全文获取类型
收费全文 | 2567篇 |
免费 | 5篇 |
专业分类
电工技术 | 20篇 |
综合类 | 1篇 |
化学工业 | 74篇 |
金属工艺 | 5篇 |
机械仪表 | 9篇 |
建筑科学 | 18篇 |
矿业工程 | 1篇 |
能源动力 | 29篇 |
轻工业 | 52篇 |
水利工程 | 4篇 |
石油天然气 | 3篇 |
无线电 | 78篇 |
一般工业技术 | 134篇 |
冶金工业 | 2050篇 |
原子能技术 | 22篇 |
自动化技术 | 72篇 |
出版年
2021年 | 8篇 |
2020年 | 9篇 |
2019年 | 7篇 |
2018年 | 10篇 |
2017年 | 8篇 |
2016年 | 13篇 |
2015年 | 4篇 |
2014年 | 13篇 |
2013年 | 35篇 |
2012年 | 15篇 |
2011年 | 21篇 |
2010年 | 19篇 |
2009年 | 33篇 |
2008年 | 34篇 |
2007年 | 16篇 |
2006年 | 25篇 |
2005年 | 21篇 |
2004年 | 21篇 |
2003年 | 25篇 |
2002年 | 24篇 |
2001年 | 29篇 |
2000年 | 15篇 |
1999年 | 69篇 |
1998年 | 663篇 |
1997年 | 353篇 |
1996年 | 236篇 |
1995年 | 146篇 |
1994年 | 92篇 |
1993年 | 121篇 |
1992年 | 27篇 |
1991年 | 28篇 |
1990年 | 34篇 |
1989年 | 33篇 |
1988年 | 21篇 |
1987年 | 21篇 |
1986年 | 25篇 |
1985年 | 41篇 |
1984年 | 6篇 |
1983年 | 7篇 |
1982年 | 22篇 |
1981年 | 9篇 |
1980年 | 15篇 |
1978年 | 8篇 |
1977年 | 59篇 |
1976年 | 99篇 |
1974年 | 4篇 |
1973年 | 3篇 |
1969年 | 3篇 |
1968年 | 5篇 |
1966年 | 4篇 |
排序方式: 共有2572条查询结果,搜索用时 15 毫秒
81.
Decrease in activity of hypothalamic beta-endorphin (beta-EP) is an important factor for inducing the preovulatory LH surge. To study whether hypothalamic mu opioid receptor is involved in this process, changes in densities of hypothalamic mu opioid receptors were observed in this study by autoradiography and image process during cupric acetate (CuAC)-induced preovulatory LH surge in rabbits. New Zealand female rabbits were injected 1% CuAC 0.9 ml or saline 0.9 ml and sacrificed at different times after the injection. The densities of mu opioid receptor in the medial basal hypothalamus (MBH) and the medial preoptic area (MPO) were measured. A transient increase in densities of MPO mu opioid receptor were observed 1 h after CuAC injection (P < 0.05). The densities of MPO mu opioid receptor decreased significantly before the onset of the LH surge (P < 0.05) and remained at a low level during the surge. The change in densities of mu opioid receptor in the MBH was similar to those in the MPO. No change was observed in the saline control group. There was a negative correlation between the changes in densities of MBH mu opioid receptor and serum LH levels in the process of LH surge. The results suggest that the decrease of hypothalamic mu opioid receptor may be involved in the preovulatory LH surge. 相似文献
82.
M Bouzyk SP Bryant C Evans S Guioli S Ford K Schmidt PN Goodfellow S Povey M Rebello S Rousseaux NK Spurr 《Canadian Metallurgical Quarterly》1997,5(5):299-307
OBJECTIVES: To determine concentrations of chondroitin sulphate (CS) and keratan sulphate (KS) epitopes, glycosaminoglycans (GAGs) and hyaluronan (HA) in knee synovial fluid (SF) from normal subjects and patients with osteoarthritis (OA) or rheumatoid arthritis (RA), to test whether these variables may be used as markers of the OA process. METHODS: OA was subdivided into large joint OA (LJOA), nodal generalised OA (NGOA), and OA with calcium pyrophosphate crystal deposition (CPA). Clinical assessment of inflammation (0-6) was undertaken on OA and RA knees. Knee SF was examined by enzyme linked immunosorbent assay for: CS epitopes, using monoclonal antibodies 3-B-3 and 7-D-4; KS epitope using monoclonal antibody 5-D-4; and HA, using biotinylated HA binding region of cartilage proteoglycan. Total sulphated GAGs were measured by dye binding with 1:9 dimethylmethylene blue. RESULTS: Increased SF 3-B-3 concentrations and 3-B-3/GAG ratio were found in OA, compared with RA or normal knees, with higher 3-B-3 and 3-B-3/GAG in LJOA and NGOA than in CPA. SF 7-D-4 and 7-D-4/GAG were reduced in RA, compared with normal and OA; SF 5-D-4 was reduced in OA compared with normal. GAG and HA concentrations were decreased in both OA and RA. No correlations with radiographic scores were observed, but SF 7-D-4 was lower in 'inflamed' compared with 'non-inflamed' RA and OA knees. In patients with bilateral samples there were strong correlations between right and left knees for all SF variables. CONCLUSIONS: Changed concentrations of SF CS and KS can be detected in OA with a profile that differs from that seen in RA. Clinical subgrouping and local joint inflammation may influence these measures, supporting different pathogenesis within OA subgroups and requirement for careful patient characterisation in SF studies. 相似文献
83.
Inhibition of sickle beta-chain (betaS)-dependent polymerization by nonhuman alpha-chains. A superinhibitory mouse-horse chimeric alpha-chain 总被引:1,自引:0,他引:1
P Nacharaju RP Roy SP White RL Nagel AS Acharya 《Canadian Metallurgical Quarterly》1997,272(44):27869-27876
Horse alpha-chain inhibits sickle beta-chain-dependent polymerization; however, its inhibitory potential is not as high as that of mouse alpha-chain. Horse alpha-(1-30) and alpha-(31-141) segments make, respectively, minor and major contributions to the inhibitory potential of horse alpha-chain. The sum of the inhibitory potential of the two segments does not account for the inhibitory potential of the full-length horse alpha-chain. Although the polymerization inhibitory potential of horse alpha-chain is lower than mouse alpha-chain, the inhibitory potential of horse alpha-(31-141) is comparable to that of mouse alpha-(31-141). When mouse alpha-(1-30) is stitched to horse alpha-(31-141), the product is a chimeric alpha-chain with an inhibitory potential greater than mouse alpha-chain. In contrast, the stitching of horse alpha-(1-30) with mouse alpha-(31-141) had no additional inhibitory potential. Molecular modeling studies of HbS containing the mouse-horse chimeric alpha-chain indicate altered side-chain interactions at the alpha1beta1 interface when compared with HbS. In addition, the AB/GH corner perturbations facilitate a different stereochemistry for the interaction of the epsilon-amino group of Lys-16(alpha) with the beta-carboxyl group of Asp-116(alpha), resulting in a decrease in the accessibility of the side chain of Lys-16(alpha) to the solvent. Based on molecular modeling, we speculate that these perturbations by themselves, or in synergy with the altered conformational aspects of the alpha1beta1 interactions, represent the molecular basis of the superinhibitory potential of the mouse-horse chimeric alpha-chains. 相似文献
84.
SL Tannheimer SL Barton SP Ethier SW Burchiel 《Canadian Metallurgical Quarterly》1997,18(6):1177-1182
A method was developed to determine in eggs 2 components [4,6-dimethyl-2-hydroxypyrimidine and 1,3-bis(4-nitrophenyl)urea] of the anticoccidial drug nicarbazin, used to treat poultry. Samples were extracted with acetonitrile, and the extracts were washed with hexane and evaporated to dryness before analysis by liquid chromatography/mass spectrometry with atmospheric pressure chemical ionization. By switching from positive to negative ion monitoring and using gradient elution, both components were measured within one run. The limit of quantitation of the assay was 10 ng/g for each component. The results of a preliminary feeding trial in which chickens were fed contamination levels of the drug are also reported. 相似文献
85.
Influences of matrix particle size distribution (PSD) (18, 25, 35 and 50 μm) and fat content (25%, 30% and 35%) on flavour release of dark chocolate volatiles were quantified by static headspace gas chromatography using GC–MS. Sixty-eight (68) flavour compounds were identified, comprising alcohols, aldehydes, esters, ketones, furans, pyrans, pyrazines, pyridines, pyroles, phenols, pyrones and thiozoles. From GC–olfactometry, 2-methylpropanal, 2-methylbutanal and 3-methylbutanal had chocolate notes. With cocoa/roasted/nutty notes were trimethyl-, tetramethyl-, 2,3-dimethyl-, 2,5-dimethyl-, 3(or 2),5-dimethyl-2(or 3)-ethyl- and 3,5(or 6)-diethyl-2-methylpyrazine and furfuralpyrrole. Compounds with fruity/floral notes included 3,7-dimethyl-1,6-octadien-3-ol and 5-ethenyltetrahydro-R,R,5-trimethyl-cis-2-furanmethanol. Caramel-like, sweet and honey notes were conferred by 2-phenylethanol, phenylacetaldehyde, 2-phenylethylacetate, 2,3,5-trimethyl-6-ethylpyrazine, 2-carboxaldehyde-1H-pyrrole, furancarboxaldehyde, furfuryl alcohol and 2,5-dimethyl-4-hydroxy-3(2H)furanone. There were direct relationships of fat content with 3-methylbutanal and branched pyrazines but inverse ones with 2-phenylethanol, furfuryl alcohol, methylpyrazine, phenylacetaldehyde, 2, 3, 5-trimethyl-6-ethylpyrazine and 2-carboxaldehyde-1-H-pyrrole. Particle size influenced higher alcohol, aldehyde, ester, ketone and pyrazine concentrations at all fat contents. A multivariate product space suggested flavour effects of the interacting factors. 相似文献
86.
研究了老化试验科学在21世纪的状况,以及取得最新突破性成果之前的漫长征程。介绍了一个全新的突破性的ASTM测试方法的诞生。 相似文献
87.
Martin G. Bakker Benjamin Fowler Michael K. Bowman Gregory S. Patience 《加拿大化工杂志》2020,98(8):1668-1681
Electron paramagnetic resonance (EPR) spectroscopy, also known as electron spin resonance spectroscopy (ESR), utilizes absorption of microwave radiation by unpaired electrons in a magnetic field. The interaction between the unpaired electron(s) and nearby magnetic nuclei helps identify paramagnetic species and can provide information about the motion of the molecule and the local polarity, pH, viscosity, concentration, and accessibility to other paramagnetic species. This mini-review discusses the fundamental underpinnings of EPR needed to correctly interpret EPR spectra. We describe various types of EPR spectra encountered by chemical engineers, and use application examples drawn from the chemical engineering literature to illustrate the information available from the technique. Few chemical engineering departments or even chemistry departments have EPR instruments, which contributes to the significant barrier that prevents this being adopted as a routine measurement technique. However, in 2016 and 2017, Web of Science indexed 7000 articles that applied EPR spectroscopy. A bibliometric map categorized the keywords in four categories based on co-occurrences: magnetic properties, films, and luminescence; crystal structure, complexes, and ligands; nanoparticles, oxidation, and degradation; and, systems, radicals, and H2 O2 . 相似文献
88.
Patrina SP Poh Cordula Hege Mohit P Chhaya Elizabeth R Balmayor Peter Foehr Rainer H Burgkart Jan‐Thorsten Schantz Stefan M Schiller Arndt F Schilling Dietmar W Hutmacher 《Polymer International》2017,66(1):77-84
The potential of the copolymer polycaprolactone‐co‐ poly‐d ,l ‐lactic acid (PCLLA ) as a biomaterial for scaffold‐based therapy for breast tissue engineering applications was assessed. First, the synthesized PCLLA was evaluated for its processability by means of additive manufacturing (AM ). We found that the synthesized PCLLA could be fabricated into scaffolds with an overall gross morphology and porosity similar to that of polycaprolactone. The PCLLA scaffolds possessed a compressive Young's modulus (ca 46 kPa ) similar to that of native breast (0.5 ? 25 kPa ), but lacked thermal stability and underwent thermal degradation during the fabrication process. The PCLLA scaffolds underwent rapid degradation in vitro which was characterized by loss of the scaffolds' mechanical integrity and a drastic decrease in mass‐average molar mass (M w) and number‐average molar mass (M n) after 4 weeks of immersion in phosphate buffer solution maintained at 37 °C. The tin‐catalysed PCLLA scaffold was also found to have cytotoxic effects on cells. Although the initial mechanical properties of the PCLLA scaffolds generally showed potential for applications in breast tissue regeneration, the thermal stability of the copolymer for AM processes, biocompatibility towards cells and degradation rate is not satisfactory at this stage. Therefore, we conclude that research efforts should be geared towards fine‐tuning the copolymer synthesizing methods. © 2016 Society of Chemical Industry 相似文献
89.
A series of imidized acrylic polymers of varying structural composition generated by reaction of methylamine with poly(methyl methacrylate) were blended with a range of styrene/acrylonitrile or SAN copolymers (0–33% AN) and with poly(vinyl chloride). On the basis of glass transition behavior determined by differential scanning calorimetry, some but not all imidized acrylic structures were found to be miscible with PVC and with SAN copolymers within a limited window of AN levels. Acid functionality in the imidized acrylics appears to hinder their miscibility with SAN rather significantly and with PVC to a lesser extent. Miscible SAN blends showed lower critical solution temperature behavior whereas miscible blends with PVC did not up to the highest attainable temperatures. The composition factors that influence the phase behavior are described and interpreted in terms of possible mechanisms. 相似文献
90.
AbstractThe paper discusses the effect of certain variables involved in the production of compacted graphite cast iron by the Inmold Process,? using a 5% Mg-FeSi alloy, such as sulphur content of the base iron, copper content and section size. Experimental results show that acceptable compacted graphite irons can be produced in castings with section sizes ranging from 12.5 to 50 mm. The required residual Mg was a function of the base sulphur as follows: 0.013–0.021 % Mg for a base sulphur of 0.0083–0.0092% and 0.019–0.024% Mg for a base sulphur of 0.017–0.019%. When the base sulphur was 0.025–0.030%, it was impossible to produce compacted graphite microstructures. As expected, copper additions increased the amount of pearlite in the microstructure. For example, a 0.42% Cu content resulted in microstructures containing more than 50% pearlite in sections of 12.5 and 25 mm. 相似文献