全文获取类型
收费全文 | 1133篇 |
免费 | 2篇 |
国内免费 | 6篇 |
专业分类
化学工业 | 14篇 |
金属工艺 | 1篇 |
机械仪表 | 12篇 |
建筑科学 | 5篇 |
能源动力 | 1篇 |
轻工业 | 21篇 |
水利工程 | 1篇 |
无线电 | 9篇 |
一般工业技术 | 18篇 |
冶金工业 | 1039篇 |
原子能技术 | 1篇 |
自动化技术 | 19篇 |
出版年
2021年 | 1篇 |
2018年 | 1篇 |
2016年 | 1篇 |
2014年 | 1篇 |
2013年 | 4篇 |
2011年 | 1篇 |
2010年 | 3篇 |
2009年 | 8篇 |
2008年 | 8篇 |
2007年 | 5篇 |
2006年 | 7篇 |
2005年 | 7篇 |
2004年 | 2篇 |
2003年 | 5篇 |
2002年 | 1篇 |
2001年 | 1篇 |
2000年 | 4篇 |
1999年 | 37篇 |
1998年 | 319篇 |
1997年 | 188篇 |
1996年 | 105篇 |
1995年 | 67篇 |
1994年 | 70篇 |
1993年 | 59篇 |
1992年 | 6篇 |
1991年 | 6篇 |
1990年 | 4篇 |
1989年 | 9篇 |
1988年 | 9篇 |
1987年 | 10篇 |
1986年 | 10篇 |
1985年 | 9篇 |
1984年 | 3篇 |
1983年 | 6篇 |
1982年 | 5篇 |
1981年 | 8篇 |
1980年 | 16篇 |
1979年 | 4篇 |
1978年 | 5篇 |
1977年 | 35篇 |
1976年 | 75篇 |
1975年 | 1篇 |
1974年 | 3篇 |
1973年 | 1篇 |
1972年 | 3篇 |
1971年 | 3篇 |
1967年 | 1篇 |
1960年 | 1篇 |
1959年 | 1篇 |
1954年 | 2篇 |
排序方式: 共有1141条查询结果,搜索用时 125 毫秒
991.
MM Uriarte KO Klein KM Barnes OH Pescovitz DL Loriaux GB Cutler 《Canadian Metallurgical Quarterly》1998,49(3):363-368
OBJECTIVE: This study was designed to test the hypothesis that hypothalamic hamartoma causes precocious puberty through a different neuroendocrine mechanism than that of normal puberty or of idiopathic precocious puberty. DESIGN AND PATIENTS: We compared the pattern of gonadotrophin secretion among 4 girls with precocious puberty due to hypothalamic hamartoma, 27 girls with idiopathic precocious puberty, and 14 girls with normal puberty. All subjects were breast stage 3 or 4. Blood samples were obtained every 20 min for 4 h during the day (1.000 hours to 1400 h) and night (22.00 hours to 0200 h). MEASUREMENTS: LH, FSH, and prolactin were measured in each blood sample. Girls also underwent LHRH-stimulation with measurement of LH and FSH before and after stimulation. RESULTS: There were no significant differences in mean LH level, LH peak amplitude, or LH or FSH peak frequency during either the day or the night among the three diagnostic groups. However, the mean +/- SD LHRH-stimulated peak LH levels were greater in girls with hypothalamic hamartoma than in girls with normal puberty or with idiopathic precocious puberty (194 +/- 142 vs 85 +/- 60 or 66 +/- 54 IU/l, respectively, P < 0.05). The LHRH-stimulated peak FSH level in girls with hypothalamic hamartoma exceeded the level for the normal pubertal girls (31 +/- 19 vs 17 +/- 7 IU/l, P < 0.05), but not the level for the girls with idiopathic precocious puberty (25 + 12 IU/l). The peak LH to peak FSH ratio in the girls with hypothalamic hamartoma exceeded the ratio for the girls with idiopathic precocious puberty (7.3 +/- 3.9 vs 2.6 +/- 3.0 IU/l, P < 0.05), but not the ratio for the normal pubertal girls (5.0 + 2.9). There were no significant differences in mean prolactin level, peak amplitude or frequency, or in the ratio of mean night to mean day prolactin, among the 3 diagnostic groups. CONCLUSIONS: We conclude that spontaneous gonadotrophin and prolactin secretion are similar among girls with hypothalamic hamartoma, idiopathic precocious puberty, or normal puberty. However, the increased LHRH-stimulated peak LH in the girls with hypothalamic hamartoma suggests subtle differences in neuroendocrine regulation that may underlie their more rapid pubertal maturation. 相似文献
992.
A Cariati A Costanzo G Pescio GC Larghero GB Secco C Prior 《Canadian Metallurgical Quarterly》1994,15(4):175-178
The Authors considering cholelithiasis as an heterogenic pathological entity report their experience of 25 surgical consecutive patients: 20 with cholesterol or combination gallstones and 5 with black pigmented gallstones. In this series the most frequent factors associated with cholesterol gallstones were LDL hypercholesterolemia and hypertriglyceridemia; while the most frequent factors associated with black pigmented gallstones were hepatopathies. The most frequent symptom was dyspepsia. Only the black pigmented and the mixed gallstones were associated with jaundice and pancreatitis. According to the Literature infection is associated to brown pigment gallstones in 95% of cases, in this series infection is rarely associated with other types of gallstones. Treatment with oral bile salts is useful only in pure cholesterol gallstones, so the distinction among different types of gallstones is useful not only for a better knowledge of their pathogenesis but also for a correct choice of the therapeutic options. 相似文献
993.
BACKGROUND: Occupational asthma caused by latex has been reported in health care workers and workers in glove manufacturing plants. OBJECTIVE: We report occupational asthma from latex in a newly identified occupational setting, a latex doll manufacturing plant. METHODS: We evaluated an index case of asthma associated with work in a latex doll manufacturing plant by performing a workplace challenge and evaluating the work environment. We then performed an occupational survey and skin testing of 22 workers in the doll manufacturing plant. RESULTS: The patient, a 21-year-old woman, had severe immediate bronchospasm within minutes of beginning a workplace challenge where sanding of latex parts was performed. Two of 22 workers surveyed (including the patient) reported flushing, rhinoconjunctivitis, and wheezing on exposure to sanded doll parts. These two workers were the only subjects surveyed to have a history of atopy and positive immediate-type skin test responses to a raw latex extract and to common aeroallergens. CONCLUSIONS: Sanding or grinding of solid latex during the manufacturing process may result in a significant incidence of occupational asthma and rhinoconjunctivitis from latex sensitization. Atopic workers appear to be most susceptible to developing latex sensitivity in this setting. 相似文献
994.
BC Horsburgh SH Chen A Hu GB Mulamba WH Burns DM Coen 《Canadian Metallurgical Quarterly》1998,178(3):618-625
To investigate how acyclovir-resistant (ACVr) herpes simplex virus (HSV) evades drug therapy and causes disease, HSV-1 isolates from a bone marrow transplant (BMT) patient were studied. The patient developed ACVr disease after an initial BMT and, following a second BMT, reactivated ACVr HSV despite high-dose acyclovir prophylaxis. ACVr isolates from each episode contained the same point mutation in the viral thymidine kinase (tk) gene, documenting the emergence, latency, and reactivation of this mutant. The mutants were exceedingly impaired for TK activity in sensitive enzyme, plaque autoradiography, and drug-susceptibility assays. Nevertheless, these mutants and a tk deletion mutant constructed in the same genetic background reactivated from latency in mouse trigeminal ganglia, in contrast to similar mutants from laboratory strains. It is hypothesized that alleles in the clinical isolate compensate for the loss of TK in this animal model. Such genetic variability may be important for ACVr disease in humans. 相似文献
995.
DNA photolyases catalyze the light-dependent repair of pyrimidine dimers in DNA. We have utilized chemical modification and site-directed mutagenesis to probe the interactions involved in substrate recognition by the yeast photolyase Phr1. Lys517 was protected from reductive methylation in the presence of substrate, but not in its absence, and the specific and nonspecific association constants for substrate binding by Phr1 (Lys517-->Ala) were decreased 10-fold. These results establish a role for Lys517 in substrate binding. Mutations at Arg507, Lys463, and Trp387 reduced both the overall affinity for substrate and substrate discrimination. Sites of altered interactions in ES complexes were identified by methylation and ethylation interference techniques. Interaction with the base immediately 3' to the dimer was altered in the Phr1(Lys517-->Ala). DNA complex, whereas interactions with the phosphate and base immediately 5' to the dimer were reduced when Phr1(Arg507-->Ala) bound substrate. Multiple interactions 5' and 3' to the dimer were perturbed in complexes containing Phr1(Trp387-->Ala) or Phr1(Lys463-->Ala). In addition the quantum yield for dimer photolysis by Phr1(Trp387-->Ala) was reduced 3-fold. The locations of these mutations establish that a portion of the DNA binding domain is comprised of residues in the highly conserved carboxyl-terminal half of the enzyme. 相似文献
996.
RE Drake GJ McHugo RE Clark GB Teague H Xie K Miles TH Ackerson 《Canadian Metallurgical Quarterly》1998,68(2):201-215
Neural correlates of saccade planning in 6-month-old infants were investigated by high-density event-related potentials. Subjects made saccades to a target stimulus following a time gap from fixation stimulus offset (gap trials) or with the fixation stimulus still present (overlap trials). Like adults, infants were slower to make a saccade to the target when the fixation stimulus was still present. Strikingly, infants did not show clear evidence of the pre-saccadic components observed in adults which are thought to reflect cortical saccade planning processes. They did, however, show a left frontal positivity, which we suggest reflects cortical disinhibition of the colliculus initiated by fixation stimulus offset, and clear post-saccadic lambda waves. These results indicate that the frontal cortex already plays a role in action control by 6 months of age, while other aspects of cortical action planning may not yet be present in certain task situations. 相似文献
997.
C Athanassopoulos LB Auerbach RL Burman I Cohen DO Caldwell BD Dieterle JB Donahue AM Eisner A Fazely FJ Federspiel GT Garvey M Gray RM Gunasingha R Imlay K Johnston HJ Kim WC Louis R Majkic J Margulies K McIlhany W Metcalf GB Mills RA Reeder V Sandberg D Smith I Stancu W Strossman R Tayloe GJ VanDalen W Vernon N Wadia J Waltz YX Wang DH White D Works Y Xiao S Yellin 《Canadian Metallurgical Quarterly》1996,54(5):2685-2708
998.
SB Gates LG Mendelsohn KA Shackelford LL Habeck JD Kursar LS Gossett JF Worzalla C Shih GB Grindey 《Canadian Metallurgical Quarterly》1996,2(7):1135-1141
Membrane-associated folate receptors (FRs) have been detected in many mammalian species, and multiple isoforms have been identified. The pharmacological properties of FRs from murine kidney, liver, and six murine tumors were characterized. Murine kidney expressed primarily folate-binding protein 1, analogous to human FR-alpha, whereas murine liver expressed predominantly folate-binding protein 2, analogous to human FR-beta. Five of six murine tumors expressed high-affinity FRs with pharmacological properties consistent with folate-binding protein 1 isoform expression. Restriction of dietary folate resulted in significant changes in the FR expression in most murine tissues. Kidney and tumor FRs showed a decreased affinity for folic acid, suggesting a change in isoform expression in response to a low folate diet. Density of the FR in the kidney decreased, and, in contrast, density of the FR in all tumors increased. The response of the liver to a low folate diet was unique in that there were no detectable changes in affinity or density of liver FR. Changes in dietary folate that modulate FR isoform expression may have relevance for cancer patients treated with antifolates. 相似文献
999.
P Bertolini GB Luciani B Vecchi P Pugliese A Mazzucco 《Canadian Metallurgical Quarterly》1998,66(2):425-430
Hypochlorous acid (HOCl) is produced by polymorphonuclear leukocytes that migrate and adhere to endothelial cells as part of the inflammatory response to tissue injury. HOCl is an extremely toxic oxidant that can react with a variety of cellular components, and concentrations reaching 200 microM have been reported in some tissues. In this study, we show that HOCl interacts with the skeletal sarcoplasmic reticulum Ca(2+)-adenosinetriphosphatase (ATPase), inhibiting transport function, HOCl inhibits sarcoplasmic reticulum Ca(2+)-ATPase activity in a concentration-dependent manner with a concentration required to inhibit ATPase activity by 50% of 170 microM and with complete inhibition of activity at 3 mM. A concomitant reduction in free sulfhydryl groups after HOCl treatment was observed, paralleling the inhibition of ATPase activity. It was also observed that HOCl inhibited the binding of the fluorescent probe fluorescein isothiocyanate to the ATPase protein, indicating some structural damage may have occurred. These findings suggest that the reactive oxygen species HOCl inhibits ATPase activity via a modification of sulfhydryl groups on the protein, supporting the contention that reactive oxygen species disrupt the normal Ca(2+)-handling kinetics in muscle cells. 相似文献
1000.
Spreading depression (SD) of electroencephalographic activity is a dynamic wave phenomenon in the central nervous system (CNS). The retina, especially the isolated chicken retina, is an excellent constituent of the CNS in which to observe the dynamic behavior of the SD wave fronts, because it changes its optical properties during a SD attack. The waves become visible as milky fronts on a black background. It is still controversial what the basic mechanistic steps of SD are, but certainly SD belongs to the self-organization phenomena occurring in neuronal tissue. In this work, spiral-shaped wave fronts are analyzed using digital video imaging techniques. We report how the inner end of the wave front, the spiral tip, breaks away repeatedly. This separation process is associated with a Z-shaped trajectory (extension approximately 1.2 mm) that is described by the tip over one spiral revolution (period 2.45+/-0.1 min). The Z-shaped trajectory does not remain fixed, but performs a complex motion across the retina with each period. This is the first time, to our knowledge, that established imaging methods have been applied to the study of the two-dimensional features of SD wave propagation and to obtaining quantitative data of their dynamics. Since these methods do not interfere with the tissue, it is possible to observe the intrinsic properties of the phenomenon without any external influence. 相似文献