全文获取类型
收费全文 | 49460篇 |
免费 | 2932篇 |
国内免费 | 49篇 |
专业分类
电工技术 | 324篇 |
综合类 | 41篇 |
化学工业 | 10148篇 |
金属工艺 | 859篇 |
机械仪表 | 914篇 |
建筑科学 | 1593篇 |
矿业工程 | 108篇 |
能源动力 | 1169篇 |
轻工业 | 7522篇 |
水利工程 | 450篇 |
石油天然气 | 236篇 |
武器工业 | 4篇 |
无线电 | 2743篇 |
一般工业技术 | 8235篇 |
冶金工业 | 11141篇 |
原子能技术 | 234篇 |
自动化技术 | 6720篇 |
出版年
2023年 | 448篇 |
2022年 | 784篇 |
2021年 | 1352篇 |
2020年 | 996篇 |
2019年 | 990篇 |
2018年 | 1781篇 |
2017年 | 1754篇 |
2016年 | 1860篇 |
2015年 | 1337篇 |
2014年 | 1804篇 |
2013年 | 3404篇 |
2012年 | 2909篇 |
2011年 | 2855篇 |
2010年 | 2246篇 |
2009年 | 2101篇 |
2008年 | 2284篇 |
2007年 | 2005篇 |
2006年 | 1508篇 |
2005年 | 1260篇 |
2004年 | 1149篇 |
2003年 | 1036篇 |
2002年 | 897篇 |
2001年 | 584篇 |
2000年 | 582篇 |
1999年 | 741篇 |
1998年 | 3575篇 |
1997年 | 2165篇 |
1996年 | 1427篇 |
1995年 | 845篇 |
1994年 | 719篇 |
1993年 | 694篇 |
1992年 | 251篇 |
1991年 | 243篇 |
1990年 | 235篇 |
1989年 | 244篇 |
1988年 | 216篇 |
1987年 | 202篇 |
1986年 | 202篇 |
1985年 | 234篇 |
1984年 | 200篇 |
1983年 | 143篇 |
1982年 | 169篇 |
1981年 | 187篇 |
1980年 | 164篇 |
1979年 | 134篇 |
1978年 | 124篇 |
1977年 | 206篇 |
1976年 | 430篇 |
1975年 | 92篇 |
1973年 | 86篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
When evaluating transportation infrastructure projects and determining which of them will be carried out from a set of projects and given a budget constraint, several criteria need to be considered in the decision. Standard evaluation practices imply the aggregation of impacts into one utility function which is later optimized. Nevertheless these techniques used for translation of different measuring units into monetary terms are highly controversial. Multicriteria techniques can explicitly deal with different measuring units, however, they are not suitable to model interdependence relationships of projects that share a common characteristic (same route, location or target population, for instance). In this research we model this transportation planning problem, the multi-objective transportation infrastructure project selection problem (MTIPSP), as a constrained multi-objective optimization problem with quadratic objective functions, using a variation of the multi-objective 0–1 knapsack problem plus some additional constraints. Given the combinatorial nature of the problem, an evolutionary-based framework is used for the identification of Pareto solutions, and later, those with non-attractive properties are filtered using a Knee Identification Procedure. The final selection of the projects portfolio is made using a well known multicriteria decision aid method and including the decision makers’ preferences based on the existing context. 相似文献
972.
Daniel Díaz-Pernil Mario J. Pérez-Jiménez Álvaro Romero-Jiménez 《Natural computing》2009,8(4):797-806
In the framework of P systems, it is known that the construction of exponential number of objects in polynomial time is not
enough to efficiently solve NP-complete problems. Nonetheless, it could be sufficient to create an exponential number of membranes in polynomial time. Working
with P systems whose membrane structure does not increase in size, it is known that it is not possible to solve computationally
hard problems (unless P = NP), basically due to the impossibility of constructing exponential number of membranes, in polynomial time, using only evolution,
communication and dissolution rules. In this paper we show how a family of recognizer tissue P systems with symport/antiport
rules which solves a decision problem can be efficiently simulated by a family of basic recognizer P systems solving the same
problem. This simulation allows us to transfer the result about the limitations in computational power, from the model of
basic cell-like P systems to this kind of tissue-like P systems. 相似文献
973.
Manuel J. Betancur Fajith Martínez Carlos Ocampo Jaime A. Moreno Germán Buitrón Iván Moreno-Andrade 《Simulation Modelling Practice and Theory》2009,17(4):680-691
This work proposes a mathematical model for the acclimatization process of a bioreactor treating toxic wastewater. Experimental data was used to identify the changing kinetic parameters of the model as acclimatization progresses. It was found that only one key parameter, the specific biomass growth rate function, changed during the acclimatization process. Therefore, an acclimatization model was proposed to explain the changes of this parameter. 相似文献
974.
Alexandre Benoit Laurent Bonnaud Alice Caplier Phillipe Ngo Lionel Lawson Daniela G. Trevisan Vjekoslav Levacic Céline Mancas Guillaume Chanel 《Personal and Ubiquitous Computing》2009,13(1):33-41
This paper presents a driver simulator, which takes into account the information about the user’s state of mind (level of
attention, fatigue state, stress state). The user’s state of mind analysis is based on video data and biological signals.
Facial movements such as eyes blinking, yawning, head rotations, etc., are detected on video data: they are used in order
to evaluate the fatigue and the attention level of the driver. The user’s electrocardiogram and galvanic skin response are
recorded and analyzed in order to evaluate the stress level of the driver. A driver simulator software is modified so that
the system is able to appropriately react to these critical situations of fatigue and stress: some audio and visual messages
are sent to the driver, wheel vibrations are generated and the driver is supposed to react to the alert messages. A multi-threaded
system is proposed to support multi-messages sent by the different modalities. Strategies for data fusion and fission are
also provided. Some of these components are integrated within the first prototype of OpenInterface: the multimodal similar
platform. 相似文献
975.
Dharani Perera R. T. Jim Eales Kathy Blashki 《Universal Access in the Information Society》2009,8(2):77-88
For people with upper limb disabilities visual art is an important activity that allows for expression of individuality and
independence. They show remarkable endurance, patience and determination to adapt their remaining capabilities to create visual
art. There are significant advantages of digital technologies in assisting artists with upper limb disabilities. Paralinguistic
voice recognition technologies have proven to be a particularly promising mode of interaction. Despite these benefits, technological
support for people with upper limb disabilities to create visual art is scarce. This paper reports on a number of case studies
of several artists with upper limb disabilities. These case studies illustrate the struggles they face to be creative and
also show the significant advantages of digital technologies in assisting such artists. An investigation into people’s ability
to use the volume of their voice to control cursor movement to create drawings on the screen is also reported. With motivation,
training and practise, use of volume to control drawing tasks shows great promise. It is believed that paralinguistic voice
has wider implications beyond assisting artists with upper limb disabilities, such as: an alternative mode of interaction
for disabled people to perform tasks other than creating visual art, alternative mode of interaction for hands busy environments
and as a voice training system for people with speech impairments. 相似文献
976.
eb
3 is a trace-based formal language created for the specification of information systems. In eb
3, each entity and association attribute is independently defined by a recursive function on the valid traces of external events.
This paper describes an algorithm that generates, for each external event, a transaction that updates the value of affected
attributes in their relational database representation. The benefits are twofold: eb
3 attribute specifications are automatically translated into executable programs, eliminating system design and implementation
steps; the construction of information systems is streamlined, because eb
3 specifications are simpler and shorter to write than corresponding traditional specifications, design and implementations.
In particular, the paper shows that simple eb
3 constructs can replace complex SQL queries which are typically difficult to write.
相似文献
Régine LaleauEmail: |
977.
Bernarde C Khoder G Lehours P Burucoa C Fauchère JL Delchier JC Mégraud F Atanassov C 《Proteomics. Clinical applications》2009,3(6):672-681
To date no reliable diagnostic method exists to predict, among the very large and clinically heterogeneous group of Helicobacter pylori‐infected patients, the extremely small group at risk for developing low‐grade gastric MALT lymphoma (LG‐MALT). Search of proteomic biomarkers holds promise for the classification of the H. pylori strains with regard to this severe clinical outcome. In the present study 69 H. pylori strains isolated from patients with two different H. pylori‐associated diseases, duodenal ulcer (DU, n=29) and LG‐MALT (n=40) were used. Protein expression patterns of the strains were analyzed by using the high‐throughput methodology SELDI. Selected proteins were purified by means of chromatographic and electrophoretic methods in view of further sequencing by LC‐MS/MS. Univariate analysis (Mann–Whitney test) of the protein expression patterns generated nine significant biomarkers that can discriminate between H. pylori strains from patients with DU and LG‐MALT. These biomarkers are of low molecular weight, ranging from 6 to 26.6 kDa. Among them, two are overexpressed in LG‐MALT strains and seven – in DU strains. Two biomarker proteins, one overexpressed in LG‐MALT strains (13.2 kDa) and another one – overexpressed in DU strains (26.6 kDa), were purified to homogeneity and identified by using LC‐MS/MS as a 50S ribosomal protein L7/L12 and a urease subunit, respectively. These biomarkers can be included in novel protein arrays for the differential diagnosis of H. pylori‐associated clinical outcomes. 相似文献
978.
Partial discharges are a transient phenomena whose measurement is remarkably important for electrical equipment diagnosis and maintenance. These discharges appear in the measurement circuit as very narrow current pulses of some nanoseconds. Therefore, discharge pulse detection is a particularly difficult problem, especially because they are superposed on the high voltage waveforms that cause them. In this paper, we present an inductively coupled probe able to measure this physical phenomenon by means of a very simple and inexpensive device that can be installed in the equipment under test. After modeling the probe, its response will be compared to that of commercial devices using both calibrated discharges and partial discharges occurring at real power. 相似文献
979.
Deneuville F Duquennoy M Ouaftouh M Jenot F Ourak M Desvaux S 《The Review of scientific instruments》2008,79(4):044901
An original inversion method specifically adapted to the estimation of Poisson coefficient of balls by using their resonance spectra is described. From the study of their elastic vibrations, it is possible to accurately characterize the balls. The proposed methodology can create both spheroidal modes in the balls and detect such vibrations over a large frequency range. Experimentally, by using both an ultrasonic probe for the emission (piezoelectric transducer) and a heterodyne optic probe for the reception (interferometer), it was possible to take spectroscopic measurements of spheroidal vibrations over a large frequency range (100 kHz-45 MHz) in a continuous regime. This method, which uses ratios between wave resonance frequencies, allows the Poisson coefficient to be determined independently of Young's modulus and the ball's radius and density. This has the advantage of providing highly accurate estimations of Poisson coefficient (+/-4.3 x 10(-4)) over a wide frequency range. 相似文献
980.
On the interpretation of the forbidden spots observed in the electron diffraction patterns of flat Au triangular nanoparticles 总被引:1,自引:0,他引:1
In many cases nanostructures present forbidden spots in their electron diffraction patterns when they are observed by transmission electron microscopy (TEM). To interpret their TEM and high resolution transmission electron microscopy (HRTEM) images properly, an understanding of the origin of these spots is necessary. In this work we comment on the origin of the forbidden spots observed in the [111] and [112] electron diffraction patterns of flat gold triangular nanoparticles. The forbidden spots were successfully indexed as corresponding to the first laue Zone (FOLZ) and the HRTEM images presented a contrast produced by the interference of the zero-order Laue zone (ZOLZ) and FOLZ spots. We discuss the use of the forbidden spots in the study of the structure of nanoparticles and show that they are related to the shape and incompleteness of layers in the very thin particles. 相似文献