全文获取类型
收费全文 | 657篇 |
免费 | 23篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 11篇 |
综合类 | 6篇 |
化学工业 | 147篇 |
金属工艺 | 13篇 |
机械仪表 | 5篇 |
建筑科学 | 72篇 |
矿业工程 | 6篇 |
能源动力 | 34篇 |
轻工业 | 56篇 |
水利工程 | 8篇 |
石油天然气 | 1篇 |
无线电 | 52篇 |
一般工业技术 | 98篇 |
冶金工业 | 53篇 |
原子能技术 | 2篇 |
自动化技术 | 117篇 |
出版年
2023年 | 3篇 |
2022年 | 14篇 |
2021年 | 12篇 |
2020年 | 5篇 |
2019年 | 8篇 |
2018年 | 14篇 |
2017年 | 13篇 |
2016年 | 21篇 |
2015年 | 18篇 |
2014年 | 18篇 |
2013年 | 36篇 |
2012年 | 24篇 |
2011年 | 42篇 |
2010年 | 24篇 |
2009年 | 26篇 |
2008年 | 31篇 |
2007年 | 32篇 |
2006年 | 34篇 |
2005年 | 30篇 |
2004年 | 18篇 |
2003年 | 21篇 |
2002年 | 21篇 |
2001年 | 19篇 |
2000年 | 12篇 |
1999年 | 14篇 |
1998年 | 11篇 |
1997年 | 8篇 |
1996年 | 7篇 |
1995年 | 7篇 |
1994年 | 6篇 |
1993年 | 12篇 |
1992年 | 6篇 |
1991年 | 6篇 |
1990年 | 7篇 |
1989年 | 8篇 |
1988年 | 8篇 |
1987年 | 4篇 |
1986年 | 8篇 |
1985年 | 10篇 |
1984年 | 10篇 |
1983年 | 7篇 |
1982年 | 3篇 |
1981年 | 5篇 |
1980年 | 7篇 |
1979年 | 4篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1976年 | 3篇 |
1975年 | 4篇 |
1974年 | 4篇 |
排序方式: 共有681条查询结果,搜索用时 15 毫秒
11.
Membrane proteins: from sequence to structure 总被引:12,自引:0,他引:12
The prediction of protein structure from sequence has been along-standing goal of molecular biology. Integral membrane proteins,once abhorred by protein chemists and crystallographers becauseof their insolubility and stubborn refusal to yield good crystals,now appear to hold great promises for efficient structure predictionand engineering. This is mainly due to the constraints on permissiblestructures imposed by the lipid environment, and to the apparentuncoupling between an initial membrane targeting and insertionprocess which determines the overall topological arrangementof the transmembrane segments and a subsequent condensationof these segments into a unique folded state. Recent work suggeststhat the membrane insertion process is controlled by simplesequence elements composed of different combinations of longhydrophobic regions and flanking charged residues. In this reviewwe sketch the most unportant structural rules relating aminoacid sequence to membrane insertion to fully folded molecule,and their use for prediction and protein-engineering purposes. 相似文献
12.
Automation of deburring and cleaning of castings is desirable for many reasons. The major reasons are dangerous working conditions, difficulties in finding workers for cleaning sections, and improved profitability. A suitable robot cell capable of using different tools, such as cup grinders, disc grinders and rotary files, is the solution. This robot should be completed with sensors in order to keep the quality of the cleaned surface at an acceptable level. Although using sensors simplifies both the programming and quality control there are still other problems that need to be solved. These involve selection of machining data, e.g. feeding rate and grinding force in a force controlled operation based on parameters such as tool type, disc grinder and geometry. In order to decrease the programming time, a process model for disc grinders has been developed. This article investigates this process model and pays attention to problems such as wavy or burned surfaces and the effect of a robot's repetition accuracy in the results obtained. Many aspects treated in this article are quite general, and can be applied in other types of grinding operations. 相似文献
13.
Maktuba Mohid Julian F. Miller Simon L. Harding Gunnar Tufte Mark K. Massey Michael C. Petty 《Soft Computing - A Fusion of Foundations, Methodologies and Applications》2016,20(8):3007-3022
Evolution-in-materio uses evolutionary algorithms to exploit properties of materials to solve computational problems without requiring a detailed understanding of such properties. We show that using a purpose-built hardware platform called Mecobo, it is possible to solve computational problems by evolving voltages and signals applied to an electrode array covered with a carbon nanotube–polymer composite. We demonstrate for the first time that this methodology can be applied to function optimization and also to the tone discriminator problem (TDP). For function optimization, we evaluate the approach on a suite of optimization benchmarks and obtain results that in some cases come very close to the global optimum or are comparable with those obtained using well-known software-based evolutionary approach. We also obtain good results in comparison with prior work on the tone discriminator problem. In the case of the TDP we also investigated the relative merits of different mixtures of materials and organizations of electrode array. 相似文献
14.
John?Gunnar?CarlssonEmail author Erik?Carlsson Raghuveer?Devulapalli 《Networks and Spatial Economics》2016,16(3):893-931
We consider a geographic optimization problem in which we are given a region R, a probability density function f(?) defined on R, and a collection of n utility density functions u i (?) defined on R. Our objective is to divide R into n sub-regions R i so as to “balance” the overall utilities on the regions, which are given by the integrals \(\iint _{R_{i}}f(x)u_{i}(x)\, dA\). Using a simple complementary slackness argument, we show that (depending on what we mean precisely by “balancing” the utility functions) the boundary curves between optimal sub-regions are level curves of either the difference function u i (x) ? u j (x) or the ratio u i (x)/u j (x). This allows us to solve the problem of optimally partitioning the region efficiently by reducing it to a low-dimensional convex optimization problem. This result generalizes, and gives very short and constructive proofs of, several existing results in the literature on equitable partitioning for particular forms of f(?) and u i (?). We next give two economic applications of our results in which we show how to compute a market-clearing price vector in an aggregate demand system or a variation of the classical Fisher exchange market. Finally, we consider a dynamic problem in which the density function f(?) varies over time (simulating population migration or transport of a resource, for example) and derive a set of partial differential equations that describe the evolution of the optimal sub-regions over time. Numerical simulations for both static and dynamic problems confirm that such partitioning problems become tractable when using our methods. 相似文献
15.
Abbas Nayebi Author Vitae Hamid Sarbazi-Azad Author Vitae Gunnar Karlsson Author Vitae 《Journal of Systems and Software》2010,83(8):1310-1317
This paper investigates a class of mobile wireless sensor networks that are unconnected most of the times; we refer to them as delay-tolerant wireless sensor networks (DTWSN). These networks inherit their characteristics from both delay tolerant networks (DTN) and traditional wireless sensor networks. After introducing DTWSNs, three main problems in the design space of these networks are discussed: routing, data gathering, and neighbor discovery. A general protocol is proposed for DTWSNs based on opportunistic broadcasting in delay-tolerant networks with radio device on-off periods. Three performance measures are defined in the study: the energy for sending queries to ask for data from possible neighbors (querying energy), data transfer energy, and absorption time (delay). A simple yet accurate approximation for the data-transfer energy is proposed. An analytic model is provided to evaluate the querying energy per contact (epc). Simulation results for the data propagation delay show that the querying energy per contact measure obtained from the analytic model is proportional to the product of the querying energy and the delay. A practical rule of thumb for an optimal query interval in terms of delay and energy is derived from different parts of the study. 相似文献
16.
This study investigated the effect of moving from small offices to a landscape environment for 19 Visual Display Unit (VDU) operators at Alcatel Denmark AS. The operators reported significantly improved lighting condition and glare situation. Further, visual discomfort was also significantly reduced on a Visual Analogue Scale (VAS). There was no significant correlation between lighting condition and visual discomfort neither in the small offices nor in the office landscape. However, visual discomfort correlated significantly with glare in small offices i.e. more glare is related to more visual discomfort. This correlation disappeared after the lighting system in the office landscape had been improved. There was also a significant correlation between glare and itching of the eyes as well as blurred vision in the small offices, i.e. more glare more visual symptoms. Experience of pain was found to reduce the subjective assessment of work capacity during VDU tasks. There was a significant correlation between visual discomfort and reduced work capacity in small offices and in the office landscape. When moving from the small offices to the office landscape, there was a significant reduction in headache as well as back pain. No significant changes in pain intensity in the neck, shoulder, forearm, and wrist/hand were observed.The pain levels in different body areas were significantly correlated with subjective assessment of reduced work capacity in small offices and in the office landscape.By careful design and construction of an office landscape with regard to lighting and visual conditions, transfer from small offices may be acceptable from a visual-ergonomic point of view. 相似文献
17.
18.
Jatinder N. D. Gupta Frank Werner Gunnar Wulkenhaar 《International Transactions in Operational Research》2003,10(3):267-294
This paper considers two-machine open shop problems with secondary criteria where the primary criterion is the minimization of makespan and the secondary criterion is the minimization of the total flow time, total weighted flow time, or total weighted tardiness time. In view of the strongly NP-hard nature of these problems, two polynomially solvable special cases are given and constructive heuristic algorithms based on insertion techniques are developed. A strongly connected neighborhood structure is derived and used to develop effective iterative heuristic algorithms by incorporating iterative improvement, simulated annealing and multi-start procedures. The proposed insertion and iterative heuristic algorithms are empirically evaluated by solving problem instances with up to 80 jobs. 相似文献
19.
This paper describes support for flexibility, mobility and collaboration in engaging with, and making sense of, information. Our focus lies on the transitions people make between different, dynamic configurations of digital and physical materials, technologies, people and spaces. The technologies we describe have been developed in partnership with landscape architects over the past two years. We show that appliances and people can come together in a way that creates scope for such transitions, collaboration, and the emergence of new ways of working. 相似文献
20.
Sebastian Kummer Susanne Rinn Gunnar Seemann Nadine Bachmann Katherine Timothy Paul S. Thornton Frank Pillekamp Ertan Mayatepek Carsten Bergmann Thomas Meissner Niels Decher 《International journal of molecular sciences》2022,23(15)
The voltage-dependent L-type calcium channel isoform CaV1.2 is critically involved in many physiological processes, e.g., in cardiac action potential formation, electromechanical coupling and regulation of insulin secretion by beta cells. Gain-of-function mutations in the calcium voltage-gated channel subunit alpha 1 C (CACNA1C) gene, encoding the CaV1.2 α1-subunit, cause Timothy syndrome (TS), a multisystemic disorder that includes autism spectrum disorders and long QT (LQT) syndrome. Strikingly, TS patients frequently suffer from hypoglycemia of yet unproven origin. Using next-generation sequencing, we identified a novel heterozygous CACNA1C mutation in a patient with congenital hyperinsulinism (CHI) and associated hypoglycemic episodes. We characterized the electrophysiological phenotype of the mutated channel using voltage-clamp recordings and in silico action potential modeling experiments. The identified CaV1.2L566P mutation causes a mixed electrophysiological phenotype of gain- and loss-of-function effects. In silico action potential modeling supports that this mixed electrophysiological phenotype leads to a tissue-specific impact on beta cells compared to cardiomyocytes. Thus, CACNA1C variants may be associated with non-syndromic hyperinsulinemic hypoglycemia without long-QT syndrome, explained by very specific electrophysiological properties of the mutated channel. We discuss different biochemical characteristics and clinical impacts of hypoglycemia in the context of CACNA1C variants and show that these may be associated with significant morbidity for Timothy Syndrome patients. Our findings underline that the potential of hypoglycemia warrants careful attention in patients with CACNA1C variants, and such variants should be included in the differential diagnosis of non-syndromic congenital hyperinsulinism. 相似文献