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   1299364篇
  免费   94205篇
  国内免费   2029篇
耳鼻咽喉   18371篇
儿科学   43073篇
妇产科学   38472篇
基础医学   189740篇
口腔科学   35621篇
临床医学   111827篇
内科学   255470篇
皮肤病学   26771篇
神经病学   101458篇
特种医学   50465篇
外国民族医学   366篇
外科学   199348篇
综合类   26772篇
现状与发展   1篇
一般理论   362篇
预防医学   95981篇
眼科学   29342篇
药学   99069篇
  2篇
中国医学   2522篇
肿瘤学   70565篇
  2018年   12308篇
  2016年   10458篇
  2015年   12067篇
  2014年   16707篇
  2013年   25490篇
  2012年   35150篇
  2011年   37629篇
  2010年   22123篇
  2009年   20804篇
  2008年   36527篇
  2007年   39583篇
  2006年   40149篇
  2005年   39469篇
  2004年   37963篇
  2003年   36894篇
  2002年   36341篇
  2001年   58246篇
  2000年   59697篇
  1999年   50903篇
  1998年   14525篇
  1997年   13026篇
  1996年   13280篇
  1995年   12542篇
  1994年   11930篇
  1993年   11026篇
  1992年   41089篇
  1991年   40454篇
  1990年   39961篇
  1989年   38794篇
  1988年   36184篇
  1987年   35422篇
  1986年   33797篇
  1985年   32215篇
  1984年   24030篇
  1983年   20926篇
  1982年   12506篇
  1981年   11036篇
  1979年   22691篇
  1978年   15937篇
  1977年   13791篇
  1976年   13011篇
  1975年   14240篇
  1974年   16715篇
  1973年   16095篇
  1972年   15343篇
  1971年   14237篇
  1970年   13218篇
  1969年   12733篇
  1968年   11994篇
  1967年   10481篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
81.
Exposure to cadmium via the diet is known to depend to a large extent on the intake of cereal grains, particularly the high-fibre fractions of wheat. Subjects with low iron status absorb more cadmium than those with better iron status. The purpose of the present study was to determine to what extent cadmium accumulation in human placenta is affected by the intake of grain fibre and maternal iron status during pregnancy. Thirty-nine pregnant women participated in the study. In each trimester the women were requested to complete a dietary history and to allow blood samples to be taken for haemoglobin, serum ferritin and serum thiocyanate determinations, the latter as a marker for smoking. At delivery the whole placenta was taken for the determination of the cadmium concentration. The 32 women who had serum thiocyanate levels less than 70 mumol/l, who had completed at least one dietary history and from whom a blood sample was obtained in the third trimester, were included in the final statistical analyses. In the group of women who consumed less than the median intake of grain fibre and had more than 15 micrograms ferritin/l serum in the third trimester, the placenta cadmium concentration was nearly half that in the placentae of women who had consumed more grain fibre or had lower iron status in late pregnancy.  相似文献   
82.
Premalignant lesions of the penis include cutaneous horn, balanitis xerotica obliterans, and leukoplakia. The true incidence of progression of each of these to squamous-cell carcinoma is unknown. Bowenoid papulosis, erythroplasia of Queyrat, and Bowen's disease are histologically identical to in situ carcinoma. Although the first is consistently benign, the latter two regularly evolve into invasive cancer. Malignant scrotal lesions include squamous-cell carcinoma, liposarcoma, leiomyosarcoma, basal-cell carcinoma, extramammary Paget's disease, erythroplasia of Queyrat, malignant melanoma, and metastases. Hemangioma can be confused with carcinoma.  相似文献   
83.
84.
Background: The association between aluminium and dialysis encephalopathy and deterioration of the neurological state during desferrioxamine treatment of dialysis patients is well established. At present little is known about the speciation and the mechanisms underlying the element's neurotoxicity. Methods. Aluminium speciation was performed in cerebrospinal fluid samples of acutely aluminium-intoxicated dialysis patients using a recently developed high-performance liquid chromatographic/electro-thermal atomic absorption spectrometric hybrid method. Results: Baseline cerebrospinal fluid aluminium levels of samples taken shortly after the intoxication were low but elevated (5.0±2.0 &mgr;g/l, n=3) as compared to subjects with normal renal function (<1 &mgr;g/l). In contrast to the situation noted in serum and to the iron speciation in cerebrospinal fluid, aluminium was not bound to transferrin but appeared as two distinct compounds, the main fraction eluting at the elution volume of aluminium citrate/silicate. The second compound was not identified. Forty-four hours after desferrioxamine administration the cerebrospinal fluid aluminium levels had increased up to a concentration of 10.3±2.5 &mgr;g/l (n=3). This was accompanied by a change in the speciation profile with aluminium appearing at the elution volume of aluminoxamine. Conclusion: Our findings may contribute to a better understanding of the neurotoxic effects of aluminium and its desferrioxamine chelate in dialysis patients.  相似文献   
85.
86.
87.
Variations of the medial and inferior choanal limits may facilitate snoring. These are: 1) short vomer without crista choanalis vomeris and adaptational formations, 2) extremely concave posterior margin of the hard palate leading to disproportion between the muscular and aponeurotic part of m. tensor veli palatini and hence to a flabby soft palate especially during sleep, and 3) neonatal relation of the height and width of the choane resulting in a very large choanal region instead of relative reduction of choanal width compared to its increasing height. All these variations result in a flabby soft palate especially during sleep and may lead to formation of whirles of inspired air and snoring.  相似文献   
88.
Various forms of signal processing are used in modern ASP hearing aids. The present study investigated the relationship between sentence recognition ability and two types of signal processing used in commercially available hearing aids. Results indicated a significant improvement in sentence recognition ability employing an instrument with adaptive compression (variable release time) versus an instrument with an adaptive high-pass filter with short attack and release times. Data were obtained for a single-talker competing message at several message-to-competition ratios. The adaptive compression system may prove to be beneficial to hearing-impaired listeners in certain background noise environments.  相似文献   
89.
90.
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