全文获取类型
收费全文 | 938篇 |
免费 | 83篇 |
国内免费 | 78篇 |
专业分类
电工技术 | 84篇 |
技术理论 | 2篇 |
综合类 | 80篇 |
化学工业 | 114篇 |
金属工艺 | 105篇 |
机械仪表 | 94篇 |
建筑科学 | 52篇 |
矿业工程 | 15篇 |
能源动力 | 8篇 |
轻工业 | 80篇 |
水利工程 | 21篇 |
石油天然气 | 44篇 |
武器工业 | 18篇 |
无线电 | 93篇 |
一般工业技术 | 172篇 |
冶金工业 | 39篇 |
原子能技术 | 9篇 |
自动化技术 | 69篇 |
出版年
2024年 | 3篇 |
2023年 | 20篇 |
2022年 | 44篇 |
2021年 | 21篇 |
2020年 | 28篇 |
2019年 | 26篇 |
2018年 | 25篇 |
2017年 | 24篇 |
2016年 | 22篇 |
2015年 | 30篇 |
2014年 | 44篇 |
2013年 | 48篇 |
2012年 | 52篇 |
2011年 | 72篇 |
2010年 | 52篇 |
2009年 | 53篇 |
2008年 | 55篇 |
2007年 | 84篇 |
2006年 | 75篇 |
2005年 | 60篇 |
2004年 | 50篇 |
2003年 | 40篇 |
2002年 | 40篇 |
2001年 | 23篇 |
2000年 | 32篇 |
1999年 | 21篇 |
1998年 | 18篇 |
1997年 | 18篇 |
1996年 | 3篇 |
1995年 | 3篇 |
1994年 | 2篇 |
1993年 | 2篇 |
1992年 | 2篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1989年 | 2篇 |
1986年 | 1篇 |
1984年 | 1篇 |
排序方式: 共有1099条查询结果,搜索用时 15 毫秒
911.
Liliana R. Pires Daniela N. Rocha Luigi Ambrosio Ana Paula Pêgo 《Journal of the Royal Society Interface》2015,12(103)
In tissue engineering, it is well accepted that a scaffold surface has a decisive impact on cell behaviour. Here we focused on microglia—the resident immune cells of the central nervous system (CNS)—and on their response to poly(trimethylene carbonate-co-ε-caprolactone) (P(TMC-CL)) fibrous and flat surfaces obtained by electrospinning and solvent cast, respectively. This study aims to provide cues for the design of instructive surfaces that can contribute to the challenging process of CNS regeneration. Cell morphology was evidently affected by the substrate, mirroring the surface main features. Cells cultured on flat substrates presented a round shape, while cells with elongated processes were observed on the electrospun fibres. A higher concentration of the pro-inflammatory cytokine tumour necrosis factor-α was detected in culture media from microglia on fibres. Still, astrogliosis is not exacerbated when astrocytes are cultured in the presence of microglia-conditioned media obtained from cultures in contact with either substrate. Furthermore, a significant percentage of microglia was found to participate in the process of myelin phagocytosis, with the formation of multinucleated giant cells being observed only on films. Altogether, the results presented suggest that microglia in contact with the tested substrates may contribute to the regeneration process, putting forward P(TMC-CL) substrates as supporting matrices for nerve regeneration. 相似文献
912.
采用氯化钙(CaCl_2)-甲酸(FA)溶解丝素,通过调整溶剂中CaCl_2质量分数来实现蚕丝原纤水平的溶解及静电纺丝过程。结果表明,区别于已有溶解丝素至分子水平的溶解方法,CaCl_2-FA溶解体系可在常温条件下通过破坏分子间氢键作用,破坏β-折叠结构而保留蚕丝原有的原纤结构而实现蚕丝溶解。溶液中观察到原纤尺寸随CaCl_2质量分数的增加呈减小趋势,溶解丝素所需时间随CaCl_2质量分数的增加而缩短。丝素溶液中原纤结构尺寸的差异对静电纺丝素纳米纤维直径和力学性能有所影响,CaCl_2质量分数由2%增加到10%,所纺纤维直径由(336±25)nm降低到(118±14)nm,5%6%纤维的断裂应力达到(13.5±5.6)MPa。乙醇及拉伸处理可以诱导丝素由无规卷曲结构向β-折叠的转变。 相似文献
913.
914.
退火、稀土Pr对Prx(Co40Ag60)100-x颗粒膜的结构与巨磁电阻效应的影响 总被引:1,自引:0,他引:1
采用磁控溅射法制备Prx(Co40Ag60)100-x颗粒膜。X射线衍射实验结果表明:稀土元素Pr有促进薄膜中溶于Ag中的Co发生相分离的作用,并且在退火过程Ag颗粒的聚集生长具有(111)轴择优取向的颗粒膜;巨磁电阻(GMR)效应测量结果表明:当退火温度小于或等于250℃时,随着Pr含量的增加,薄膜的GMR值先升后降,其峰值出现在x=0.5~1.0处。适量的Pr元素能够增强GMR效应以及提高GMR效应对磁场的灵敏度,GMR效应以及灵敏度的最大值分别为:-14.34%和0.67×10-3(A/m)-1。 相似文献
915.
Ladiwala AR Mora-Pale M Lin JC Bale SS Fishman ZS Dordick JS Tessier PM 《Chembiochem : a European journal of chemical biology》2011,12(11):1749-1758
Substantial evidence suggests that soluble prefibrillar oligomers of the Aβ42 peptide associated with Alzheimer's disease are the most cytotoxic aggregated Aβ isoform. Limited previous work has revealed that aromatic compounds capable of remodeling Aβ oligomers into nontoxic conformers typically do so by converting them into off-pathway aggregates instead of dissociating them into monomers. Towards identifying small-molecule antagonists capable of selectively dissociating toxic Aβ oligomers into soluble peptide at substoichiometric concentrations, we have investigated the pathways used by polyphenol aglycones and their glycosides to remodel Aβ soluble oligomers. We find that eleven polyphenol aglycones of variable size and structure utilize the same remodeling pathway whereby Aβ oligomers are rapidly converted into large, off-pathway aggregates. Strikingly, we find that glycosides of these polyphenols all utilize a distinct remodeling pathway in which Aβ oligomers are rapidly dissociated into soluble, disaggregated peptide. This disaggregation activity is a synergistic combination of the aglycone and glycone moieties because combinations of polyphenols and sugars fail to disaggregate Aβ oligomers. We also find that polyphenolic glycosides and aglycones use the same opposing pathways to remodel Aβ fibrils. Importantly, both classes of polyphenols fail to remodel nontoxic Aβ oligomers (which are indistinguishable in size and morphology to Aβ soluble oligomers) or promote aggregation of freshly disaggregated Aβ peptide; thus revealing that they are specific for remodeling toxic Aβ conformers. We expect that these and related small molecules will be powerful chemical probes for investigating the conformational and cellular underpinnings of Aβ-mediated toxicity. 相似文献
916.
驱动频率对超磁致伸缩致动器的损耗和温升特性的影响 总被引:2,自引:0,他引:2
从超磁致伸缩材料的压磁效应入手,基于能量极小值条件和磁学理论,分析了磁化过程中磁弹性力对材料中磁场的影响,分析了不同驱动频率下材料的涡流损耗、磁滞损耗以及复数磁导率的频率特性,对致动器中的磁能损耗以及损耗带来的温升特性进行仿真实验.结果表明,利用涡流损耗的计算公式得到的结果与有限元仿真结果吻合较好,该公式可适用于超磁致伸缩材料在中低频下的损耗计算,而高频下复数磁导率的变化将增大材料内部磁场的滞回非线性.实验结果表明,致动器中超磁致伸缩材料轴向温度分布随驱动频率的变化而变化;实验验证了计算与仿真结果的正确性,在此基础上分析了强制水冷对致动器温升的控制,所得结论为超磁致伸缩致动器的设计提供参考. 相似文献
917.
918.
为驱动超磁致伸缩伺服阀,结合超磁致伸缩执行器驱动电源与伺服阀用伺服放大器的性能要求设计了超磁致伸缩伺服阀用伺服放大器,并建立了其电路模型,仿真分析了功率运算放大器的开环增益对其输出性能的影响.仿真结果表明,在功率运算放大器开环增益大于80 dB时,电路特性可满足设计要求.在驱动负载为额定值时,测试结果表明,样机的输出电流线性度为3%;输出电流2A时,其阶跃响应的调节时间小于0.5 ms,幅频宽可达2 kHz;在驱动频率小于1 kHz时,输出电流失真小且无相位滞后. 相似文献
919.
Yeyu Fang R. K. Dumas T. N. Anh Nguyen S. M. Mohseni S. Chung C. W. Miller Johan Åkerman 《Advanced functional materials》2013,23(15):1919-1922
A continuum of stable remanent resistance states is reported in perpendicularly magnetized pseudo spin valves with a graded anisotropy free layer. The resistance states can be systematically set by an externally applied magnetic field. The gradual reversal of the free layer with applied field and the field‐independent fixed layer leads to a range of stable and reproducible remanent resistance values, as determined by the giant magnetoresistance of the device. An analysis of first‐order reversal curves combined with magnetic force microscopy shows that the origin of the effect is the field‐dependent population of up and down domains in the free layer. 相似文献
920.
Hiroki Sakai Ken Watanabe Yuya Asanomi Yumiko Kobayashi Yoshiro Chuman Lihong Shi Takuya Masuda Thomas Wyttenbach Michael T. Bowers Kohei Uosaki Kazuyasu Sakaguchi 《Advanced functional materials》2013,23(39):4881-4887
Amyloid peptides have great potential as building blocks in the creation of functional nanowires due to their natural ability to self‐assemble into nanofibrillar structures and because they can be easily modified with various functional groups. However, significant modifications of an amyloid peptide generally alter its self‐assembly property, making it difficult to construct functionalized fibrils with a desired structure and function. In this study, a very effective method to overcome this problem is demonstrated by using our structure‐controllable amyloid peptides (SCAPs) terminated with a three‐amino‐acid‐residue cap. The method consists on mixing two or more structurally related amyloid peptides with a fraction of modified SCAPs which co‐assemble into a fibril. This SCAP‐mixing method provides remarkable control over the self‐assembly process both on the small oligomers level and the macroscopic fibrils level. Furthermore, it is shown that the modified peptides imbedded in the resulting fibril can subsequently be functionalized to generate nanowires with the desired properties, highlighting the importance of this SCAP method for nanotechnology applications. 相似文献