全文获取类型
收费全文 | 2348篇 |
免费 | 90篇 |
国内免费 | 4篇 |
专业分类
电工技术 | 64篇 |
综合类 | 1篇 |
化学工业 | 454篇 |
金属工艺 | 23篇 |
机械仪表 | 67篇 |
建筑科学 | 61篇 |
能源动力 | 70篇 |
轻工业 | 120篇 |
水利工程 | 7篇 |
石油天然气 | 1篇 |
无线电 | 445篇 |
一般工业技术 | 480篇 |
冶金工业 | 272篇 |
原子能技术 | 18篇 |
自动化技术 | 359篇 |
出版年
2023年 | 10篇 |
2022年 | 30篇 |
2021年 | 46篇 |
2020年 | 30篇 |
2019年 | 25篇 |
2018年 | 37篇 |
2017年 | 45篇 |
2016年 | 54篇 |
2015年 | 48篇 |
2014年 | 65篇 |
2013年 | 162篇 |
2012年 | 110篇 |
2011年 | 128篇 |
2010年 | 113篇 |
2009年 | 142篇 |
2008年 | 128篇 |
2007年 | 131篇 |
2006年 | 78篇 |
2005年 | 75篇 |
2004年 | 75篇 |
2003年 | 59篇 |
2002年 | 58篇 |
2001年 | 45篇 |
2000年 | 43篇 |
1999年 | 54篇 |
1998年 | 103篇 |
1997年 | 93篇 |
1996年 | 53篇 |
1995年 | 43篇 |
1994年 | 39篇 |
1993年 | 38篇 |
1992年 | 28篇 |
1991年 | 29篇 |
1990年 | 38篇 |
1989年 | 25篇 |
1988年 | 34篇 |
1987年 | 22篇 |
1986年 | 16篇 |
1985年 | 20篇 |
1984年 | 9篇 |
1983年 | 12篇 |
1982年 | 3篇 |
1981年 | 9篇 |
1980年 | 3篇 |
1979年 | 6篇 |
1977年 | 4篇 |
1976年 | 6篇 |
1975年 | 6篇 |
1973年 | 2篇 |
1971年 | 2篇 |
排序方式: 共有2442条查询结果,搜索用时 15 毫秒
91.
92.
Experimental results are reported for the adsorption of propane and n-butane in a column packed with Linde 5A zeolite crystals, and methane, propan n- and iso-butane in a column packed with silicalite crystals. The adsorption equilibrium constant K and crystal diffusivity Dc, we obtained at different temperatures in the range 100–300°C, for each sorbate and packing and the heat of adsorption and diffusional activation energ were determined.The results show that in order to separate the effects of K and the pressure drop, the latter must be independently estimated by a suitable correla 相似文献
93.
ABSTRACT: The recombinant goat lactoferrin (rGLF) was expressed in the methylotropic yeast Pichia pastoris using pGAPZαC vector, GAP as promoter, and Zeocin as the selective marker. After transformation of the GLF-pGAPZαC into Pichia pastoris X-33 expression host, the GLF-pGAPZαC vector was integrated into the GAP promoter locus of Pichia pastoris X-33 chromosome. The rGLF was expressed and secreted into the broth using α-factor preprosequence. SDS-PAGE and PAS staining analysis indicated that the rGLF could be purified to electrophoretic homogeneity by heparin-Sepharose 6 Fast Flow affinity chromatography and glycosylated by the expression host. The yield of purified rGLF was approximately 2.0 mg/L of culture broth. The N-terminal sequence was identical to the native goat lactoferrin (nGLF). The iron-binding behavior, papain-inhibiting property, and thermal stability of the purified rGLF were comparable to nGLF. This is the 1st report of intact goat lactoferrin expression using the P. pastoris system. 相似文献
94.
Zu-Chian Chiang Hsing-Ya Li An-Chong Chao Yu-Ru Su 《Journal of Polymer Research》2011,18(6):2205-2212
The morphology and affinity of a scaffold influence the attachment of cells to its surfaces. In this study, the morphology
and hydrophilicity of chitosan/caffeic acid hybrid scaffolds were investigated. Grafting caffeic acid onto chitosan hybrid
scaffolds by using high levels of potassium persulfate produced scaffolds with looser morphology and higher porosity, as indicated
by scanning electron microscopy (SEM) and porosity analysis. SEM analysis showed that the prepared scaffolds had a macroporous
morphology with interconnected pores. Differential scanning calorimetry (DSC) revealed that the scaffolds’ hydrophilicity
decreased after caffeic acid grafting. The scaffolds were cultured with human osteosarcoma UMR-106 cells, but SEM analysis
showed that cell attachment was poor. However, calcification of the scaffolds promoted the attachment of UMR-106 cells onto
the scaffold. This study shows that calcified chitosan/caffeic acid hybrid scaffolds could be suitable for use in hard-tissue
engineering. 相似文献
95.
An innovative magnetically levitated system design is presented in this paper. The proof mass, used as the seismic detection
components for gyroscopes, is levitated by the presented micro-coil actuator so that the concerns that mechanical fatigue,
asymmetry and mis-alignments, which are inevitably present in the traditional mechanical springs design, can be ruled out.
In addition, the limited range of dual-axis motion of the proof mass is completely relaxed and therefore the resolution and
sensitivity of the gyroscope can be greatly upgraded. That is, the proof mass can be much at higher frequencies and the stroke
of the sense-mode motion can be more enlarged, in comparison with the conventional design (i.e., mechanical springs). In addition,
self-sensing technique is employed to replace the gap sensors which provide the feedback signal for position regulation of
the proof mass, for the sake of cost-down for mass production. A sliding mode control strategy is included to account for
the effects of nonlinearity of the maglev system dynamics and hysteresis uncertainty of the micro-coil actuator. The proposed
controller is verified by computer simulations and experiments to illustrate its superior capability to stabilize the inherently
unstable maglev system and ensure fast response for the lateral position regulation of the seismic proof mass. 相似文献
96.
We study the problem of disseminating data of time-constrained services through multiple broadcast channels. By time-constrained services, we mean those services whose data must reach clients before a certain constrained time. Otherwise, the data would become useless or substantially less valuable to the clients. We first explore the difficulties of solving the problem and derive the theoretical minimum number of channels required for the task. Then, we propose a transformation-based data allocation (TDA) algorithm that guarantees to fulfill the task (i.e., all requested data reach the clients within the constrained time) by using the minimum number of channels. Finally, we analyze the computation complexity and prove the validity and optimality of the TDA algorithm. 相似文献
97.
Feng-Yun Wang Guo-Bin Jung Ay Su Shih-Hung Chan Xiang-Ai Li Yu-Chun Chiang 《Materials Letters》2009,63(11):952-954
A new method is studied for preparing nano-ceria by acid leaching MgO from CeO2−MgO mixed powder made by calcining a gel. The MgO in the mixed powder can be leached completely with acetic acid solution at room temperature, but the CeO2 remains unaffected. The surface area (Sg) of the resulting CeO2 increases with Mg/Ce ratio, but approaches constant after the ratio is larger than a given value which is higher for the higher gel calcining temperature. When Mg/Ce is 8 (molar ratio) and the calcining temperature is 1253 K, the Sg of the resulting ceria remains 25.1 m2/g even after annealed at 1253 K for 4 h. In comparison with the conventional methods, CeO2 from the new method shows higher surface area and higher thermal stability. 相似文献
98.
Yunqi Liu Ho Wai Lee Kin Seng Chiang Tao Zhu Yun Jiang Rao 《Lightwave Technology, Journal of》2009,27(7):857-863
We investigate in detail the process of CO2-laser writing of long-period fiber gratings (LPFGs) in unannealed and annealed boron-doped fiber samples by using repeated scanning of CO2-laser pulses. We find that the writing dynamics depends strongly on the CO2-laser energy density and the annealing temperature of the fiber. Our results from analyzing the writing dynamics reveal the relative importance of various physical effects arising from glass structure changes due to different writing conditions and thus provide a better understanding of the formation and the properties of CO2-laser written LPFGs. 相似文献
99.
长期保存(LTP)是一个极具吸引力的新研究领域,其目标是使档案的持续性能保持一段可预见的足够时间。然而这项研究一开始就遭遇了诸多挑战,比如归档时框架、正规方法和工作流模型的缺失,进一步的亏损无法保持档案间的互操作性,以及无信息衰减迹象的信息丢失等。本研究旨在探究各类文件的LTP如何不受时间演变、技术、数字环境变化的影响。基本需求源于存储管理与信息管理的整合,以及数据、元数据、索引等的安全保存。
本文介绍了政府档案管理和知识管理LTP流程有关上述需求的演变发展。资源的有效搜索、数据的有效存储/访问、一致的用户界面、共置备份的恢复图、以及认证和安全管理的动态调整构成随后的任务。接着,论文详细阐述了示范语义数据网格及其注解和服务配套机制,这当中本体起到关键作用。最后,论文总结了习得经验,以及有关LTP语义网格的未来工作。 相似文献
100.
In this paper, two mutation-based evolving artificial neural networks, which are based on the Fuzzy ARTMAP (FAM) network and
evolutionary programming, are proposed. The networks utilize the knowledge base extracted from a set of data to perform search
and adaptation. The performances of the two networks are assessed using benchmark problems, with the results analyzed and
discussed. The effects of the network parameters are evaluated through a parametric study. The applicability of the networks
is also demonstrated using a real fault detection and diagnosis task in a power generation plant. The experimental results
consistently indicate the usefulness of the proposed evolutionary FAM-based networks in yielding good classification performances
with parsimonious network structures. 相似文献