全文获取类型
收费全文 | 4031篇 |
免费 | 275篇 |
国内免费 | 281篇 |
专业分类
4587篇 |
出版年
2024年 | 10篇 |
2023年 | 63篇 |
2022年 | 130篇 |
2021年 | 225篇 |
2020年 | 169篇 |
2019年 | 160篇 |
2018年 | 172篇 |
2017年 | 138篇 |
2016年 | 192篇 |
2015年 | 261篇 |
2014年 | 316篇 |
2013年 | 343篇 |
2012年 | 354篇 |
2011年 | 309篇 |
2010年 | 217篇 |
2009年 | 189篇 |
2008年 | 207篇 |
2007年 | 165篇 |
2006年 | 147篇 |
2005年 | 139篇 |
2004年 | 97篇 |
2003年 | 85篇 |
2002年 | 72篇 |
2001年 | 56篇 |
2000年 | 55篇 |
1999年 | 59篇 |
1998年 | 41篇 |
1997年 | 22篇 |
1996年 | 31篇 |
1995年 | 26篇 |
1994年 | 22篇 |
1993年 | 16篇 |
1992年 | 16篇 |
1991年 | 13篇 |
1990年 | 14篇 |
1989年 | 11篇 |
1988年 | 9篇 |
1987年 | 10篇 |
1986年 | 9篇 |
1985年 | 8篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1981年 | 2篇 |
1979年 | 4篇 |
排序方式: 共有4587条查询结果,搜索用时 0 毫秒
81.
Cheng Chu Gang Xu Xiaocong Li Zuowei Duan Lihong Tao Hongxia Cai Ming Yang Xinjiang Zhang Bin Chen Yanyu Zheng Hongcan Shi Xiaoyu Li 《Journal of cellular and molecular medicine》2021,25(1):110-119
Shear stress was reported to regulate the expression of AC007362, but its underlying mechanisms remain to be explored. In this study, to isolate endothelial cells of blood vessels, unruptured and ruptured intracranial aneurysm (IA) tissues were collected from IA patients. Subsequently, quantitative real-time PCR (qRT-PCR), Western blot and luciferase assay were performed to investigate the relationships between AC007362, miRNAs-493 and monocyte chemoattractant protein-1 (MCP-1) in human umbilical vein endothelial cells (HUVECs) exposed to shear stress. Reduced representation bisulphite sequencing (RRBS) was performed to assess the level of DNA methylation in AC007362 promoter. Accordingly, AC007362 and MCP-1 were significantly up-regulated while miR-493 was significantly down-regulated in HUVECs exposed to shear stress. AC007362 could suppress the miR-493 expression and elevate the MCP-1 expression, and miR-493 was shown to respectively target AC007362 and MCP-1. Moreover, shear stress in HUVECs led to the down-regulated DNA methyltransferase 1 (DNMT1), as well as the decreased DNA methylation level of AC007362 promoter. Similar results were also observed in ruptured IA tissues when compared with unruptured IA tissues. In conclusion, this study presented a deep insight into the operation of the regulatory network of AC007362, miR-493 and MCP-1 upon shear stress. Under shear stress, the expression of AC007362 was enhanced by the inhibited promoter DNA methylation, while the expression of MCP-1 was enhanced by sponging the expression of miR-493. 相似文献
82.
83.
Wang Ting Qian Yanyan Huang Jian Hua Keqin Ma Duan 《Cell biochemistry and biophysics》2013,67(3):1041-1047
We sought to investigate the relationship between the changes of CpG island methylation status of LMNA gene and insulin resistance in polycystic ovary syndrome (PCOS) patients. The genome-wide methylation microarray screening was done in three PCOS cases of insulin resistance and one case of a normal woman. The PCOS insulin resistance-related genes were identified as indicated by the results of gene chip screening. Then, 24 cases of insulin-resistant PCOS patients and 24 cases of normal individuals were studied to identify the effects of the candidate genes using genome-wide study of DNA from the peripheral blood analyzed by MassARRAY®EpiTYPER? DNA methylation analysis technique. We found that the methylation status of CpG island in the promoter area of LMNA gene was changed. The 20 CG sites in CpG island of LMNA gene were examined using case control experiment among which 12 CpG sites differed significantly (P < 0.05) between two groups while the remaining eight CpG sites differed non-significantly. We, therefore, concluded that the changes in the hypermethylation status of CpG island of LMNA gene were related to the insulin resistance in PCOS patients, indicating that this gene may be involved in the regulation of PCOS-associated insulin resistance. 相似文献
84.
Michael J. Stewart Praphaporn Stewart Morakot Sroyraya Nantawan Soonklang Scott F. Cummins Peter J. Hanna Wei Duan Prasert Sobhon 《Comparative biochemistry and physiology. Part A, Molecular & integrative physiology》2013,164(2):276-290
The crustacean X-organ–sinus gland (XO–SG) complex controls molt-inhibiting hormone (MIH) production, although extra expression sites for MIH have been postulated. Therefore, to explore the expression of MIH and distinguish between the crustacean hyperglycemic hormone (CHH) superfamily, and MIH immunoreactive sites (ir) in the central nervous system (CNS), we cloned a CHH gene sequence for the crab Portunus pelagicus (Ppel-CHH), and compared it with crab CHH-type I and II peptides. Employing multiple sequence alignments and phylogenic analysis, the mature Ppel-CHH peptide exhibited residues common to both CHH-type I and II peptides, and a high degree of identity to the type-I group, but little homology between Ppel-CHH and Ppel-MIH (a type II peptide). This sequence identification then allowed for the use of MIH antisera to further confirm the identity and existence of a MIH-ir 9 kDa protein in all neural organs tested by Western blotting, and through immunohistochemistry, MIH-ir in the XO, optic nerve, neuronal cluster 17 of the supraesophageal ganglion, the ventral nerve cord, and cell cluster 22 of the thoracic ganglion. The presence of MIH protein within such a diversity of sites in the CNS, and external to the XO–SG, raises new questions concerning the established mode of MIH action. 相似文献
85.
Jie Ni Paul Cozzi Jingli Hao Julia Beretov Lei Chang Wei Duan Sarah Shigdar Warick Delprado Peter Graham Joseph Bucci John Kearsley Yong Li 《The international journal of biochemistry & cell biology》2013,45(12):2736-2748
Prostate cancer (CaP) is the second leading malignancy in men. The role of epithelial cell adhesion molecule (EpCAM), also known as CD326, in CaP progression and therapeutic resistance is still uncertain. Here, we aimed to investigate the roles of EpCAM in CaP metastasis and chemo/radioresistance. Expression of EpCAM in CaP cell lines and human CaP tissues was assessed using immunofluorescence and immunohistochemistry, respectively. EpCAM was knocked down (KD) in PC-3, DU145 and LNCaP-C4-2B cells using small interfering RNA (siRNA), and KD results were confirmed by confocal microscope, Western blotting and quantitative real time polymerase chain reaction (qRT-PCR). Cell growth was evaluated by proliferation and colony formation assays. The invasive potential was assessed using a matrigel chamber assay. Tumorigenesis potential was measured by a sphere formation assay. Chemo-/radiosensitivity were measured using a colony formation assay. Over-expression of EpCAM was found in primary CaP tissues and lymph node metastases including cancer cells and surrounding stromal cells. KD of EpCAM suppressed CaP proliferation and invasive ability, reduced sphere formation, enhanced chemo-/radiosensitivity, and down-regulated E-cadherin, p-Akt, p-mTOR, p-4EBP1 and p-S6K expression in CaP cells. Our findings suggest that EpCAM plays an important role in CaP proliferation, invasion, metastasis and chemo-/radioresistance associated with the activation of the PI3K/Akt/mTOR signaling pathway and is a novel therapeutic target to sensitize CaP cells to chemo-/radiotherapy. 相似文献
86.
Virtualization is widely used in cloud computing environments to efficiently manage resources, but it also raises several challenges. One of them is the fairness issue of resource allocation among virtual machines. Traditional virtualized resource allocation approaches distribute physical resources equally without taking into account the actual workload of each virtual machine and thus often leads to wasting. In this paper, we propose a virtualized resource auction and allocation model (VRAA) based on incentive and penalty to correct this wasting problem. In our approach, we use Nash equilibrium of cooperative games to fairly allocate resources among multiple virtual machines to maximize revenue of the system. To illustrate the effectiveness of the proposed approach, we then apply the basic laws of auction gaming to investigate how CPU allocation and contention can affect applications’ performance (i.e., response time), and its effect on CPU utilization. We find that in our VRAA model, the fairness index is high, and the resource allocation is closely proportional to the actual workloads of the virtual machines, so the wasting of resources is reduced. Experiment results show that our model is general, and can be applied to other virtualized non-CPU resources. 相似文献
87.
Background
Esterases with excellent merits suitable for commercial use in ester production field are still insufficient. The aim of this research is to advance our understanding by seeking for more unusual esterases and revealing their characterizations for ester synthesis.Methodology/Principal Findings
A novel esterase-encoding gene from Rhizomucor miehei (RmEstA) was cloned and expressed in Escherichia coli. Sequence analysis revealed a 975-bp ORF encoding a 324-amino-acid polypeptide belonging to the hormone-sensitive lipase (HSL) family IV and showing highest similarity (44%) to the Paenibacillus mucilaginosus esterase/lipase. Recombinant RmEstA was purified to homogeneity: it was 34 kDa by SDS-PAGE and showed optimal pH and temperature of 6.5 and 45°C, respectively. The enzyme was stable to 50°C, under a broad pH range (5.0–10.6). RmEstA exhibited broad substrate specificity toward p-nitrophenol esters and short-acyl-chain triglycerols, with highest activities (1,480 U mg−1 and 228 U mg−1) for p-nitrophenyl hexanoate and tributyrin, respectively. RmEstA efficiently synthesized butyl butyrate (92% conversion yield) when immobilized on AOT-based organogel.Conclusion
RmEstA has great potential for industrial applications. RmEstA is the first reported esterase from Rhizomucor miehei. 相似文献88.
Hong Wu Hong Zeng Aiping Dong Fengling Li Hao He Guillermo Senisterra Alma Seitova Shili Duan Peter J. Brown Masoud Vedadi Cheryl H. Arrowsmith Matthieu Schapira 《PloS one》2013,8(12)
Polycomb repressive complex 2 (PRC2) is an important regulator of cellular differentiation and cell type identity. Overexpression or activating mutations of EZH2, the catalytic component of the PRC2 complex, are linked to hyper-trimethylation of lysine 27 of histone H3 (H3K27me3) in many cancers. Potent EZH2 inhibitors that reduce levels of H3K27me3 kill mutant lymphoma cells and are efficacious in a mouse xenograft model of malignant rhabdoid tumors. Unlike most SET domain methyltransferases, EZH2 requires PRC2 components, SUZ12 and EED, for activity, but the mechanism by which catalysis is promoted in the PRC2 complex is unknown. We solved the 2.0 Å crystal structure of the EZH2 methyltransferase domain revealing that most of the canonical structural features of SET domain methyltransferase structures are conserved. The site of methyl transfer is in a catalytically competent state, and the structure clarifies the structural mechanism underlying oncogenic hyper-trimethylation of H3K27 in tumors harboring mutations at Y641 or A677. On the other hand, the I-SET and post-SET domains occupy atypical positions relative to the core SET domain resulting in incomplete formation of the cofactor binding site and occlusion of the substrate binding groove. A novel CXC domain N-terminal to the SET domain may contribute to the apparent inactive conformation. We propose that protein interactions within the PRC2 complex modulate the trajectory of the post-SET and I-SET domains of EZH2 in favor of a catalytically competent conformation. 相似文献
89.
Insulin-like growth factor-binding proteins (IGFBPs) control bioactivity and distribution of insulin-like growth factors (IGFs) through high-affinity complex of IGFBP and IGF. To get more insight into the binding interaction of IGF system, the site-directed mutagenesis and force-driving desorption methods were employed to study the interaction mechanism of IGFBP4 and IGF-I by molecular dynamics (MD) simulation. In IGF-I, residues Gly7 to Asp12 were found to be the hot spots and they mainly anchored on the N-domain of IGFBP4. The contact area, the shape and size of protein, the surroundings of the binding site, the hydrophobic and electrostatic interaction between the two proteins worked as a complex network to regulate the protein-protein interaction. It was also found that the unfolding of the helix was not inevitable in the mutant, and it could be regulated by careful selection of the substituted amino acid. Figure
Binding network of IGF-I on the cavity surface of IGFBP4 相似文献
90.
Jin Zhou Zhiyan Du Cuimi Duan Zhiyan Li Changyong Wang 《Journal of cellular and molecular medicine》2013,17(6):782-791
Induced pluripotent stem cell (iPSC) provides a promising seeding cell for regenerative medicine. However, iPSC has the potential to form teratomas after transplantation. Therefore, it is necessary to evaluate the tumorigenic risks of iPSC and all its differentiated derivates prior to use in a clinical setting. Here, murine iPSCs were transduced with dual reporter gene consisting of monomeric red fluorescent protein (mRFP) and firefly luciferase (Fluc). Undifferentiated iPSCs, iPSC derivates from induced differentiation (iPSC‐derivates), iPSC‐derivated cardiomyocyte (iPSC‐CMs) were subcutaneously injected into the back of nude mice. Non‐invasive bioluminescence imaging (BLI) was longitudinally performed at day 1, 7, 14 and 28 after transplantation to track the survival and proliferation of transplanted cells. At day 28, mice were killed and grafts were explanted to detect teratoma formation. The results demonstrated that transplanted iPSCs, iPSC‐derivates and iPSC‐CMs survived in receipts. Both iPSCs and iPSC‐derivates proliferated dramatically after transplantation, while only slight increase in BLI signals was observed in iPSC‐CM transplanted mice. At day 28, teratomas were detected in both iPSCs and iPSC‐derivates transplanted mice, but not in iPSC‐CM transplanted ones. In vitro study showed the long‐term existence of pluripotent cells during iPSC differentiation. Furthermore, when these cells were passaged in feeder layers as undifferentiated iPSCs, they would recover iPSC‐like colonies, indicating the cause for differentiated iPSC's tumourigenicity. Our study indicates that exclusion of tumorigenic cells by screening in addition to lineage‐specific differentiation is necessary prior to therapeutic use of iPSCs. 相似文献