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81.
Won Seok Lyoo Han Do Ghim Hee‐Sam Kim Joon Ho Kim Sam Soo Kim Won Sik Yoon Jinwon Lee Sang‐Seob Lee 《应用聚合物科学杂志》2002,86(14):3667-3672
N‐Vinylcarbazole (VCZ) was solution‐polymerized in tetrahydrofuran (THF) at ?20, 0, and 20°C using the photoinitiation method; the effects of the amount of solvent, polymerization temperature, and photoinitiator concentration were investigated. On the whole, the experimental results corresponded to predicted ones. Low polymerization temperature using photoinitiation proved to be successful in obtaining poly(N‐vinylcarbazole) (PVCZ) of a high molecular weight with a smaller temperature rise during polymerization; nevertheless of free radical polymerization by 2,2′‐azobis(2,4‐dimethylvaleronitrile) (ADMVN). The photo‐solution polymerization rate of VCZ in THF was proportional to the 0.47 power of ADMVN concentration. The molecular weight was higher and the molecular weight distribution was narrower with PVCZ polymerized at lower temperatures. For PVCZ prepared in THF at ?20°C using a photoinitiator concentration of 0.00005 mol/mol of VCZ, a weight‐average molecular weight of 510,000 was obtained, with a polydispersity index of 1.73, and a degree of lightness converged to about 99%. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 3667–3672, 2002 相似文献
82.
All experiments of pressure fluctuations were carried out in a bubble column with a moderately large column of 0.376 m ID.
The recently developed technique of wavelet packet transform based on localized wavelet functions is applicable to analysis
of the fluctuating signals. The time series of pressure fluctuation signals have been analyzed by means of wavelet packet
transform components, decomposition through best basis algorithm and timefrequency representation. By resorting to this technique,
the objects in bubbly flow regime have fine scales and frequencies than ones in churn-turbulent flow regime. Thus, this wavelet
packet transform method enables us to obtain the frequency content of local complex flow behaviors in a bubble column. 相似文献
83.
We prepared poly(p‐phenylene pyromellitimide) (PMDA–PDA), poly(p‐phenylene 4,4′‐hexafluoroisopropylidene diphthalimide), and their copolyimides with various compositions to explore the relationship between the water sorption and structure. The water sorption behaviors were gravimetrically investigated as a function of composition and temperature and interpreted with a Fickian diffusion model in films. Overall, the water sorption behaviors were strongly dependent on the changes in morphological structure, which originated from the variations in composition. When the content of the bulky hexafluoroisopropylidene group (6FDA) was increased, the water uptake decreased from 5.80 to 3.18 wt %, whereas the diffusion coefficient increased from 3.6 × 10?10 to 11.3 × 10?10 cm2/s. The relatively high water uptake in the PMDA–PDA polyimide film was successfully healed by the incorporation of 6FDA, which may have resulted from the increases in the intermolecular packing order and hydrophobicity. The degree of orientation and crystallinity, which are in‐plane characteristics, were directly correlated to the diffusion coefficient and activation energy in the polyimide film. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3442–3446, 2003 相似文献
84.
Sang?Sung?Lee Soo?Chool?Lee Jae?Chang?KimEmail author 《Korean Journal of Chemical Engineering》2002,19(3):406-410
O-alkylation reaction of hydroquinone with excess methanol was performed by using alkali metal ion-exchanged zeolite catalysts
in a slurry type reactor to substitute the solid zeolite catalysts for the homogeneous liquid phase catalysts. This was also
done to produce selectively mono-alkylated 4-methoxyphenol, a valuable intermediate for the perfume, flavor, food and photo
industries. The effects of the basicity of various zeolites and reaction conditions such as temperature, reaction time and
the amount of catalyst on the catalytic activity and selectivity were tested to maximize the yield of 4-methoxyphenol. Thus
far, 84% selectivity at 95% conversion of hydroquinone was obtained at the optimum reaction conditions (240 ‡C, reaction with
0.6 g catalyst for 16 h), which was thought to result from the strong basic property and shape selectivity of the Cs ion-exchanged
NaX zeolite. 相似文献
85.
The hydrodynamic and gas mixing characteristics have been determined in a FCC regenerator (0.48 m I.D.x3.4 m high) with FCC
particles. Solids holdup in the dense bed decreases with increasing gas velocity, but it increases in the freeboard region.
The bubble/void fraction increases with an increase along the bed height at a given gas velocity and increases with increasing
gas velocity at a constant bed height. Backmixed tracer gas at the wall region is higher than that at the center region of
the bed. The gas backmixing coefficient decreases with increasing gas velocity. 相似文献
86.
Stormer-numerov approximation for numerical solutions of ordinary and partial differential equations
Stormer-Numerov approximations of high accuracy were developed for solutions of non-linear boundary value problems and nonlinear
elliptic partial differential equations. The approximations can be easily adopted also for parabolic partial differential
equations in one and more space dimensions and feature fourth-order accuracy. For boundary value problems only three nodes
are necessary to obtain the desired fourth order accuracy. The finite difference formula for parabolic partial differential
equations can be readily generalized to a nonequidistant mesh so that automatic regridding in space may be used. The Stomer-Numerov
approximations are important for solution of problems where storage limitations and computer time expenditure preclude standard
second order methods. Because of the fourth order approximations a low number of mesh points can be used for a majority of
chemical engineering problems. The application of Stormer-Numerov approximations is illustrated on a number of examples. 相似文献
87.
88.
The effects of reaction temperature, pressure and residence time were investigated with a flow apparatus. Cellobiose decomposition
kinetics and products in suband supercritical water were examined at temperatures from 320 to 420 °C at pressures from 25
to 40 MPa, and at residence times within 3 sec. Cellobiose was found to decompose via hydrolysis and pyrolysis. The yield
of desired hydrolysis product, glucose, was the maximum value of 36.8% at 320 °C, 35 MPa, but the amount of 5-(hydroxymethyl)furfural
(HMF), fermentation inhibitor increased too because residence time increased in the subcritical region owing to decrease of
reaction rate. Meanwhile, though the yield of glucose is low in the supercritical region, the yield of HMF decreased compared
with the subcritical region; and at the minimum yield of HMF (380 °C, 25 MPa), the yield of glucose was 21.4%. The decomposition
of cellobiose followed first-order kinetics and the activation energy for the decomposition of cellobiose was 51.05 kJ/mol
at 40MPa. 相似文献
89.
Electrochemical cell current requirements for toxic organic waste destruction in Ce(IV)-mediated electrochemical oxidation process 总被引:1,自引:0,他引:1
Vasily V. Kokovkin Sang Joon Chung Subramanian Balaji Manickam Matheswaran Il-Shik Moon 《Korean Journal of Chemical Engineering》2007,24(5):749-756
The electrochemical cell for cerium oxidation and reactor for organic destruction are the most important operation units for
the successful working mediated electrochemical oxidation (MEO) process. In this study, electrochemical cells with DSA electrodes
of two types, single stack and double stack connected in series, were used. The performances towards the electrochemical generation
of Ce(IV) in nitric acid media at 80 °C were studied. The current-voltage curves and cerium electrolysis kinetics showed the
dependence on number of cell stacks needed to be connected in series for the destruction of a given quantity of organic pollutant.
The presence of an optimum region for Ce(III) oxidation with a contribution of oxygen evolution, especially at low Ce(III)
concentration (high conversion ratios), was found. The cells were applied for the Ce(IV) regeneration during the organic destruction.
The cell and reactor processes were fitted in a simple model proposed and used to calculate the current needed in terms of
Ce(III) oxidation rate and the number of cell stacks required for maintaining Ce(IV)/Ce(III) ratio at the same level during
the organic destruction. This consideration was based on the kinetic model previously developed by us for the organic destruction
in the MEO process. 相似文献
90.
含氟有机化合物氟化反应研究进展 总被引:2,自引:0,他引:2
介绍了含氟有机化合物的优点,一些常用的含氟有机化合物的分类和适用性,并介绍了主要的合成方法,按照合成物质的种类分为含氟非成环烷烃类、含氟环烷烃类及其衍生物和各自不同的应用.叙述了引入F原子或引入含氟端基的方法:电化学反应法、聚合反应法和其它反应法. 相似文献