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   1423篇
  免费   75篇
  国内免费   11篇
耳鼻咽喉   12篇
儿科学   56篇
妇产科学   42篇
基础医学   190篇
口腔科学   53篇
临床医学   157篇
内科学   288篇
皮肤病学   48篇
神经病学   48篇
特种医学   111篇
外科学   122篇
综合类   3篇
预防医学   94篇
眼科学   31篇
药学   90篇
肿瘤学   164篇
  2023年   9篇
  2021年   16篇
  2020年   12篇
  2019年   31篇
  2018年   25篇
  2016年   12篇
  2015年   17篇
  2014年   31篇
  2013年   43篇
  2012年   57篇
  2011年   51篇
  2010年   35篇
  2009年   28篇
  2008年   57篇
  2007年   59篇
  2006年   50篇
  2005年   41篇
  2004年   52篇
  2003年   38篇
  2002年   27篇
  2001年   36篇
  2000年   39篇
  1999年   35篇
  1998年   34篇
  1997年   40篇
  1996年   47篇
  1995年   41篇
  1994年   34篇
  1993年   23篇
  1992年   27篇
  1991年   32篇
  1990年   22篇
  1989年   39篇
  1988年   32篇
  1987年   38篇
  1986年   30篇
  1985年   31篇
  1984年   15篇
  1982年   12篇
  1981年   13篇
  1980年   17篇
  1979年   22篇
  1978年   18篇
  1977年   15篇
  1976年   10篇
  1975年   14篇
  1974年   14篇
  1973年   9篇
  1972年   8篇
  1969年   7篇
排序方式: 共有1509条查询结果,搜索用时 31 毫秒
1.
Birth weight on 12,644 singleton infants from 6,196 sibships born in Maryland between 1980 and 1984 were used to estimate the effects of nine maternal and infant covariates on the sibship correlation in birth weight. Assuming a homogeneous correlation across all families, the estimated intraclass correlation was 0.4664 (+/- 0.0099). This high sibship correlation makes it possible to predict, with reasonable accuracy, the birth weight of a child given information on previous sibs, as well as covariates on the mother and/or infant pertinent to a given pregnancy. The reduction in variance associated with incorporating information on the nine covariates used here was approximately equal to that obtained by conditioning on a single previous sib. Testing for heterogeneity in correlation among different groups of families showed that a crude measure of parity (first live birth vs. other), time between births, mother's marital status, and maternal age at the birth of the last child significantly influenced the sibship correlation in birth weight.  相似文献   
2.
Carcinogenesis, 25, 229–235, 2004 We reported the association of  相似文献   
3.
Humans are environmentally and occupationally exposed to polycyclic aromatic hydrocarbons (PAH). PAH's are a class of tumorigenic compounds which act through metabolic transformation to chemically reactive forms, epoxides, which covalently bind to DNA forming DNA adducts. To evaluate the genotoxic effects of PAH's, air and urine samples were analyzed for PAH. Blood samples were analyzed for benzo(a)pyrene-diol-epoxide-DNA (BPDE-DNA) adducts. New methods for analyzing DNA adducts in lymphocytes have been used to study the genotoxic effects of human exposure to carcinogens. BPDE-DNA adducts in lymphocytes have been used as internal dosimeters of exposure to PAH's and several studies have been conducted. We measured BPDE-DNA adducts in aluminium plant workers with immuno-assay and physico-chemical methods. PAH-DNA adducts were detectable to a lesser extent in subjects working in an aluminium plant compared to subjects working in a coke oven plant.  相似文献   
4.
Gamma-linolenic acid in the form of a particular variety of evening primrose oil (Epogam) has been reported of value in the treatment of atopic eczema. Nine controlled trials of evening primrose oil were performed in eight centres. Four of the trials were parallel and five cross-over. Doctors and patients assessed the severity of eczema by scoring measures of inflammation, dryness, scaliness, pruritus and overall skin involvement. Individual symptom scores were combined to give a single global score at each assessment point. In the analysis of the parallel studies, both patient and doctor scores showed a highly significant improvement over baseline (P less than 0.0001) due to Epogam: for both scores the effect of Epogam was significantly better than placebo. Similar results were obtained on analysis of the cross-over trials, but in this case the difference between Epogam and placebo in the doctors' global score, although in favour of Epogam, failed to reach significance. The effects on itch were particularly striking. There was no placebo response to this symptom, whereas there was a substantial and highly significant response to Epogam (P less than 0.0001). When the improvements, or otherwise, in clinical condition were related to changes in plasma levels of dihomogammalinolenic and arachidoni acids, it was found that there was a positive correlation between an improvement in clinical score and a rise in the fatty acid levels.  相似文献   
5.
BACKGROUND: Developments in accelerator mass spectrometry (AMS) now permit the determination of femtogram amounts of 26Al in blood and in various tissues with good precision and free of external contamination. METHODS: In the present study we used trace quantities of 26Al to investigate the intestinal absorption and compartmentalization of aluminium in rats with renal failure (Nx, 5/6 nephrectomy) and in pair- fed controls (C). Single oral doses of 20 ng 26Al were administered to six animals in each group and, subsequently, 24-h post-load 26Al was analysed in serum, urine, bone, liver, and spleen by means of AMS. RESULTS: Serum concentrations of 26Al were significantly lower in uraemic rats compared to controls, whereas urinary excretion was comparable (Nx, 7.11 +/- 5.78 pg/day vs C, 9.46 +/- 6.10 pg/day), suggesting a higher fraction of ultrafiltrable serum 26Al in uraemia. The target tissues of cellular transferrin-mediated 26Al uptake, liver and spleen, tended to show a larger degree of aluminium accumulation in controls (0.26 +/- 0.31 pg/g vs Nx, 0.14 +/- 0.10 pg/g and 0.37 +/- 0.27 pg/g vs Nx, 0.25 +/- 0.27 pg/g respectively). In contrast, in bone, a site of extracellular aluminium deposition, 26Al concentrations were more elevated in uraemia (1.22 +/- 0.59 pg/g vs C: 0.68 +/- 0.30 pg/g). Estimated total 26Al accumulation in all measured target tissues was significantly higher in uraemic rats (28.15 +/- 9.90 pg vs C: 17.03 +/- 7.03 pg) and total recovery of 26Al from tissue and urine was 26.58 +/- 6.74 pg in controls and 35.75 +/- 7.03 pg in uraemic animals, suggesting a fractional absorption of 0.133% and 0.175% respectively. CONCLUSIONS: Our data suggest that fractional absorption from a dietary level dose of 26Al is about 0.13%. Compartmentalization occurs in transferrin-dependent target tissues such as liver and spleen; however, in quantitative terms extracellular deposition in bone is more important. Uraemia has a significant effect on the intestinal absorption and compartmentalization of aluminium. It enhances fractional absorption and increases subsequent extracellular deposition of aluminium in bone. However, at the same time uraemia does not increase transferrin-dependent cellular accumulation of aluminium in liver and spleen.   相似文献   
6.
7.
For solid-phase peptide synthesis, 2, 4-dimethoxy-4′ -hydroxybenzhydrol linker was prepared via lithium borohydride reduction of 2, 4-dimethoxy-4′-hydroxybenzophenone. The potassium salt of the linker was coupled to chloromethylpolystyrene. This method proved to be better than use of the cesium salt. This new synthesis gave a polymer with appropriate structure and a good degree of substitution.  相似文献   
8.
Postmenopausal women enrolled in the Iowa portion of the postmenopausal estrogen/progestin interventions randomized clinical trial (n= 105) during 1989–1991 were studied for (i) the prevalence of human papillomavirus (HPV) in this older age population (ages 45–64), and (ii) the association between hormone replacement therapies (HRTs) and changes in detection of HPV over a 2-year time period. HPV is causative in most cervical and some other genital cancers and in the presence of steroid hormones has been shown to increase neoplastic transformation by HPVin vitro.Using PCR to detect HPV DNA, the overall frequency of the virus regardless of time period was 50.3% (n= 53) with a baseline (BL) frequency of 38.1% and the second year follow-up (FU) of 22.9%. The oncogenic types HPV-16 (75.5%) and HPV-31 (20.8%) were the most commonly reported. All those with persistently detected infection (10.5%), defined as HPV+ at both BL and FU, were identified with HPV-16 or -18. Between these two time periods there were no significant differences in HPV frequency between the placebo and combined HRT groups (BL−/FU+, 21% vs 18%; BL+/FU−, 71% vs 80%). While the study is based on a small sample, the findings suggest that short-term use of HRTs is not associated with an increased risk of HPV detection, but assessment of effects from long-term use is needed. The data also indicate that the frequency of HPV found in older women is higher than previously suspected but that short-term changes in HPV detected in this age group are unrelated to the development of precancerous cervical lesions.  相似文献   
9.
This case report describes the anaesthetic management of a patient with sporadic-type long QT interval syndrome (LQTS), and increased QT dispersion, who presented for removal of an ovarian cyst. Beta adrenergic blockade and adequate depth of anaesthesia for successful management is emphasized. The Successful use of epidural administration of lignocaine and opioids in addition to general anaesthesia is described.  相似文献   
10.
Reiman  TH; Heiken  JP; Totty  WG; Lee  JK 《Radiology》1988,169(2):564-566
Limited-field-of-view radio-frequency receiver antennas provide improved near-field sensitivity for magnetic resonance imaging by decreasing the antenna volume. The Helmholtz-type surface coil, consisting of two flat rings, is an organ-encompassing antenna that takes advantage of this principle to yield an improved signal-to-noise ratio (S/N). The coil was tested in a group of 50 patients and 16 healthy volunteers. Images obtained with the Helmholtz coil demonstrated quantitatively superior S/N of 2.2-fold or greater than that of comparison body coil images, as well as qualitatively superior anatomic resolution.  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