全文获取类型
收费全文 | 3382篇 |
免费 | 119篇 |
国内免费 | 70篇 |
专业分类
3571篇 |
出版年
2023年 | 23篇 |
2022年 | 68篇 |
2021年 | 66篇 |
2020年 | 64篇 |
2019年 | 69篇 |
2018年 | 73篇 |
2017年 | 69篇 |
2016年 | 58篇 |
2015年 | 105篇 |
2014年 | 243篇 |
2013年 | 205篇 |
2012年 | 200篇 |
2011年 | 292篇 |
2010年 | 230篇 |
2009年 | 157篇 |
2008年 | 189篇 |
2007年 | 205篇 |
2006年 | 199篇 |
2005年 | 153篇 |
2004年 | 146篇 |
2003年 | 104篇 |
2002年 | 65篇 |
2001年 | 34篇 |
2000年 | 37篇 |
1999年 | 39篇 |
1998年 | 45篇 |
1997年 | 32篇 |
1996年 | 33篇 |
1995年 | 43篇 |
1994年 | 36篇 |
1993年 | 33篇 |
1992年 | 27篇 |
1991年 | 31篇 |
1990年 | 28篇 |
1989年 | 16篇 |
1988年 | 19篇 |
1987年 | 20篇 |
1986年 | 20篇 |
1985年 | 15篇 |
1984年 | 14篇 |
1983年 | 4篇 |
1982年 | 10篇 |
1981年 | 12篇 |
1980年 | 8篇 |
1979年 | 4篇 |
1978年 | 6篇 |
1976年 | 4篇 |
1973年 | 3篇 |
1972年 | 3篇 |
1970年 | 4篇 |
排序方式: 共有3571条查询结果,搜索用时 15 毫秒
41.
Simon J. Foulcer Courtney M. Nelson Maritza V. Quintero Balagurunathan Kuberan Jonathan Larkin Maria T. Dours-Zimmermann Dieter R. Zimmermann Suneel S. Apte 《The Journal of biological chemistry》2014,289(40):27859-27873
Proteolysis of the Glu441-Ala442 bond in the glycosaminoglycan (GAG) β domain of the versican-V1 variant by a disintegrin-like and metalloproteinase domain with thrombospondin type 1 motif (ADAMTS) proteases is required for proper embryo morphogenesis. However, the processing mechanism and the possibility of additional ADAMTS-cleaved processing sites are unknown. We demonstrate here that if Glu441 is mutated, ADAMTS5 cleaves inefficiently at a proximate upstream site but normally does not cleave elsewhere within the GAGβ domain. Chondroitin sulfate (CS) modification of versican is a prerequisite for cleavage at the Glu441-Ala442 site, as demonstrated by reduced processing of CS-deficient or chondroitinase ABC-treated versican-V1. Site-directed mutagenesis identified the N-terminal CS attachment sites Ser507 and Ser525 as essential for processing of the Glu441-Ala442 bond by ADAMTS5. A construct including only these two GAG chains, but not downstream GAG attachment sites, was cleaved efficiently. Therefore, CS chain attachment to Ser507 and Ser525 is necessary and sufficient for versican proteolysis by ADAMTS5. Mutagenesis of Glu441 and an antibody to a peptide spanning Thr432-Gly445 (i.e. containing the scissile bond) reduced versican-V1 processing. ADAMTS5 lacking the C-terminal ancillary domain did not cleave versican, and an ADAMTS5 ancillary domain construct bound versican-V1 via the CS chains. We conclude that docking of ADAMTS5 with two N-terminal GAG chains of versican-V1 via its ancillary domain is required for versican processing at Glu441-Ala442. V1 proteolysis by ADAMTS1 demonstrated a similar requirement for the N-terminal GAG chains and Glu441. Therefore, versican cleavage can be inhibited substantially by mutation of Glu441, Ser507, and Ser525 or by an antibody to the region of the scissile bond. 相似文献
42.
Novel mechanism that Trypanosoma cruzi uses to adhere to the extracellular matrix mediated by human galectin-3 总被引:1,自引:0,他引:1
Binding of Trypanosoma cruzi trypomastigotes to laminin is enhanced by galectin-3, a beta-galactoside binding lectin. The galectin-3 enhanced binding of trypanosomes to laminin is inhibited by lactose. Co-immunoprecipitations indicate that galectin-3 binds to the 45, 32 and 30 kDa trypanosome surface proteins. Binding of galectin-3 to the 45, 32 and 30 kDa surface proteins is inhibited by lactose. Polyclonal and a monoclonal antibodies to galectin-3 immunoprecipitated a major 64 kDa trypanosome surface protein. T. cruzi monoclonal antibody to mucin recognized the 45 kDa surface protein. The 45, 32 and 30 kDa surface proteins interact with galectin-3 in order to enhance trypanosome adhesion to laminin. 相似文献
43.
Extracellular superoxide dismutase 总被引:1,自引:0,他引:1
Nozik-Grayck E Suliman HB Piantadosi CA 《The international journal of biochemistry & cell biology》2005,37(12):2466-2471
The extracellular space is protected from oxidant stress by the antioxidant enzyme extracellular superoxide dismutase (EC-SOD), which is highly expressed in selected tissues including blood vessels, heart, lungs, kidney and placenta. EC-SOD contains a unique heparin-binding domain at its carboxy-terminus that establishes localization to the extracellular matrix where the enzyme scavenges superoxide anion. The EC-SOD heparin-binding domain can be removed by proteolytic cleavage, releasing active enzyme into the extracellular fluid. In addition to protecting against extracellular oxidative damage, EC-SOD, by scavenging superoxide, preserves nitric oxide bioactivity and facilitates hypoxia-induced gene expression. Loss of EC-SOD activity contributes to the pathogenesis of a number of diseases involving tissues with high levels of constitutive extracellular superoxide dismutase expression. A thorough understanding of the biological role of EC-SOD will be invaluable for developing novel therapies to prevent stress by extracellular oxidants. 相似文献
44.
Merja Hurskainen Florence Ruggiero Pasi H?gg Taina Pihlajaniemi Pirkko Huhtala 《The Journal of biological chemistry》2010,285(8):5258-5265
The C-terminal end of collagen XV, restin, has been the focus of several studies, but the functions of full-length collagen XV have remained unknown. We describe here studies on the production, purification, and function of collagen XV and the production of a monoclonal N-terminal antibody to it. Full-length human collagen XV was produced in insect cells using baculoviruses and purified from the cell culture medium. The yield was 15 mg/liter of cell culture medium. The collagen XV was shown to be trimeric, with disulfide bonds in the collagenous region. Rotary shadowing electron microscopy revealed rod-like molecules with a mean length of 241.8 nm and with a globular domain at one end. The globular domain was verified to be the N-terminal end by N-terminal antibody binding. The molecules show flexibility in their conformation, presumably due to the many interruptions in their collagenous domains. The ability of collagen XV to serve as a substrate for cells was tested in cell adhesion assays, and it was shown that cells did not bind to collagen XV-coated surfaces. When added to the culture medium of fibroblasts and fibrosarcoma cells, however, collagen XV rapidly bound to their fibronectin network. Solid phase assays showed that collagen XV binds to fibronectin, laminin, and vitronectin and that it binds to the collagen/gelatin-binding domain of fibronectin. No binding was detected to fibrillar collagens, fibril-associated collagens, or decorin. Interestingly, collagen XV was found to inhibit the adhesion and migration of fibrosarcoma cells when present in fibronectin-containing matrices. 相似文献
45.
Mokkapati S Fleger-Weckmann A Bechtel M Koch M Breitkreutz D Mayer U Smyth N Nischt R 《The Journal of biological chemistry》2011,286(3):1911-1918
The nidogen-laminin interaction is proposed to play a key role in basement membrane (BM) assembly. However, though there are similarities, the phenotypes in mice lacking nidogen 1 and 2 (nidogen double null) differ to those of mice lacking the nidogen binding module (γ1III4) of the laminin γ1 chain. This indicates different cell- and tissue-specific functions for nidogens and their interaction with laminin and poses the question of whether the phenotypes in nidogen double null mice are caused by the loss of the laminin-nidogen interaction or rather by other unknown nidogen functions. To investigate this, we analyzed BMs, in particular those in the skin of mice lacking the nidogen binding module. In contrast to nidogen double null mice, all skin BMs in γ1III4-deficient mice appeared normal. Furthermore, although nidogen 1 deposition was strongly reduced, nidogen 2 appeared unchanged. Mice with additional deletion of the laminin γ3 chain, which contains a γ1-like nidogen binding module, showed a further reduction of nidogen 1 in the dermoepidermal BM; however, this again did not affect nidogen 2. This demonstrates that in vivo only nidogen 1 deposition is critically dependent on the nidogen binding modules of the laminin γ1 and γ3 chains, whereas nidogen 2 is independently recruited either by binding to an alternative site on laminin or to other BM proteins. 相似文献
46.
Balasubramanian S Fan M Messmer-Blust AF Yang CH Trendel JA Jeyaratnam JA Pfeffer LM Vestal DJ 《The Journal of biological chemistry》2011,286(22):20054-20064
47.
Claassen H Cellarius C Scholz-Ahrens KE Schrezenmeir J Glüer CC Schünke M Kurz B 《Cell and tissue research》2006,324(2):279-289
Certain drugs or treatments that are known to affect bone quality or integrity might have side effects on the extracellular matrix of articular cartilage. We investigated the effects of vitamin D and calcium deficiency, estrogen deficiency, and hypercortisolism alone or in combination with bisphosphonates or sodium fluoride in an animal model, viz., the Göttingen miniature pig (n=29). The articular cartilage from knee joints was analyzed for its content of glycosaminoglycans (GAGs, as macromolecules responsible for the elasticity of articular cartilage) by a spectrometric method with dimethylene blue chloride. In cryo- or paraffin sections, alkaline phosphatase (AP, as an enzyme indicating mineralization or reorganization of articular cartilage matrix) was localized by enzyme histochemistry, and positive cells were counted, whereas differently sulfated GAGs were stained histochemically. A significant decrease in GAG content was measured in ovariectomized and long-term glucocorticoid-treated animals compared with untreated animals. In the glucocorticoid/sodium fluoride group, GAGs were significantly diminished, and significantly fewer AP-positive chondrocytes were counted compared with the control. GAG content was slightly higher, and significantly more AP-positive chondrocytes were counted in short-term glucocorticoid-treated animals then in the control group. GAGs, as part of proteoglycans, are responsible for the water-storage capacity that gives articular cartilage its unique property of elasticity. Thus, ovariectomy and long-term glucocorticoid therapy, especially when combined with sodium fluoride, have detrimental effects on this tissue.This work was in part supported by Deutsche Forschungsgemeinschaft (DFG) project no. Schr 430/5–1, 5–2 and G 1289/1–1, 1–2 相似文献
48.
目的:探讨基质金属蛋白酶-9(MMP-9)在大鼠80%门静脉分支结扎模型中大鼠增生肝脏组织中的表达及其与肝再生作用的关系。方法:健康SD雄性大鼠48只,随机平均分成假手术对照组(Sham)和门静脉结扎实验组(PVL)。观察术后1、3、7和14d保留侧肝叶重量/体重比值;下腔静脉采血后检测血清谷丙转氨酶(ALT)、谷草转氨酶(AST)值的变化;光镜下观察保留侧肝脏组织的病理形态变化;用免疫组化法检测增殖细胞核抗原(Proliferating cell nuclear antigen,PCNA)的表达,用免疫印记法检测MMP-9的表达,并进行统计分析。结果:80%门静脉分支结扎后,结扎侧肝叶呈进行性萎缩,保留侧肝叶重量/体重比值逐渐增加,7d达“平台期”;与对照纽明显不同,PVL组的ALT、AST的值在1h达到高峰,7d后回到正常水平;保留侧肝脏组织中PCNA阳性细胞计数与对照组比较,3d开始表述增强(P〈0.05),7d以后逐渐恢复至正常水平(P〉0.05);保留侧肝叶MMP-9蛋白的表达在术后3d开始增加,术后7d达到高峰。结论:MMP-9蛋白的表达在80%门静脉结扎后大鼠肝再生过程中发挥重要作用。 相似文献
49.
50.
Transforming growth factor β (TGF-β) is a very strong pro-fibrotic factor which mediates its action, at least in part, through the expression of connective tissue growth factor (CTGF/CCN2). Along with these cytokines, the involvement of phospholipids in wound healing and the development of fibrosis has been revealed. Among them, lysophosphatidic acid (LPA) is a novel, potent regulator of wound healing and fibrosis that has diverse effects on many types of cells. We decided to evaluate the effect of LPA together with TGF-β on CTGF expression. We found that myoblasts treated with LPA and TGF-β1 produced an additive effect on CTGF expression. In the absence of TGF-β, the induction of CTGF expression by LPA was abolished by a dominant negative form of the TGF-β receptor type II (TGF-βRII) and by the use of SB 431542, a specific inhibitor of the serine/threonine kinase activity of TGF-βRI, suggesting that CTGF induction is dependent on LPA and requires active TGF-βRs. Moreover, we show that LPA requires Smad-2/3 proteins for the induction of CTGF expression, but not their phosphorylation or their nuclear translocation. The requirement of TGF-βRI for LPA mediated-effects is differential, since treatment of myoblasts with LPA in the presence of SB 431542 abolished the induction of stress fibers but not the induction of proliferation. Finally, we demonstrated that CTGF induction in response to LPA requires the activation of JNK, but not ERK, signaling pathways. The JNK requirement is independent of TGF-βRI-mediated activity. These novel results for the mechanism of action of LPA and TGF-β are important for understanding the role of pro-fibrotic growth factors and phospholipids involved in wound healing and related diseases. 相似文献