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   1499篇
  免费   121篇
  2023年   13篇
  2022年   10篇
  2021年   70篇
  2020年   27篇
  2019年   37篇
  2018年   49篇
  2017年   40篇
  2016年   62篇
  2015年   96篇
  2014年   111篇
  2013年   141篇
  2012年   139篇
  2011年   158篇
  2010年   85篇
  2009年   57篇
  2008年   86篇
  2007年   88篇
  2006年   67篇
  2005年   44篇
  2004年   61篇
  2003年   46篇
  2002年   54篇
  2001年   16篇
  2000年   7篇
  1999年   5篇
  1998年   7篇
  1997年   5篇
  1996年   1篇
  1995年   2篇
  1994年   4篇
  1993年   2篇
  1992年   6篇
  1991年   3篇
  1990年   4篇
  1988年   3篇
  1987年   1篇
  1986年   2篇
  1984年   1篇
  1983年   2篇
  1982年   1篇
  1980年   1篇
  1979年   2篇
  1978年   1篇
  1976年   1篇
  1972年   2篇
排序方式: 共有1620条查询结果,搜索用时 281 毫秒
961.
Carbamazepine (CBZ) is an iminostilbene derivative commonly used for treatment of neuralgic pain and bipolar affective disorders. CBZ blood levels of treated patients are within the range of micromolar concentrations and therefore, significant interactions of this drug with erythrocytes are very likely. Moreover, the lipid domains of the cell membrane are believed to be one of the sites where iminostilbene derivatives exert their effects. The present study aimed to deeply characterize CBZ effects on erythrocytes, in order to identify extra and/or cytosolic cell targets. Our results indicate that erythrocyte morphological changes promoted by the drug, may be triggered by an alteration in band 3 functionality i.e. at the level of anionic flux. In addition, from a metabolic point of view this perturbation could be considered, at least in part, as a beneficial event because it could favour the CO2 elimination.  相似文献   
962.
Systemic lupus erythematosus (SLE) is a multifactorial autoimmune disease. Although genetic factors confer susceptibility to the disease, only 15 % of the genetic contribution has been identified. TRAF3IP2 gene, associated with susceptibility to psoriatic arthritis and psoriasis, encodes for Act1, a negative regulator of adaptive immunity and a positive signaling adaptor in IL-17-mediated immune responses. The aim of this study was to assess the role of TRAF3IP2 gene variability in SLE susceptibility and disease phenotype in an Italian population. Two hundred thirty-nine consecutive SLE patients were enrolled. Study protocol included complete physical examination; the clinical and laboratory data were collected. Two hundred seventy-eight age- and ethnicity-matched healthy subjects served as controls. TRAF3IP2 polymorphisms (rs33980500, rs13190932, and rs13193677) were analyzed in both cases and controls. Genotype analysis was performed by allelic discrimination assays. A case–control association study and a genotype–phenotype correlation were performed. The rs33980500 and rs13193677 resulted significantly associated with SLE susceptibility (P?=?0.021, odds ratio (OR)?=?1.71, and P?=?0.046, OR?=?1.73, respectively). All three TRAF3IP2 single nucleotide polymorphisms resulted associated with the development of pericarditis; in particular, rs33980500 showed the strongest association (P?=?0.002, OR 2.59). This association was further highlighted by binary logistic regression analysis. In conclusion, our data show for the first time the contribution of TRAF3IP2 genetic variability in SLE susceptibility, providing further suggestions that common variation in genes that function in the adaptive and innate arms of the immune system are important in establishing SLE risk. Our study also shows that this gene may affect disease phenotype and, particularly, the occurrence of pericarditis.  相似文献   
963.
Primary human cytomegalovirus (HCMV) infections during pregnancy are associated with a high risk of virus transmission to the fetus. To identify correlates of intrauterine HCMV transmission, serial serum samples from HCMV transmitter and non-transmitter pregnant women with primary HCMV infection were analyzed for the presence of neutralizing antibodies against different glycoproteins and glycoprotein complexes, which are known to mediate entry into distinct types of host cells. Neutralizing activity was detected in the sera early after primary infection; absorption with a soluble pentameric complex formed by gH/gL/pUL128-131, but not with gH/gL dimer or with gB, abolished the capacity of sera to neutralize infection of epithelial cells. Importantly, an early, high antibody response to pentamer antigenic sites was associated with a significantly reduced risk of HCMV transmission to the fetus. This association is consistent with the high in vitro inhibition of HCMV infection of epithelial/endothelial cells as well as cell-to-cell spreading and virus transfer to leukocytes by anti-pentamer antibodies. Taken together, these findings indicate that the HCMV pentamer complex is a major target of the antibody-mediated maternal immunity.  相似文献   
964.
965.
Knowledge of the transmission field (B1 +) of radio-frequency coils is crucial for high field (B0 = 3.0 T) and ultrahigh field (B0≥7.0 T) magnetic resonance applications to overcome constraints dictated by electrodynamics in the short wavelength regime with the ultimate goal to improve the image quality. For this purpose B1 + mapping methods are used, which are commonly magnitude-based. In this study an analysis of five phase-based methods for three-dimensional mapping of the B1 + field is presented. The five methods are implemented in a 3D gradient-echo technique. Each method makes use of different RF-pulses (composite or off-resonance pulses) to encode the effective intensity of the B1 + field into the phase of the magnetization. The different RF-pulses result in different trajectories of the magnetization, different use of the transverse magnetization and different sensitivities to B1 + inhomogeneities and frequency offsets, as demonstrated by numerical simulations. The characterization of the five methods also includes phantom experiments and in vivo studies of the human brain at 3.0 T and at 7.0 T. It is shown how the characteristics of each method affect the quality of the B1 + maps. Implications for in vivo B1 + mapping at 3.0 T and 7.0 T are discussed.  相似文献   
966.
Neuroinflammation is believed to be involved in the pathophysiological mechanisms of silent brain infarcts (SBI). However, the immunological profile of SBI has been scarcely investigated. In the context of a national research project named SILENCE, aimed at investigating clinical, biochemical and pathogenic features of SBI, we have measured the plasma profile of some inflammatory-related molecules in SBI patients (n = 21), patients with recent lacunar infarcts (LI, n = 28) and healthy controls (n = 31), consecutively enrolled in four Italian centres. A panel of chemokines (MIG, CTACK, IL16, SDF1a, MCP1), growth factors (SCF, SCGFb, HGF, IL3), immunoglobulin-type adhesion molecules (ICAM1, VCAM1), proinflammatory cytokines (IL18, INFa2, MIF, IL12p40), cell surface receptors on T-cells (IL2Ra), and inductors of apoptosis (TRAIL) was assessed in plasma samples by Luminex xMAP™ technology. Immunological parameters were compared using non-parametric statistics and performance to distinguish SBI and LI was evaluated by receiver operating characteristic (ROC) analysis. Plasma levels of ICAM1 were significantly higher in both SBI and LI patients as compared to controls (SBI≥LI>Ctrl). A different trend was observed for IL16 (SBI<LI>Ctrl), SCF (LI<SBI>Ctrl) and SCGFb (SBI>LI<Ctrl). SBI subjects had significantly increased levels of MIG when compared to controls (LI≤SBI>Ctrl) and IL18 when compared to LI patients (Ctrl≤SBI>LI). All the other immunological markers did not significantly differ among groups. According to ROC analysis, the best predictor for SBI condition was the chemokine MIG (AUC = 0.84, sensitivity 86%, specificity 77%), while SCF had the best performance in distinguishing LI patients (AUC = 0.84, sensitivity 86%, specificity 68%). These results confirm the involvement of inflammatory processes in cerebrovascular disorders, particularly in SBI, a very common age-related condition. The differences in plasma profile of inflammatory molecules may underlie different pathological mechanisms in SBI and LI patients.  相似文献   
967.
A stochastic advection-reaction-diffusion model with terms of multiplicative white Gaussian noise, valid for weakly mixed waters, is studied to obtain the vertical stationary spatial distributions of two groups of picophytoplankton, i.e., picoeukaryotes and Prochlorococcus, which account about for 60% of total chlorophyll on average in Mediterranean Sea. By numerically solving the equations of the model, we analyze the one-dimensional spatio-temporal dynamics of the total picophytoplankton biomass and nutrient concentration along the water column at different depths. In particular, we integrate the equations over a time interval long enough, obtaining the steady spatial distributions for the cell concentrations of the two picophytoplankton groups. The results are converted into chlorophyll a and divinil chlorophyll a concentrations and compared with experimental data collected in two different sites of the Sicily Channel (southern Mediterranean Sea). The comparison shows that real distributions are well reproduced by theoretical profiles. Specifically, position, shape and magnitude of the theoretical deep chlorophyll maximum exhibit a good agreement with the experimental values.  相似文献   
968.
Light pollution is known to affect important biological functions of wild animals, including daily and annual cycles. However, knowledge about long-term effects of chronic exposure to artificial light at night is still very limited. Here we present data on reproductive physiology, molt and locomotor activity during two-year cycles of European blackbirds (Turdus merula) exposed to either dark nights or 0.3 lux at night. As expected, control birds kept under dark nights exhibited two regular testicular and testosterone cycles during the two-year experiment. Control urban birds developed testes faster than their control rural conspecifics. Conversely, while in the first year blackbirds exposed to light at night showed a normal but earlier gonadal cycle compared to control birds, during the second year the reproductive system did not develop at all: both testicular size and testosterone concentration were at baseline levels in all birds. In addition, molt sequence in light-treated birds was more irregular than in control birds in both years. Analysis of locomotor activity showed that birds were still synchronized to the underlying light-dark cycle. We suggest that the lack of reproductive activity and irregular molt progression were possibly the results of i) birds being stuck in a photorefractory state and/or ii) chronic stress. Our data show that chronic low intensities of light at night can dramatically affect the reproductive system. Future studies are needed in order to investigate if and how urban animals avoid such negative impact and to elucidate the physiological mechanisms behind these profound long-term effects of artificial light at night. Finally we call for collaboration between scientists and policy makers to limit the impact of light pollution on animals and ecosystems.  相似文献   
969.
In this paper, we present a method to quantify the extent of disorder in a system by using conditional entropies. Our approach is especially useful when other global, or mean field, measures of disorder fail. The method is equally suited for both continuum and lattice models, and it can be made rigorous for the latter. We apply it to mixing and demixing in multicomponent fluid membranes, and show that it has advantages over previous measures based on Shannon entropies, such as a much diminished dependence on binning and the ability to capture local correlations. Further potential applications are very diverse, and could include the study of local and global order in fluid mixtures, liquid crystals, magnetic materials, and particularly biomolecular systems.  相似文献   
970.

Background

Periodontitis is a multi-factorial disease and several risk-factors such as infections, inflammatory responses, oral hygiene, smoke, aging and individual predisposition are involved in the disease. Pathogens trigger chronic inflammation with cytokines release which in turn leads to the destruction of the connective and the teeth supporting bone. The identification of genetic factors controlling oral inflammation may increase our understanding of genetic predisposition to periodontitis.Single nucleotide polymorphisms in the promoter region of Vascular Endothelial Growth Factor, Alpha-1-Antichymotripsin, hydroxy-methyl-glutaryl CoA reductase, Interferon alpha, Interleukin-1 Beta, Interleukin 10, Interleukin 6 and Tumor Necrosis Factor- alpha genes from a case/control study were investigated.

Results

The C allele of Vascular Endothelial Growth Factor, A allele of Interleukin 10 and GG genotype of Tumor Necrosis Factor-α were individually associated with chronic periodontitis. However, the concomitant presence of the three genetic markers in the same subjects appeared to play a synergistic role and increased several folds the risk of the disease.

Conclusions

Our findings offer new tools to implement the screening of unaffected subjects with an increased susceptibility of periodontitis and increase our understanding regarding the genetic inflammatory background related to familiarity of the disease.
  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