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61.
Oil dispersants, the tool of choice for treating oil spills in tropical marine environments, is potentially harmful to marine life, including reef corals. In a previous study, we found that dispersed oil and oil dispersants are harmful to soft and hard coral species at early life stages. In this broader study, we employed a "nubbin assay" on more than 10 000 coral fragments to evaluate the short- and long-term impacts of dispersed oil fractions (DOFs) from six commercial dispersants, the dispersants and water-soluble-fractions (WSFs) of Egyptian crude oil, on two Indo Pacific branching coral species, Stylophora pistillata and Pocillopora damicornis. Survivorship and growth of nubbins were recorded for up to 50 days following a single, short (24 h) exposure to toxicants in various concentrations. Manufacturer-recommended dispersant concentrations proved to be highly toxic and resulted in mortality for all nubbins. The dispersed oil and the dispersants were significantly more toxic than crude oil WSFs. As corals are particularly susceptible to oil detergents and dispersed oil, the results of these assays rules out the use of any oil dispersant in coral reefs and in their vicinity. The ecotoxicological impacts of the various dispersants on the corals could be rated on a scale from the least to the most harmful agent, as follows: Slickgone > Petrotech > Inipol = Biorieco > Emulgal > Dispolen. 相似文献
62.
Cryptographic computations are often carried out on insecure devices for which the threat of key exposure represents a serious
concern. Forward security allows one to mitigate the damage caused by exposure of secret keys. In a forward-secure scheme,
secret keys are updated at regular periods of time; exposure of the secret key corresponding to a given time period does not
enable an adversary to "break" the scheme (in the appropriate sense) for any prior time period. We present the first constructions
of (non-interactive) forward-secure public-key encryption schemes. Our main construction achieves security against chosen-plaintext
attacks in the standard model, and all parameters of the scheme are poly-logarithmic in the total number of time periods.
Some variants and extensions of this scheme are also given. We also introduce the notion of binary tree
encryption and construct a binary tree encryption scheme in the standard model. Our construction implies the first hierarchical
identity-based encryption scheme in the standard model. (The notion of security we achieve, however, is slightly weaker than
that achieved by some previous constructions in the random oracle model.) 相似文献
63.
This paper describes a new and efficient method for low bit-rate image coding which is based on recent development in the theory of multivariate nonlinear piecewise polynomial approximation. It combines a binary space partition scheme with geometric wavelet (GW) tree approximation so as to efficiently capture curve singularities and provide a sparse representation of the image. The GW method successfully competes with state-of-the-art wavelet methods such as the EZW, SPIHT, and EBCOT algorithms. We report a gain of about 0.4 dB over the SPIHT and EBCOT algorithms at the bit-rate 0.0625 bits-per-pixels (bpp). It also outperforms other recent methods that are based on "sparse geometric representation." For example, we report a gain of 0.27 dB over the Bandelets algorithm at 0.1 bpp. Although the algorithm is computationally intensive, its time complexity can be significantely reduced by collecting a "global" GW n-term approximation to the image from a collection of GW trees, each constructed separately over tiles of the image. 相似文献
64.
The dynamics of the impact process of a non‐Newtonian gelled fuel simulant droplet was studied experimentally. A comparison between the impact process of the gel simulant and that of a neat Newtonian fluid reveals a similar behaviour during the kinematic phase of the droplet impact. However, significant differences, both quantitatively and qualitatively, between the investigated fluids were found during the later spreading, relaxation and equilibrium phases of the impact process. Numerical simulations for the neat Newtonian fluid were found to accurately predict the centreline height during the kinematic phase for both of the fluids. A novel dynamic model for drop shape based on elastic spring and dashpot elements using the Bessel function to describe the periodic term is presented. Very good agreement of the dynamic model with the experimental data was obtained. 相似文献
65.
Terri A. Stortz Alexander K. Zetzl Shai Barbut Andrea Cattaruzza Alejandro G. Marangoni 《Lipid Technology》2012,24(7):151-154
Organogelators such as 12‐hydroxystearic acid and ethylcellulose have been shown to structure vegetable oils at levels below 8%. The resultant gels retain the fatty acid profile of the vegetable oil, yet provide solid‐like properties that can successfully replace saturated fats in a variety of food products including cookies, creams, and frankfurters and sausages. Furthermore, organogel technology can be used for the controlled or delayed release of nutraceuticals and pharmaceuticals. With the development of food grade organogelators, this will allow for the use of oleogels in a large variety of food and pharmaceutical applications. 相似文献
66.
A microcountercurrent flame photometric detector (microcc-FPD) was adapted and optimized for ultrafast gas chromatographic (GC) separation and detection of organophosphor (OP) and organosulfur (OS) compounds on short chromatographic columns. Air and hydrogen are introduced to the microcc-FPD from opposite directions, creating a hydrogen-rich flame. In this microcc-FPD, combustion takes place between the burner tips without touching them. The separation between the tips and the flame reduces heat loss from the flame to the surrounding environment, resulting in low hydrogen consumption and a compact flame. The microcc-FPD is capable of detecting very narrow (13 ms) chromatographic peaks. An ultrafast GC separation of a group of six OP and OS compounds is achieved within less than 5 s using fast temperature programming of a 0.5-m-long microbore column. Very fast separations are also demonstrated on a 1-m-long microfabricated column consisting of 150-microm-wide, 240-microm-deep channels, etched in a 1.9-cm square silicon chip, covered with a Pyrex wafer, and statically coated with dimethyl polysiloxane. With a hydrogen flow rate of 10 mL/min, the detection limit for OP is 12 pg of P/s and 3 ng of S/s for OS compounds at a signal-to-noise ratio of 2. The coupling of a microfabricated column and a miniature FPD is an important step toward the development of a miniaturized GC-FPD capable of ultrafast detection of low levels of OP and OS compounds. 相似文献
67.
E Gazit N Burshtein DJ Ellar T Sawyer Y Shai 《Canadian Metallurgical Quarterly》1997,36(49):15546-15554
The CytA toxin exerts its activity by the formation of pores within target cell membranes. However, the exact mechanism of pore formation and the structural elements that are involved in the toxic activity are yet to be determined. Recently, the structure of the highly similar CytB toxin was solved (Li et al., 1996), and a beta-barrel was suggested as a possible structure of the pores. Due to the similarity between the toxins, the existence and positioning of alpha-helices and beta-sheets in CytA were predicted from the alignment of the sequences. Here peptides corresponding to beta5, beta6, and beta7 strands, to a conserved nonhelical region of the CytA toxin (P149-170), to helices B and D, and to an analogue of helix A were synthesized, fluorescently labeled, and characterized. We found that, unlike helices A and C (Gazit and Shai, 1993), neither the beta-strand peptides nor helix B could interact with lipid membranes, whereas P149-170 and helix D bind the membrane weakly. Membrane permeation experiments suggested that CytA toxin exerts its activity by aggregation of several monomers. To learn about the structural elements that may mediate CytA oligomerization, the ability of the synthetic peptides to interact with membrane-bound CytA was studied. Helices A and C, but not the beta-strands, helix D, or a control peptide, caused a large increase in the fluorescence of membrane-bound fluorescein-labeled CytA, whereas helix B had only a slight effect. Moreover, the addition of rearranged helix A, a peptide with the same composition as helix A, but with only two pairs of amino acids rearranged, did not affect the fluorescence. The addition of unlabeled CytA also caused an increase in the fluorescence intensity, further demonstrating the interaction between CytA monomers within the membrane. Taken together, our results provide further support for the suggestion that the CytA toxin self-assembles within membrane and that helices A and C are major structural elements involved in the membrane interaction and intermolecular assembly of the toxin. 相似文献
68.
A. K. Aleshin V. A. Glazunov G. V. Rashoyan Offer Shai 《Journal of Machinery Manufacture and Reliability》2016,45(4):291-296
The kinematic screws that determine the topology of singular zones of parallel-structure robots are studied. It has been established that the kinematic screws depend on the actuator mount points. 相似文献
69.
A unified approach to the synthesis of chelating phase transfer agents which uses attachment of various side-chains to a single chelating molecular precursor (such as 2-acetyl-4-chloromethyl phenol, 4-chloromethyl salicylaldehyde, 5-chloromethyl-8-hydroxyquinoline), by alkylation at carbon (on aromatic substrates), at oxygen (on alkanols, oligoethylene glycols) or at nitrogen (dialkylamines), is presented. The reaction of a model precursor, 2-acetyl-4-chloromethyl phenol, is studied in detail. The proton–ligand and proton–metal stability constants and Cu(II) phase transfer properties is determined. 相似文献
70.
Hanoch Efraim Shai Arogeti Amir Shapiro Gera Weiss 《Journal of Intelligent and Robotic Systems》2017,87(1):169-186
We present a new image based visual servoing (IBVS) approach for control of micro aerial vehicles (MAVs) in indoor environments. Specifically, we show how a MAV can be stabilized and guided using only corridor lines viewed on a front facing camera and angular velocity measurements. Since the suggested controller does not include explicit attitude feedback it does not require the use of accelerometers which are susceptible to vibrations, nor complex attitude estimation algorithms. The controller also does not require direct velocity measurements which are difficult to obtain in indoor environments. The paper presents the new method, stability analysis, simulations and experiments. 相似文献