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951.
Emilie Calvié Lucile Joly-Pottuz Claude Esnouf Philippe Clément Vincent Garnier Jérôme Chevalier Yves Jorand Annie Malchère Thierry Epicier Karine Masenelli-Varlot 《Journal of the European Ceramic Society》2012,32(10):2067-2071
The behavior of alumina nano-particles taken from a commercial powder is investigated during in situ compression experiments in a transmission electron microscope (TEM). Small particles of 40 nm in diameter can undergo severe plastic deformation without failure, whereas brittle fracture is observed for 120 nm sized nano-particles. This is evidence of a critical size under which alumina, at least in the form of nano-particles, cannot be considered as brittle materials even at room temperature and a direct observation of the grinding limit generally observed during ball milling. 相似文献
952.
Sofia Benyahya Bernard Boutevin Sylvain Caillol Vincent Lapinte Jean‐Pierre Habas 《Polymer International》2012,61(6):918-925
Polyhydroxyurethanes (PHUs) produced by the reaction between dicyclocarbonate and diamine groups are often presented as possible candidates to substitute for classical polyurethanes based on isocyanate precursors. In the literature, the synthesis of this class of polymers is often performed according to arbitrary conditions of time and temperature without any scientific justification. As such, the real potential of PHUs is probably not fully known. Numerous contradictions in previously published results seem to support this hypothesis. Our paper proposes two methodologies based on dynamic rheometry to determine optimized conditions for the synthesis of PHUs. The case of a PHU formed by the reaction between 1,10‐diaminodecane and a dicyclocarbonate bearing a central aromatic group is described more precisely. The first approach consists of conducting various rheological experiments (kinetics, thermomechanical analyses) in situ on the reaction mixture. The second one retains the same technique to qualify the viscoelastic properties of PHUs synthesized according to various conditions. In this latter case, all samples show thermomechanical behaviour of amorphous thermoplastic polymers. But discrepancies are observed with regard to the value of the glass transition temperature and the existence or not of a rubbery zone. Comparison of these data with size exclusion chromatography results shows that these differences are direct consequences of the polymer molecular weight that can be predicted using macromolecular theory. The properties of the PHUs obtained after optimization of the polymerization reaction were compared with literature data in order to complete the evaluation of the efficiency of the rheological methodology. Copyright © 2012 Society of Chemical Industry 相似文献
953.
Vincent Dureau 《现代电视技术》2001,(6)
导言 数字电视基础设施日新月异,正迅速地从模拟电视过渡到数字电视。虽然数字传输仅在10年前才得以实现,但全球的数字接收机已超过5,000万台。卫星电视的数字化改造速度最快,有线电视也正在进行数字化改造。一些国 相似文献
954.
In fretting, without a lubricant, structures fail through wear involving debris. Various metallographic assessments show that this debris creation derives from a special structure, hereafter called the “tribologically transformed structure” (TTS). The latter is nucleated at the very beginning of a contact's life, and eventually masks the initial material's tribological behaviour. This TTS is very hard and brittle, and is quickly destroyed, which explains why TTS is rather difficult to observe. This study focuses on initiation mechanisms which, up to now, are still highly controversial. Large amounts of TTS are observed after fretting tests, which is the reason why they were chosen as the means of investigation. In this paper, the various possible creation mechanisms for TTS will be analysed. From this overview, two nucleation models are chosen: one is based on “mechanical alloying” considerations, and the other is linked to high-strain-recrystallisation phenomena. Transmission electron microscopy (TEM) investigations are used to check these assumptions. 相似文献
955.
Pyruvate-Kinase-Coupled Glycosyltransferase Assays: Limitations,Struggles and Problem Resolution 下载免费PDF全文
Huixiao Fu Prof. Weidong Pan Prof. Stéphane P. Vincent 《Chembiochem : a European journal of chemical biology》2017,18(21):2129-2136
Enzyme assays involving coupled pyruvate kinase (PK) have been used for many years to monitor the activity of major classes of enzymes including glycosyltransferases. Numerous potent inhibitors have been discovered and kinetically characterized thanks to this technology. However, when inhibitors of these important enzymes are screened, PK inhibitors or activators are very often observed. In this study we report solutions to resolve the problems encountered either during the screening or during the kinetic characterization of glycosyltransferase inhibitors by means of PK-coupled assays. The enzyme under study—WaaC—is an important glycosyltransferase involved in the bacterial lipopolysaccharide (LPS) biosynthesis pathway. Firstly we showed that alternative kinases such as nucleoside 5-diphosphate kinase (NDPK), myokinase (MK), and ADPdependent hexokinase that catalyze similar reactions to PK are prone to the same troubles. Moreover, an ADP chemosensor was used as an alternative but the sensitivity was not sufficient to allow a proper screening. Finally, we found that a stepwise PK/luciferase assay resolved the problems encountered with PK inhibitors and that a WaaC HPLC assay allowed the identification of WaaC inhibitors acting as PK activators, thus allowing false positive and false negative results linked to the coupling to PK to be eliminated. 相似文献
956.
957.
Ivan Lillamand Jean-François Chaix Marie-Aude Ploix Vincent Garnier 《NDT & E International》2010,43(8):655-660
This study deals with the general matter of non-destructive evaluation of pre-stressed structures in civil engineering. Usually such structures are composed of concrete and are steel reinforced. Proposed idea is the evaluation of mechanical stress state of a concrete body (instead of steel cables) via ultrasonic non-destructive evaluation (NDE), by using the link between ultrasonic velocities and mechanical stresses provided by the acoustoelasticity theory. Velocities of the ultrasonic waves (longitudinal and transversal with different polarizations) are observed during propagation through a concrete body submitted to uni-axial loading (compressive testing). Obvious variations in velocity are found depending on the mechanical stress state (e.g. Δc=92 m/s at σ=16 MPa for longitudinal waves). Thus acoustoelastic behavior of concrete is demonstrated. Further analyses provide acoustoelastic coefficients of concrete about ten times higher than the common ones of steel. The feasibility of stress evaluation using ultrasounds in concrete structures is proved under laboratory conditions. 相似文献
958.
959.
960.
L. Gerrer M. Rafik G. Ribes G. Ghibaudo E. Vincent 《Microelectronics Reliability》2010,50(9-11):1259-1262
Several simplifications on MOSFET compact model for oxide breakdown degradation are presented. The current partitioning coefficient is systematically investigated, including influence of drain voltage and increasing breakdown strength. It reveals that several conduction paths are formed during breakdown and that the reduction of channel conductance is the dominant phenomenon at operating voltages. Based on these observations, a new physically based compact model including soft breakdown (SBD) is proposed. KW: soft breakdown, characterization, modeling, reliability. 相似文献