全文获取类型
收费全文 | 1616篇 |
免费 | 8篇 |
专业分类
电工技术 | 3篇 |
综合类 | 1篇 |
化学工业 | 29篇 |
金属工艺 | 2篇 |
机械仪表 | 5篇 |
建筑科学 | 4篇 |
能源动力 | 5篇 |
轻工业 | 23篇 |
水利工程 | 2篇 |
无线电 | 14篇 |
一般工业技术 | 16篇 |
冶金工业 | 1507篇 |
原子能技术 | 4篇 |
自动化技术 | 9篇 |
出版年
2018年 | 2篇 |
2017年 | 2篇 |
2015年 | 3篇 |
2013年 | 10篇 |
2012年 | 1篇 |
2011年 | 2篇 |
2010年 | 1篇 |
2009年 | 4篇 |
2008年 | 7篇 |
2007年 | 4篇 |
2006年 | 4篇 |
2005年 | 3篇 |
2004年 | 5篇 |
2003年 | 4篇 |
2002年 | 4篇 |
2000年 | 5篇 |
1999年 | 51篇 |
1998年 | 460篇 |
1997年 | 245篇 |
1996年 | 178篇 |
1995年 | 112篇 |
1994年 | 83篇 |
1993年 | 85篇 |
1992年 | 11篇 |
1991年 | 10篇 |
1990年 | 20篇 |
1989年 | 23篇 |
1988年 | 27篇 |
1987年 | 18篇 |
1986年 | 15篇 |
1985年 | 14篇 |
1984年 | 3篇 |
1983年 | 4篇 |
1982年 | 9篇 |
1981年 | 7篇 |
1980年 | 16篇 |
1979年 | 5篇 |
1978年 | 5篇 |
1977年 | 47篇 |
1976年 | 88篇 |
1975年 | 4篇 |
1973年 | 3篇 |
1972年 | 1篇 |
1971年 | 1篇 |
1970年 | 3篇 |
1969年 | 1篇 |
1955年 | 2篇 |
1944年 | 1篇 |
1890年 | 4篇 |
1882年 | 2篇 |
排序方式: 共有1624条查询结果,搜索用时 15 毫秒
41.
Independent control of HVOF particle velocity and temperature 总被引:3,自引:0,他引:3
Independent control of high velocity oxygen fuel (HVOF) spray particle velocity and temperature has not been possible in the
past, confusing the effect of either parameter on coating properties. This study describes a method by which velocity and
temperature may be varied independently. Commercial HVOF equipment that was fitted with a special conical supersonic nozzle
having four distinct particle injection locations was used. The present results, which were predicted in simulations and demonstrated
in experiments, revealed several pertinent facts. First, particle velocity is principally related to combustion chamber pressure
and is relatively unaffected by other design or operating conditions. Second, particle temperature is related to particle
residence time within the nozzle, which can be controlled by the choice of particle injection location. In these experiments,
the impact velocity and temperature of stainless steel particles were controlled within the ranges 340 to 660 m/s and 1630
to 2160 K, respectively. This range of parameters produced significant variations in splat morphology, coating microstructure,
and coating oxide content. Such particle control allows the effects of velocity and temperature on coating properties to be
assessed and controlled independently. These results also have commercial application, potentially enabling the user to tailor
particle impact velocity and temperature to achieve specific coating properties. 相似文献
42.
Rate theory modeling was used to simulate the effects of oversized solute additions on radiation-induced segregation in austenitic stainless steels. The purpose was to understand the effects of a solute-vacancy trapping mechanism on radiation-induced segregation and to define key parameters that most affect segregation behavior. Sensitivity analysis of the model showed the solute-vacancy binding energy to be the most important model parameter. Binding energies from ab initio first principles were calculated for oversized solutes of Pt, Ti, Hf and Zr, with energies of 0.31, 0.39, 0.71 and 1.08 eV, respectively. Differences in binding energies, despite similar sizes of the atoms, suggests that the short-range electronic interactions play an important role in determining binding energy. The model results show oversized solutes to be most effective at reducing grain boundary Cr depletion at temperatures of 450-500 °C for a dose rate applicable to proton irradiations. The reduction increases with increasing oversized solute concentration, where it saturates at approximately 0.1 at.%. 相似文献
43.
44.
RR Bosch AM Patel SE Van Emst-de Vries RL Smeets JJ De Pont PH Willems 《Canadian Metallurgical Quarterly》1998,346(2-3):345-351
We investigated the effects of nitric oxide (NO) donors, S-nitroso-N-acetylpenicillamine and sodium nitroprusside on basal and K+-evoked release of [3H]noradrenaline from superfused synaptosomes from the rat cerebral cortex. Both substances produced concentration-dependent increases in the release of the labeled transmitter under basal and depolarized conditions. The effects of the donors on basal release were Ca2+-independent but were not inhibited by the carrier-uptake blocker, desipramine; the effects were abolished by hemoglobin (an NO scavenger). Thirty-five minutes after stimulation with sodium nitroprusside, the synaptosomes were still responsive to KCl stimulation, indicating that the donor's effects were not caused by damage to the synaptosome membrane. The cGMP analogue, 8-bromo-cGMP, had no effect on basal release, and the enhanced release produced by sodium nitroprusside was not inhibited by the specific inhibitor of soluble guanylate cyclase, 1H-[1,2,4]oxadiazolo[4,3-alpha]quinoxalin-1-one, indicating that NO's effects on basal release of the neurotransmitter are guanylate cyclase-independent. Both of the NO donors had more marked effects on release of [3H]noradrenaline during K+-stimulated depolarization. The NO-mediated increase in this case was partially antagonized by 10 microM LH-[1,2,4]oxadiazolo[4,3-alpha]quinoxalin-1-one, and 8-Br-cGMP was also capable of producing concentration-dependent increases in the K+-stimulated release of the transmitter. These findings indicate that the effects of the NO donors on [3H]noradrenaline release during depolarization are partially mediated by the activation of guanylate cyclase. 相似文献
45.
A Errami DM He AA Friedl WJ Overkamp B Morolli EA Hendrickson F Eckardt-Schupp M Oshimura PH Lohman SP Jackson MZ Zdzienicka 《Canadian Metallurgical Quarterly》1998,26(13):3146-3153
DNA-dependent protein kinase (DNA-PK) plays an important role in DNA double-strand break (DSB) repair and V(D)J recombination. We have isolated a new X-ray-sensitive CHO cell line, XR-C1, which is impaired in DSB repair and which was assigned to complementation group 7, the group that is defective in the XRCC7 / SCID ( Prkdc ) gene encoding the catalytic subunit of DNA-PK (DNA-PKcs). Consistent with this complementation analysis, XR-C1 cells lackeddetectable DNA-PKcs protein, did not display DNA-PK catalytic activity and were complemented by the introduction of a single human chromosome 8 (providing the Prkdc gene). The impact of the XR-C1 mutation on V(D)J recombination was quite different from that found in most rodent cells defective in DNA-PKcs, which are preferentially blocked in coding joint formation, whereas XR-C1 cells were defective in forming both coding and signal joints. These results suggest that DNA-PKcs is required for both coding and signal joint formation during V(D)J recombination and that the XR-C1 mutant cell line may prove to be a useful tool in understanding this pathway. 相似文献
46.
AW Bach L Unger R Sprengel G Mengod J Palacios PH Seeburg MM Voigt 《Canadian Metallurgical Quarterly》1993,13(1-4):479-502
Using polymerase chain reaction (PCR) a complementary DNA (cDNA) encoding a 5-hydroxytryptamine (5-HT) receptor was isolated from rat forebrain. The amplified cDNA specifies an open reading frame of 374 amino acids comprising seven putative transmembrane regions. Expression of the cloned cDNA in human embryonic kidney cells (HEK 293) was used to establish the pharmacological profile of the encoded receptor polypeptide. Membranes containing the cloned receptor showed high affinity binding of [3H]-5-HT. Competition binding experiments with a variety of serotonin receptor ligands displayed a rank order of affinities corresponding to a 5-HT1D subtype: 5-CT > 5-HT = metergoline > CGS 12066 > methysergide > sumatriptan > mianserin = (-)alpha-Me-5-HT = yohimbine > 8-OH-DPAT > or = rauwolscine > spiperone > DOI > propranolol > or = 2-Me-5-HT > or = ICS 205930. Ketanserin and ritanserin displaced [3H]-5-HT-binding in a biphasic manner. In situ hybridization revealed highest expression of the corresponding mRNA in the pyramidal layer of the olfactory tubercle and the nucleus caudatus and accumbens. 相似文献
47.
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
48.
MA Charles DJ Pettitt RL Hanson PH Bennett MF Saad QZ Liu WC Knowler 《Canadian Metallurgical Quarterly》1994,140(2):123-131
High blood pressure, abnormal glucose tolerance, and obesity are frequently associated with each other, but the mechanism of these associations is poorly understood. Studying them in children may help in understanding the pathogenesis of hypertension. Blood pressure, height, weight, and plasma glucose and serum insulin concentrations during a 75-g oral glucose tolerance test were measured in 1,698 Pima Indian children aged 6-17 years who participated in an ongoing epidemiologic study. Weight relative to height was used as an index of obesity. The parents of many of the children were also examined. Fasting and 2-hour glucose and insulin concentrations, adjusted for age, sex, and relative weight, were positively related to systolic blood pressure but not to diastolic blood pressure. Relative weight, 2-hour glucose, and fasting insulin concentrations were independently and significantly associated with systolic blood pressure in a stepwise regression analysis that included age and sex. After parental hypertension was taken into account, maternal but not paternal non-insulin-dependent diabetes mellitus, controlled for the child's relative weight and glucose and insulin concentrations, was significantly associated with higher blood pressure in children. The stronger association with maternal diabetes suggests a greater sharing of environmental factors between mother and child than between father and child, but familial similarities in obesity and glucose and insulin concentrations, the diabetic intrauterine milieu, and shared environmental factors probably all contribute to this association. 相似文献
49.
50.
A variety of gynaecological phenomena such as menstrual disorders, infertility and premature menopause are associated with ovarian dysfunction. In this paper, a factor is considered that may play a role in the aetiology of ovarian dysfunction. Animal research has shown that preovulatory overripeness of the oocyte may cause various developmental and chromosomal anomalies. Among the developmental anomalies observed in amphibia and fish are a number of gonadal aberrations, often occurring in otherwise normal specimens. This may be the consequence of a degeneration of the 'germinal cytoplasm', cytoplasmic structures located in the vegetative pole region of the oocyte, destined to become part of future primordial germ cells. Indirect evidence suggests that preovulatory overripeness of the oocyte also plays a significant role in human reproductive failure. An increased risk of preovulatory overripeness is expected during periods of endocrine irregularities, such as the first postmenarcheal years, the last premenopausal years, the first months after a pregnancy and, possibly, during certain seasons. If the overripeness-induced gonadal maldevelopment observed in animals also occurs in humans, this may explain variations in reproductive function according to month of birth, as observed in women. It is hypothesized that females conceived during periods of maternal endocrine irregularities face an increased risk of ovarian dysfunction through overripeness-induced gonadal maldevelopment. 相似文献