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991.
992.
JE Norman JJ Bailey AS Berson WK Haisty D Levy PM Macfarlane PM Rautaharju 《Canadian Metallurgical Quarterly》1998,31(2):83-89
During the last years several reports have demonstrated that melatonin is a efficient free radical scavenger and general antioxidant. In addition, it has been shown that this neurohormone is able to increase the activity of glutathione peroxidase in rat brain cortex as well as the gene expression for some antioxidant enzymes in the Harderian gland of female Syrian hamster. Also, it is well known that brain cells are particularly exposed to free radicals, with antioxidant enzymes as the major defense mechanism that the brain uses to neutralize reactive oxygen species. The aim of the present study was to examine the influence of melatonin on gene expression for antioxidant enzymes in rat brain cortex. Our results clearly demonstrate that exogenously administered melatonin increases the levels of mRNA for glutathione peroxidase, copper-zinc superoxide dismutase, and manganese superoxide dismutase in this tissue. These stimulatory effects are observed after both acute and chronic treatment with this hormone, producing in the latter case the more marked increase. We therefore conclude that melatonin exerts an important role in providing indirect protection against free radical injury by stimulating gene expression for antioxidant enzymes. Consequently, melatonin could be considered as a potential therapeutic agent in some age-related neurodegenerative diseases where excessive free radical production has been implicated. 相似文献
993.
994.
M Blanco JE Blanco MP Alonso A Mora C Balsalobre F Mu?oa A Juárez J Blanco 《Canadian Metallurgical Quarterly》1997,148(9):745-755
A total of 243 Escherichia coli strains isolated from patients with urinary tract infections (UTI) were investigated for the presence of pap, sfa and afa adhesin-encoding operons by using the polymerase chain reaction. It was found that 54%, 53% and 2% of the strains exhibited the pap, sfa and afa genotypes, respectively. Pap+ and/or sfa+ strains were more frequent in cases of acute pyelonephritis (94%) than in cases of cystitis (67%) (P < 0.001) and asymptomatic bacteriuria (57%) (P < 0.001). The pap and/or sfa operons were found in 90% of strains expressing mannose-resistant haemagglutination (MRHA) versus 37% of MRHA-negative strains (P < 0.001). The presence of pap and sfa operons was especially significant in strains belonging to MRHA types III (100%) (without P adhesins) and IVa (97%) (expressing the specific Gal-Gal binding typical of P adhesins). Both pap and sfa operons were closely associated with toxigenic E. coli producing alpha-haemolysin (Hly+) and/or the cytotoxic necrotizing factor type 1. There was an apparent correlation between the pap and sfa operons and the O serogroups of the strains. Thus, 93% of strains belonging to O1, O2, O4, O6, O7, O14, O15, O18, O22, O75 and O83 possessed pap and/or sfa operons, versus only 32% of strains belonging to other serogroups (P < 0.001). The results obtained in this study confirm the usefulness of our MRHA typing system for presumptive identification of pathogenic E. coli exhibiting different virulence factors. Thus, 85% of strains that possessed both pap and sfa adhesin-encoding operons showed MRHA types III or IVa previously associated with virulence of E. coli strains that cause UTI and bacteraemia. 相似文献
995.
JE Baumgartner JW Wheless S Kulkarni H Northrup KS Au A Smith B Brookshire 《Canadian Metallurgical Quarterly》1997,27(6):311-318
Using the pig as a model, it was shown that stimulation of the distal nerve ending of the pudendal nerve leads to the isolated stimulation of the external anal sphincter muscle. No difference in pressure response was noted after application of between 0.5 and 1.5 mA unilateral or bilateral stimulation. Major advantages observed using between 1.5 and 2.5 mA bilateral stimulation; with a stimulation between 2.0 and 2.5 mA the pressure response was twice as high compared to unilateral stimulation. Continuous stimulation of the striated anal sphincter muscle leads to fatigue, reaching 50% fatigue after a median time between 40-90 s. In cyclic stimulation (alternation every 15 s, duration 20 min) a fatigue reaction was also seen. The peak pressure decreased after 20 min for a median of 11%, the final pressure was lowered in 15% following a logarithmic curve pattern. The experimental application of variable impulse ranges also caused pressure differences. Increasing the impulse range from 200 to 450 microseconds (peak pressure) vs. 400 microseconds (final pressure) resulted in a statistically significant pressure increase. Therefore, it was proven that selective stimulation of the external anal sphincter muscle can lead to a transient pressure increase, which possibly improves fecal continence. 相似文献
996.
JE C?té 《Canadian Metallurgical Quarterly》1997,20(5):577-597
In a previous issue of this journal, the identity capital model was presented as part of an effort to better understand the relationship between social context and identity formation (C?té, 1996a). The present paper provides an empirical test of that model as it applies to the late-adolescent passage of university students toward adulthood. A series of research questions are explored which reveal the following: (1) concepts used in the model can be reliably measured; (2) significant relationships exist among certain measures of identity capital resources; (3) these resources have significant associations with measures of identity capital acquisition; (4) over 2 years of university, identity capital increases overall for female students (on a measure of adult identity resolution) and for those of lower social class background (on a measure of community identity resolution); and (5) certain resources acquired before attending university are predictors of identity capital acquisition after 2 years of attendance, net of the identity capital with which students begin university. 相似文献
997.
A new multilayer approach to gradient coil design, which allows the production of very strong gradient coils with reasonable resistance and consequent power dissipation, has been developed. Using this approach we have designed and built a strong z-gradient coil that will accommodate vertically mounted samples contained in 5-mm nuclear magnetic resonance tubes. The coil has an efficiency of 1.73 Tm-1A-1, an inductance of 49 microH, and a resistance of 1.8 omega, with a homogeneous volume consisting of a central cylinder of 4.5-mm length and diameter. This coil has been used to monitor the diffusion of water in Nylon 6.6 at room temperature, during desorption. This system is difficult to monitor via nuclear magnetic resonance (NMR), because the diffusion coefficients are typically less than 10(-13) m2s-1, while the T2 relaxation time is less than 1 ms even when the sample is fully saturated. The resulting measurements show a strong concentration dependence of the T2 relaxation time and self-diffusion coefficient of the absorbed water. The measured concentration profiles are consistent with a Fickian diffusion process with a concentration-dependent diffusion coefficient. The measured self-diffusion values are in reasonable agreement with those inferred from the variation of the concentration profiles as a function of time, using the one-dimensional Fickian diffusion equation. 相似文献
998.
BF Boeve MH Silber TJ Ferman E Kokmen GE Smith RJ Ivnik JE Parisi EJ Olson RC Petersen 《Canadian Metallurgical Quarterly》1998,51(2):363-370
It is commonly believed that MgATP2- is the substrate of F1-ATPases and ATP4- acts as a competitive inhibitor. However, the velocity equation for such competitive inhibition is equivalent to that for a rapid equilibrium ordered binding mechanism in which ATP4- adds first and the binding of Mg2+ is dependent on the formation of the E x ATP4- complex. According to this ordered-binding model, solution formed MgATP2- is not recognized by the ATPase as a direct substrate, and the high-affinity binding of Mg2+ to the E x ATP4- complex is the key reaction towards the formation of the ternary complex. These models (and others) were tested with an F1- ATPase, isolated from Halobacterium saccharovorum, by evaluating the rate of ATP hydrolysis as a function of free [ATP4-] or free [Mg2+]. The rates were asymmetrical with respect to increasing [ATP4-] versus increasing [Mg2+]. For the ordered-binding alternative, a series of apparent dissociation constants were obtained for ATP4-(K(A)aPP), which decreased as [Mg2+] increased. From this family of K(A)aPP the true K(A) was retrieved by extrapolation to [Mg2+] = 0 and was found to be 0.2 mM. The dissociation constants for Mg2+, established from these experiments, were also apparent (K(B)aPP) and dependent on [ATP4-] as well as on the pH. The actual K(B) was established from a series of K(B)aPP by extrapolating to [ATP4-] = infinity and to the absence of competing protons, and was found to be 0.0041 mM. The pKa of the protonable group for Mg2+ binding is 8.2. For the competitive inhibition alternative, rearrangement of the constants and fitting to the velocity equation gave an actual binding constant for MgATP2- (K(EAB)) of 0.0016 mM and for ATP4- (K(EA)) of 0.2 mM. Decision between the two models has far-reaching mechanistic implications. In the competitive inhibition model MgATP2- binds with high affinity, but Mg2+ cannot bind once the E x ATP4- complex is formed, while in the ordered-binding model binding of Mg2+ requires that ATP4- adds first. The steric constraints evident in the diffraction structure of the ATP binding site in the bovine mitochondrial F-ATPase [Abrahams, J. P., Leslie, A. G. W., Lutter, R. & Walker, J. E. (1994) Nature 370, 621-628] tend to favor the ordered-binding model, but the final decision as to which kinetic model is valid has to be from further structural studies. If the ordered-binding model gains more experimental support, a revision of the current concepts of unisite catalysis and negative cooperativity of nucleotide binding will be necessary. 相似文献
999.
J Bartels S Maune JE Meyer R Kulke C Schlüter J R?wert E Christophers JM Schr?der 《Canadian Metallurgical Quarterly》1997,35(4):171-174
The Escherichia coli low molecular mass penicillin-binding proteins (PBP4, PBP5 and PBP6) are a group of penicillin-sensitive enzymes involved in the final stages of cell wall assembly. It has been suggested that these proteins may interact with the periplasmic face of the inner membrane via C-terminal amphiphilic alpha-helices. Theoretical analysis has predicted that these C-terminal helical regions may be membrane interactive. We have tested this hypothesis by assaying PBP C-terminal homologues (P4, P5 and P6) for haemolytic activity. Our results show that the PBP5 and PBP6 C-terminal homologues readily lyse sheep erythrocytes in a pH-dependent manner with LD50's of 3.5 x 10(-6) M and 6.8 x 10(-7) M respectively at pH 7. These results appear to support the present model for the membrane anchoring of PBP5 and PBP6. The PBP4 C-terminal homologue shows no evidence of haemolytic activity which could imply a different means of membrane association for PBP4. 相似文献
1000.