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   873篇
  免费   79篇
  2023年   3篇
  2022年   4篇
  2021年   13篇
  2020年   4篇
  2019年   16篇
  2018年   5篇
  2017年   16篇
  2016年   26篇
  2015年   28篇
  2014年   33篇
  2013年   49篇
  2012年   52篇
  2011年   59篇
  2010年   49篇
  2009年   43篇
  2008年   53篇
  2007年   54篇
  2006年   51篇
  2005年   59篇
  2004年   61篇
  2003年   52篇
  2002年   29篇
  2001年   10篇
  2000年   3篇
  1999年   5篇
  1998年   15篇
  1997年   18篇
  1996年   5篇
  1995年   10篇
  1994年   6篇
  1993年   6篇
  1992年   11篇
  1991年   9篇
  1990年   4篇
  1989年   5篇
  1988年   7篇
  1987年   9篇
  1986年   5篇
  1985年   3篇
  1984年   4篇
  1983年   9篇
  1982年   5篇
  1981年   3篇
  1980年   6篇
  1978年   5篇
  1977年   4篇
  1975年   5篇
  1974年   4篇
  1972年   4篇
  1970年   3篇
排序方式: 共有952条查询结果,搜索用时 31 毫秒
21.
A reproducible therapy model for advanced intracerebral B16 melanoma is reported. Implanted tumors (D0), suppressed by a single 15 Gy radiosurgical dose of 100 kVp X-rays (D8), were further suppressed by a single ip injection of a Treg-depleting mAb given 2 days prior to the initiation (D9) of four weekly then eight bi-monthly sc injections of GMCSF-transfected, mitotically disabled B16 cells. The trends of seven independent experiments were similar to the combined result: The median (days) [SD/total N] of survival went from 15[1.09/62] (no treatment control) to 35.8[8.8/58] (radiation therapy only) to 52.5[13.5/57] (radiation therapy plus immunotherapy). Within 2 weeks after immunization, tumors in mice receiving radiation therapy plus immunotherapy were significantly smaller than tumors in mice treated only with radiosurgery. Splenocytes and lymph node cells from immunized mice showed increased interferon γ production when cultured with syngeneic tumor cells. We suggest that our model will be useful for the development and testing of novel combination therapies for brain tumors.  相似文献   
22.
Bioassay-directed fractionation of the leaf and root extracts of the antiproliferative Madagascar plant Stuhlmannia moavi afforded 6-acetyl-5,8-dihydroxy-2-methoxy-7-methyl-1,4-naphthoquinone (stuhlmoavin, 1) as the most active compound, with an IC50 value of 8.1 μM against the A2780 human ovarian cancer cell line, as well as the known homoisoflavonoid bonducellin (2) and the stilbenoids 3,4,5′-trihydroxy-3′-methoxy-trans-stilbene (3), piceatannol (4), resveratrol (5), rhapontigenin (6), and isorhapontigenin (7). The structure elucidation of all compounds was based on NMR and mass spectroscopic data, and the structure of 1 was confirmed by a single crystal X-ray analysis. Compounds 2?5 showed weak A2780 activities, with IC50 values of 10.6, 54.0, 41.0, and 74.0 μM, respectively. Compounds 1?3 also showed weak antimalarial activity against Plasmodium falciparum with IC50 values of 23, 26, and 27 μM, respectively.  相似文献   
23.
Background: Hepatoblastoma is a malignant embryonal tumor typically diagnosed in children younger than five years of age. Little is known on hepatoblastoma etiology. Methods: We matched California Cancer Registry records of hepatoblastomas diagnosed in children younger than age 6 from 1988 to 2007 to birth records using a probabilistic record linkage program, yielding 261 cases. Controls (n = 218,277), frequency matched by birth year to all cancer cases in California for the same time period, were randomly selected from California birth records. We examined demographic and socioeconomic information, birth characteristics, pregnancy history, complications in pregnancy, labor and delivery, and abnormal conditions and clinical procedures relating to the newborn, with study data taken from birth certificates. Results: We observed increased risks for hepatoblastoma among children with low [1500–2499 g, Odds Ratio (OR) = 2.02, 95% confidence interval (CI) 1.29–3.15] and very low birthweight (<1500 g, OR = 15.4, 95% CI 10.7–22.3), preterm birth <33 weeks (OR = 7.27, 95% CI 5.00, 10.6), small size for gestational age (OR = 1.75, 95% CI 1.25–2.45), and with multiple birth pregnancies (OR = 2.52, 95% CI 1.54–4.14). We observed a number of pregnancy and labor complications to be related to hepatoblastoma, including preeclampsia, premature labor, fetal distress, and congenital anomalies. Conclusion: These findings confirm previously reported associations with low birthweight and preeclampsia. The relation with multiple birth pregnancies has been previously reported and may indicate a relation to infertility treatments.  相似文献   
24.
Fruit bats (Pteropodidae) have received increased attention after the recent emergence of notable viral pathogens of bat origin. Their vagility hinders data collection on abundance and distribution, which constrains modeling efforts and our understanding of bat ecology, viral dynamics, and spillover. We addressed this knowledge gap with models and data on the occurrence and abundance of nectarivorous fruit bat populations at 3 day roosts in southeast Queensland. We used environmental drivers of nectar production as predictors and explored relationships between bat abundance and virus spillover. Specifically, we developed several novel modeling tools motivated by complexities of fruit bat foraging ecology, including: (1) a dataset of spatial variables comprising Eucalypt‐focused vegetation indices, cumulative precipitation, and temperature anomaly; (2) an algorithm that associated bat population response with spatial covariates in a spatially and temporally relevant way given our current understanding of bat foraging behavior; and (3) a thorough statistical learning approach to finding optimal covariate combinations. We identified covariates that classify fruit bat occupancy at each of our three study roosts with 86–93% accuracy. Negative binomial models explained 43–53% of the variation in observed abundance across roosts. Our models suggest that spatiotemporal heterogeneity in Eucalypt‐based food resources could drive at least 50% of bat population behavior at the landscape scale. We found that 13 spillover events were observed within the foraging range of our study roosts, and they occurred during times when models predicted low population abundance. Our results suggest that, in southeast Queensland, spillover may not be driven by large aggregations of fruit bats attracted by nectar‐based resources, but rather by behavior of smaller resident subpopulations. Our models and data integrated remote sensing and statistical learning to make inferences on bat ecology and disease dynamics. This work provides a foundation for further studies on landscape‐scale population movement and spatiotemporal disease dynamics.  相似文献   
25.
26.
In the World Health Organization's forthcoming eleventh revision of the International Classification of Diseases and Related Health Problems (ICD‐11), substantial changes have been proposed to the ICD‐10 classification of mental and behavioural disorders related to sexuality and gender identity. These concern the following ICD‐10 disorder groupings: F52 Sexual dysfunctions, not caused by organic disorder or disease; F64 Gender identity disorders; F65 Disorders of sexual preference; and F66 Psychological and behavioural disorders associated with sexual development and orientation. Changes have been proposed based on advances in research and clinical practice, and major shifts in social attitudes and in relevant policies, laws, and human rights standards. This paper describes the main recommended changes, the rationale and evidence considered, and important differences from the DSM‐5. An integrated classification of sexual dysfunctions has been proposed for a new chapter on Conditions Related to Sexual Health, overcoming the mind/body separation that is inherent in ICD‐10. Gender identity disorders in ICD‐10 have been reconceptualized as Gender incongruence, and also proposed to be moved to the new chapter on sexual health. The proposed classification of Paraphilic disorders distinguishes between conditions that are relevant to public health and clinical psychopathology and those that merely reflect private behaviour. ICD‐10 categories related to sexual orientation have been recommended for deletion from the ICD‐11.  相似文献   
27.
Primary open angle glaucoma (POAG) is a complex disease and is one of the major leading causes of blindness worldwide. Genome-wide association studies have successfully identified several common variants associated with glaucoma; however, most of these variants only explain a small proportion of the genetic risk. Apart from the standard approach to identify main effects of variants across the genome, it is believed that gene-gene interactions can help elucidate part of the missing heritability by allowing for the test of interactions between genetic variants to mimic the complex nature of biology. To explain the etiology of glaucoma, we first performed a genome-wide association study (GWAS) on glaucoma case-control samples obtained from electronic medical records (EMR) to establish the utility of EMR data in detecting non-spurious and relevant associations; this analysis was aimed at confirming already known associations with glaucoma and validating the EMR derived glaucoma phenotype. Our findings from GWAS suggest consistent evidence of several known associations in POAG. We then performed an interaction analysis for variants found to be marginally associated with glaucoma (SNPs with main effect p-value <0.01) and observed interesting findings in the electronic MEdical Records and GEnomics Network (eMERGE) network dataset. Genes from the top epistatic interactions from eMERGE data (Likelihood Ratio Test i.e. LRT p-value <1e-05) were then tested for replication in the NEIGHBOR consortium dataset. To replicate our findings, we performed a gene-based SNP-SNP interaction analysis in NEIGHBOR and observed significant gene-gene interactions (p-value <0.001) among the top 17 gene-gene models identified in the discovery phase. Variants from gene-gene interaction analysis that we found to be associated with POAG explain 3.5% of additional genetic variance in eMERGE dataset above what is explained by the SNPs in genes that are replicated from previous GWAS studies (which was only 2.1% variance explained in eMERGE dataset); in the NEIGHBOR dataset, adding replicated SNPs from gene-gene interaction analysis explain 3.4% of total variance whereas GWAS SNPs alone explain only 2.8% of variance. Exploring gene-gene interactions may provide additional insights into many complex traits when explored in properly designed and powered association studies.  相似文献   
28.
Cobamides (Cbas) are essential cofactors of reductive dehalogenases (RDases) in organohalide-respiring bacteria (OHRB). Changes in the Cba structure can influence RDase function. Here, we report on the cofactor versatility or selectivity of Desulfitobacterium RDases produced either in the native organism or heterologously. The susceptibility of Desulfitobacterium hafniense strain DCB-2 to guided Cba biosynthesis (i.e. incorporation of exogenous Cba lower ligand base precursors) was analysed. Exogenous benzimidazoles, azabenzimidazoles and 4,5-dimethylimidazole were incorporated by the organism into Cbas. When the type of Cba changed, no effect on the turnover rate of the 3-chloro-4-hydroxy-phenylacetate-converting enzyme RdhA6 and the 3,5-dichlorophenol-dehalogenating enzyme RdhA3 was observed. The impact of the amendment of Cba lower ligand precursors on RDase function was also investigated in Shimwellia blattae, the Cba producer used for the heterologous production of Desulfitobacterium RDases. The recombinant tetrachloroethene RDase (PceAY51) appeared to be non-selective towards different Cbas. However, the functional production of the 1,2-dichloroethane-dihaloeliminating enzyme (DcaA) of Desulfitobacterium dichloroeliminans was completely prevented in cells producing 5,6-dimethylbenzimidazolyl-Cba, but substantially enhanced in cells that incorporated 5-methoxybenzimidazole into the Cba cofactor. The results of the study indicate the utilization of a range of different Cbas by Desulfitobacterium RDases with selected representatives apparently preferring distinct Cbas.  相似文献   
29.
Which processes drive the productivity benefits of biodiversity remain a critical, but unanswered question in ecology. We tested whether the soil microbiome mediates the diversity‐productivity relationships among late successional plant species. We found that productivity increased with plant richness in diverse soil communities, but not with low‐diversity mixtures of arbuscular mycorrhizal fungi or in pasteurised soils. Diversity‐interaction modelling revealed that pairwise interactions among species best explained the positive diversity‐productivity relationships, and that transgressive overyielding resulting from positive complementarity was only observed with the late successional soil microbiome, which was both the most diverse and exhibited the strongest community differentiation among plant species. We found evidence that both dilution/suppression from host‐specific pathogens and microbiome‐mediated resource partitioning contributed to positive diversity‐productivity relationships and overyielding. Our results suggest that re‐establishment of a diverse, late successional soil microbiome may be critical to the restoration of the functional benefits of plant diversity following anthropogenic disturbance.  相似文献   
30.
Janich P  Corbeil D 《FEBS letters》2007,581(9):1783-1787
The apical domain of epithelial cells is composed of distinct subdomains such as microvilli, primary cilia and a non-protruding region. Using the cholesterol-binding protein prominin-1 as a specific marker of plasma membrane protrusions we have previously proposed the co-existence of different cholesterol-based lipid microdomains (lipid rafts) within the apical domain [R?per, K., Corbeil, D. and Huttner, W.B. (2000), Retention of prominin in microvilli reveals distinct cholesterol-based lipid microdomains in the apical plasma membrane. Nat. Cell Biol. 2, 582-592]. To substantiate the hypothesis that the microvillar plasma membrane subdomains contain a distinct set of lipids compared to the planar portion we have investigated the distribution of prominin-1 and two raft-associated gangliosides GM(1) and GM(3) by fluorescence microscopy. GM(1) was found to co-localize with prominin-1 on microvilli whereas GM(3) was segregated from there suggesting its localization in the planar region. Regarding the primary cilium, overlapping fluorescent signals of GM(1) or GM(3) and prominin-1 were observed. Thus, our data demonstrate that specific ganglioside-enriched rafts are found in different apical subdomains and reveal that two plasma membrane protrusions with different structural bases (actin for the microvillus and tubulin for the cilium) are composed of distinct types of lipid.  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