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141.
Capillary electrophoresis/electrospray ionization-mass spectrometry (CE/ESI-MS) was applied to the analysis of underivatized amino acids and the separation of their D/L-enantiomers. Under full-scan mode, all standard protein amino acids were separated and detected at low-femtomole levels using a 130-cm-long, 20-microm-i.d., 150-microm-o.d. underivatized fused-silica capillary with 1 M formic acid as the background electrolyte. The CE/ESI-MS technique was also applied to the separation of L-arginine from L-canavanine (a close analogue of arginine where the terminal methylene linked to the guanidine group of arginine is replaced by an oxygen atom) in a complex mixture containing all standard protein amino acids. The utility of CE/ESI-MS in the analysis of real-world samples was demonstrated by the identification of two metabolic diseases (PKU and tyrosinemia) through blood analysis with minimal sample preparation. In addition, the on-line separation of 11 underivatized L-amino acids from their D-enantiomers was achieved by using a 30 mM solution of (+)-(18-crown-6)-2,3,11,12-tetracarboxylic acid as the background electrolyte. 相似文献
142.
A new capillary electrophoresis/mass spectrometry technique is introduced for attomole detection of primary amines (including several neurotransmitters), amino acids, and their d/l enantiomers in one run through the use of a complexation reagent while using only approximately 1 nL of sample. The technique uses underivatized amino acids in conjunction with an underivatized capillary, which significantly reduces cost and analysis time. It was found that when (+)-(18-crown-6)-2,3,11,12-tetracarboxylic acid (18-C-6-TCA, MW 440) was used as the background electrolyte/complexation reagent during the capillary electrophoresis/electrospray ionization-mass spectrometry (CE/ESI-MS) analysis of underivatized amino acids, stable complexes were formed between the amino acids and the 18-C-6-TCA molecules. These complexes, which exhibited high ionization efficiencies, were detectable at attomole levels for most amino acids. The detection limits of the AA/18-C-6-TCA complexes were on the average more than 2 orders of magnitude lower than that of the free amino acids in solution. In addition to lower detection limits under CE/ESI-MS, a solution of 18-C-6-TCA in the concentration range of 5-30 mM provided high separation efficiency for mixtures of l-amino acids as well as mixtures of d/l-amino acids. By using a solution of 18-C-6-TCA as the background electrolyte in conjunction with an underivatized, 130-cm-long, 20-microm-i.d., 150-microm-o.d. fused-silica capillary and by monitoring the m/z range of the amino acid/18-C-6-TCA complexes (m/z 515-700), most of the standard amino acids and many of their enantiomers were separated and detected with high separation efficiency and high sensitivity (nanomolar concentration detection limits) in one run. The solutions of 18-C-6-TCA also worked well as the CE/ESI-MS BGE for low-level detection of several neurotransmitters and some of their d/l enantiomers as well as for the analysis of amino acids at endogenous levels in lysed red blood cells. 相似文献
143.
Jakob PM Wang T Schultz G Hebestreit H Hebestreit A Elfeber M Hahn D Haase A 《Magma (New York, N.Y.)》2002,15(1-3):10-17
The unique characteristics of the human lung arising from low proton density and multiple air-tissue interfaces of the alveoli
cause difficulty in1H lung magnetic resonance imaging. In addition, the dominating signal from sources such as the thoracic muscle and subcutaneous
fat hampers the visualization of the lung parenchyma. In this contribution, an efficient tissue suppression technique is presented
which allows one to significantly enhance lung parenchyma visibility. A short inversion time inversion recovery (STIR) experiment
combined with a magnetization transfer (MT) experiment was used for magnetization preparation in order to suppress the signal
from muscle. A half-Fourier single-shot turbo spin-echo sequence was used as acquisition module. This approach was used to
perform lung anatomical imaging in eight healthy human subjects and five patients withcystic fibrosis. The results obtained demonstrate that with MT-STIR approach high quality human lung images can be obtained and that this
approach has the potential for the evaluation of lung pathologies. 相似文献
144.
A theoretical study was conducted using a multiple-voltage probe sensor for detecting nonconducting inclusions in conducting media. Results show that the multiple-voltage probe sensor is capable of providing precise quantitative measurements of submerged nonconducting objects if the surface voltage response has a standard two-peak form. The standard response is observed for well-localized non-slender single inclusions below the sensor surface. In this case, the peak separation distance is associated with the inclusion depth whereas the peak magnitude is associated with the inclusion volume. Linear dependencies of the inclusion depth and the inclusion volume are observed for a wide variety of inclusion shapes. The predefined form of the surface voltage response makes it feasible to identify useful signal responses at very high noise levels. This is accomplished by using a 2D neural network classifier, based on the probabilistic neural network. A reasonable recognition error of less than 20 % is obtained if the signal-to-noise ratio is larger than or equal to 1/10. A metal casting example shows that the multiple-voltage probe sensor can measure inclusion concentrations in hot conducting melts (gas bubbles and sludge) with inclusion radii in the range from 100 to 1000 m. In contrast to existing particle counter technology, this sensor construction is simple to construct and does not require special aperture and vacuum treatment. 相似文献
145.
Simeon Keates Ray Adams Cathy Bodine Sara Czaja Wayne Gordon Peter Gregor Emily Hacker Vicki Hanson John Kemp Mark Laff Clayton Lewis Michael Pieper John Richards David Rose Anthony Savidis Greg Schultz Paul Snayd Shari Trewin Philip Varker 《Universal Access in the Information Society》2007,5(4):329-339
In October 2005, the IBM Human Ability and Accessibility Center and T.J. Watson Research Center hosted a symposium on “cognitive
and learning difficulties and how they affect access to IT systems”. The central premise of the symposium was the recognition
that cognitive and learning difficulties have a profound impact on a person’s ability to interact with information technology
(IT) systems, but that little support is currently being offered by those systems. By bringing together internationally renowned
experts from a variety of different, but complementary, research fields, the symposium aimed to provide a complete overview
of the issues related to this topic. This paper summarises the discussions and findings of the symposium. 相似文献
146.
We propose a novel approach to cross-lingual language model and translation lexicon adaptation for statistical machine translation
(SMT) based on bilingual latent semantic analysis. Bilingual LSA enables latent topic distributions to be efficiently transferred
across languages by enforcing a one-to-one topic correspondence during training. Using the proposed bilingual LSA framework,
model adaptation can be performed by, first, inferring the topic posterior distribution of the source text and then applying
the inferred distribution to an n-gram language model of the target language and translation lexicon via marginal adaptation. The background phrase table is
enhanced with the additional phrase scores computed using the adapted translation lexicon. The proposed framework also features
rapid bootstrapping of LSA models for new languages based on a source LSA model of another language. Our approach is evaluated
on the Chinese–English MT06 test set using the medium-scale SMT system and the GALE SMT system measured in BLEU and NIST scores.
Improvement in both scores is observed on both systems when the adapted language model and the adapted translation lexicon
are applied individually. When the adapted language model and the adapted translation lexicon are applied simultaneously,
the gain is additive. At the 95% confidence interval of the unadapted baseline system, the gain in both scores is statistically
significant using the medium-scale SMT system, while the gain in the NIST score is statistically significant using the GALE
SMT system. 相似文献
147.
Subramanya Sarma Vadlamani Joerg Eickemeyer Ludwig Schultz Bernhard Holzapfel 《Journal of Materials Science》2007,42(17):7586-7591
The development of strongly cube textured Cu based substrates is important in the cost effective production of long lengths
of high temperature superconducting cables. The present paper reports textures (deformation and recrystallisation) development
in pure Cu, Cu–Al, Cu–Mn (with a solute content of 1–3 at.%) and Cu–35 at.% Ni alloys. 相似文献
148.
Greegor R.B. Parazzoli C.G. Nielsen J.A. Thompson M.A. Tanielian M.H. Vier D.C. Schultz S. Smith D.R. Schurig D. 《Microwaves, Antennas & Propagation, IET》2007,1(1):108-115
Negative index of refraction materials (NIMs) were first postulated by Veselago in 1968 and have recently been realised using structures formed with rings and wires deposited on printed circuit boards. The proof of the existence of negative index of refraction was established using a Snell's law experiment with a wedge. The predicted and measured refraction angles were found to be consistent for a negative index material and in excellent agreement with the theoretical expectations. For microwave lenses NIMs have the advantage of being lighter, having better focusing properties and potentially lower aberrations. Simulation and experimental results on NIM configurations including gradient index of refraction and spherical 3D lenses are presented. Both focusing and beam collimating applications will be considered. These results will be compared to normal positive index of refraction material lenses 相似文献
149.
Indirect measuring of crack growth by means of a key-curve-method in pre-cracked Charpy specimens made of nodular cast iron 总被引:1,自引:0,他引:1
Andreas Emrich Uwe Michael Mühlich Meinhard Kuna Annette Ludwig Peter Trubitz 《International Journal of Fracture》2007,145(1):47-61
The determination of dynamic crack resistance curves from single specimen fracture tests requires information about the crack
advance during the experiment. Here, attention is focused on crack resistance curves for nodular cast iron based on experimental
data from instrumented Charpy tests. In order to estimate the actual crack length a key curve method (KCM) is employed. On
the other hand, the Charpy impact tests were realized numerically using finite element calculations in conjunction with a
continuum damage model (CDM) to simulate ductile crack growth. The parameters of the CDM model were determined from the experimental
data of single specimen fracture tests. Equivalence between the experimental and the numerical realization of a fracture test
was ensured by validating the predictions of the numerical simulations by means of low blow fracture tests. Comparison between
the crack advance predicted by the numerical simulations and the results obtained using the proposed KCM shows a sufficiently
well agreement with the actual crack length. Furthermore, crack resistance curves obtained from single specimen tests using
either standard estimation schemes in conjunction with the KCM or numerical simulations are compared with the predictions
based on low blow fracture tests. 相似文献
150.
引言 越来越激烈的市场竞争引发了人们对不断革新的、性价比高和具有更多功能产品的需求,这种需求对产品设计和整个制造工艺都产生了影响. 相似文献