全文获取类型
收费全文 | 23085篇 |
免费 | 799篇 |
国内免费 | 84篇 |
专业分类
电工技术 | 295篇 |
综合类 | 44篇 |
化学工业 | 5169篇 |
金属工艺 | 479篇 |
机械仪表 | 465篇 |
建筑科学 | 1729篇 |
矿业工程 | 160篇 |
能源动力 | 692篇 |
轻工业 | 2190篇 |
水利工程 | 183篇 |
石油天然气 | 58篇 |
武器工业 | 1篇 |
无线电 | 1494篇 |
一般工业技术 | 4216篇 |
冶金工业 | 2813篇 |
原子能技术 | 137篇 |
自动化技术 | 3843篇 |
出版年
2023年 | 153篇 |
2022年 | 308篇 |
2021年 | 544篇 |
2020年 | 317篇 |
2019年 | 333篇 |
2018年 | 501篇 |
2017年 | 431篇 |
2016年 | 531篇 |
2015年 | 479篇 |
2014年 | 699篇 |
2013年 | 1511篇 |
2012年 | 1087篇 |
2011年 | 1525篇 |
2010年 | 1096篇 |
2009年 | 1043篇 |
2008年 | 1271篇 |
2007年 | 1105篇 |
2006年 | 948篇 |
2005年 | 872篇 |
2004年 | 782篇 |
2003年 | 700篇 |
2002年 | 664篇 |
2001年 | 400篇 |
2000年 | 380篇 |
1999年 | 417篇 |
1998年 | 429篇 |
1997年 | 377篇 |
1996年 | 350篇 |
1995年 | 300篇 |
1994年 | 310篇 |
1993年 | 302篇 |
1992年 | 252篇 |
1991年 | 215篇 |
1990年 | 204篇 |
1989年 | 230篇 |
1988年 | 188篇 |
1987年 | 177篇 |
1986年 | 174篇 |
1985年 | 242篇 |
1984年 | 216篇 |
1983年 | 185篇 |
1982年 | 169篇 |
1981年 | 196篇 |
1980年 | 130篇 |
1979年 | 148篇 |
1978年 | 144篇 |
1977年 | 129篇 |
1976年 | 143篇 |
1975年 | 121篇 |
1974年 | 105篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
142.
As part of a study of the chemistry of the steam-stimulated recovery of heavy oils, the hydrolysis and subsequent desulphurization of tetrahydrothiophene and thiophene by aqueous solutions of vanadyl and nickel salts was investigated. Vanadyl sulphate and vanadyl chloride were shown to behave very differently, emphasizing that these salts have different molecular species in aqueous solutions. 相似文献
143.
The objective of this study was to identify how physiological measures relate to self-reported vehicle seating discomfort. Twelve subjects of varied anthropometric characteristics were enrolled in the study. Subjects sat in two seats over a 2-h period and were evaluated via three physiological measures (near-infrared spectroscopy, electromyography and pressure mapping) yielding six testing sessions. Subjective discomfort surveys were recorded before and after each session for nine regions of the body. Conditional classification discomfort models were developed through dichotomised physiological responses and anthropometry to predict subjective discomfort in specific body locations. Models revealed that subjects taller than 171 cm with reduced blood oxygenation in the biceps femoris or constant, low-level muscle activity in the trapezius tended to report discomfort in the lower extremities or neck, respectively. Subjects weighing less than 58 kg with reduced blood oxygenation in the biceps femoris or unevenly distributed pressure patterns tended to report discomfort in the buttocks. The sensitivities and specificities of cross-validated models ranged between 0.69 and 1.00. 相似文献
144.
Peter Meszmer Karla Hiller Steffen Hartmann Alexey Shaporin Daniel May Raul David Rodriguez Jörg Arnold Gianina Schondelmaier Jan Mehner Dietrich R. T. Zahn Bernhard Wunderle 《Microsystem Technologies》2014,20(6):1041-1050
In this paper, a novel concept of a thermo-mechanical MEMS actuator using aluminum thin-film heaters on a thermal oxide for electrical insulation is presented. The actuator is part of an universal tensile testing platform for thermo-mechanical material characterization of one dimensional materials on a micro- and nano-scopic scale under different environmental conditions, as varying temperatures, pressure, moisture or even vacuum and is realised in BDRIE technology. It is shown, that the actuator concept fulfills the requirements for the use in a tensile loading stage along with heterogeneously integrated nanofunctional elements, following a specimen centered approach in line with bottom-up self-assembly processes. Simulation and experiment agree very well in the thermal and mechanical domain and allow subsequent optimisation of the actuator performance. 相似文献
145.
1H dipolar decoupled 13C n.m.r. experiments with the aid of the magic angle spinning technique have been used to determine the graft content and the isomer content of the polybutadiene grafts in a graft copolymer with isotactic polypropylene. 相似文献
146.
The autocorrelation functions and corresponding relaxation times obtained from the forward depolarized quasi-elastic light scattering experiment are exhibited for two quite similar models of flexible polymer chains in solution. A very small change in the chain dynamics is found to be sufficient to change the relaxation time from a relatively short time independent of chain length, with an autocorrelation function suggestive of an unweighted sum of contributions from all the relaxation times in the spectrum of chain motion, to a long time with an autocorrelation function identical with that for the end-to-end vector, strongly dependent upon chain length and dominated by the longest relaxation time in the spectrum. These results raise the question whether widely-used models in which information about short-range chain structure and motion is deliberately omitted can be expected to be appropriate for the interpretation of depolarized scattering experiments. 相似文献
147.
A 2-layer drawing represents a bipartite graph where each vertex is a point on one of two parallel lines, no two vertices on the same line are adjacent, and the edges are straight-line segments. In this paper we study 2-layer drawings where any two crossing edges meet at right angle. We characterize the graphs that admit this type of drawing, provide linear-time testing and embedding algorithms, and present a polynomial-time crossing minimization technique. Also, for a given graph G and a constant k, we prove that it is $\mathcal{NP}$ -complete to decide whether G contains a subgraph of at least k edges having a 2-layer drawing with right angle crossings. 相似文献
148.
Geschäftsmodelle 总被引:1,自引:1,他引:0
Prof. Dr. Daniel Veit Prof. Eric Clemons Prof. Dr. Alexander Benlian Prof. Dr. Peter Buxmann Prof. Dr. Thomas Hess Prof. Dr. Dennis Kundisch Prof. Dr. Jan Marco Leimeister Prof. Dr. Peter Loos Prof. Dr. Martin Spann 《WIRTSCHAFTSINFORMATIK》2014,56(1):55-64
The business model concept, although a relatively new topic for research, has garnered growing attention over the past decade. Whilst it has been robustly defined, the concept has so far attracted very little substantive research. In the context of the wide-spread digitization of businesses and society at large, the logic inherent in a business model has become critical for business success and, hence, a focus for academic inquiry. The business model concept is identified as the missing link between business strategy, processes, and Information Technology (IT). The authors argue that the BISE community offers distinct and unique competencies (e.g., translating business strategies into IT systems, managing business and IT processes, etc.) that can be harnessed for significant research contributions to this field. Within this research gap three distinct streams are delineated, namely, business models in IT industries, IT enabled or digital business models, and IT support for developing and managing business models. For these streams, the current state of the art, suggest critical research questions, and suitable research methodologies are outlined. 相似文献
149.
The heterogeneous bulk polymerization of acrylonitrile initiated by AIBN has been studied by means of an improved dilatometric technique and a new method of analysis, where the initial reaction rate (vw)0 results from the intercept of a straight line in a \documentclass{article}\pagestyle{empty}\begin{document}$ \frac {\ln \left( 1 \hbox{---} {\rm U} \right)} {{\rm e}^{{- 0,5} {\rm k}_{\rm s}{\rm t} \hbox{---} 1}}$\end{document} versus t plot. It has been found that the initial reaction rate is proportional to the square root of the initial catalyst concentration S0. The ratio of the rate coefficients of propagation and termination\documentclass{article}\pagestyle{empty}\begin{document}$\frac { {\rm k}_{\rm a} } { {\rm k}_{ {\rm w}^{2} } } $\end{document} could be calculated from the slope of a straight line passing through the origin in a plot of (vw)0 versus \documentclass{article}\pagestyle{empty}\begin{document}$\sqrt { {\rm S}_{0} }$\end{document} and yielded a value of 280 mol 1?1. 相似文献
150.
Dieter Braun Manfred Rtzsch Peter Fiedler Günter Weber Heinz Hofmann Bernd Gutschalk 《大分子材料与工程》1991,187(1):101-121
Based on the example of PE-LD grades and on model substances obtained by preparative fractionation (fractions in the molecular weight range M?w = 1.2 ? 390·104 g/mol), comprehensive investigations regarding the problems of structure/properties have been carried out. The correlations of M?w with 15 physical and application technological perameters have been investigated taking into account the reaction mechanism during the manufacturing of PE-LD in the tubular and agitated autoclave reactor, resulting in the formation of so-called primary structure perameters M?n, M?w, molar mass distribution, short chain branching and long chain branching. For the interpretation of the results, among other factors, also the morphological conditions have been taken into consideration, which in connection with the molecular parameters reveal — for specific M?w-ranges — strong changes and saturation ranges, resp., for the physical and application technological properties. 相似文献