全文获取类型
收费全文 | 2632篇 |
免费 | 22篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 10篇 |
化学工业 | 149篇 |
金属工艺 | 17篇 |
机械仪表 | 14篇 |
建筑科学 | 36篇 |
矿业工程 | 1篇 |
能源动力 | 14篇 |
轻工业 | 144篇 |
水利工程 | 15篇 |
石油天然气 | 5篇 |
无线电 | 120篇 |
一般工业技术 | 102篇 |
冶金工业 | 1896篇 |
原子能技术 | 5篇 |
自动化技术 | 127篇 |
出版年
2021年 | 11篇 |
2019年 | 9篇 |
2015年 | 8篇 |
2014年 | 20篇 |
2013年 | 34篇 |
2012年 | 17篇 |
2011年 | 21篇 |
2010年 | 15篇 |
2009年 | 29篇 |
2008年 | 18篇 |
2007年 | 18篇 |
2006年 | 20篇 |
2005年 | 25篇 |
2004年 | 14篇 |
2003年 | 21篇 |
2002年 | 17篇 |
2001年 | 24篇 |
2000年 | 19篇 |
1999年 | 61篇 |
1998年 | 556篇 |
1997年 | 325篇 |
1996年 | 239篇 |
1995年 | 139篇 |
1994年 | 139篇 |
1993年 | 133篇 |
1992年 | 32篇 |
1991年 | 38篇 |
1990年 | 37篇 |
1989年 | 25篇 |
1988年 | 40篇 |
1987年 | 38篇 |
1986年 | 35篇 |
1985年 | 41篇 |
1984年 | 29篇 |
1983年 | 17篇 |
1982年 | 20篇 |
1981年 | 20篇 |
1980年 | 31篇 |
1979年 | 21篇 |
1978年 | 20篇 |
1977年 | 52篇 |
1976年 | 106篇 |
1975年 | 18篇 |
1974年 | 6篇 |
1973年 | 13篇 |
1972年 | 8篇 |
1970年 | 7篇 |
1969年 | 8篇 |
1968年 | 8篇 |
1967年 | 6篇 |
排序方式: 共有2655条查询结果,搜索用时 31 毫秒
71.
72.
PL Spath 《Canadian Metallurgical Quarterly》1998,2(3):124-8; quiz 129
Over 100 years ago, Florence Nightingale showed caregivers how to analyze mortality data to improve their clinical processes. The nurses of today are facing a new performance measurement challenge. Consumers of health care services want information that will help them compare quality among providers. This article describes the types of nursing performance measures most appropriate to include on these public-oriented report cards and several issues that influence report card design and dissemination. 相似文献
73.
PL Bradhsaw 《Canadian Metallurgical Quarterly》1998,6(5):257-259
Magnesium chloride (MgCl2) has been proposed for the treatment of seizures of different etiologies. The present study investigated the effect of MgCl2 on aldrin-induced seizures. Initially, 50 male rats received 60 mg aldrin/kg po and the effects were classified as muscular twitches, clonic convulsions or tonic-clonic convulsions. Another group of 40 rats dosed with 60 mg aldrin/kg po received 0, 4, 8, or 12 mg MgCl2/kg i.m. The percentage of tonic-clonic convulsant rats that resulted from MgCl2 treatment were 90% at 0 mg/kg, 50% at 4 mg/kg, 40% at 8 mg/kg and 20% at 12 mg MgCl2/kg. The percentage of survivors in the group receiving 12 mg MgCl2/kg was 80% while the control group had 20% survival. The clonic convulsions were not modified by MgCl2 treatment. Blood and brain concentrations of aldrin and dieldrin (metabolite of aldrin) did not differ among groups. The MgCl2 administration decreased the neuroexcitability induced by aldrin and increased survivability. 相似文献
74.
Julie Y. Qian Raymond A. Pearson Victoria L. Dimonie Mohamed S. El-Aasser 《应用聚合物科学杂志》1995,58(2):439-448
Poly(butadiene-co-styrene) [P(B-S)] core-poly(methyl methacrylate) (PMMA) shell particles were prepared using a two-step emulsion polymerization. These core-shell particles were used to toughen an epoxy polymer. The role of particle-epoxy interfaces were studied by systematically varying the shell compositions of the core-shell particles such as PMMA, P[MMA-acrylonitrile (AN)], P[MMA-glycidyl methacrylate (GMA)] and P[MMA-divinyl benzene(DVB)]. Therefore, the nature of the particle-epoxy interfaces is varied in terms of physical interactions and chemical bonding. The fracture toughness values of the toughened epoxies were measured using linear elastic fracture mechanics. Results indicate that the morphology of the dispersed particles in the epoxy matrix plays an important role in the toughening of epoxies. This degree of dispersion can be varied by incorporating AN and GMA comonomers in the PMMA shells or by crosslinking the shell. In summary, nanoscale interactions of the rubber-matrix interface do not directly influence fracture toughness, instead, it was found that the nanoscale interactions could be used to control the blend morphology which has a dramatic effect on toughness. © 1995 John Wiley & Sons, Inc. 相似文献
75.
A. R. Johnson A. C. Fogerty Judith A. Pearson F. S. Shenstone Audrey M. Bersten 《Lipids》1969,4(4):265-269
Hen liver preparations which desaturate stearic acid at the 9,10 position to form oleic acid have been found to desaturate
other saturated fatty acids of carbon chain length from 12 to 20 and 22. The 9,10-monoenoic fatty acid of the same chain length
as the substrate fatty acid is the major product formed. Minor amounts of the 10,11- and 11, 12-monoenoic acids are also formed.
Maximum desaturation occurred with the C14 fatty acid substrate and with the fatty acids C17 and C18, suggesting the presence of at least two desaturating systems. The cyclopropene fatty acids, sterculic and malvalic acids,
inhibited the desaturation of all thefatty acids at the 9,10 position but desaturation at the 10,11 and 11, 12 positions was
affected only slightly. The effect is not due to inhibition of the primary activating enzyme, the long chain acyl CoA synthetase.
Sterculic acid is a more effective inhibitor than either malvalic acid or sterculyl alcohol, probably because these cyclopropene
compounds do not block the desaturating site of the enzyme as completely as sterculic acid. 相似文献
76.
The objective of this research is to investigate the feasibility of using surface treated recycled rubber particles for toughening of epoxy polymers. These particles are obtained through grinding of scrap tires followed by oxidizing the surface of the particles in a reactive gas atmosphere. Surface treated recycled rubber particles with a nominal particle size of approximately 75 μm and a commonly used reactive liquid elastomer, CTBN, have been incorporated in a DGEBA epoxy resin. It has been shown that the recycled rubber particles are not as effective as CTBN in toughening of the epoxy matrix. However, blending of the two modifiers results in a synergistic toughening. Microscopy reveals that, when used alone, recycled rubber particles simply act as large stress concentrators and modestly contribute to toughening via crack deflection and microcracking. In the presence of micron size CTBN particles, which cavitate and induce massive shear yielding in the matrix, however, the recycled particles “stretch” the plastic deformation to distances far from the crack tip. This mechanism causes plastic zone branching and provides an unexpectedly high fracture toughness value. This study, therefore, provides a practical approach for manufacturing engineering polymer blends utilizing the surface modified recycled rubber particles. 相似文献
77.
Previously, it was reported that the direct partial oxidation (DPO) of CH4 with O2 over HZSM-5 catalysts produces C5+ hydrocarbon liquids when the feed contains a propane or propene additive. This work studies additive effects on C5+ production in this system by processing a CH4/C3H8 feed with subsequent removal of the C3 additive and by processing natural gas feed. Results show C5+ production is maintained at constant yields for HZSM-5 catalysts having different zeolitic Al contents after removal of the C3 additive. Mechanistic implications are discussed. Natural gas DPO consistently produced C5+ liquids due to the presence of C2+ components in the feed. While C5+ yields from natural gas DPO are higher than those observed for CH4/C3 feeds, increasing feed O2 concentration, and thus conversion, deleteriously affected C5+ selectivity. 相似文献
78.
Erik E Luther Fred F. Lange Dale S. Pearson 《Journal of the American Ceramic Society》1995,78(8):2009-2014
Two different methods are used to coat silicon nitride particles with an alumina precursor to make Si3 N4 behave like Al2 O3 in aqueous slurries. The first method involves the precipitation of an aluminum hydroxycarbonate from dissolved Al(NO3 )3 during the decomposition of urea. In the second method, dry silicon nitride powder is reacted with aluminum tri- sec -butoxide in hexane at room temperature. Both methods produce a coated powder in which the electrophoretic and rheological properties of aqueous slurries mimic those of alumina. When salt is added to slurries consisting of coated Si3 N4 powder, all rheological evidence suggests the presence of a short-range repulsive potential that produces a weakly attractive particle network similar to that previously reported for Al2 O3 powder. Although electrophoretic and rheological data showed that the coated powder behaved like Al2 O3 , consolidation data indicated that slurries of coated powder with added salt did not pack to high density. In addition, these bodies were not plastic as found for bodies consolidated from dispersed and salt-added Al2 O3 slurries. 相似文献
79.
Four cyclopropene fatty acids, having the double bond of the cyclopropene ring at the 8,9, 9,10, 10,11 and 11,12 positions,
respectively, were tested as inhibitors of stearic acid desaturation by the desaturase enzyme system of hen liver. The first
three were powerful inhibitors, but the last was not. The cyclopropene acids with the 9,10 and 10,11 double bonds were equally
strong inhibitors, while the acid with the 8,9 double bond was less effective. To account for the specificity of those cyclopropene
fatty acids in which the C9 or C10 carbon atom is included in the cyclopropene ring, it is suggested that the conformation
and structure of the CoA derivatives of these acids is such that they can irreversibly occupy the site on the enzyme responsible
for 9,10-desaturation. 相似文献
80.
Matrix models are ubiquitous for constraint problems. Many such problems have a matrix of variables $\mathcal{M}$ , with the same constraint C defined by a finite-state automaton $\mathcal{A}$ on each row of $\mathcal{M}$ and a global cardinality constraint $\mathit{gcc}$ on each column of $\mathcal{M}$ . We give two methods for deriving, by double counting, necessary conditions on the cardinality variables of the $\mathit{gcc}$ constraints from the automaton $\mathcal{A}$ . The first method yields linear necessary conditions and simple arithmetic constraints. The second method introduces the cardinality automaton, which abstracts the overall behaviour of all the row automata and can be encoded by a set of linear constraints. We also provide a domain consistency filtering algorithm for the conjunction of lexicographic ordering constraints between adjacent rows of $\mathcal{M}$ and (possibly different) automaton constraints on the rows. We evaluate the impact of our methods in terms of runtime and search effort on a large set of nurse rostering problem instances. 相似文献