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991.
YF Smets JW van der Pijl JT van Dissel J Ringers JW de Fijter HH Lemkes 《Canadian Metallurgical Quarterly》1997,12(4):764-771
Gram-positive thermophilic Bacillus species contain cytochrome caa3-type cytochrome c oxidase as their main terminal oxidase in the respiratory chain. To identify alternative oxidases, we isolated several mutants from B. stearothermophilus defective in the caa3-type oxidase activity [Sakamoto, J. et al (1996) FEMS Microbiol. Lett. 143, 151-158]. A novel oxidase was isolated from membrane preparations of one of the mutants, K17. The oxidase was composed of two subunits with molecular masses of 56 and 19 kDa, and contained protoheme IX, heme O, heme A, and Cu in a ratio of 1:0.7:0.2:3. CO difference spectra indicate that the high-spin heme is mainly heme O. These results suggest that the enzyme belongs to the heme-copper oxidase family and is a cytochrome b(o/a)3-type oxidase, whose high-spin heme is mainly heme O and partly heme A. The enzyme oxidized cytochrome c-551, which is a membrane-bound lipoprotein of thermophilic Bacillus. The turnover rate of the activity (Vmax = 190 s[-1]) and its affinity for cytochrome c-551 (Km = 0.15 microM) were much higher than those for yeast and equine heart cytochromes c. The oxidase activity was enhanced by the presence of salts and inhibited by sodium cyanide with a Ki value of 19 microM. The enzyme kinetics suggests that cytochrome c-551 is the natural substrate to this oxidase. Furthermore, the oxidase had similarity to cytochrome ba3-type oxidase from Thermus thermophilus in the subunit composition, partial amino acid sequence, and prosthetic groups, and therefore is suggested to belong to a unique subgroup of the heme-copper oxidase family together with the Thermus enzyme and archaeal oxidases such as Sulfolobus SoxABCD. 相似文献
992.
993.
A Radominska-Pandya JM Little JT Pandya TR Tephly CD King GW Barone JP Raufman 《Canadian Metallurgical Quarterly》1998,1394(2-3):199-208
While UDP-glucuronosyltransferases (UGTs) are known to be expressed at high levels in human liver, relatively little is known about extrahepatic expression. In the present study, UGT2B family isoforms involved in the glucuronidation of steroid hormones and bile acids have been characterized in microsomes prepared from jejunum, ileum and colon from six human subjects. Glucuronidation of androsterone and testosterone was highly significant and increased from proximal to distal intestine. In contrast, hyodeoxycholic acid was glucuronidated at a low level in jejunum and ileum and activity was barely detectable in colon. No significant glucuronidation of lithocholic acid was found. Small phenols were glucuronidated with much lower activity than found in liver. High levels of UGT protein were detected with polyclonal anti-rat androsterone- and testosterone-UGT antibodies, whereas UGT2B4, a major hepatic hyodeoxycholic acid-specific UGT, was undetectable using a highly specific anti-human UGT2B4 antibody. Screening for RNA expression by RT-PCR confirmed the absence of UGT2B4 and UGT1A6 and showed expression of UGT2B7, a hepatic isoform shown to glucuronidate androsterone, in all intestinal segments. To our knowledge, the presence of functional androsterone and testosterone directed isoforms in human intestine is a novel finding which supports the idea that the intestinal tract functions as a steroid-metabolizing organ and plays a significant role in steroid hormone biotransformation. 相似文献
994.
MJ Econs NE Friedman PS Rowe MC Speer F Francis TM Strom C Oudet JA Smith JT Ninomiya BE Lee H Bergen 《Canadian Metallurgical Quarterly》1998,83(10):3459-3462
Previous investigators described a kindred with an X-linked dominant form of phosphate wasting in which affected children did not have radiographic evidence of rickets, whereas older individuals were progressively disabled by severe bowing. They proposed that this kindred suffered from a distinct disorder that they referred to as adult-onset vitamin D-resistant hypophosphatemic osteomalacia (AVDRR). We recently identified a gene, PHEX, that is responsible for the disorder X-linked hypophosphatemic rickets. To determine whether AVDRR is a distinct form of phosphate wasting, we searched for PHEX mutations in affected members of the original AVDRR kindred. We found that affected individuals have a missense mutation in PHEX exon 16 that results in an amino acid change from leucine to proline in residue 555. Clinical evaluation of individuals from this family indicates that some of these individuals display classic features of X-linked hypophosphatemic rickets, and we were unable to verify progressive bowing in adults. In light of the variability in the clinical spectrum of X-linked hypophosphatemic rickets and the presence of a PHEX mutation in affected members of this kindred, we conclude that there is only one form of X-linked dominant phosphate wasting. 相似文献
995.
DN Marinoff EH Spitzberg JT Chueh JM Goldman T Downs 《Canadian Metallurgical Quarterly》1998,43(12):1051-1054
BACKGROUND: Delayed-interval delivery is infrequent in twin gestation and more rare in triplet and quadruplet gestation. Coexistence of a triploid pregnancy with a normal fetus has not previously been reported to have resulted in survival of the normal fetus. CASE: A 26-year-old woman, gravida 2, para 0-0-1-0, was diagnosed with a quadruplet pregnancy. At 16 1/2 weeks' gestation she developed preeclampsia and severe hyperemesis. Ultrasound was consistent with partial molar pregnancy in quadruplet D. Quadruplet D died in utero, and the preeclampsia and hyperemesis resolved. At 19 5/7 weeks, spontaneous rupture of the membranes and preterm labor occurred, and quadruplet A, stillborn female weighing 260 g, was delivered. With the use of antibiotic therapy, tocolysis and bed rest, the remaining two fetuses were maintained in utero until 32 6/7 weeks' gestation, when quadruplet B, a 1,470-g female, and quadruplet C, a 1,700-g female, were delivered. CONCLUSION: This was the first reported case of surviving fetuses coexisting with a partial molar pregnancy. This case was also complicated by preterm delivery and successful delayed-interval birth in a quadruplet pregnancy. 相似文献
996.
BM Gogel JA Kuhn KM Ferry TL Fisher JT Preskitt JC O''Brien ZH Lieberman JS Stephens DN Krag 《Canadian Metallurgical Quarterly》1998,176(6):544-547
Serum levels of leptin are decreased in underweight AN patients and increase with weight restoration. To assess the relationship of decreased leptin levels with other hormonal abnormalities in AN and to evaluate the possible role of increasing leptin levels, alone or in combination with other hormones, in the resumption of menses that accompanies weight gain, we studied cross-sectionally sixty-five consecutively enrolled AN patients. Subjects were divided in three groups: (I) underweight and amenorrheic; (II) weight-recovered but still amenorrheic; and (III) weight-recovered and eumenorrheic women. Patients in group I had decreased BMI, serum leptin, estradiol (E2), insulin-like growth factor 1 (IGF-1) and urinary growth hormone (GH) levels and increased sex hormone-binding globulin (SHBG) levels, compared to AN patients in groups II and III. Moreover, although no differences in leptin levels or BMI were observed between amenorrheic and eumenorrheic weight-recovered patients (groups II and III), free E2 and GH levels were higher (P<0.02) in weight-recovered, eumenorrheic women. Thus, it appears that leptin is a necessary, but not a sufficient, factor for the resumption of menses in AN patients. 相似文献
997.
UB Sleytr H Bayley M Sára A Breitwieser S Küpcü C Mader S Weigert FM Unger P Messner B Jahn-Schmid B Schuster D Pum K Douglas NA Clark JT Moore TA Winningham S Levy I Frithsen J Pankovc P Beale HP Gillis DA Choutov KP Martin 《Canadian Metallurgical Quarterly》1997,20(1-2):151-175
The wealth of information existing on the general principle of S-layers has revealed a broad application potential. The most relevant features exploited in applied S-layer research are: (i) pores passing through S-layers show identical size and morphology and are in the range of ultrafiltration membranes; (ii) functional groups on the surface and in the pores are aligned in well-defined positions and orientations and accessible for binding functional molecules in very precise fashion; (iii) isolated S-layer subunits from many organisms are capable of recrystallizing as closed monolayers onto solid supports at the air-water interface, on lipid monolayers or onto the surface of liposomes. Particularly their repetitive physicochemical properties down to the subnanometer scale make S-layers unique structures for functionalization of surfaces and interfaces down to the ultimate resolution limit. The following review focuses on selected applications in biotechnology, diagnostics, vaccine development, biomimetic membranes, supramolecular engineering and nanotechnology. Despite progress in the characterization of S-layers and the exploitation of S-layers for the applications described in this chapter, it is clear that the field lags behind others (e.g. enzyme engineering) in applying recent advances in protein engineering. Genetic modification and targeted chemical modification would allow several possibilities including the manipulation of pore permeation properties, the introduction of switches to open and close the pores, and the covalent attachment to surfaces or other macromolecules through defined sites on the S-layer protein. The application of protein engineering to S-layers will require the development of straightforward expression systems, the development of simple assays for assembly and function that are suitable for the rapid screening of numerous mutants and the acquisition of structural information at atomic resolution. Attention should be given to these areas in the coming years. 相似文献
998.
999.
This study investigated the parafascicular (PF) neuronal nociceptive responses and their modulation following electrical stimulation of the locus coeruleus (LC) and intrathecal (i.t.) or intracerebroventricular (i.c.v.) administration of two alpha-adrenoceptor antagonists, the alpha2-antagonist, yohimbine, and the alpha1-antagonist, prazosin. The main results were as follows: (1) the nociceptive evoked discharges in PF neurons were suppressed by preceding stimulation of LC; (2) the suppressive effect of LC stimulation on PF neurons was replaced by a facilitatory effect following pretreatment of i.t. yohimbine in 14 units tested, while i.t. prazosin failed to alter the LC-induced suppression, even when the prazosin dose was doubled; (3) i.c.v. pretreatment with prazosin strengthened the suppressive effect of LC stimulation on PF neurons; (4) i.c.v. norepinephrine (NE) administration induced, in PF neurons, a biphasic response to noxious stimulation; an early, brief (about 10 min) inhibitory effect followed by a late, long-lasting facilitatory effect; and (5) i.c.v. pretreatment of yohimbine or prazosin prevented the inhibitory or facilitatory responses released by NE, respectively. These results provide evidence that: (1) the LC-descending projections exhibit a suppressive effect on nociceptive transmission at the spinal level through alpha2-receptors; and (2) the LC-ascending projections exhibit dual effects, facilitatory and inhibitory, at the medial thalamus (PF) level through alpha1- and alpha2-receptors, respectively. 相似文献
1000.
Neutralization of conservative charged transmembrane residues in the Na+/glucose cotransporter SGLT1
M Panayotova-Heiermann DD Loo JT Lam EM Wright 《Canadian Metallurgical Quarterly》1998,37(29):10522-10528
Our goal was to identify pairs of charged residues in the membrane domains of the Na+/glucose cotransporter (SGLT1) that form salt bridges, to obtain information about packing of the transmembrane helices. The strategy was to neutralize Glu225, Asp273, Asp294, and Lys321 in helices 6-8, express the mutants in oocytes, measure [14C]-alphaMDG uptake, and then attempt to find second-site mutations of opposite charge that restored function. alphaMDG uptake by E225A was identical to that by SGLT1, whereas transport was reduced by over 90% for D273A, D294A, and K321A and was not restored in the double mutants D273A/K321A or D294A/K321A. This suggested that K321 did not form salt bridges with D273 or D294 and that E225 was not involved in salt-bridging. Neutralization of K321 dramatically changed the Na+ uniport and Na+/glucose cotransport kinetics. The maximum rate of uniport in K321A increased 3-5-fold with a decrease in the apparent affinity for Na+ (70 vs 3 mM) and no change in apparent H+ affinity (0.5 microM). The change in Na+ affinity caused a +50 mV shift in the charge/voltage (Q/V) and relaxation time constant (tau)/voltage curves in the presteady-state kinetics. The presteady-state kinetics in H+ remained unchanged. The lower Na+ affinity resulted also in a 200-fold increase in the apparent K0.5 for alphaMDG and phlorizin. Replacements of K321 with alanine, valine, glutamine, arginine, or glutamic acid residues changed the steady-state kinetics in a similar way. Therefore, we suggest that K321 determines, directly or indirectly, (i) the rate and selectivity of SGLT1 uniport activity and (ii) the apparent affinities of SGLT1 for Na+, and indirectly sugar in the cotransport mode. 相似文献