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   6532篇
  免费   506篇
  国内免费   30篇
耳鼻咽喉   25篇
儿科学   227篇
妇产科学   122篇
基础医学   931篇
口腔科学   155篇
临床医学   705篇
内科学   1409篇
皮肤病学   174篇
神经病学   664篇
特种医学   189篇
外科学   747篇
综合类   58篇
一般理论   3篇
预防医学   623篇
眼科学   135篇
药学   488篇
中国医学   16篇
肿瘤学   397篇
  2024年   15篇
  2023年   89篇
  2022年   126篇
  2021年   262篇
  2020年   171篇
  2019年   237篇
  2018年   245篇
  2017年   175篇
  2016年   213篇
  2015年   234篇
  2014年   261篇
  2013年   344篇
  2012年   512篇
  2011年   524篇
  2010年   289篇
  2009年   227篇
  2008年   429篇
  2007年   384篇
  2006年   427篇
  2005年   376篇
  2004年   347篇
  2003年   318篇
  2002年   225篇
  2001年   58篇
  2000年   43篇
  1999年   66篇
  1998年   52篇
  1997年   38篇
  1996年   31篇
  1995年   38篇
  1994年   27篇
  1993年   15篇
  1992年   36篇
  1991年   35篇
  1990年   26篇
  1989年   25篇
  1988年   14篇
  1987年   12篇
  1986年   14篇
  1985年   11篇
  1984年   9篇
  1983年   13篇
  1982年   8篇
  1980年   5篇
  1979年   7篇
  1978年   5篇
  1971年   4篇
  1970年   4篇
  1969年   4篇
  1966年   5篇
排序方式: 共有7068条查询结果,搜索用时 15 毫秒
71.
72.
The net impact of cytomegalovirus (CMV) DNAemia on overall mortality (OM) and nonrelapse mortality (NRM) following allogeneic hematopoietic stem cell transplantation (allo-HSCT) remains a matter of debate. This was a retrospective, multicenter, noninterventional study finally including 749 patients. CMV DNA monitoring was conducted by real-time polymerase chain reaction (PCR) assays. Clinical outcomes of interest were OM and NRM through day 365 after allo-HSCT. The cumulative incidence of CMV DNAemia in this cohort was 52.6%. A total of 306 out of 382 patients with CMV DNAemia received preemptive antiviral therapy (PET). PET use for CMV DNAemia, but not the occurrence of CMV DNAemia, taken as a qualitative variable, was associated with increased OM and NRM in univariate but not in adjusted models. A subcohort analysis including patients monitored by the COBAS Ampliprep/COBAS Taqman CMV Test showed that OM and NRM were comparable in patients in whom either low or high plasma CMV DNA threshold (<500 vs ≥500 IU/mL) was used for PET initiation. In conclusion, CMV DNAemia was not associated with increased OM and NRM in allo-HSCT recipients. The potential impact of PET use on mortality was not proven but merits further research.  相似文献   
73.
Archives of Sexual Behavior - Gender variance is a broad term used to describe gender non-conforming behaviors. Past studies have used the parental response to Child Behavior Checklist (CBCL) Item...  相似文献   
74.
We recently described the cloning of a fifth member of the 5-hydroxytryptamine (5-HT)1 (serotonin1) receptor class that inhibits adenylyl cyclase, namely the human 5-HT1F receptor (Adham et al. 1993 a). In the present study we have examined in greater detail the functional coupling of the 5-HT1F receptor in two different cell lines, NIH-3T3 and LM(tk) fibroblasts (receptor densities of 1.7 and 4.4 pmol/mg protein, respectively). The maximal inhibitory response elicited by 5-HT was significantly greater in NIH-3T3 as compared to LM(tk) cells, whereas the EC50 values were comparable.To investigate the relationship between receptor occupancy and inhibition of cAMP accumulation mediated by 5-HT1F receptors in NIH-3T3 cells (and hence the degree of receptor reserve), we used the irreversible receptor antagonist N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ). The half-maximal response required only about 10% receptor occupancy, consistent with a receptor reserve of 90% (88±2.1%, n = 4) for 5-HT-induced inhibition of FSCA. Despite the presence of such a high degree of receptor reserve, a range of intrinsic activities was displayed by structurally diverse classes of compounds. For example, sumatriptan and lysergol were as efficacious as 5-HT itself and thus acted as full agonists, whereas metergoline and 1-NP behaved as partial agonists and as shown previously (Adham et al. 1993a), methiothepin was a silent antagonist (Kb = 438 nM).We have also investigated activation of additional signal transduction pathways by the 5-HT1F receptor and found that the responses differ in the two cell lines with respect to stimulation of phospholipase C. For example, in NIH-3T3 cells no elevation of inositol phosphates (IP) of [Ca2+]i was observed even at very high agonist concentrations (100 M). In contrast, in LM(tk) cells concentrations of 5-HT as low as 10 nM induced stimulation of IP and a rapid increase of [Ca2+]i. The 5-HT1F receptor failed to alter arachidonic acid release in either cell line.The maximal increase in IP accumulation in LM(tk) cells was modest, averaging about 100% above basal. The increases of IP and [Ca2+]i required 5-HT concentrations less than one order of magnitude greater than those inhibiting FSCA (EC50 = 17, 55 and 8 nM, respectively), and both responses were blocked by 100 M methiothepin. All three responses (cAMP, IP, and [Ca2+]i) were sensitive to pertussis toxin pre-treatment, suggesting the involvement of Gi/Go protein(s) in these signal transduction pathways. [Ca2+]i was also elevated by sumatriptan, which may provide a mechanism by which this drug causes constriction of the vasculature. In conclusion, these data indicate that the human 5-HT1F receptor can couple to multiple effectors, and that this coupling is cell-type dependent.Abbreviations FSCA forskolin-stimulated cAMP accumulation - [Ca2+] intracellular free calcium concentration - AA arachidonic acid - EEDQ N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline - CHO chinese hamster ovary cell - LM(tk) mouse fibroblast cell - Bmax maximal binding site density - Ki apparent dissociation constant obtained from competition binding studies - G protein guanine nucleotide-binding protein - HBS HEPES-buffered saline - IP inositol phosphates - IP3 inositol 1,4,5 trisphosphate - PLC phospholipase C - Kb antagonist dissociation constant - Kd equilibrium dissociation constant - N-1F-6 stable NIH-3T3 cells expressing the cloned 5-HT1F receptor - L-1F-3 stable LM(tk) cells expressing the cloned 5-HT1F receptor - PTX pertussis toxin - BSA bovine serum albumin - METH methiothepin - SUMA sumatriptan - 5-MeO-DMT 5-methoxy-N,N-dimethyltryptamine - 1-NP 1-(1-napthyl)piperazine - 5-CT 5-carboxyamidotryptamine Correspondence to: N. Adham at the above address  相似文献   
75.
Three different domains of behavioral action of ethanol (ETOH) were examined in a battery of seven inbred strains and in the selectively bred Long-Sleep (LS) and Short-Sleep (SS) mice. Sedative effects were examined with the loss of the righting reflex test at 3.8 g/kg. The variation among inbred strains was only half the size of the difference between LS and SS mice which were selectively bred for extremes in this phenotype; such a result is expected for phenotypes controlled polygenically. Blood ETOH levels at waking from the narcosis also showed a range of differences among the inbred strains that was less than the LS/SS difference. Ataxia was measured with the grid test, and the inbred strains fell into two groups, resembling the highly ataxic LS line, and the less ataxic SS line. Biphasic effects of ETOH on locomotor activity were strongly genotype dependent. Variation in degree of activation/disinhibition produced by doses up to 1.5 g/kg (IP) ranged from no activation, in the C57BL/6Abg strain, to a stimulation effect in the MOLD/RkAbg strain which was larger than that seen for SS mice. The patterns of strain differences for both ataxia and activation were highly different from the duration of loss of righting reflex measure, suggesting multiple independent genetically based sensitivities to ETOH.  相似文献   
76.
The association between severe aplastic anemia (AA) and DR2 antigen seems to be well established. However, since discrimination between two DR2-associated splits, namely DR15 and DR16, rarely was performed, it remains unclear whether one or both of these subvariants are responsible for AA susceptibility. In this study, we have analyzed the HLA-DR allelic distribution in a group of 37 AA patients of slavic origin from North-Western Russia. The experimental design included PCR-based amplification of DRB-specific sequences, followed by reverse dot-blot hybridization of the biotinylated PCR-product with the set of sequence-specific oligonucleotide probes. HLA-DRB alleles were identified by non-radioactive enzymatic reaction, then standard serological specificities of HLA-DR antigen were estimated according to the WHO nomenclature. Whereas DR15 subtype occurred more often in the patients (23.0% vs. 13.3%, p< 0.05), DR16 split did not show the same tendency. The results, show the overall predominance of HLA-DR2 specificity (DR15+DR16) did not reach statistical significance (24.4% vs.17.5%, p<0.2). Thus, we conclude that repeatedly reported DR2 frequency increase in AA patients is mainly attributed to the prevalence of DR15 subtype.  相似文献   
77.
We present results from a simulation study for the estimation of a common odds ratio in multiple 2 × 2 tables when the data are correlated within clusters. We model the correlation of the data by the beta-binomial distribution. Through a simulation study, we compare the Mantel—Haenszel estimator with Rao and Scott'S estimator in terms of their biases, observed variances, relative efficiencies of their variances and 95 per cent coverage proportions. We limit the simulation study to the case where there are the same number of subjects in each cluster and the same number of observations in each row of each stratum. When ρ = 0, we recommend use of the Mantel—Haenszel estimator γMH with an unadjusted variance and Rao and Scott'S estimator γ with a pooled design effect. In general, when ρ >0, we recommend the Mantel—Haenszel estimator γMH with an adjusted variance and Rao and Scott'S estimator γ with a pooled design effect.  相似文献   
78.
Metabotropic glutamate (mGlu) receptors have been implicated in a number of physiological and pathological responses to glutamate, but the exact role of group I mGlu receptors in causing postischaemic injury is not yet clear. In this study, we examined whether the recently-characterized and relatively selective mGlu1 receptor antagonists 1-aminoindan-1,5-dicarboxylic acid (AIDA) and (S)-(+)-2-(3'-carboxybicyclo[1.1.1]pentyl)-glycine (CBPG) could reduce neuronal death in vitro, following oxygen-glucose deprivation (OGD) in murine cortical cell and rat organotypic hippocampal cultures, and in vivo, after global ischaemia in gerbils. When present in the incubation medium during the OGD insult and the subsequent 24 h recovery period, AIDA and CBPG significantly reduced neuronal death in vitro. The extent of protection was similar to that observed with the nonselective mGlu receptor antagonist (+)-alpha-methyl-4-carboxyphenylglycine [(+)MCPG] and with typical ionotropic glutamate (iGlu) receptor antagonists. Neuroprotection was also observed when AIDA or CBPG were added only after the OGD insult was terminated. Neuronal injury was not attenuated by the inactive isomer (-)MCPG, but was significantly enhanced by the nonselective mGlu receptor agonist (1S,3R)-1-aminocyclopentane-1, 3-dicarboxylic acid [(1S,3R)-ACPD] and the group I mGlu receptor agonist 3,5-dihydroxyphenylglycine (3,5-DHPG). The antagonists (+)MCPG, AIDA and CBPG were also neuroprotective in vivo, because i. c.v. administration reduced CA1 pyramidal cell degeneration examined 7 days following transient carotid occlusion in gerbils. Our results point to a role of mGlu1 receptors in the pathological mechanisms responsible for postischaemic neuronal death and propose a new target for neuroprotection.  相似文献   
79.
WB 4101-related benzodioxans 3-9 were synthesized, and their biological profiles at alpha(1)-adrenoreceptor subtypes and 5-HT(1A) serotoninergic receptors were assessed by binding assays in CHO and HeLa cells membranes expressing the human cloned receptors. Furthermore, receptor selectivity of selected benzodioxan derivatives was further determined in functional experiments in isolated rat vas deferens (alpha(1A)) and aorta (alpha(1D)) and guinea pig spleen (alpha(1B)), in additional receptor binding assays in rat cortex membranes containing alpha(2)-adrenoreceptors and 5-HT(2) serotoninergic receptors, and in rat striatum membranes containing D(2) dopaminergic receptors. An analysis of the results of receptor binding experiments for benzodioxan-modified derivatives 3-9 showed high affinity and selectivity toward the alpha(1a)-adrenoreceptor subtype for compounds 3-5 and 7 and a reversed selectivity profile for 9, which was a selective alpha(1d) antagonist. Furthermore, the majority of structural modifications performed on the prototype 1 (WB 4101) led to a marked decrease in the affinity for 5-HT(1A) serotoninergic receptors, which may have relevance in the design of selective alpha(1A)-adrenoreceptor antagonists. The exception to these findings was the chromene derivative 8, which exhibited a 5-HT(1A) partial agonist profile.  相似文献   
80.
Dehydroepiandrosterone and 5-en-Androstene-3beta, 17beta-diol affect MCF-7 human breast cancer cell growth through estrogen receptor, as shown by Tamoxifen counteraction. To assess whether the aromatization of these adrenal androgens to classical estrogens is required to stimulate proliferation, we evaluated the aromatase activity of MCF-7 cells. Aromatase activity was determined in both whole cells grown as monolayer cultures and microsomal fraction of cell homogenates. The conversion of Androstendione to Estrone was very low in cell cultures. By contrast, a high aromatase activity was found in cell homogenates, indicating that in isolated microsomal fractions of MCF-7 cells aromatase is unveiled. Since in whole cultured MCF-7 cells the conversion of androgens to estrogens is negligible, we suggest that the stimulatory effect of DHEA and ADIOL on the 'in vitro' growth of MCF-7 does not involve the aromatase pathway.  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