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   42872篇
  免费   3648篇
  国内免费   1199篇
耳鼻咽喉   840篇
儿科学   653篇
妇产科学   547篇
基础医学   7405篇
口腔科学   1942篇
临床医学   3818篇
内科学   7105篇
皮肤病学   540篇
神经病学   3704篇
特种医学   1175篇
外国民族医学   4篇
外科学   2872篇
综合类   3695篇
现状与发展   5篇
一般理论   1篇
预防医学   3276篇
眼科学   1377篇
药学   4475篇
  12篇
中国医学   1436篇
肿瘤学   2837篇
  2024年   111篇
  2023年   810篇
  2022年   1378篇
  2021年   2314篇
  2020年   1825篇
  2019年   1606篇
  2018年   1599篇
  2017年   1548篇
  2016年   1580篇
  2015年   1730篇
  2014年   2586篇
  2013年   3526篇
  2012年   2138篇
  2011年   2371篇
  2010年   1841篇
  2009年   1925篇
  2008年   1870篇
  2007年   1730篇
  2006年   1627篇
  2005年   1384篇
  2004年   1215篇
  2003年   1089篇
  2002年   911篇
  2001年   793篇
  2000年   669篇
  1999年   607篇
  1998年   552篇
  1997年   504篇
  1996年   441篇
  1995年   417篇
  1994年   410篇
  1993年   352篇
  1992年   341篇
  1991年   342篇
  1990年   270篇
  1989年   253篇
  1988年   247篇
  1987年   240篇
  1986年   257篇
  1985年   369篇
  1984年   334篇
  1983年   219篇
  1982年   294篇
  1981年   193篇
  1980年   179篇
  1979年   165篇
  1978年   104篇
  1977年   100篇
  1976年   86篇
  1975年   52篇
排序方式: 共有10000条查询结果,搜索用时 500 毫秒
81.
本文对81例乙型肝炎病人的肝活检组织进行了电镜观察,发现HBsAg的阳性率达93.8%。电镜下,HBsAg细丝不仅有一般的管状细丝型,还有分枝管型和管泡型,而且CAH病人肝组织不易找到HBsAg丝(易见者仅9%),CPH,CLH则多数(79.5%)为易见及可见,二者有高度显著性差异(P<0.01)。  相似文献   
82.
It has been previously demonstrated that the generation of measles virus (MV)-specific cytotoxicity (CTL) is reduced in patients with multiple sclerosis (MS). By contrast, CTL specific for influenza virus (FLU) and mumps virus is normal. It is uncertain if reduced CTL is limited to MV in MS patients, or if reduced CTL may be found to other viruses as well. Since MV-specific CTL is predominantly restricted by HLA class II molecules, while FLU-specific and mumps-specific CTL have large HLA class I-restricted components, reduced MV-specific CTL may reflect a broader reduction in HLA class II-restricted CTL in patients with MS. To examine this question we studied the generation of CTL specific for herpes simplex virus type I (HSV). HSV-specific CTL, like MV-specific CTL is predominantly restricted by HLA class II molecules. We found that patients with MS had reduced generation of CTL to both MV and HSV. Most, but not all patients who had reduced generation of CTL to one virus also had a similar impairment with respect to the second virus. Some patients, however, had a reduction in the generation of CTL only to MV or to HSV. These findings extend our earlier observations regarding reduced MV-specific CTL in patients with MS to a second HLA class II-restricted virus, HSV. Such a reduction may reflect discrete impairments in immune function to separate viruses, possibly those that are associated with viral persistence, or may reflect a more generalized defect in HLA class II-restricted CTL.  相似文献   
83.
The β‐adhesin part of the Porphyromonas gingivalis W50 (ATCC 53978) protease HRgpA was cloned in an eukaryotic expression vector and expressed in COS‐7 cells. The monoclonal antibody MAb (61BG1.3), specific for the hemagglutinating domain of β‐adhesin, recognized the expressed β‐adhesin in the transfected cells both by immunoblot and immunofluorescence. Sprague Dawley rats were immunized intramuscularly with β‐adhesin encoding expression plasmid and expression plasmid without β‐adhesin insert. Skeletal muscle tissue at the site of immunization in the β‐adhesin immunized animals was shown to express this protein. The immunization induced a β‐adhesin‐specific antibody response. Sera from the immunized animals were tested for hemagglutination inhibiting activity. Due to high natural inhibiting activity in all rat sera tested, no increased hemagglutination inhibition was detected in sera from the β‐adhesin immunized animals.  相似文献   
84.
A novel balanced SSFP technique for the separation or suppression of different resonance frequencies (e.g., fat suppression) is presented. The method is based on applying two alternating and different repetition times, TR(1) and TR(2). This RF scheme manipulates the sensitivity of balanced SSFP to off-resonance effects by a modification of the frequency response profile. Starting from a general approach, an optimally broadened stopband within the frequency response function is designed. This is achieved with a TR(2) being one third of TR(1) and an RF-pulse phase increment of 90 degrees . With this approach TR(2) is too short ( approximately 1 ms) to switch imaging gradients and is only used to change the frequency sensitivity. Without a significant change of the spectral position of the stopband, TR(1) can be varied over a range of values ( approximately 2.5-4.5 ms) while TR(2) and phase cycling is kept constant. On-resonance spins show a magnetization behavior similar to balanced SSFP, but with maximal magnetization at flip angles about 10 degrees lower than in balanced SSFP. The total scan time is increased by about 30% compared to conventional balanced SSFP. The new technique was applied on phantoms and volunteers to produce rapid, fat suppressed images.  相似文献   
85.
Background  Hydroxyisohexyl 3-cyclohexene carboxaldehyde (HICC) is a synthetic fragrance ingredient. Case reports of allergy to HICC appeared in the 1980s, and HICC has recently been included in the European baseline series. Human elicitation dose–response studies performed with different allergens have shown a significant relationship between the patch-test threshold and the repeated open application test (ROAT) threshold, which mimics some real-life exposure situations. Fragrance ingredients are special as significant amounts of allergen may evaporate from the skin.
Objectives  The study aimed to investigate the relationship between elicitation threshold doses at the patch test and the ROAT, using HICC as the allergen. The expected evaporation rate was calculated.
Materials and methods  Seventeen HICC-allergic persons were tested with a dilution series of HICC in a patch test and a ROAT (duration up to 21 days). Seventeen persons with no HICC allergy were included as control group for the ROAT.
Results  The response frequency to the ROAT (in μg HICC cm−2 per application) was significantly higher than the response frequency to the patch test at one of the tested doses. Furthermore the response rate to the accumulated ROAT dose was significantly lower at half of the doses compared with the patch test. The evaporation rate of HICC was calculated to be 72% over a 24-h period.
Conclusions  The ROAT threshold in dose per area per application is lower than the patch test threshold; furthermore the accumulated ROAT threshold is higher than the patch test threshold, which can probably be explained by the evaporation of HICC from the skin in the open test.  相似文献   
86.
Ganoderma sinensis has been used widely in Oriental countries for the prevention and treatment of various diseases including cancer. Previous studies have shown that the lipid extract from Ganoderma exhibits direct cytotoxicity against tumor cells. Here, it is reported that the lipid extract from germinating G. sinensis spores, at lower concentrations that have no direct tumoricidal activity, induce potent antitumor immune responses in human monocytes/macrophages. Upon stimulation with the lipid extract, monocytes/macrophages exhibited markedly increased production of proinflammatory cytokines and surface expression of costimulatory molecules. Conditioned medium from stimulated cells effectively suppressed the growth of tumor cells. Apparently, the lipid extract triggered macrophage activation via a mechanism different from that associated with LPS. Moreover, it was observed that the lipid extract could partially re‐establish the antitumor activity of the immunosuppressive tumor‐associated macrophages. These results indicated that in addition to its direct tumoricidal activity, the lipid extract from G. sinensis spores could exert antitumor activity by stimulating the activation of human monocytes/macrophages. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   
87.
Serum levels of Epinephrine (E), norepinephrine (NE), heart rate (HR), skin conductance reaction (SCR) and skin conductance level (SCL) were measured in schizophrenic, endogenous depressed and anxiety patients as well as in normal controls. Conditions were rest, noise and a mental arithmetic (MA) task. Schizophrenic and depressed patients had an attenuated HR response to MA. Moreover, Schizophrenic patients also had higher NE base level and the highest NE secretion during noise. Anxiety and depressed patients showed significantly lower phasic electrodermal activity (SCR) throughout the whole trial, exclusively anxiety patients had significantly higher tonic electrodermal activity (SCL). These findings indicate that autonomous reactions discriminate between patient groups and controls as well as between each other.  相似文献   
88.
Seventeen patients who had undergone extensive small bowel resection were studied for calcium absorption (FACa) and plasma vitamin D metabolites. FACa was measured by a double radio-tracer technique and expressed as percentage of total oral dose. FACa was decreased compared with controls (34%, range: 3-46 v 65%, range: 57-73, P less than 0.01). A positive correlation (r = 0.49, P = 0.05) was found between FACa and the remaining length of small bowel (SBL). As wide variations in both SBL and duration after surgery were observed among the seventeen investigated patients, we were led to individualize less heterogeneous subgroups of patients. Better correlations were found when the patients were divided into two subgroups according to whether the time interval between the resection and the investigation was shorter (r = 0.75, n = 11, P less than 0.02) or longer (r = 0.89, n = 6, P = 0.05) than 2 years. In thirteen patients who had a SBL shorter than 100 cm, a positive correlation was observed between FACa and the time interval after surgery (months): r = 0.65, P less than 0.05. Plasma 1,25 (OH)2D was markedly reduced in the whole group (31 pmol l-1, range: 8-108) compared with controls (103 pmol-1, range: 59-134, P less than 0.01). The present study shows that in extensively small bowel resected patients, calcium absorption is reduced, the alteration being dependent both on the length of the remnant small bowel and on the time after surgery.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   
89.
目的 探讨磁共振脑表面成像技术在矢状窦旁腩膜瘤手术中的应用价值.方法 分析本院经头颅CT及MRI诊断为矢状窦旁脑膜瘤,利用显微手术技术切除并经病理证实的的22例患者;术前均运用磁共振脑表面成像技术评估与肿瘤关系密切的脑表面回流静脉情况.术中根据成像结果有目的 地保护重要的回流静脉,对比患者手术前后神经功能恢复状况,并进行随访来评价手术效果.结果 22例患者的术前磁共振脑表面成像中脑表面回流静脉与术中所见高度一致.术后患者恢复良好,未出现与静脉损伤相关的并发症.结论 磁共振脑表面成像技术能在术前明确矢状窦旁脑膜瘤与脑表面回流静脉之间关系,可在术前对患者肿瘤表面脑回流静脉做出正确的评估,对脑表面重要回流静脉的保护提供了准确的影像学依据,对患者神经功能的保护及术后恢复起到重要作用.  相似文献   
90.
The aim was to determine whether the immunogenicity of an investigational hepatitis B vaccine (spHB) is at least as high as that of a licensed control vaccine, Engerix B®, and to evaluate its safety before inclusion in new pediatric combination vaccines. Two randomized, controlled, blind-observer, Phase 3 trials were performed: one in Argentina (344 participants aged 10–15 years, 10 μg HBsAg/dose) and one in Uruguay (344 participants aged 16–45 years, 20 μg HBsAg/dose). Both vaccines were given in a 0, 1, 6 month schedule to all participants with a baseline anti-Hep B antibody titer <0.6 mIU/mL. Antibody titers were measured pre-dose 1, 1 month after dose 2, pre-dose 3, and 1 month after dose 3. Statistical non-inferiority analyses were performed on seroprotection rates (SP) post-dose 3 (% with anti-Hep B titers ≥10 mIU/mL; delta non-inferiority limit of −10%). In both studies, SP for the spHB vaccine was 100% and the spHB vaccine was non-inferior in terms of SP to the licensed control vaccine. GMTs post-dose 3 were approximately 1.8- and 4.1-fold higher for spHB in the 10–15 year and 16–45 year age groups, respectively. Reactogenicity was low for each vaccine, after each dose. This highly immunogenic hepatitis B candidate vaccine was selected for further investigation as a component of new pediatric combination vaccines.  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