全文获取类型
收费全文 | 220篇 |
免费 | 9篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 5篇 |
化学工业 | 51篇 |
金属工艺 | 4篇 |
机械仪表 | 19篇 |
建筑科学 | 6篇 |
能源动力 | 7篇 |
轻工业 | 10篇 |
水利工程 | 4篇 |
石油天然气 | 1篇 |
无线电 | 19篇 |
一般工业技术 | 44篇 |
冶金工业 | 29篇 |
原子能技术 | 3篇 |
自动化技术 | 29篇 |
出版年
2023年 | 7篇 |
2022年 | 19篇 |
2021年 | 25篇 |
2020年 | 9篇 |
2019年 | 13篇 |
2018年 | 8篇 |
2017年 | 15篇 |
2016年 | 10篇 |
2015年 | 7篇 |
2014年 | 12篇 |
2013年 | 8篇 |
2012年 | 8篇 |
2011年 | 14篇 |
2010年 | 9篇 |
2009年 | 10篇 |
2008年 | 9篇 |
2007年 | 8篇 |
2006年 | 3篇 |
2005年 | 3篇 |
2004年 | 4篇 |
2003年 | 3篇 |
2002年 | 2篇 |
2001年 | 3篇 |
2000年 | 3篇 |
1999年 | 3篇 |
1998年 | 4篇 |
1997年 | 3篇 |
1996年 | 1篇 |
1994年 | 1篇 |
1992年 | 1篇 |
1989年 | 1篇 |
1985年 | 2篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1976年 | 1篇 |
排序方式: 共有231条查询结果,搜索用时 15 毫秒
11.
Methylglyoxal synthase provides bacteria with an alternative to triosephosphate isomerase for metabolizing dihydroxyacetone phosphate (DHAP). In the present studies, the methylglyoxal synthase gene in Escherichia coli has been cloned and sequenced. The identified open reading frame (ORF) codes for a polypeptide of 152 amino acids, consistent with the 17 kDa purified protein. The sequence of this protein is not similar to any other protein of known function, including the functionally similar protein triosephosphate isomerase. The methylglyoxal synthase gene was amplified by PCR, subcloned into the pET16B expression vector, and expressed in the host E. coli BL21(DE3). Sequence comparison of the methylglyoxal protein and related ORFs from four different bacterial species revealed that four aspartic acid and no glutamic acid residues are absolutely conserved. The function of the four aspartic acid residues was tested by mutating them to either asparagine or glutamic acid. Thermal denaturation, CD spectroscopy, and gel filtration experiments showed that the mutant enzymes had the same secondary and quaternary structure as the wild-type enzyme. Kinetic characterization of both Asp 71 and Asp 101 mutant proteins shows reduced kcat/Km by 10(3)- and 10(4)-fold respectively, suggesting that they are both intimately involved in catalysis. A time-dependent inhibition of both Asp 20 and Asp 91 asparagine mutants by DHAP suggests that these two residues are involved with protecting the enzyme from DHAP or reactive intermediates along the catalytic pathway. In combination with the results of 2-phosphoglycolate binding studies, a catalytic mechanism is proposed. 相似文献
12.
In this paper, we consider two equivalent differentiable reformulations of the nondifferentiable Euclidean multifacility location problem (EMFLP). The first of these is derived via a Lagrangian dual approach based on the optimum of a linear function over a unit ball (circle). The resulting formulation turns out to be identical to the known dual problem proposed by Francis and Cabot [1]. Hence, besides providing an easy direct derivation of the dual problem, this approach lends insights into its connections with classical Lagrangian duality and related results. In particular, it characterizes a straightforward recovery of primal location decisions. The second equivalent differentiable formulation is constructed directly in the primal space. Although the individual constraints of the resulting problem are generally nonconvex, we show that their intersection represents a convex feasible region. We then establish the relationship between the Karush-Kuhn-Tucker (KKT) conditions for this problem and the necessary and sufficient optimality conditions for EMFLP. This lends insights into the possible performance of standard differentiable nonlinear programming algorithms when applied to solve this reformulated problem. Some computational results on test problems from the literature, and other randomly generated problems, are also provided. 相似文献
13.
Siddiqui Pirzada Jamal Ahmed Khan Adnan Uddin Nizam Khaliq Saima Rasheed Munawwer Nawaz Shazia Dar Ahsana Hanif Muhammad 《Food science and biotechnology》2017,26(4):1055-1062
Food Science and Biotechnology - Recently, considerable attention has been paid to drug exploration from natural sources for treating memory loss, a major manifestation of various neurodegenerative... 相似文献
14.
This paper introduces the use of conditional-value-at-risk (CVaR) as a criterion for stochastic scheduling problems. This criterion has the tendency of simultaneously reducing both the expectation and variance of a performance measure, while retaining linearity whenever the expectation can be represented by a linear expression. In this regard, it offers an added advantage over traditional nonlinear expectation-variance-based approaches. We begin by formulating a scenario-based mixed-integer program formulation for minimizing CVaR for general scheduling problems. We then demonstrate its application for the single machine total weighted tardiness problem, for which we present both a specialized l-shaped algorithm and a dynamic programming-based heuristic procedure. Our numerical experimental results reveal the benefits and effectiveness of using the CVaR criterion. Likewise, we also exhibit the use and effectiveness of minimizing CVaR in the context of the parallel machine total weighted tardiness problem. We believe that minimizing CVaR is an effective approach and holds great promise for achieving risk-averse solutions for stochastic scheduling problems that arise in diverse practical applications. 相似文献
15.
Silicon - In the present experimental work emission studies of silicon (Si) plasma produced by the fundamental (1064 nm) and second (532 nm) harmonics of a Nd: YAG laser are studied. The electron... 相似文献
16.
Leak Detection in Pipes by Frequency Response Method 总被引:4,自引:0,他引:4
Witness Mpesha Sarah L. Gassman M. Hanif Chaudhry 《Canadian Metallurgical Quarterly》2001,127(2):134-147
The frequency response method is used to determine the location and rate of leakage in open loop piping systems. A steady-oscillatory flow, produced by the periodic opening and closing of a valve, is analyzed in the frequency domain by using the transfer matrix method, and a frequency response diagram at the valve is developed. For a system with leaks, this diagram has additional resonant pressure amplitude peaks (herein referred to as the secondary pressure amplitude peaks) that are lower than the resonant pressure amplitude peaks (herein called primary amplitude peaks) for the system with no leaks. Several piping systems are successfully analyzed for all practical values of the friction factor to detect and locate individual leaks of up to 0.5% of the mean discharge. The method, requiring the measurement of pressure and discharge fluctuations at only one location, has the potential to detect leaks in real-life pipe systems conveying different types of fluids, such as water, petroleum, and so on. 相似文献
17.
18.
Multimedia Tools and Applications - Swapping a row with a row, a column with a column or row with a column are usual operations carried out to scramble the given input plain image. To introduce... 相似文献
19.
20.
Stochastic Dynamic Programming (SDP) is widely used in reservoir operation problems. Besides its advantages, a few drawbacks have leaded many studies to improve its structure. Handling the infeasible conditions and curse of dimensionality are two major challenges in this method. The main goal of this paper is proposing a new method to avoid infeasible conditions and enhance the solution efficiency with new discretization procedure. For this purpose, an optimization module is incorporated into regular SDP structure, so that, near optimal values of state variables are determined based on the available constraints. The new method (RISDP) employs reliability concept to maximize the reservoir releases to satisfy the downstream demands. Applying the proposed technique improves the reservoir operating policies compared to regular SDP policies with the same assumptions of discretization. Simulation of reservoir operation in a real case study indicates about 15% improvement in objective function value and elimination of infeasible conditions by using RISDP operating policies. 相似文献