全文获取类型
收费全文 | 1202篇 |
免费 | 2篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 2篇 |
化学工业 | 20篇 |
金属工艺 | 4篇 |
机械仪表 | 7篇 |
建筑科学 | 6篇 |
能源动力 | 1篇 |
轻工业 | 11篇 |
水利工程 | 2篇 |
无线电 | 7篇 |
一般工业技术 | 44篇 |
冶金工业 | 1088篇 |
自动化技术 | 13篇 |
出版年
2021年 | 3篇 |
2019年 | 1篇 |
2018年 | 2篇 |
2016年 | 2篇 |
2015年 | 1篇 |
2014年 | 1篇 |
2013年 | 7篇 |
2012年 | 4篇 |
2011年 | 8篇 |
2010年 | 6篇 |
2009年 | 5篇 |
2008年 | 3篇 |
2007年 | 4篇 |
2006年 | 2篇 |
2005年 | 7篇 |
2004年 | 1篇 |
2003年 | 5篇 |
2001年 | 2篇 |
2000年 | 4篇 |
1999年 | 34篇 |
1998年 | 329篇 |
1997年 | 222篇 |
1996年 | 127篇 |
1995年 | 72篇 |
1994年 | 50篇 |
1993年 | 75篇 |
1992年 | 8篇 |
1991年 | 9篇 |
1990年 | 15篇 |
1989年 | 13篇 |
1988年 | 10篇 |
1987年 | 19篇 |
1986年 | 8篇 |
1985年 | 10篇 |
1984年 | 4篇 |
1983年 | 4篇 |
1982年 | 3篇 |
1981年 | 8篇 |
1980年 | 8篇 |
1979年 | 1篇 |
1978年 | 7篇 |
1977年 | 27篇 |
1976年 | 62篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1973年 | 3篇 |
1971年 | 1篇 |
1969年 | 1篇 |
1964年 | 1篇 |
1955年 | 1篇 |
排序方式: 共有1205条查询结果,搜索用时 15 毫秒
81.
Precision measurements of third sound in atomically thin4He films on Ne, Ar, and CO2 substrates reveal a periodic structure not corresponding to whole layers. Treating the He film as an incompressible, continuous fluid, the data indicate that the chemical potential has a contribution proportional to l–6, where l is the He coverage in layers, which is modulated at intervals of 0.62±0.04 layers and which weakens the van der Waals potential. Alternatively the data indicates the existence in the film of a damped smectic density wave with a 0.54±0.40 layer periodicity. 相似文献
82.
K. A. Gillis 《International Journal of Thermophysics》1997,18(1):73-135
Measurements of the speed of sound in seven halogenated hydrocarbons are presented. The compounds in this study are 1-chloro-1,2,2,2-tetrafluoroethane
(CHClFCF3 or HCFC-124), pentafluoroethane (CHF2 CF3 or HFC-125), 1,1,1-trifluoroethane (CF3CH3 or HFC-143a), 1,1-difluoroethane (CHF2CH3 or HFC-152a), 1,1,1,2,3,3-hexafluoropropane (CF3CHFCHF2 or HFC-236ea), 1,1,1,3,3,3-hexafluoropropane (CF3CH2CF3 or HFC-236fa), and 1,1,2,2,3-pentafluoropropane (CHF2CF2CH2F or HFC-245ca). The measurements were performed with a cylindrical resonator at temperatures between 240 and 400 K and at
pressures up to 1.0 MPa. Ideal-gas heat capacities and acoustic virial coefficients were directly deduced from the data. The
ideal-gas heat capacity of HFC-125 from this work differs from spectroscopic calculations by less than 0.2% over the measurement
range. The coefficients for virial equations of state were obtained from the acoustic data and hard-core square-well intermolecular
potentials. Gas densities that were calculated from the virial equations of state for HCFC-124 and HFC-125 differ from independent
density measurements by at most 0.15%, for the ranges of temperature and pressure over which both acoustic and Burnett data
exist. The uncertainties in the derived properties for the other five compounds are comparable to those for HCFC-124 and HFC-125. 相似文献
83.
84.
The effects of repeated amphetamine (AMPH) pretreatment on norepinephrine (NE) neurotransmission in the hypothalamus and hippocampus were assessed using in vivo microdialysis. Rats were pretreated with either saline or an escalating-dose AMPH regimen (1-->10 mg/kg) over 10 consecutive days, and then were withdrawn from AMPH for either 1 day or 30 days, at which time the animals underwent two consecutive days of testing. As expected, repeated treatment with AMPH resulted in time-dependent changes in both spontaneous locomotor activity and in the psychomotor response to a subsequent challenge injection of AMPH. In addition, repeated exposure to AMPH resulted in time-dependent and regionally-specific changes in the basal concentrations of NE in dialysate, and in the NE response to an AMPH challenge. For example, AMPH pretreatment produced a persistent (at least one month) increase in the basal concentration of NE in the hippocampus, but not the hypothalamus, although the response to an AMPH challenge was altered in both structures. It is suggested that AMPH treatment produces adaptations in NE systems that far outlast the acute effects of the drug, and that these may contribute to both transient and more persistent behavioral sequelae associated with the discontinuation of chronic AMPH use. 相似文献
85.
M Xu TE Koeltzow GT Santiago R Moratalla DC Cooper XT Hu NM White AM Graybiel FJ White S Tonegawa 《Canadian Metallurgical Quarterly》1997,19(4):837-848
The dopamine D3 receptor is expressed primarily in regions of the brain that are thought to influence motivation and motor functions. To specify in vivo D3 receptor function, we generated mutant mice lacking this receptor. Our analysis indicates that in a novel environment, D3 mutant mice are transiently more active than wild-type mice, an effect not associated with anxiety state. Moreover, D3 mutant mice exhibit enhanced behavioral sensitivity to combined injections of D1 and D2 class receptor agonists, cocaine and amphetamine. However, the combined electrophysiological effects of the same D1 and D2 agonists on single neurons within the nucleus accumbens were not altered by the D3 receptor mutation. We conclude that one function of the D3 receptor is to modulate behaviors by inhibiting the cooperative effects of postsynaptic D1 and other D2 class receptors at systems level. 相似文献
86.
The purpose of this study was to determine whether a brace designed to unload varus degenerative knees actually alters medial compartment loads by decreasing the adduction moment. Eleven patients who had arthrosis confined to the medial compartment were fitted with a valgus brace and tested before and after brace wear with pain and function scoring instruments and by automated gait analysis. The biomechanical data from these patients were compared with those from 11 healthy control subjects. Scores from an analog pain scale decreased 48% with brace wear, and function with activities of daily living increased 79%. Mean adduction moment without the brace measured 4.0 +/- 0.8% body weight times height versus 3.6 +/- 0.8% body weight times height when wearing the brace (10% decrease). The mean adduction moment for control subjects was 3.5 +/- 0.6% body weight times height. Thus, the mean adduction moment decreased from approximately one standard deviation from the normal mean to a value that is similar to the control value. Nine of 11 patients had a decrease in the adduction moment with the brace, five of 11 patients had a reduction higher than 10%, and decreases in this moment were as high as 32%. This study shows that pain, function, and biomechanical knee loading can be altered by a brace designed to unload the medial compartment of the knee. 相似文献
87.
The P2Y2 receptor is a uridine/adenosine triphosphate (UTP/ATP)-sensitive G-protein-linked nucleotide receptor that previously has been reported to stimulate the phosphoinositide signaling pathway. Messenger RNA for this receptor has been detected in brain tissue. We have investigated the coupling of the molecularly defined rat P2Y2 receptor to neuronal N-type Ca2+ channels and to M-type K+ channels by heterologous expression in rat superior cervical sympathetic (SCG) neurons. After the injection of P2Y2 cRNA, UTP inhibited the currents carried by both types of ion channel. As previously reported [Filippov AK, Webb TE, Barnard EA, Brown DA (1997) Inhibition by heterologously expressed P2Y2 nuerones. Br J Pharmacol 121:849-851], UTP inhibited the Ca2+ current (ICa(N)) by up to 64%, with an IC50 of approximately 0.5 microM. We now find that UTP also inhibited the K+M current (IK(M)) by up to 61%, with an IC50 of approximately 1.5 microM. UTP had no effect on either current in neurons not injected with P2Y2 cRNA. Structure-activity relations for the inhibition of ICa(N) and IK(M) in P2Y2 cRNA-injected neurons were similar, with UTP >/= ATP > ITP > GTP,UDP. However, coupling to these two channels involved different G-proteins: pretreatment with Pertussis toxin (PTX) did not affect UTP-induced inhibition of IK(M) but reduced inhibition of ICa(N) by approximately 60% and abolished the voltage-dependent component of this inhibition. In unclamped neurons, UTP greatly facilitated depolarization-induced action potential discharges. Thus, the single P2Y2 receptor can couple to at least two G-proteins to inhibit both Ca2+N and K+M channels with near-equal facility. This implies that the P2Y2 receptor may induce a broad range of effector responses in the nervous system. 相似文献
88.
T Genzini A de Oliveira e Silva MP de Miranda CR de Melo RJ Felipe TE dos Santos ES Cardoso CF Costa-Filho RG Haetinger EC Pereira 《Canadian Metallurgical Quarterly》1995,32(4):162-167
Hemangiomas are the most common benign vascular tumor found in the liver. In this study, 103 cases of hepatic hemangiomas were analysed in a retrospective manner. Image aspects such as those seen in ultrassonography, computed tomography, nuclear magnetic resonance and arteriography are discussed. The incidence was higher amongst the female sex, between individuals from 40 to 60 years old, which presented predominantly without symptoms (66%) and localized mainly in the right hepatic lobe (74%). The meaning of those aspects, when adopted, permits the clinicians to differentiate benign from malignant nodular lesions in the liver. 相似文献
89.
AD Harries TE Nyirenda A Banerjee C Mundy FM Salaniponi 《Canadian Metallurgical Quarterly》1998,2(11):914-918
SETTING: Government hospitals and health centres in 23 districts in Malawi. OBJECTIVE: To determine 1) the number and smear-positivity rate of sputum samples submitted at health centres and hospitals, and 2) the time for sputum samples to get from health centres to smear examination. DESIGN: Prospective data collection on sputum specimens coming from health centres to hospital laboratories, and over the equivalent time period, retrospective data collection from laboratory sputum registers. RESULTS: Information was collected over a period of 5.6 months during 1997. Of 21 527 patients submitting sputum samples, 16995 (79%) were from within the hospital and 4532 (21%) were from health centres. Of 15 833 new TB suspects, 12 804 (81%) submitted sputum within the hospital and 3029 (19%) were from health centres. The overall smear-positivity rate was 11.9%: the proportion of new suspects who were smear-positive was significantly higher in health centres (14.1%) compared with hospital-based patients (11.4%, P < 0.05); 27% of all sputum specimens from health centres took 8 days or longer to get to smear examination. Sputum smears were positive from 1-30 days between submission and laboratory examination. CONCLUSION: Fewer sputum samples are submitted at health centres compared with hospitals, and there may be long delays between sputum submission and smear examination. The precise reasons are unclear, but health centre staff need training about the importance of timely case finding procedures. 相似文献
90.
We report a patient diagnosed prenatally on routine fetal ultrasound, at 30 weeks' gestation, with subdural haemorrhage. The mother had suffered a mild abdominal trauma and had Factor XI deficiency; however, both were felt to be aetiologically insignificant. Prenatal follow-up showed a complete resolution of the haematoma and no postnatal sequelae have been noted to date. The aetiologies and outcomes in the few previously reported cases are reviewed and compared with our case. 相似文献