全文获取类型
收费全文 | 4429篇 |
免费 | 203篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 56篇 |
化学工业 | 1325篇 |
金属工艺 | 139篇 |
机械仪表 | 72篇 |
建筑科学 | 93篇 |
矿业工程 | 12篇 |
能源动力 | 127篇 |
轻工业 | 565篇 |
水利工程 | 11篇 |
石油天然气 | 9篇 |
无线电 | 88篇 |
一般工业技术 | 668篇 |
冶金工业 | 1073篇 |
原子能技术 | 22篇 |
自动化技术 | 375篇 |
出版年
2023年 | 38篇 |
2022年 | 171篇 |
2021年 | 279篇 |
2020年 | 98篇 |
2019年 | 84篇 |
2018年 | 150篇 |
2017年 | 152篇 |
2016年 | 160篇 |
2015年 | 122篇 |
2014年 | 163篇 |
2013年 | 267篇 |
2012年 | 182篇 |
2011年 | 227篇 |
2010年 | 146篇 |
2009年 | 130篇 |
2008年 | 130篇 |
2007年 | 130篇 |
2006年 | 78篇 |
2005年 | 63篇 |
2004年 | 70篇 |
2003年 | 55篇 |
2002年 | 52篇 |
2001年 | 29篇 |
2000年 | 30篇 |
1999年 | 27篇 |
1998年 | 191篇 |
1997年 | 210篇 |
1996年 | 141篇 |
1995年 | 97篇 |
1994年 | 50篇 |
1993年 | 73篇 |
1992年 | 24篇 |
1991年 | 14篇 |
1990年 | 21篇 |
1989年 | 17篇 |
1988年 | 18篇 |
1987年 | 17篇 |
1986年 | 18篇 |
1985年 | 21篇 |
1984年 | 33篇 |
1983年 | 23篇 |
1982年 | 42篇 |
1981年 | 48篇 |
1980年 | 57篇 |
1979年 | 29篇 |
1978年 | 37篇 |
1977年 | 110篇 |
1976年 | 239篇 |
1975年 | 14篇 |
1973年 | 12篇 |
排序方式: 共有4635条查询结果,搜索用时 15 毫秒
81.
This paper presents methods for improving the quality of IR images that significantly facilitate the detection of physical and structural non-uniformities in layered objects. The methods are based on wavelets transformations. Both, discrete and continuous wavelet transforms were used. The space-scale representation of thermal image are used for the detection thermal non-uniformities in the objects examined. Examples of recorded and improved images are presented in this paper. 相似文献
82.
Atomic force microscopy (AFM) has been used to study the effect of various photoinitiators doped into poly(methyl methacrylate) (PMMA) on the mechanical properties of PMMA films at the nanometer scale. Pure and modified PMMA films (containing four different photoinitiators) were exposed to a mercury vapor lamp in air atmosphere. Force–distance curves for hardness, Young modulus, and adhesion forces were obtained using different AFM modes (tapping or contact-mode) and different tips (diamond or silicon nitride). The results revealed that the added photoinitiators slightly changed the nanomechanical properties of PMMA as a result of alterations in the photochemical reactions and physical processes occurring in the studied systems. tert-Butyl peroxybenzoate had the most efficient effect on the measured parameters in UV-irradiated PMMA, whereas benzoyl peroxide was less active. The mechanism of the observed processes is discussed. 相似文献
83.
Beata Zielińska Ewa Borowiak-PalenBarbara Grzmil Ryszard J. Kalenczuk 《Journal of Alloys and Compounds》2011,509(17):5414-5419
Titanate nanorods with high photocatalytic activity was successfully synthesized through a simple catalyst-free hydrothermal method. The photocatalytic degradation of a model organic dye (Reactive Red 198) was accelerated by the calcination of the nanorods prior the reaction. The calcination of nanorods did not modify their morphology, however the crystallinity of the samples was significantly improved. Therefore, the quality of the samples is a key parameter determining their activity in the investigated photocatalytic process. The as-produced and annealed catalysts were characterized by high-resolution transmission electron microscopy (HR-TEM), X-ray diffraction (XRD), Diffuse Reflectance (DR) UV-Vis and resonance Raman spectroscopy. 相似文献
84.
J.A. MorkowskiG. Che?kowska M. WerwińskiA. Szajek R. Tro?C. Neise 《Journal of Alloys and Compounds》2011,509(25):6994-6998
The room temperature X-ray photoemission spectrum of the ferromagnetic compound UCu2Si2 (TC = 100 K) was measured using an Al Kα source. Related theoretical spectra were computed from densities of electronic states obtained in the local density approximation (LDA), the generalized gradient approximation (GGA), and using the GGA + U method. The calculated spectrum is in a good agreement with the experimental one. The spin polarized calculations based on the GGA + U approach as well as GGA/LSDA with orbital polarization (OP) corrections taken into account provide values of the total magnetic moment in reasonable agreement with the experimental values ranging between 1.6 and 2.0 μB/U atom. 相似文献
85.
The high alumina cements were ground together with special sulphate–lime sinter to produce an expansive additive to Portland cement. This expansive additive in the environment of hydrating cement transforms into the hydrated calcium sulfoaluminate phase known as ettringite at “right time” to give the expansion before the early hardening process is completed. The studies were focused at first on the synthesis of the sulphate–lime sinter and subsequently on the mixture proportions between the basic Portland cement, calcium aluminate cement and sulphate–lime component giving the compensation of shrinkage or expansion effect during the hydration process. The measurements of volume changes of cementitious materials thus produced, followed by the compressive strength tests, rate of hydration determination, phase composition studies and microstructure of hydration products observations have been carried out to find the optimum proportions of blended cementitious material, as the controlled expansion and hardening are concerned. 相似文献
86.
Concentration dependant emission spectra and fluorescence dynamic profiles have been investigated in PrxLa1−xAlO3 single crystals in order to better understand processes responsible for concentration quenching of the praseodymium 3P0 and 1D2 emissions. The cross-relaxation transfer rates were experimentally determined as a function of Pr3+ concentration. Decays were modeled and nearest-neighbor trapping rates were calculated. 相似文献
87.
L. Demkowicz P. Gatto J. Kurtz M. Paszyński W. Rachowicz E. Bleszyński M. Bleszyński M. Hamilton C. Champlin D. Pardo 《Computer Methods in Applied Mechanics and Engineering》2011,200(21-22):1757-1773
We focus on the development of a reliable numerical model for investigating the bone-conduction of sound in the human head. The main challenge of the problem is the lack of fundamental knowledge regarding the transmission of acoustic energy through non-airborne pathways to the cochlea. A fully coupled model based on the acoustic/elastic interaction problem with a detailed resolution of the cochlea region and its interface with the skull and the air pathways, should provide an insight into this fundamental, long standing research problem. To this aim we have developed a 3D hp-finite element code that supports elements of all shapes (tetrahedra, prisms and pyramids) to better capture the geometrical features of the head. We have tested the code on a multilayered sphere and employed it to solve an idealized model of head. In the future we hope to attack a model with a more realistic geometry. 相似文献
88.
In this paper the minmax (regret) versions of some basic polynomially solvable deterministic network problems are discussed. It is shown that if the number of scenarios is unbounded, then the problems under consideration are not approximable within log1−?K for any ?>0 unless NP⊆DTIME(npolylogn), where K is the number of scenarios. 相似文献
89.
Solid‐State NMR Study of Mn2+ for Ca2+ Substitution in Thermally Processed Hydroxyapatites 下载免费PDF全文
Joanna Kolmas Mateusz Jabłoński Anna Ślósarczyk Waclaw Kolodziejski 《Journal of the American Ceramic Society》2015,98(4):1265-1274
In the present study calcium hydroxyapatites enriched at 0.08 wt% in Mn2+ ions (Mn–HA) and their unsubstituted forms (HA) were synthesized using the same standard wet chemical route. Mn‐HA and HA were both calcined at 800°C to give Mn‐HAc and HAc, respectively or sintered at 1250°C, to give Mn‐HAs and HAs, respectively. The influence of the heat treatment on physicochemical properties of Mn‐HA was investigated using powder X‐ray diffraction (PXRD), scanning, and transmission electron microscopy (SEM and TEM), and solid‐state nuclear magnetic resonance (ssNMR). Mn‐HAc and Mn‐HAs were compared to each other and to HAc and HAs, respectively. Assignment of the proton ssNMR peaks from high‐temperature‐treated apatites has been revised. It was found that Mn–HAc and HAc were nanocrystalline, while Mn‐HAs and HAs comprised micrometer sized, partially fused particles (SEM and TEM). PXRD and ssNMR demonstrated that the incorporation of Mn2+ into the crystal lattice of hydroxyapatite significantly facilitates its dehydroxylation and decomposition to oxyhydroxyapatite during calcination at 800°C, and induces its transformation to tetracalcium phosphate (TTCP) and alpha‐tricalcium phosphate (α‐TCP) at 1250°C. Contamination by CaO has also been detected. The 1H→31P NMR cross‐polarization experiments have indicated that the Mn2+ ions preferentially occupied the Ca(I) position in the crystallographic unit cell of Mn‐HAc. In Mn‐HAs, the Mn2+ ions were evenly distributed between the Ca(I) and Ca(II) positions. 相似文献
90.
Effect of the structure of polymer inclusion membranes on zn(II) transport from chloride aqueous solutions 下载免费PDF全文
This article presents application of polymer inclusion membranes (PIM) containing polymer matrices: cellulose triacetate (CTA) or poly(vinyl) chloride (PVC), o‐nitrophenyloctyl ether (NPOE) as a plasticizer and phosphonium ionic liquids, i.e., trihexyltetradecylphosphonium chloride (Cyphos IL 101), bis(2,4,4‐trimethylpentyl)phosphinate (Cyphos IL 104) and tributyltetradecylphosphonium chloride (Cyphos IL 167), as carriers for Zn(II) transport from chloride medium. Cyphos IL167 application as an ion carrier in PIMs is reported for the first time. The membrane composition is found to affect Zn(II) transport significantly. SEM and AFM images show the differences in the surface morphology of PVC and CTA based membranes. Better transport abilities of CTA membranes (Zn(II) recovery factors exceed 80%) compared with those of PVC, indicate that the structural differences between the two polymers play a crucial role for the membrane permeability. The best initial flux and permeability coefficient are obtained for the membranes with Cyphos IL 101 and Cyphos IL 104 as carriers. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42319. 相似文献