0.05) after weight reduction. A reduction in fat mass achieved by VLCD is associated with reduced lipid oxidation and, because of substrate competition, enhanced glucose oxidation. The physiological consequence is improved insulin sensitivity.  相似文献   
3.

Background  

Hypertension is one of the major causes of disease burden affecting the Finnish population. Over the last decade, evidence-based care has emerged to complement other approaches to antihypertensive care, often without health economic assessment of its costs and effects. This study looks at the extent to which changes proposed by the 2002 Finnish evidence-based Current Care Guidelines concerning the prevention, diagnosis, and treatment of hypertension (the ACCG scenario) can be considered cost-effective when compared to modelled prior clinical practice (the PCP scenario).  相似文献   
4.
Two hundred patients with node positive stage II breast cancer were randomised to four groups after radical mastectomy and axillary evacuation: (1) Postoperative radiotherapy, (2) Adjuvant chemotherapy with eight courses of CAFt (cyclophosphamide 500 mg m-2 + doxorubicin 40 mg/m-2 + ftorafur 20 mg kg-1 orally day 1-14) every fourth week, (3) Postoperative radiotherapy and adjuvant chemotherapy and (4) postoperative radiation, adjuvant chemotherapy and tamoxifen 40 mg daily for 2 years. Thirty-two per cent of the patients discontinued treatment due to GI-toxicity, while 26% required dose reductions due to leukopenia. Radiation pneumonitis was more frequent after the combination of postoperative radiotherapy with chemotherapy. There was a better relapse-free survival in the groups receiving chemotherapy compared to radiotherapy alone (P = 0.05), which was highly significant in a multivariate Cox analysis (P = 0.004). No significant survival differences were seen. Tamoxifen had no clear overall effect but there were better relapse-free (P = 0.04) and overall (P = 0.004) survival with tamoxifen in estrogen receptor positive patients, while estrogen receptor negative patients had a somewhat poorer survival (P = 0.07) after tamoxifen. Local control was better (NS) after the combination (93%) radiotherapy and chemotherapy compared to either treatment alone (76% with radiotherapy and 74% with chemotherapy at 5 years).  相似文献   
5.
Conventional density measures by dual-energy X-ray absorptiometry (DXA) are confounded by increases in bone size and do not assess bone geometry. We assessed precision of magnetic resonance imaging (MRI) and used MRI, DXA, and hip structure analysis (HSA) to assess 7-mo changes in bone structure at the femoral neck in 18 prepubertal girls. At baseline, girls were 10.4 (0.5) yr, 144.0 (8.2) cm, and 35.2 (7.0) kg, on average. Total bone and cortical cross-sectional area (ToA and CoA) were calculated from high-resolution T1-weighted MRI oblique axial images of the femoral neck. We used proximal femur DXA scans (Hologic QDR-4500) and the HSA program to estimate bone cross-sectional area (CSA), and calculate section modulus. MRI precision was determined by scanning 10 volunteers (13-46 yr old) three times with and without repositioning. Precision (CVrms) was 2% for ToA and 7% for CoA. Significant correlations were observed between FN area and MRI-derived ToA (r = 0.57, p = 0.013) and CoA (r = 0.47, p = 0.050). There were significant positive changes over 7 mo by both methods. In conclusion, MRI provides useful information on femoral neck bone area in children. The reproducibility of cortical dimensions at the femoral neck needs improvement through technical modifications and appropriate analysis software.  相似文献   
6.
Weight and mortality in Finnish men   总被引:2,自引:0,他引:2  
Mortality rates of 22,995 Finnish men aged 25 and over followed up for a median of 12 years were analyzed in relation to body mass index (BMI) at the initial examination. All-cause mortality followed a "U"-shaped distribution, being greatest for the thinnest and fattest men at all ages, or about 1.5-fold for those with BMI less than 19.0 kg/m2 and BMI greater than or equal to 34.0 kg/m2, as compared with men of normal weight (BMI 22.0-24.9 kg/m2). Mortality from cardiovascular diseases (CVD) increased with increasing BMI beyond the normal range. This depended mostly on the association of BMI with the biological risk factors of CVD. Mortality rates from CVD were also elevated among thin men under age 55, which could not be explained by the effect of the biological variables. Mortality rates from non-cardiovascular diseases, including cancers were inversely related to BMI among men of all ages. The high overall mortality of thin men was partly but not entirely attributable to smoking, low social class and antecedent disease. We conclude that both thinness and overweight are detrimental to longevity, but through differing mechanisms and disease patterns.  相似文献   
7.
The induction of hepatic peroxisome proliferation and drug metabolizing enzymes and of sister chromatid exchange (SCE) in lymphocytes was studied in male Han/Wistar rats after exposing them for 2 weeks to a commercial chlorophenolate formulation (Ky-5) (100mg/kg/ day), to 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD; 0.05–5 g/kg/wk) and to the pure phenoxyacetic acids, 2,4-dichlorophenoxyacetic acid (2,4-D; 100 mg/kg/day) and 2-chloro-4-methylphenoxyacetic acid (MCPA; 100 mg/kg/day). The chlorophenolate formulation and pure 2,4-D and MCPA caused significant increases in the number of peroxisomes in liver cells, although the average size of peroxisomes was not affected, whereas the effect of even the highest dose of 2,3,7,8-TCDD remained small. This finding indicates that dioxin impurities do not account for the peroxisome proliferation induced by chlorophenolate. The relative weight of the liver increased significantly in rats treated with the chlorophenolate formulation and with 2,3,7,8-TCDD (5.0 and 0.5 g/kg). The pattern of induction of xenobiotic metabolizing enzymes showed some differences between chlorophenolate treatment and 2,3,7,8-TCDD treatment. Furthermore, the effects of pure phenoxyacetic acids were different from that seen with chlorophenolate and 2,3,7,8-TCDD. The highest dose of 2,3,7,8-TCDD increased the frequency of SCE in circulating lymphocytes slightly, but significantly.  相似文献   
8.
BACKGROUND: Alternaria alternata and Cladosporium herbarum are common fungi in outdoor environments, but their clinical significance has not been elucidated in Finland. OBJECTIVE: To evaluate the prevalence of IgE-mediated allergy and clinical outcomes caused by sensitization to fungal allergens in patients with suspected allergy. METHODS: Skin prick tests (SPTs) were performed with C. herbarum in 6,376 patients and also with A. alternata in 1,504 of these patients. SPTs were repeated in 40 patients who showed a positive reaction to either allergen using commercial and in-house extracts. The association of SPT with allergen-specific IgE antibodies in serum was evaluated. Seven patients also underwent a conjunctival challenge test with these fungal allergens. RESULTS: The prevalence of positive SPT results to A. alternata and C. herbarum was low (2.8% and 2.7%, respectively). Among the 40 patients, atopic eczema/dermatitis syndrome was found in 58%, asthma in 44%, and rhinitis in 31%. Most of the patients displayed SPT reactions also to several other fungal allergens, and 75% to 80% showed a positive SPT reaction to allergens of pet animals or pollens. Four patients had a positive reaction to A. alternata and 6 to C. herbarum in the conjunctival challenge test. CONCLUSION: In the Finnish population with allergic symptoms, IgE-mediated sensitization to 2 common fungal allergens was rare and of minor clinical importance. SPT reactions to fungi are mostly observed in patients with multiple sensitivity to various allergens.  相似文献   
9.
Genome of the European elk papillomavirus (EEPV)   总被引:1,自引:0,他引:1  
The genome of the European elk papillomavirus (EEPV) was found to be 8,095 base pairs (bp) long and its genetic organization was similar to that of other papillomaviruses. Ten open reading frames (ORFs), designated E1-E7 and L1-L3, were identified in the genome, all located on one strand. The presence of the L3 ORF is rare among the papillomaviruses and to date has only been identified in the genomes of EEPV, the deer papillomavirus (DPV) and the Cottontail papillomavirus (CRPV). The ORF is well conserved beteeen DPV and EEPV with regard to both length and sequence. Potential promoter regions were identified at the 5-end of the E6 ORF, at the 3-end of the E1 ORF and downstream of the L1 ORF. Furthermore, two potential polyadenylation signals were found, one located in the long control region (LCR), downstream of the L1 ORF, and another preceding the L2 ORF. The EEVP genome is closely related to the genome of the DPV, the most highly conserved regions being ORFs E1 (70%), E5 (69%), and L1 (74%).  相似文献   
10.
Vascular endothelial growth factor (VEGF) is a hypoxia-inducible endothelial cell mitogen and survival factor. Its receptor VEGFR-2 (KDR/Flk-1) mediates these effects. We studied the expression of VEGF and VEGFR-2 in ischemic human and rabbit skeletal muscle by immunohistochemistry and in situ hybridization. Human samples were obtained from eight lower limb amputations because of acute or chronic critical ischemia. In chronically ischemic human skeletal muscle VEGF and VEGFR-2 expression was restricted to atrophic and regenerating skeletal myocytes, whereas in acutely ischemic limbs VEGF and VEGFR-2 were expressed diffusely in the affected muscle. Hypoxia-inducible factor-1alpha was associated with VEGF and VEGFR-2 expression both in acute and chronic ischemia but not in regeneration. Hindlimb ischemia was induced in 20 New Zealand White rabbits by excising the femoral artery. Magnetic resonance imaging and histological sections revealed extensive ischemic damage in the thigh and leg muscles of ischemic rabbit hindlimbs with VEGF expression similar to acute human lower limb ischemia. After 1 and 3 weeks of ischemia VEGF expression was restricted to regenerating myotubes and by 6 weeks regeneration and expression of VEGF was diminished. VEGFR-2 expression was co-localized with VEGF expression in regenerating myotubes. Macrophages and an increased number of capillaries were associated with areas of ischemic muscle expressing VEGF and VEGFR-2. In conclusion, two patterns of VEGF and VEGFR-2 expression in human and rabbit ischemic skeletal muscle are demonstrated. In acute skeletal muscle ischemia VEGF and VEGFR-2 are expressed diffusely in the affected muscle. In chronic skeletal muscle ischemia and in skeletal muscle recovering from ischemia VEGF and VEGFR-2 expression are restricted to atrophic and regenerating muscle cells suggesting the operation of an autocrine pathway that may promote survival and regeneration of myocytes.  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