全文获取类型
收费全文 | 1743篇 |
免费 | 69篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 84篇 |
化学工业 | 509篇 |
金属工艺 | 43篇 |
机械仪表 | 40篇 |
建筑科学 | 26篇 |
矿业工程 | 2篇 |
能源动力 | 63篇 |
轻工业 | 189篇 |
水利工程 | 4篇 |
石油天然气 | 7篇 |
无线电 | 141篇 |
一般工业技术 | 365篇 |
冶金工业 | 149篇 |
原子能技术 | 41篇 |
自动化技术 | 152篇 |
出版年
2023年 | 13篇 |
2022年 | 31篇 |
2021年 | 61篇 |
2020年 | 19篇 |
2019年 | 31篇 |
2018年 | 34篇 |
2017年 | 29篇 |
2016年 | 49篇 |
2015年 | 37篇 |
2014年 | 51篇 |
2013年 | 108篇 |
2012年 | 87篇 |
2011年 | 115篇 |
2010年 | 78篇 |
2009年 | 79篇 |
2008年 | 96篇 |
2007年 | 76篇 |
2006年 | 80篇 |
2005年 | 63篇 |
2004年 | 50篇 |
2003年 | 68篇 |
2002年 | 55篇 |
2001年 | 38篇 |
2000年 | 41篇 |
1999年 | 42篇 |
1998年 | 69篇 |
1997年 | 52篇 |
1996年 | 37篇 |
1995年 | 45篇 |
1994年 | 25篇 |
1993年 | 24篇 |
1992年 | 13篇 |
1991年 | 16篇 |
1990年 | 5篇 |
1989年 | 8篇 |
1988年 | 6篇 |
1987年 | 8篇 |
1986年 | 4篇 |
1985年 | 7篇 |
1984年 | 12篇 |
1983年 | 7篇 |
1982年 | 7篇 |
1981年 | 5篇 |
1980年 | 5篇 |
1979年 | 7篇 |
1978年 | 2篇 |
1977年 | 7篇 |
1976年 | 3篇 |
1975年 | 2篇 |
1974年 | 2篇 |
排序方式: 共有1815条查询结果,搜索用时 15 毫秒
71.
72.
The effect of fatty acid structure of polyethyleneimine (PEI)-fatty acid complex, which was designed as a polymer dispersant for multi-component non-aqueous slurries, on the overall processing chain of Si3N4 ceramics involving slurry stabilization, spray drying, compaction, and liquid sintering was investigated using PEI-oleic acid (PEI-OA) and PEI-isostearic (PEI-ISA) complexes. Si3N4-Y2O3-Al2O3-AlN-TiO2/toluene slurries were selected as a real model for Si3N4-based multicomponent slurries. It was observed that both PEI-OA and PEI-ISA can stabilize Si3N4-Y2O3-Al2O3-AlN-TiO2/toluene slurries; however, the PEI-ISA system tended to have slightly higher slurry viscosity, which was suspected to be due to the interactions between protruded PEI segments among short ISA chains. The spray-dried granules from PEI-ISA-stabilized slurry were observed to have filled structures with higher surface roughness whereas those prepared from PEI-OA-stabilized slurry were observed to have hollow-structured granules. The granules prepared from PEI-OA slurry had improved flow and compaction properties with higher relative density of green compacts compared with those prepared from PEI-ISA-stabilized slurry, whereas the relative density and microstructural homogeneity of S3N4 ceramics sintered at 1600?°C for 2?h were observed to be higher for the PEI-ISA system. It is suspected that PEI-OA effectively improved the dispersion stability of multicomponent slurries and flow/compaction properties of granules; however, the inhomogeneous microstructures of green compacts induced by the hollow-structured granules had an adverse effect on the sintering of Si3N4 ceramics. 相似文献
73.
74.
75.
V. A. Shvarts K. J. Kless N. Matsunaga E. D. Adams J. S. Xia E. A. Schuberth 《Journal of Low Temperature Physics》2002,126(1-2):169-178
Simultaneous measurements of magnetic susceptibility from 0.5 to 10 mK and pressure from 2.88 to 3.54 MPa have been made in
3
He nano-clusters embedded in a
4
He matrix, following phase separation. The susceptibility of the 3.54 MPa, all-solid sample behaves similarly to that of bulk
3
He for v=21.3 cm
3
/mole, with a Weiss constant =–250K. For the 2.88 MPa, liquid-droplet sample, =140K, indicating a ferromagnetic tendency, similar to 2-D films at some coverages. At intermediate pressures, has a peak near 1.05 mK, but without a discontinuity. For all samples, had a solid-like contribution to the lowest temperatures. Magnetic ordering in nano-clusters appears to be different than the U2D2 phase of bulk
3
He. 相似文献
76.
This paper presents calibration of the Vehicle Routing and scheduling Problems with Time Windows-Probabilistic (VRPTW-P) model
which takes into account the uncertainty of travel times. Probe vehicle data of travel times were obtained from usual operation
of pickup-delivery trucks in South Osaka area. The optimal solution of the VRPTW-P model resulted in reducing total cost,
running times and CO2, NOx and Particle Materials (PM) emissions compared with the usual operation. This is attributed to better routing of VRPTW-P
to choose more reliable roads. Therefore, VRPTW-P can contribute to establish efficient and environmentally friendly delivery
systems in urban area. 相似文献
77.
The rare earth manganite BaLn2Mn2O7 (Ln=rare earth element) has a Sr3Ti2O7-type layered perovskite structure with double-block oxygen octahedra belonging to the Ruddlesden-Popper-type homologous series AO(ABO3)2. In Pr-manganite, a novel phase transition was first observed in situ at 1040 K by a thermal transmission electron microscope. At 1040 K, reflections began to split along the c-direction in the selected area diffraction pattern. This indicates that a new phase appears in the original phase matrix; the c length of the new phase is 1.5% longer than that of the original phase. After about 5 min, the original phase disappears. No change in the crystal symmetry (space group I4/mmm) is observed above 1040 K. 相似文献
78.
Molecular mechanism of magnet formation in bacteria 总被引:7,自引:0,他引:7
Magnetic bacteria have an ability to synthesize intracellular ferromagnetic crystalline particles consisting of magnetite (Fe3O4) or greigite (Fe3S4) which occur within a specific size range (50-100 nm). Bacterial magnetic particles (BMPs) can be distinguished by the regular morphology and the presence of an thin organic membrane enveloping crystals from abiologically formed magnetite. The particle is the smallest magnetic crystal that has a regular morphology within the single domain size. Therefore, BMPs have an unfathomable amount of potential value for various technological applications not only scientific interests. However, the molecular and genetic mechanism of magnetite biomineralization is hardly understood although iron oxide formation occurs widely in many higher animals as well as microorganisms. In order to elucidate the molecular and genetic mechanisms of magnetite biomineralization, a magnetic bacterium Magnetospirillum sp. AMB-1, for which gene transfer and transposon mutagenesis techniques had been recently developed, has been used as a model organism. Several findings and information on the BMPs formation process have been obtained within this decade by means of studies with this model organism and its related one. Biomineralization mechanism and potential availability in biotechnology of bacterial magnets have been elucidated through molecular and genetic approach. 相似文献
79.
Production of eicosapentaenoic acid by a recombinant marine cyanobacterium, Synechococcus sp. 总被引:1,自引:0,他引:1
The eicosapentaenoic acid (EPA) synthesis gene cluster from an EPA-producing bacterium, Shewanella sp. SCRC-2738, was cloned into a broad-host range vector, pJRD215, and then introduced into a marine cyanobacterium, Synechococcus sp. NKBG15041c, by conjugation. The transconjugant cyanobacteria produced 3.7±0.2% (2.24±0.13 mg/L) EPA (n-3) and 2.5 ±0.2%
(1.49±0.06 mg/L) eicosatetraenoic acid (n-3) of the total fatty acids when the cells were cultured at 23°C at a light intensity
of 1,000–1,500 Lux. The EPA and eico-satetraenoic acid contents of the cells were increased to 4.6±0.6% (3.86±1.11 mg/L) and
4.7±0.3% (3.86±0.82 mg/L), and 7.5±0.3% (1.76±0.10 mg/L) and 5.1±0.2% (1.19±0.06 mg/L) when they were cultured at low temperature
(18°C) and at lower light intensity (40 Lux), respectively. 相似文献
80.
We describe a novel automated flow immunoassay system for quantification of anti-double-stranded (ds) DNA autoimmune antibodies in the serum of patients suffering from systemic lupus erythematosus. dsDNA (360 bp) was covalently coupled with alkaline phosphatase (ALP) to form a novel analytical reagent (ALP-DNA). After immunoreaction, antibody-antigen complexes between ALP-DNA and anti-dsDNA monoclonal antibody were separated from unreacted ALP-DNA by an ion-exchange column on the basis of the difference in isoelectric point. Antibody-antigen complexes were subsequently quantified by luminescence following addition of 3-(2'-spiroadamantane)-4-methoxy-4-(3"-phosphoryloxy)phenyl- 1,2-dioxetane. The assay yielded a linear relationship between signal and concentration of anti-dsDNA monoclonal antibody in the range of 0-300 micrograms/mL. This simple technique permits the assay of anti-dsDNA autoimmune antibodies within 25 min. The ion-exchange column was simply regenerated by occasional elution with eluent (20 mM N-methylpiperazine, pH 5.5) supplemented with 0.5 M NaCl, to remove unreacted ALP-DNA. 相似文献