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   6076篇
  免费   585篇
  国内免费   647篇
  7308篇
  2024年   23篇
  2023年   94篇
  2022年   236篇
  2021年   336篇
  2020年   239篇
  2019年   291篇
  2018年   292篇
  2017年   231篇
  2016年   276篇
  2015年   413篇
  2014年   461篇
  2013年   455篇
  2012年   591篇
  2011年   509篇
  2010年   303篇
  2009年   313篇
  2008年   304篇
  2007年   279篇
  2006年   210篇
  2005年   224篇
  2004年   212篇
  2003年   179篇
  2002年   152篇
  2001年   116篇
  2000年   96篇
  1999年   77篇
  1998年   61篇
  1997年   60篇
  1996年   38篇
  1995年   29篇
  1994年   35篇
  1993年   40篇
  1992年   34篇
  1991年   31篇
  1990年   11篇
  1989年   13篇
  1988年   6篇
  1987年   8篇
  1986年   12篇
  1985年   7篇
  1984年   2篇
  1983年   3篇
  1982年   5篇
  1981年   1篇
排序方式: 共有7308条查询结果,搜索用时 9 毫秒
61.
62.
HIV replication can be inhibited by CXCR5+CD8 T cells (follicular cytotoxic T cell [TFC]) which transfer into B-cell follicles where latent HIV infection persists. However, how cytokines affect TFC remain unclear. Understanding which cytokines show the ability to affect TFC could be a key strategy toward curing HIV. Similar mechanisms could be used for the growth and transfer of TFCs and follicular helper T (TFH) cells; as a result, we hypothesized that cytokines IL-6, IL-21, and transforming growth factor-β (TGF-β), which are necessary for the differentiation of TFH cells, could also dictate the development of TFCs. In this work, lymph node mononuclear cells and peripheral blood mononuclear cells from HIV-infected individuals were cocultured with IL-6, IL-21, and TGF-β. We then carried out T-cell receptor (TCR) repertoire analysis to compare the differences between CXCR5 and CXCR5+CD8 T cells. Our results showed that the percentage and function of TFC can be enhanced by stimulation with TGF-β. Besides, TGF-β stimulation enhanced the diversity of TCR and complementarity-determining region 3 sequences. HIV DNA showed a negative correlation with TFC. The use of TGF-β to promote the expression of CXCR5+CD8 T cells could become a new treatment approach for curing HIV.  相似文献   
63.
Breast cancer is a popularly diagnosed malignant tumor. Genomic profiling studies suggest that breast cancer is a disease with heterogeneity. Chemotherapy is one of the chief means to treat breast cancer, while its responses and clinical outcomes vary largely due to the conventional clinicopathological factors and inherent chemosensitivity of breast cancer. Using the least absolute shrinkage and selection operator (LASSO) Cox regression model, our study established a multi-mRNA-based signature model and constructed a relative nomogram in predicting distant-recurrence-free survival for patients receiving surgery and following chemotherapy. We constructed a signature of eight mRNAs (IPCEF1, SYNDIG1, TIGIT, SPESP1, C2CD4A, CLCA2, RLN2, and CCL19) with the LASSO model, which was employed to separate subjects into groups with high- and low-risk scores. Obvious differences of distant-recurrence-free survival were found between these two groups. This eight-mRNA-based signature was independently associated with the prognosis and had better prognostic value than classical clinicopathologic factors according to multivariate Cox regression results. Receiver operating characteristic results demonstrated excellent performance in diagnosing 3-year distant-recurrence by the eight-mRNA signature. A nomogram that combined both the eight-mRNA-based signature and clinicopathological risk factors was constructed. Comparing with an ideal model, the nomograms worked well both in the training and validation sets. Through the results that the eight-mRNA signature effectively classified patients into low- and high-risk of distant recurrence, we concluded that this eight-mRNA-based signature played a promising predictive role in prognosis and could be clinically applied in breast cancer patients receiving adjuvant chemotherapy.  相似文献   
64.
Non-small-cell lung cancer (NSCLC) remains the leading cause of cancer death worldwide. As a platinum-based chemotherapeutic drug, cisplatin has been used for over 30 years in NSCLC treatment while its effects are diminished by drug resistance. Therefore, we aimed to study the potential role of UCA1 in the development of chemoresistance against cisplatin. Real-time polymerase chain reaction, western-blot analysis, and immunofluorescence were used to study the involvement of UCA1, miR-495, and NRF2 in chemoresistance against cisplatin. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay was performed to determine the effect of cisplatin on cell proliferation. Computational analysis and luciferase assay were carried out to explore the interaction among UCA1, miR-495, and NRF2. The cisplatin-R group exhibited lower levels of UCA1 and NRF2 expression but a higher level of miR-495 expression than the cisplatin-S group. The growth rate and half-maximal inhibitory concentration of cellular dipeptidyl peptidase (cisplatinum) of the cisplatin-R group were much higher than those in the cisplatin-S group. MiR-495 contained a complementary binding site of UCA1, and the luciferase activity of wild-type UCA1 was significantly reduced after the transfection of miR-495 mimics. MiR-495 directly targeted the 3′-untranslated region (3′-UTR) of NRF2, and the luciferase activity of wild-type NRF2 3′-UTR was evidently inhibited by miR-495 mimics. Finally, UCA1 and NRF2 expressions in the effective group were much lower than that in the ineffective group, along with a much higher level of miR-495 expression. We suggested for the first time that high expression of UCA1 contributed to the development of chemoresistance to cisplatin through the UCA1/miR-495/NRF2 signaling pathway.  相似文献   
65.
Breast carcinoma is one of the most commonly diagnosed tumors and also one of the deadliest cancers in the female. Long noncoding RNAs (lncRNAs) are emerging as novel targets and biomarkers for breast cancer diagnosis and treatment. In this study, we aimed to study the lncRNAs associated with the outcomes in patients using the breast invasive carcinoma datasets from The Cancer Genome Atlas. The Cox proportional hazards regression model was fitted to each lncRNA. Hierarchy clustering was carried out using these survival-related lncRNAs and the log-rank test was carried out for the clustered groups. DNA methylation status was utilized to identify the lncRNAs regulated by epigenetics. Finally, the coexpressed messenger RNA with the potential lncRNAs were utilized to study the possible functions and mechanisms of lncRNAs. In total, 182 lncRNAs had an impact on the survival time of the patients with a cutoff <0.01. The patients were clustered into three groups using these survival-related genes, which performed significantly different prognosis. Two lncRNAs, which were significantly correlated with the outcomes of breast cancer and were regulated by methylation status, were obtained. These two lncRNAs were TP53TG1 and RP5-1061H20.4. We proposed that TP53TG1 was activated by the wild-type TP53 and performed an impact on the PI3Ks family by binding YBX2 in breast cancer.  相似文献   
66.
Glutathione S-transferase P1 (GSTP1) is one of the important mutant sites for the cancer risk at present. The conclusions of the published reports on the relationship between GSTP1 A/G gene polymorphism and the risk of breast cancer are still debated. This meta-analysis was performed to evaluate the association between GSTP1 and the risk of breast cancer. The association reports were identified from PubMed and Cochrane Library, and eligible studies were included and synthesized using meta-analysis method. 35 investigations were included into this meta-analysis for the association of GSTP1 A/G gene polymorphism and breast cancer susceptibility, consisting of 40,347 subjects (18,665 patients with breast cancer and 21,682 controls). The association between GSTP1 A/G gene polymorphism and breast cancer risk was not found for overall population, Caucasians and Africans. Interestingly, the GSTP1 A/G gene polymorphism was associated with the susceptibility of breast cancer in Asians (G allele: OR = 1.10, 95 % CI: 1.04–1.17, P = 0.001; GG genotype: OR = 1.36, 95 % CI: 1.14–1.62, P = 0.0008; AA genotype: OR = 0.92, 95 % CI: 0.85–0.98, P = 0.02). Furthermore, the GSTP1 A/G gene polymorphism was associated with the susceptibility of breast cancer for the analysis of the controls from hospital. In conclusion, GSTP1 A/G gene polymorphism is associated with the breast cancer susceptibility in Asians. However, more studies on the relationship between GSTP1 A/G gene polymorphism and the risk of breast cancer should be performed in further.  相似文献   
67.

Key message

A gene encoding a coproporphyrinogen III oxidase mediates disease resistance in plants by the salicylic acid pathway.

Abstract

A number of genes that regulate powdery mildew resistance have been identified in Arabidopsis, such as ENHANCED DISEASE RESISTANCE 1 to 3 (EDR1 to 3). To further study the molecular interactions between the powdery mildew pathogen and Arabidopsis, we isolated and characterized a mutant that exhibited enhanced resistance to powdery mildew. The mutant also showed dramatic powdery mildew-induced cell death as well as growth defects and early senescence in the absence of pathogens. We identified the affected gene by map-based cloning and found that the gene encodes a coproporphyrinogen III oxidase, a key enzyme in the tetrapyrrole biosynthesis pathway, previously known as LESION INITIATION 2 (LIN2). Therefore, we designated the mutant lin2-2. Further studies revealed that the lin2-2 mutant also displayed enhanced resistance to Hyaloperonospora arabidopsidis (H.a.) Noco2. Genetic analysis showed that the lin2-2-mediated disease resistance and spontaneous cell death were dependent on PHYTOALEXIN DEFICIENT 4 (PAD4), SALICYLIC ACID INDUCTION-DEFICIENT 2 (SID2), and NONEXPRESSOR OF PATHOGENESIS-RELATED GENES 1 (NPR1), which are all involved in salicylic acid signaling. Furthermore, the relative expression levels of defense-related genes were induced after powdery mildew infection in the lin2-2 mutant. These data indicated that LIN2 plays an important role in cell death control and defense responses in plants.  相似文献   
68.
69.
The relationships of extant and extinct lineages of Adephaga were analysed formally for the first time. Emphasis is placed on the aquatic and semiaquatic groups and their evolution in the Mesozoic. ?Triadogyrus and ?Mesodineutus belong to Gyrinidae, the sister group of the remaining families. ?Triaplidae are the sister group of the following groups (Haliplidae, Geadephaga, Dytiscoidea incl. ?Liadytidae, ?Parahygrobiidae and ?Coptoclavidae [major part]). The lack of a ventral procoxal joint and a very short prosternal process are plesiomorphies of ?Triaplidae. ?Coptoclavidae and ?Timarchopsinae are paraphyletic. ?Timarchopsis is placed in a geadephagan clade. In contrast to other coptoclavids, its metathorax is close to the condition found in Haliplidae, with a complete transverse ridge and coxae with large plates and free mesal walls. ?Coptoclavidae s.str., i.e. excl. ?Timarchopsis, is a dytiscoid subgroup. The mesal metacoxal walls are fused, the coxal plates are reduced, and the transverse ridge is absent. ?Stygeonectes belongs to this dytiscoid coptoclavid unit and is therefore misplaced in ?Timarchopsinae. ?Liadytidae belongs to a dytiscoid subgroup, which also comprises the extant families Aspidytidae, Amphizoidae, Hygrobiidae and Dytiscidae. ?Parahygrobia is the sister group of Hygrobiidae. The larvae are characterized by a broad gula, the absence of the lacinia, retractile maxillary bases and very long urogomphi set with long setae. ?Liadytiscinae is the sister group of extant Dytiscidae. There is no support for a clade ?Eodromeinae and for Trachypachidae incl. ?Eodromeinae. ?Fortiseode is nested within Carabidae. The exclusion of fossil taxa has no effect on the branching pattern. The evolution of Adephaga in the Mesozoic is discussed. Possible reasons for the extinction of ?Coptoclavidae are the rise of teleost fish and the competition of Gyrinidae and Dytiscidae, which possess efficient defensive glands and larval mandibular sucking channels.  相似文献   
70.
Congenital human cytomegalovirus (HCMV) infection is the most frequent infectious cause of birth defects, primarily neurological disorders. Neural progenitor/stem cells (NPCs) are the major cell type in the subventricular zone and are susceptible to HCMV infection. In culture, the differentiation status of NPCs may change with passage, which in turn may alter susceptibility to virus infection. Previously, only early-passage (i.e., prior to passage 9) NPCs were studied and shown to be permissive to HCMV infection. In this study, NPC cultures derived at different gestational ages were evaluated after short (passages 3 to 6) and extended (passages 11 to 20) in vitro passages for biological and virological parameters (i.e., cell morphology, expression of NPC markers and HCMV receptors, viral entry efficiency, viral gene expression, virus-induced cytopathic effect, and release of infectious progeny). These parameters were not significantly influenced by the gestational age of the source tissues. However, extended-passage cultures showed evidence of initiation of differentiation, increased viral entry, and more efficient production of infectious progeny. These results confirm that NPCs are fully permissive for HCMV infection and that extended-passage NPCs initiate differentiation and are more permissive for HCMV infection. Later-passage NPCs being differentiated and more permissive for HCMV infection suggest that HCMV infection in fetal brain may cause more neural cell loss and give rise to severe neurological disabilities with advancing brain development.  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