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   1866篇
  免费   124篇
  2024年   2篇
  2023年   12篇
  2022年   20篇
  2021年   74篇
  2020年   35篇
  2019年   47篇
  2018年   58篇
  2017年   41篇
  2016年   67篇
  2015年   111篇
  2014年   102篇
  2013年   152篇
  2012年   190篇
  2011年   207篇
  2010年   107篇
  2009年   99篇
  2008年   120篇
  2007年   93篇
  2006年   92篇
  2005年   83篇
  2004年   83篇
  2003年   61篇
  2002年   51篇
  2001年   9篇
  2000年   4篇
  1999年   7篇
  1998年   10篇
  1997年   6篇
  1996年   8篇
  1995年   7篇
  1994年   1篇
  1993年   5篇
  1992年   1篇
  1991年   4篇
  1990年   1篇
  1989年   4篇
  1988年   1篇
  1986年   1篇
  1983年   1篇
  1982年   2篇
  1981年   2篇
  1968年   8篇
  1964年   1篇
排序方式: 共有1990条查询结果,搜索用时 15 毫秒
61.
International Journal of Primatology - Information on parasite biodiversity and abundance can improve our understanding of parasitic infections on endangered wildlife, as parasites can affect host...  相似文献   
62.
The most prevalent malignancy in the oral cavity is represented by oral squamous cell carcinoma, an aggressive disease mostly detected in low-income communities. This neoplasia is mostly diffused in older men particularly exposed to risk factors such as tobacco, alcohol, and a diet rich in fatty foods and poor in vegetables. In oral squamous cell carcinoma, a wide range of matrix-cleaving proteinases are involved in extracellular matrix remodeling of cancer microenvironment. In particular, matrix metalloproteinases (MMPs) represent the major and most investigated protagonists. Owing to their strong involvement in malignant pathologies, MMPs are considered the most promising new biomarkers in cancer diagnosis and prognosis. The interest in studying MMPs in oral cancer biology is also owing to their prominent role in epithelial-to-mesenchymal transition (EMT). EMT is an intricate process involving different complex pathways. EMT-related proteins are attractive diagnostic biomarkers that characterize the activation of biological events that promote cancer's aggressive expansion. Different antioncogenic natural compounds have been investigated to counteract oral carcinogenesis, with the scope of obtaining better clinical results and lower morbidity. In particular, we describe the role of different nutraceuticals used for the regulation of MMP-related invasion and proliferation of oral cancer cells.  相似文献   
63.
Excitatory amino acids (EAAs) are found present in the nervous and reproductive systems of animals. Numerous studies have demonstrated a regulatory role for Glutamate (Glu), d -aspartate ( d -Asp) and N-methyl- d -aspartate (NMDA) in the control of spermatogenesis. EAAs are able to stimulate the Glutamate receptors, including the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR). Here in, we assess expression of the main AMPAR subunits, GluA1 and GluA2/3, in the mouse testis and in spermatogonial GC-1 cells. The results showed that both GluA1 and GluA2/3 were localized in mouse testis prevalently in spermatogonia. The subunit GluA2/3 was more highly expressed compared with GluA1 in both the testis and the GC-1 cells. Subsequently, GC-1 cells were incubated with medium containing l -Glu, d -Glu, d -Asp or NMDA to determine GluA1 and GluA2/3 expressions. At 30 minutes and 2 hours of incubation, EAA-treated GC-1 cells showed significantly higher expression levels of both GluA1 and GluA2/3. Furthermore, p-extracellular signal-regulated kinase (ERK), p-Akt, proliferating cell nuclear antigen (PCNA), and Aurora B expressions were assayed in l -Glu-, d -Glu-, and NMDA-treated GC-1 cells. At 30 minutes and 2 hours of incubation, treated GC-1 cells showed significantly higher expression levels of p-ERK and p-Akt. A consequent increase of PCNA and Aurora B expressions was induced by l -Glu and NMDA, but not by d -Glu. Our study demonstrates a direct effect of the EAAs on spermatogonial activity. In addition, the increased protein expression levels of GluA1 and GluA2/3 in EAA-treated GC-1 cells suggest that EAAs could activate ERK and Akt pathways through the AMPAR. Finally, the increased PCNA and Aurora B levels may imply an enhanced proliferative activity.  相似文献   
64.
Senescence of adipose precursor cells (APC) impairs adipogenesis, contributes to the age‐related subcutaneous adipose tissue (SAT) dysfunction, and increases risk of type 2 diabetes (T2D). First‐degree relatives of T2D individuals (FDR) feature restricted adipogenesis, reflecting the detrimental effects of APC senescence earlier in life and rendering FDR more vulnerable to T2D. Epigenetics may contribute to these abnormalities but the underlying mechanisms remain unclear. In previous methylome comparison in APC from FDR and individuals with no diabetes familiarity (CTRL), ZMAT3 emerged as one of the top‐ranked senescence‐related genes featuring hypomethylation in FDR and associated with T2D risk. Here, we investigated whether and how DNA methylation changes at ZMAT3 promote early APC senescence. APC from FDR individuals revealed increases in multiple senescence markers compared to CTRL. Senescence in these cells was accompanied by ZMAT3 hypomethylation, which caused ZMAT3 upregulation. Demethylation at this gene in CTRL APC led to increased ZMAT3 expression and premature senescence, which were reverted by ZMAT3 siRNA. Furthermore, ZMAT3 overexpression in APC determined senescence and activation of the p53/p21 pathway, as observed in FDR APC. Adipogenesis was also inhibited in ZMAT3‐overexpressing APC. In FDR APC, rescue of ZMAT3 methylation through senolytic exposure simultaneously downregulated ZMAT3 expression and improved adipogenesis. Interestingly, in human SAT, aging and T2D were associated with significantly increased expression of both ZMAT3 and the P53 senescence marker. Thus, DNA hypomethylation causes ZMAT3 upregulation in FDR APC accompanied by acquisition of the senescence phenotype and impaired adipogenesis, which may contribute to FDR predisposition for T2D.  相似文献   
65.
In the early 1800s, the European roe deer (Capreolus capreolus) was probably extirpated from Switzerland, due to overhunting and deforestation. After a federal law was enacted in 1875 to protect lactating females and young, and limiting the hunting season, the roe deer successfully recovered and recolonized Switzerland. In this study, we use mitochondrial DNA and nuclear DNA markers to investigate the recolonization and assess contemporary genetic structure in relation to broad topographic features, in order to understand underlying ecological processes, inform future roe deer management strategies, and explore the opportunity for development of forensic traceability tools. The results concerning the recolonization origin support natural, multidirectional immigration from neighboring countries. We further demonstrate that there is evidence of weak genetic differentiation within Switzerland among topographic regions. Finally, we conclude that the genetic data support the recognition of a single roe deer management unit within Switzerland, within which there is a potential for broad‐scale geographic origin assignment using nuclear markers to support law enforcement.  相似文献   
66.
The high-yield expression of a neutralizing epitope from human immunodeficiency virus type 1 (HIV-1) on the surface of a plant virus and its immunogenicity are presented. The highly conserved ELDKWA epitope from glycoprotein (gp) 41 was expressed as an N-terminal translational fusion with the potato virus X (PVX) coat protein. The resulting chimeric virus particles (CVPs), purified and used to immunize mice intraperitoneally or intranasally, were able to elicit high levels of HIV-1-specific immunoglobulin G (IgG) and IgA antibodies. Furthermore, the human immune response to CVPs was studied with severe combined immunodeficient mice reconstituted with human peripheral blood lymphocytes (hu-PBL-SCID). hu-PBL-SCID mice immunized with CVP-pulsed autologous dendritic cells were able to mount a specific human primary antibody response against the gp41-derived epitope. Notably, sera from both normal and hu-PBL-SCID mice showed an anti-HIV-1-neutralizing activity. Thus, PVX-based CVPs carrying neutralizing epitopes can offer novel perspectives for the development of effective vaccines against HIV and, more generally, for the design of new vaccination strategies in humans.  相似文献   
67.
We have used polymorphic chloroplast simple sequence repeats (cpSSRs) to analyse levels of diversity and relationships within the genusZea. Between two and nine alleles were found at 15 polymorphic loci and combining the data from these loci gave 32 haplotypes in the 37 accessions studied. Genetic differentiation between the two sections within the genus was calculated using theST statistic which showed that 70% of the total variation was found to exist between the sections. A phylogenetic analysis based on the 2 distance metric showed a large split between the two sections and suggested multiple origins of modern cultivated maizeZea mays subsp.mays. The agreement of the phylogenetic tree with other molecular, morphological and karyological studies suggests that cpSSRs may have value in phylogenetic studies in plants.  相似文献   
68.
The extracellular domain of the receptor tyrosine kinase Tie2/TEK (exTEK) has been used as an angiopoietin decoy to study the role of angiopoietins in the tumor–host interactions, using a syngeneic model of experimental metastases and subcutaneous tumor. Soluble exTEK secreted by transfected tumor cells inhibited HUVECs from forming tubes in Matrigel. ExTEK-transfected C26 colon carcinoma and TS/A mammary tumor cells displayed reduced growth rate when injected subcutaneously, and reduced ability to form experimental metastases when injected intravenously. Immunohistochemical analysis of tumors and metastases showed increased leukocytes infiltration and signs of inflammation in exTEK-secreting compared to parental tumor, as well as impairment in neo-vessel growth and organization. However, while neoangiogenesis eventually rescued in the subcutis, it failed to organize in the experimental metastases of exTEK-secreting tumor, contributing to the hampering of metastatic growth and to increased mice survival. The reactive infiltrate of C26TEK contained a different percentage of leukocytes and was responsible for the tumor inhibition. In fact, leukopenia induced by -irradiation of recipient mice or injection into interferon gamma (IFN-) gene knockout (GKO) mice resulted in reduced mouse survival and an increased number of lung metastases. On the other hand, interleukin (IL)-12 treatment prolonged the survival of mice bearing subcutaneous C26TEK but not of those bearing lung metastases, suggesting that IL-12 could exert further antiangiogenic effects at the site where the tumor can restore neoangiogenesis. These results show in vivo that reduced angiopoietin availability at the tumor site induces a local inflammatory response and impairment of neoangiogenesis which act synergistically to limit tumor growth and metastasis.Abbreviations AEC amino-ethylcarbazole - ELISA enzyme-linked immunosorbent assay - HRP horseradish peroxidase - HUVEC human umbilical vascular endothelial cell - i.v. intravenous - s.c. subcutaneous - TBS Tris-HCl buffered solution  相似文献   
69.
We have characterized the ferric and ferrous forms of the heme-containing (1-56 residues) N-fragment of horse heart cytochrome c (cyt c) at different pH values and low ionic strength by UV-visible absorption and resonance Raman (RR) scattering. The results are compared with native cyt c in the same experimental conditions as this may provide a deeper insight into the cyt c unfolding-folding process. Folding of cyt c leads to a state having the heme iron coordinated to a histidine (His18) and a methionine (Met80) as axial ligands. At neutral pH the N-fragment (which lacks Met80) shows absorption and RR spectra that are consistent with the presence of a bis-His low spin heme, like several non-native forms of the parental protein. In particular, the optical spectra are identical to those of cyt c in the presence of a high concentration of denaturants; this renders the N-fragment a suitable model to study the heme pocket microenvironment of the misfolded (His-His) intermediate formed during folding of cyt c. Acid pH affects the ligation state in both cyt c and the N-fragment. Data obtained as a function of pH allow a correlation between the structural properties in the heme pocket of the N-fragment and those of non-native forms of cyt c. The results underline that the (57-104 residues) segment under native-like conditions imparts structural stability to the protein by impeding solvent access into the heme pocket.  相似文献   
70.
In some sponges peculiar proteins called silicateins catalyze silica polymerization in ordered structures, and their study is of high interest for possible biotechnological applications in the nanostructure industry. In this work we describe the isolation and the molecular characterization of silicatein from spicules of Petrosia ficiformis, a common Mediterranean sponge, and the development of a cellular model (primmorphs) suitable for in vitro studies of silicatein gene regulation. The spicule of P. ficiformis contains an axial filament composed of 2 insoluble proteins, of 30 and 23 kDa. The 23-kDa protein was characterized, and the full-length cDNA was cloned. The putative amino acid sequence has high homology with previously described silicateins from other sponge species and also is very similar to cathepsins, a cystein protease family. Finally, P. ficiformis primmorphs express the silicatein gene, suggesting that they should be a good model for biosilicification studies.  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