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101.
HY Song CH Régnier CJ Kirschning DV Goeddel M Rothe 《Canadian Metallurgical Quarterly》1997,94(18):9792-9796
102.
A gene encoding a bifunctional homodimeric dihydrofolate reductase-
thymidylate synthase (DHFR-TS) was constructed by destroying the stop codon
of Escherichia coli dihydrofolate reductase (DHFR) and joining the coding
sequences of the monofunctional enzymes by a five amino acid linker. The
protein was designed to mimic features of active site proximity and
electrostatics in the protozoan DHFR-TSs which are believed to be important
in channeling of the DHFR substrate, H2folate, to TS. The genetically
engineered catalytically active homodimeric bifunctional DHFR-TS was
expressed, purified and characterized. The component activities of the
purified bifunctional enzyme had kinetic properties similar to those of the
monofunctional TS and DHFR, but unlike the authentic bifunctional enzymes
from protozoa this enzyme did not kinetically channel dihydrofolate from
DHFR to TS.
相似文献
103.
Recent evidence suggests that conservative elites' claims of a liberal media are having an impact upon public perceptions of news coverage. With this in mind, we examined two related questions in the context of the 1988, 1992, and 1996 presidential elections. First, what factors may be prompting conservative elites to make allegations of liberal media bias? Second, what factors may influence when news media report these criticisms during presidential campaigns? Findings suggest that these criticisms of news media are at least partly strategic and reflect a dynamic relationship between political elites and journalists during a presidential campaign. 相似文献
104.
An unusual energetic composite, in which spherical nano‐dimensional particles of CL‐20 were uniformly coated with HDI‐cross‐linked nitrocellulose, was synthesized by the sol‐gel to cryogel method. Up to 90% solid loading was achieved. The particle size of CL‐20 was determined to be in the range of 20–200 nm by transmission electron microscopy, atomic force microscopy, and X‐ray powder diffraction. The decomposition characteristics of the composite were investigated by DSC and T‐jump/FTIR spectroscopy. The decomposition properties were controlled mostly by nitrocellulose until the percentage of CL‐20 was well above 50%. The drop weight impact sensitivity of the cryogels was essentially independent of the composition. 相似文献
105.
DavidE. Chavez BryceC. Tappan BenjaminAaron Mason Damon Parrish 《Propellants, Explosives, Pyrotechnics》2009,34(6):475-479
This paper describes the synthesis and characterization of bis‐(triaminoguanidinium)‐3,3′‐dinitro‐5,5′‐azo‐1,2,4‐triazolate (TAGDNAT), a novel high‐nitrogen molecule that derives its energy release from both a high heat of formation and intramolecular oxidation reactions. TAGDNAT shows promise as a propellant or explosive ingredient not only due to its high nitrogen content (66.35 wt.‐%) but also due to its high hydrogen content (4.34 wt.‐%). This new molecule has been characterized with respect to its morphology, sensitivity properties, explosive, and combustion performance. The heat of formation of TAGDNAT was also experimentally determined. The results of these studies show that TAGDNAT has one of the fastest low‐pressure burning rates (at 6.9 MPa) measured till date, 6.79 cm s−1 at 6.9 MPa (39% faster than triaminoguanidinium azotetrazolate (TAGzT), a comparable high‐nitrogen/high‐hydrogen material). Furthermore, its pressure sensitivity is 0.507, a 33% reduction compared to TAGzT. 相似文献
106.
107.
Virginia W. Manner Steven J. Pemberton Jake A. Gunderson Tommy J. Herrera Joseph M. Lloyd Patrick J. Salazar Philip Rae Bryce C. Tappan 《Propellants, Explosives, Pyrotechnics》2012,37(2):198-206
In order to improve understanding of how aluminum contributes in non‐ideal explosive mixtures, cast‐cured formulations have been analyzed in a series of cylinder tests and plate‐pushing experiments. This study describes the contribution of 15 % aluminum (median size of 3.2 μm) vs. lithium fluoride (an inert substitute for aluminum; <5 μm) in cast‐cured HMX formulations in different temporal regimes. Small cylinder tests were performed to analyze the detonation and wall velocities (1–20 μs) for these formulations. Near‐field blast effects of 58 mm diameter spherical charges were measured at 152 mm and 254 mm using steel plate acceleration. Pressure measurements at 1.52 m gave information about free‐field pressure at several milliseconds. While the observed detonation velocities for all formulations were within uncertainty, significantly higher cylinder wall velocities, plate velocities, and pressures were observed for the aluminum formulations at ≥2 μs. Additionally, hydrocode calculations were performed to determine how non‐ideal behavior affected the plate test results. Collectively, this work gives a clearer picture of how aluminum contributes to detonation on timescales from 1 μs to about 2 ms, and how the post‐detonation energy release contributes to wall velocities and blast effects. The experiments indicate that significant aluminum reactions occur after the CJ plane, and continue to contribute to expansion at late times. 相似文献
108.
Robert Knepper Katie Browning Ryan R. Wixom Alexander S. Tappan Mark A. Rodriguez M. Kathleen Alam 《Propellants, Explosives, Pyrotechnics》2012,37(4):459-467
Vapor‐deposited hexanitroazobenzene (HNAB) films were observed to form a dense amorphous structure that crystallizes to a mixture of the HNAB‐II polymorph and an unidentified structure over a period ranging from hours to weeks depending on the ambient temperature. Films crystallized at various temperatures were characterized using scanning electron microscopy, atomic force microscopy, X‐ray diffraction, and Raman spectroscopy to measure the impact of crystallization temperature on resultant microstructure. Crystallization temperature was observed to have different effects on film microstructure over two temperature regimes. At temperatures below approximately 65 °C, increases in temperature led to a greater fraction of the film forming the HNAB‐II polymorph and caused subtle changes in morphology. However, at higher temperatures, a thin surface layer was observed to form prior to crystallization, which led to films composed primarily of the unknown crystal structure with conspicuous differences in morphology. 相似文献
109.
BryceC. Tappan ArifN. Ali StevenF. Son ThomasB. Brill 《Propellants, Explosives, Pyrotechnics》2006,31(3):163-168
The high‐nitrogen compound triaminoguanidinium azotetrazolate (TAGzT) belongs to a class of C, H and N compounds that are free of both oxygen and metal, but retain energetic material properties as a result of their high heat of formation. Its decomposition thus lacks secondary oxidation reactions of carbon and hydrogen. The fact that TAGzT is over 80% nitrogen makes it potentially useful as a gas generant and energetic material with a low flame temperature to increase the impulse in gun or rocket propellants. The burning rate, laser ignition and flash pyrolysis (T‐jump/FTIR spectroscopy) characteristics were determined. It was found that TAGzT exhibits one of the fastest low‐pressure burning rates yet measured for an organic compound. Both the decomposition and ignition behavior of TAGzT are dominated by condensed phase reactions. T‐Jump/FTIR spectroscopy indicates that condensed phase reactions release about 65% of the energy, which helps to explain the high burning rate at low pressure. 相似文献
110.
L Ozzello CM De Rosa EW Blank K Cantell RL Ceriani DV Habif 《Canadian Metallurgical Quarterly》1993,25(3):265-276
An immunoconjugate composed of natural interferon alpha (nIFN alpha) bound in a noncleavable fashion to a monoclonal antibody (MoAb) recognizing a breast epithelial membrane mucin (Mc5) was used to to treat xenografts of a human mammary carcinoma cell line (MCF-7) growing in nude mice. The immunoconjugate (nIFN alpha/Mc5) was administered as 20 intralesional (i.l.) injections to 1 of 2 xenografts in each animal. It was found that nIFN alpha/Mc5 produced a significant enhancement of the growth inhibitory actions of nIFN alpha on the injected tumors. Further enhancement was obtained when nIFN gamma or nIFN gamma together with Mc5 (at a dose 10 times larger than that present in nIFN alpha/Mc5) were added to the immunoconjugate. Biodistribution experiments showed that the uptake of 125I-nIFN alpha/Mc5 by the tumors was greater and its elimination slower than for 125I-nIFN alpha alone or conjugated to irrelevant mouse IgG1. In addition, the immunoconjugate up-regulated the antigenic expression of a breast epithelial membrane mucin by the carcinoma cells, an up-regulation which was not significantly different from that produced by nIFN alpha alone. The contralateral noninjected tumors exposed to systemic levels of the immunoconjugate showed an enhancement of antitumor effects, but to a lesser extent than the injected tumors. These findings suggest that the enhancement of the growth inhibitory action of the immunoconjugate was related to the specific binding of Mc5 which targeted the IFN to the carcinoma cells and impeded its elimination. It is likely that the targeting was favored by the IFN-mediated up-regulation of antigenic expression by the carcinoma cells, thereby producing a cascade of interrelated effects. The results of this study point out the feasibility and potential usefulness of IFN treatment by means of immunoconjugates as well as the worth of pursuing and improving this form of therapy. 相似文献