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   4351篇
  免费   591篇
  国内免费   14篇
耳鼻咽喉   27篇
儿科学   196篇
妇产科学   135篇
基础医学   400篇
口腔科学   43篇
临床医学   917篇
内科学   819篇
皮肤病学   40篇
神经病学   551篇
特种医学   157篇
外科学   451篇
综合类   56篇
一般理论   6篇
预防医学   597篇
眼科学   122篇
药学   188篇
中国医学   3篇
肿瘤学   248篇
  2023年   67篇
  2022年   41篇
  2021年   78篇
  2020年   93篇
  2019年   92篇
  2018年   142篇
  2017年   158篇
  2016年   145篇
  2015年   164篇
  2014年   165篇
  2013年   258篇
  2012年   202篇
  2011年   254篇
  2010年   219篇
  2009年   232篇
  2008年   252篇
  2007年   246篇
  2006年   222篇
  2005年   241篇
  2004年   210篇
  2003年   210篇
  2002年   180篇
  2001年   73篇
  2000年   59篇
  1999年   48篇
  1998年   69篇
  1997年   58篇
  1996年   55篇
  1995年   50篇
  1994年   33篇
  1993年   35篇
  1992年   46篇
  1991年   56篇
  1990年   36篇
  1989年   24篇
  1988年   42篇
  1987年   44篇
  1986年   40篇
  1985年   25篇
  1984年   22篇
  1983年   29篇
  1982年   25篇
  1981年   21篇
  1980年   13篇
  1979年   23篇
  1977年   15篇
  1975年   19篇
  1974年   23篇
  1971年   12篇
  1970年   13篇
排序方式: 共有4956条查询结果,搜索用时 15 毫秒
31.
32.
33.
34.
BackgroundOxygenated right ventricular assist device (oxyRVAD) placement has become more streamlined with the introduction of the dual-lumen pulmonary artery cannula. Peripherally cannulated oxyRVAD may provide oxygenation support with right heart support as an alternative to venoarterial extracorporeal membrane oxygenation (ECMO) as a bridge to lung transplantation.MethodsA single-institution, retrospective analysis was performed on patients placed on oxyRVAD with a dual-lumen pulmonary artery cannula with the intention of bridging to lung transplantation in 2019.ResultsFour patients with idiopathic pulmonary fibrosis were placed on oxyRVAD as a bridge to transplantation. Two patients were extubated and ambulated while waiting for a lung offer, and two patients required conversion to venoarteriovenous ECMO (VAV ECMO) from oxyRVAD. The median waiting time for extracorporeal life support (ECLS) was 42 h. All patients underwent double lung transplantation. Two patients stayed on oxyRVAD, and one patient was placed on venovenous ECMO (VV ECMO) after transplantation. Primary graft dysfunction score at 72 h after transplantation was grade 1 in three patients and grade 3 in one patient.ConclusionsPeripherally cannulated oxyRVAD with percutaneous dual-lumen venous cannula could be an ambulatory bridge for lung transplantation. It is unknown whether oxyRVAD is feasible as a long-term bridge to lung transplantation.  相似文献   
35.
The DNA-dependent protein kinase catalytic subunit (DNA-PKcs; encoded byPRKDC) functions in DNA non-homologous end-joining (NHEJ), themajor DNA double strand break (DSB) rejoining pathway. NHEJ also functions duringlymphocyte development, joining V(D)J recombination intermediates during antigenreceptor gene assembly. Here, we describe a patient with compound heterozygousmutations in PRKDC, low DNA-PKcs expression, barely detectableDNA-PK kinase activity, and impaired DSB repair. In a heterologous expression system,we found that one of the PRKDC mutations inactivated DNA-PKcs, whilethe other resulted in dramatically diminished but detectable residual function. Thepatient suffered SCID with reduced or absent T and B cells, as predicted fromPRKDC-deficient animal models. Unexpectedly, the patient was alsodysmorphic; showed severe growth failure, microcephaly, and seizures; and hadprofound, globally impaired neurological function. MRI scans revealedmicrocephaly-associated cortical and hippocampal dysplasia and progressive atrophyover 2 years of life. These neurological features were markedly more severe thanthose observed in patients with deficiencies in other NHEJ proteins. Although loss ofDNA-PKcs in mice, dogs, and horses was previously shown not to impair neuronaldevelopment, our findings demonstrate a stringent requirement for DNA-PKcs duringhuman neuronal development and suggest that high DNA-PK protein expression isrequired to sustain efficient pre- and postnatal neurogenesis.  相似文献   
36.
Bouget, D. (1998). The Juppé Plan and the future of the French social welfare system. Journal of European Social Policy, 8(2) 154-172.  相似文献   
37.
The effect of experimentally induced seizure activity on the functional reorganization of motor maps has not previously been investigated. Furthermore, while the functional reorganization of motor maps has been thought to involve increases in synaptic communication, there has yet to be a test of this hypothesis. Here we show that repeated seizure activity (kindling), that is accompanied by increased synaptic strength within adult rat motor cortex, results in a doubling of the caudal forelimb motor area. We measured neo-cortical evoked potentials in the right hemisphere prior to 25 days of electrical kindling of the medial frontal corpus callosum or amygdala and re-measured them either 1 or 21 days following the last kindling session. Then, using high resolution intracortical microstimulation (ICMS), the caudal forelimb area in the left hemisphere was mapped. This is the first report of any procedure causing a motor representation to double in size. Furthermore, this expansion was related to the enhanced area of a neocortical polysynaptic field potential and not the motor convulsions per se. Moreover, both the motor map and field potential enhancements were persistent in nature and could be driven from either cortical or limbic sites. The data have implications for human populations with epilepsy.  相似文献   
38.
The concentration of melatonin was determined in serum samples obtained at 15-min intervals during a 4-h period from seven normal girls, 9.5-16.5 yr of age, and eight normal boys, 9.0-16.8 yr of age. All samples were obtained between 0800 and 1300 h. An episodic pattern of melatonin secretion was found in all subjects. There was no significant (P greater than 0.1) difference between girls and boys as to number of episodes [3.1 +/- 0.4 (+/- SD) vs. 3.4 +/- 0.5 per 4 h), absolute melatonin increase (49.0 +/- 6.7 vs. 50.4 +/- 4.1 pg/ml), or apparent melatonin half-life (20.3 +/- 0.8 vs. 20.8 +/- 1.0 min). The mean absolute increase during secretory episodes correlated (r = 0.843; P less than 0.005) with the mean melatonin concentration per 4 h, and a significant (P less than 0.05) inverse correlation (r = -0.508) was found between the mean percent increment of the melatonin secretory episode and the mean apparent melatonin half-life. A significant correlation between melatonin secretion and previously reported (22) episodic LH secretion was not found. In girls and boys, the mean melatonin concentration increased with advancing puberty. The increase in melatonin concentration was due to an increase in the amplitude of secretory episodes. These data are consistent with an influence of gonadal function on melatonin secretion.  相似文献   
39.
Introduction: We sought to the ideal sites for botulinum toxin injection by examining the intramuscular nerve patterns of the ankle invertors. Methods: A modified Sihler method was performed on the flexor hallucis longus, tibialis posterior, and flexor digitorum longus muscles (10 specimens each). The muscle origins, nerve entry points, and intramuscular arborization areas were measured as a percentage of the total distance from the most prominent point of the lateral malleolus (0%) to the fibular head (100%). Results: Intramuscular arborization patterns were observed at 20–50% for the flexor hallucis longus, 70–80% for the tibialis posterior, and 30–40% for the flexor digitorum longus. Conclusions: These findings suggest that treatment of muscle spasticity of the ankle invertors involves botulinum toxin injections in specific areas. These areas, corresponding to the areas of maximum arborization, are recommended as the most effective and safest points for injection. Muscle Nerve 53 : 742–747, 2016  相似文献   
40.
It has been shown that the risk of breast cancer developing in certain morphologically identifiable benign breast lesions correlates with expression of estrogen receptor alpha (ER-alpha). Although ER-alpha and ER-beta genes share a large degree of homology, it is generally thought that their distribution and functions are substantially different in many tissues. Recent development of reliable antibodies to ER-beta has provided this first opportunity to test the hypothesis that the likelihood of malignant transformation in morphologically benign breast lesions can be accurately defined by the distribution and level of ER-beta expression relative to that of ER-alpha. Using a monoclonal antibody, ER-beta protein expression has been analyzed in 53 normal breasts and compared with a cohort of histologically distinct breast lesions of different prognostic risk (54 hyperplasia of usual type, 35 ductal carcinoma in situ, and 141 invasive cancers). All of these tissues were also assessed for ER-alpha. Expression of ER-beta protein was also analyzed in an additional spectrum of benign breast lesions with low or negligible risk of progression to malignancy. The median proportion of cells expressing ER-beta was highest in normal breast lobules (median 94.33%, interquartile range 78.25-99.00) but declined significantly through usual ductal hyperplasia (median 76.67, interquartile range 49.17-95.00, P = 0.002) and ductal carcinoma in situ (median 70.00, interquartile range 59.00-85.00, P = 0.009) to invasive cancer (median 60.00, interquartile range 50.00-80.00, P < 0.001). An appreciable proportion (33.81%) of ER-alpha-negative invasive cancers expressed ER-beta. A high but variable level of ER-beta expression occurred in the benign lesions. The data from the intact histologic tissues were evaluated with respect to the relative expression of ER-alpha and ER-beta in five mammary cell lines of different behavioral phenotype (MCF7, ZR-75, T47D, MDAMB231, HUMA121). The highly significant differences in expression and distinct tissue distributions of ER-alpha and ER-beta within the histologic lesions of defined risk, together with the data from the cell lines, support the original hypothesis that the tissue concentration, relative occurrence, and/or interaction of these two types of estrogen receptor may play an important role in modulating mammary tumorigenesis.  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