全文获取类型
收费全文 | 1064篇 |
免费 | 16篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 4篇 |
化学工业 | 35篇 |
金属工艺 | 5篇 |
机械仪表 | 10篇 |
矿业工程 | 1篇 |
能源动力 | 13篇 |
轻工业 | 11篇 |
石油天然气 | 4篇 |
无线电 | 29篇 |
一般工业技术 | 33篇 |
冶金工业 | 902篇 |
原子能技术 | 1篇 |
自动化技术 | 33篇 |
出版年
2023年 | 1篇 |
2022年 | 7篇 |
2021年 | 9篇 |
2020年 | 7篇 |
2019年 | 8篇 |
2018年 | 19篇 |
2017年 | 7篇 |
2016年 | 6篇 |
2015年 | 7篇 |
2014年 | 8篇 |
2013年 | 9篇 |
2012年 | 3篇 |
2011年 | 8篇 |
2010年 | 11篇 |
2009年 | 10篇 |
2008年 | 3篇 |
2007年 | 4篇 |
2006年 | 10篇 |
2005年 | 3篇 |
2004年 | 2篇 |
2003年 | 8篇 |
2002年 | 2篇 |
2001年 | 2篇 |
2000年 | 5篇 |
1999年 | 36篇 |
1998年 | 310篇 |
1997年 | 186篇 |
1996年 | 91篇 |
1995年 | 62篇 |
1994年 | 39篇 |
1993年 | 65篇 |
1992年 | 7篇 |
1991年 | 9篇 |
1990年 | 5篇 |
1989年 | 4篇 |
1988年 | 11篇 |
1987年 | 4篇 |
1986年 | 4篇 |
1985年 | 6篇 |
1984年 | 4篇 |
1983年 | 1篇 |
1982年 | 6篇 |
1981年 | 4篇 |
1980年 | 5篇 |
1978年 | 3篇 |
1977年 | 16篇 |
1976年 | 40篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1955年 | 1篇 |
排序方式: 共有1081条查询结果,搜索用时 31 毫秒
101.
M. Ramadan N. El-Bagoury N. Fathy M. A. Waly A. A. Nofal 《Journal of Materials Science》2011,46(11):4013-4019
This research is directed towards studying the effect of semi-solid processing (using cooling plate technique) on the microstructure,
fluidity, and mechanical properties of ductile iron (DI). Sand mold castings with constant width of 25 mm and length of 150 mm
with the thicknesses of 6, 12, 18, and 25 mm were used in this study. Microstructure, fluidity, and tensile strength properties
were investigated as a function of fraction of solid. The results indicated that by increasing fraction of solid microstructure
becomes finer and more globular. However, increasing primary fraction of solid increases the cementite content in the matrix.
Above a certain fraction of solid (f
s = 0.28, f
s = 0.1, and f
s = 0.05 for 25, 18, and 12 mm wall thickness, respectively), the fluidity of semi-solid processed DI decreases steeply. For
low fraction of solid (f
s ≤ 0.15), increasing the fraction of solid results in an increment in the tensile strength, comparing with the ordinary DI
due to the fine and globular structure formation. Any further increment of fraction of solid (f
s > 0.15) leads to the cementite increment and gas porosity formation, consequently the tensile strength decreased. The fraction
of solid of DI and casting wall thickness should be considered in order to obtain the best combination of microstructure,
fluidity, and mechanical properties of semi-solid processed DI. 相似文献
102.
Electrochemistry: Development and Simulation of Sulfur‐doped Graphene Supported Platinum with Exemplary Stability and Activity Towards Oxygen Reduction (Adv. Funct. Mater. 27/2014)
下载免费PDF全文
![点击此处可从《Advanced functional materials》网站下载免费的PDF全文](/ch/ext_images/free.gif)
103.
Development and Simulation of Sulfur‐doped Graphene Supported Platinum with Exemplary Stability and Activity Towards Oxygen Reduction
下载免费PDF全文
![点击此处可从《Advanced functional materials》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Drew Higgins Md Ariful Hoque Min Ho Seo Rongyue Wang Fathy Hassan Ja‐Yeon Choi Mark Pritzker Aiping Yu Jiujun Zhang Zhongwei Chen 《Advanced functional materials》2014,24(27):4325-4336
Sulfur‐doped graphene (SG) is prepared by a thermal shock/quench anneal process and investigated as a unique Pt nanoparticle support (Pt/SG) for the oxygen reduction reaction (ORR). Particularly, SG is found to induce highly favorable catalyst‐support interactions, resulting in excellent half‐cell based ORR activity of 139 mA mgPt ?1 at 0.9 V vs RHE, significant improvements over commercial Pt/C (121 mA mgPt ?1) and Pt‐graphene (Pt/G, 101 mA mgPt ?1). Pt/SG also demonstrates unprecedented stability, maintaining 87% of its electrochemically active surface area following accelerated degradation testing. Furthermore, a majority of ORR activity is maintained, providing 108 mA mgPt ?1, a remarkable 171% improvement over Pt/C (39.8 mA mgPt ?1) and an 89% improvement over Pt/G (57.0 mA mgPt ?1). Computational simulations highlight that the interactions between Pt and graphene are enhanced significantly by sulfur doping, leading to a tethering effect that can explain the outstanding electrochemical stability. Furthermore, sulfur dopants result in a downshift of the platinum d‐band center, explaining the excellent ORR activity and rendering SG as a new and highly promising class of catalyst supports for electrochemical energy technologies such as fuel cells. 相似文献
104.
Cemin Zhang Fathy A.E. Mahfouz M. 《Microwave and Wireless Components Letters, IEEE》2007,17(12):873-875
An ultra-wideband (UWB) sampling mixer has been developed based on utilizing the combined advantages of two known circuit topologies: a wideband balun and a balanced-feed mixer. The developed sampler is integrated with a step-recovery diode strobe-step generator to sub-sample UWB signals. The fabricated sub-sampler demonstrated a 3.5-dB radio frequency to intermediate frequency (RF-IF) conversion loss up to 1 GHz (without the IF amplification), and a wide 3 dB bandwidth that exceeded 3.5-GHz. It has a reduced spurious level of better than -38 dBc, a lower sensitivity to the Schottky diode-placement, an excellent input match, and good isolation. 相似文献
105.
The objective of this study was to evaluate the potential of Fourier transform infrared spectroscopy (FTIR) for rapid identification of Bacillus cereus isolates. Ten B. cereus group isolates (comprising B. cereus, Bacillus mycoides, and Bacillus thuringiensis strains), five other Bacillus spp., and five non-Bacillus spp. were used. Two types of media, brain heart infusion (BHI) and Trypticase soy agar (TSA), were tested. The results indicated that all B. cereus group isolates produced characteristic absorbance peaks at wave numbers between 1738 and 1740 cm-1. These peaks were not affected by the growth medium. None of the other bacteria tested showed a similar peak after growth on BHI or TSA. Absorbance peaks between 1800 and 1500 cm-1 of members of the B. cereus group had different shapes and sizes, suggesting that FTIR may be useful for rapid identification of species within the B. cereus group. 相似文献
106.
Although screening sigmoidoscopy (SS) reduces colorectal cancer mortality, surveys indicate that fewer than half of primary care physicians routinely recommend SS and less than 10% of eligible patients receive this test. The purpose of this study was to explore barriers to compliance with SS through a cross-sectional survey of general medicine patients. Clinician advice, perceived benefit of the test, and having a family member who has had the test are associated with SS, while perceived pain is a barrier to compliance and can negate the positive effects of clinician advice. These factors can be targeted as part of efforts to improve compliance with SS. 相似文献
107.
We have used Arabidopsis calmodulin (CaM) covalently coupled to horseradish peroxidase to screen a barley aleurone cDNA expression library for CaM binding proteins. The deduced amino acid sequence of one cDNA obtained by this screen was shown to be a unique protein of 702 amino acids with CaM and cyclic nucleotide binding domains at the carboxyl terminus and high similarity to olfactory and K+ channels. This cDNA was designated HvCBT1 (Hordeum vulgare CaM binding transporter). Hydropathy plots of HvCBT1 showed the presence of six putative transmembrane domains, but sequence alignment indicated a pore domain that was unlike the consensus domains in K+ and olfactory channels. Expression of a subclone of amino acids 482-702 in Escherichia coli generated a peptide that bound CaM. When a fusion protein of HvCBT1 and green fluorescent protein was expressed in barley aleurone protoplasts, fluorescence accumulated in the plasma membrane. Expression of HvCBT1 in the K+ transport deficient Saccharomyces cerevisiae mutant CY162 showed no rescue of the mutant phenotype. However, growth of CY162 expressing HvCBT1 with its pore mutated to GYGD, the consensus sequence of K+ channels, was compromised. We interpret these data as indicating that HvCBT1 acts to interfere with ion transport. 相似文献
108.
TJ Tucker SF Brady WC Lumma SD Lewis SJ Gardell AM Naylor-Olsen Y Yan JT Sisko KJ Stauffer BJ Lucas JJ Lynch JJ Cook MT Stranieri MA Holahan EA Lyle EP Baskin IW Chen KB Dancheck JA Krueger CM Cooper JP Vacca 《Canadian Metallurgical Quarterly》1998,41(17):3210-3219
As part of an ongoing effort to prepare therapeutically useful orally active thrombin inhibitors, we have synthesized a series of compounds that utilize nonbasic groups in the P1 position. The work is based on our previously reported lead structure, compound 1, which was discovered via a resin-based approach to varying P1. By minimizing the size and lipophilicity of the P3 group and by incorporating hydrogen-bonding groups on the N-terminus or on the 2-position of the P1 aromatic ring, we have prepared a number of derivatives in this series that exhibit subnanomolar enzyme potency combined with good in vivo antithrombotic and bioavailability profiles. The oxyacetic amide compound 14b exhibited the best overall profile of in vitro and in vivo activity, and crystallographic studies indicate a unique mode of binding in the thrombin active site. 相似文献
109.
DR Holmes KE Kip W Yeh SF Kelsey KM Detre DO Williams 《Canadian Metallurgical Quarterly》1998,32(3):590-595
Researchers examining clinical decision-making often explored the role of the nurse's experience. In these studies, experience was conceptualized as either the time spent in nursing or the knowledge which came from practice. This paper reports on the conceptualization of the nurse's experience emerging from a grounded theory study describing one decision-making process: 'knowing the patient'. Data included in-depth interview text, participant observation fieldnotes, and documents. Data were analysed using the constant comparative method and open, axial and selective coding techniques. In the analysis, the nurse's experience was conceptually defined as 'the application of that learned from previous practice situations'. Three attributes of the nurse's experience emerged. These included a focus on the patient, confidence in practice, and knowledge of antecedents and consequences of similar patient situations. Each aspect enhanced the individualization of nursing interventions. The findings are related to other investigations in nursing and insights for practice are offered. 相似文献
110.
Changes in calorie intake and weight gain were evaluated in five children with cystic fibrosis (CF) who received behavioral intervention and four children with CF who served as wait list controls. The behavioral intervention was a 6-week group treatment that provided nutritional education plus management strategies aimed at mealtime behaviors that parents find most problematic. The control group was identified prospectively and was evaluated on all dependent measures at the same points in time pre- and posttreatment as the intervention group. Difference scores on calorie intake and weight gain from pre- to posttreatment were compared between groups using t tests for independent samples. The behavioral intervention group increased their calorie intake by 1,032 calories per day, while the control group's intake increased only 244 calories per day from pre- to posttreatment [t(6) = 2.826, p = 0.03]. The intervention group also gained significantly more weight (1.7 kg) than the control group (0 kg) over the 6 weeks of treatment [t(7) = 2.588, p = 0.03] and demonstrated catchup growth for weight, as indicated by improved weight Z scores (-1.18 to -0.738). The control group showed a decline in weight Z scores over this same time period (-1.715 to -1.76). One month posttreatment, the intervention was replicated with two of the four children from the control group. Improved calorie intake and weight gain pre- to posttreatment were again found in these children. At 3- and 6-month follow-up study of children receiving intervention, maintenance of calorie intake and weight gain was confirmed. No changes were found on pulmonary functioning, resting energy expenditure, or activity level pre- to posttreatment. This form of early intervention appears to be promising in improving nutritional status and needs to be investigated over a longer period of time to evaluate the effects of treatment gains on the disease process. 相似文献