全文获取类型
收费全文 | 1270篇 |
免费 | 97篇 |
国内免费 | 3篇 |
学科分类
工业技术 | 1370篇 |
出版年
2024年 | 4篇 |
2023年 | 17篇 |
2022年 | 50篇 |
2021年 | 186篇 |
2020年 | 42篇 |
2019年 | 48篇 |
2018年 | 57篇 |
2017年 | 47篇 |
2016年 | 51篇 |
2015年 | 48篇 |
2014年 | 68篇 |
2013年 | 91篇 |
2012年 | 74篇 |
2011年 | 90篇 |
2010年 | 71篇 |
2009年 | 73篇 |
2008年 | 69篇 |
2007年 | 44篇 |
2006年 | 36篇 |
2005年 | 22篇 |
2004年 | 11篇 |
2003年 | 20篇 |
2002年 | 18篇 |
2001年 | 11篇 |
2000年 | 12篇 |
1999年 | 4篇 |
1998年 | 13篇 |
1997年 | 11篇 |
1996年 | 11篇 |
1995年 | 13篇 |
1994年 | 7篇 |
1993年 | 4篇 |
1992年 | 5篇 |
1991年 | 5篇 |
1990年 | 3篇 |
1989年 | 7篇 |
1988年 | 3篇 |
1987年 | 4篇 |
1985年 | 1篇 |
1984年 | 5篇 |
1982年 | 3篇 |
1981年 | 3篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1978年 | 3篇 |
1977年 | 1篇 |
1976年 | 1篇 |
排序方式: 共有1370条查询结果,搜索用时 140 毫秒
121.
As a new approach, LiFePO4 nanoparticles were directly synthesized from precursors iron(III) nitrate and lithium dihydrogen phosphate by a polyol process without post heat treatment in one step. The obtained powders were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and combined thermogravimetry and differential scanning calorimetry and mass spectroscopy TG/DSC/MS. The X-ray diffraction showed the orthorhombic crystal structure of LiFePO4 without any impurity phases. The synthesized LiFePO4 has rhombohedral morphology with high aspect ratio with a thickness of less than 100 nm. TG/DSC/MS revealed a weight loss of only 10.9 wt.% when heating up to 1000 °C. Electrodes prepared from the LiFePO4 particles were electrochemically characterized by cycling at 0.1C current rate and temperatures in half cell measurements against lithium foil between 2 and 4.2 V in an EC/DMC electrolyte with 1 M LiPF6 as conductive salt. A reversible specific capacity of 146 mAh/g was achieved by applying carbon coating on the rhombohedral particles. 相似文献
122.
Monika Pinchas 《Signal, Image and Video Processing》2011,5(1):29-37
Recently, a Maximum Entropy (MaxEnt) algorithm and its derivation called WNEW algorithm were presented by the same author.
It was shown that the MaxEnt and WNEW algorithm have improved equalization performance compared with Godard’s, reduced constellation
algorithm and the sign reduced constellation algorithm. In this paper, a new equalization method is proposed for the 16QAM
and 64QAM input constellation based on the WNEW algorithm which is extended with some polynomials of the equalized output
and optimized with the mean square error criteria. According to simulation results, the new equalization method leads to over
15 dB advantage in the residual Intersymbol Interference compared to the results presented by Godard, 10 dB advantage compared
with the WNEW algorithm and 5 dB advantage compared with the MaxEnt algorithm. 相似文献
123.
The determination of the fluorescence quantum yields (QY, Φ(f)) of a series of fluorescent dyes that span the absorption/excitation and emission ranges of 520-900 and 600-1000 nm is reported. The dyes encompass commercially available rhodamine 101 (Rh-101, Φ(f) = 0.913), cresyl violet (0.578), oxazine 170 (0.579), oxazine 1 (0.141), cryptocyanine (0.012), HITCI (0.283), IR-125 (0.132), IR-140 (0.167), and four noncommercial cyanine dyes with specific spectroscopic features, all of them in dilute ethanol solution. The QYs have been measured relative to the National Institute of Standards and Technology's standard reference material (SRM) 936a (quinine sulfate, QS) on a traceably characterized fluorometer, employing a chain of transfer standard dyes that include coumarin 102 (Φ(f) = 0.764), coumarin 153 (0.544), and DCM (0.435) as links between QS and Rh-101. The QY of Rh-101 has also been verified in direct measurements against QS using two approaches that rely only on instrument correction. In addition, the effects of temperature and the presence of oxygen on the fluorescence quantum yield of Rh-101 have been assessed. 相似文献
124.
Pulse propagation through chalcogenide As(2)Se(3) glass photonic crystal fiber (PCF) is numerically investigated using fourth-order Runge-Kutta in the interaction picture (RK4IP) method. The fully vectorial effective index method (FVEIM) is used to calculate the variation of effective refractive index, effective area, dispersion, and nonlinear coefficient (γ) in As(2)Se(3) PCF with wavelength for different values of pitch and air hole size. The RK4IP method is used to demonstrate the soliton propagation, self-phase modulation (SPM), soliton collision and cross phase modulation (XPM) in the designed As(2)Se(3) PCF. The numerically obtained value of soliton collision length (L(col)=51.3L(D)) using the RK4IP method is found to be in good agreement with the theoretical value of soliton collision length (L(col)=51.408L(D)) obtained from inverse scattering transform method, thus providing a verification of the RK4IP accuracy in solving generalized nonlinear schr?dinger equation (GLNSE). We also evaluate and apply the value of wavelength for distortionless (L(NL)=L(D)) propagation of the soliton pulse. 相似文献
125.
126.
In-vitro antioxidant and antibacterial activities of pumpkin,quince, muskmelon and bottle gourd seeds 总被引:1,自引:0,他引:1
Tawheed Amin H. R. Naik Syed Zameer Hussain Abida Jabeen Monika Thakur 《Sensing and Instrumentation for Food Quality and Safety》2018,12(1):182-190
Ethanol and chloroform extracts of pumpkin, quince, muskmelon, and bottle gourd seeds were studied for in-vitro antioxidant and antibacterial activities. Crude protein and fat contents of all the seeds compared favorably with high protein legumes and high oil containing oilseeds. Ethanol and chloroform extracts of bottle gourd seeds had highest phenolic content. A direct positive relationship between antioxidant activities and extract concentration was observed with the relationship being more pronounced in chloroform extract of quince seeds (R2?=?0.9685 and 0.9829) followed by ethanol extract of pumpkin seeds (R2?=?0.9666 and 0.9685) as per 1,1-diphenyl-2-picrylhydrazyl and hydrogen peroxide (H2O2) method, respectively. Seed extracts were also studied for in-vitro antibacterial activity against Salmonella typhii, Enterococcus sp., Escherichia coli, Bacillus subtilis and Staphylococcus aureus. Ethanol extract of pumpkin seeds inhibited the growth of all bacteria; however, both the extracts of quince seeds did not show any activity against S. typhii, E. coli and S. aureus. 相似文献
127.
128.
Danijela A. Skobir Franc Vodopivec Ladislav Kosec Monika Jenko Jelena Vojvodi
‐Tuma 《国际钢铁研究》2004,75(3):196-203
The effect of microstructure on creep resistance of the low carbon chromium steel X20CrMoV121 after 100‐hours of static‐load test at a temperature of 580 °C and constant stress of 170 MPa was investigated. The specimens for the experiments were extracted from steam pipes of a steam power plant and heat treated. The effect of isothermal annealing on the microstructure and hardness as well as the kinetics of the precipitation of the carbide particles were determined. 相似文献
129.
BS Goldman DL Beckman A Bali EM Monika KK Gabbert RG Kranz 《Canadian Metallurgical Quarterly》1997,268(4):724-738
The helABC genes are predicted to encode an ATP-binding cassette (ABC) transporter necessary for heme export for ligation in bacterial cytochrome c biogenesis. The recent discoveries of homologs of the helB and helC genes in plant mitochondrial genomes suggest this is a highly conserved transporter in prokaryotes and some eukaryotes with the HelB and HelC proteins comprising the transmembrane components. Molecular genetic analysis in the Gram-negative bacterium Rhodobacter capsulatus was used to show that the helABC and helDX genes are part of an operon linked to the secDF genes. To facilitate analysis of this transporter, strains with non-polar deletions in each gene, epitope and reporter-tagged HelABCD proteins, and antisera specific to the HelA and HelX proteins were generated. We directly demonstrate that this transporter is present in the cytoplasmic membrane as an HelABCD complex. The HelB and HelC but not HelD proteins are necessary for the binding and stability of the HelA protein, the cytoplasmic subunit containing the ATP-binding region. In addition we show that the HelA protein co-immunoprecipitates with either the HelC or HelD proteins. Thus, the HelABCD heme export complex is distinguished by the presence of four membrane-associated subunits and represents a unique subfamily of ABC transporters. 相似文献
130.
This paper focuses on the labor force participation and earnings of the working age disabled in the United States, as they
vary by gender, age, and minority status. Expenditure on public and private sector programs targeted to persons with disabilities
exceed $100 billion for approximately 8m individuals. Program objectives are to increase employment opportunities among the
disabled as well as, provide public assistance through various welfare provisions. This paper argues public policies and public
expenditures have favored assistance and short run equity concerns relative to rehabilitation and vocational training, thus
providing work disincentives to people with disabilities and undermining their long-term welfare. 相似文献