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   1738篇
  免费   119篇
  1857篇
  2023年   8篇
  2022年   19篇
  2021年   34篇
  2020年   11篇
  2019年   29篇
  2018年   32篇
  2017年   26篇
  2016年   40篇
  2015年   64篇
  2014年   79篇
  2013年   115篇
  2012年   98篇
  2011年   99篇
  2010年   87篇
  2009年   56篇
  2008年   71篇
  2007年   79篇
  2006年   80篇
  2005年   71篇
  2004年   62篇
  2003年   50篇
  2002年   51篇
  2001年   60篇
  2000年   29篇
  1999年   39篇
  1998年   11篇
  1997年   9篇
  1996年   14篇
  1995年   18篇
  1994年   9篇
  1993年   15篇
  1992年   27篇
  1991年   28篇
  1990年   30篇
  1989年   24篇
  1988年   23篇
  1987年   18篇
  1986年   14篇
  1985年   24篇
  1984年   22篇
  1983年   15篇
  1982年   20篇
  1981年   15篇
  1980年   13篇
  1979年   16篇
  1977年   11篇
  1975年   11篇
  1974年   10篇
  1973年   13篇
  1967年   8篇
排序方式: 共有1857条查询结果,搜索用时 0 毫秒
991.
Despite the widespread use of kinase-targeted agents in clear cell renal cell carcinoma (CC-RCC), comprehensive kinase activity evaluation (kinomic profiling) of these tumors is lacking. Thus, kinomic profiling of CC-RCC may assist in devising a classification system associated with clinical outcomes, and help identify potential therapeutic targets. Fresh frozen CC-RCC tumor lysates from 41 clinically annotated patients who had localized disease at diagnosis were kinomically profiled using the PamStation®12 high-content phospho-peptide substrate microarray system (PamGene International). Twelve of these patients also had matched normal kidneys available that were also profiled. Unsupervised hierarchical clustering and supervised comparisons based on tumor vs. normal kidney and clinical outcome (tumor recurrence) were performed and coupled with advanced network modeling and upstream kinase prediction methods. Unsupervised clustering analysis of localized CC-RCC tumors identified 3 major kinomic groups associated with inflammation (A), translation initiation (B), and immune response and cell adhesions (C) processes. Potential driver kinases implicated include PFTAIRE (PFTK1), PKG1, and SRC, which were identified in groups A, B, and C, respectively. Of the 9 patients who had tumor recurrence, only one was found in Group B. Supervised analysis showed decreased kinase activity of CDK1 and RSK1-4 substrates in those which progressed compared to others. Twelve tumors with matching normal renal tissue implicated increased PIM’s and MAPKAPK’s in tumors compared to adjacent normal renal tissue. As such, comprehensive kinase profiling of CC-RCC tumors could provide a functional classification strategy for patients with localized disease and identify potential therapeutic targets.  相似文献   
992.

Background

Dengue and chikungunya are rapidly expanding viruses transmitted by mosquitoes of the genus Aedes. Few epidemiological studies have examined the extent of transmission of these infections in South India despite an increase in the number of reported cases, and a high suitability for transmission.

Methods and findings

We conducted a household-based seroprevalence survey among 1010 individuals aged 5-40 years living in fifty randomly selected spatial locations in Chennai, Tamil Nadu. Participants were asked to provide a venous blood sample and to complete a brief questionnaire with basic demographic and daily activity information. Previous exposure to dengue and chikungunya was determined using IgG indirect ELISA (Panbio) and IgG ELISA (Novatec), respectively. We used this data to estimate key transmission parameters (force of infection and basic reproductive number) and to explore factors associated with seropositivity. While only 1% of participants reported history of dengue and 20% of chikungunya, we found that 93% (95%CI 89-95%) of participants were seropositive to dengue virus, and 44% (95%CI 37-50%) to chikungunya. Age-specific seroprevalence was consistent with long-tem, endemic circulation of dengue and suggestive of epidemic chikungunya transmission. Seropositivity to dengue and chikungunya were significantly correlated, even after adjusting for individual and household factors. We estimate that 23% of the susceptible population gets infected by dengue each year, corresponding to approximately 228,000 infections. This transmission intensity is significantly higher than that estimated in known hyperendemic settings in Southeast Asia and the Americas.

Conclusions

These results provide unprecedented insight into the very high transmission potential of dengue and chikungunya in Chennai and underscore the need for enhanced surveillance and control methods.  相似文献   
993.

Background

Dentatorubropallidoluysian atrophy (DRPLA) is a rare autosomal dominant neurodegenerative disease that is associated with numerous movement disorders. Ocular problems also occur with DRPLA with reports of corneal endothelial degeneration in some patients living with the disease. We report a new visual problem associated with DRPLA, optic atrophy.

Case presentation

A 47 year-old man presented complaining of progressive visual loss associated with optic atrophy on ophthalmological evaluation. He gradually developed a progressive ataxia with dystonia. Brain MRI revealed a diffuse leukoencephalopathy. Genetic analysis revealed 62 CAG repeats in one allele of the DRPLA gene and he was diagnosed with DRPLA.

Conclusion

Optic atrophy should be included in the clinical spectrum of DRPLA.
  相似文献   
994.
Oxidative stress resistant Deinococcus radiodurans surprisingly exhibited moderate sensitivity to tellurite induced oxidative stress (LD50 = 40 μM tellurite, 40 min exposure). The organism reduced 70% of 40 μM potassium tellurite within 5 h. Tellurite exposure significantly modulated cellular redox status. The level of ROS and protein carbonyl contents increased while the cellular reduction potential substantially decreased following tellurite exposure. Cellular thiols levels initially increased (within 30 min) of tellurite exposure but decreased at later time points. At proteome level, tellurite resistance proteins (TerB and TerD), tellurite reducing enzymes (pyruvate dehydrogense subunits E1 and E3), ROS detoxification enzymes (superoxide dismutase and thioredoxin reductase), and protein folding chaperones (DnaK, EF‐Ts, and PPIase) displayed increased abundance in tellurite‐stressed cells. However, remarkably decreased levels of key metabolic enzymes (aconitase, transketolase, 3‐hydroxy acyl‐CoA dehydrogenase, acyl‐CoA dehydrogenase, electron transfer flavoprotein alpha, and beta) involved in carbon and energy metabolism were observed upon tellurite stress. The results demonstrate that depletion of reduction potential in intensive tellurite reduction with impaired energy metabolism lead to tellurite toxicity in D. radiodurans.  相似文献   
995.

Background

While infections are a major cause of neonatal mortality in India even in full-term neonates, this is an especial problem in the large proportion (~20%) of neonates born underweight (or small-for-gestational-age; SGA). One potential contributory factor for this susceptibility is the possibility that immune system maturation may be affected along with intrauterine growth retardation.

Methods

In order to examine the possibility that differences in immune status may underlie the susceptibility of SGA neonates to infections, we enumerated the frequencies and concentrations of 22 leukocyte subset populations as well as IgM and IgA levels in umbilical cord blood from full-term SGA neonates and compared them with values from normal-weight (or appropriate-for-gestational-age; AGA) full-term neonates. We eliminated most SGA-associated risk factors in the exclusion criteria so as to ensure that AGA-SGA differences, if any, would be more likely to be associated with the underweight status itself.

Results

An analysis of 502 such samples, including 50 from SGA neonates, showed that SGA neonates have significantly fewer plasmacytoid dendritic cells (pDCs), a higher myeloid DC (mDC) to pDC ratio, more natural killer (NK) cells, and higher IgM levels in cord blood in comparison with AGA neonates. Other differences were also observed such as tendencies to lower CD4:CD8 ratios and greater prominence of inflammatory monocytes, mDCs and neutrophils, but while some of them had substantial differences, they did not quite reach the standard level of statistical significance.

Conclusions

These differences in cellular lineages of the immune system possibly reflect stress responses in utero associated with growth restriction. Increased susceptibility to infections may thus be linked to complex immune system dysregulation rather than simply retarded immune system maturation.  相似文献   
996.
Recently, it has been reported that 25-hydroxyvitamin D3-1alpha-hydroxylase [1alpha(OH)ase, CYP27B1], required to convert non-toxic 25-hyxdroxyvitamin D3 [25(OH)D(3)] to its active metabolite [1alpha,25(OH)(2)D(3)], is present in the epithelial cells of the human colon. In the present study, the potential chemoprotective role of 25(OH)D(3) was evaluated for colon cancer using the HT-29, human colon cancer cell line. Colon cancer cells were treated with 25(OH)D(3) (500nM or 1muM), 1alpha,25(OH)(2)D(3) (500nM), cholecalciferol (D3, 1muM) or vehicle and cell number determined at days 2 and 5 post-treatment. Results showed that both 25(OH)D(3) and 1alpha,25(OH)(2)D(3) induced dose- and time-dependent anti-proliferative effects on the HT-29 cells, with maximum inhibition noted at day 5. Western blot analyses revealed an up-regulation of VDR and 1alpha(OH)ase expression following 24h of treatment with 25(OH)D(3), and 1alpha,25(OH)(2)D(3). These results are consistent with the expression of VDR and 1alpha(OH)ase in samples of normal colonic tissue, aberrant crypt foci (ACFs) and colon adenocarcinomas. The VDR expression was sequentially increased from normal to pre-cancerous lesions to well-differentiated tumors and then decreased in poorly differentiated tumors. Expression of 1alpha(OH)ase was equally expressed in normal, pre-cancerous lesions and malignant human colon tissues. The increased expression of 1alpha(OH)ase in colon cancer cells treated with the pro-hormone and its anti-proliferative effects, suggest that 25(OH)D(3) may offer possible therapeutic and chemopreventive option in colon cancer.  相似文献   
997.
Several 1,8-naphthyridine-3-carboxamide derivatives (8-23) were synthesized and tested for in vitro cytotoxicity against eight cancer cell lines and a normal cell line. Compound 12 exhibited high cytotoxicity (IC(50)=1.37microM) in HBL-100 (breast) cell line while compounds 17 (IC(50)=3.7microM) and 22 (IC(50)=3.0microM) have shown high cytotoxicity in KB (oral) and SW-620 (colon) cell lines, respectively. The synthesized 1,8-naphthyridine-3-carboxamides were also evaluated for anti-inflammatory and myeloprotective activities, indicated by modulation in cytokine and chemokine levels secreted by dendritic cells.  相似文献   
998.
R/qtlbim is an extensible, interactive environment for the Bayesian Interval Mapping of QTL, built on top of R/qtl (Broman et al., 2003), providing Bayesian analysis of multiple interacting quantitative trait loci (QTL) models for continuous, binary and ordinal traits in experimental crosses. It includes several efficient Markov chain Monte Carlo (MCMC) algorithms for evaluating the posterior of genetic architectures, i.e. the number and locations of QTL, their main and epistatic effects and gene-environment interactions. R/qtlbim provides extensive informative graphical and numerical summaries, and model selection and convergence diagnostics of the MCMC output, illustrated through the vignette, example and demo capabilities of R (R Development Core Team 2006). Availability: The package is freely available from cran.r-project.org.  相似文献   
999.
Active spatial perception in the vibrissa scanning sensorimotor system   总被引:2,自引:1,他引:1  
Haptic perception is an active process that provides an awareness of objects that are encountered as an organism scans its environment. In contrast to the sensation of touch produced by contact with an object, the perception of object location arises from the interpretation of tactile signals in the context of the changing configuration of the body. A discrete sensory representation and a low number of degrees of freedom in the motor plant make the ethologically prominent rat vibrissa system an ideal model for the study of the neuronal computations that underlie this perception. We found that rats with only a single vibrissa can combine touch and movement to distinguish the location of objects that vary in angle along the sweep of vibrissa motion. The patterns of this motion and of the corresponding behavioral responses show that rats can scan potential locations and decide which location contains a stimulus within 150 ms. This interval is consistent with just one to two whisk cycles and provides constraints on the underlying perceptual computation. Our data argue against strategies that do not require the integration of sensory and motor modalities. The ability to judge angular position with a single vibrissa thus connects previously described, motion-sensitive neurophysiological signals to perception in the behaving animal.  相似文献   
1000.
Elevated expression of tissue transglutaminase (TG2) in cancer cells has been implicated in the development of drug resistance and metastatic phenotypes. However, the role and the mechanisms that regulate TG2 expression remain elusive. Here, we provide evidence that protein kinase Cdelta (PKCdelta) regulates TG2 expression, which in turn inhibits autophagy, a type II programmed cell death, in pancreatic cancer cells that are frequently insensitive to standard chemotherapeutic agents. Rottlerin, a PKCdelta-specific inhibitor, and PKCdelta small interfering RNA (siRNA) down-regulated the expression of TG2 mRNA and protein and induced growth inhibition without inducing apoptosis in pancreatic cancer cells. Inhibition of PKCdelta by rottlerin or knockdown of TG2 protein by a TG2-specific siRNA resulted in a marked increase in autophagy shown by presence of autophagic vacuoles in the cytoplasm, formation of the acidic vesicular organelles, membrane association of microtubule-associated protein 1 light chain 3 (LC3) with autophagosomes, and a marked induction of LC3-II protein, important hallmarks of autophagy, and by electron microscopy. Furthermore, inhibition of TG2 by rottlerin or by the siRNA led to accumulation of green fluorescent protein (GFP)-LC3-II in autophagosomes in pancreatic cancer cells transfected with GFP-LC3 (GFP-ATG8) expression vector. Knockdown of Beclin-1, a specific autophagy-promoting protein and the product of Becn1 (ATG6), inhibited rottlerin-induced and TG2 siRNA-induced autophagy, indicating that Beclin-1 is required for this process. These results revealed that PKCdelta plays a critical role in the expression of TG2, which in turn regulates autophagy. In conclusion, these results suggest a novel mechanism of regulation of TG2 and TG2-mediated autophagy in pancreatic cancer cells.  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