全文获取类型
收费全文 | 2748篇 |
免费 | 71篇 |
国内免费 | 5篇 |
专业分类
电工技术 | 24篇 |
综合类 | 3篇 |
化学工业 | 720篇 |
金属工艺 | 38篇 |
机械仪表 | 40篇 |
建筑科学 | 178篇 |
矿业工程 | 62篇 |
能源动力 | 62篇 |
轻工业 | 245篇 |
水利工程 | 55篇 |
石油天然气 | 1篇 |
无线电 | 203篇 |
一般工业技术 | 347篇 |
冶金工业 | 380篇 |
原子能技术 | 18篇 |
自动化技术 | 448篇 |
出版年
2021年 | 24篇 |
2018年 | 26篇 |
2017年 | 27篇 |
2016年 | 60篇 |
2015年 | 54篇 |
2014年 | 80篇 |
2013年 | 104篇 |
2012年 | 142篇 |
2011年 | 130篇 |
2010年 | 81篇 |
2009年 | 89篇 |
2008年 | 109篇 |
2007年 | 101篇 |
2006年 | 143篇 |
2005年 | 66篇 |
2004年 | 52篇 |
2003年 | 59篇 |
2002年 | 57篇 |
2001年 | 40篇 |
2000年 | 47篇 |
1999年 | 51篇 |
1998年 | 79篇 |
1997年 | 60篇 |
1996年 | 49篇 |
1995年 | 32篇 |
1994年 | 50篇 |
1993年 | 54篇 |
1992年 | 33篇 |
1991年 | 44篇 |
1990年 | 42篇 |
1989年 | 36篇 |
1988年 | 34篇 |
1987年 | 31篇 |
1986年 | 33篇 |
1985年 | 42篇 |
1984年 | 47篇 |
1983年 | 34篇 |
1982年 | 36篇 |
1981年 | 47篇 |
1980年 | 35篇 |
1979年 | 47篇 |
1978年 | 37篇 |
1977年 | 35篇 |
1976年 | 41篇 |
1975年 | 34篇 |
1974年 | 34篇 |
1973年 | 26篇 |
1972年 | 29篇 |
1971年 | 23篇 |
1970年 | 28篇 |
排序方式: 共有2824条查询结果,搜索用时 31 毫秒
51.
Conventional gasification processes use coal not only as feedstock to be gasified but also for supply of energy for reaction heat, steam production, and other purposes. With a nuclear high temperature reactor (HTR) as a source for process heat, it is possible to transform the whole of the coal feed into gas. This concept offers advantages over existing gasification processes: saving of coal, as more gas can be produced from coal; less emission of pollutants, as the HTR is used for the production of steam and electricity instead of a coal-fired boiler; and a lower production cost for the gas. However, the process has the disadvantage that the temperature is limited to the outlet temperature (950 °C max) of the helium cooling gas of the HTR. Therefore the possibility of catalytic steam gasification was examined. Model calculations based on experimental results show that use of 3–4 wt% relative to coal of K2CO3 catalyst increases the throughput of a large scale nuclear gasification plant by ≈65%, while gas production costs decrease by ≈15%. Corrosion by catalysts is not significant at low concentration (< 5 wt%) and low temperature (< 900 °C). 相似文献
52.
53.
Stefan Luidold Helmut Antrekowitsch Robert Ressel 《International Journal of Refractory Metals and Hard Materials》2007,25(5-6):423-432
In the last years, a variety of processes respectively process steps have been investigated for the production of niobium powder. This is due to the fact that niobium capacitors could be a viable alternative to tantalum capacitors from a performance, availability, and price point of view. The reduction of niobium pentoxide by magnesium results in fine powders with high specific surface area but has the disadvantages of a very exothermic nature and the formation of magnesium niobate. It is shown in this work that the application of a continuously operating cyclone reactor and the use of niobium(IV) oxide as raw material solve these problems. A good control of the highly exothermic reaction within the cyclone reactor was achieved in the cyclone reactor by the ratio between gas flow rate and powder flow rate as well as by a proper preheating of the gas. 相似文献
54.
Object-oriented design is an approach to systems development that proposes the use of system objects to build new systems and rebuild old ones. An important goal of object-oriented development is to change the nature of traditional software development from designing and writing models from scratch to building systems through the assembly of reusable software objects. This article discusses the productivity potential as well as the limitations of object-oriented systems development and makes recommendations for its use. 相似文献
55.
Timo Baur Rebecca Breu Tibor Kálmán Tobias Lindinger Anne Milbert Gevorg Poghosyan Helmut Reiser Mathilde Romberg 《Journal of Grid Computing》2009,7(3):319-333
In many Grid infrastructures different kinds of information services are in use, which utilize different incompatible data structures and interfaces to encode and provide their data. Homogeneous monitoring of these infrastructures with the monitoring data being accessible everywhere independently of the middleware which provided it, is the basis for a consistent status reporting on the Grids’ resources and services. Thus, interoperability or interoperation between the different information services in a heterogeneous Grid infrastructure is required. Monitoring data must contain the identity of the affected Virtual Organization (VO) so that it can be related to the resources and services the VO has allocated to enable VO-specific information provision. This paper describes a distributed architecture for an interoperable information service, which combines data unification and categorization with policies for VO membership, VO resource management and data transformations. This service builds the basis for an integrated and interoperating monitoring of Grids, which provide their data to more than one VO and utilize heterogeneous information services. 相似文献
56.
Helmut Reimer 《Datenschutz und Datensicherheit - DuD》2009,33(8):509-516
DuD Report
DuD Report 相似文献57.
Christoph Riedl Tilo Böhmann Michael Rosemann Helmut Krcmar 《Information Systems and E-Business Management》2009,7(2):199-221
Service-oriented architectures and Web services mature and have become more widely accepted and used by industry. This growing
adoption increased the demands for new ways of using Web service technology. Users start re-combining and mediating other
providers’ services in ways that have not been anticipated by their original provider. Within organisations and cross-organisational
communities, discoverable services are organised in repositories providing convenient access to adaptable end-to-end business
processes. This idea is captured in the term Service Ecosystem. This paper addresses the question of how quality management
can be performed in such service ecosystems. Service quality management is a key challenge when services are composed of a
dynamic set of heterogeneous sub-services from different service providers. This paper contributes to this important area
by developing a reference model of quality management in service ecosystems. We illustrate the application of the reference
model in an exploratory case study. With this case study, we show how the reference model helps to derive requirements for
the implementation and support of quality management in an exemplary service ecosystem in public administration. 相似文献
58.
Structure and Magnetic Property Control of Copper Hydroxide Acetate by Non‐Classical Crystallization
下载免费PDF全文
![点击此处可从《Small (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
RuiQi Song Theodora Krasia‐Christoforou Christian Debus Helmut Cölfen 《Small (Weinheim an der Bergstrasse, Germany)》2017,13(9)
Copper hydroxide acetate (CHA), one layered hydroxide compound with tunable magnetism, attracts great interest because of its potential applications in memory devices. However, ferromagnetism for CHA is only demonstrated by means of GPa pressure. Herein, a new method is reported, involving the combination of different crystallization pathways to control crystallization of amorphous CHA toward the formation of CHA/polymer composites with tunable magnetic properties and even a tunability that can be tested at room temperature. By using poly[(ethylene glycol)6 methyl ether methacrylate]‐block‐poly[2‐(acetoacetoxy) ethyl methacrylate] (PEGMA‐b‐PAEMA) diblock copolymers as additives in combination with a post‐treatment process by ultracentrifugation, it is demonstrated that CHA and PEGMA‐b‐PAEMA form composites exhibiting different magnetic properties, depending on CHA in‐plane nanostructures. Analytical characterization reveals that crystallization of CHA is induced by ultracentrifugation, during which CHA nanostructures can be well controlled by changing the degrees of polymerization of the PEGMA and PAEMA blocks and their block length ratios. These findings not only present the first example of using crystallization from polymer stabilized amorphous precursors toward the generation of magnetic nanomaterials with tunable magnetism but also pave the way for the future design of functional composite materials. 相似文献
59.
Z Dong Y Patel P Saikumar JM Weinberg MA Venkatachalam 《Canadian Metallurgical Quarterly》1998,78(6):657-668
Studies during the past decade have led to the recognition of a fundamental, widely expressed mechanism of structural damage in energy-deprived cells, which is suppressed by physiologic levels of glycine and is independent of Ca2+ availability or alterations of cytosolic free Ca2+. To gain insight into this process, Madin-Darby canine kidney (MDCK) cells were depleted of adenosine triphosphate (ATP) by a mitochondrial uncoupler in glucose-free medium, and intracellular free Ca2+ was clamped at 100 nM to avoid calcium cytotoxicity. Although the ATP-depleted cells swelled and blebbed and their plasma membranes appeared to be under tension, they nevertheless became permeable to macromolecules. The plasma membranes of these cells retained structural continuity, as determined by morphologic observations, and confocal microscopy of a plasma membrane protein label (Biotin: Ultra Avidin-Texas Red) and a lipid label (NBD-sphingomyelin). Using fluoresceinated dextrans of graded molecular size, membrane permselectivity was examined noninvasively by confocal microscopy. Measured as inside/outside ratios of fluorescence intensity, the permeability indices showed progressively greater restriction to diffusion of increasingly larger dextran molecules across plasma membranes, with sharp break-points between 70,000 and 145,000 daltons (d). The results indicated that the membranes behaved as if they were perforated by water-filled channels or "pores," with size-exclusion limits of molecular dimensions. The membrane defects evolved from small pores permeable only to propidium iodide (668 d) and the smallest dextran (4,000 d), before enlarging with time to become permeable to larger dextrans. Inclusion of glycine during ATP depletion did not affect cell swelling or blebbing but completely prevented the development of permeability defects. Treatment of cells before ATP depletion with a membrane-impermeant homobifunctional "nearest neighbor" cross-linking agent, 3,3' dithiobis(sulfosuccinimidylpropionate), suppressed the development of permeability defects, even in the absence of glycine. These observations suggest that the cellular abnormality that is suppressed by glycine involves rearrangement of plasma membrane proteins to form water-filled pores large enough to leak macromolecules. 相似文献
60.
Reasoning about change is a central issue in research on human and robot planning. We study an approach to reasoning about action and change in a dynamic logic setting and provide a solution to problems which are related to the Frame problem. Unlike most work on the frame problem the logic described in this paper is monotonic. It (implicitly) allows for the occurrence of actions of multiple agents by introducing non-stationary notions of waiting and test. The need to state a large number of frame axioms is alleviated by introducing a concept of chronological preservation to dynamic logic. As a side effect, this concept permits the encoding of temporal properties in a natural way. We compare the relative merits of our approach and non-monotonic approaches as regards different aspects of the frame problem. Technically, we show that the resulting extended systems of propositional dynamic logic preserve (weak) completeness, finite model property and decidability. 相似文献