全文获取类型
收费全文 | 4122篇 |
免费 | 21篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 23篇 |
综合类 | 1篇 |
化学工业 | 122篇 |
金属工艺 | 46篇 |
机械仪表 | 7篇 |
建筑科学 | 60篇 |
矿业工程 | 5篇 |
能源动力 | 33篇 |
轻工业 | 107篇 |
水利工程 | 8篇 |
石油天然气 | 4篇 |
无线电 | 114篇 |
一般工业技术 | 223篇 |
冶金工业 | 3214篇 |
原子能技术 | 11篇 |
自动化技术 | 166篇 |
出版年
2022年 | 8篇 |
2021年 | 13篇 |
2020年 | 10篇 |
2019年 | 10篇 |
2018年 | 13篇 |
2017年 | 17篇 |
2016年 | 20篇 |
2015年 | 18篇 |
2014年 | 17篇 |
2013年 | 61篇 |
2012年 | 25篇 |
2011年 | 39篇 |
2010年 | 29篇 |
2009年 | 27篇 |
2008年 | 42篇 |
2007年 | 47篇 |
2006年 | 40篇 |
2005年 | 36篇 |
2004年 | 50篇 |
2003年 | 34篇 |
2002年 | 36篇 |
2001年 | 44篇 |
2000年 | 31篇 |
1999年 | 113篇 |
1998年 | 1035篇 |
1997年 | 550篇 |
1996年 | 383篇 |
1995年 | 222篇 |
1994年 | 164篇 |
1993年 | 173篇 |
1992年 | 41篇 |
1991年 | 60篇 |
1990年 | 49篇 |
1989年 | 58篇 |
1988年 | 57篇 |
1987年 | 59篇 |
1986年 | 57篇 |
1985年 | 44篇 |
1984年 | 20篇 |
1983年 | 15篇 |
1982年 | 18篇 |
1981年 | 27篇 |
1980年 | 27篇 |
1979年 | 10篇 |
1978年 | 9篇 |
1977年 | 72篇 |
1976年 | 158篇 |
1975年 | 14篇 |
1973年 | 8篇 |
1972年 | 5篇 |
排序方式: 共有4144条查询结果,搜索用时 31 毫秒
101.
Binding and localization of the vasodilator and antitumor drug coactivator dipyridamole (DIP) and one of its derivatives, RA25, to phospholipid vesicles of DMPC (dimyristoylphosphatidylcholine) and DPPC (dipalmitoylphosphatidylcholine) was studied using fluorescence spectroscopy as well as quenching of fluorescence. The analysis of fluorescence data indicates that neutral dipyridamole binds to the phospholipids in their liquid crystalline phase with an association constant of 950 M(-1) and 1150 M(-1) to DMPC and DPPC, respectively. Protonation of DIP leads to a 3-fold reduction of the association constant. For the gel phospholipid phase, the binding is smaller (a factor of 2), independently of pH, suggesting that the more flexible lipid packing in the liquid crystalline phase facilitates the binding of the drug. The association constant of RA25 neutral form is considerably lower than for DIP, being around 295 M(-1). Fluorescence quenching with nitroxides TEMPO and stearic acid doxyl derivatives suggests the localization of DIP to be closer to the 5th carbon of alkyl chain. The quenching effect of 5-DSA below the lipid phase transition suggests that a strong static quenching may be operative. The quenching effect of 16-DSA is almost as great as that for 5-DSA below the phase transition, being even higher above the phase transition. This effect is probably due to the trans-gauche isomerization of the stearic acid nitroxide, making the encounter of its paramagnetic fragment with the DIP chromophore possible. Our data are consistent with DIP location close to the bilayer surface in the border of hydrophobic-polar heads interface which is similar to the data in micellar systems. In the case of RA25, the drug is in the outer part of the head group interface being much exposed to the aqueous phase and being significantly less accessible to the membrane nitroxide quenchers. 相似文献
102.
DM Clark PM Salkovskis LG Ost E Breitholtz KA Koehler BE Westling A Jeavons M Gelder 《Canadian Metallurgical Quarterly》1997,65(2):203-213
Cognitive accounts of panic predict that panic disorder patients will be particularly prone to misinterpret autonomic sensations. Several studies have produced results consistent with this prediction, but each is open to alternative interpretation. To clarify matters, 2 studies administered the Body Sensations Interpretation Questionnaire (BSIQ) to panic patients and controls. Panic patients were more likely to interpret ambiguous autonomic sensations as signs of immediately impending physical or mental disaster and were more likely than other anxiety disorder patients and nonpatients to believe these interpretations. In a 3rd study, a brief version of the BSIQ was shown to have satisfactory test-retest reliability, to change with treatment, and to discriminate treatments that varied in their effects on panic. 相似文献
103.
The effect of water salinity on the reactions occurring during pressure acid leaching of an arid-region laterite ore, using hypersaline water, seawater, sub-potable water and tap water, is examined. Particular emphasis is placed on the mineralogy of the residue and its implications with regard to residue volume/mass, overall acid consumption and nickel extraction. Analysis of a pressure acid leach residue by electron microprobe indicates that the residual nickel is present in phases that contain silicon and varying concentrations of aluminium, but are deficient in sulphur. Incomplete extraction of nickel from the ore may not be attributed to any one mineral phase. 相似文献
104.
Walsh Benjamin M.; Matthews Russell A.; Tuller Michael D.; Parks Kizzy M.; McDonald Daniel P. 《Canadian Metallurgical Quarterly》2010,15(2):191
To date, minimal work has explored associations between equal opportunity (EO) climate and employee work attitudes, and no known research has investigated the effects of EO climate beyond the individual level. We address these gaps in the literature by testing a multilevel structural equation model in which effects of EO climate are considered at both the individual and unit levels. At the individual level, we predicted that psychological EO climate would be directly associated with job stress and job satisfaction, as well as indirectly related to job satisfaction via stress. In addition, cross-level associations between unit EO climate and job stress and job satisfaction were hypothesized to be mediated by cohesion. Findings supported the proposed model; hypothesized relations were supported at both levels of analysis. We conclude with a discussion of the findings, study limitations, and directions for future EO climate research. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
105.
The metabolism of α-linolenic acid from canola oil was studied in eight normolipidemic men. The 42-day study was divided into
three periods: a 6-day pre-experimental and two 18-day experimental. Approximately 75% of the dietary fat (28% of total energy)
was provided by a mixture of fats during the pre-experimental period and either canola oil (CO) or sunflower oil (SO) during
the experimental periods. The CO and SO diets were fed in a cross-over design. The ratios of linoleic to linolenic acid were
2.6∶1 and 73.9∶1 in the CO and SO diets, respectively. Dietary fat source had an effect on plasma phospholipid fatty acids:
18∶1n−9, 18∶3n−3 and 20∶5n−3 were higher (p<0.05), and 18∶2n−6 was lower in the phosphatidylcholine fraction; 18∶1n−9 was
higher and 20∶4n−6 lower in the phosphatidyl-ethanolamine fraction; and 18∶1n−9 and 20∶5n−3 were higher and 20∶4n−6 and 22∶6n−3
were lower in the alkenylacyl-ethanolamine phospholipid fraction on the CO diet as compared to the SO diet. Consumption of
the canola oil diet resulted in higher n−3 fatty acid levels and lower n−6 fatty acid levels in plasma phospholipids than
consumption of the sunflower oil diet. 相似文献
106.
107.
108.
Lignin valorization by forming toughened thermally stimulated shape memory copolymeric elastomers: Evaluation of different fractionated industrial lignins 下载免费PDF全文
Lignin‐based thermal responsive dual shape memory copolymeric elastomers were prepared with a highly branched prepolymer (HBP, A2B3 type) via a simple one‐pot bulk polycondensation reaction. The effect of fractionated lignin type (with good miscibility in the HBP) on copolymer properties was investigated. The thermal and mechanical properties of the copolymers were characterized by DMA, DSC, and TGA. Tensile properties were dominated by HBP <45% lignin content while lignin dominated >45% content. The copolymers glass transition temperature (Tg) increased with lignin content and lignin type did not play a significant role. Thermally stimulated dual shape memory effects (SME) of the copolymers were quantified by cyclic thermomechanical tests. All copolymers had shape fixity rate >95% and >90% shape recovery for all compositions. The copolymer shape memory transition temperature (Ttrans) increased with lignin content and Ttrans was 20°C higher than Tg. Lignin, a renewable resource, can be used as a netpoint segment in polymer systems with SME behavior. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41389. 相似文献
109.
Courtney L. Herring Paola Massoli Donna Sueper Matthew H. Erickson Jacob D. McDonald 《Aerosol science and technology》2013,47(11):1131-1148
This article presents a new methodology to potentially quantify polycyclic aromatic hydrocarbon (PAH) isomers using high-resolution time of flight aerosol mass spectrometer (HR-AMS). The fragmentation of PAHs within the HR-AMS is such that significant signal remains at the molecular ion. After quantifying the molecular ion signal and taking into account potential interferences, the amount of the parent PAH in the aerosol may be inferred once its fragmentation pattern is also known. The potential of this approach was evaluated using mixed gasoline and diesel engine exhaust sampled under varying conditions. This dataset led to the identification and quantification within the aerosol mass spectra of the molecular ions associated with 53 PAH isomers, including both unsubstituted and functionalized species. An evaluation of anticipated interferences shows that interferences from larger molecular weight PAHs (i.e., PAH/PAH interferences) could be constrained based on the fragmentation behavior of PAHs from existing HR-AMS laboratory spectra. Other signal interferences for this data set are typically less than 5% of the total signal or, for 13C isotopic interferents, are well constrained by measurements of the dominant isotope. The experimental data reveal that the fractional PAH molecular ion signal remained stable despite dramatic temporal variability of the total particulate organic signal. The fractional contributions of the molecular ions for grouped PAH species and even individual compounds were remarkably consistent across experiments. The distribution of PAHs showed no apparent dependence on engine load or exhaust type. Full application of this approach will require a greater number of standard HR-AMS spectra for PAHs, so that the relationship between compounds and their molecular ions may be understood more precisely.Copyright 2015 American Association for Aerosol Research 相似文献
110.
Magnetic resonance studies of cement based materials in inhomogeneous magnetic fields 总被引:1,自引:0,他引:1
Joanna Boguszynska Peter J. McDonald Jonathan Mitchell Jadwiga Tritt-Goc 《Cement and Concrete Research》2005,35(10):2033-2040
Single-sided magnets give hope that Nuclear Magnetic Resonance (NMR) might in future be used for in situ characterisation of hydration and water transport in the surface layers of concrete slabs. Towards that end, a portable NMR-MOUSE (MObile Universal Surface Explorer) has been used to follow the hydration of gypsum based plaster, a Portland cement paste and concrete mortar. The results compare favourably to those obtained using a standard laboratory bench-top spectrometer. Further, stray field imaging (STRAFI) based methods have been used with embedded NMR detector coils to study water transport across a mortar/topping interface. The measured signal amplitudes are found to correlate with varying sample conditions. 相似文献