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991.
Methyl ethyl ketone peroxide (MEKPO) is a typical organic peroxide with thermally unstable nature that has been broadly employed in the manufacturing process of acrylic resins, as a hardening agent for fiberglass-reinforced plastics, and as a curing agent for unsaturated polyester resins. The aim of this study was to identify the characteristics of MEKPO 31 wt.% while mixing with contaminants, such as H(2)SO(4), HCl, and NaCl under runaway conditions. To acquire the thermal runaway data, DSC and a simulation were used for thermal analysis. The results showed that the thermal decomposition of MEKPO and MEKPO+H(2)SO(4) follows two stages. The first one can be modeled by using an empirical nth order rate equation. The second stage can be modeled as autocatalytic. MEKPO+HCl and MEKPO+NaCl included two independent autocatalytic reactions. The decomposition of MEKPO in the presence of Cl- ions (added in MEKPO either in the form of HCl or NaCl) follows a significantly different path, an earlier decomposition "onset" temperature, higher amount of generated thermal power and smaller temperature of no return (T(NR)) and time to maximum rate (TMR) values. Simulations based on experimental data indicated that the effect of H(2)SO(4) was the most dangerous contaminant on MEKPO 31 wt.%. However, the impact of Cl ions was also important. It is therefore recommended that the means of fire fighting employed for this substance to be free of Cl-. 相似文献
992.
Campanella L Magrì AL Tomassetti M Rossi V Vecchio S 《Drug development and industrial pharmacy》2007,33(8):830-840
In this paper our previous researches dealing with compatibility, thermoanalytical characterization, the kinetics of thermal degradation of acetaminophen, either pure or contained in some commercial pharmaceutical formulations, have found applications outlets. In a previous investigation the possible interactions between acetaminophen and four excipients contained in the commercial pharmaceutical formulations were tested. As a continuation of this research in the present study an analytical method based on differential scanning calorimetry (DSC) was applied to determine the acetaminophen content of four commercial pharmaceutical formulations. For a fifth drug it was shown that the method is not applicable owing to observed incompatibility with one of the excipients. Finally, the analytical results obtained were compared with those derived from two UV spectrophotometric methods (one, i.e., “direct method,” recommended by the Pharmacopeia and the other based on the first-order derivative UV spectra). 相似文献
993.
Wei L Li J Guo L Nie S Pan W Sun P Liu H 《Drug development and industrial pharmacy》2007,33(9):990-998
Carvedilol has been made into a novel osmotic pump tablet which includes Gelucire 44/14, Lutrol F68, Transcutol P, silicon dioxide, mannitol, citric acid, and sodium hydrogen carbonate. The Self-emulsifying osmotic pump tablet (SEOPT) has two outstanding features. It could improve the bioavailability of carvedilol by self-emulsifying drug delivery system (SEDDS), control the release rate and make the plasma concentrations more stable by elementary osmotic pump tablet. The results of transmission electron microscope (TEM) and particle size assessment showed that the shape of the resultant emulsion was round and regular, the average diameter of the particles was 246 nm. Since the solubility of carvedilol was improved by the emulsion, the elementary SEOPT could guarantee a complete release of carvedilol under the osmotic pressure of mannitol. The cumulative release at 12 hr was 85.18%. Therefore the disadvantage that lipophilic drugs can not be released completely when prepared into elementary osmotic pump tablet was resolved. The results of Differential scanning calorimetry (DSC), Infrared spectroscopy (IR) and X-ray diffraction diffraction (XRD) proved that carvedilol was amorphous in the preparation. The relative bioavailability of carvedilol in beagle dogs was 156.78%. The plasma concentrations were more stable compared with that of commercially available tablet (Luode®). And the in vitro and in vivo correlation was good (r = 0.9725). Therefore, the elementary SEOPT developed in this paper might provide a new idea for preparing lipophilic drugs into osmotic pump tablet conveniently. 相似文献
994.
S. Pérez-Díaz J. R. Sendra C. Villarino 《Applicable Algebra in Engineering, Communication and Computing》2007,18(1-2):91-105
We present an algorithm with the following characteristics: given a real non-polynomial rational parametrization of a plane curve and a tolerance , is decomposed as union of finitely many intervals, and for each interval I of the partition, with the exception of some isolating intervals, the algorithm generates a polynomial parametrization . Moreover, as an option, one may also input a natural number N and then the algorithm returns polynomial parametrizations with degrees smaller or equal to N. In addition, we present an error analysis where we prove that the curve piece is in the offset region of at distance at most , and conversely.
Authors partially supported by the Spanish “Ministerio de Educación y Ciencia” under the Project MTM2005-08690-C02-01, and
by the “Dirección General de Universidades de la Consejería de Educación de la CAM y la Universidad de Alcalá” under the project
CAM-UAH2005/053. 相似文献
995.
Fethallah Benmansour Laurent D. Cohen 《Journal of Mathematical Imaging and Vision》2009,33(2):209-221
In this paper, we present a new method for segmenting closed contours and surfaces. Our work builds on a variant of the minimal
path approach. First, an initial point on the desired contour is chosen by the user. Next, new keypoints are detected automatically
using a front propagation approach. We assume that the desired object has a closed boundary. This a-priori knowledge on the
topology is used to devise a relevant criterion for stopping the keypoint detection and front propagation. The final domain
visited by the front will yield a band surrounding the object of interest. Linking pairs of neighboring keypoints with minimal
paths allows us to extract a closed contour from a 2D image. This approach can also be used for finding an open curve giving
extra information as stopping criteria. Detection of a variety of objects on real images is demonstrated. Using a similar
idea, we can extract networks of minimal paths from a 3D image called Geodesic Meshing. The proposed method is applied to
3D data with promising results.
相似文献
Laurent D. CohenEmail: |
996.
S.K. Rakshit S.C. Parida S. Dash Z. Singh R. Prasad V. Venugopal 《Materials Research Bulletin》2005,40(2):323-332
The citrate-nitrate gel combustion route was used to prepare SrFe12O19(s) powder sample and the compound was characterized by X-ray diffraction analysis. A solid-state electrochemical cell of the type: (−)Pt, O2(g)/{CaO(s) + CaF2(s)}//CaF2(s)//{SrFe12O19(s) + SrF2(s) + Fe2O3(s)}/O2(g), Pt(+) was used for the measurement of emf as a function of temperature from 984 to 1151 K. The standard molar Gibbs energy of formation of SrFe12O19(s) was calculated as a function of temperature from the emf data and is given by: (SrFe12O19, s, T)/kJ mol−1 (±1.3) = −5453.5 + 1.5267 × (T/K). Standard molar heat capacity of SrFe12O19(s) was determined in two different temperature ranges 130-325 K and 310-820 K using a heat flux type differential scanning calorimeter (DSC). A heat capacity anomaly was observed at 732 K, which has been attributed to the magnetic order-disorder transition from ferrimagnetic state to paramagnetic state. The standard molar enthalpy of formation, (298.15 K) and the standard molar entropy, (298.15 K) of SrFe12O19(s) were calculated by second law method and the values are −5545.2 kJ mol−1 and 633.1 J K−1 mol−1, respectively. 相似文献
997.
We present a prediction (estimation, calculation, screening) method for the estimation of the self-accelerating decomposition temperature (SADT) for liquid organic peroxides from differential scanning calorimetry (DSC) measurements based on the concepts of thermal explosion theory originally introduced by Semonov which are adopted to our problem assuming nth-order reaction kinetics. For the peroxides under investigation, we demonstrate good agreement with the experimental SADT. This method can be used as a quick and easy applicable method for the estimation of the critical temperatures. 相似文献
998.
999.
A. A. Agrachev N. N. Chtcherbakova I. Zelenko 《Journal of Dynamical and Control Systems》2005,11(3):297-327
Pairs (Hamiltonian system, Lagrangian distribution) called dynamical Lagrangian distributions, appear naturally in differential geometry, calculus of variations, and rational mechanics. The basic differential invariants
of a dynamical Lagrangian distribution with respect to the action of the group of symplectomorphisms of the ambient symplectic
manifold are the curvature operator and curvature form. These invariants can be considered as generalizations of the classical curvature tensor in Riemannian geometry. In particular,
in terms of these invariants one can localize the focal points along extremals of the corresponding variational problems.
In the present paper we study the behavior of the curvature operator, the curvature form, and the focal points of a dynamical
Lagrangian distribution after its reduction by arbitrary first integrals in involution. An interesting phenomenon is that
the curvature form of so-called monotone increasing Lagrangian dynamical distributions, which appear naturally in mechanical
systems, does not decrease after reduction. It also turns out that the set of focal points to the given point with respect
to the monotone increasing dynamical Lagrangian distribution and the corresponding set of focal points with respect to its
reduction by one integral are alternating sets on the corresponding integral curve of the Hamiltonian system of the considered
dynamical distributions. Moreover, the first focal point corresponding to the reduced Lagrangian distribution comes before
any focal point related to the original dynamical distribution. We illustrate our results on the classical N-body problem.
2000 Mathematics Subject Classification. 37J15, 37J05, 53D20. 相似文献
1000.
高分辨率超声Lamb波频散曲线测量与板厚估计 总被引:1,自引:1,他引:0
许凯亮张正罡刘丹他得安胡波 《数据采集与处理》2017,32(2):286-292
超声Lamb波在工业无损检测与
评价中具有广阔的应用前景。但受制于超声导波多模式频散与混叠的影响,如何实现高分辨率超声导波的模式分离与频散曲线提取,进而定量分析材料的健康状况一直是研究的热点与难点。本文旨在将现代信号处理中广泛采用的谱估计技术应用于超声Lamb波阵列信号分析,并通过提取频散曲线定量测量板厚度。以经典参数谱估计法中的Yule-Walker法与Burg法为例,实验测量和分析了3 mm,4 mm和 5 mm厚铝板中的宽带多模式Lamb波信号,准确地提取了铝板中的宽带Lamb波频散曲线,并比较了两种经典谱估计方法与二维傅氏变换法的性能,最终实现了铝板厚度估计。 相似文献