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21.
Spillways are hydraulic structures which transfer water to the downstream. Stepped spillways areseriously attended to, since they are highly efficient regarding energy dissipation. In this study, the flow pattern over stepped spillways was simulated with five different pool configurations. The VOF method was used to simulate the flow free surface, and K??(RNG) was employed to model turbulence. The results obtained fromthe numerical model were fairly consistent with the experimental results. The results demonstrated that theflow velocity and the residual head showed significant differences in the spillway width with regard to different pool configurations. The pool configuration in which the pools were installed as staggered configuration of flat and pooled steps showed the least residual head at the downstream and as a result the greatest energy dissipation. 相似文献
22.
Morteza Nikooghadam Author VitaeAuthor Vitae Mohsen Ebrahimi Moghaddam Author Vitae 《Journal of Systems and Software》2010,83(10):1917-1929
The elliptic curve cryptosystem (ECC) has recently received significant attention by researchers due to its high performance, low computational cost, and small key size. In this paper, an efficient key management and derivation scheme based on ECC is proposed to solve dynamic access problems in a user hierarchy. Compared to previous ECC based works, the proposed method does not require constructing interpolate polynomials, therefore, the computational complexity of key generation and key derivation is significantly reduced. At the same time, time complexity of adding/deleting security classes, modifying their relationships, and changing of secret keys is decreased in the proposed method. 相似文献
23.
Masoud Baghelani Habib Badri Ghavifekr Afshin Ebrahimi 《Microsystem Technologies》2011,17(10-11):1599-1609
One of the most encumbering issues in RF MEMS resonators is spurious modes. The problem of spurious modes becomes more critical, when the ring type resonators are used. In the ring shape anchored contour mode disk resonator, for achieving a low serial resistance, the inner radius of the disk must be increased. This causes the spurious modes to become too close to the desired mode and degrade the operation of the resonator. In this work, spurious modes of before-mentioned device are introduced and their characteristics are evaluated by exact analytical approach. Based on those analytical approaches, we introduce two techniques for spurious mode suppression. The first technique is based on exciting the desired mode by proper electrode engineering and hence is an electrical approach. The second technique is reconfiguring of the anchor from a continuous ring to crossed ring segments and locating the segments on the phase discriminating lines to increase the insertion loss for spurious modes and decrease the losses for the fundamental mode. The final harmonic analysis verifies that the proposed techniques result a resonator with a pure frequency spectrum and spurious modes excluded over a very wide frequency range. 相似文献
24.
The assumption of proportional hazards (PH) fundamental to the Cox PH model sometimes may not hold in practice. In this paper, we propose a generalization of the Cox PH model in terms of the cumulative hazard function taking a form similar to the Cox PH model, with the extension that the baseline cumulative hazard function is raised to a power function. Our model allows for interaction between covariates and the baseline hazard and it also includes, for the two sample problem, the case of two Weibull distributions and two extreme value distributions differing in both scale and shape parameters. The partial likelihood approach can not be applied here to estimate the model parameters. We use the full likelihood approach via a cubic B-spline approximation for the baseline hazard to estimate the model parameters. A semi-automatic procedure for knot selection based on Akaike’s information criterion is developed. We illustrate the applicability of our approach using real-life data. 相似文献
25.
Mohsen Ebrahimi Moghaddam Mohammad Reza Bonyadi 《International journal of parallel programming》2012,40(2):225-257
Multiprocessor task scheduling is an important problem in parallel applications and distributed systems. In this way, solving
the multiprocessor task scheduling problem (MTSP) by heuristic, meta-heuristic, and hybrid algorithms have been proposed in literature. Although the problem has been addressed
by many researchers, challenges to improve the convergence speed and the reliability of methods for solving the problem are
still continued especially in the case that the communication cost is added to the problem frame work. In this paper, an Immune-based
Genetic algorithm (IGA), a meta-heuristic approach, with a new coding scheme is proposed to solve MTSP. It is shown that the proposed coding reduces the search space of MTSP in many practical problems, which effectively influences
the convergence speed of the optimization process. In addition to the reduced search space offered by the proposed coding
that eventuate in exploring better solutions at a shorter time frame, it guarantees the validity of solutions by using any
crossover and mutation operators. Furthermore, to overcome the regeneration phenomena in the proposed GA (generating similar
chromosomes) which leads to premature convergence, an affinity based approach inspired from Artificial Immune system is employed
which results in better exploration in the searching process. Experimental results showed that the proposed IGA surpasses related works in terms of found makespan (20% improvement in average) while it needs less iterations to find the
solutions (90% improvement in average) when it is applied to standard test benches. 相似文献
26.
Iradj Ebrahimi 《Forschung im Ingenieurwesen》1976,42(1):33-35
Zusammenfassung Die bisher bekannten Beziehungen zur Berechnung des axialen Geschwindigkeitsverlaufs in isothermen Luft-Freistrahlen gelten
nur für das Strahlende etwa im Gebiet von x/d>50, in dem die Reynoldszahl keinen Einflu? mehr auf den Geschwindigkeits-oder
Impulsabfall hat. In dem Gebiet4<x/d<50 nimmt das Verh?ltnis
mit wachsender Reynoldszahl bis zu einer Grenz-Reynoldszahl zu. Durch Definition einer axialen Halbwertl?nge x0,5 (x0,5=x bei
) wurde eine Beziehung gefunden, die den Einflu? der Reynoldszahl am Strahlanfang berücksichtigt.
Mitteilung aus dem Engler-Bunte-Institut, Bereich Feuerungstechnik, der Universit?t Karlsruhe (TH), Direktor des Instituts:
Prof. Dr.-Ing. R. Günther. 相似文献
27.
Uniaxial tensile studies concerning electrodeposited nanocrystalline face‐centered cubic Ni and Ni–Fe alloys are reported on p. 1969 by Ebrahimi and Li. The nanograined metals display a transition in the deformation mechanism at a critical grain size. The cover shows that their fracture surfaces exhibited a ductile‐to‐brittle transition from the “cup–cup” (intragranular, ductile failure, dislocation controlled) (top panels) to “cup–cone” (intergranular, brittle fracture, probably due to breaking of atomic bonds) (bottom panels) characteristics at room temperature across this critical grain size value. 相似文献
28.
Two bar-press experiments with rats tested the rule that reducing expectation of reward increases the variation from which reward selects. Experiment 1 used a discrete-trial random-interval schedule, with trials signaled by light or sound. One signal always ended with reward; the other signal ended with reward less often. The 2 signals were randomly mixed. Bar-press duration (how long the bar was held down) varied more during the signal with the lower probability of reward. Experiment 2 closely resembled Experiment 1 but used a random-ratio schedule rather than a random-interval schedule. Again, bar-press duration varied more during the signal with the lower probability of reward. The results support the rule--the first well-controlled comparisons to do so. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
29.
Ali Akbar Jamali Afshin Tavakoli Jafar Ezzati Nazhad Dolatabadi 《European Food Research and Technology》2012,235(3):367-373
Flavonoids play an important role in pharmaceutical and biomedical sciences. Various flavonoids, especially Morin, have potential to interact with DNA. Their prospective clinical and pharmacological utilities have attracted researchers?? attention in last two decades. Due to their interaction with DNA and their anticancer effects, a lot of investigations have been carried out all over the world. In this paper, we will review the properties of Morin and its different metal complexes as well as their interactions with DNA that have been reported by several research groups. Also, further details have been provided about binding mechanisms of these materials with DNA using analytical techniques such as UV?CVisible and fluorescence spectroscopies, viscosity and voltammetry. Structural analysis showed Morin binds to DNA through non-intercalation mode, but its metal complexes interact with DNA via intercalation mode and binding mode of Morin, and its metal complexes with DNA will be helpful in the determination of anticancer drugs binding mechanism to DNA. Therefore, it will be useful in new drug designs. 相似文献
30.