首页 | 官方网站   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   2628篇
  免费   558篇
  国内免费   51篇
医药卫生   3237篇
  2024年   7篇
  2023年   14篇
  2022年   32篇
  2021年   53篇
  2020年   129篇
  2019年   167篇
  2018年   165篇
  2017年   177篇
  2016年   181篇
  2015年   178篇
  2014年   205篇
  2013年   226篇
  2012年   194篇
  2011年   193篇
  2010年   170篇
  2009年   105篇
  2008年   117篇
  2007年   100篇
  2006年   92篇
  2005年   80篇
  2004年   72篇
  2003年   95篇
  2002年   88篇
  2001年   77篇
  2000年   47篇
  1999年   25篇
  1998年   29篇
  1997年   21篇
  1996年   25篇
  1995年   13篇
  1994年   17篇
  1993年   17篇
  1992年   6篇
  1991年   10篇
  1990年   11篇
  1989年   8篇
  1988年   7篇
  1987年   10篇
  1986年   10篇
  1985年   8篇
  1984年   11篇
  1983年   3篇
  1982年   6篇
  1981年   11篇
  1980年   4篇
  1979年   5篇
  1978年   4篇
  1977年   6篇
  1974年   2篇
  1970年   2篇
排序方式: 共有3237条查询结果,搜索用时 9 毫秒
1.
Patients with multiple system atrophy (MSA) present large changes in blood pressure (BP) due to autonomic disturbances. We analyzed how this change may influence dynamic cerebral autoregulation (DCA). Simultaneous recordings of arterial BP (Finapres) and middle cerebral artery (MCA) blood flow velocity (BFV) (transcranial Doppler) were performed in 10 patients with MSA (61 +/- 12 yr of age) and 12 healthy volunteers (61 +/- 11 yr of age): cerebral BFV response to oscillations in mean BP was studied in the supine position by cross-spectral analysis of mean BP and mean MCA BFV. The DCA was also studied during the decrease in BP the first seconds when standing up from a sitting position by the assessment of the cerebrovascular resistance index (CR; mean BP/mean MCA BFV ratio). The MCA BFV/BP cross-spectral analysis showed a phase for the mid-frequency band (0.07-0.2 Hz) significantly larger in MSA, suggesting more active autoregulation in response to larger changes in BP. Changes in CR reflecting the rate of autoregulation, when standing did not differ between the two groups. These data suggest that dynamic cerebral autoregulation is preserved in MSA.  相似文献   
2.
目的分析各种因素对手工凝聚胺试验的影响;方法应用手工凝聚胺(manual polgbrene test,MPT)做交叉配血及抗体筛选试验;结果血液标本、操作手法、凝聚胺试剂、药物(肝素、止血敏、高浓度KCl等)等对试验均有影响;其中以药物、操作手法影响较大,可致假阴性和假阳性结果;结论手工凝聚胺试验做交叉配血及抗体筛选时应注意排除药物和操作手法对试验结果的影响。  相似文献   
3.
BACKGROUND: Alternaria alternata is one of the most important allergenic fungi worldwide. Mannitol dehydrogenase (MtDH) has previously been shown to be a major allergen of Cladosporium herbarum and cross-reactivity has been demonstrated for several fungal allergens. OBJECTIVE: The present study's objective was to clone the MtDH from an A. alternata cDNA library, express and purify the recombinant non-fusion protein and test its IgE-binding properties. Methods A cDNA library prepared from A. alternata hyphae and spores was screened for mannitol dehydrogenase by DNA hybridization with the radioactively labelled C. herbarum homologue as a probe. The resulting clone was sequenced and heterologously expressed in Escherichia coli as a recombinant non-fusion protein, which was purified to homogeneity and analysed for its IgE-binding capacity. RESULTS: The coding sequence of the full-length cDNA clone comprises 798 bp encoding a protein with a molecular mass of 28.6 kDa and a predicted pI of 5.88. Protein sequence analysis revealed an identity of 75% and a homology of 86% between the MtDHs of A. alternata and C. herbarum. The functional mannitol dehydrogenase was expressed in the E. coli strain BL21(DE3) transformed with the vector pMW172 and purified to homogeneity. The enzyme catalyses the NADPH-dependent conversion of d-fructose to d-mannitol. In IgE-ELISA and immunoblots, MtDH is recognized by 41% of A. alternata-allergic patients. In vivo immunoreactivity of the recombinant MtDH was verified by skin prick testing. Finally, inhibition-ELISA experiments confirmed cross-reactivity between the MtDHs of A. alternata and C. herbarum. CONCLUSION: Mannitol dehydrogenase (Alt a 8) represents an important new allergen of the ascomycete A. alternata that might be suitable for improving diagnostic and therapeutic procedures.  相似文献   
4.
The immunologic risk associated with donor-specific antibodies (DSA) against Class II human leukocyte antigens (HLA) in kidney transplant (KTx) recipients is unclear. The aim of this study was to determine the outcome of KTx when DSA was detected only against HLA Class II. To isolate the impact of anti-Class II DSA, we retrospectively analyzed 12 KTx recipients who at baseline had a positive B-cell flow cytometric crossmatch (FXM) and a negative T-cell FXM. Using alloantibody specification analysis, 58.3% (7/12) had DSA against donor Class II and 41.7% had no demonstrable DSA. Biopsy-proven AMR occurred in 57% (4/7) in the Class II(+) group and 0% in the Class II(-) group (p > 0.05). Peritubular capillaries stained positive for C4d in 86% (6/7) of the Class II(+) patients and in 40% (2/5) of the Class II(-) patients (p > 0.05). One patient in the Class II(+) group lost their graft at 3 months to accelerated transplant glomerulopathy, while all other grafts were functioning 3-37 months posttransplant despite the persistence of anti-Class II DSA. We conclude that KTx recipients with clearly defined anti-Class II DSA are at risk for humoral rejection suggesting that desensitization and/or close posttransplant monitoring may be needed to prevent AMR.  相似文献   
5.
In an open, randomized cross-over study in 124 patients, we compared the efficacy, safety and patient preference of oral and subcutaneous sum triptan in the acute treatment of migraine. Patients were treated for 3 attacks or 3 months and then crossed over. Primary clinical efficacy was defined as a reduction in headache severity on a four-point self-rating scale from severe (3) or moderate (2) to mild (1) or none (0), or mild (1) to none (0). Efficacy was evaluated 2 h after the administration of subcutaneous and 4h after the administration of oral sumatriptan. Subcutaneous sumatriptan was significantly more effective than oral sumatriptan in relieving headache (over all three attacks 78% vs 61% improvement), improving clinical disability (55% vs 41 % improvement) and relieving nausea (69% vs 53%), vomiting (72% vs 32%) and phono- or photophobia (67% vs 49%). Median time to recurrence was shorter after subcutaneous (12.5 h) than after oral sumatriptan (18 h); the number of patients experiencing a recurrence was similar Patients reported more adverse events after subcutaneous sumatriptan (1.32 per attack) than after the oral form (0.85 per attack), but all adverse events were mild to moderate in intensity and of short duration. Patient opinion was more often positive after subcutaneous sumatriptan. These results may be useful in counselling patients to choose between the available marketed formulations of sumatriptan.  相似文献   
6.
目的 探讨在“2× 4”矫治技术中弓丝弯制的方法及原理。方法 替牙牙合时期前牙反牙合患者 2 4例 ,使用粗弓丝 ,在其弓丝上弯制各种曲形 ,并根据不同错牙合类型 ,处理各种曲与牙齿、带环关系 ,防止出现磨牙旋转移动等异常。结果  2~ 6个月纠正反牙合 ,2 4例替牙牙合时期反牙合患者得以早期矫治。结论 本方法矫治时间短 ,效果明显 ,操作简单 ,能够达到较为理想的矫治效果  相似文献   
7.
介绍了我院1993年7月1日~1993年12月20日出院的1031例病人医院感染病率的监测分析,半年中感染率为8.4%,妇产科疗区发病率高于外科疗区,感染部位以泌尿道、下呼吸道、手术伤口为最多,侵袭性操作及易感因素引起的感染在感染病例中分别占40.2%和59.8%。  相似文献   
8.
It has been suggested that apparent diffusion coefficient (ADC) contrast can be sensitive to cerebral blood flow (CBF) changes during brain activation. However, current ADC imaging techniques have an inherently low temporal resolution due to the requirement of multiple acquisitions with different b-factors, as well as potential confounds from cross talk between the deoxyhemoglobin-induced background gradients and the externally applied diffusion-weighting gradients. In this report a new method is proposed and implemented that addresses these two limitations. Specifically, a single-shot pulse sequence that sequentially acquires one gradient-echo (GRE) and two diffusion-weighted spin-echo (SE) images was developed. In addition, the diffusion-weighting gradient waveform was numerically optimized to null the cross terms with the deoxyhemoglobin-induced background gradients to fully isolate the effect of diffusion weighting from that of oxygenation-level changes. The experimental results show that this new single-shot method can acquire ADC maps with sufficient signal-to-noise ratio (SNR), and establish its practical utility in functional MRI (fMRI) to complement the blood oxygenation level-dependent (BOLD) technique and provide differential sensitivity for different vasculatures to better localize neural activity originating from the small vessels.  相似文献   
9.
目的 探讨更有效矫治前反牙合的方法。方法 本文选择了 38例恒前牙反牙合、反覆牙合深而反覆盖浅、下牙列基本整齐、磨牙关系基本中性的病例 ,采用上颌方丝弓加下颌后牙牙合垫相结合的方法进行矫治。结果 平均 7个月完成矫治 ,并取得满意疗效。结论 对具有较深反覆牙合的恒前牙反牙合 ,采用上颌方丝弓与下颌后牙牙合垫相结合的方法矫治 ,明显的提高了矫治效率  相似文献   
10.
①目的 了解重型病毒性肝炎病人医院感染病原微生物的分布及耐药情况。②方法 对595例重型病毒性肝炎住院病人进行医院感染的调查分析,并用分离培养法鉴定感染菌,使用E-test法进行耐药谱的检测。③结果 在595例病人中,有182例发生医院感染,感染率为30.6%,感染部位以腹腔为主,占49.7%,共分离出病原菌188株,以革兰阴性杆菌为主,占75.4%,多数感染菌对常用抗生素耐药。④结论 重型病毒性肝炎医院感染发生率较高,应引起足够重视。  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-23

京公网安备 11010802026262号