全文获取类型
收费全文 | 5537篇 |
免费 | 229篇 |
国内免费 | 7篇 |
专业分类
电工技术 | 139篇 |
综合类 | 13篇 |
化学工业 | 1425篇 |
金属工艺 | 117篇 |
机械仪表 | 104篇 |
建筑科学 | 431篇 |
矿业工程 | 10篇 |
能源动力 | 122篇 |
轻工业 | 751篇 |
水利工程 | 36篇 |
石油天然气 | 13篇 |
无线电 | 287篇 |
一般工业技术 | 919篇 |
冶金工业 | 637篇 |
原子能技术 | 58篇 |
自动化技术 | 711篇 |
出版年
2022年 | 44篇 |
2021年 | 69篇 |
2020年 | 55篇 |
2019年 | 58篇 |
2018年 | 66篇 |
2017年 | 85篇 |
2016年 | 114篇 |
2015年 | 137篇 |
2014年 | 149篇 |
2013年 | 249篇 |
2012年 | 227篇 |
2011年 | 242篇 |
2010年 | 208篇 |
2009年 | 224篇 |
2008年 | 217篇 |
2007年 | 250篇 |
2006年 | 202篇 |
2005年 | 203篇 |
2004年 | 183篇 |
2003年 | 125篇 |
2002年 | 135篇 |
2001年 | 111篇 |
2000年 | 99篇 |
1999年 | 77篇 |
1998年 | 87篇 |
1997年 | 85篇 |
1996年 | 82篇 |
1995年 | 75篇 |
1994年 | 55篇 |
1993年 | 78篇 |
1992年 | 80篇 |
1991年 | 53篇 |
1990年 | 62篇 |
1989年 | 61篇 |
1987年 | 71篇 |
1986年 | 58篇 |
1985年 | 72篇 |
1984年 | 65篇 |
1983年 | 61篇 |
1982年 | 63篇 |
1981年 | 68篇 |
1980年 | 67篇 |
1979年 | 68篇 |
1978年 | 51篇 |
1977年 | 54篇 |
1976年 | 57篇 |
1975年 | 56篇 |
1974年 | 67篇 |
1973年 | 49篇 |
1970年 | 41篇 |
排序方式: 共有5773条查询结果,搜索用时 31 毫秒
61.
Abstract. This paper analyzes the presence and consequences of a unit root in periodic autoregressive models for univariate quarterly time series. First, we consider various representations of such models, including a new parametrization which facilitates imposing a unit root restriction. Next, we propose a class of likelihood ratio tests for a unit root, and we derive their asymptotic null distributions. Likelihood ratio tests for periodic parameter variation are also proposed. Finally, we analyze the impact on unit root inference of misspecifying a periodic process by a constant-parameter model. 相似文献
62.
Stan De Spiegelaere Guy Van Gyes Hans De Witte Wendy Niesen Geert Van Hootegem 《Creativity & Innovation Management》2014,23(3):318-330
European policy is focusing on innovation as a way out of the economic crisis. At the same time, job insecurity is rising as Europe is still in crisis. In this paper, we examine whether job insecurity affects the innovative work behaviour of employees by focusing on the relation between job insecurity, job autonomy, work engagement and innovative work behaviour (IWB). Using employee level survey data, we use structural equation modelling to disentangle the relations between these variables. The partially mediated model shows the best fit with the data. This model shows that job insecurity and autonomy are both directly and indirectly, through work engagement, related with IWB. For autonomy these relations are positive, while they are negative (and smaller) for job insecurity. Moreover, a negative covariance is observed between job insecurity and autonomy. 相似文献
63.
Alfthan Kaija; Takkinen Kristiina; Sizmann Dorothea; Soderlund Hans; Teeri Tuula T. 《Protein engineering, design & selection : PEDS》1995,8(7):725-731
Single-chain antibodies were constructed using six differentlinker peptides to join the VH and VL domains of an anti-2-phenyloxazolone(Ox) antibody. Four of the linker peptides originated from theinterdomain linker region of the fungal cellulase CBHI and consistedof 28, 11, six and two amino acid residues. The two other linkerpeptides used were the (GGGGS)3 linker with 15 amino acid residuesand a modified IgG2b hinge peptide with 22 residues. Proteolyticstability and Ox binding properties of the six different scFvderivatives produced in Escherichia coli were investigated andcompared with those of the corresponding Fv fragment containingno joining peptide between the V domains. The hapten bindingproperties of different antibody fragments were studied by ELISAand BIAcoreTM. The interdomain linker peptide improved the haptenbinding properties of the antibody fragment when compared withFv fragment, but slightly increased its susceptibility to proteases.Single-chain antibodies with short CBHI linkers of 11, six andtwo residues had a tendency to form multimers which led to ahigher apparent affinity. The fragments with linkers longerthan 11 residues remained monomeric. 相似文献
64.
Induction of systemic resistance to feeding of beet armyworm, Spodoptera exigua, was investigated in two isogenic lines of Stoneville 213 cotton, Gossypium hirsutum, that differed in the presence of pigment glands. In laboratory bioassays, larvae strongly preferred to feed on glandless cotton plants when presented a choice between undamaged terminal leaves of undamaged glanded and glandless plants. Feeding damage inflicted by S. exigua larvae on the two oldest leaves of glanded plants seven days prior to feeding bioassays caused larvae to prefer by 33-fold the undamaged terminal foliage from undamaged plants compared to that from damaged plants. Feeding damage on glandless plants caused only a 2.6-fold greater preference for terminal foliage from undamaged plants over foliage from previously damaged plants. Extracts of terminal foliage from glanded cotton damaged seven days earlier had significantly greater quantities of terpenoid aldehydes (hemigossypolone, gossypol, and heliocides) than did foliage from undamaged glanded plants. Terpenoid aldehydes were undetectable in extracts of both undamaged and previously damaged glandless plants. The profile of volatile compounds collected from the headspace of mechanically damaged terminal leaves of undamaged glanded and glandless plants differed. Both cotton isolines released large quantities of lipoxygenase products (hexenyl alcohols, acetates, and butyrates), but glandless plants released only small amounts of mono- and sesquiterpenes compared to glanded plants. Glandless plants damaged seven days prior to volatile collection released significantly greater quantities of lipoxygenase products, -ocimene, and - and -farnesene than did undamaged glandless plants. Previously damaged glanded plants released significantly greater quantities of all mono- and sesquiterpenes and hexenyl acetates and butyrates, but not alcohols. The relative importance of volatile compounds versus terpenoid aldehydes in induced feeding deterrence in cotton to S. exigua larvae is still unclear. 相似文献
65.
Hans J. Liebe George A. Hufford Takeshi Manabe 《Journal of Infrared, Millimeter and Terahertz Waves》1991,12(7):659-675
Experimental permittivity data of liquid water, compiled from the open literature, were selectively applied to support a modeling strategy. Frequencies up to 1 THz and atmospheric temperatures are covered with an expression made up by two relaxation (Debye) terms. The double-Debye model reduces to one term when the high frequency limit is set at 100 GHz, and the model can be extended to 30 THz by adding two resonance (Lorentzian) terms. The scheme was carried out by employing nonlinear least-squares fitting routines to data we considered reliable. 相似文献
66.
In this study, the underlying mechanism for improved spinnability when mixing lignin and cellulose in solution was investigated. Co-processing of lignin and cellulose has previously been identified as a potential route for production of inexpensive and bio-based carbon fibers. The molecular order of cellulose contributes to the strength of the fibers and the high carbon content of lignin improves the yield during conversion to carbon fibers. The current work presents an additional benefit of combining lignin and cellulose; solutions that contain both lignin and cellulose could be air-gap spun at substantially higher draw ratios than pure cellulose solutions, that is, lignin improved the spinnability. Fibers were spun from solutions containing different ratios of lignin, from 0 to 70 wt%, and the critical draw ratio was determined at various temperatures of solution. The observations were followed by characterization of the solutions with shear and elongational viscosity and surface tension, but none of these methods could explain the beneficial effect of lignin on the spinnability. However, by measuring the take-up force it was found that lignin seems to stabilize against diameter fluctuations during spinning, and plausible explanations are discussed. 相似文献
67.
Đurović Gordana Van Neerbos Francine A. C. Bossaert Sofie Herrera-Malaver Beatriz Steensels Jan Arnó Judit Wäckers Felix Sobhy Islam S. Verstrepen Kevin J. Jacquemyn Hans Lievens Bart 《Journal of chemical ecology》2021,47(8-9):788-798
Journal of Chemical Ecology - There is increasing evidence that microorganisms, particularly fungi and bacteria, emit volatile compounds that mediate the foraging behaviour of insects and therefore... 相似文献
68.
69.
70.
Johan M. M. van Rooij Marcel E. van Kooten Niekerk Hans L. Bodlaender 《Theory of Computing Systems》2013,52(4):687-718
We consider the Partition Into Triangles problem on bounded degree graphs. We show that this problem is polynomial-time solvable on graphs of maximum degree three by giving a linear-time algorithm. We also show that this problem becomes $\mathcal{NP}$ -complete on graphs of maximum degree four. Moreover, we show that there is no subexponential-time algorithm for this problem on graphs of maximum degree four unless the Exponential-Time Hypothesis fails. However, the Partition Into Triangles problem on graphs of maximum degree at most four is in many cases practically solvable as we give an algorithm for this problem that runs in $\mathcal{O}(1.02220^{n})$ time and linear space. 相似文献