全文获取类型
收费全文 | 5160篇 |
免费 | 151篇 |
国内免费 | 12篇 |
专业分类
电工技术 | 68篇 |
综合类 | 7篇 |
化学工业 | 949篇 |
金属工艺 | 119篇 |
机械仪表 | 168篇 |
建筑科学 | 132篇 |
矿业工程 | 6篇 |
能源动力 | 202篇 |
轻工业 | 282篇 |
水利工程 | 10篇 |
石油天然气 | 16篇 |
无线电 | 915篇 |
一般工业技术 | 927篇 |
冶金工业 | 529篇 |
原子能技术 | 26篇 |
自动化技术 | 967篇 |
出版年
2023年 | 27篇 |
2022年 | 96篇 |
2021年 | 131篇 |
2020年 | 39篇 |
2019年 | 63篇 |
2018年 | 77篇 |
2017年 | 79篇 |
2016年 | 101篇 |
2015年 | 106篇 |
2014年 | 148篇 |
2013年 | 429篇 |
2012年 | 264篇 |
2011年 | 351篇 |
2010年 | 295篇 |
2009年 | 348篇 |
2008年 | 287篇 |
2007年 | 254篇 |
2006年 | 209篇 |
2005年 | 167篇 |
2004年 | 148篇 |
2003年 | 140篇 |
2002年 | 110篇 |
2001年 | 108篇 |
2000年 | 77篇 |
1999年 | 95篇 |
1998年 | 217篇 |
1997年 | 148篇 |
1996年 | 130篇 |
1995年 | 85篇 |
1994年 | 96篇 |
1993年 | 87篇 |
1992年 | 56篇 |
1991年 | 37篇 |
1990年 | 38篇 |
1989年 | 36篇 |
1988年 | 36篇 |
1987年 | 19篇 |
1986年 | 18篇 |
1985年 | 15篇 |
1984年 | 16篇 |
1983年 | 10篇 |
1982年 | 17篇 |
1980年 | 9篇 |
1979年 | 20篇 |
1978年 | 12篇 |
1977年 | 11篇 |
1976年 | 9篇 |
1975年 | 9篇 |
1974年 | 8篇 |
1973年 | 9篇 |
排序方式: 共有5323条查询结果,搜索用时 15 毫秒
71.
Cheng-Chang Lee Chen-Chia Chou Dah-Shyang Tsai 《Journal of the American Ceramic Society》1997,80(11):2885-2890
The 1/3 <111>-type ordering of Ba(Zn1/3 Ta2/3 )O3 (BZT) can be transformed to 1/2 <111>–type ordering by substituting the La3+ cation into the A site. The 1/3 <111> ordering in BZT is shown to be reduced, discontinued, and then replaced by 1/2 <111> ordering, using X–ray diffraction, electron microscopy, and Raman spectroscopy. On the other hand, potassium–substituted BZT only displays a reduction in the degree of ordering. 相似文献
72.
Optically active exo-exo-2,3-camphanediol (CPO) (3) was synthesized from (+)-camphor. Chiral polymers poly(CPO-co-TDI) ( 6 ) and poly(CPO-co-IPDI) ( 7 ) were synthesized by the step polymerization of chiral compound CPO ( 3 ) with toluene-2,4-diisocyanate (TDI) and isophorone diisocyanate (IPDI). To investigate the stereo structure of the chiral polymers, two kinds of model compounds, exo-exo-2,3-di[(phenylamido)oxy]camphane ( 4 ) and exo-exo-2,3-di[(propylamido)oxy]camphane ( 5 ), related to polymers ( 6 ) and ( 7 ) were synthesized. Chiroptical characteristics and stereo structures of the chiral polymers were investigated using a circular dichroic spectrometer. The results obtained in this investigation suggest that the chiral polymers ( 6 ) and ( 7 ) have no one-handed helix conformation. The optical resolution ability as chiral adsorbent for HPLC of the chiral polymers was investigated. It was found that chiral polymers ( 6 ) and ( 7 ) are effective for the optical resolution of some racemates. © 1995 John Wiley & Sons, Inc. 相似文献
73.
Y. L. Song S. C. Tsai C. Y. Chen T. K. Tseng C. S. Tsai J. W. Chen Y. D. Yao 《Journal of the American Ceramic Society》2004,87(10):1864-1871
This paper presents new findings on ultrasonic spray pyrolysis of zirconium hydroxyl acetate precursor drops whose sizes were precisely measured using laser light diffraction technique. Precursor concentration plays a predominant role in determination of product particle size. At 0.01 wt% precursor concentration, conventional spray pyrolysis at 750°C using precursor drops 5–8 μm in diameter, generated by an ultrasonic nebulizer at 2.66 MHz, yielded uniform spherical yttria-stabilized zirconia (YSZ) particles 73 nm in diameter measured by scanning electron microscopy. The YSZ particle diameters were much smaller than those predicted by the one-particle-per-drop mechanism. Under similar reaction conditions, the high-throughput ultrasound-modulated two-fluid (UMTF) spray pyrolysis of larger precursor drops (28-μm peak diameter) also yielded spherical dense particles; they were significantly smaller in size than those produced by the low-throughput conventional ultrasonic spray pyrolysis of smaller drops (6.8-μm peak diameter). 相似文献
74.
Callus cultures ofTheobroma cacao L., initiated from explants of immature cocoa bean cotyledons, contained 5.3%–6.4% lipids (dry wt basis). The major fatty
acids were palmitic, oleic and linoleic acids. Cell suspensions contained 5.7–7.7% total lipids which had a higher polyunsaturated
fatty acid content than total lipids of the calli. Phospholipids and glycolipids were the predominant lipid classes of calli
and cell suspensions. Immature cocoa beans at early stages of development contained much higher polyunsaturated fatty acids,
higher polar lipids and lower triglycerides than did mature ripe beans. Ripe cocoa beans contained 54% total lipids of which
96.8% where triglycerides. The fatty acid composition of total lipids of calli and cell suspensions were similar to those
of the immature cocoa beans. 相似文献
75.
Steve Lien‐Chung Hsu Keng‐Chuan Chang Yuan‐Pin Huang Shih‐Jung Tsai 《应用聚合物科学杂志》2003,88(10):2388-2391
A poly(imide benzoxazole) was prepared directly from trimellitic anhydride chloride and 2,2‐bis(3‐amino‐4‐hydroxyphenyl)hexafluoropropane (BisAPAF) monomers in a two‐step method. In the first step, a poly(hydroxyamide amic acid) precursor was synthesized by the low‐temperature solution polymerization in an organic solvent. Subsequently, thermal cyclodehydration of the poly(hydroxyamide amic acid) precursor at 350°C produced the corresponding poly(imide benzoxazole). The inherent viscosity of the precursor polymer was 0.22 dL/g. The cyclized poly(imide benzoxazole) showed a glass transition temperature (Tg) at 329°C and a 5% weight loss temperature at 530°C in nitrogen and at 525°C in air. The poly(imide benzoxazole) is amorphous as evidenced by the wide‐angle X‐ray diffraction measurement. The structures of the precursor polymer and the fully cyclized polymer were characterized by Fourier transform infrared (FTIR) and proton nuclear magnetic resonance spectroscopy (1H NMR). © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2388–2391, 2003 相似文献
76.
The effect of recycle on heat (and mass) transfer in concentric circular tubes has been investigated by finite difference methods. Theoretical results show that recycle can enhance the heat transfer rate for large Graetz numbers compared with that in an open tube (without an inner tube inserted and without recycle). Competition between a preheating effect and a residence-time effect can be used to explain the heat transfer behavior. The heat transfer rate can be further augmented, with nearly no increase in total pressure drop, by employing flow pattern B instead of flow pattern A. 相似文献
77.
A series of novel types of diblock poly(trans-4-hydroxy-N-benzyloxycarbonyl-l-proline)-block-poly(ε-caprolactone) (PHpr10-b-PCL) copolymers were synthesized by ring-opening polymerization from macroinitiator poly(trans-4-hydroxy-N-benzyloxycarbonyl-l-proline) (PHpr10) and ε-caprolactone (ε-CL) in the presence of organocatalyst dl-lactic acid (dl-LA). The Mn of the copolymers increased from 3370 to 19,040 g mol−1 with the molar ratio (10-100) of ε-CL to PHpr10. These products were characterized by differential scanning calorimetry (DSC), 1H NMR, and gel permeation chromatography. According to DSC, the glass-transition temperature (Tg) of the diblock copolymers depend on the molar ratio of monomer/initiator that were added. The hydrolytic degradation behavior of PHpr-b-PCLs was evaluated from weight-loss measurements and the change of Mn and Mw/Mn. With higher PCL contents resulted in a slower weight loss, while having a higher molecular weight loss percentage. Their micellar characteristics in an aqueous phase were investigated by fluorescence spectroscopy, transmission electron microscopy (TEM), and dynamic light scattering (DLS). The block copolymers formed micelles in the aqueous phase with critical micelle concentrations (CMCs) in the range of 1.33-4.22 mg L−1. The micelles exhibited a spindly shape and showed a narrow monodisperse size distribution. The obtained micelles have a relatively high drug-loading of about 26% when the feed weight ratio of amitriptyline hydrochloride (AM) to polymer was 1/1. An increase of molecular weight and hydrophobic components in copolymers produced a higher CMC value and greater loading efficiencies were observed. 相似文献
78.
A novel noncovalent and inorganic method was used to disperse multiwalled carbon nanotubes (MWCNTs) in aqueous solutions through alumina-coated silica (ACS) nanoparticle halos. MWCNTs were directly dispersed into a highly charged ACS nanoparticle aqueous solution without functionalization of their surfaces. The dispersed MWCNTs were characterized by transmission electron microscopy and atomic force microscopy. Raman spectroscopy of MWCNTs prepared from dispersion in the ACS solution revealed reduced bundling compared to the corresponding untreated MWCNTs. The characteristic Raman peak at about 1570 cm−1, corresponding to the G band, shifted to a higher wavenumber with a narrower peak. It was possible to disperse up to 20 mg/mL of MWCNTs in a 1 wt% ACS nanoparticle aqueous solution at pH 2. This homogeneous MWCNT-ACS aqueous solution was stable for weeks after ultrasonication. 相似文献
79.
A sol–gel process to unsophisticatedly synthesize Ba(Mg1/3 Ta2/3 )O3 (BMT) ceramics at low cost has been developed in the present work. This process involves the reaction of TaCl5 with acetates of Ba and Mg in the presence of citric acid. Pure BMT polycrystalline powders can be obtained by calcining the synthesized products at 1000°C. The BMT powders were found to have a primary particle size as small as 100 nm. BMT ceramics with favorable structural characteristics can be obtained from sintering of the sol–gel BMT at temperatures much lower than that for the conventional solid-state BMT. Sintering the sol–gel BMT in pellet form at 1300°C resulted in an ordering parameter of 0.72 for the pellet, and a relative density of >95% was achieved with sintering at 1500°C. The grain size of the sintered sol–gel BMT was large and uniform in comparison with the products from the solid-state method. Using the sol–gel route, sintering at temperatures as low as 1400°C gave ceramics with acceptable microwave dielectric properties (a dielectric constant of 16 and Qf factor of 14 400 GHz), while higher temperatures (>1600°C) are needed for the solid-state route to give similar properties. 相似文献
80.
I.H. Farag S.B. Reddy Karri R. Breault K.Y. Tsai 《Chemical Engineering Communications》1986,48(4):331-348
The design of multistage fluidized beds for heat exchange necessitates the solution of the mass and energy balance equations combined with the equilibrium relations for each stage. This paper presents a novel way of applying well known methodology to a different technology, one where it has not been widely applied.
In the present work a McCabe-Thiele type of graphical approach is presented for both counter-current and cross-current contacting multiple fluidized beds. The necessary equations for a multistage calciner are developed and the application of the proposed method is demonstrated. Generalized fluidized bed efficiency for counter-current and cross-current multiple fluidized bed is presented. 相似文献
In the present work a McCabe-Thiele type of graphical approach is presented for both counter-current and cross-current contacting multiple fluidized beds. The necessary equations for a multistage calciner are developed and the application of the proposed method is demonstrated. Generalized fluidized bed efficiency for counter-current and cross-current multiple fluidized bed is presented. 相似文献