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951.
952.
Nucleation of solidification in liquid droplets 总被引:2,自引:0,他引:2
Analytical and numerical methods have been developed to analyze the solidification kinetics of a mass of liquid droplets dispersed
in a fluid or solid matrix using classical nucleation theory. The resulting analytical expressions and numerical calculations
can be compared directly with calorimetric measurements of the droplet solidification exotherms to obtain information about
the nucleation mechanism. With increasing contact angle at the solid-liquid-matrix triple point, the solidification onset,
peak, and end temperatures and exothermic peak height all decrease sharply and the droplet solidification exotherms become
broader. Decreasing either the droplet radius or the number of potential catalytic nucleation sites produces a similar but
smaller effect. Distributions in droplet radius, contact angle, and nucleation sites have no effect on the solidification
peak temperature, but the droplet solidification exotherms become broader and more symmetric. The solidification onset temperature
is independent of cooling rate in the calorimeter, but the solidification peak and end temperatures decrease and the exothermic
peak height increases with increasing cooling rate. Predicted droplet solidification exotherms are in excellent agreement
with detailed experimental measurements on 10-nm-radius Cd droplets embedded in a solid Al matrix. Analytical predictions
give best-fit values of 43 deg and 430 for the contact angle and the number of potential catalytic nucleation sites per droplet,
respectively; numerical predictions give best-fit values of 43 deg and 750 for the contact angle and the number of potential
catalytic nucleation sites per droplet, respectively. 相似文献
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39 3–6 mo old male Long-Evans rats were trained in a discrete-trial forward autoshaping paradigm to touch an extended lever to earn food pellets. Reinforcement was delivered either simultaneously with or 6 sec after lever retraction, which occurred either noncontingently after 15 sec or when the Ss touched the lever. Treatment with subcutaneous des-glycinamide arginine vasopressin (DGAVP [15 μg/kg]) 1 hr before sessions increased the rate of acquisition of the extended-lever-touch response and also facilitated development of intertrial (adjunctive) nose poking. The effects of the peptide were more robust in the more difficult delayed reinforcement task. Results are consistent with previous findings that DGAVP lacks the classical peripheral activity of vasopressin. In both experiments, peptide treatment was terminated before asymptotic levels of performance were attained; the continued facilitation of acquisition in treated groups suggests a specific enhancement of learning and/or enhanced memory retrieval. (22 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
959.
Heat shock induces thermotolerance and inhibition of lysis in a lysogenic strain of Lactococcus lactis. 总被引:1,自引:0,他引:1
P Boutibonnes B Gillot Y Auffray B Thammavongs 《International journal of food microbiology》1991,14(1):1-9
In this preliminary work, the heat shock response of lactic acid bacteria was investigated and characterized. Log-phase Lactococcus lactis cells pre-incubated at 40 degrees C before heat challenge at 52 degrees C for 30 min demonstrated increased thermotolerance as compared with cells pre-incubated at 30 degrees C. The response persisted for at least 60 min. Additionally, we demonstrated that: (i) the physiological expression of the heat shock response is temperature dependent; (ii) ethanol 4.0% (v/v) caused, to a lesser extent, a response similar to the heat shock; and (iii) hydrogen peroxide failed to induce a detectable response. Furthermore, we suggest that the induction of the heat shock response increases the resistance of a lysogenic strain of L. lactis, treated by mitomycin C (1.25 micrograms/ml), to lysis by the bacteriophage. 相似文献
960.
Equalization with oversampling in multiuser CDMA systems 总被引:2,自引:0,他引:2
Some of the major challenges in the design of new-generation wireless mobile systems are the suppression of multiuser interference (MUI) and inter-symbol interference (ISI) within a single user created by the multipath propagation. Both of these problems were addressed successfully in a recent design of A Mutually Orthogonal Usercode-Receiver (AMOUR) for asynchronous or quasisynchronous code division multiple access (CDMA) systems. AMOUR converts a multiuser CDMA system into parallel single-user systems regardless of the multipath and guarantees ISI mitigation, irrespective of the channel locations. However, the noise amplification at the receiver can be significant in some multipath channels. In this paper, we propose to oversample the received signal as a way of improving the performance of AMOUR systems. We design Fractionally Spaced AMOUR (FSAMOUR) receivers with integral and rational amounts of oversampling and compare their performance with the conventional method. An important point that is often overlooked in the design of zero-forcing channel equalizers is that sometimes, they are not unique. This becomes especially significant in multiuser applications where, as we will show, the nonuniqueness is practically guaranteed. We exploit this flexibility in the design of AMOUR and FSAMOUR receivers and achieve noticeable improvements in performance. 相似文献