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   5451篇
  免费   314篇
  国内免费   20篇
耳鼻咽喉   40篇
儿科学   143篇
妇产科学   139篇
基础医学   729篇
口腔科学   562篇
临床医学   398篇
内科学   1201篇
皮肤病学   166篇
神经病学   568篇
特种医学   172篇
外科学   569篇
综合类   48篇
预防医学   522篇
眼科学   46篇
药学   288篇
中国医学   37篇
肿瘤学   157篇
  2023年   43篇
  2022年   99篇
  2021年   162篇
  2020年   111篇
  2019年   187篇
  2018年   202篇
  2017年   150篇
  2016年   147篇
  2015年   172篇
  2014年   211篇
  2013年   283篇
  2012年   440篇
  2011年   445篇
  2010年   239篇
  2009年   191篇
  2008年   350篇
  2007年   347篇
  2006年   273篇
  2005年   245篇
  2004年   152篇
  2003年   162篇
  2002年   157篇
  2001年   106篇
  2000年   94篇
  1999年   68篇
  1998年   46篇
  1997年   45篇
  1996年   40篇
  1995年   34篇
  1994年   39篇
  1993年   30篇
  1992年   43篇
  1991年   31篇
  1990年   29篇
  1989年   38篇
  1988年   38篇
  1987年   30篇
  1986年   32篇
  1985年   35篇
  1984年   21篇
  1983年   14篇
  1982年   13篇
  1981年   17篇
  1979年   19篇
  1977年   14篇
  1976年   20篇
  1975年   13篇
  1970年   13篇
  1969年   15篇
  1968年   14篇
排序方式: 共有5785条查询结果,搜索用时 15 毫秒
91.

Cd is a non-essential metal and highly toxic to plants, animals and humans, even at very low concentrations. Cd has been found in cocoa beans and in their products, as in the case of chocolate. Mn plays an important role in photosynthetic and can interact with Cd and attenuate its toxic effects on plants. The objective of this work was to evaluate the mechanisms of Mn response in the mitigation of Cd toxicity in young plants of the CCN 51 cacao genotype submitted to 0.8?mmol?Cd kg?1, 1.6?mmol Mn kg?1 or the combination of 0.4?mmol?Cd kg?1?+?0.8?mmol Mn kg?1 soil, together with the control treatment (without addition of Cd and Mn in soil), by means of analysis of changes in the profile of exclusive proteins (EP) and differentially accumulated proteins (DAP). Leaf and root proteins were extracted and quantified from the different treatments, followed by proteomic analysis. About eight DAP and 38 EP were identified in leaves, whereas in roots 43 DAP and 21 EP were identified. Some important proteins induced in the presence of Cd and repressed in the presence of Cd?+?Mn or vice versa, were ATPases, isoflavone reductase, proteasome and chaperonin. It was concluded that proteins involved in oxidoreduction and defense and stress response processes, in addition to other processes, were induced in the presence of Cd and repressed in the presence of Cd?+?Mn. This demonstrated that Mn was able to mitigate the toxic effects of Cd on young plants of the CCN 51 cocoa genotype.

  相似文献   
92.
93.
94.
Our previous studies have shown that stimulation of the anteroventral third ventricle (AV3V) region of the brain increases atrial natriuretic peptide (ANP) release, whereas lesions of the AV3V region or median eminence of the tuber cinereum block the release of ANP caused by blood volume expansion. These results suggest that participation of the central nervous system is critical to this response. The role of baroreceptors in the response was evaluated in the current research by studying the response of plasma ANP to blood volume expansion induced by intravenous injection of hypertonic saline solution (0.3 M NaCl, 2 ml/100 g of body weight, over 1 min) in conscious, freely moving male rats. Plasma samples were assayed for ANP by radioimmunoassay. In sham-operated rats, blood volume expansion induced a rapid increase in plasma ANP: the concentration peaked at 5 min and remained elevated at 15 min after saline injection. One week after deafferentation of the carotid-aortic baroreceptors, basal plasma ANP concentrations were highly significantly decreased on comparison with values of sham-operated rats; plasma ANP levels 5 min after blood volume expansion in the deafferented rats were greatly reduced. Unilateral right vagotomy reduced resting levels of plasma ANP but not the response to blood volume expansion; resting concentrations of plasma ANP and responses to expansion were normal in bilaterally vagotomized rats. In rats that had undergone renal deafferentation, resting levels of ANP were normal but the response to blood volume expansion was significantly suppressed. The evidence indicates that afferent impulses via the right vagus nerve may be important under basal conditions, but they are not required for the ANP release induced by blood volume expansion. In contrast, baroreceptor impulses from the carotid-aortic sinus regions and the kidney are important pathways involved in the neuroendocrine control of ANP release. The evidence from these experiments and our previous stimulation and lesion studies indicates that the ANP release in response to volume expansion is mediated by afferent baroreceptor input to the AV3V region, which mediates the increased ANP release via activation of the hypothalamic ANP neuronal system.  相似文献   
95.
BACKGROUND & AIMS: Interleukin (IL)-1 gene cluster proinflammatory polymorphisms have been associated with development of gastric atrophy and with increased risk of gastric carcinoma. We aimed to determine the association between IL-1 loci polymorphisms and increased risk of gastric carcinoma in samples from a Portuguese population, and to find whether there was any relationship with the histologic types of gastric carcinoma. METHODS: In a case-control study including 220 controls and 152 patients with gastric carcinoma (intestinal, 76; diffuse, 37; and atypical, 39), both the IL-1B-511 biallelic polymorphism and the IL-1RN penta-allelic variable number of tandem repeats were genotyped. RESULTS: We found a significant association between the IL-1 polymorphisms and increased risk for tumor development in patients with intestinal-type gastric carcinoma. A trend towards an increased risk of tumor development was also observed in patients with diffuse-type gastric carcinoma. No significant relationship was observed in patients with atypical carcinoma. Carriers of IL-1B-511T and IL-1RN*2 homozygotes had increased risk for developing intestinal-type gastric carcinoma with odds ratios of 2.7 (95% confidence interval [CI], 1.5-4.9) and 3.1 (95% CI, 1.5-6.5), respectively. Statistical analysis showed an interaction between the 2 loci with the risk conferred by the IL-1B-511T allele substantially increased (odds ratio, 9.0; 95% CI, 3.5-23.0) in individuals homozygous for the IL-1RN*2 allele. CONCLUSIONS: Our results provide further support to the association between IL-1 gene cluster proinflammatory polymorphisms and increased risk of gastric carcinoma. Furthermore, we found evidence pointing to the existence of a synergistic interaction between the IL-1B and IL-1RN polymorphisms.  相似文献   
96.

Purpose of Review

Describe the characteristics of chikungunya, dengue, and Zika in transplant recipients and immunocompromised hosts.

Recent Findings

Stem cell/bone marrow grafts, organs, and blood transfusions can transmit CHIKV/DENV/ZIKV infections, which are clinically similar, resembling influenza-like illness. Laboratory confirmation is necessary. In the acute phase, RT-PCR is preferred. DENV and ZIKV serology may cross-react. Delayed engraftment and extended viruria is observed in ZIKV+/HSCT recipients, while longer viremia is observed in DENV+/HSCT patients. Arbovirus persistence in organ tissues is generally unknown. Vaccine development is in early stages for CHIKV/ZIKV. No data is available to recommend the licensed DENV vaccine in transplant recipients.

Summary

In endemic areas, the assessment of epidemiological risk is mandatory. Donor deferral for 120 days in suspected or confirmed ZIKV+ has been recommended, while CHIKV+ donors should wait 30 days. No deferral is recommended for DENV+ donors. CHIKV/DENV/ZIKV tests should be included in the differential of febrile neutropenia and other transplant syndromes. Reassessment of DENV serology is urgently needed. Prospective studies are necessary to determine the impact of CHIKV/DENV/ZIKV in this special population.
  相似文献   
97.
98.
BACKGROUND: Obesity is one of the worlds greatest health problems. The Roux-en-Y gastric bypass is the gold standard treatment for severe obesity. Surgery in obese patients has an acceptable level of morbidity and mortality. The superobese patient, a subcategory of severe obese patients with a high surgical risk has not yet been analyzed as a group. METHODS: A retrospective and prospective cohort study was conducted enrolling 135 patients submitted to Roux-en-Y gastric bypass for treatment of severe obesity at the " Hospital das Clínicas" , Federal University of Pernambuco, Recife, PE, Brazil, between November 1997 and September 2003. The independent variables were possible risk factors of adverse outcomes: age, gender, weight, body mass index, diabetes, hypertension, hypercholesterolemia, sleep apnea, cardiopathy/coronariopathy, pneumopathy or any other co-morbidity. The dependent variables were major complications, minor complications and death. RESULTS: Diabetes (RR = 1.6 and CI = 1.02-2.40) and sleep apnea (RR = 1.8 and CI = 1.18-2.64) were associated to minor complications. Cardiopathy/coronariopathy were associated with major complications (RR = 5.42 and CI = 1.22-2.40) and death (RR = 16.25 and CI = 3.00-87.95). BMI >or=55 kg/m2 was associated with minor complications (RR = 1.58 and CI = 1.04-2.40), major complications (RR = 3.17 and CI = 1.03-9.80) and death (P = 0.007). After logistic regression, the body mass index >55 kg/m2 remained as a strong risk factor of death (OR = 3.6 and CI = 1.05-12.32). CONCLUSIONS: The body mass index >or=55 kg/m2 was the main risk factor for severe complications and death. Other risk factors affecting the outcome were diabetes, obstructive sleep apnea and cardiopathy/coronariopathy.  相似文献   
99.
100.
The impact of intra operative ultrasound in metastases liver surgery   总被引:1,自引:0,他引:1  
BACKGROUND: Twenty-five to 50% of the patients with hepatic metastases are potential candidates for curative surgery. Intraoperative ultrasound has been employed to guide the surgery. AIM: To evaluate this method in liver surgeries and compare it to other imaging methods. PATIENTS AND METHODS: Thirty-five patients (20 females, with median age of 56 years) with hepatic metastases were prospectively studied between February 2001 and July 2003. Patients had as primary tumors: colorectal cancer (24), neuroendocrine tumors (3), renal cell carcinoma (2), melanoma (2), others (4). Each patient was submitted to at least: computed tomography (30), ultrasonography (14) and magnetic resonance imaging (8). Intraoperative ultrasound was performed in all patients in order to detect liver nodules. The number and location of liver lesions were compared to preoperative results. RESULTS: Intraoperative ultrasound was useful in 23 (65.6%) of the 35 surgeries and changed the planned surgical strategy in 9 (25.7%). There was a statistical significant correlation between the mean number of nodules identified by ultrasonography, computed tomography, magnetic resonance imaging and intraoperative ultrasound. We found no statistical difference between magnetic resonance imaging and intraoperative ultrasound in identifying hepatic nodules. Fifty-five nodules were submitted to histological evaluation, the gold standard method and 52/55 (94.5%) were identified by intraoperative ultrasound. Intraoperative ultrasound identified 91.6% of the smaller than 1.5 cm lesions, ultrasonography identified 15.0% of them, computed tomography 33.3% and magnetic resonance imaging 66.6%. CONCLUSIONS: Intraoperative ultrasound is crucial in the evaluation and decision making in hepatic surgery. Intraoperative ultrasound presents the highest sensibility in the detection of hepatic nodules compared to other imaging methods, especially for small lesions.  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