首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   166篇
  免费   0篇
化学工业   3篇
金属工艺   1篇
石油天然气   1篇
一般工业技术   1篇
冶金工业   160篇
  2013年   2篇
  2012年   1篇
  2010年   1篇
  2003年   1篇
  1999年   1篇
  1998年   57篇
  1997年   27篇
  1996年   21篇
  1995年   13篇
  1994年   8篇
  1993年   8篇
  1992年   2篇
  1990年   3篇
  1989年   2篇
  1988年   2篇
  1986年   1篇
  1985年   2篇
  1981年   1篇
  1980年   1篇
  1977年   4篇
  1976年   8篇
排序方式: 共有166条查询结果,搜索用时 974 毫秒
71.
72.
PURPOSE: The objective of this study was to highlight differences in the pulmonary absorption of a monoPEGylated rhG-CSF and rhG-CSF after intratracheal instillation and aerosol delivery. METHODS: Male Sprague Dawley rats (250 g) were anesthetized and intratracheally instilled (IT) with protein solution or were endotracheally intubated and administered aerosol for 20 min via a Harvard small animal ventilator. A DeVilbiss "Aerosonic" nebulizer containing 5 ml of protein solution at approximately 3 mg/ml was used to generate aerosol. The volume of protein solution deposited in the lung lobes was estimated to be approximately 13 microliters after delivery of Tc-99m HSA solutions. The PEGylated proteins consisted of a 6 kDa (P6) or 12 kDa PEG (P12) linked to the N-terminus of rhG-CSF. rhG-CSF also was administered IT in buffers at pH 4 and pH 7 and in dosing volumes ranging from 100 to 400 microliters. Blood samples were removed at intervals after dosing and the total white blood cell counts (WBC) were determined. Plasma was assayed for proteins by an enzyme immuno assay. RESULTS: The plasma protein concentration v. time profiles were strikingly different for aerosol v. IT delivery. The Cmax values for rhG-CSF and P12 after aerosol delivery were greater than found after IT (Aerosol: 598 +/- 135 (ng/ml) rhG-CSF; 182 +/- 14 P12 v. IT: 105 +/- 12 rhG-CSF; 65.9 +/- 5 P12). Similarly, Tmax was reached much earlier after aerosol administration (Aerosol: 21.7 +/- 4.8 (min) rhG-CSF; 168 +/- 31 P12 v. IT: 100 +/- 17 rhG-CSF; 310 +/- 121 P12). Estimated bioavailabilities (F(lung)%) were significantly greater via aerosol delivery than those obtained after IT (Aerosol: 66 +/- 14 rhG-CSF; 12.3 +/- 1.9 P12 v. IT: 11.9 +/- 1.5 rhG-CSF; 1.6 +/- 0.1 P12). An increase in circulating WBC counts was induced by all proteins delivered to the lungs. The rate and extent of absorption of rhG-CSF was not influenced by the pH employed nor the instilled volume. CONCLUSIONS: Estimates of bioavailability are dependent upon the technique employed to administer drug to the lungs. Aerosol administration provides a better estimate of the systemic absorption of macromolecules.  相似文献   
73.
The possibility of stimulation of receptor structures with focused ultrasound (focused beam of high frequency mechanical waves) was investigated. Stimulation of single Pacinian corpuscle isolated from cat's mesentery resulted in receptor and action potentials. Stimulation of frog's ear labyrinth resulted in evoked potentials recorded from midbrain auditory area, their characteristics being much the same as those for responses to adequate sound stimuli. It is concluded that focused ultrasound is an advantageous agent for stimulation of various mechanoreceptors both isolated and, especially, located deep in the body. Some problems related to sensory specificity are discussed.  相似文献   
74.
The formation of cardiac cushion tissue, which ultimately contributes to formation of the valves and septa, is dependent on the regional activation of cardiac endothelial cells to undergo an epithelial-mesenchymal transition. This endothelial transition was correlated with activin betaA mRNA expression by Northern and in situ hybridization in both a temporal and spatial manner in developing mouse embryos. Activin betaA was the only subunit of the inhibin family detected during the initial phase of endothelial cell transition; activin betaB was detected at later stages, and inhibin alpha was not detectable in the heart. An in vitro assay that has been used to study mesenchymal cell formation in chick was modified for use with mammalian embryos. Conditioned media from embryonic mouse cardiocyte cultures was shown to substitute for the endogenous inductive signal in these assays. The presence of activin betaA was demonstrated by Western blot analysis of the cardiocyte conditioned media (CCM). Modified antisense oligonucleotides to activin betaA inhibited the endothelial-mesenchymal transition in the assay system, which was not affected by control oligonucleotides. Adapting the avian culture system for use with mice enabled the use of tissue from mice with a null allele for activin betaA. CCM produced from embryos homozygous for the mutant betaA allele did not contain activin betaA and was used in in vitro assays. CCM lacking activin betaA produced fewer mesenchymal cells from cardiac endothelial monolayers than CCM with activin betaA. Localized expression of activin betaA in the embryonic heart indicates a possible role in the endothelial-mesenchymal transition. Bioassays in which activin betaA expression is blocked or activin betaA is absent from the media indicate that activin betaA promotes the formation of mesenchymal cells in the endothelial cushions, which are required for normal septation.  相似文献   
75.
Brain metastases from small cell lung cancer respond to chemotherapy, but response duration is short and the intracerebral concentration of chemotherapy may be too low because of the characteristics of the blood-brain barrier. Positron emission tomography has been applied in a variety of tumors for studies of metabolic and hemodynamic features. This study was performed to determine regional cerebral metabolic rate of glucose (rCMRglu), regional cerebral blood flow (rCBF), and regional cerebral blood volume (rCBV) in brain metastases from small cell lung cancer and the surrounding brain. Tumor rCMRglu, rCBF, and rCBV exerted a broad variability, but were higher than the corresponding values in white matter and higher than or similar to those of gray matter. Tumor rCMRglu and rCBF were highly correlated (P < 0.01, r = 0.79). No correlation between survival and metabolic or hemodynamic parameters could be demonstrated. After radiotherapy, mean tumor rCMRglu decreased from 0.40 to 0.31 micromol/g/min (not significant), and rCBF and rCBV remained unchanged. However, cortical rCBF demonstrated a trend of increased values after radiotherapy from 0.37 to 0.49 ml/g/min (P = 0.13). No change in rCMRglu was observed in gray or white matter after radiotherapy. Global CBF seems to be reversibly depressed by the metastases, but local hemodynamic changes in the tumor could not be detected with positron emission tomography in this study. An association between high tumor rCMRglu and rCBF as an indicator of hypoxia was not observed. Other methods for noninvasive in vivo analysis of tumor hemodynamics are needed, especially for discrimination between tumor necrosis and hypoxia.  相似文献   
76.
BACKGROUND: Placement of stents above an intact sphincter of Oddi might prevent migration of bacteria and deposition of organic material into the stent. In patients with malignant obstructive jaundice prolongation of function time of the stent would be expected if it is placed above the sphincter of Oddi. METHODS: Thirty-four patients were randomized to stent placement either above (n = 17) or across (n = 17) the sphincter of Oddi. Straight 10F gauge Teflon stents were used. The patients were evaluated clinically and biochemically at monthly intervals during follow-up. RESULTS: The median stent function time (i.e., the time from insertion of the stent until stent replacement, patient death, or study termination) were 110 days (25th to 75th percentiles, 61 to 320 days) for stents placed above the sphincter of Oddi and 126 days (25th to 75th percentiles, 89 to 175 days) for stents placed across the sphincter of Oddi (nonsignificant [NS]). Stent replacement rates were 58.8% (10 of 17) in patients with stents placed above the sphincter and 29.4% (5 of 17) in patients with stents placed across the sphincter (NS). Significantly more patients in the former group experienced stent migration (9 vs. 2, p = 0.026). The median time from stent insertion until replacement of the stents placed above and across the sphincter of Oddi were 82 days (25th to 75th percentiles, 31 to 185 days) and 89 days (25th to 75th percentiles, 13 to 150 days), respectively (NS). CONCLUSIONS: No significant difference in overall stent performance between the two groups was found, although more stents placed above the sphincter of Oddi migrated. The time until dysfunction of the stent might be increased if migration of stents placed inside the common bile duct could be avoided.  相似文献   
77.
OBJECTIVE: We sought to describe the effects of ouabain on the human uteroplacental vasculature. STUDY DESIGN: Stem villous vessels and intramyometrial arteries isolated from placental and myometrial biopsy specimens at term were mounted in organ baths. Moreover, isolated human placental cotyledons were perfused. RESULTS: Contractions induced by the thromboxane A2 analog U46619 were unaffected by pretreatment with ouabain 10(-10) to 10(-6) mol/L. In fetal vessels nitric oxide (10(-8) to 3 x 10(-5) mol/L) induced relaxation of vascular tonus induced by U46619 and potassium. This relaxation was inhibited by pretreatment with ouabain 10(-7) to 10(-6) mol/L. These associations were unaffected by removal of the endothelium. In maternal arteries ouabain (10(-6) mol/L) failed to significantly affect nitric oxide-induced relaxation. Ouabain (10(-9) mol/L) significantly affected pressure-flow relationships in perfused cotyledons. CONCLUSIONS: Ouabain impairs nitric oxide-induced relaxation of human stem villous arteries and veins, which may explain the changes induced by therapeutically relevant concentrations of the drug on pressure-flow relationships in the perfused cotyledon. Thus treatment with cardiac glycosides in pregnancy may impair uteroplacental blood flow.  相似文献   
78.
The purpose of this study was to validate a food-frequency questionnaire (FFQ) and a 3-d weighed food record (3d-WFR) by comparing nutrient intakes estimated using these methods with serum folate, RBC folate and serum vitamin B-12 concentrations in 105 females aged 16-19 y. During an early morning clinic visit, subjects completed a self-administered, 116-item FFQ, blood was collected and they were trained to complete a 3d-WFR. Folate intakes as determined by the 3d-WFR (r = 0.65, P < 0.01) exhibited a stronger association with serum folate than did intakes from the FFQ (r = 0.48, P < 0.01) (P = 0.017). The correlations between folate intakes and RBC folate as determined by the FFQ (r = 0.42, P < 0.01) and 3d-WFR (r = 0.50, P < 0.01) methods did not differ. Vitamin B-12 intakes showed only a modest association with serum vitamin B-12 when supplement users were included in the analyses (FFQ, r = 0.25, P < 0.05; 3d-WFR, r = 0.32, P < 0.05). After excluding supplement users from the analyses, the relationship between vitamin B-12 intakes as determined by FFQ and serum vitamin B-12 was no longer significant. Median daily folate intakes (346 vs. 212 microgram) and vitamin B-12 (4.9 vs. 1.9 microgram) estimated from the FFQ were higher than those obtained from the 3d-WFR. In sum, these data suggest that both the FFQ and 3d-WFR are valid measures of assessing the folate intake of young women, and both appear to be useful in determining vitamin B-12 intake when supplemental users are included. The markedly different conclusions about absolute folate and vitamin B-12 intakes obtained using these two dietary methodologies should be taken into consideration when making recommendations about optimal folate intakes in relation to disease prevention.  相似文献   
79.
Despite many years of meticulous immunophenotyping of childhood acute lymphoblastic leukaemia (ALL) cases the prognostic significance of some subtypes remains unclear. The Medical Research Council UKALLXI trial (1990-1996) in which uniform treatment has been given to 2090 children with ALL below the age of 18 years and above the age of 1 year, has afforded the opportunity to review these issues. Children with ALL of mature B cell type were not entered into this trial. Immunophenotype analysis was performed in each individual trial centre, but results were centrally reviewed in all cases, and were both available and considered adequate in 1934 (93%) of the first 2090 patients entered. The main diagnostic categories were early pre-B or null reported in 60 cases (3.1%), common ALL in 1242 (64.2%), pre-B in 252 (13.0%), 'common' or pre-B in 172 (8.9%) and T cell in 207 (10.7%) cases. Children with T cell disease were significantly more likely to be over the age of 10 years, with central nervous system disease at diagnosis and to be CD34 negative. They also had a higher incidence of high white cell count and were more likely to be of the French-American-British (FAB) L2 morphological subtype. Patients with 'null' cell disease tended to be less than 2 years or greater than 10 years of age, and CD13 and CD33 positive. CD10 was associated with lower white cell count (WBC) at diagnosis, younger age and FAB L1 morphological subtype. The presence of cytoplasmic immunoglobulin in pre-B cells was not associated with any specific clinical or laboratory features. CD34 positivity was less common in T cell patients and was associated with low WBC. Disease-free survival (DFS) and 95% confidence intervals (CI) at 5 years from diagnosis was 52% (95% CI: 44-59%) for T cell disease, 58% (95% CI: 43-73%) for early pre-B (or null cell) disease and 65% (95% CI: 62-68%) for common or pre-B disease; there being no significant difference between common and pre-B disease with regard to disease outcome. Patients with T cell disease had a worse prognosis than any other immunophenotype group (P < 0.00005). However this worse outcome was no longer significant after allowing for the other principal prognostic factors of age, gender and white cell count at diagnosis except for the very small number with WBC <20 x 10(9)/l and T cell disease. Those with CD10-positive leukaemia did better than those who were CD10 negative (P < 0.00005), with DFS at 5 years 64% (95% CI: 62-67%) for positive vs 56% (95% CI: 49-62%) for CD10 negative. CD10 positivity did not have independent significance when white count, gender and age were taken into account. CD13, CD33, and cytoplasmic mu positivity carried no prognostic significance.  相似文献   
80.
The morphological picture of different bacteria (Salmonella typhimurium, Proteus vulgaris, Klebsiella pneumoniae, Pseudomonas aeruginosa, Yersinia enterocolitica O3, Y.pseudotuberculosis 1, Y.frederiksenii, Y.intermedia, Y.kristensenii) on environmental objects was studied with the use of scanning electron microscopy (SEM). Bacteria adhered to the surface of pieces of fodder, egg shell, cabbage leaves and form microcolonies, whose morphology was similar to colonies, grown on nutrient media. The cells produced extracellular substances, seen in SEM as integuments. These integuments were gourd to protect the population from the action of unfavorable factors.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号