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排序方式: 共有1687条查询结果,搜索用时 15 毫秒
91.
Shahnila Islam 《国际水资源开发杂志》2012,28(4):601-613
India has developed a national biofuel policy to increase energy security, reduce greenhouse gas emissions, and stimulate rural development. In this policy, the government has set blending targets for mixing ethanol and biodiesel with gasoline and diesel, respectively. In India, ethanol is produced from irrigated sugar-cane while biodiesel is produced from jatropha, which is said to require no irrigation. This paper analyzes the possible impacts of an increase in sugar-cane and jatropha production on water management and use. It finds that India's biofuel policy is likely to place additional pressure on scarce water resources. Although the development of biofuels may be necessary, care must be taken to anticipate its likely impacts on water resources. 相似文献
92.
Raman amplifiers for telecommunications 总被引:9,自引:0,他引:9
Raman amplifiers are being deployed in almost every new long-haul and ultralong-haul fiber-optic transmission systems, making them one of the first widely commercialized nonlinear optical devices in telecommunications. This paper reviews some of the technical reasons behind the wide-spread acceptance of Raman technology. Distributed Raman amplifiers improve the noise figure and reduce the nonlinear penalty of fiber systems, allowing for longer amplifier spans, higher bit rates, closer channel spacing, and operation near the zero-dispersion wavelength. Lumped or discrete Raman amplifiers are primarily used to increase the capacity of fiber-optic networks, opening up new wavelength windows for wavelength-division multiplexing such as the 1300 nm, 1400 nm, or short-wavelength S-band. As an example, using a cascade of S-band lumped amplifiers, a 20-channel, OC-192 system is shown that propagates over 867 km of standard, single-mode fiber. Raman amplifiers provide a simple single platform for long-haul and ultralong-haul amplifier needs and, therefore, should see a wide range of deployment in the next few years 相似文献
93.
A questionnaire comprising 80 self-report items was designed to measure student Approaches to Studying in a higher education context. The items were conceptualized and designed from five learning orientations: a Deep Approach, a Surface Approach, a Strategic Approach, Clarity of Direction and Academic Self-Confidence, to include 40 attitude items and 40 corresponding behavior items. The study aimed to create a scale and investigate its psychometric properties using a Rasch measurement model. The convenience sample consisted of 350 students at an Australian university in 1998. The analysis supported the conceptual structure of the Scale as involving studying attitudes and behaviors towards five orientations to learning. Attitudes are mostly easier than behaviors, in line with the theory. Sixty-eight items fit the model and have good psychometric properties. The proportion of observed variance considered true is 92% and the Scale is well-targeted against the students. Some harder items are needed to improve the targeting and some further testing work needs to be done on the Surface Approach. In the Surface Approach and Clarity of Direction in Studying, attitudes make a lesser contribution than behaviors to the variable, Approaches to Studying. 相似文献
94.
Quantitative scanning electron microscope (SEM) studies of cement-stabilized waste specimens exposed to a leaching solution at constant pH in the range 4-7 have shown that the acid neutralization capacity (ANC) of the waste matrix is consumed at two consecutive leaching fronts. The first front is associated with the dissolution of portlandite (Ca(OH)2) and the partial reaction of calcium silicate hydrate (CSH) gel. The second front marks the dissolution of Ca-Al hydroxy sulfate minerals. The advancement of the first front is limited by the diffusion of OH- ions from the first front toward the leaching solution. The advancement of the second front, however, is controlled by the diffusion of H+ ions from the leaching solution toward the second front. Leaching of copper, zinc, and lead only occurs between the second front and the specimen surface. The leaching behavior of metals is modeled by considering that metals are leached from the waste matrix as a result of the advancement of the second front. The proposed model takes into account the leachable metal fraction in the waste matrix and the effect of metal remineralization on metal mobility. 相似文献
95.
Thin film CdS/Cu2S heterojunction solar cells were fabricated on gold grid plated glass substrates by first depositing Cu2S by elemental evaporation of copper and sulphur and then evaporating CdS. The Cu2S layer and the grid contacts were thus sandwiched between the glass substrate and the CdS layer and were prevented from coming in contact with air and humidity. Open-circuit voltages of 450–470 mV and short-circuit current densities of 14–16 mA cm-2 were found. The cell efficiencies were between 4.8% and 5%. The degradation of the cells was minimized and the cells were found to be stable. 相似文献
96.
Md. Raisul Islam N. E. Wijeysundera J. C. Ho 《International Journal of Refrigeration》2003,26(8):909-917
This paper describes the development of a novel film-inverting design concept for falling-film absorbers. The solid surface of the absorber is segmented so that both surfaces of the falling-film are alternatively cooled in a periodic manner. A conventional tubular absorber is modified by introducing film-guiding fins between tubes to produce a film-inverting arrangement. A maximum increase in vapour absorption rate of about 100% is obtained with the film-inverting design compared to the tubular absorber. The numerical simulation indicates that the vapour absorption rate can be increased by using a large number of film-inverting segments in the absorber. 相似文献
97.
Single-Mixture Audio Source Separation by Subspace Decomposition of Hilbert Spectrum 总被引:1,自引:0,他引:1
Md. Khademul Islam Molla Keikichi Hirose 《IEEE transactions on audio, speech, and language processing》2007,15(3):893-900
A novel technique is developed to separate the audio sources from a single mixture. The method is based on decomposing the Hilbert spectrum (HS) of the mixed signal into independent source subspaces. Hilbert transform combined with empirical mode decomposition (EMD) constitutes HS, which is a fine-resolution time-frequency representation of a nonstationary signal. The EMD represents any time-domain signal as the sum of a finite set of oscillatory components called intrinsic mode functions (IMFs). After computing the spectral projections between the mixed signal and the individual IMF components, the projection vectors are used to derive a set of spectral independent bases by applying principal component analysis (PCA) and independent component analysis (ICA). A k-means clustering algorithm based on Kulback-Leibler divergence (KLd) is introduced to group the independent basis vectors into the number of component sources inside the mixture. The HS of the mixed signal is projected onto the space spanned by each group of basis vectors yielding the independent source subspaces. The time-domain source signals are reconstructed by applying the inverse transformation. Experimental results show that the proposed algorithm performs separation of speech and interfering sound from a single mixture 相似文献
98.
Chong Zhang Islam A. Salama Nathaniel R. Quick Aravinda Kar 《International Journal of Thermophysics》2007,28(3):980-995
Determination of the thermophysical properties of thin film materials is important for modeling and optimizing laser microvia
drilling of organic substrates in microelectronics applications. Techniques to measure the density, thermal conductivity,
thermal diffusivity, thermal decomposition point, and specific ablation heat of thin polymer films are described. An experimental
apparatus was set up for laser heating of the sample. To measure the thermal diffusivity, an analytic heat transfer model
is developed. One-dimensional heat conduction is assumed due to the small thickness of the film compared to the radius of
the laser beam. The value of thermal diffusivity is obtained by fitting the experimental data to the theory. The specific
ablation heat is obtained by measuring the mass loss during laser ablation. The experimental apparatus and the property determination
methodology can also be applied to thin samples of other materials. 相似文献
99.
Comments on the article by Fowers and Davidov, "The virtue of multiculturalism: Personal transformation, character and openess to the other," (see record 2006-11202-002). Fowers and Davidov offered a virtue-based approach to understanding and fostering multiculturalism in psychology. Fowers and Davidov argued that multiculturalism fulfills the classical components of being a virtue, being a worthy goal that requires the wise use of consistent and worthwhile goods. They concluded that the virtue of multiculturalism and its correlate, openness, provide a sound basis for transformative cultural dialogue. It appears that Fowers and Davidov may be caught in what Meiland (1980) has called "The Paradox of Cognitive Relativism." I would argue that the problem, rather than being a faulty argument on their part, is the intrinsic incoherence of an ethic of multiculturalism, which insists that we respect a diversity of cultural backgrounds, and yet insists. The virtue model of ethics is relevant to our cultural concerns as psychologists but certainly does not resolve them. Instead, because it is soundly based in the idea of personal character, its value lies in bringing to light the very dilemmas involving human similarity and difference that have troubled psychologists since the inception of the field. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
100.
Krishnamurthy V. Kai Yiu Luk Cornell B. Prashar J. di Maio I.L. Islam H. Battle A.R. Valenzuela S.M. Martin D.K. 《IEEE sensors journal》2007,7(9):1281-1288
This paper deals with the experimental construction, stochastic modeling, and statistical signal processing of a novel, artificially constructed biosensor comprised of biological ion channels. Such nanoscale biosensors have been built by incorporating dimeric gramicidin A (bis-gA) ion channels into bilayer membranes of giant unilamellar liposomes, and then excising small patches of the membrane loaded with ion channels. We present a stochastic model for the response of the biosensor and present statistical model validation tests to verify the adequacy of the model. We show that in the presence of specific target molecules, the statistics of the gating mechanisms of the gA channels are altered. By capturing the change in real time, we devise a maximum-likelihood detector to detect the presence of target molecules. To test the sensitivity of this model, we conducted patch-clamp experiments with two compounds known to inhibit conduction of the gA channels. We found experimentally that the real-time detection algorithm was able to accurately identify the addition of the compounds even when the alterations in the patch-clamp recordings were very small. This algorithm provides the sensitive detection system for ongoing development of lipid-based nanosensors. 相似文献