全文获取类型
收费全文 | 1001篇 |
免费 | 54篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 12篇 |
综合类 | 8篇 |
化学工业 | 223篇 |
金属工艺 | 22篇 |
机械仪表 | 13篇 |
建筑科学 | 67篇 |
能源动力 | 56篇 |
轻工业 | 80篇 |
水利工程 | 8篇 |
石油天然气 | 4篇 |
无线电 | 67篇 |
一般工业技术 | 212篇 |
冶金工业 | 86篇 |
原子能技术 | 4篇 |
自动化技术 | 196篇 |
出版年
2023年 | 17篇 |
2022年 | 9篇 |
2021年 | 23篇 |
2020年 | 18篇 |
2019年 | 35篇 |
2018年 | 32篇 |
2017年 | 17篇 |
2016年 | 23篇 |
2015年 | 38篇 |
2014年 | 30篇 |
2013年 | 62篇 |
2012年 | 69篇 |
2011年 | 77篇 |
2010年 | 49篇 |
2009年 | 58篇 |
2008年 | 67篇 |
2007年 | 40篇 |
2006年 | 51篇 |
2005年 | 30篇 |
2004年 | 34篇 |
2003年 | 20篇 |
2002年 | 26篇 |
2001年 | 26篇 |
2000年 | 13篇 |
1999年 | 11篇 |
1998年 | 23篇 |
1997年 | 14篇 |
1996年 | 11篇 |
1995年 | 10篇 |
1994年 | 16篇 |
1993年 | 8篇 |
1992年 | 5篇 |
1991年 | 4篇 |
1990年 | 3篇 |
1989年 | 6篇 |
1987年 | 3篇 |
1986年 | 7篇 |
1985年 | 5篇 |
1984年 | 5篇 |
1982年 | 4篇 |
1981年 | 4篇 |
1980年 | 3篇 |
1979年 | 3篇 |
1978年 | 8篇 |
1977年 | 7篇 |
1976年 | 4篇 |
1975年 | 7篇 |
1974年 | 5篇 |
1973年 | 3篇 |
1969年 | 2篇 |
排序方式: 共有1058条查询结果,搜索用时 15 毫秒
11.
In the last decade there was growing interest in strategic management literature about factors that influence a company's ability to use IT. There is general consensus that knowledge and competency are necessary in developing an IT capability, but there is very little understanding of what the necessary competencies are, and how they influence IS usage in different contexts. The small and medium-sized enterprise context is particularly interesting for two reasons: it constitutes a major part of the economy and it has been relatively unsuccessful in exploiting e-business. 相似文献
12.
Previous studies indicate a suppressive influence of fish oils on rodent malaria. The present work was carried out to study
(i) the dose-effect relation between dietary fish oils and lethality of primary malaria infection in mice; (iii) the modifying
influence of vitamin E; and (iii) the effect of previous fish oil feeding on parasitemia and lethality of a rechallenge infection.
For two or four weeks, groups of weanling male mice were fed a standard laboratory diet or one of eight purified diets containing
various amounts of fish oil (providing 6–21% of energy). The diets were prepared with and without vitamin E. After the two-or
four-week feeding period, the mice were injected intraperitoneally withPlasmodium yoelii yoelii-infected erythrocytes. Six months after the primary infection (four months after discontinuing fish oil feeding), the surviving
mice were again injected intraperitoneally with parasitized red blood cells (or even better—erythrocytes, erythrocytes are
used elsewhere). Primary malaria infection was lethal in mice fed standard diet alone or with fish oil and vitamin E added.
In contrast, feeding a fish oil-based diet without vitamin E improved survival to at least 70% if the mice had been fed these
diets for four weeks. Protection against malaria did not seem to be related to the fish oil dose used. Regardless of the previous
fish oil dose, all the mice surviving the primary infection survived the rechallenge infection with low parasitaemias. The
results suggest that the prooxidant nature of highly unsaturated fatty acids in fish oils may beneficially influence malaria
infection, and may also increase the resistance against reinfection for some time after discontinuing fish oil intake. 相似文献
13.
Pt/Al2O3 catalysts with platinum contents of 0.1, 1.0 and 3.0 wt% were used for the low temperature combustion of methanol in the absence and the respective presence of a trace amount of ammonia. It is observed that ammonia inhibits the combustion of methanol, which is due to competition between methanol and ammonia for the same sites. For a fixed space velocity and without ammonia in the gas, the performances of the catalysts increase up to a Pt loading of 1.0 wt%. In the presence of ammonia, however, no upper limit of performance is observed with increased Pt content. The results are discussed in terms of both Pt–support interface and the Pt surface being active. 相似文献
14.
Ammoxidation of toluene over the perovskites YBa2Cu3O6.1, YBa2Cu2CoO6.7 and YBaCuCoO4.9 was investigated at 400 °C. At low partial pressures of O2 benzonitrile was selectively formed, while CO2 was the main product at high pressures of O2. Systematic differences in activity were observed for the three phases and are related to the crystal contents of Cu and Co. At low O2 pressures, Cu-sites are active for nitrile formation, while Co-sites give CO2. At high O2 pressures, the activity for CO2 of Cu-sites increases more than that of Co-sites due to filling of near-surface oxygen vacancies. 相似文献
15.
In statistical modeling, parameter estimation is an essential and challengeable task. Estimation of the parameters in the Dirichlet mixture model (DMM) is analytically intractable, due to the integral expressions of the gamma function and its corresponding derivatives. We introduce a Bayesian estimation strategy to estimate the posterior distribution of the parameters in DMM. By assuming the gamma distribution as the prior to each parameter, we approximate both the prior and the posterior distribution of the parameters with a product of several mutually independent gamma distributions. The extended factorized approximation method is applied to introduce a single lower-bound to the variational objective function and an analytically tractable estimation solution is derived. Moreover, there is only one function that is maximized during iterations and, therefore, the convergence of the proposed algorithm is theoretically guaranteed. With synthesized data, the proposed method shows the advantages over the EM-based method and the previously proposed Bayesian estimation method. With two important multimedia signal processing applications, the good performance of the proposed Bayesian estimation method is demonstrated. 相似文献
16.
Arne Ketil Eidsvik Randi Karlsen Gordon Blair Paul Grace 《Journal of Computer and System Sciences》2008,74(2):158-169
Transaction execution in mobile environments needs to be flexible, not only to support typical mobile computing characteristics, like movement, disconnections and limited resources, but also to support the variety of transactional properties that might be required by different applications. Existing models for mobile transaction management solve different aspects of transaction execution, but are not flexible enough to solve all required aspects. Instead of designing a new transaction model, we propose a middleware (MobileTSe) which utilize existing transaction models to handle various requirements for mobile transaction execution. This paper presents an approach for flexible transaction processing in mobile applications, and describes how MobileTSe makes transaction services with different properties available on mobile units. We suggest a solution with transaction service discovery and control using UPnP. 相似文献
17.
The robustness of an architecture to changes is a major concern in the design of efficient and reliable state-of-the-art embedded real-time systems. Robustness is important during design process to identify if and in how far a system can accommodate later changes or updates, or whether it can be reused in a next generation product. In the product life-cycle, robustness helps the designer to perform changes as a result of product updates, integration of new components and subsystems, or modifications of the environment. In this paper we determine robustness as a performance reserve, the slack in performance before a system fails to meet timing requirements. This is measured as design sensitivity. Due to complex component interactions, resource sharing and functional dependencies, one-dimensional sensitivity analysis might not cover all effects that modifications of one system property may have on system performance. One reason is that the variation of one property can also affect the values of other system properties requiring new approaches to keep track of simultaneous parameter changes. In this paper we present a framework for one-dimensional and multi-dimensional sensitivity analysis of real-time systems. The framework is based on compositional analysis that is scalable to large systems. The one-dimensional sensitivity analysis combines a binary search technique with a set of formal equations derived from the real-time scheduling theory. The multi-dimensional sensitivity analysis engine consists of an exact algorithm that extends the one-dimensional approach, and a stochastic algorithm based on evolutionary search techniques. 相似文献
18.
Due to the increasing deployment of conversational real-time applications like VoIP and videoconferencing, the Internet is
today facing new challenges. Low end-to-end delay is a vital QoS requirement for these applications, and the best effort Internet
architecture does not support this natively. The delay and packet loss statistics are directly coupled to the aggregated traffic
characteristics when link utilization is close to saturation. In order to investigate the behavior and quality of such applications
under heavy network load, it is therefore necessary to create genuine traffic patterns. Trace files of real compressed video and audio are text files containing the number of bytes per video and audio frame. These can serve
as material to construct mathematical traffic models. They can also serve as traffic generators in network simulators since
they determine the packet sizes and their time schedule. However, to inspect perceived quality, the compressed binary content
is needed to ensure decoding of received media. The EvalVid streaming video tool-set enables this using a sophisticated reassembly
engine. Nevertheless, there has been a lack of research solutions for rate adaptive media content. The Internet community fears a congestion collapse if the usage of non-adaptive media content continues to
grow. This paper presents a solution named Evalvid-RA for the simulation of true rate adaptive video. The solution generates
real rate adaptive MPEG-4 streaming traffic, using the quantizer scale for adjusting the sending rate. A feedback based VBR
rate controller is used at simulation time, supporting TFRC and a proprietary congestion control system named P-AQM. Example
ns-2 simulations of TFRC and P-AQM demonstrate Evalvid-RA’s capabilities in performing close-to-true rate adaptive codec operation
with low complexity to enable the simulation of large networks with many adaptive media sources on a single computer. 相似文献
19.
Kirsten Bobzin Erich Lugscheider Felix Ernst Reimo Nickel Nazlim Bagcivan Daniel Parkot Arne Schlegel Stefania Ferrara Tatyana Kashko Noémi Leick 《Microsystem Technologies》2008,14(12):1887-1894
Nowadays, micro components have to fulfill rising optical requirements for different scientific and industrial fields like
astronomy, medicine or multimedia. For this purpose, advanced miniaturized chip-cameras are produced for the microsystems
engineering market. The assembly and joining technologies play a very important role in the production of these micro components.
Several challenges are associated with the joining of chip-cameras. In this study, the application of the soldering technology
has been considered in order to face these challenges. Two joining technologies have been investigated: active soldering and
transient liquid phase (TLP) bonding. Both soldering processes have shown a big potential for hybrid microsystems joining
in previous studies. For both processes, soldering alloys and parameters have been conceived in order to fulfill the joining
requirements of the micro camera components. For instance, the joining temperature represents a major challenge because the
chip-camera consists of a plastic material, polymethyl methacrylate (PMMA). Therefore, particular attention has been directed
to the soldering as well as to the coating temperature. The experimental investigations concerning the solders application
through physical vapor deposition (PVD) have been supported by finite element method (FEM) simulations. The analysis of the
temperature distribution in the micro components during the coating process was the focus of the calculations. Possible undesirable
local overheated areas of the chip-camera components can be detected through simulation.
相似文献
Tatyana KashkoEmail: |
20.
Dipl.-Ing. Dipl.-Wirt.?Ing. Arne Katzmarzik 《WIRTSCHAFTSINFORMATIK》2011,53(1):21-35
The market for the new provisioning type Software-as-a-Service (SaaS) has reached a significant size and still shows enormous growth rates. By varying size of SaaS products, providers can improve their market position and profits by successfully acting in the tension area of customer acquisition, pricing and costs. We first elaborate differences concerning product differentiation between classic software provisioning models and SaaS. Then, we introduce a micro-economic based decision model to maximize the return of a provider by finding an optimal granularity, i.e. by varying the size of services. This paper makes two contributions in this context: (1) it provides a conceptual foundation for product differentiation within the scope of SaaS and (2) it presents the first implementation of variable reproduction costs for web based software offers. The model is illustrated by a real world case with data from a SaaS provider. 相似文献