全文获取类型
收费全文 | 5429篇 |
免费 | 0篇 |
国内免费 | 1篇 |
专业分类
化学工业 | 19篇 |
建筑科学 | 4篇 |
轻工业 | 2篇 |
无线电 | 5篇 |
一般工业技术 | 5篇 |
冶金工业 | 5391篇 |
原子能技术 | 1篇 |
自动化技术 | 3篇 |
出版年
2014年 | 1篇 |
2013年 | 1篇 |
2011年 | 1篇 |
2009年 | 1篇 |
2006年 | 3篇 |
2004年 | 2篇 |
2003年 | 8篇 |
2000年 | 1篇 |
1999年 | 157篇 |
1998年 | 1645篇 |
1997年 | 893篇 |
1996年 | 636篇 |
1995年 | 324篇 |
1994年 | 313篇 |
1993年 | 330篇 |
1992年 | 36篇 |
1991年 | 58篇 |
1990年 | 77篇 |
1989年 | 65篇 |
1988年 | 62篇 |
1987年 | 82篇 |
1986年 | 58篇 |
1985年 | 57篇 |
1984年 | 1篇 |
1983年 | 11篇 |
1982年 | 30篇 |
1981年 | 34篇 |
1980年 | 39篇 |
1979年 | 1篇 |
1978年 | 8篇 |
1977年 | 143篇 |
1976年 | 336篇 |
1975年 | 10篇 |
1965年 | 1篇 |
1955年 | 5篇 |
排序方式: 共有5430条查询结果,搜索用时 0 毫秒
991.
A method is presented for approximating fractional power averages of relaxation times for data equispaced in log time, without the need to invert multiexponential relaxation data. This form of average permits giving emphasis to short or long times depending on the choice of the p value, thus giving the possibility of representing different specific properties of porous media. This method has been tested on a large number of nuclear magnetic resonance (NMR) relaxation measurements in porous samples. This new algorithm appears to be robust with respect to both measurement and computation, and its major advantage is that it does not depend on a particular inversion method. Moreover, it permits a very fast computation. 相似文献
992.
Previously, we have described a template-assisted combinatorial peptide library based on the anti-tryptic reactive site loop of a Bowman-Birk inhibitor (BBI). Sequences that displayed inhibitory activity re-directed towards chymotrypsin were found to have a consensus binding motif, with their most striking feature being that exclusively threonine was found at the P2 position. The present study investigates the reason for this surprising specificity by maintaining the binding motif but systematically varying the P2 residue. From analysis of 26 variants, it is found that the requirements for inhibitory activity at P2 are finely tuned, and in agreement with the library work, threonine at P2 provides optimal inhibition. In addition, peptides with threonine at P2 are significantly less susceptible to hydrolysis. Examination of all available BBI sequences shows that threonine is very highly conserved at P2, which implies that the functional requirement extends to the full-length BBI protein. Our results are consistent with a dual requirement for hydrophobic recognition within the S2 pocket and maintenance of an inhibitory conformation via hydrogen bonding within the reactive-site loop. As the isolated peptide loop reproduces the active region of full-length BBI, these results explain why threonine is well conserved at P2 in this class of inhibitor. Furthermore, they illustrate that proteinase inhibitor specificity can have characteristics that are not easily predicted from information on the substrate preferences of a proteinase. 相似文献
993.
Diabetes mellitus places a significant burden on the U.S. healthcare system. Because of the potential to reduce diabetic complications and costs through intensive management, diabetes has become a primary target for disease management programs. We performed a retrospective analysis of short-term baseline and follow-up clinical, economic, and member and provider satisfaction data from approximately 7,000 people with diabetes being treated through seven managed care plans using Diabetes Treatment Centers of America's Diabetes NetCare, (Nashville, TN), a comprehensive diabetes management program. Our analysis indicates that Diabetes NetCare achieved gross economic adjusted savings of $50 per diabetic member per month (12.3%), with gross unadjusted savings of $44 (10.9%) per diabetic member per month. Hospital admissions per 1,000 diabetic member years decreased by 18%, and bed days fell by 21%. Patients with diabetes were more likely to get HbAlc tests, foot exams, eye exams, and cholesterol screenings while enrolled in the program. These data suggest that implementation of a comprehensive healthcare management program for people with diabetes can lead to substantial improvements in costs and clinical outcomes in the short-term. It is expected that improvements will increase over time, with continuing improvements in health status and a reduction in the number of future diabetic complications. 相似文献
994.
ZM Bhujwalla CL McCoy JD Glickson RJ Gillies M Stubbs 《Canadian Metallurgical Quarterly》1998,78(5):606-611
Quantification of metabolite or drug concentrations in living tissues requires determination of intra- and extracellular volumes. This study demonstrates how this can be achieved non-invasively by 31P magnetic resonance spectroscopy (MRS) employing dimethyl methylphosphonate (DMMP) as a marker of total water space, 3-aminopropylphosphonate (3-APP) as a marker of extracellular space and P and 3-APP as markers of intracellular pH (pH) and extracellular pH (pHe) respectively. The MRS measurements of the tumour volumes were validated by classic radiolabelling methods using 3H2O and [14C]inulin as markers of total and extracellular space respectively. The extracellular volume fraction measured by radiolabelling of RIF-1 tumours was 23 +/- 0.83% (mean +/- s.e.m. n = 9), not significantly different (P > 0.1) from that found by MRS (27 +/- 2.9%, n = 9, London, and 35 +/- 6.7, n = 14, Baltimore). In untreated RIF-1 tumours, pH was about 0.2 units higher than pHe (P < 0.01). 5-Fluorouracil (5FU) treatment (165 mg kg(-1)) caused no significant changes in either pHe or per cent extracellular volume. However significant increases in pH, 48 h after treatment (P < 0.01) correlated with decreased tumour size and improved bioenergetic status [NTP/inorganic phosphate (Pi) ratio]. This study shows the feasibility of an MR method (verified by a 'gold standard') for studying the effects of drug treatment on intra- and extracellular spaces and pH in solid tumours in vivo. 相似文献
995.
The effect of a calculus scaling gel was evaluated as an adjunct to instrumentation in a double blind, split-mouth, clinical study. Fifteen comparable periodontally involved teeth from 5 patients were instrumented on the mesio-buccal root surface with the aid of either the test gel, placebo gel, or no gel until smoothness was achieved. Test or placebo gel was applied subgingivally for 10 minutes. Instrumentation time, ease, number of strokes, and gingival/tooth surfaces changes were recorded. Scanning electronic microscopic (SEM) evaluation of root surface topography was evaluated. The results demonstrated effective calculus removal in all treatment groups with no differences found between them. Instrumentation time, ease, and number of strokes were similar for all treatment groups. There were no harmful effects to soft or hard tissues. The results of this study do not support the use of calculus scaling gel as an adjunct to root instrumentation. 相似文献
996.
RJ Butterfield JD Sudweeks EP Blankenhorn R Korngold JC Marini JA Todd RJ Roper C Teuscher 《Canadian Metallurgical Quarterly》1998,161(4):1860-1867
Experimental allergic encephalomyelitis (EAE), the principal animal model of multiple sclerosis, is a genetically determined phenotype. In this study, analyses of the cumulative disease frequencies in parental, F1 hybrid, and F2 mice, derived from the EAE-susceptible SJL/J strain and the EAE-resistant B10.S/DvTe strain, confirmed that susceptibility to EAE is not inherited as a simple Mendelian trait. Whole genome scanning, using 150 informative microsatellite markers and a panel of 291 affected and 390 unaffected F2 progeny, revealed significant linkage of EAE susceptibility to marker loci on chromosomes 7 (eae4) and 17, distal to H2 (eae5). Quantitative trait loci for EAE severity, duration, and onset were identified on chromosomes 11 (eae6, and eae7), 2 (eae8), 9 (eae9), and 3 (eae10). While each locus reported in this study is important in susceptibility or disease course, interactions between marker loci were not statistically significant in models of genetic control. One locus, eae7, colocalizes to the same region of chromosome II as Orch3 and Idd4, susceptibility loci in autoimmune orchitis and insulin-dependent diabetes mellitus, respectively. Importantly, eae5 and eae7 are syntenic with human chromosomes 6p21 and 17q22, respectively, two regions of potential significance recently identified in human multiple sclerosis genome scans. 相似文献
997.
M Jeffrey CM Goodsir A Holliman RJ Higgins ME Bruce PA McBride JR Fraser 《Canadian Metallurgical Quarterly》1998,142(20):534-537
Brains from 17 histopathologically confirmed cases of scrapie, five of which had congophilic vascular amyloid, were stained immunohistochemically for prion protein (PrP) using a polyclonal antibody. Two clinically suspect but pathologically unconfirmed cases of natural sheep scrapie and the brains of four mice infected with the 111A murine scrapie strain were also examined. Selected sections containing amyloid were stained with each of two peptide antibodies which recognise the N-terminal amino acid residues which are lost following protease digestion of the disease-specific isoform of PrP. The mice infected with the 111A murine scrapie strain had large numbers of hypermature plaques. All the amyloid plaques from both natural sheep scrapie brains and experimental murine brains were heavily immunostained by the polyclonal and both peptide antibodies. In addition, disease-specific accumulations of PrP were detected in endothelial cells or in the intima of blood vessels of the cerebral cortex of sheep scrapie brains. The affected blood vessels were located in areas which otherwise lacked typical scrapie pathology. Vascular accumulations of PrP were also found in leptomeningeal and choroid plexus blood vessels. Vascular amyloid was found mainly in the neocortex. Vascular amyloid and disease-specific parenchymal accumulations of PrP were found in two sheep which showed clinical signs of scrapie but lacked its typical vacuolar pathology. These results show that the mature amyloid of scrapie is composed of, or contains a substantial proportion of, whole length PrP protein. Thus truncation of PrP is not essential for the aggregation of PrP into amyloid. The vascular amyloid of natural sheep scrapie originates from the accumulation and release of PrP from endothelial cells presumably following systemic scrapie infection. The topography of vascular amyloid distribution in Great Britain differs from that reported in the Netherlands. As amyloid deposition in mice is largely controlled by the strain of the infecting agent it is possible that the strain of the agent may influence vascular amyloid deposition. 相似文献
998.
RJ Gardner DO Robinson L Lamont JP Shield IK Temple 《Canadian Metallurgical Quarterly》1998,54(6):522-525
Transient neonatal diabetes mellitus occurs in growth-retarded infants, has an incidence of 1 in 400000 live births and has been associated with both paternal uniparental disomy of chromosome 6 and paternal duplications of 6q. We analysed samples from our cohort of patients with transient neonatal diabetes mellitus for uniparental disomy of chromosome 6 using polymorphic microsatellite repeat analysis. We report here the fifth case of paternal uniparental disomy of chromosome 6 associated with classic transient neonatal diabetes mellitus and estimate that uniparental disomy of chromosome 6 accounts for approximately one fifth of cases of transient neonatal diabetes mellitus. 相似文献
999.
M Tarquino RL Geggel RS Strauss J Rhodes B Wunderlich RJ Rohrer 《Canadian Metallurgical Quarterly》1998,37(8):505-509
Accusations of rape or sexual harassment are currently very high-profile in the military. This article discusses rape allegations in the military legal system from a psychiatric perspective. The original definition of "rape trauma syndrome" and subsequent psychiatric thinking about the diagnosis are briefly outlined. Common reactions seen in military victims in this era are described. A prototypical military case is presented. An adequate evaluation of an alleged victim is outlined. Credentials and preparation of an expert witness are also briefly discussed, with cautions about the use of expert testimony in cases of alleged sexual assault and rape trauma syndrome. 相似文献
1000.
Stability and distribution of orally administered epidermal growth factor (EGF) were examined in newborn and 5-day-old pigs. Forty-five minutes after oral administration of iodine-125 labeled EGF, 60 and 50% of the radioactivity administered were recovered from the internal organs in newborn and 5-day-old pigs, respectively. In both age groups, over 95% of the recovered radioactivity was found in the gastrointestinal tract, of which 78-86% was found in the luminal contents with the remaining found in the gastrointestinal wall. Within the gastrointestinal tract, 65-71% of radioactivity was found in the stomach, 27-30% in the proximal and mid small intestine and 3-4% was found in the distal part of the small intestine. There were no significant differences in the overall distribution of orally administered radioactivity between two age groups. Based on liquid chromatography and trichloroacetic acid precipitation, a substantial amount of EGF recovered from the luminal contents (63-86%) and the gastrointestinal wall (42-81%) remained "intact". The receptor binding ability of the EGF recovered from the gastric contents was 96-102% comparable to the native EGF tracer. The receptor binding ability remained high (40-58%) in the proximal small intestinal lumen and it decreased to 15% in the distal small intestinal lumen in newborn pigs. In 5-day-old pigs, EGF recovered from the small intestinal contents had 5 to 24% receptor binding ability when compared with native EGF tracer. The receptor binding ability of the EGF recovered from all other organs was below 5% with an exception of the gastric wall, from which recovered EGF retained 9 to 26% receptor binding ability. These results indicate that most of orally ingested EGF remained in the gastrointestinal tract in neonatal pigs 45 min after oral ingestion, and significant amount of the ingested EGF remained biologically active. It suggests that milk-borne EGF can survive in the gastrointestinal tract and may play a role in regulating gut development in neonatal animals. 相似文献