全文获取类型
收费全文 | 6685篇 |
免费 | 105篇 |
国内免费 | 23篇 |
专业分类
电工技术 | 67篇 |
综合类 | 3篇 |
化学工业 | 673篇 |
金属工艺 | 104篇 |
机械仪表 | 80篇 |
建筑科学 | 43篇 |
矿业工程 | 4篇 |
能源动力 | 115篇 |
轻工业 | 149篇 |
水利工程 | 26篇 |
石油天然气 | 31篇 |
无线电 | 319篇 |
一般工业技术 | 673篇 |
冶金工业 | 4091篇 |
原子能技术 | 38篇 |
自动化技术 | 397篇 |
出版年
2024年 | 10篇 |
2023年 | 44篇 |
2022年 | 64篇 |
2021年 | 89篇 |
2020年 | 103篇 |
2019年 | 73篇 |
2018年 | 88篇 |
2017年 | 106篇 |
2016年 | 99篇 |
2015年 | 71篇 |
2014年 | 105篇 |
2013年 | 244篇 |
2012年 | 110篇 |
2011年 | 158篇 |
2010年 | 135篇 |
2009年 | 127篇 |
2008年 | 135篇 |
2007年 | 130篇 |
2006年 | 99篇 |
2005年 | 71篇 |
2004年 | 66篇 |
2003年 | 64篇 |
2002年 | 58篇 |
2001年 | 44篇 |
2000年 | 48篇 |
1999年 | 170篇 |
1998年 | 1351篇 |
1997年 | 751篇 |
1996年 | 450篇 |
1995年 | 302篇 |
1994年 | 256篇 |
1993年 | 271篇 |
1992年 | 61篇 |
1991年 | 73篇 |
1990年 | 73篇 |
1989年 | 53篇 |
1988年 | 53篇 |
1987年 | 61篇 |
1986年 | 46篇 |
1985年 | 50篇 |
1984年 | 19篇 |
1983年 | 25篇 |
1982年 | 25篇 |
1981年 | 28篇 |
1980年 | 35篇 |
1979年 | 16篇 |
1978年 | 19篇 |
1977年 | 83篇 |
1976年 | 142篇 |
1975年 | 16篇 |
排序方式: 共有6813条查询结果,搜索用时 15 毫秒
991.
CA Dujovne J Eff L Ferraro RJ Goldstein AM Gotto WD Hall WS Harris SJ Held A Herd DB Hunninghake 《Canadian Metallurgical Quarterly》1993,72(15):1131-1136
Antihypertensive drugs may affect serum lipoprotein levels in mixed populations but data in hyperlipidemic patients are scanty. Atenolol versus celiprolol effects on serum lipoproteins were compared in 159 hyperlipoproteinemic hypertensive patients. This was a randomized, double-blind, parallel-group, positive-controlled multicenter trial with centralized lipoprotein laboratory and diet constancy monitoring. Blood pressure reduction and serum lipoprotein and apoprotein levels were monitored for 3 months. Both drugs reduced systolic and diastolic blood pressures. Atenolol had greater effects than celiprolol on diastolic pressure, but effects on systolic blood pressure were not different. Patients receiving atenolol had lower serum high-density lipoprotein cholesterol levels and higher low-density lipoprotein/high-density lipoprotein cholesterol ratios, whereas patients treated with celiprolol showed no contrasting changes. These differences in lipoprotein levels between drug treatment groups were statistically significant at weeks 9 and 12. The difference between drug treatments was also significant if the values of the 9- and 12-week visits were averaged. Patients taking atenolol had statistically significantly higher serum levels of total cholesterol, triglycerides and apoprotein B at 9 weeks. These divergent directional changes were consistent throughout and statistically significantly different between drugs. 相似文献
992.
Ulcer prevention efficacy of orally, rectally and sublingually administered omeprazole was evaluated and compared using ulcer index and percentage inhibition of ulcerogenicity in three different acute gastric ulcer models viz, indomethacin, 0.6N HCl and aspirin (after pylorus ligation) induced ulcers in rats. The ulcer prevention efficacy after oral, rectal and sublingual administration were statistically significant (P < 0.01) in all the models. The differences in ulcer index and percentage inhibition of ulcerogenicity for rectal and sublingual administration were insignificant (P < 0.05) in indomethacin and HCl induced ulcers and were significant (P < 0.05) in aspirin induced ulcers. The ulcer prevention activity was significantly higher (P < 0.05) after rectal and sublingual routes when compared to oral administration in all three models evaluated. Results revealed a faster onset and higher extent of pharmacodynamic activity of omeprazole after rectal and sublingual administration. 相似文献
993.
GA Jansen SJ Mihalik PA Watkins HW Moser C Jakobs S Denis RJ Wanders 《Canadian Metallurgical Quarterly》1996,229(1):205-210
Phytanic acid (3,7,11,15-tetramethylhexadecanoic acid) is a branched-chain fatty acid which accumulates in a number of inherited diseases in human. Because beta-oxidation is blocked by the methyl group at C-3, phytanic acid first undergoes decarboxylation via an alpha-oxidation mechanism. The structure and subcellular localization of the phytanic acid alpha-oxidation pathway have remained enigmatic through the years, although they have generally been assumed to involve phytanic acid and not its CoA-ester. This view has recently been challenged by the findings that in rat liver phytanic acid first has to be activated to its CoA-ester before alpha-oxidation and by the discovery of a new enzyme, phytanoyl-CoA hydroxylase, which converts phytanoyl-CoA to 2-hydroxyphytanoyl-CoA. We now show that this newly discovered enzyme is also present in human liver. Furthermore, we show that this enzyme is located in peroxisomes and deficient in liver from Zellweger patients who lack morphologically distinguishable peroxisomes, which provides an explanation for the long-known deficient oxidation of phytanic acid in these patients. These results suggest that phytanic acid alpha-oxidation is peroxisomal and that it utilizes the coenzyme A derivative as substrate, thus giving further support in favour of the new, revised pathway of phytanic acid alpha-oxidation. 相似文献
994.
SJ Milstein EN Barantsevitch VA Grechanovski DJ Sarubbi 《Canadian Metallurgical Quarterly》1996,13(6):651-665
Soybean hydrolysate is a hydrophilic mixture of amino acids and low molecular peptides which are soluble over the whole pH range. Chemical modification of soybean hydrolysate with aromatic acyl chlorides resulted in a product that yielded pH-dependent microspheres. Investigation into the physiochemical properties of the microsphere forming material indicated that acylation had alerted the hydrophobic/hydrophilic ratio as evidenced by an increased column retention time on reverse phase HPLC. This was further confirmed by analysis of the amino acid composition of the modified material. The data indicated that the hydrophobic/hydrophilic ratio and low molecular were critical factors in the formation of this supramolecular complex. An estimation based on sedimentation rate revealed an average molecular weight of these microspheres as 10(7)-10(8) Daltons. Light scattering experiments indicated that the microspheres have discrete chambers in the interior. Included among the properties of the microspheres that have been determined are the pH range of the phase transition, size distribution and zeta-potential. The physiochemical characteristics of the microspheres prepared from modified soybean protein are similar to the microsphere forming material produced by thermal condensation of amino acids. Formation of microspheres in solution containing either porcine insulin or salmon calcitonin resulted in the encapsulation of nearly 60% of the dissolved proteins. Oral gavage of encapsulated porcine insulin or salmon calcitonin into the stomach of rats resulted in significant titers of either protein in the systematic circulation. 相似文献
995.
Stimulation with inducers that cause persistent activation of NF-kappa B results in the degradation of the NF-kappa B inhibitors, I kappa B alpha and I kappa B beta. Despite the rapid resynthesis and accumulation of I kappa B alpha, NF-kappa B remains induced under these conditions. We now report that I kappa B beta is also resynthesized in stimulated cells and appears as an unphosphorylated protein. The unphosphorylated I kappa B beta forms a stable complex with NF-kappa B in the cytosol; however, this binding fails to mask the nuclear localization signal and DNA binding domain on NF-kappa B, and the I kappa B beta-NF-kappa B complex enters the nucleus. It appears therefore that during prolonged stimulation, I kappa B beta functions as a chaperone for NF-kappa B by protecting it from I kappa B alpha and allowing it to be transported to the nucleus. 相似文献
996.
997.
KL Duffin GW Lange JK Welply R Florman PJ O'Brien A Dell AJ Reason HR Morris SJ Fliesler 《Canadian Metallurgical Quarterly》1993,3(4):365-380
The N-linked oligosaccharides of frog (Rana pipiens) rhodopsin were analysed by sequential exoglycosidase digestion and gel filtration chromatography, following reductive tritiation. In addition, selected tryptic glycopeptides obtained from frog retinal rod outer segment membranes were examined by electrospray mass spectrometry (ES-MS), fast atom bombardment mass spectrometry (FAB-MS), amino acid sequence and composition analysis, and carbohydrate composition analysis. The amino acid sequence data demonstrated that the glycopeptides were derived from rhodopsin and confirmed the presence of two N-glycosylation sites, at residues Asn2 and Asn15. The predominant glycan (approximately 60% of total) had the structure GlcNAc beta 1-2Man alpha 1-3(Man alpha 1-6) Man beta 1-4GlcNAc beta 1-4GlcNAc-(Asn), with the remaining structures containing 1-3 additional hexose residues, as reported previously for bovine rhodopsin. Unlike bovine rhodopsin, however, a sizable fraction of the total glycans of frog rhodopsin also contained sialic acid (NeuAc), with the sialylated oligosaccharides being present exclusively at the Asn2 site. FAB-MS analysis of oligosaccharides released from the Asn2 site gave, among other signals, an abundant quasimolecular ion corresponding to a glycan of composition NeuAc1Hex6HexNAc3 (where Hex is hexose and HexNAc is N-acetylhexosamine), consistent with a hybrid structure. The potential biological implications of these results are discussed in the context of rod outer segment membrane renewal. 相似文献
998.
A 4-year-old boy with congenital pseudarthrosis of the tibia had two unsuccessful operative attempts for union. After these procedures the patient had a 6-cm leg length discrepancy and an equinovalgus foot deformity. Because of these deformities he underwent Syme amputation at the ankle and was fitted with a total contact prosthesis. Eight months after the amputation, a solid union was seen across the pseudarthrosis site, although no attempt was made to achieve union with internal fixation or bone grafting. The authors think that vertical alignment of the limb in a total contact prosthesis, along with the compressive forces of weightbearing, allowed the pseudarthrosis site to heal in the patient. 相似文献
999.
1000.
D van Leenen T van der Poll M Levi H ten Cate SJ van Deventer CE Hack LA Aarden JW ten Cate 《Canadian Metallurgical Quarterly》1993,151(4):2318-2325
Costimulation of neutrophils and cytokines may play an important role in organ injury in sepsis. Pentoxifylline inhibits various neutrophil functions in vitro, and attenuates endotoxin-induced production of TNF in both in vitro and in vivo models. To assess the effect of pentoxifylline on neutrophil activation in endotoxemia, nine adult chimpanzees (Pan troglodytes) were i.v. injected with saline (n = 2), Escherichia coli endotoxin (4 ng/kg; n = 4), or E. coli endotoxin (4 ng/kg) in combination with pentoxifylline (500 mg/3 h, starting 30 min before the endotoxin injection; n = 3). Serial blood samples were obtained for measurements of leukocyte counts and the granulocytic proteinases elastase complexed with alpha 1-antitrypsin and lactoferrin, and cytokines during the next 5 h. No changes were observed in the saline-treated chimpanzees. Endotoxin induced a marked leukocytosis and neutrophilia, which were slightly reduced by pentoxifylline. In contrast, pentoxifylline almost completely prevented endotoxin-induced neutrophil degranulation: peak elastase-alpha 1-antitrypsin was 164 +/- 21 ng/ml (mean +/- SE) after endotoxin alone, vs 71 +/- 7 ng/ml after endotoxin with pentoxifylline (t = 3 h; p < 0.05); peak lactoferrin was 329 +/- 15 and 182 +/- 5 ng/ml, respectively (t = 5 h; p < 0.05). Pentoxifylline also inhibited the endotoxin-induced release of TNF (271 +/- 26 vs 55 +/- 23 pg/ml at t = 1.5 h; p < 0.05) and IL-6 (225 +/- 42 vs 73 +/- 25 pg/ml at t = 2 h; p < 0.05). IL-8 release was not significantly inhibited by pentoxifylline. In none of the animals activation of the C system could be detected. We conclude that pentoxifylline attenuates neutrophil activation in endotoxemia in chimpanzees, probably in part by inhibiting the release of TNF. 相似文献