全文获取类型
收费全文 | 1971篇 |
免费 | 5篇 |
专业分类
电工技术 | 3篇 |
化学工业 | 45篇 |
金属工艺 | 8篇 |
机械仪表 | 2篇 |
建筑科学 | 1篇 |
能源动力 | 6篇 |
轻工业 | 5篇 |
水利工程 | 3篇 |
无线电 | 16篇 |
一般工业技术 | 35篇 |
冶金工业 | 1838篇 |
自动化技术 | 14篇 |
出版年
2022年 | 9篇 |
2021年 | 3篇 |
2020年 | 5篇 |
2019年 | 6篇 |
2018年 | 9篇 |
2017年 | 4篇 |
2016年 | 4篇 |
2015年 | 1篇 |
2014年 | 7篇 |
2013年 | 11篇 |
2012年 | 8篇 |
2011年 | 9篇 |
2010年 | 3篇 |
2009年 | 6篇 |
2008年 | 9篇 |
2007年 | 2篇 |
2006年 | 2篇 |
2005年 | 4篇 |
2004年 | 5篇 |
2003年 | 7篇 |
2002年 | 2篇 |
2001年 | 3篇 |
2000年 | 7篇 |
1999年 | 55篇 |
1998年 | 555篇 |
1997年 | 313篇 |
1996年 | 219篇 |
1995年 | 99篇 |
1994年 | 107篇 |
1993年 | 123篇 |
1992年 | 16篇 |
1991年 | 21篇 |
1990年 | 25篇 |
1989年 | 21篇 |
1988年 | 18篇 |
1987年 | 16篇 |
1986年 | 18篇 |
1985年 | 13篇 |
1983年 | 2篇 |
1982年 | 8篇 |
1981年 | 11篇 |
1980年 | 13篇 |
1979年 | 2篇 |
1978年 | 3篇 |
1977年 | 59篇 |
1976年 | 124篇 |
1975年 | 5篇 |
1974年 | 1篇 |
1955年 | 3篇 |
排序方式: 共有1976条查询结果,搜索用时 956 毫秒
81.
82.
In accordance with the FAA certification requirements, all modern commercial turbofan engines must successfully demonstrate its ability to withstand a fan blade-out (FBO) event through actual test. Possibility of losing a rotating fan blade from a running engine is a flight safety consideration, which must be addressed during the design phase of the engine. A typical fan blade-out event involves very complex nonlinear transient dynamics with large deflection of the release blade and rigid body rotation of the trailing blade as well as progressive failure and fragmentation of various components. Due to the nature of the impact type loading, the solution to the problem should also address dependence of the material behavior such as yield strength as a function of strain rates. In short, the transient dynamic analysis of a fan blade-out event highlights the complexity of the numerical technique, which includes all the nonlinearities of structural dynamics: plastic behavior of the materials, large displacements, and contact interaction between structural elements. In this paper, we present the results of a LS-DYNA simulation of a FBO event on a full-engine analytical model, which covers both the primary as well as secondary damages. 相似文献
83.
M Dong XQ Ding DI Pinon EM Hadac RP Oda JP Landers LJ Miller 《Canadian Metallurgical Quarterly》1999,274(8):4778-4785
The molecular basis of ligand binding to receptors provides important insights for drug development. Here, we explore domains of the cholecystokinin (CCK) receptor that are critical for ligand binding, using a novel series of fluorescent photolabile probes, receptor proteolysis, and rapid high resolution separation of peptide fragments by capillary electrophoresis. Each probe incorporated the same fluorophore and a photolabile p-benzoylphenylalanine at the amino terminus of the pharmacophoric domain (residue 24 of CCK-33) of CCK analogues representing full agonist, partial agonist, and antagonist of this receptor. Each was used to label the CCK receptor expressed on Chinese hamster ovary-CCKR cells, with the labeled domain then released by cyanogen bromide cleavage. Capillary electrophoresis with laser-induced fluorescence detection achieved an on-capillary mass sensitivity of 1.6 attomoles (10(-18) mol), with an excellent signal-to-noise ratio. Each of the biologically divergent, but structurally similar probes saturably and specifically labeled the same receptor domain, consistent with conservation of "docking" determinants. This had an apparent mass of 2.9 kDa, most consistent with the first extracellular loop domain. An additional probe having its site of covalent attachment in a different region of the probe (residue 29 of CCK-33) labeled a distinct receptor fragment with differential migration on capillary electrophoresis (third extracellular loop). Identification of the specific receptor residue(s) covalently linked to the amino-terminal probes must await further fragmentation and sequence analysis. 相似文献
84.
85.
IV Bychkovskaia RP Stepanov PV Antonov DN Cherniakova 《Canadian Metallurgical Quarterly》1996,36(6):926-931
Electron microscopic investigation of capillary endothelium cells in myocardium of irradiated rats revealed an unusual effect of persistent increase of probability of cell damage, similar in many relations to that described earlier for various unicellular species. New effect, unlike those traditionally studied, is characterised by non-stochastic nature, large number of the involved cells, reveals itself even after faint influences, and can be induced as well by agents other than radiation. The question is put on the probable commonness between these changes and the pseudomutagenesis which has the similar phenomenology. 相似文献
86.
PH Allaire JM Messick JE Oesterling DE Byer RP Myers MM Lieber RC Chantigian JO Welna DE Patterson ML Blute 《Canadian Metallurgical Quarterly》1992,67(11):1031-1041
In a prospective, randomized study, continuous infusion of epidural fentanyl citrate (group E) was compared with patient-controlled intravenously administered morphine sulfate (group P) for analgesia in 66 men after radical retropubic prostatectomy. Although both methods provided satisfactory analgesia, the mean comfort level scores were lower (that is, greater comfort) in group E than in group P at all observation times. The difference in mean resting comfort level scores between groups E and P was statistically significant (P < or = 0.05) at 9 of the 11 observation times. In addition, significant differences in comfort level scores were noted at 8 of the 11 observation times during deep breathing, 5 of 11 during coughing, and 3 of 9 during ambulation. Maximal and minimal comfort level scores recorded by each patient during the course of the study were significantly lower (that is, less pain) in group E than in group P for all four categories of activity. The percentage of patients who reported no pain was significantly higher in group E than in group P at 9 of 11 observation times during resting and 5 of 11 observation times during deep breathing. No significant differences were noted in side effect profiles or duration of hospital stay. In summary, when two effective methods of analgesia used after radical retropubic prostatectomy were compared prospectively, patients who received epidural infusion of fentanyl were more comfortable than those with patient-controlled intravenous administration of morphine, as evidenced by lower mean, maximal, and minimal comfort level scores and a greater proportion of patients with complete relief of pain. 相似文献
87.
SM Kurtz L Pruitt CW Jewett RP Crawford DJ Crane AA Edidin 《Canadian Metallurgical Quarterly》1998,19(21):1989-2003
The yielding, plastic flow, and fracture behavior of UHMWPE plays an important role in wear and failure mechanisms of total joint replacement components. The primary objective of this study was to compare the yielding, plastic flow, and fracture behavior of two implantable grades of UHMWPE (GUR 1120 vs 4150 HP). The first part of this work explored the hypothesis that up to the polymer yield point, the monotonic loading behavior of UHMWPE displays similar true stress strain behavior in tension and compression. Uniaxial tension and compression tests were conducted to compare the equivalent true stress vs strain response of UHMWPE up to 0.12 true strain. During monotonic loading, the equivalent true stress strain behavior was similar in tension and compression up to the yield point. However, investigation of the unloading behavior and permanent plastic deformations showed that classical deviatoric rate independent plasticity theory may dramatically overpredict the permanent strains in UHMWPE. A secondary goal of this study was to determine the ultimate true stress and strain for UHMWPE and to characterize the fracture surfaces after failure. Using a fracture mechanics approach, the critical flaw sizes were used in combination with the true ultimate stresses to predict the fracture toughness of the two resins. A custom video-based strain measurement system was developed and validated to characterize the true stress-strain behavior up to failure and to verify the accuracy of the incompressibility assumption in calculating the true stress-strains up to failure. In a detailed uncertainty analysis, theoretical expressions were derived for the relative uncertainty in digital video-based estimates of nominal strain, true strain, homogeneous stress, and true stress. Although the yielding behavior of the two UHMWPE resins was similar, the hardening and plastic flow behavior clearly discriminated between the GUR 1120 and 4150 HP. A statistically significant difference between the fracture toughness of the two resins was also evident. The long-term goal of this research is to provide detailed true stress strain data for UHMWPE under uniaxial tension and compression for future numerical simulations and comparison with more complex multiaxial loading conditions. 相似文献
88.
RP Millman CL Rosenberg CC Carlisle NR Kramer DM Kahn AE Bonitati 《Canadian Metallurgical Quarterly》1998,113(4):992-996
Twenty-four patients who failed uvulopalatopharyngoplasty (UPPP) for obstructive sleep apnea (OSA) had an adjustable oral (Herbst) appliance made to treat the persistent apnea. Six patients discontinued the device prior to sleep evaluation. Eighteen patients had polysomnographic evaluations at baseline, post-UPPP, and with the Herbst appliance in place. The apnea-hypopnea index baseline (AHI) and arterial oxygen saturation (SaO2) nadir were 42.3+/-6.1 and 83.6+/-1.8%, respectively. There was no significant change in either parameter with surgery. With the oral appliance, the AHI fell to 15.3+/-4.4 (p < or = 0.01) and the SaO2 nadir increased to 87.9+/-1.2% (p < or = 0.05). Ten of the patients had control of the OSA with the Herbst appliance with a fall in the AHI to < 10. There were, in addition, two partial responders as defined by an AHI of <20 and a >50% fall in AHI compared with baseline and post-UPPP values. All but one of the responders and partial responders had complete resolution of subjective symptoms of daytime sleepiness with the appliance. An adjustable oral appliance appears to be an effective mode of therapy to control OSA after an unsuccessful UPPP. 相似文献
89.
E López-Juez RP Jarvis A Takeuchi AM Page J Chory 《Canadian Metallurgical Quarterly》1998,118(3):803-815
We searched for new components that are involved in the positive regulation of nuclear gene expression by light by extending a screen for Arabidopsis cue (chlorophyll a/b-binding [CAB] protein-underexpressed) mutants (H.-M. Li, K. Culligan, R.A. Dixon, J. Chory [1995] Plant Cell 7: 1599-1610). cue mutants display reduced expression of the CAB3 gene, which encodes light-harvesting chlorophyll protein, the main chloroplast antenna. The new mutants can be divided into (a) phytochrome-deficient mutants (hy1 and phyB), (b) virescent or delayed-greening mutants (cue3, cue6, and cue8), and (c) uniformly pale mutants (cue4 and cue9). For each of the mutants, the reduction in CAB expression correlates with the visible phenotype, defective chloroplast development, and reduced abundance of the light-harvesting chlorophyll protein. Levels of protochlorophyllide oxidoreductase (POR) were reduced to varying degrees in etiolated mutant seedlings. In the dark, whereas the virescent mutants displayed reduced CAB expression and the lowest levels of POR protein, the other mutants expressed CAB and accumulated POR at near wild-type levels. All of the mutants, with the exception of cue6, were compromised in their ability to derepress CAB expression in response to phytochrome activation. Based on these results, we propose that the previously postulated plastid-derived signal is closely involved in the pathway through which phytochrome regulates the expression of nuclear genes encoding plastid proteins. 相似文献
90.
The aim of the study was to quantify the distribution of elastic fibers within the wall of the basilar artery. Three age groups were studied: 1) 0-1 yr.; 2) 20-50 yr. 3) > 50 yr. A histomorphometrical study was undertaken using an estimation of the linear density of the components of the fibrous elastic tissue system: the full length in the proximal and distal segments of the basilar artery was evaluated. Our results showed that: The elastic tissue of the basilar artery is not evenly distributed throughout the tunica media. Compared to the 0 to 1-year age group, mature elastic, elauninic and oxytalan fibers decreased with age. In all age groups the linear density of the mature elastic fibers was more evident in the proximal than in the distal segment of the artery. 相似文献