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   3356篇
  免费   196篇
  国内免费   8篇
耳鼻咽喉   32篇
儿科学   55篇
妇产科学   68篇
基础医学   505篇
口腔科学   53篇
临床医学   378篇
内科学   717篇
皮肤病学   37篇
神经病学   346篇
特种医学   145篇
外科学   490篇
综合类   7篇
一般理论   1篇
预防医学   137篇
眼科学   48篇
药学   265篇
中国医学   2篇
肿瘤学   274篇
  2023年   21篇
  2022年   99篇
  2021年   148篇
  2020年   67篇
  2019年   81篇
  2018年   88篇
  2017年   58篇
  2016年   89篇
  2015年   98篇
  2014年   123篇
  2013年   136篇
  2012年   214篇
  2011年   245篇
  2010年   141篇
  2009年   104篇
  2008年   195篇
  2007年   229篇
  2006年   174篇
  2005年   202篇
  2004年   161篇
  2003年   161篇
  2002年   157篇
  2001年   32篇
  2000年   45篇
  1999年   34篇
  1998年   26篇
  1997年   20篇
  1996年   17篇
  1995年   14篇
  1994年   12篇
  1992年   28篇
  1991年   22篇
  1990年   26篇
  1989年   26篇
  1988年   23篇
  1987年   16篇
  1986年   21篇
  1985年   18篇
  1984年   15篇
  1983年   10篇
  1979年   17篇
  1976年   9篇
  1974年   10篇
  1972年   11篇
  1971年   12篇
  1970年   12篇
  1969年   15篇
  1968年   8篇
  1967年   11篇
  1966年   8篇
排序方式: 共有3560条查询结果,搜索用时 218 毫秒
1.
BACKGROUND: Stringent transcranial Doppler (TCD) criteria for diagnosing occlusion are needed for more reliable TCD performance at bedside in the acute stroke setting. SUBJECTS AND METHODS: At three academic stroke centers, we performed TCD examination for patients with symptoms of cerebral ischemia who underwent digital subtraction angiography (DSA). We used a standard insonation protocol with power M-mode Doppler (PMD) TCD (TCD 100 M, Spencer Technologies Inc., Seattle, WA). We collected mean flow velocity (MFV), pulsatility indices (PI), and power M-mode resistance signature (absent, high, or low) in symptomatic middle (MCA), anterior (ACA), posterior (PCA), and in affected (a), ipsilateral (i), and contralateral (c-lat) cerebral arteries. Ratios of aMCA/c-lat MCA, aMCA/iACA, and aMCA/iPCA MFV were subsequently calculated. PMD-TCD flow findings were evaluated with a receiver-operating characteristic (ROC) analysis for angiographically proven MCA occlusion. RESULTS: We studied 120 patients with acute cerebral ischemia with PMD-TCD examinations prior to or immediately after DSA. Lower aMCA velocities pointed to higher probability of occlusion (P= .055). The aMCA/iPCA MFV ratio was superior to the aMCA/iACA ratio and strongly predictive of occlusion at a threshold ratio of 0.5 (RR 2.31 CI(95) 2.13-2.51). High resistance or absent M-mode flow signatures in the proximal MCA were present in 87% of M1 and M2 MCA occlusions (probability 87%). In the presence of a low-resistance PMD signature, obtaining the aMCA/iPCA MFV ratio <0.5 increases probability of occlusion to 87%. Normal MFV ratios and low-resistance M-mode signatures are highly predictive of a negative angiogram for MCA occlusion. CONCLUSION: In acute cerebral ischemia, reliable criteria for proximal MCA occlusion have been developed based on combination of MFV ratios and M-mode flow resistance signatures. Validation of these criteria will require multicenter studies.  相似文献   
2.
OBJECTIVES: CD62L was evaluated as a determinant of human pre-effector T cells. STUDY DESIGN AND SETTING: Phenotype and cytokine secretion profiles of CD62L cells were determined based on activation status. RESULTS: CD62L(Low) T cells demonstrated significantly higher secretion of interleukin (IL)-10 and interferon (IFN)-gamma than did CD62L(High) T cells. After activation, the majority of cells expressed high levels of the CD62L surface marker. Postactivation levels of IL-10 production remained elevated or unchanged. In a murine B16 melanoma model, freshly isolated CD62L(Low) tumor draining lymph nodes (TDLN) T cells showed increased secretion of IL-2 and IL-4 but not of IL-10 or IFN-gamma. The surface expression of CD62L and cytokine secretion patterns were maintained after activation with concomitant increases in IL-10. CONCLUSION: Our results provide evidence that CD62L(Low) T cells in TDLNs of progressively growing squamous cell carcinoma of the head and neck differ phenotypically and functionally from those of mouse origin. SIGNIFICANCE: Characterization of this human CD62L(Low) T cell population provides initial insight regarding novel surface markers in TDLN T cells that might correlate with antitumor reactivity.  相似文献   
3.
Cancer chemotherapy with the application of several drugs is studied. The negative and inhibiting effect of the tumour on normal cells is taken into account. Under certain hypotheses, we determine the optimal regimen that minimizes the tumour burden at the end of a fixed period of therapy while maintaining several normal cell populations above prescribed levels. More precisely, it is demonstrated that the optimal drug administration corresponds to the strategy of intensive chemotherapy.  相似文献   
4.
5.
The USSR statistics on malignant neoplastic diseases of the urinary system and male sexual organs which comprised 5.7 per cent in the total mortality was presented for the first time. More than a 50 per cent increment in the death rate from these tumors was documented between 1975 and 1987. Annually, prostatic carcinoma is diagnosed in almost 10 thousand patients and cancer of the urinary bladder in 15 thousand patients. Maximal prevalence of the disease has been recorded in the Baltic republics, the Ukraine and Byelorussia. The detection rate of the aforementioned diseases, Stages I-II, is about 40 per cent. The estimate revealed that the total number of the registered oncological patients was 100 thousand persons. The problems in organization of the oncological care system, material and technical supplies and professional training should be considered.  相似文献   
6.
7.
8.
9.
BACKGROUND: Intravenous tissue plasminogen activator (TPA) therapy can be monitored with 2 MHz transcranial Doppler (TCD). This article describes the design of CLOTBUST (combined lysis of thrombus in brain ischemia using transcranial ultrasound and systemic TPA), the first prospective international multicenter randomized clinical trial of noninvasive externally applied ultrasound to enhance systemic thrombolysis in human stroke. SUBJECTS: Patients with acute ischemic stroke eligible for intravenous TPA therapy within 3 hours of symptom onset who have detectable middle cerebral artery occlusion on a prebolus TCD are included in this trial. All patients receive standard 0.9 mg/kg TPA therapy. Patients are randomized (1:1) to either 2 hours of continuous monitoring with TCD or placebo monitoring. FDA-approved portable diagnostic TCD equipment and standard headframes (Marc series, Spencer Technologies, Seattle, WA) are used. Output of TCD units is set at 100% power achievable at depths of insonation that display the worst TIBI flow grade signals. METHODS AND END-POINTS: Acute MCA occlusion on prebolus TCD is defined as thrombolysis in brain ischemia (TIBI) flow grades 0-3. Treating physicians are blinded to randomization assignment, and certified scorers measure stroke severity using the National Institute of Health Stroke Scale (NIHSS). Safety of continuous TCD monitoring is determined by rates of symptomatic (NIHSS score increase by 4+ points) intracerebral hemorrhage within 72 hours after initial symptom onset. Potential enhancement of TPA therapy will be determined using combined primary end-point of early complete recanalization on TCD (TIBI flow grades 4-5), dramatic recovery (NIHSS < or = 3 points), or decline in the NIHSS > or = 10 points repeatedly measured every 30 minutes within 2 hours after TPA bolus. Other end-points include recovery at 24 hours and 3 months, modified Rankin scores (mRS) are obtained at 90 days, and favorable outcome is determined as NIHSS or mRS scores 0-1. CONCLUSIONS: The aim of phase II CLOTBUST trial is to determine the rates of early complete recanalization and dramatic/early clinical recovery in TPA + TCD and TPA groups. The sample size is set at 126 patients since a medium effect size (.50) is anticipated for TPA + TCD group vs TPA alone to achieve combined primary end-point.  相似文献   
10.
Among mutations associated with autosomal dominant and sporadic Parkinson's disease (PD) the G2019S substitution in the leucine-rich repeat kinase 2 (LRRK2) gene is the most frequently identified. To estimate its frequency in Russia, we analyzed 208 patients with PD from the Northwestern region of Russia. Of these, 51 patients were probands from families with PD compatible with autosomal dominant inheritance. The control group represented 161 subjects without neurological disorders settled in the same region. The frequency of the G2019S mutation was greater in familial PD (2 [3.9%] of 51) than in sporadic PD (1 [0.6%] of 157). In addition, this mutation was found in the proband's father, who also had PD, in 1 PD family, and in 1 carrier without signs of PD at age 40 in another PD family. All carriers were heterozygous for the G2019S mutation and reported the Ashkenazi Jewish origin. The mutation was not found in the control group.  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