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Ginsburg K.S. Lin J.C. O''Neill W.D. 《IEEE transactions on bio-medical engineering》1992,39(10):1011-1021
Excitable tissues have been reported to respond to weak microwave (MW) fields, possibly by nonlinear perturbation of a cellular process such as ion conduction across membranes. We sought effects of MW (continuous wave, 2.45 GHz, specific absorption rates 12.5 or 125 mW/g) on input resistances and action potential (AP) intervals of neurons in ganglia of snails (Helix aspersa), at 20.9 +/- 0.1 degrees C. At 12.5 mW/g, input resistance did not change during irradiation, but increased (p < 0.05) afterward. At 125 mW/g, input resistance during irradiation was lower than in unirradiated controls. Serial correlograms changed marginally more frequently in MW experiments than in controls, but the changes had no consistent pattern. The AP firing rate was affected by MW, but the direction was not consistent across cells. When AP generation was modeled as being due to a neuronal input current, MW did not affect its mean, standard deviation, or autocorrelation. Unlike MW, temperature changes caused neurons to respond robustly and reversibly. Threshold for changing input resistance was 0.63 degree C. The data suggest that MW may enhance degenerative effects such as metabolic rundown or loss of ion channel patency, but do not indicate a specific mechanism for MW interaction with neurons. 相似文献
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(1) The effects of long term treatment with 3-acetylpyridine on the stability of enzymes towards heat and trypsin treatment were studied. (2) In the liver NAD or NADP provided a similar degree of protection against heat inactivation at 55 degrees C for 6-phosphogluconate dehydrogenase (24%), glyceraldehyde-3-phosphate dehydrogenase (24%) and malic enzyme (20%), low level of protection of lactate dehydrogenase (13%) but didn't affect acetylcholinesterase at all. In the muscle, however, there was substantial protection against heat inactivation by coenzyme of glyceraldehyde-3-phosphate dehydrogenase (52%), an intermediate level of protection of lactate dehydrogenase (25%), low level of protection of 6-phosphogluconate dehydrogenase (17%) and malic enzyme (17%) and almost no protection of acetylcholinesterase. (3) In the susceptibility towards trypsin a low but similar degree of protection for dehydrogenases by coenzymes was observed in the liver whereas in the muscle there was substantial protection against trypsin inactivation by NAD of glyceraldehyde-3-phosphate dehydrogenase, an intermediate level of protection of 6-phosphogluconate dehydrogenase and malic enzyme and very little protection of lactate dehydrogenase but no protection of acetylcholinesterase. Among enzymes tested, glyceraldehyde-3-phosphate dehydrogenase showed the greatest protection against heat and trypsin inactivation by NAD. (4) The results suggest that the effect of 3-acetylpyridine treatment on the stability of muscle glyceraldehyde-3-phosphate dehydrogenase appears to be quite specific and selective. 相似文献
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BV Murthy AS Muerhoff SM Desai SN Natov BA Bouthot R Ruthazer CH Schmid AS Levey IK Mushahwar BJ Pereira 《Canadian Metallurgical Quarterly》1998,53(6):1769-1774
The etiology of liver disease remains unknown in about 4 to 23% of dialysis patients and 10 to 16% of renal transplant recipients. A search for other causative agents of liver disease led to the discovery of the GB group of viruses. We studied the association between the presence of GB virus C (GBV-C) infection, known risk factors for parenterally-transmitted infections and history or laboratory evidence of liver disease among end-stage renal disease (ESRD) patients referred for renal transplantation to the New England Organ Bank, MA. Stored sera from patients on the renal transplantation waiting list between November 1986 and June 1990 were tested for antibody to hepatitis C virus (HCV). Sera were available in 1544 of 3243 (48%) patients, and anti-HCV was detected by ELISA3 in 287 (19%). All 287 anti-HCV positive patients formed the anti-HCV positive cohort and 286 randomly selected anti-HCV negative patients formed the anti-HCV negative cohort (573 patients overall). Additional sera were available for GBV-C RNA testing in 465 of 573 (81%) patients, and GBV-C RNA was detected by RT-PCR in 146. The overall extrapolated prevalence of serum GBV-C RNA was 29%. The prevalence of serum GBV-C RNa among anti-HCV positive patients (35%) was not significantly different from that among anti-HCV negative patients (29%; P = 0.22). In a univariate analysis, compared to patients without GBV-C RNA, patients with serum GBV-C RNA were younger [odds ratio (OR) 0.98 per year of age, P = 0.01], had a lower proportion of males (OR 0.64, P = 0.03), lower proportion of patients with diabetes mellitus (OR 0.44, P = 0.01), higher proportion of patients with a previous transplantation (OR 1.53, P = 0.04), longer duration of dialysis at the time of enrollment (OR 1.004 per month on dialysis, P = 0.03), and a higher proportion of patients with history of transfusions (OR 4.58, P = 0.01). Serum GBV-C RNA was not associated with a significantly increased OR for history of liver disease or non-A, non-B hepatitis, or elevated serum alanine aminotransferase levels. In a step-wise multivariate regression analysis, a younger age (OR 0.98 per year of age, P = 0.03), and history of blood transfusions (OR 3.89, P = 0.03) were associated with an increased OR for serum GBV-C RNA, while diabetes mellitus was associated with a decreased OR for GBV-C RNA (OR 0.47, P = 0.01). Anti-HCV was not a predictor of serum GBV-C RNA (OR 1.07, P = 0.77). The results of this study support the fact that GBV-C is a parenterally transmitted virus and shed light on the modes of transmission of GBV-C among ESRD patients. However, the association with liver disease remains to be established. 相似文献
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The Kjeldahl and Dumas (combustion) methods were compared in 11 laboratories analyzing samples of milk, skim milk powder, whole milk powder, whey protein concentrate, infant formula, casein, caseinate, 2 reference compounds (glycine and EDTA), and a secondary reference skim milk powder. The comparison was conducted by using international standards where applicable. Overall means were 8.818 g N/100 g by the Kjeldahl method and 8.810 g N/100 g by the Dumas method. No evidence was found for a consistent bias between methods that may be of concern in the trading of dairy produce. A review of more than 10 related trials revealed a lack of consensus in the bias between the 2 methods, suggesting that differences in methodology and sources of systematic error may be contributors. For samples containing > 2 g N/100 g, the Dumas relative repeatability and reproducibility standard deviations were consistently about 0.35 and 0.75%, respectively, whereas the corresponding Kjeldahl values declined generally with N content and were significantly larger. The Dumas precision characteristics may be due to the dominance of Leco analyzers in this trials, and in most other recent trials, rather than an inherent method attribute. Protein determination methods for dairy products need to be reviewed and updated. The Dumas method needs Codex Alimentarius status as a recognized test method. 相似文献
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JR Bearder VM Frydman P Gaskin IK Hatton WE Harvey J McMillan BO Phinney 《Canadian Metallurgical Quarterly》1976,39(2):178-183
Angiotensin II (A II) and analogues were tested for their ability to restore electrical and mechanical activity to cardiac muscle preparations in which the fast Na+ channels had been inactivated by partial depolarization (22-27 mM K+) or by tetrodotoxin (TTX). The partially depolarized or TTX-blocked preparations were chosen because under these conditions electrical and mechanical responses are primarily Ca2+ -dependent. In depolarized rabbit right atria, A II restored spontaneous mechanical and electrical activity (measured by both intracellular and extracellular recording techniques). The frequency of action potential discharge was concentration-dependent; the threshold concentration of A II was 10(-10) M, the ED50 was 8 X 10(-9) M, and the maximum effect was observed at 5 X 10(-8) M. In contrast, depolarized guinea pig atria were insensitive to A II, Sar1-angiotensin II, and des-Asp1-angiotensin II, even at concentrations as high as 10(-5) M. Rabbit papillary muscle (TTX-blocked), embryonic (18-day) chick heart (partially depolarized) and chick heart reaggregates (TTX-blocked) responded similarly to rabbit atria in that A II (9.6 X 10(-7) M) restored both electrical and mechanical activity. We found that in these preparations the action of A II was unaffected by propranolol (5.0 X 10(-6) M to 5.0 X 10(-5) M) but was blocked by Mn2+ (10(-3) M), D-600 (1 X 10(-7) g/ml) and the specific A II antagonists Sar1-Ala8-angiotensin II (P-113) (5.0 X 10(-5) M) and Sar1-Ile8-angiotensin II (5.28 X 10(-5) M). We conclude that the positive inotropic effect of A II on the myocardium is due to its ability to increase transmembrane ion movements in or through the cell membrane. The ability of Mn2+ and D-600 to block this effect suggests that this ion movement is via the so-called "slow channels." 相似文献
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用于测量GIS中瞬态外壳电压的电阻性阻抗分压器 总被引:6,自引:2,他引:4
设计了用于测量GIS中TEV的阻抗分压器及其测量系统 ;分析了该系统的特性 ,并对其刻度因数和阶跃响应进行了实测 ,在实验室和现场进行了应用。结果表明 ,该系统主要性能满足IEC6 132 1标准的要求 ,可以在工程中应用 相似文献
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