全文获取类型
收费全文 | 1506篇 |
免费 | 401篇 |
国内免费 | 21篇 |
出版年
2024年 | 8篇 |
2023年 | 56篇 |
2022年 | 61篇 |
2021年 | 101篇 |
2020年 | 110篇 |
2019年 | 91篇 |
2018年 | 77篇 |
2017年 | 76篇 |
2016年 | 83篇 |
2015年 | 103篇 |
2014年 | 152篇 |
2013年 | 122篇 |
2012年 | 113篇 |
2011年 | 118篇 |
2010年 | 65篇 |
2009年 | 50篇 |
2008年 | 62篇 |
2007年 | 72篇 |
2006年 | 62篇 |
2005年 | 51篇 |
2004年 | 39篇 |
2003年 | 36篇 |
2002年 | 36篇 |
2001年 | 15篇 |
2000年 | 15篇 |
1999年 | 8篇 |
1998年 | 9篇 |
1997年 | 15篇 |
1996年 | 5篇 |
1995年 | 13篇 |
1994年 | 18篇 |
1993年 | 9篇 |
1992年 | 9篇 |
1991年 | 12篇 |
1990年 | 9篇 |
1989年 | 11篇 |
1988年 | 7篇 |
1987年 | 2篇 |
1986年 | 6篇 |
1985年 | 1篇 |
1984年 | 5篇 |
1983年 | 4篇 |
1982年 | 5篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1976年 | 1篇 |
排序方式: 共有1928条查询结果,搜索用时 15 毫秒
91.
Cristie Grazziotin Noschang Rachel Krolow Leticia Ferreira Pettenuzzo Mônica Colpini Ávila Andrelisa Fachin Danusa Arcego Eduardo von Pozzer Toigo Leonardo Machado Crema Luísa Amália Diehl Deusa Vendite Carla Dalmaz 《Neurochemical research》2009,34(9):1568-1574
We studied the effect of chronic caffeine on parameters related to oxidative stress in different brain regions of stressed
and non-stressed rats. Wistar rats were divided into three groups: control (receiving water), caffeine 0.3 g/L and caffeine
1.0 g/L (in the drinking water). These groups were subdivided into non-stressed and stressed (repeated restraint stress during
40 days). Lipid peroxide levels and the total radical-trapping potential were assessed, as well as antioxidant enzyme activities
superoxide dismutase, gluthatione peroxidase, and catalase in hippocampus, striatum and cerebral cortex. Results showed interactions
between stress and caffeine, especially in the cerebral cortex, since caffeine increased the activity of some antioxidant
enzymes, but not in stressed animals. We concluded that chronic administration of caffeine led, in some cases, to increased
activity of antioxidant enzymes. However, these effects were not observed in the stressed animals. 相似文献
92.
Peng Qi Yue-ming Chen Hao Wang Meng Fang Qiang Ji Yun-peng Zhao Xiao-juan Sun Yan Liu Chun-fang Gao 《Cancer immunology, immunotherapy : CII》2009,58(9):1433-1440
Hepatocellular carcinoma (HCC) is one of the most common malignant tumors worldwide. The risk for developing HCC increases
with severity of inflammation and fibrosis. Transforming growth factor-β1 (TGF-β1) is most frequently upregulated in tumor
cells. The most studied −509C>T polymorphism of TGF-β1 gene has been associated with colorectal, gynecologic, and lung cancers.
To assess whether this polymorphism in TGF-β1 gene is associated with susceptibility to and/or clinicopathologic characteristics
of HBV-related HCC, a total of 575 patients with chronic HBV infection and 299 healthy volunteers with no evidence of recent
or remote HBV infection were prospectively enrolled. The patients were divided into two groups: those without (n = 196) and those with HCC (n = 379). These 379 HCC patients with chronic HBV infection were designated as cases, the remaining 196 patients without HCC
and 299 healthy volunteers served as disease and healthy controls, respectively. −509C>T polymorphism in the TGF-β1 gene promoter
was studied using restriction fragment-length polymorphism. In addition, tumor tissues of liver (n = 60) were obtained from the studied HCC patients for measurement of TGF-β1 mRNA expression levels. We also assessed the
plasma TGF-β1 levels of HBV patients without (n = 94) or with HCC (n = 136) and healthy subjects (n = 120). In our study group, the risk of HCC in Chinese patients with HBV infection was significantly lower with the TT genotypes
than in those with the CC genotypes at position −509 of TGF-β1 gene (P = 0.01). In addition, in the case group, patients with the CC genotype had a statistically significant higher median plasma
TGF-β1 or liver tumor tissue TGF-β1 mRNA level compared with the individuals with the TT genotype. However, in a subsequent
analysis of the association between this polymorphism and clinicopathological characteristics including tumor number, size,
grade, stage, and invasiveness, there was no significant difference in both the distribution of genotype or allelic frequency
within HCC patients, indicating that −509C>T exchange in TGF-β1 gene may play an important role in the occurrence, not the
progression of HBV-related HCC through influencing plasma concentrations of TGF-β1 or TGF-β1 mRNA expression of liver tumor
tissue. 相似文献
93.
The bacterium Pseudomonas aeruginosa is commonly isolated from the general environment and also infects the lungs of patients with cystic fibrosis (CF). Iron
in mammals is not freely available to infecting pathogens although significant amounts of extracellular iron are available
in the sputum that occurs in the lungs of CF patients. P. aeruginosa has a large number of systems to acquire this essential nutrient and many of these systems have been characterised in the
laboratory. However, which iron acquisition systems are active in CF is not well understood. Here we review recent research
that sheds light on how P. aeruginosa obtains iron in the lungs of CF patients. 相似文献
94.
Sergio Papa Vittoria Petruzzella Salvatore Scacco Arcangela Iuso Rita Vitale Domenico De Rasmo Claudia Piccoli Michele Scivetti Teresa Rizza 《BBA》2009,1787(5):502-764
This paper covers genetic and biochemical aspects of mitochondrial bioenergetics dysfunction in hereditary neurological disorders associated with complex I defects. Three types of hereditary complex I dysfunction are dealt with: (i) homozygous mutations in the nuclear genes NDUFS1 and NDUFS4 of complex I, associated with mitochondrial encephalopathy; (ii) a recessive hereditary epileptic neurological disorder associated with enhanced proteolytic degradation of complex I; (iii) homoplasmic mutations in the ND5 and ND6 mitochondrial genes of the complex, cohexistent with mutation in the nuclear PINK1 gene in familial Parkinsonism. The genetic and biochemical data examined highlight different mechanisms by which mitochondrial bioenergetics is altered in these hereditary defects of complex I. This knowledge, besides clarifying molecular aspects of the pathogenesis of hereditary diseases, can also provide hints for understanding the involvement of complex I in sporadic neurological disorders and aging, as well as for developing therapeutical strategies. 相似文献
95.
抑郁症模型大鼠学习记忆能力变化研究 总被引:3,自引:0,他引:3
为探讨抑郁症发生发展过程中学习记忆能力的变化模式及其可能机制.分别采用21天慢性非预见性刺激法和嗅球切除法建立的抑郁症模型大鼠.运用旷场行为实验(open—field behavior)检测大鼠主动性活动能力,用Morris水迷宫法检测大鼠空间学习记忆能力,HPLC—UV法测定大鼠血清皮质醇含量。电生理法记录海马CA1区LTP与LTD,观察海马神经元的突触可塑性。结果显示:与对照组相比,两种模型的自主活动性、空间探索兴趣和学习能力都明显降低,而记忆的反馈功能没有明显的变化。同时.两种模型大鼠海马神经细胞的突触可塑性显著下降,血清皮质醇的含量则明显上升。提示两种建模方法均导致大鼠产生抑郁症状和学习能力障碍.但对记忆反馈功能无明显影响。 相似文献
96.
摘要 目的:分析不同类型慢性心力衰竭患者临床特征及心功能危险因素、预后影响因素。方法:回顾性分析2020年1月-2022年1月我院收治的慢性心力衰竭患者80例,根据左室射血分数(LVEF)分为A组(n=25,LVEF<30%)、B组(n=25,LVEF 40%~50%)、C组(n=25,LVEF≥50%)三组,另根据随访1年后是否存活分为生存组(n=51)和死亡组(n=29)。比较不同组别临床相关指标,采用Pearson检验分析患者临床特征与慢性心力衰竭患者心功能、预后之间的相关性,采用多因素Logistic回归分析影响慢性心力衰竭患者心功能、预后的独立危险因素。结果:A组的心率及患有冠心病、心律失常1年以上、合并非心血管疾病人数占比、LAD、RAD、Scr、Hcy水平高于B组和C组(P<0.05)。死亡组的心率及患有冠心病、心律失常1年以上、LAD、RAD、Scr水平明显高于生存组(P<0.05)。Pearson相关性检验显示,心率、冠心病、心律失常、合并非心血管疾病、LAD、RAD、Scr、Hcy水平与慢性心力衰竭患者心功能之间呈正相关(P<0.05);心率、冠心病、心律失常、LAD、RAD、Scr水平与慢性心力衰竭患者预后之间呈正相关(P<0.05)。多因素Logistic回归分析结果显示,心率、冠心病、心律失常、合并非心血管疾病、LAD、RAD、Scr、Hcy水平是影响慢性心力衰竭患者心功能的独立危险因素(P<0.05);心率、冠心病、心律失常、LAD、RAD、Scr水平是影响慢性心力衰竭患者预后的独立危险因素(P<0.05)。结论:心率、冠心病、心律失常、LAD、RAD、Scr水平与慢性心力衰竭患者心功能、预后之间均呈正相关,是影响慢性心力衰竭患者心功能、预后的独立危险因素,可用来预测慢性心力衰竭的发生。 相似文献
97.
Compared to upland forests, riparian forest soils have greater potential to remove nitrate (NO3) from agricultural runoff through denitrification. It is unclear, however, whether prolonged exposure of riparian soils to nitrogen (N) loading will affect the rate of denitrification and its end products. This research assesses the rate of denitrification and nitrous oxide (N2O) emissions from riparian forest soils exposed to prolonged nutrient runoff from plant nurseries and compares these to similar forest soils not exposed to nutrient runoff. Nursery runoff also contains high levels of phosphate (PO4). Since there are conflicting reports on the impact of PO4 on the activity of denitrifying microbes, the impact of PO4 on such activity was also investigated. Bulk and intact soil cores were collected from N-exposed and non-exposed forests to determine denitrification and N2O emission rates, whereas denitrification potential was determined using soil slurries. Compared to the non-amended treatment, denitrification rate increased 2.7- and 3.4-fold when soil cores collected from both N-exposed and non-exposed sites were amended with 30 and 60 μg NO3-N g−1 soil, respectively. Net N2O emissions were 1.5 and 1.7 times higher from the N-exposed sites compared to the non-exposed sites at 30 and 60 μg NO3-N g−1 soil amendment rates, respectively. Similarly, denitrification potential increased 17 times in response to addition of 15 μg NO3-N g−1 in soil slurries. The addition of PO4 (5 μg PO4-P g−1) to soil slurries and intact cores did not affect denitrification rates. These observations suggest that prolonged N loading did not affect the denitrification potential of the riparian forest soils; however, it did result in higher N2O emissions compared to emission rates from non-exposed forest soils. 相似文献
98.
慢性复合应激对大鼠学习和记忆及海马神经元神经颗粒素表达的影响 总被引:1,自引:0,他引:1
目的探讨慢性复合应激对大鼠学习和记忆功能及海马内神经元神经颗粒素(neurogranin,Ng)表达的影响。方法成年雄性Wistar大鼠随机分为对照组和复合应激组,复合应激组动物每天无规律交替暴露于复合应激原环境中,为期6周。应激结束后,用Morris水迷宫测试大鼠空间学习和记忆成绩,同时用免疫组织化学方法观察海马各亚区Ng表达的变化,并用RT-PCR技术分析各组大鼠海马Ng mRNA水平的变化。结果Morris水迷宫测试显示,应激组动物寻找隐蔽平台潜伏期明显短于对照组(P<0.05);应激组大鼠海马DG和CA3区Ng的蛋白表达水平明显高于对照组(P<0.05),而两组海马CA1区的Ng的免疫反应性无明显差别;与对照组相比,应激组动物的Ng mRNA水平亦明显上调(P<0.05)。结论慢性复合性应激大鼠的学习与记忆能力增强;Ng在海马中的表达和Ng mRNA转录水平增高,提示Ng参与了该增强机制。 相似文献
99.
目的探讨儿童慢性鼻窦炎的有效治疗方法。方法回顾分析2001年1月~2004年10月在大连大学附属中山医院治疗的113例儿童慢性鼻窦炎的临床资料,分析5种治疗方法的疗效。结果根据患儿的病情,分别采取5种治疗方法,按1997年海口会议标准评定疗效,总有效率为88.5%。结论儿童慢性鼻窦炎的治疗要根据病情及伴随的相关疾病采取相应的治疗方法,才能提高疗效。 相似文献
100.
目的研究牙斑幽门螺杆菌与慢性胃炎之间的关系。方法对胃炎组、胃炎治疗组分别进行牙斑和胃黏膜幽门螺杆菌培养和比较。结果牙斑细菌培养:胃炎组阳性14例,阳性率为12.8%;治疗组阳性11例,阳性率为10.1%。胃黏膜细菌培养:胃炎组阳性47例,阳性率为43.1%;治疗组阳性19例,阳性率为17.4%。治疗前后比较牙斑标本差异无显著性(P〉0.05),胃黏膜标本差异有非常显著性(P〈0.001)。结论牙斑中确实存在着幽门螺杆菌,而且是胃内反复感染的源泉,以致慢性胃病反复发作,难以治愈。 相似文献