全文获取类型
收费全文 | 4575篇 |
免费 | 76篇 |
国内免费 | 5篇 |
专业分类
电工技术 | 48篇 |
综合类 | 6篇 |
化学工业 | 798篇 |
金属工艺 | 93篇 |
机械仪表 | 57篇 |
建筑科学 | 272篇 |
矿业工程 | 55篇 |
能源动力 | 123篇 |
轻工业 | 409篇 |
水利工程 | 64篇 |
石油天然气 | 27篇 |
武器工业 | 1篇 |
无线电 | 292篇 |
一般工业技术 | 654篇 |
冶金工业 | 1223篇 |
原子能技术 | 35篇 |
自动化技术 | 499篇 |
出版年
2022年 | 16篇 |
2021年 | 50篇 |
2020年 | 34篇 |
2019年 | 45篇 |
2018年 | 56篇 |
2017年 | 40篇 |
2016年 | 52篇 |
2015年 | 27篇 |
2014年 | 71篇 |
2013年 | 276篇 |
2012年 | 140篇 |
2011年 | 225篇 |
2010年 | 182篇 |
2009年 | 146篇 |
2008年 | 217篇 |
2007年 | 196篇 |
2006年 | 212篇 |
2005年 | 210篇 |
2004年 | 170篇 |
2003年 | 140篇 |
2002年 | 111篇 |
2001年 | 85篇 |
2000年 | 94篇 |
1999年 | 105篇 |
1998年 | 143篇 |
1997年 | 95篇 |
1996年 | 97篇 |
1995年 | 78篇 |
1994年 | 87篇 |
1993年 | 78篇 |
1992年 | 70篇 |
1991年 | 55篇 |
1990年 | 77篇 |
1989年 | 74篇 |
1988年 | 60篇 |
1987年 | 59篇 |
1986年 | 57篇 |
1985年 | 60篇 |
1984年 | 80篇 |
1983年 | 49篇 |
1982年 | 70篇 |
1981年 | 63篇 |
1980年 | 50篇 |
1979年 | 44篇 |
1978年 | 35篇 |
1977年 | 35篇 |
1976年 | 32篇 |
1975年 | 28篇 |
1974年 | 28篇 |
1973年 | 27篇 |
排序方式: 共有4656条查询结果,搜索用时 187 毫秒
61.
A high-performance liquid chromatographic method, using post-column detection with diphenyl-1-pyrenyl-phosphine (DPPP), was
developed for the quantitative and qualitative determination of isomeric lipid hydroperoxides (OOH). The OOH eluted from a
normal-phase column were passed through a photodiode array detector and then mixed with DPPP solution in a reaction coil heated
at 80°C. DPPP oxide formed by the reaction with OOH was determined by monitoring the fluorescence intensity at 380 nm and
excitation at 352 nm. The conjugated diene OOH (13-cis, trans- and 9-cis, trans-OOH) and nonconjugated OOH (12-cis-trans- and 10-cis, trans-OOH) from photosensitized oxidation of methyl linoleate were determined in a molar ratio of 31∶29∶19∶21, respectively. However,
only the two conjugated hydroperoxides were detected by ultraviolet absorption at 234 nm. Further applications were carried
out for the determination of OOH of methyl oleate and methyl linolenate. This method proved to be useful for the determination
of the OOH containing both conjugated and nonconjugated diene structures. 相似文献
62.
Structure–property relationships in poly(urethane urea)s synthesized with ultra‐low monol content poly(propylene glycol) soft segments were investigated as soft segment molecular weight (2000, 4000, and 8000 g/mol) and hard segment content (6.3 and 9.0 wt %) were varied. Morphological features such as interdomain spacing and interphase thickness were quantified and revealed with small‐angle X‐ray scattering (SAXS) and atomic force microscopy (AFM). The thermal and mechanical behavior was assessed with a dynamic mechanical analyzer (DMA) and by differential scanning calorimetry (DSC) and stress‐strain tests. Hard segment content, over the limited range studied, had little effect on the morphology and soft segment thermal and mechanical properties. The molecular weight of the soft segments had considerably more influence on the morphology and mechanical properties. Increasing soft segment molecular weight resulted in greater interdomain spacings, as shown by SAXS, and a noticeable change in the structure, as shown by AFM. Additionally, as soft segment molecular weight decreased the soft segment glass transition broadened and rose to higher temperatures. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 229–243, 2002; DOI 10.1002/app.10168 相似文献
63.
The solubility of H2S and CO2 in aqueous solutions of the sterically hindered amine, 2-amino-2-methyl-1-propanol (AMP), was determined at 40 and 100°C. Partial pressures of C)2 ranged from approximately 2 to 6000 kPa and of H2S from 2 to 2200 kPa. The solubility results were compared with previously reported acid gas solubilities in aqueous monoethanolamine (MEA) solutions. 相似文献
64.
The Thermodynamic Properties of Silicon Oxynitride 总被引:1,自引:0,他引:1
A critical assessment of thermal and equilibrium data for silicon oxynitride (Si2 N2 O) is presented. Selected values for the heat of formation of Si2 N2 O from the elements and the absolute entropy of Si2 N2 O at 298.15 K are ΔH0 f,298 =−947.7 ± 5.4 kJ/mol and S0 298 = 45.35 ± 0.4 J/mol·K, respectively. A table of thermodynamic functions for Si2 N2 Ofrom 298 to 2500 K, which has been calculated from the analysis of the literature data, is also presented. 相似文献
65.
The provision of a downcomer to classical turbulent bed Contactor (TBC) increases the gas treating capacity of the equipment. When the downcomer is provided, it is expected that all the liquid passes through the downcomer only without any liquid flow through the distributor. In the present study, the operational regime for the flow of liquid only through the downcomer is experimentally evaluated for various geometric parameters and particle characteristics. It is observed that the preferred operational regime without dumping and weeping increases with an increase in Archimedes number and downcomer diameter, and decreases with an increase in static bed height and downcomer weir height. Correlations are proposed to satisfactorily predict experimentally observed operational regime. 相似文献
66.
Carsten Dachsbacher Jaroslav Křivánek Miloš Hašan Adam Arbree Bruce Walter Jan Novák 《Computer Graphics Forum》2014,33(1):88-104
Recent years have seen increasing attention and significant progress in many‐light rendering, a class of methods for efficient computation of global illumination. The many‐light formulation offers a unified mathematical framework for the problem reducing the full lighting transport simulation to the calculation of the direct illumination from many virtual light sources. These methods are unrivaled in their scalability: they are able to produce plausible images in a fraction of a second but also converge to the full solution over time. In this state‐of‐the‐art report, we give an easy‐to‐follow, introductory tutorial of the many‐light theory; provide a comprehensive, unified survey of the topic with a comparison of the main algorithms; discuss limitations regarding materials and light transport phenomena and present a vision to motivate and guide future research. We will cover both the fundamental concepts as well as improvements, extensions and applications of many‐light rendering. 相似文献
67.
Gilles Bussod Alexander Pechenik Chung-tse Chu Bruce Dunn 《Journal of the American Ceramic Society》1989,72(1):137-139
The knowledge of the steady-state stress for plastic deformation as a function of temperature and strain rate is essential for hot-forming superconducting material into commercially useful shapes. In this paper, results are presented on the experimental determination of the rheology of fully dense polycrystalline Y1 Ba2 Cu3 O7−x superconducting material at temperatures ranging from 750° to 950°C and strain rates of 10−4 , 10−5 , and 10−6 s−1 . The data are best fitted by a power law: ε(s−1 )=8.9 × 10−17 . (s−1 ) σ2.5 (Pa) exp [−2.01 × 105 (J·mol−1 )|RT]. X-ray analysis shows that the superconducting material retains its phase composition after nearly 70% total strain of the sample. A strong anisotropy in the resistivity of the deformed samples is observed because of the development of a preferred orientation of the a or b axis of Y1 Ba2 Cu3 O7−x orthorhombic perovskite single crystals perpendicular to the principal maximum compressive stress. 相似文献
68.
Roland Schmidt Ulrich Hammon Stefan Gottfried M. Bruce Welch Helmut G. Alt 《应用聚合物科学杂志》2003,88(2):476-482
The synthesis of iron(II) complexes with various tridentate di(imino)pyridine ligands and their potential as ethene oligomerization catalysts are described. The ligands are characterized by 1H‐ and 13C‐NMR spectroscopy and the complexes only by mass spectrometry due to their paramagnetism. After activation either with methylalumoxane (MAO) or with a heterogeneous cocatalyst consisting of partially hydrolyzed trimethylaluminum and silica gel, the prepared complexes proved to be good catalysts for the oligomerization of ethene. 1‐Octene, 1‐hexene, and 1‐decene were the major products, formed in very high isomeric purity (99.9 %). © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 476–482, 2003 相似文献
69.
The rates of CO and CO/CO2 hydrogenation at 4.2 MPa and 523 K are reported for a series of Cu/SiO2 catalysts containing 2 to 88 wt.% Cu. These catalysts were prepared on a variety of silica sources using several different Cu deposition techniques. In CO/CO2 hydrogenation, the rate of methanol formation is proportional to the exposed Cu surface area of the reduced catalyst precursor, as determined by N2O frontal chromatography. The observed rate, 4.2×10–3 mole CH3OH/Cu site-sec, is within a factor of three of the rates reported by others over Cu/ZnO and Cu/ZnO/Al2O3 catalysts under comparable conditions. These results suggest that the ZnO component is only a moderate promoter in methanol synthesis. Hydrogenation of CO over these catalysts also gives methanol with high selectivity, but the synthesis rate is not proportional to the Cu surface area. This implies that another type of site, either alone or in cooperation with Cu, is involved in the synthesis of methanol from CO. 相似文献
70.
The degradation kinetics of poly(3‐hydroxybutyrate‐co‐3‐hydroxyhexanoate), a member of the Nodax family of polymers, were investigated using transient constant shear rate and dynamic time sweep rheological tests. The rate of chain scission at several times and temperatures was correlated with viscosity data and verified using molecular weight determination of the degraded samples. The experimental results show that the molecular weight and the viscosity of Nodax decrease with time over the range of temperatures that were studied (155–175°C). The degradation kinetics, which exhibited first‐order behavior, were determined as a function of the flow history and thermal history. An apparent activation energy of 189 ± 5 kJ/mol for thermal degradation was found by modeling variations in the rate with temperature using an Arrhenius law model. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 66–74, 2005 相似文献