全文获取类型
收费全文 | 331篇 |
免费 | 28篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 4篇 |
化学工业 | 105篇 |
金属工艺 | 1篇 |
机械仪表 | 5篇 |
建筑科学 | 11篇 |
能源动力 | 6篇 |
轻工业 | 29篇 |
石油天然气 | 9篇 |
无线电 | 63篇 |
一般工业技术 | 38篇 |
冶金工业 | 48篇 |
原子能技术 | 1篇 |
自动化技术 | 41篇 |
出版年
2024年 | 1篇 |
2023年 | 3篇 |
2022年 | 5篇 |
2021年 | 8篇 |
2020年 | 7篇 |
2019年 | 8篇 |
2018年 | 6篇 |
2017年 | 8篇 |
2016年 | 15篇 |
2015年 | 12篇 |
2014年 | 8篇 |
2013年 | 19篇 |
2012年 | 5篇 |
2011年 | 16篇 |
2010年 | 10篇 |
2009年 | 12篇 |
2008年 | 15篇 |
2007年 | 11篇 |
2006年 | 14篇 |
2005年 | 14篇 |
2004年 | 9篇 |
2003年 | 10篇 |
2002年 | 7篇 |
2001年 | 8篇 |
2000年 | 7篇 |
1999年 | 10篇 |
1998年 | 16篇 |
1997年 | 17篇 |
1996年 | 11篇 |
1995年 | 6篇 |
1994年 | 5篇 |
1993年 | 3篇 |
1992年 | 4篇 |
1991年 | 8篇 |
1990年 | 5篇 |
1989年 | 4篇 |
1988年 | 4篇 |
1986年 | 1篇 |
1985年 | 6篇 |
1984年 | 3篇 |
1983年 | 4篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 3篇 |
1978年 | 1篇 |
1976年 | 3篇 |
1975年 | 1篇 |
1973年 | 2篇 |
排序方式: 共有361条查询结果,搜索用时 15 毫秒
41.
Teh Y. Tan 《Materials Chemistry and Physics》1995,40(4):245-252
For the Ga sublattice of GaAs, the recent understanding of the impurity and self-diffusion mechanisms and the nature of the point defects responsible are discussed. Analyses of doping enhanced AlAs/GaAs superlattice disordering data and impurity diffusion data have led to the conclusion that, under thermal equilibrium and intrinsic conditions, the triply-negatively-charged Ga vacancy ((VGa3−) governs Ga self-diffusion and Al---Ga interdiffusion in As-rich crystals, while the doubly-positively-charged Ga self-interstitial (IGa2+) dominates in Ga-rich crystals. When doped sufficiently, dominates in n-type crystals, while IGa2+ dominates in p-type crystals, irrespective of the crystal composition. The VGa3− species also contributes to the diffusion of the main donor species Si, while IGa2+ also governs the diffusion of the main acceptor species Zn and Be via the kick-out mechanism. The thermal equilibrium concentration of VGa3− (CVGa3−) has been found to exhibit a temperature independence or even a small negative temperature dependence in that, when the temperature is lowered, CVGa3−; is either unchanged or even slightly increases. This CVGa3− behavior is consistent with many outstanding experimental results. 相似文献
42.
Asphalt in a colloidal context can be considered as a sol, sol-gel or gel type where in all three cases the asphaltene particle plays an important role. Usually the three colloidal types can be differentiated by refinery processes or by rheological properties. The aggregation or clustering of the asphaltene particles (or micelles) from sol to sol-gel and finally to the gel state with a fixed lattice can follow the stochastic process of fractal Brownian motion which can fit a hyperbolic (or Korcak) distribution. A test was carried out using the same mass of various asphalts of different colloidal types for floc formation with a series of n-alkanes (dispersion media) of increasing characteristic lengths. Results from floc formation studies indicate that the value of the size distribution for the gel type is small, is higher for the sol-gel type, and is highest for the sol type. On the other hand, the surface irregularities for all three types of asphalt do not have any correlation. These observed facts are consistent with principles based on the fractal approach. 相似文献
43.
Oil palm (E. guineensis) fruits at three stages of development were studied. At week 12–13 after anthesis, the endosperm had started accumulating
oil and tissue slices incorporated [1-14C] acetate into fatty acids which resembled those found in the mature endosperm. The mesocarp contained very little oil and
incorporated acetate into polar lipids. At week 16–17, the mesocarp started to accumulate oil; this was reflected in the [14C] lipid products from acetate incubation. At or just prior to this stage, an increase in the endogenous linoleic and linolenic
acid content and the increase in fruit size indicated cellular growth in the mesocarp tissue. At week 20–21 the fruit was
ripe, and both endosperm and mesocarp tissues were filled with storage oil. [14C] Fatty acids synthesized from acetate by mesocarp slices at this stage were the same as the endogenous storage fatty acids
in bothE. guineensis andE. oleifera. A very weak fatty acid synthesizing activity was seen in the mature endosperm, but the products had no relationship to the
storage lipid. 相似文献
44.
Saima Usman Hebah Aldehlawi Thuan Khanh Ngoc Nguyen Muy-Teck Teh Ahmad Waseem 《International journal of molecular sciences》2022,23(11)
Vimentin, a type III intermediate filament protein, is found in most cells along with microfilaments and microtubules. It has been shown that the head domain folds back to associate with the rod domain and this association is essential for filament assembly. The N-terminally tagged vimentin has been widely used to label the cytoskeleton in live cell imaging. Although there is previous evidence that EGFP tagged vimentin fails to form filaments but is able to integrate into a pre-existing network, no study has systematically investigated or established a molecular basis for this observation. To determine whether a tag would affect de novo filament assembly, we used vimentin fused at the N-terminus with two different sized tags, AcGFP (239 residues, 27 kDa) and 3 × FLAG (22 residues; 2.4 kDa) to assemble into filaments in two vimentin-deficient epithelial cells, MCF-7 and A431. We showed that regardless of tag size, N-terminally tagged vimentin aggregated into globules with a significant proportion co-aligning with β-catenin at cell–cell junctions. However, the tagged vimentin aggregates could form filaments upon adding untagged vimentin at a ratio of 1:1 or when introduced into cells containing pre-existing filaments. The resultant filament network containing a mixture of tagged and untagged vimentin was less stable compared to that formed by only untagged vimentin. The data suggest that placing a tag at the N-terminus may create steric hinderance in case of a large tag (AcGFP) or electrostatic repulsion in case of highly charged tag (3 × FLAG) perhaps inducing a conformational change, which deleteriously affects the association between head and rod domains. Taken together our results shows that a free N-terminus is essential for filament assembly as N-terminally tagged vimentin is not only incapable of forming filaments, but it also destabilises when integrated into a pre-existing network. 相似文献
45.
Clinical experience of arthroscopy in 12 temporomandibular joints with a clinical diagnosis of closed lock was described. There were 10 patients and all were females with a mean age of 31.2 years (range 20 to 59 years). The antero-lateral approach was used for entry into 11 joints. The clinical findings were adhesions (64%), fibrillation (64%), anterior displacement of disc (36%) and scuffing of the articular surface of the glenoid fossa (9%). Two of the joints that had arthrocentesis prior to arthroscopy did not show any different findings from the rest. Of the 8 patients who had pre-arthroscopy pain, 7 patients (88%) had reduction of the symptom. Three patients (38%) had complete resolution of pain. The range of mouth opening (measured as maximal incisor opening) increased in all patients two weeks following arthroscopy. The average change in maximal incisor opening was 40.3% with a range of 22% to 85%. The mean follow-up was 34 months (range 4 to 68 months). 相似文献
46.
47.
Ju Han Lee Peh Chiong Teh Petropoulos P. Ibsen M. Richardson D.J. 《Lightwave Technology, Journal of》2002,20(1):36-46
We demonstrate an elementary grating-based optical code division multiple access (OCDMA) code generation and recognition system incorporating a nonlinear optical loop mirror (NOLM) within the receiver. We show that the NOLM can act as a nonlinear processing element capable of reducing both the pedestal associated with conventional matched filtering and the width of the associated code-recognition pulse. The pedestal rejection allows for an improved code recognition signal-to-noise ratio (SNR) relative to simple matched filtering alone, and reduced intra- and interchannel interference noise due to code overlap. The system benefits of using the NOLM are experimentally demonstrated under both single- and multiuser operation within a variety of seven- and 63-chip 160-Gchip/s code generation, recognition, and transmission experiments based on the use of bipolar superstructure fiber Bragg grating (SSFBG) coding-decoding pairs. Incorporation of the NOLM is shown to allow error-free penalty-free operation at data rates as high as 2.5 Gb/s under single-user operation, and to provide error-free performance with reduced power penalty in two-user experiments. The narrowed pulse recognition signature offers major advantages in terms of the further all-optical processing of decoded signals, such as code regeneration and recoding 相似文献
48.
A composite was prepared that contained diglycidyl ether of tetrabromobisphenol A (DGETBA) and 1,5‐di(2,3‐epoxypropoxy)naphthalene (A), 4,4′‐bis(2,3‐epoxypropoxy)benzylideneaniline (B), or 4,4′‐bis(2,3‐epoxypropoxy)biphenyl (C), and then was cured using different ratios of dicyandiamide (DICY). The results of DSC, TGA, coefficient of thermal expansion, dielectric constant, and dissipation factor testing of the composite epoxy resins were analyzed, and investigation of the copper‐clad laminate using the composite epoxy resins as prepreg was also performed. Additionally, moisture absorption, peel strength, arc resistance, comparative tracking index, and flammability of the copper‐clad laminate were examined. Clearly, some of the physical or mechanical properties of the composite and the copper‐clad laminate can be improved by optimal addition of naphthalene–phenyl‐based epoxy. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 95: 1485–1492, 2005 相似文献
49.
50.
Previously, we developed a simple, one-parameter model reproducing the observed inhibiting effect of nitrogen species in the hydrodesulfurization (HDS) of hindered sulfur heterocycles. The model owes its simplicity to some nontrivial assumptions. Here we develop a full model by relaxing these assumptions, which gives a more quantitative picture of how sulfur, nitrogen, and catalyst surface interact on many widely disparate time scales. Computational results build a strong case for the accuracy of the previous one-parameter theory. As such, the theory should be applicable to reaction systems in which catalyst poisoning is driven by nonequilibrium adsorption. Some of the complexities and subtleties in modeling the competitive adsorption effects in distillate HDS are discussed, giving special attention to the design of robust catalyst-deactivation-compensation operating strategies. 相似文献