全文获取类型
收费全文 | 2805篇 |
免费 | 196篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 60篇 |
综合类 | 1篇 |
化学工业 | 937篇 |
金属工艺 | 17篇 |
机械仪表 | 79篇 |
建筑科学 | 105篇 |
矿业工程 | 2篇 |
能源动力 | 83篇 |
轻工业 | 419篇 |
水利工程 | 27篇 |
石油天然气 | 5篇 |
无线电 | 229篇 |
一般工业技术 | 383篇 |
冶金工业 | 83篇 |
原子能技术 | 12篇 |
自动化技术 | 560篇 |
出版年
2023年 | 34篇 |
2022年 | 171篇 |
2021年 | 185篇 |
2020年 | 90篇 |
2019年 | 84篇 |
2018年 | 109篇 |
2017年 | 84篇 |
2016年 | 135篇 |
2015年 | 91篇 |
2014年 | 117篇 |
2013年 | 201篇 |
2012年 | 168篇 |
2011年 | 217篇 |
2010年 | 152篇 |
2009年 | 179篇 |
2008年 | 125篇 |
2007年 | 129篇 |
2006年 | 109篇 |
2005年 | 87篇 |
2004年 | 65篇 |
2003年 | 57篇 |
2002年 | 59篇 |
2001年 | 35篇 |
2000年 | 28篇 |
1999年 | 23篇 |
1998年 | 30篇 |
1997年 | 23篇 |
1996年 | 30篇 |
1995年 | 16篇 |
1994年 | 27篇 |
1993年 | 8篇 |
1992年 | 11篇 |
1991年 | 5篇 |
1990年 | 18篇 |
1989年 | 10篇 |
1988年 | 7篇 |
1987年 | 6篇 |
1986年 | 4篇 |
1985年 | 4篇 |
1984年 | 10篇 |
1983年 | 8篇 |
1982年 | 10篇 |
1981年 | 6篇 |
1980年 | 11篇 |
1977年 | 3篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1971年 | 2篇 |
1965年 | 2篇 |
1909年 | 2篇 |
排序方式: 共有3002条查询结果,搜索用时 15 毫秒
91.
Matthew J. Graham S. G. Djorgovski Ashish Mahabal Ciro Donalek Andrew Drake Giuseppe Longo 《Distributed and Parallel Databases》2012,30(5-6):371-384
Astronomy has been at the forefront of the development of the techniques and methodologies of data intensive science for over a decade with large sky surveys and distributed efforts such as the Virtual Observatory. However, it faces a new data deluge with the next generation of synoptic sky surveys which are opening up the time domain for discovery and exploration. This brings both new scientific opportunities and fresh challenges, in terms of data rates from robotic telescopes and exponential complexity in linked data, but also for data mining algorithms used in classification and decision making. In this paper, we describe how an informatics-based approach—part of the so-called “fourth paradigm” of scientific discovery—is emerging to deal with these. We review our experiences with the Palomar-Quest and Catalina Real-Time Transient Sky Surveys; in particular, addressing the issue of the heterogeneity of data associated with transient astronomical events (and other sensor networks) and how to manage and analyze it. 相似文献
92.
Michele?RisiEmail author Giuseppe?Scanniello Genoveffa?Tortora 《Formal Aspects of Computing》2012,24(3):307-330
In this paper we present an approach to automate the architecture recovery process of software systems. The approach is built
on information retrieval and clustering techniques, and, in particular, uses Latent Semantic Indexing (LSI) to get similarities
among software entities (e.g., programs or classes) and the k-means clustering algorithm to form groups of software entities
that implement similar functionality. In order to improve computational time in the context of the software evolution and
then reduce energy waste, the architecture recovery process can be also applied by using fold-in and fold-out mechanisms that,
respectively, add and remove software entities to the LSI representation of the understudy software system. The approach has
been implemented in a prototype of a supporting software system as an Eclipse plug-in. Finally, to assess the approach and
the plug-in, we have conducted an empirical investigation on five open source software systems implemented using the programming
languages Java and C/C++. In the investigation special emphasis has been also given to the effect of using the fold-in and
fold-out mechanisms. 相似文献
93.
Maria Letizia Corradini Valentino Fossi Andrea Giantomassi Gianluca Ippoliti Sauro Longhi Giuseppe Orlando 《Control Engineering Practice》2012,20(8):816-822
This paper presents a robust discrete-time sliding mode control coupled with an uncertainty estimator designed for planar robotic manipulators. Experimental evidence shows satisfactory trajectory tracking performances and noticeable robustness in the presence of model inaccuracies, disturbances and payload perturbations. Ultimate boundedness of the tracking errors is proved, as well as boundedness of the estimation error with arbitrary precision. 相似文献
94.
Reinhard Miller Dmitri Grigoriev Jürgen Krägel Alexander V. Makievski Valentin B. Fainerman Volodymyr I. Kovalchuk Libero Liggieri Francesca Ravera Michele Ferrari Eva Santini Giuseppe Loglio Victoria Dutschk Thodoris Karapantsios 《Microgravity science and technology》2006,18(3-4):104-107
The utilisation of particle-surfactants nanostructures as stabilising agents represents today the technologic and scientific frontier in the stabilisation of liquid films in emulsion and foams. This topic will be addressed by the proposal STEFAN (STabilisation of Emulsions and FoAms by Nanoparticles), proposed by European groups in the framework of the ESA AO-2004 for Life and Physical Sciences and Applied Research projects Similarly to what can be observed for surfactant-stabilised emulsions and foams, microgravity provides ideal conditions for the investigation of the hierarchy of involved objects: interfacial layer, liquid film, dispersed systems foam or emulsion. Microgravity experiments are planned by refurbishing the Experimental Container FASES for the ISS Fluid Science Laboratory and the facility FASTER for the European Drawer Rack, already under development in existing research programmes. Here the scientific guidelines of the project are presented together with examples and preliminary results on the effect of nano-particle-surfactant structures adsorbed at liquid interfaces. First experimental results have been achieved for particle monolayers at the water/air interface and a thermodynamic model was derived to describe the obtained surface pressure-area isotherms. 相似文献
95.
Dania Esposito Andrea Margonelli Emanuela Pace Maria Teresa Giardi Cecilia Faraloni Giuseppe Torzillo Alba Zanini 《Microgravity science and technology》2006,18(3-4):215-218
Photosynthetic microorganisms are expected to be useful to maintain an oxygenic atmosphere and to provide biomass for astronauts in the International Space Station as well as in future long-term space flights. However, fluxes of complex ionizing radiation of various intensities and energies make space an extreme environment for the microorganisms, affecting their photosynthetic efficiency. To automatically monitor the photosynthetic Photosystem II (PSII) activity of microorganisms under space conditions an optical biosensor, which utilizes chlorophyll fluorescence as biological transduction system, was built; the PSII activity was monitored by the biosensor during balloon flights at stratospheric altitudes of about 40 km. The effect of space stress on quantum yield of PSII varied among the tested species depending on the growth light conditions at which they were exposed during the flights. 相似文献
96.
Felice Strollo Lia Pecorelli Giovanna Strollo Massimo Morè Giuseppe Riondino Maria Angela Masini Bianca Maria Uva 《Microgravity science and technology》2006,18(3-4):226-229
A significant reversible decrease in testosterone (T) has been associated with microgravity in male rodents and humans. Urinary T excretion increases in primates under hypergravity. Hypogonadism is somehow related to abnormally high levels of leptin (L), a hormone produced by the adipose tissue which has been found to increase under microgravity simulation conditions like head down bed rest (HDBR). The aim of this study was to assess hemodynamic and pituitary-adrenal and -gonadal adaptation to an acute HDBR test to be eventually used on a routine basis to get better prepared to next space flights. The Authors performed a 1 hour ?12° HDBR in 6 male and 6 female volunteers who underwent heart rate and blood pressure measurement together with a blood draw three times at 30 min intervals from the start to the end of the test for L, T, estradiol (E2), LH, androstenedione (A), cortisol (F), ACTH. 12 age- and sexmatched control subjects followed the same protocol except for keeping the sitting position all the time. According to the ANOVA for repeated measures, no changes occurred in L, T, E2 or LH whereas A, F and ACTH significantly decreased independently of gender. During HDBR systolic blood pressure decreased in both genders, diastolic blood pressure decreased significantly only in men and HR showed a more clear-cut decrease in women than in men. As a conclusion, such an acute steep-slope HDBR protocol may be efficiently used to testing immediate individual haemodynamic or adrenal response to microgravity but is not suitable for studies concerning gonadal adaptation. 相似文献
97.
Alexander V. Makievski Volodymyr I. Kovalchuk Jürgen Krägel Madine Simoncini Libero Liggieri M. Ferrari Piero Pandolfini Giuseppe Loglio Reinhard Miller 《Microgravity science and technology》2005,16(1-4):215-218
The present work shows the first experimental and theoretical results for investigations on the rheology of liquid films. The experiments are planned to be performed under microgravity conditions. This environment will allow forming films of different thickness, which is impossible under ground conditions due to drainage. Then the films are forced to harmonic oscillations of the film area so that the film elasticity can be measured as a function of frequency. The presented theoretical model demonstrates the main relationships to be solved under corresponding boundary conditions 相似文献
98.
Michela Mortara Giuseppe Patané Michela Spagnuolo Bianca Falcidieno Jarek Rossignac 《Algorithmica》2003,38(1):227-248
Tools for the automatic decomposition of a surface into shape
features will facilitate the editing, matching, texturing,
morphing, compression and simplification of three-dimensional shapes. Different
features, such as flats, limbs, tips, pits and various blending
shapes that transition between them, may be characterized in terms
of local curvature and other differential properties of the
surface or in terms of a global skeletal organization of the
volume it encloses. Unfortunately, both solutions are extremely
sensitive to small perturbations in surface smoothness and to
quantization effects when they operate on triangulated surfaces.
Thus, we propose a multi-resolution approach, which not only
estimates the curvature of a vertex over neighborhoods of variable
size, but also takes into account the topology of the surface in
that neighborhood. Our approach is based on blowing a spherical
bubble at each vertex and studying how the intersection of that
bubble with the surface evolves. We describe an efficient approach
for computing these characteristics for a sampled set of bubble
radii and for using them to identify features, based on easily
formulated filters, that may capture the needs of a particular
application. 相似文献
99.
Giuseppe Ferri Ernesto Massa 《International Journal of Circuit Theory and Applications》2003,31(2):139-155
We present a low‐supply voltage (2V) low‐power consumption (500W) analogue phase‐locked loop (PLL), working at two low frequencies (1 and 10kHz), to be used in an integrated lock‐in amplifier. An externally settable control bit allows the switching operation between the two different frequencies. The circuit has been designed in a standard 0.6–m CMOS technology and differs from the standard analogue PLL architectures for the current mode implementation of both the loop filter and of the oscillator. Three different locked waveforms (sinusoidal, triangular, squared) can be obtained at the PLL output. Simulation results, obtained through the use of PSPICE and using accurate transistor models, will be proposed. The pull‐in ranges are about ±250Hz around 1 and ±1.3kHz around 10kHz, with pull‐in times of about 10 and 4ms, respectively. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
100.
Approximate similarity retrieval with M-trees 总被引:4,自引:0,他引:4
Pavel Zezula Pasquale Savino Giuseppe Amato Fausto Rabitti 《The VLDB Journal The International Journal on Very Large Data Bases》1998,7(4):275-293
Motivated by the urgent need to improve the efficiency of similarity queries, approximate similarity retrieval is investigated
in the environment of a metric tree index called the M-tree. Three different approximation techniques are proposed, which
show how to forsake query precision for improved performance. Measures are defined that can quantify the improvements in performance
efficiency and the quality of approximations. The proposed approximation techniques are then tested on various synthetic and
real-life files. The evidence obtained from the experiments confirms our hypothesis that a high-quality approximated similarity
search can be performed at a much lower cost than that needed to obtain the exact results. The proposed approximation techniques
are scalable and appear to be independent of the metric used. Extensions of these techniques to the environments of other
similarity search indexes are also discussed.
Received July 7, 1998 / Accepted October 13, 1998 相似文献