全文获取类型
收费全文 | 1987篇 |
免费 | 74篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 22篇 |
综合类 | 1篇 |
化学工业 | 369篇 |
金属工艺 | 22篇 |
机械仪表 | 32篇 |
建筑科学 | 104篇 |
矿业工程 | 5篇 |
能源动力 | 32篇 |
轻工业 | 230篇 |
水利工程 | 24篇 |
石油天然气 | 4篇 |
无线电 | 133篇 |
一般工业技术 | 284篇 |
冶金工业 | 606篇 |
原子能技术 | 8篇 |
自动化技术 | 186篇 |
出版年
2023年 | 18篇 |
2022年 | 31篇 |
2021年 | 49篇 |
2020年 | 33篇 |
2019年 | 32篇 |
2018年 | 35篇 |
2017年 | 38篇 |
2016年 | 43篇 |
2015年 | 30篇 |
2014年 | 40篇 |
2013年 | 108篇 |
2012年 | 70篇 |
2011年 | 118篇 |
2010年 | 88篇 |
2009年 | 91篇 |
2008年 | 103篇 |
2007年 | 109篇 |
2006年 | 83篇 |
2005年 | 70篇 |
2004年 | 67篇 |
2003年 | 45篇 |
2002年 | 56篇 |
2001年 | 32篇 |
2000年 | 37篇 |
1999年 | 35篇 |
1998年 | 80篇 |
1997年 | 57篇 |
1996年 | 53篇 |
1995年 | 18篇 |
1994年 | 30篇 |
1993年 | 31篇 |
1992年 | 23篇 |
1991年 | 10篇 |
1990年 | 10篇 |
1989年 | 14篇 |
1988年 | 20篇 |
1987年 | 11篇 |
1986年 | 11篇 |
1985年 | 16篇 |
1984年 | 14篇 |
1983年 | 20篇 |
1982年 | 18篇 |
1981年 | 15篇 |
1980年 | 17篇 |
1979年 | 8篇 |
1978年 | 10篇 |
1977年 | 11篇 |
1976年 | 11篇 |
1975年 | 13篇 |
1954年 | 6篇 |
排序方式: 共有2062条查询结果,搜索用时 31 毫秒
1.
Liangtao Yang Liang-Yin Kuo Juan Miguel López del Amo Prasant Kumar Nayak Katherine A. Mazzio Sebastian Maletti Daria Mikhailova Lars Giebeler Payam Kaghazchi Teófilo Rojo Philipp Adelhelm 《Advanced functional materials》2021,31(38):2102939
A known strategy for improving the properties of layered oxide electrodes in sodium-ion batteries is the partial substitution of transition metals by Li. Herein, the role of Li as a defect and its impact on sodium storage in P2-Na0.67Mn0.6Ni0.2Li0.2O2 is discussed. In tandem with electrochemical studies, the electronic and atomic structure are studied using solid-state NMR, operando XRD, and density functional theory (DFT). For the as-synthesized material, Li is located in comparable amounts within the sodium and the transition metal oxide (TMO) layers. Desodiation leads to a redistribution of Li ions within the crystal lattice. During charging, Li ions from the Na layer first migrate to the TMO layer before reversing their course at low Na contents. There is little change in the lattice parameters during charging/discharging, indicating stabilization of the P2 structure. This leads to a solid-solution type storage mechanism (sloping voltage profile) and hence excellent cycle life with a capacity of 110 mAh g-1 after 100 cycles. In contrast, the Li-free compositions Na0.67Mn0.6Ni0.4O2 and Na0.67Mn0.8Ni0.2O2 show phase transitions and a stair-case voltage profile. The capacity is found to originate from mainly Ni3+/Ni4+ and O2-/O2-δ redox processes by DFT, although a small contribution from Mn4+/Mn5+ to the capacity cannot be excluded. 相似文献
2.
Nelaka Govinna Papatya Kaner Davette Ceasar Anita Dhungana Cody Moers Katherine Son Ayse Asatekin Peggy Cebe 《Polymer International》2019,68(2):231-239
Nonwoven super‐hydrophobic fiber membranes have potential applications in oil–water separation and membrane distillation, but fouling negatively impacts both applications. Membranes were prepared from blends comprising poly(vinylidene fluoride) (PVDF) and random zwitterionic copolymers of poly(methyl methacrylate) (PMMA) with sulfobetaine methacrylate (SBMA) or with sulfobetaine‐2‐vinylpyridine (SB2VP). PVDF imparts mechanical strength to the membrane, while the copolymers enhance fouling resistance. Blend composition was varied by controlling the PVDF‐to‐copolymer ratio. Nonwoven fiber membranes were obtained by electrospinning solutions of PVDF and the copolymers in a mixed solvent of N,N‐dimethylacetamide and acetone. The PVDF crystal phases and crystallinities of the blends were studied using wide‐angle X‐ray diffraction and differential scanning calorimetry (DSC). PVDF crystallized preferentially into its polar β‐phase, though its degree of crystallinity was reduced with increased addition of the random copolymers. Thermogravimetry (TG) showed that the degradation temperatures varied systematically with blend composition. PVDF blends with either copolymer showed significant increase of fouling resistance. Membranes prepared from blends containing 10% P(MMA‐ran‐SB2VP) had the highest fouling resistance, with a fivefold decrease in protein adsorption on the surface, compared to homopolymer PVDF. They also exhibited higher pure water flux, and better oil removal in oil–water separation experiments. © 2018 Society of Chemical Industry 相似文献
3.
4.
Patrick D. Sullivan Mark J. Rood Katherine D. Dombrowski K. James Hay 《Canadian Metallurgical Quarterly》2004,130(3):258-267
Activated-carbon-fiber cloth (ACFC) is an alternative adsorbent to granular activated carbon (GAC) for removing and recovering organic vapors from gas streams. Electrothermal desorption (ED) of ACFC provides rapid regeneration while requiring less energy compared to traditional regeneration techniques used with GAC. This paper provides proof-of-concept results from a bench-scale ACFC adsorption system. The automated system captured 1,000 ppmv of hazardous air pollutants/volatile organic compounds (HAPs/VOCs) from air streams and demonstrated the use of ED, using ac voltage, to recover the HAP/VOC as a pure liquid. The desorbed HAP/VOC condensed onto the inner walls of the adsorber and was collected at the bottom of the vessel, without the use of ancillary cooling. Seventy percent of the HAP/VOC was collected per cycle as condensate, with the balance being retained in the regenerated adsorber or recycled to the second adsorber. ED with in-vessel condensation results in minimal N2 consumption and short regeneration cycle times allowing the process to be cost competitive with conventional GAC-based adsorption processes. This technology extends the application of carbon adsorption systems to situations that were previously economically and physically impractical. 相似文献
5.
6.
This paper presents key findings from a case study on the Grand Coulee Dam conducted by the authors for the World Commission on Dams. The analysis demonstrates that the distribution of project benefits has been tilted in favour of irrigation interests and hydroelectric power users and that the project's major cost bearers have been riparian-based indigenous tribes of the Upper Columbia River. The study identifies lessons learned that are applicable to many large multi-purpose water resources development projects. Within the paper, the impacts of the following factors are discussed: low stakeholder participation in decision making; absence of just compensation to Native Americans and Canadian First Nations adversely affected by the loss of fishery resources; modernization of agricultural technology; differing stakeholder perceptions of project costs and benefits; and changes in values attached to anadromous fish. The lessons highlight the need for careful, broad-based a priori assessments of the irreversible and cumulative impacts of large water resources development projects as well as planned re-evaluations of water allocations and project operations. 相似文献
7.
The tentative standard impact test procedure, adopted by the Porcelain Enamel Institute, was used to test and compare cylinders coated with several experimental and commercial enamels. The important facts noted were (1) the effect of cubic thermal expansion on the impact resistance, (2) the importance of the ground coat to the resistance of any one cover enamel, and (3) the wide variation between cover enamels in resistance to impact. 相似文献
8.
Jones Kevin M.; Wickstrom Katherine F.; Friman Patrick C. 《Canadian Metallurgical Quarterly》1997,12(4):316
Evaluated the effects of performance feedback on levels of treatment integrity in school-based behavioral consultation. Three teachers employed in a residential treatment community were responsible for treatment implementation. Treatment integrity was defined as the percentage of 2-min intervals during which contingent teacher reinforcement for student on-task behavior was directly observed. Teacher and child behavior were monitored across baseline, traditional consultation, and consultation with performance feedback conditions in a multiple baseline design. Following a Problem Identification Interview and Problem Analysis Interview (J. R. Bergan, 1977), mean levels of treatment integrity for the 3 teachers ranged from 9% to 37%. The addition of a performance feedback package increased treatment integrity for all 3 teachers to levels ranging from 60% to 83%. The findings contribute to a growing literature supporting the need for direct assessment of treatment integrity in school-based consultation research and practice. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
9.
Berninger Virginia W.; Vaughan Katherine; Abbott Robert D.; Brooks Allison; Abbott Sylvia P.; Rogan Laura; Reed Elizabeth; Graham Steve 《Canadian Metallurgical Quarterly》1998,90(4):587
Poor spellers in 2nd grade (n?=?128) participated in 24 20-min sessions that included (a) direct instruction in the alphabet principle (most frequent phoneme-spelling connections); (b) modeling of different approaches, singly and in combination, for developing connections between spoken and written words for 48 words ordered by sound-spelling predictability; and (c) practice in composing. Results of this multilayered intervention showed that (a) more than 1 way of developing sound-spelling connections is effective in teaching spelling but that after training in the alphabet principle, combining whole word and onset-rime training is most effective in achieving transfer of the alphabet principle across word contexts; (b) functional spelling units of not only a single letter but also 2 or more letters are important in beginning spelling; and (c) training in spelling transfers to composition and word recognition. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
10.
CM Wheeler CA Parmenter WC Hunt TM Becker CE Greer A Hildesheim MM Manos 《Canadian Metallurgical Quarterly》1993,20(5):286-289
OBJECTIVES: To confirm the risk factors for genital human papillomavirus (HPV) infection. GOAL OF THIS STUDY: To investigate risk factors for HPV detection apart from the correlated risk factors for cervical neoplasia. STUDY DESIGN: Cervical human papillomavirus (HPV) DNA was assessed in 357 cytologically normal women attending the University of New Mexico student health center. Cervical swab samples were obtained for HPV DNA detection and typing using a PCR-based DNA amplification system. Possible determinants of cervical HPV were examined including age, ethnicity, history of sexually transmitted disease, oral contraceptive use, smoking, age at first intercourse, lifetime number of sex partners, marital status, and history of pregnancy. RESULTS: A 44.3% overall prevalence of cervical HPV was observed. On univariate analysis, factors associated with increasing HPV prevalence included higher lifetime number of sex partners and single marital status. After adjustment for potential confounding variables, we found that HPV prevalence increased with higher lifetime number of sexual partners. CONCLUSION: These findings, along with those from the companion reports in this issue of the journal, support the sexual route of transmission of the virus. 相似文献