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排序方式: 共有660条查询结果,搜索用时 15 毫秒
621.
In this paper, we propose and experimentally demonstrate a simple, cost-effective hybrid gigabit fiber-wireless system for in-building wireless access. Simplicity and cost-effectiveness are achieved in all parts of the system by utilizing direct laser modulation, optical frequency up-conversion, combined single mode/multimode fiber transmission and envelope detection. Error-free transmission of 2-Gbps data in 60-GHz band over a composite channel including 10-km standard single-mode fiber (SSMF)/1-km multimode fiber (MMF) and 6.5-m air transmission was successfully achieved.  相似文献   
622.
For more than two decades, an extensive scientific effort has been underway to determine whether Yucca Mountain, Nevada, is a suitable site for a deep underground repository for spent nuclear fuel and high-level radioactive waste. Even though the geologic site is stable, additional engineered barriers are planned, including waste packages, drip shields, and tunnel inverts that will be within the emplacement tunnels. Research is under way into the best materials for corrosion prevention in those engineered barriers to ensure their long-term mechanical integrity.  相似文献   
623.
ABSTRACT: The localized irradiation of Si allows a precise patterning at the microscale of nanostructured materials such as porous silicon (PS). PS patterns with precisely defined geometries can be fabricated by using ion stopping masks. The nanoscale textured micro patterns were used to explore their influence as microenviroments for human mesenchymal stem cells (hMSCs). In fact, the change of photoluminescence emission from PS upon aging in physiological solution suggests the intense formation of silanol surface groups, which may play a relevant role in ulterior cell adhesion. The experimental results show that hMSCs are sensitive to the surface micropatterns. In this regard, preliminary -catenin labeling studies reveal the formation of cell-cell interaction structures, while microtubule orientation is strongly influenced by the selective adhesion conditions. Relevantly, Ki67 assays support a proliferative state of hMSCs on such nanostructured micropatterns comparable to that of standard cell culture platforms, which reinforces the candidature of porous silicon micropatterns to become a conditioning structure for in-vitro culture of hMSCs.  相似文献   
624.
PURPOSE: To compare the initial comfort afforded by silicone hydrogel lenses (lotrafilcon A) versus the comfort afforded by conventional hydrogel lenses (etafilcon A) in extended wear (EW). DESIGN: Prospective, double-masked and randomized controlled trial. METHODS: Lotrafilcon A and etafilcon A contact lenses were eye randomly fitted on an EW basis for 7 days and nights in 20 subjects. A forced-choice subject preference questionnaire was made. Subjects were comfort, dryness, red eye and visual quality after night wear and at the end of the day. Subjective scored satisfaction (scale: 1-5) and lens preference were assessed. RESULTS: Lotrafilcon A proved more comfortable after night wear (60%, CI95% 38-82%) and at the end of the day (70%, CI95% 49-90%) than etafilcon A after night wear (10%, CI95% 0-23%, P<0.05) and at the end of the day (20%, CI95% 2-38%, P<0.05). The feeling of dryness was more marked with etafilcon A after night wear (50%, CI95% 27-72%) and at the end of the day (50%, CI95% 27-72%) than it was with lotrafilcon A (15%, CI95% 0%-31%) after night wear (P>0.05) and at the end of the day (25%, CI95% 5%-44%, P<0.05). General satisfaction with the lotrafilcon A lens was 3.65 points (CI95% 3-4.2) and with etafilcon A 2.95 points (CI95% 2.5-3.3, P<0.05). Eighty percent (CI95% 62%-98%) of subjects preferred lotrafilcon A (P<0.05) for EW. CONCLUSIONS: In EW, lotrafilcon A contact lenses were more comfortable and led to less dryness after night wear and at the end of the day than etafilcon A contact lenses.  相似文献   
625.
Amit Kumar  Raul F. Lobo  Norman J. Wagner   《Carbon》2005,43(15):3099-3111
An algorithm has been developed to create structural models for amorphous carbons using Monte Carlo simulations in the canonical ensemble. The simulation method used follows the experimental preparation of nanoporous carbons (NPC) by pyrolysis from polyfurfuryl alcohol as a guideline. The resulting structure exhibits properties that compare favorably to those observed experimentally for real NPCs. These atomistic NPC models are approaching a realistic representation of NPCs used for gas separations and as such, are being used to study the diffusion of small gas molecules in these materials. Limitations of the method and possible improvements are discussed.  相似文献   
626.
High-capacity transmission over polymer optical fiber   总被引:6,自引:0,他引:6  
Polymer optical fiber (POF) is a promising transmission medium to provide broad-band telecommunication services within the customer's premises. POF offers several attractive features for data transmission such as broad bandwidth and low cost for in-house, access, and local-area-network (LAN) applications. This paper presents a review on optical transmission systems using POF and their enabling technologies. A summary is given of experimental data links with record capacity over record transmission distances. To conclude, we discuss trends for further development and research  相似文献   
627.
We outline a novel method for all-optical envelope detection of wireless signals by exploiting cross-gain modulation effects in a distributed feedback laser operating with optical injection. We successfully demonstrate envelope detection of a 20-GHz carrier amplitude-shift-keying modulated signal at 2.5 Gb/s and its transmission over a 70-km optical fiber link. We present results including bit-error-rate measurements, signal waveforms, and receiver sensitivity penalties associated with envelope detection and fiber transmission.  相似文献   
628.
Palladium particles were generated by reduction of palladate anions bound to an ion exchange resin inside microreactors. The size and distribution of the palladium particles differed substantially depending on the degree of cross‐linking and the density of ion exchange sites on the polymer/glass composites, the latter parameter having a larger influence than the former. The polymer phase of the composite materials was used for the loading with clusters composed of palladium particles which are 1 to 10 nm in diameter. The reactivity and stability of six different palladium‐doped polymer/glass composite samples for transfer hydrogenations was investigated both under conventional and microwave heating in the batch mode as well as under continuous flow conditions using the cyclohexene‐promoted transfer hydrogenation of ethyl cinnamate as a model reaction. Regarding the heating method it was found that catalysts that are composed of larger metal particles perform better under microwave irradiating conditions whereas samples with smaller particle sizes perform better under conventional heating. Comparing batch experiments with flow‐through experiments the latter technique gives better conversion. Reusability was better in microwave heated experiments than in traditional heating.  相似文献   
629.
We develop a robust and fully unsupervised algorithm for the detection of action potentials from extracellularly recorded data. Using the continuous wavelet transform allied to probabilistic mixture models and Bayesian probability theory, the detection of action potentials is posed as a model selection problem. Our technique provides a robust performance over a wide range of simulated conditions, and compares favorably to selected supervised and unsupervised detection techniques.  相似文献   
630.
Electrical impedance tomography is a technique to estimate the impedance distribution within a domain, based on measurements on its boundary. In other words, given the mathematical model of the domain, its geometry and boundary conditions, a nonlinear inverse problem of estimating the electric impedance distribution can be solved. Several impedance estimation algorithms have been proposed to solve this problem. In this paper, we present a three-dimensional algorithm, based on the topology optimization method, as an alternative. A sequence of linear programming problems, allowing for constraints, is solved utilizing this method. In each iteration, the finite element method provides the electric potential field within the model of the domain. An electrode model is also proposed (thus, increasing the accuracy of the finite element results). The algorithm is tested using numerically simulated data and also experimental data, and absolute resistivity values are obtained. These results, corresponding to phantoms with two different conductive materials, exhibit relatively well-defined boundaries between them, and show that this is a practical and potentially useful technique to be applied to monitor lung aeration, including the possibility of imaging a pneumothorax.  相似文献   
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