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排序方式: 共有141条查询结果,搜索用时 15 毫秒
41.
P. Sarin P.E. Driemeyer R.P. Haggerty D.-K. Kim J.L. Bell Z.D. Apostolov W.M. Kriven 《Journal of the European Ceramic Society》2010,30(11):2375-2386
High temperature oxidation of ZrB2 and the effect of SiC on controlling the oxidation of ZrB2 in ZrB2–SiC composites were studied in situ, in air, using X-ray diffraction. Oxidation was studied by quantitatively analyzing the crystalline phase changes in the samples, both non-isothermally, as a function of temperature, up to ~1650 °C, as well as isothermally, as a function of time, at ~1300 °C. During the non-isothermal studies, the formation and transformation of intermediate crystalline phases of ZrO2 were also observed. The change in SiC content, during isothermal oxidation studies of ZrB2–SiC composites, was similar in the examined temperature range, regardless of sample microstructure and composition. Higher SiC content, however, markedly retarded the oxidation rate of the ZrB2 phase in the composites. A novel approach to quantify the extent of oxidation by estimating the thickness of the oxidation layer formed during oxidation of ZrB2 and ZrB2–SiC composites, based on fractional conversion of ZrB2 to ZrO2 in situ, is presented. 相似文献
42.
According to proposed National Mission on biodiesel in India, we have undertaken studies on stability of biodiesel from tree borne non-edible oil seeds Jatropha. European biodiesel standard EN-14214 calls for determining oxidation stability at 110 °C with a minimum induction time of 6 h by the Rancimat method (EN-14112). Neat Jatropha biodiesel (JBD) exhibited oxidation stability of 3.95 h and research was conducted to investigate influence of presence of transition metals, likely to be present in the metallurgy of storage tanks and barrels, on oxidation stability of Jatropha methyl ester. It was found that influence of metal was detrimental to oxidation stability and catalytic. Even small concentrations of metal contaminants showed nearly same influence on oxidation stability as large amounts. Copper showed strongest detrimental and catalytic effect. The dependence of the oxidation stability on the type of metal showed that long-term storage tests in different types of metal containers for examining the influence of container material on oxidation stability of biodiesel may be replaced by significantly faster Rancimat test serving as an accelerated storage test. 相似文献
43.
44.
Amit Sarin Rajneesh Arora N. P. Singh Rakesh Sarin Meeta Sharma R. K. Malhotra 《Journal of the American Oil Chemists' Society》2010,87(5):567-572
According to the proposed National Mission on biodiesel in India, we have undertaken studies on the stability of biodiesel
from tree-borne non-edible oil seeds like Pongamia pinnata. Neat Pongamia methyl ester (PoME) exhibited an oxidation stability (OS) of 2.54 h and research was conducted to investigate
the effect of the presence of transition metals likely to be present in the metallurgy of storage tanks and barrels, on the
OS of PoME. It was found that the influence of metal was detrimental to OS and was catalytic, as even small concentrations
of metal contaminants showed nearly the same influence on OS as large amounts. Copper showed the strongest detrimental and
catalytic effect on OS. The OS of metal-contaminated PoME was found to increase with an increase in the dosage of antioxidant
but the dosage required for copper-contaminated PoME became approximately four times than required for neat PoME. The dependence
of the OS on the type of metal showed that long-term storage tests in different types of metal containers for examining the
influence of container material on OS of biodiesel may be replaced by the significantly faster Rancimat test serving as an
accelerated storage test. 相似文献
45.
46.
The atmospheric abundances of elemental carbon (EC), organic carbon (OC) and water-soluble organic carbon (WSOC) have been measured in aerosol samples collected during wintertime (December–March) from selected sites (urban, rural and high-altitude) in northern India. A characteristic feature of their abundance pattern, at urban sites, is reflected in the OC/EC ratios (range: 2.4–14.5, Av=7.8±2.4, n=77) indicating dominant contribution from biomass burning sources (wood-fuel and agriculture waste). This is in sharp contrast to the OC/EC ratios at a rural site (range: 2.1–4.0, Av=3.1±0.6, n=7) influenced by emissions from coal-fired industries. The long-term measurements made from a high-altitude site (~2000 m amsl) reveal significantly lower abundances of EC and OC; suggesting that boundary layer dynamics (during wintertime) play an important role in efficient trapping of pollutants within the Indo-Gangetic Plain (northern India). The WSOC/OC ratios are fairly uniform (~0.35) in aerosols over urban sites but relatively enhanced contribution of WSOC and higher ratios (~0.5) at a high-altitude site emphasizes the significance of secondary organic aerosols. The comprehensive data set on EC, OC and WSOC/OC ratios from northern India is crucial to improve model parameterization of carbonaceous aerosols for atmospheric scattering and absorption of solar radiation on a regional scale. 相似文献
47.
Kim J.H. Sarin S.V. Yasunaga M. Oh H. 《Vehicular Technology, IEEE Transactions on》2001,50(1):278-286
We are proposing a new noncoherent pseudonoise code acquisition method for code-division multiple-access (CDMA) mobile communication systems. The proposed method employs two digital matched filters, and the code acquisition is based on a double dwell process. Through serial cascading of the dual-matched filters, the proposed code acquisition method does not lose the track of the incoming sequence even after returning from the false alarm state. This unique feature imparts on our design much desired stability. Moreover, the use of two matched filters increases the acquisition speed, which is of prime importance. One important issue in CDMA acquisition is how to determine the threshold values for optimal performance, the measure of optimality being the minimum mean acquisition time. In our performance analysis, we have derived the probability of detection and false alarm as a function of threshold values, then determine the threshold values that achieve the minimum mean acquisition time. Our performance analysis shows that the mean acquisition time is 35 ms at -15 dB input chip signal-to-noise ratio, much faster than the conventional active correlation technique 相似文献
48.
Recognizing the complexity of coal mining management, e.g., the scarcity of financial resources and a variation in the quality of coal found in different sections of a mine, in this paper, we develop a mixed-binary programming model as an aid for generating mine production schedules in order to obtain coal of the desired quality and maximize the associated net present value. The model is based on the definition of the mine layout as a precedence network, with the nodes representing mining sections. A general solution methodology based on the Benders' decomposition of the model is developed. It exploits the special nature of the resulting subproblems in order to develop an effective solution procedure. Computational experience of this procedure, along with the results of its application to a mining case, are presented. 相似文献
49.
In this paper, we address a university-timetabling problem and present a methodology that relies on Benders’ partitioning
for its solution. This partitioning results from the special nature of the underlying integer programming formulation for
this problem. We have used our methodology to schedule courses offered by the College of Engineering as well as to those offered
university-wide at Virginia Tech. The results clearly depict an improvement in the quality of course schedules obtained by
our methodology over those currently used, when the performance of a timetable is measured by the total distance traveled
by the faculty members from their offices in respective departments to the classrooms, where the courses are offered. 相似文献
50.
Chuda Chittasupho Amornrat Manthaisong Siriporn Okonogi Sarin Tadtong Weerasak Samee 《International journal of molecular sciences》2022,23(1)
Wound healing impairment due to a postponed, incomplete, or uncoordinated healing process has been a challenging clinical problem. Much research has focused on wound care, particularly on discovery of new therapeutic approaches for acute and chronic wounds. This study aims to evaluate the effect of the combination of quercetin and curcuminoids at three different ratios on the antimicrobial, antioxidant, cell migration and wound healing properties. The antioxidant activities of quercetin, curcuminoids and the mixtures were tested by DPPH and ABTS free radical scavenging assays. The disc diffusion method was performed to determine the antibacterial activities of quercetin, curcuminoids and the mixtures against S. aureus and P. aeruginosa. The cytotoxicity and cell migratory enhancing effects of quercetin, curcuminoids and the mixtures against human dermal fibroblasts were investigated by MTT assay, scratch assay and Transwell migration assay, respectively. The results showed the synergism of the quercetin and curcuminoid combination to inhibit the growth of S. aureus and P. aeruginosa, with the inhibition zone ranging from 7.06 ± 0.25 to 8.78 ± 0.38 mm, respectively. The DPPH free radical scavenging assay demonstrated that the combination of quercetin and curcuminoids yielded lower IC50 values (15.38–23.70 µg/mL) than curcuminoids alone (25.75 µg/mL). Quercetin and a 3:1 quercetin/curcuminoid mixture at non-toxic concentrations showed the ability to stimulate the migration of fibroblasts across the matrix, whereas only quercetin alone accelerated the wound closure of fibroblasts. In conclusion, the mixture of quercetin and curcuminoids at a 3:1 ratio was the best formulations for use in wound healing due to the antimicrobial, antioxidant and cell-migration-enhancing activities. 相似文献