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   5086篇
  免费   597篇
  国内免费   95篇
耳鼻咽喉   21篇
儿科学   75篇
妇产科学   24篇
基础医学   608篇
口腔科学   74篇
临床医学   695篇
内科学   843篇
皮肤病学   36篇
神经病学   595篇
特种医学   325篇
外科学   368篇
综合类   493篇
现状与发展   1篇
预防医学   586篇
眼科学   68篇
药学   604篇
  7篇
中国医学   209篇
肿瘤学   146篇
  2024年   9篇
  2023年   91篇
  2022年   161篇
  2021年   240篇
  2020年   265篇
  2019年   240篇
  2018年   233篇
  2017年   229篇
  2016年   188篇
  2015年   213篇
  2014年   315篇
  2013年   445篇
  2012年   294篇
  2011年   290篇
  2010年   242篇
  2009年   237篇
  2008年   219篇
  2007年   200篇
  2006年   172篇
  2005年   169篇
  2004年   147篇
  2003年   161篇
  2002年   128篇
  2001年   129篇
  2000年   108篇
  1999年   78篇
  1998年   68篇
  1997年   67篇
  1996年   53篇
  1995年   45篇
  1994年   46篇
  1993年   37篇
  1992年   42篇
  1991年   26篇
  1990年   39篇
  1989年   26篇
  1988年   23篇
  1987年   11篇
  1986年   16篇
  1985年   17篇
  1984年   10篇
  1983年   13篇
  1982年   14篇
  1981年   8篇
  1980年   9篇
  1979年   3篇
  1978年   1篇
  1976年   1篇
排序方式: 共有5778条查询结果,搜索用时 15 毫秒
51.
目的 了解青藏线水源水质卫生状况,为施工部队水源选择、洁治消毒提供参考依据。方法 硬度使用EDTA-2Na进行滴定,其余指标使用88型检水检毒箱测定。结果施工沿线基本无现成可利用的水源,所调查22个水源中9个存在生物污染,3个水源氯化物或硫酸盐严重超标;5个水源总铁严重超标。结论 摸清了放工沿线水源水质卫生状况,为部队施工和以后执行任 务时选择水源、进行水质改善提供了科学依据。  相似文献   
52.
The present study was undertaken to investigate the effects of modulation of the (NMDA) receptor on learning and memory. Thus, the performance of rats treated with d-cycloserine, a partial agonist at the glycine recognition site of the NMDA receptor complex, and MK-801, a noncompetitive NMDA receptor antagonist, either alone or concurrently were assessed in radial arm maze and water maze tasks. Administration of MK-801 (0.1 mg/kg, i.p.) impaired acquisition in the water maze (increased escape latency and distance) and working memory in the radial arm maze (increased re-entries) in rats. Moreover, in the radial arm maze, MK-801 disrupted locomotion (increased latencies and decreased arm entries per minute) and impaired the acquisition of reference memory (increased number of errors) performance of rats. d-Cycloserine (0.03, 0.3, 1.0, 3.0, 10 mg/kg, i.p.) had no effects on acquisition or memory performance of control or MK-801-treated rats in either of these tasks. However, d-cycloserine (0.03, 0.3, 3.0 mg/kg) reversed the MK-801-induced disruption in locomotion. Furthermore, 3.0 mg/kg d-cycloserine increased behavioral activity and also decreased the time needed to complete the task in control animals. To conclude, our results suggest that the consequences of NMDA receptor modulation on learning and memory processes and sensorimotor functions may be functionally different or have distinct anatomical locations.  相似文献   
53.
We studied the characteristics of bone mineral density (BMD) and soft tissue composition in obese Japanese women using dual-energy X-ray absorptiometry. Eighty-nine women, aged 45–85 years, were divided into three groups according to their body mass index (BMI): a thin group (n = 38; BMI < 21), a standard weight group (n = 31; BMI, 21–25), and an obese group (n = 20; BMI ≥ 25). The mean BMD of the second to fourth lumbar vertebrae and BMD of the lumbar spine, thoracic spine, pelvis, legs, and ribs of the thin group were significantly lower than those of the standard weight group or the obese group (P < 0.05), whereas no significant difference in total body BMD was observed among the three groups. There was a significant difference in total and regional fat mass among the three groups (P < 0.05). Lean mass of legs and total lean mass showed a significant difference between the thin group and the obese group (P < 0.05). The results showed that obesity was associated with higher BMD of weight bearing-bones and ribs, high total and regional fat mass, and high lean mass of bilateral legs and total lean mass. We suggest that obesity may contribute to the prevention of bone loss of weight-bearing bones and ribs and muscular atrophy of the legs. Received: Sept. 30, 1998 / Accepted: Dec. 10, 1998  相似文献   
54.
Adachi S  Takeda T  Fukao K 《Surgery today》1999,29(4):301-306
Conducting the qualitative evaluation of reconstruction methods is difficult because of their complexity. The aim of the present study was to compare esophageal bile and food reflux by performing gastrointestinal and hepatobiliary dual scintigraphy (GHDS) after various methods of reconstruction following total gastrectomy. Of 17 patients studied, 4 had undergone Roux-en-Y anastomoses (R-Y); 6, jejunal pouch-Y anastomoses (P-Y); and 7, jejunal pouch interposition (P-I). GHDS was performed 1 year after surgery using111In-diethylene triamine pentaacetic acid administered orally, and99mTc-pyridoxyl-5-methyl tryptophan administered intravenously. Imaging data from a gamma camera were stored in and processed by a data analyzer. Three patients who had undergone R-Y and one who had undergone P-I complained of heartburn, while one who had undergone R-Y, two who had undergone P-Y, and three who had undergone P-I complained of a feeling of fullness. Esophageal bile reflux was confirmed by GHDS in four of the patients who had undergone R-Y, one who had undergone P-Y, and four who had undergone P-I. Moreover, GHDS demonstrated food retention in two patients who had undergone R-Y, five who had undergone P-Y, and four who had undergone P-I. Weight loss was closely related to the esophageal reflux of bile or food which can be accurately detected by GHDS. Despite the absence of heartburn, patients diagnosed as having bile reflux by GHDS showed poor recovery of body weight.  相似文献   
55.
Summary This paper introduces the concept of the resolution matrix as the basis for an objective theoretical comparison of distributed linear inverse solutions to the neuroelectromagnetic inverse problem. In particular, we describe how figures of merit derived from the resolution matrices can be represented graphically to evaluate merits and shortcomings of the different solutions. The use of the figures of merit is illustrated with two solutions that consider minimal a priori information about the generators: Classical Minimum Norm and Backus Gilbert. We recommend to start any analysis with the individual exploration of the resolution kernel for each grid point or at least for those points where the activity is likely to occur. This analysis might help in selecting the optimal inverse for the sources that are supposed to be active in the process under study.This work was supported by a grant from the Deutsche Forschungsgemeinschaft (Klinische Forschergruppe Biomagnetismus and Biosignalanalyse). Partial support was received from Swiss National Foundation grant 4038-044081/1.  相似文献   
56.
Functional imaging and localization of electromagnetic brain activity   总被引:7,自引:0,他引:7  
Functional imaging of electric brain activity requires specific models to transform the signals recorded at the surface of the human head into an image. Two categories of model are available: single-time-point and spatio-temporal methods. The instantaneous methods rely only on the few voltage differences measured at one sampling point. To create a spatial image from this limited information, they require strict assumptions that rarely conform with the underlying physiology. Spatio-temporal models create two kinds of images: first, a spatial image of discrete equivalent multiple dipoles or regional sources, and second, an image of source current waveforms that reflect the temporal dynamics of the brain activity in circumscribed areas. The accuracy of the spatial image is model dependent and limited, but it can be validated from the spatio-temporal data by the "regional source imaging" technique, introduced here. The source waveforms are linear combinations of the scalp waveforms, and thus, specific derivations which image local brain activities at a macroscopic level. Brain source imaging of somatosensory evoked potentials revealed temporally overlapping activities from the brainstem, thalamus and from multiple sources in the region of the contralateral somatosensory projection areas.  相似文献   
57.
陈军  陈燕华  刁雨辉  李俐 《中国药房》2003,14(6):362-363
目的 :用双波长分光光度法测定复方间苯二酚洗剂中间苯二酚的含量。方法 :以水为溶剂 ,在273 5nm和266 1nm波长处测定吸收度并计算差值。结果 :间苯二酚在20 32~60 96μg/ml浓度范围内线性关系良好 (r=0 9998) ;平均回收率为99 59 % ,RSD=0 45% (n=9)。结论 :本方法简便、快捷 ,测定结果准确  相似文献   
58.
玉米粉水解物作为红霉素发酵培养基的研究   总被引:2,自引:0,他引:2  
研究了摇瓶试验中玉米粉水解物替代葡萄糖发酵红霉素的最佳培养基组成。用均匀设计法得到发酵基础培养基的最佳配比(wB,%):玉米粉3.6,黄豆饼粉2.0,玉米浆0.23,碳酸钙0.5,淀粉0.6;用正交试验得到了优化的补混合料配比(%):玉米粉4.5,黄豆饼粉2.0,硫酸铵1.0,酵母粉2.0;并得到了玉米粉的最适水解条件。30t发酵罐放大实验结果表明,用玉米粉水解物替代葡萄糖作碳源发酵红霉素,发酵单位提高5.8%,综合生产成本降低26.0%。  相似文献   
59.
The ubiquity of human cytomegalovirus (CMV) and human herpesvirus-7 (HHV-7), as well as activation of these viruses during immunosuppression, allows the suggestion that both viruses could participate in the development of 'CMV disease' in patients after renal transplantation (RT). The aim of our research was to study the prevalence of latent CMV and HHV-7 infections in patients before RT, to determine interaction between these viruses in dual infection and possible association of their reactivation with the progression of 'CMV disease' after RT. Peripheral blood samples were collected from 49 patients before and up to 10-12 wk after RT. The methods used for diagnostics of viral infections were: serology, nested polymerase chain reaction (nPCR) analysis of peripheral blood leukocytes (PBL) and plasma, and virus isolation in cell cultures (morphological changes, nPCR analysis of cellular and cell-free samples, indirect immunofluorescence analysis). Before RT, CMV and HHV-7 DNAs were detected in PBL but not in the plasma samples, which indicates the presence of latent viral infection in patients. Latent dual (CMV + HHV-7) infection was prevalent (51.0%) in 49 patients, while CMV and HHV-7 infections alone were detected in 26.5 and 12.2% of patients, respectively. Risk of viral disease after RT, for recipients with latent dual infection before RT, was 12- and 2.2-fold higher in comparison with CMV and HHV-7 infections alone, respectively. Frequency of dual infection in 18 recipients with 'viral syndrome' or 'CMV disease' after RT was reliably higher (13/18, 81.3%) than CMV (1/18, 6.2%) (p < 0.025) and HHV-7 (2/18, 12.5%) (p < 0.025) infections alone. HHV-7 reactivation preceded CMV reactivation in 77.0% of the cases of dual infection in the recipients with viral disease and reactivation of both viruses preceded the development of viral disease. Severe 'CMV disease' developed in 2 out of 2 recipients with CMV primary infection and 'viral syndrome' in 1 recipient with CMV reinfection. The reactivation of CMV was detected in all recipients prior to onset of the disease. Correlation was shown between reactivation of latent HHV-7 infection and development of febrile syndrome in 2 out of 2 recipients with HHV-7 infection alone. Taking into account that dual infection is an increased risk factor for 'viral syndrome' and 'CMV disease' development, screening diagnostic should include testing for both viral infections in transplant donors as well as in recipients before and after RT.  相似文献   
60.
利用均匀实验优化利福霉素SV发酵培养基氮源配比   总被引:3,自引:0,他引:3  
应用均匀设计的方法对利福霉素SV发酵培养基中的氮源配比进行优化。研究了氮源中各成分对发酵效价的影响。确定各成分的最佳配比并用实验验证,使摇瓶发酵效价提高了10%以上。并对利福霉素SV产生菌在新、老培养基中的代谢特性进行了比较。  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