全文获取类型
收费全文 | 2246篇 |
免费 | 156篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 15篇 |
综合类 | 14篇 |
化学工业 | 663篇 |
金属工艺 | 30篇 |
机械仪表 | 32篇 |
建筑科学 | 116篇 |
矿业工程 | 18篇 |
能源动力 | 44篇 |
轻工业 | 516篇 |
水利工程 | 26篇 |
石油天然气 | 8篇 |
武器工业 | 1篇 |
无线电 | 110篇 |
一般工业技术 | 351篇 |
冶金工业 | 192篇 |
原子能技术 | 2篇 |
自动化技术 | 266篇 |
出版年
2023年 | 32篇 |
2022年 | 104篇 |
2021年 | 144篇 |
2020年 | 43篇 |
2019年 | 54篇 |
2018年 | 60篇 |
2017年 | 68篇 |
2016年 | 88篇 |
2015年 | 77篇 |
2014年 | 100篇 |
2013年 | 165篇 |
2012年 | 144篇 |
2011年 | 175篇 |
2010年 | 125篇 |
2009年 | 119篇 |
2008年 | 116篇 |
2007年 | 99篇 |
2006年 | 81篇 |
2005年 | 78篇 |
2004年 | 69篇 |
2003年 | 65篇 |
2002年 | 56篇 |
2001年 | 25篇 |
2000年 | 27篇 |
1999年 | 28篇 |
1998年 | 20篇 |
1997年 | 16篇 |
1996年 | 19篇 |
1995年 | 25篇 |
1994年 | 15篇 |
1993年 | 13篇 |
1992年 | 8篇 |
1991年 | 8篇 |
1990年 | 9篇 |
1989年 | 13篇 |
1988年 | 13篇 |
1987年 | 6篇 |
1986年 | 7篇 |
1985年 | 5篇 |
1983年 | 7篇 |
1982年 | 12篇 |
1980年 | 4篇 |
1979年 | 5篇 |
1978年 | 4篇 |
1969年 | 3篇 |
1968年 | 3篇 |
1967年 | 3篇 |
1942年 | 3篇 |
1941年 | 3篇 |
1940年 | 3篇 |
排序方式: 共有2404条查询结果,搜索用时 15 毫秒
31.
Poly(p-tert-butoxycarbonyloxystyrene): a convenient precursor to p-hydroxystyrene resins 总被引:1,自引:0,他引:1
An efficient synthetic route to pure, high molecular weight poly(p-hydroxystyrene) is reported. The route involves synthesis of a new monomer, p-tert-butoxycarbonyloxystyrene, polymerization by radical initiation or by cationic initiation in liquid SO2, followed by thermolysis or acidolysis of the tert-butoxycarbonyl protecting group. Porous, crosslinked resin beads containing the nucleophilic, phenol pendant group have been prepared in a similar fashion from the precursor terpolymer of p-tert-butoxycarbonyloxystyrene, styrene and divinylbenzene. The utility of this resin for solid-phase synthesis has been demonstrated. 相似文献
32.
Conium maculatum, a Eurasian weed naturalized in North America, contains high concentrations of piperidine alkaloids that act as chemical defenses against herbivores. C. maculatum was largely free from herbivory in the United States, until approximately 30 yr ago, when it was reassociated via accidental introduction with a monophagous European herbivore, the oecophorid caterpillar Agonopterix alstroemeriana. At present, A. alstroemeriana is found in a continuum of reassociation time and intensities with C. maculatum across the continent; in the Pacific Northwest, A. alstroemeriana can cause severe damage, resulting in some cases in complete defoliation. Studies in biological control and invasion biology have yet to determine whether plants reassociated with a significant herbivore from the area of indigeneity increase their chemical defense investment in areas of introduction. In this study, we compared three locations in the United States (New York, Washington, and Illinois) where C. maculatum experiences different levels of herbivory by A. alstroemeriana to determine the association between the intensity of the interaction, as measured by damage, and chemical defense production. Total alkaloid production in C. maculatum was positively correlated with A. alstroemeriana herbivory levels: plants from New York and Washington, with higher herbivory levels, invested two and four times more N to alkaloid synthesis than did plants from Illinois. Individual plants with lower concentrations of alkaloids from a single location in Illinois experienced more damage by A. alstroemeriana, indicative of a preference on the part of the insect for plants with less chemical defense. These results suggest that A. alstroemeriana may act either as a selective agent or inducing agent for C. maculatum and increase its toxicity in its introduced range. 相似文献
33.
Natural rubber vulcanizates of two formulations, with sulfur/N-cyclohexyl-2-benzothiazolesulfenamide (CBS) and tetramethylthiuram disulfide (TMTD), respectively, were analyzed by pyrolysis gas chromatography. A sulfur-selective flame-photometric detector was utilized. The main pyrolysis products were identified as CS2 and some thiophenes. The yields of the pyrolysis products from the two types of rubber were very different. The yields also varied with the curing time of the rubbers. 相似文献
34.
Beatriz Miranda Eva Díaz Salvador Ordez Fernando V. Díez 《Catalysis communications》2006,7(12):945-949
The performance of 0.5% Ru/Al2O3 for the deep oxidation of trichloroethene (1000–2500 ppmV, WHSV = 55 h−1) in air was studied in this work. Experiments were carried out both at dry and wet (20,000 ppmV of H2O) conditions. Catalytic performance was studied in terms of activity and selectivity for the different reaction products (CO2, HCl, Cl2, C2Cl4, CCl4 and CHCl3). Both the activity and the selectivity for total combustion are higher than other catalysts suggested in the literature for this process (especially Pd and Pt).The main organic by-products are CCl4 and CHCl3, whereas in all the other catalysts tested in the literature, tetrachloroethene is the main organic by-product. This fact suggests that the mechanism of the combustion reaction, involving a double-bond scission, is essentially specific for this catalyst.Kinetic data was fit to a pseudo-first order kinetic expression, providing fairly good fit. 相似文献
35.
36.
Sufficient conditions for stability and stabilization of networked control systems with uncertainties and nonlinearities 下载免费PDF全文
In this paper, we consider the problem of robust stability and stabilization for networked control systems (NCS) with uncertain/nonlinear dynamics AUTHOR: Please check that authors and their affiliations are correct. in which the network‐induced delays are time‐varying and bounded. Based on some recent achievements, a relatively simple Lyapunov–Krasovskii functional is proposed to derive sufficient conditions both for analysis and synthesis of NCS in the form of LMIs depending on the delay bounds. The effectiveness of the proposed method is illustrated by several benchmark examples available in the literature. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
37.
38.
Most of the literature on innovation management highlights the fundamental role played by people in the innovation process and the need to fully develop the creative and innovative potential of organizations' members. This article offers the result of extensive research carried out among some of the most innovative companies in the Basque Country, a highly innovative region located in the north of Spain. It draws interesting conclusions about how these innovative companies combine strong leadership, human resource practices, and an organizational culture that enhances innovation capabilities among the company's employees. More specifically, it answers questions such as the following: Are human resources policies, leadership, and innovation culture implemented equally in Basque innovative companies? Do companies make the same effort in deploying these elements or routines and practices related to them? Can we see a pattern in the use of these elements among innovative firms? © 2012 Wiley Periodicals, Inc. 相似文献
39.
In this work, a review and comprehensive evaluation of heuristics and metaheuristics for the m-machine flowshop scheduling problem with the objective of minimising total tardiness is presented. Published reviews about this objective usually deal with a single machine or parallel machines and no recent methods are compared. Moreover, the existing reviews do not use the same benchmark of instances and the results are difficult to reproduce and generalise. We have implemented a total of 40 different heuristics and metaheuristics and we have analysed their performance under the same benchmark of instances in order to make a global and fair comparison. In this comparison, we study from the classical priority rules to the most recent tabu search, simulated annealing and genetic algorithms. In the evaluations we use the experimental design approach and careful statistical analyses to validate the effectiveness of the different methods tested. The results allow us to clearly identify the state-of-the-art methods. 相似文献
40.