全文获取类型
收费全文 | 6848篇 |
免费 | 0篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 13篇 |
化学工业 | 34篇 |
金属工艺 | 1篇 |
机械仪表 | 5篇 |
建筑科学 | 1篇 |
能源动力 | 5篇 |
轻工业 | 16篇 |
石油天然气 | 2篇 |
无线电 | 11篇 |
一般工业技术 | 25篇 |
冶金工业 | 6723篇 |
原子能技术 | 2篇 |
自动化技术 | 11篇 |
出版年
2022年 | 1篇 |
2018年 | 1篇 |
2017年 | 1篇 |
2016年 | 1篇 |
2014年 | 2篇 |
2013年 | 2篇 |
2012年 | 6篇 |
2011年 | 4篇 |
2010年 | 1篇 |
2009年 | 1篇 |
2008年 | 1篇 |
2007年 | 8篇 |
2006年 | 3篇 |
2005年 | 4篇 |
2004年 | 6篇 |
2003年 | 13篇 |
2002年 | 5篇 |
2000年 | 6篇 |
1999年 | 218篇 |
1998年 | 2308篇 |
1997年 | 1286篇 |
1996年 | 810篇 |
1995年 | 422篇 |
1994年 | 339篇 |
1993年 | 419篇 |
1992年 | 37篇 |
1991年 | 49篇 |
1990年 | 54篇 |
1989年 | 51篇 |
1988年 | 55篇 |
1987年 | 56篇 |
1986年 | 54篇 |
1985年 | 38篇 |
1984年 | 1篇 |
1983年 | 18篇 |
1982年 | 24篇 |
1981年 | 31篇 |
1980年 | 62篇 |
1979年 | 3篇 |
1978年 | 14篇 |
1977年 | 136篇 |
1976年 | 278篇 |
1975年 | 11篇 |
1973年 | 1篇 |
1971年 | 2篇 |
1970年 | 1篇 |
1968年 | 2篇 |
1955年 | 3篇 |
排序方式: 共有6849条查询结果,搜索用时 15 毫秒
991.
MJ Kupferminc I Gull A Bar-Am Y Daniel A Jaffa M Shenhav JB Lessing 《Canadian Metallurgical Quarterly》1998,77(5):548-550
We report a 27-year-old woman who developed Coombs' negative hemolytic anemia and fulminant hepatic failure as the initial manifestation of Wilson's disease. Unmeasurably low level of serum alkaline phosphatase provided a clue to the diagnosis of Wilson's disease. The diagnosis was established with the presence of Kayser-Fleischer ring, decreased serum ceruloplasmin level, and elevated urine and serum copper levels. In spite of repeated plasmapheresis, she died of multiorgan failure on the fifth hospital day. 相似文献
992.
K Ichinose DJ Bedford D Tornus A Bechthold MJ Bibb WP Revill HG Floss DA Hopwood 《Canadian Metallurgical Quarterly》1998,5(11):647-659
BACKGROUND: The granaticins are members of the benzoisochromanequinone class of aromatic polyketides, the best known member of which is actinorhodin made by Streptomyces coelicolor A3(2). Genetic analysis of this class of compounds has played a major role in the development of hypotheses about the way in which aromatic polyketide synthases (PKSs) control product structure. Although the granaticin nascent polyketide is identical to that of actinorhodin, post-PKS steps involve different pyran-ring stereochemistry and glycosylation. Comparison of the complete gene clusters for the two metabolites is therefore of great interest. RESULTS: The entire granaticin gene cluster (the gra cluster) from Streptomyces violaceoruber T-22 was cloned on either of two overlapping cosmids and expressed in the heterologous host, Streptomyces coelicolor A3(2), strain CH999. Chemical analysis of the recombinant strains demonstrated production of granaticin, granaticin B, dihydrogranaticin and dihydrogranaticin B, which are the four known metabolites of S. violaceoruber. Analysis of the complete 39,250 base pair sequence of the insert of one of the cosmids, pOJ466-22-24, revealed 37 complete open reading frames (ORFs), 15 of which resemble ORFs from the act (actinorhodin) gene cluster of S. coelicolor A3(2). Among the rest, nine resemble ORFs potentially involved in deoxysugar metabolism from Streptomyces spp. and other bacteria, and six resemble regulatory ORFs. CONCLUSIONS: On the basis of these resemblances, putative functional assignments of the products of most of the newly discovered ORFs were made, including those of genes involved in the PKS and tailoring steps in the biosynthesis of the granaticin aglycone, steps in the deoxy sugar pathway, and putative regulatory and export functions. 相似文献
993.
J Whittle CJ Lin JR Lave MJ Fine KM Delaney DZ Joyce WW Young WN Kapoor 《Canadian Metallurgical Quarterly》1998,36(7):977-987
OBJECTIVES: The authors describe the relation of provider characteristics to processes, costs, and outcomes of medical care for elderly patients hospitalized for community-acquired pneumonia. METHODS: Using Medicare claims data, Medicare beneficiaries discharged from Pennsylvania hospitals during 1990 with community-acquired pneumonia were identified. Claims data were used to ascertain mortality, readmissions, use of procedures and physician consultations, and the costs of care. The relationship of these measures to provider characteristics was analyzed using regression techniques to adjust for patient characteristics, including comorbidity and microbial etiology. RESULTS: Among 22,294 pneumonia episodes studied, 30-day mortality was 17.0%. After adjusting for patient characteristics, 30-day mortality and readmission rates were unrelated to hospital teaching status or urban location or to physician specialty. Use of procedures and physician consultations was more common and costs were 11% higher among patients discharged from teaching hospitals compared with nonteaching hospitals. Similarly, costs were 15% higher at urban hospitals compared with rural hospitals. General internists and medical subspecialists used more procedures and had higher costs than family practitioners. CONCLUSIONS: Processes and costs of care for community-acquired pneumonia varied by provider characteristics, but neither mortality nor readmission rates did. These differences cannot be explained by clinical variables in the database. Further studies should determine whether less costly patterns of care for pneumonia, and perhaps other conditions, could replace more costly ones without compromising patient outcomes. 相似文献
994.
Unsegmented double-stranded (ds)RNA viruses belonging to the family Totiviridae persistently infect protozoa and fungi. In this study, two totiviruses were found to coinfect the filamentous fungus Sphaeropsis sapinea, a well known pathogen of pines. Isometric, virus-like particles approximately 35 nm in diameter were isolated from extracts of this fungus. The nucleotide sequences of the genomes of the two S. sapinea RNA viruses named SsRV1 and SsRV2 were established. The linear genomes of 5163 and 5202 bp, respectively, are identically organized with two large, overlapping ORFs. The 5' located ORF1 probably encodes the coat protein, whereas the gene product of ORF2 shows the typical features of RNA-dependent RNA polymerases. The absence of a pseudoknot and a slippery site at the overlapping region between ORF1 and ORF2, as well as the shortness of that region, leads us to suggest that the translation of ORF2 of both viruses is internally initiated. The mode of translation and the genomic organization are similar to those of Helminthosporium victoriae 190S virus (Hv190SV; Huang, S., and Ghabrial, S. A. (1996). Proc. Natl. Acad. Sci. USA 93, 12541-12546). Hv190SV thus appears to be closely related to the SsRVs. Interestingly, based on amino acid sequence homology SsRV1 is more closely related to Hv190SV than to SsRV2. 相似文献
995.
Crystals were grown of the 5-amide, 9-amide, and 17-amide nylon 6 monodisperse oligoamides and investigated using electron microscopy (real space and diffraction) and X-ray diffraction. Analyses of the data allowed us to determine the crystalline structures and relate them to the morphology. Under our crystallization conditions, the 5-amide chains are unfolded and crystallize in the usual nylon 6 alpha-structure, i.e., an apolar arrangement of chains, directed parallel to the layer normal, within hydrogen-bonded sheets which stack via van der Waals interactions. In chain-folded nylon polymers such as nylon 6, the length of the straight stems is approximately 5 to 7 nm; this is equivalent to about six to eight amide units. Therefore it is not too surprising that the 5-amide molecule, of length 4.6 nm, remains unfolded. If the 9-amide molecules (length 8 nm) fold, we would expect them to create hairpin-like structures with four, or close to four, amide units in adjacent straight stems. Our results show that, depending on the crystallization conditions, both unfolded and once-folded conformations can occur for this 9-amide oligomer. In the unfolded conformation, the straight-stem chains crystallize in the nylon 6 gamma-phase structure as opposed to the usual alpha-phase structure. The once-folded structure for the 9-amide chain represents the onset of folding in these nylon 6 monodisperse oligoamides and the lamellar stacking periodicity (LSP) is 4.60 nm. This once-folded conformation is similar to the usual nylon 6 alpha-phase structure. The 17-amide chains crystallize in a twice-folded conformation, also with the nylon 6 alpha-phase structure, reinforcing the notion that once the chains are long enough to start folding, the pattern of behavior approaches that of the nylon 6 polymer. In this case, the LSP value is 5.36 nm. 相似文献
996.
SE Kilpatrick WG Ward AR Chauvenet MJ Pettenati 《Canadian Metallurgical Quarterly》1998,11(10):923-928
A 13-year-old girl developed atonic seizure at 2 years of age. At the age of 10 years, gelastic seizures were noted. Magnetic resonance imaging (MRI) revealed a hypothalamic mass protruding down into the basal cistern and up into the third ventricle. An interictal electroencephalogram (EEG) showed paroxysmal spike and wave complex discharges. Since the seizures failed to respond to medical therapy, it was decided to try to control them by removing the mass. The operation was carried out through an interhemispheric trans-lamina terminalis approach. The lesion was so similar to normal brain tissue that the resection had to be limited enough to avoid complications. Histological examination of the mass showed a hamartoma. Postoperative MRI showed residual mass, but no seizure has been noted since the operation. The EEG recorded one year after the operation showed no spike and wave complex discharge, although she was still on anticonvulsant drugs. The authors propose that surgical therapy should be considered as a treatment for intractable gelastic epilepsy with hypothalamic hamartoma and that the first operation should be conservative enough to avoid complications, because it can bring about good results even if it is only a partial resection. 相似文献
997.
MJ Coffey SE Wilcoxen PH Sporn M Peters-Golden 《Canadian Metallurgical Quarterly》1998,56(2-3):103-117
The proinflammatory leukotrienes (LT) play important roles in host defense and disease states. However, no endogenous mechanisms to downregulate 5-lipoxygenase (5-LO), the enzyme catalyzing LT synthesis, have been described. We observed that the cytosolic fraction of rat alveolar macrophages (AMs) and peritoneal macrophages (PMs), and of peripheral blood monocytes (PBMs) contain substantial amounts of 5-LO protein, but little detectable 5-LO activity. We therefore examined these mononuclear phagocyte (MNP) cytosolic fractions for inhibitory activity against 5-LO. MNP cytosol dose-dependently reduced the 5-LO activity in neutrophil (PMN) cytosol and AM membrane. Furthermore, MNP cytosol dose-dependently prolonged the lag phase of soybean lipoxygenase (LO) without affecting the rate of product formation. This effect was overcome by subsequent addition of 13(S)-hydroperoxy-9-cis-11-trans-octadecadienoic acid (13-HpOD), suggesting that the active factor scavenges hydroperoxides. Inactivation by boiling and roteinase K suggest that is a protein. We speculate that this cytosolic factor(s) may serve as an endogenous means for the down-regulation of 5-LO in macrophages. 相似文献
998.
KL Hipkins BL Materna MJ Kosnett JW Rogge JE Cone 《Canadian Metallurgical Quarterly》1998,46(7):330-339
1. The "lead standards" established by OSHA for general industry in 1978 and the construction industry in 1993 require employers and clinicians to follow very specific guidelines for protecting lead exposed workers. Depending on the level of exposure, medical surveillance may be legally required. 2. Lead affects multiple body systems and can cause permanent damage. Low level exposures that in the past were thought safe are now considered hazardous as new information emerges about the toxicity of lead. 3. Lead poisoning, if undetected, often results in misdiagnosis and costly care. Adults are exposed to lead in many different workplace settings. All clinicians caring for lead exposed workers need to be informed about the health effects of lead, employer and physician responsibilities, and worker rights. 4. Occupational and environmental health nurses can help identify workers at risk and prevent lead poisoning by education and early intervention through collaboration with the workers, the employer, the company physician, and other health and safety professionals. 相似文献
999.
TG Phan J Estell G Duggin I Beer D Smith MJ Ferson 《Canadian Metallurgical Quarterly》1998,169(11-12):644-646
Kombucha tea is an alternative therapy that is gaining popularity as a remedy for a diverse range of ailments. We report two cases of symptomatic lead poisoning requiring chelation therapy in a married couple who had been drinking Kombucha tea for six months, brewing the tea in a ceramic pot. We postulate that acids in the tea eluted lead from the glaze pigment used in the ceramic pot, in a manner analogous to elution of lead from crystal decanters by wine and spirits. 相似文献
1000.