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991.
M. Isabel Burguete Eduardo García-Verdugo Ignacio Garcia-Villar Fabien Gelat Peter Licence Santiago V. Luis Victor Sans 《Journal of Catalysis》2010,269(1):150-160
New polymeric materials containing functional sites analogous to ionic liquids have been synthesized. Those materials are a supported reservoir for the active Pd species. Their catalytic activity has been evaluated for the Heck reaction proving an excellent performance in terms of both activity and recyclability. Although soluble Pd species seem to participate in the catalytic cycle, as for many other supported Pd-systems, the g-SILLPs present the ability to efficiently release and recapture those soluble species. This allows to dramatically reduce or eliminate the amount of Pd leached to the final solution, in particular at higher temperatures, and opens the way, based on a release and catch strategy, for the development of active-supported Pd catalytic systems, easily recoverable and reusable for a large number of catalytic cycles. The exact nature of the polymer (SILLPs) has a remarkable influence on the overall process. The appropriate design of the g-SILLPs is a key factor for the optimization of the release and catch system. The functionalized polymers prepared can be reused for a significant number of catalytic cycles without any loss in performance. 相似文献
992.
993.
Victor Zamora Angel L. Ortiz Fernando Guiberteau Mats Nygren 《Journal of the European Ceramic Society》2012,32(10):2529-2536
We have explored the feasibility of reducing the spark-plasma-sintering (SPS) temperature of additive-free ZrB2 ultra-high-temperature ceramics (UHTCs) via crystal size refinement of the starting powder down to the low nanoscale. We found that under otherwise the same SPS conditions (75 MPa pressure, and 100 °C/min heating ramp) nanoscale ZrB2 can be densified at temperatures about 450 °C lower than for the typical micrometre and submicrometre ZrB2 powders, and at least 250 °C below the ultra-fine powder temperature. Furthermore, the nanoscale crystal refinement also promotes the production of fine-grained ZrB2 UHTCs. We also found that elimination of the B2O3 impurities plays an important role in the complete densification. The unequalled sinterability of the nanoscale ZrB2 powders highlights the need to use high-energy ball-milling for the comminution of the typical commercially available ZrB2 powders. 相似文献
994.
995.
The formal specification component of verification can be exported to simulation through the idea of property checkers. The
essence of this approach is the automatic construction of an observer from the specification in the form of a program that
can be interfaced with a simulator and alert the user if the property is violated by a simulation trace. Although not complete,
this lighter approach to formal verification has been effectively used in software and digital hardware to detect errors.
Recently, the idea of property checkers has been extended to analog and mixed-signal systems. 相似文献
996.
We report the observation of the electromechanical self-oscillations excited in a vacuum diode with a field emission cathode made of single-wall carbon nanotubes. The mechanical oscillations of the cathode accompanied by the periodic variations of the emission current intensity have been observed under the action of a constant voltage applied between the cathode and the anode of the diode. An empirical model of the phenomenon is proposed. It provides a qualitative agreement of the experimental results and the theoretical predictions. The modeling assuming a common behavior of the electromechanical systems with nano-sized mechanically flexible field emitters has been performed. It has demonstrated a dependence of the oscillation frequency value on the geometrical size of flexible emitters and on the value of voltage applied. This phenomenon opens a way for generation of the high frequency electromagnetic waves by using the electromechanical systems with emitters of nanometer size. 相似文献
997.
998.
Andrew Yakimov Victor Kirienko Vyacheslav Timofeev Aleksei Bloshkin Anatolii Dvurechenskii 《Nanoscale research letters》2014,9(1):504
We study the effect of delta-doping on the hole capture probability in ten-period p-type Ge quantum dot photodetectors. The boron concentration in the delta-doping layers is varied by either passivation of a sample in a hydrogen plasma or by direct doping during the molecular beam epitaxy. The devices with a lower doping density is found to exhibit a lower capture probability and a higher photoconductive gain. The most pronounced change in the trapping characteristics upon doping is observed at a negative bias polarity when the photoexcited holes move toward the δ-doping plane. The latter result implies that the δ-doping layers are directly involved in the processes of hole capture by the quantum dots. 相似文献
999.
Oral Absorption and Disposition of alpha‐Linolenic,Rumenic and Vaccenic Acids After Administration as a Naturally Enriched Goat Dairy Fat to Rats
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Luís Miguel Rodríguez‐Alcalá Irma Ares Javier Fontecha Manuela Juarez Victor Castellano María Rosa Martínez‐Larrañaga Arturo Anadón María Aránzazu Martínez 《Lipids》2015,50(7):659-666
Although there is extensive information describing the positive biological effects of conjugated linoleic acid and its main isomer rumenic acid (RA; C18:2 cis 9, trans 11), and alpha‐linolenic acid (ALA) and vaccenic acid (TVA), data about their bioavailability are not available. In this work, we investigated the oral absorption and disposition of these fatty acids in Wistar rats. A naturally enriched goat dairy fat (EDF) was obtained by supplementing ruminant diets with oils or oilseeds rich in polyunsaturated fatty acids (PUFA). The EDF was administered orally (single dose of 3000 mg EDF/kg body weight equivalent to 153 mg TVA/kg body weight, 46 mg RA/kg body weight and 31 mg ALA/kg body weight), and serial blood and liver samples were collected and TVA, RA and ALA concentrations determined by GC/MS. The fatty acids TVA, RA and ALA were rapidly absorbed (t1/2a, 0.36, 0.66 and 0.76 h, respectively, for plasma) and slowly eliminated (t1/2β, 17.04, 18.40 and 16.52 h, respectively, for plasma). The maximum concentration (Cmax) was detected in liver > plasma > erythrocyte. Our study shows that when orally administered EDF, its components TVA, RA and ALA were rapidly absorbed and distributed throughout the body by the blood circulation to exert systemic effects. 相似文献
1000.
Phase Transformation in Ca3(PO4)2:Eu2+ via the Controlled Quenching and Increased Eu2+ Content: Identification of New Cyan‐Emitting α‐Ca3(PO4)2:Eu2+ Phosphor
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Haipeng Ji Zhaohui Huang Zhiguo Xia Maxim S. Molokeev Mingyue Chen Victor V. Atuchin Minghao Fang Yan'gai Liu Xiaowen Wu 《Journal of the American Ceramic Society》2015,98(10):3280-3284
A case of phosphor is reported where the cooling rate parameter significantly influences the luminescence property. By quenching the sample after the high‐temperature solid‐state reaction at 1250°C, we successfully prepared the Eu2+‐doped α form Ca3(PO4)2 (α‐TCP:Eu2+) as a new kind of bright cyan‐emitting phosphor. The unusual emission color variation (from cyan to blue) depends on the cooling rate after sintering and Eu2+ doping level as it was observed in the TCP‐based phosphors. By the Rietveld analysis, it is revealed that the cyan‐ and blue‐emitting phosphors are two different TCP forms crystallizing in the monoclinic (space group P21/a, α‐TCP) and the rhombohedral structure (space group R3c, β‐TCP), respectively. Upon 365 nm UV light excitation, α‐TCP:Eu2+ exhibits an asymmetric broad‐band cyan emission peaking at 480 nm, while β‐TCP:Eu2+ displays a relatively narrow‐band blue emission peaking at 416 nm. The Eu2+‐doping in Ca3(PO4)2 shifts the upper temperature limit of the stable structural range of β form from 1125°C to ≥1250°C. Moreover, the crystal structures of α/β‐TCP:Eu2+ were compared in the aspects of compactness and cation site sets. The emission thermal stability of α/β‐TCP:Eu2+ was comparatively characterized and the difference was related to the specific host structural features. 相似文献