全文获取类型
收费全文 | 4137篇 |
免费 | 62篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 43篇 |
综合类 | 2篇 |
化学工业 | 347篇 |
金属工艺 | 39篇 |
机械仪表 | 49篇 |
建筑科学 | 81篇 |
矿业工程 | 6篇 |
能源动力 | 67篇 |
轻工业 | 261篇 |
水利工程 | 10篇 |
石油天然气 | 23篇 |
无线电 | 230篇 |
一般工业技术 | 330篇 |
冶金工业 | 2518篇 |
原子能技术 | 15篇 |
自动化技术 | 180篇 |
出版年
2022年 | 19篇 |
2021年 | 24篇 |
2020年 | 26篇 |
2019年 | 31篇 |
2018年 | 29篇 |
2017年 | 36篇 |
2016年 | 42篇 |
2015年 | 18篇 |
2014年 | 30篇 |
2013年 | 82篇 |
2012年 | 67篇 |
2011年 | 93篇 |
2010年 | 57篇 |
2009年 | 71篇 |
2008年 | 72篇 |
2007年 | 61篇 |
2006年 | 44篇 |
2005年 | 47篇 |
2004年 | 62篇 |
2003年 | 57篇 |
2002年 | 38篇 |
2001年 | 32篇 |
2000年 | 41篇 |
1999年 | 112篇 |
1998年 | 754篇 |
1997年 | 438篇 |
1996年 | 297篇 |
1995年 | 169篇 |
1994年 | 155篇 |
1993年 | 182篇 |
1992年 | 38篇 |
1991年 | 53篇 |
1990年 | 48篇 |
1989年 | 45篇 |
1988年 | 50篇 |
1987年 | 37篇 |
1986年 | 45篇 |
1985年 | 44篇 |
1984年 | 31篇 |
1983年 | 23篇 |
1982年 | 43篇 |
1981年 | 44篇 |
1980年 | 35篇 |
1979年 | 28篇 |
1978年 | 29篇 |
1977年 | 102篇 |
1976年 | 178篇 |
1975年 | 18篇 |
1974年 | 20篇 |
1973年 | 14篇 |
排序方式: 共有4201条查询结果,搜索用时 15 毫秒
1.
A cell vertex finite volume method for the solution of steady compressible turbulent flow problems on unstructured hybrid
meshes of tetrahedra, prisms, pyramids and hexahedra is described. These hybrid meshes are constructed by firstly discretising
the computational domain using tetrahedral elements and then by merging certain tetrahedra. A one equation turbulence model
is employed and the solution of the steady flow equations is obtained by explicit relaxation. The solution process is accelerated
by the addition of a multigrid method, in which the coarse meshes are generated by agglomeration, and by parallelisation.
The approach is shown to be effective for the simulation of a number of 3D flows of current practical interest.
Sponsored by The Research Council of Norway, project number 125676/410
Dedicated to the memory of Prof. Mike Crisfield, a respected colleague 相似文献
2.
Decreasing carboxyl retention in deposits from the glow region of an acrylic acid plasma was measured by X-ray photoelectron spectroscopy and chemical derivatisation as the collection distance from the monomer vapour inlet was increased. Volatilisation of plasma polymerised acrylic acid was detected after trifluoroethanol derivatisation; this is correlated with evaporation of low molecular weight components observed previously. 相似文献
3.
4.
ESR spin trapping was used to investigate the reaction of rabbit cytochrome P450 (P450) 1A2 with cumene hydroperoxide. Cumene hydroperoxide-derived peroxyl, alkoxyl, and carbon-centered radicals were formed and trapped during the reaction. The relative contributions of each radical adduct to the composite ESR spectrum were influenced by the concentration of the spin trap. Computer simulation of the experimental data obtained at various 5,5-dimethyl-1-pyrroline N-oxide (DMPO) concentrations was used to quantitate the contributions of each radical adduct to the composite ESR spectrum. The alkoxyl radical was the initial radical produced during the reaction. Experiments with 2-methyl-2-nitrosopropane identified the carbon-centered adducts as those of the methyl radical, hydroxymethyl radical, and a secondary carbon-centered radical. The reaction did not require NADPH-cytochrome P450 reductase or NADPH. It is concluded that the reaction involves the initial homolytic scission of the peroxide O-O bond to produce the cumoxyl radical. Methyl radicals were produced from the beta-scission of the cumoxyl radical. The peroxyl adduct was not observed in the absence of molecular oxygen. We conclude that the DMPO peroxyl radical adduct detected in the presence of oxygen was due to the methylperoxyl radical formed by the reaction of the methyl radical with oxygen. At a higher P450 concentration, a protein-derived radical adduct was also detected. 相似文献
5.
OL Lopez RP Brenner JT Becker RF Ulrich F Boller ST DeKosky 《Canadian Metallurgical Quarterly》1997,48(6):1521-1525
We examined whether either psychotic features (e.g., delusions and hallucinations) or EEG abnormalities are associated with more rapid progression of Alzheimer's disease (AD). AD patients with psychosis have exhibited more EEG abnormalities than those without psychosis, and both abnormal EEG and psychosis have been noted to be predictors of functional and cognitive decline in AD. Ninety-five probable AD patients participating in a longitudinal study of dementia had an EEG and a semistructured psychiatric interview at baseline. Using EEG spectral analysis, we classified records as normal/abnormal based on the parasagittal mean frequency. Patients with abnormal EEGs were more functionally (e.g., Blessed Rating Scale for activities of daily living) and cognitively (e.g., Mini-Mental State) impaired than patients with normal EEG. AD patients with psychosis were only more functionally impaired than patients without psychosis. A two-factor analysis showed no interaction between abnormal EEG and psychosis. In addition, using a Cox proportional hazard model adjusted for age and education, the presence of an abnormal EEG or psychotic symptom at study entry was associated with higher risk of reaching severe cognitive and functional impairment during follow-up. Neither abnormal EEG nor the presence of psychosis predicted death. These results indicate that both abnormal EEG and psychosis are independent predictors of disease progression but not of physical survival. 相似文献
6.
Existence conditions are given for maximum likelihood (ML) parameter estimates for several families of 2-parameter software-reliability Poisson-process models. For each such model, the ML equations can be expressed in terms of one equation in one unknown. Bounds are given on solutions to these one equation problems to serve as initial intervals for search algorithms like bisection. Uniqueness of the solutions is established in some cases. Solutions are also tabulated for certain simple cases. Results are given for ungrouped failure data (exact times are available for all failures). ML estimation problems for such a situation are treated as limiting cases of problems based on failure times grouped into intervals of decreasing mesh 相似文献
7.
8.
Previous solid state analyses of sintering in Ti4+ -doped-commercial alumina are shown to be in error because a liquid phase exists in the appropriate region of the Al2 O3 −TiO3 −Na2 Ophase diagram at least by 1350° C, a temperature lower than that at which "solid state" studies were conducted. It is suggested that liquid-phase sintering is a much more common occurrence than was realized formerly. 相似文献
9.
D. A. Morgan D. B. Shaw M. J. Sidebottom T. C. Soon R. S. Taylor 《Journal of the American Oil Chemists' Society》1985,62(2):292-299
The results presented in the literature, which attempt to elucidate the mechanisms by which triglyceride oils are bleached
by earths, are reviewed. The impact of this work and how the mechanistic proposals affect changes in oil properties are considered,
with particular emphasis on the needs of the palm oil processor. Important properties include color, metals and phosphorus
content and oxidative stability of the oil.
Investigations made in our own laboratories have been aimed at elucidating the effect of varying physical and chemical properties
of the bleaching earth on the quality of bleached and deodorized oils. Techniques used in this work are pore-size distribution,
surface area, scanning and transmission electron microscopy and a variety of chemical and X-ray analysis methods.
The ability to vary such parameters in montmorillonite clays by alteration of process conditions to give materials with specific
performance characteristics is demonstrated.
Comparisons are made between acid-activated montmorillonites and other clay types. 相似文献
10.
This study investigated the ability of the Millon Clinical Multiaxial Inventory--Third Edition (MCMI-III) to discriminate students malingering psychopathology (n=106) from bona fide psychiatric inpatients (n=202). Students were randomly assigned to a fake-bad or an honest-responding condition. Analyses investigated the ability of the modifier indices to discriminate fake-bad group participants from the psychiatric inpatients. Scale X raw cutoff score >178 yielded a positive predictive power (PPP) of 0.0, a negative predictive power (NPP) of 63.1, and a hit rate of 63.1%. Optimal cutoff scores were developed. Scale X Base Rate (BR) >84 provided a PPP of 55.6, an NPP of 72.1, and a hit rate of 65.2%. Scale Y BR 相似文献