全文获取类型
收费全文 | 3689篇 |
免费 | 107篇 |
国内免费 | 15篇 |
专业分类
电工技术 | 73篇 |
综合类 | 2篇 |
化学工业 | 781篇 |
金属工艺 | 134篇 |
机械仪表 | 89篇 |
建筑科学 | 45篇 |
矿业工程 | 5篇 |
能源动力 | 176篇 |
轻工业 | 210篇 |
水利工程 | 30篇 |
石油天然气 | 24篇 |
无线电 | 394篇 |
一般工业技术 | 914篇 |
冶金工业 | 439篇 |
原子能技术 | 32篇 |
自动化技术 | 463篇 |
出版年
2023年 | 36篇 |
2022年 | 88篇 |
2021年 | 117篇 |
2020年 | 105篇 |
2019年 | 87篇 |
2018年 | 120篇 |
2017年 | 114篇 |
2016年 | 102篇 |
2015年 | 77篇 |
2014年 | 133篇 |
2013年 | 233篇 |
2012年 | 144篇 |
2011年 | 194篇 |
2010年 | 169篇 |
2009年 | 180篇 |
2008年 | 139篇 |
2007年 | 126篇 |
2006年 | 84篇 |
2005年 | 87篇 |
2004年 | 70篇 |
2003年 | 82篇 |
2002年 | 74篇 |
2001年 | 62篇 |
2000年 | 55篇 |
1999年 | 55篇 |
1998年 | 108篇 |
1997年 | 84篇 |
1996年 | 55篇 |
1995年 | 51篇 |
1994年 | 57篇 |
1993年 | 59篇 |
1992年 | 30篇 |
1991年 | 31篇 |
1990年 | 35篇 |
1989年 | 31篇 |
1988年 | 40篇 |
1987年 | 40篇 |
1986年 | 27篇 |
1985年 | 57篇 |
1984年 | 45篇 |
1983年 | 33篇 |
1982年 | 33篇 |
1981年 | 31篇 |
1980年 | 38篇 |
1979年 | 24篇 |
1978年 | 12篇 |
1977年 | 23篇 |
1976年 | 37篇 |
1975年 | 14篇 |
1973年 | 20篇 |
排序方式: 共有3811条查询结果,搜索用时 265 毫秒
51.
Barium ferrite has been prepared by a novel non-conventional preparation method known as the liquid mix technique which involves the preparation of citrates of the metals concerned. The decomposition of the citrates indicated a gradual transition from an amorphous material to a crystalline phase leading to the formation of barium ferrite at 600° C as indicated by the X-ray diffraction and Mössbauer measurements. Submicrometre-sized particles of the ferrite could be obtained directly on decomposition of the citrates, thus avoiding the milling or grinding operations normally employed to reduce the particles to the size required for obtaining good magnetic properties. The best properties (coercivity and remanence) were obtained for the ferrite sintered around 990° C. 相似文献
52.
A suspension of mica particles (40m diameter and 3.7 thick) obtained in a mechanically stirred Al-4 wt % Cu-1.5 wt % Mg melt was poured and solidified in a variety of moulds under different heat flow configurations. The resulting cast structure showed a non-uniform distribution of dispersed mica particles with mica-depleted and segregated zones due to their flotation before and during solidification. The experimentally observed profiles of mica-free regions deviate significantly from those computed on the basis of Stokes's law and freezing-time computations. In relatively thick castings, segregation of mica could be minimized by using low pouring temperatures and/or side as well as bottom chilling. It was found, however, that thin castings (12.5 mm) could easily be produced with a homogeneous distribution of mica particles. 相似文献
53.
P. K. Siwach H. K. Singh N. Khare A. K. Singh O. N. Srivastava 《Journal of Alloys and Compounds》2003,350(1-2):56-61
A new manganite type CMR material, La0.7Hg0.3MnO3 has been successfully synthesized and has been found to exhibit magnetoresistance (≈9%) at low fields (≈1.5 kG). The synthesis has been carried out through a solid state reaction route consisting of the formation of La0.7MnO3 followed by diffusion of Hg leading to La0.7Hg0.3MnO3. The as grown samples are polycrystalline and correspond to an orthorhombic unit cell with the lattice parameters; a=5.5183 Å, b=5.6383 Å and c=7.5368 Å. The typical grain size as revealed by scanning electron microscopy is in the range of 0.5–2 μm. The ρ–T behaviour shows a peak at TIM=227 K. The ρ–T behaviour above this temperature corresponds to that of an insulator and below this to that of a metal. The ρ–T behaviour remains unaltered when a magnetic field (Hdc=1.5 kG) is applied. However, with this magnetic field a drop in the resistivity is observed up to 77 K. At room temperature the magnetoresistance ratio (MRR) is too small but it steadily increases as the temperature is decreased. Thus, MRRs at 227.13 and 77 K are 3.41 and 9.05%, respectively, in an applied field of Hdc=1.5 kG. At a given temperature the variation in MRR with field Hdc is rapid at lower field values (Hdc<1.2 kG) and scales linearly for higher field values (Hdc>1.2 kG). It may be mentioned that the present work on the synthesis and magnetoresistance behaviour of La0.7Hg0.3MnO3, is the first of its type. 相似文献
54.
Sanjeev Chawla Vanessa Shehu Pradeep K. Gupta Kavindra Nath Harish Poptani 《International journal of molecular sciences》2021,22(8)
Glioblastoma (GBM) is the most malignant brain tumor in adults, with a dismal prognosis despite aggressive multi-modal therapy. Immunotherapy is currently being evaluated as an alternate treatment modality for recurrent GBMs in clinical trials. These immunotherapeutic approaches harness the patient’s immune response to fight and eliminate tumor cells. Standard MR imaging is not adequate for response assessment to immunotherapy in GBM patients even after using refined response assessment criteria secondary to amplified immune response. Thus, there is an urgent need for the development of effective and alternative neuroimaging techniques for accurate response assessment. To this end, some groups have reported the potential of diffusion and perfusion MR imaging and amino acid-based positron emission tomography techniques in evaluating treatment response to different immunotherapeutic regimens in GBMs. The main goal of these techniques is to provide definitive metrics of treatment response at earlier time points for making informed decisions on future therapeutic interventions. This review provides an overview of available immunotherapeutic approaches used to treat GBMs. It discusses the limitations of conventional imaging and potential utilities of physiologic imaging techniques in the response assessment to immunotherapies. It also describes challenges associated with these imaging methods and potential solutions to avoid them. 相似文献
55.
Shalu Kataria Yogendra L. Verma Himani Gupta Shishir K. Singh Nitin Srivastava Ravindra Dhar 《Polymer-Plastics Technology and Engineering》2020,59(9):952-958
ABSTRACTNano-composite polymer gel electrolytes (NPGEs) based on polymer poly(vinylidene fluoride-co-hexafluoropropylene) PVdF-HFP, ionic liquid, 1-butyl-3- methylimidazolium bis(trifluoromethanesulfonyl)imide BMIMTFSI, Li-salt along with the addition of SiO2 nanoparticles have been synthesized and characterized by various techniques. Prepared NPGEs show high room temperature ionic conductivity (~10?3 S/cm) and have a wide electrochemical window (ECW) (~3.3–3.5 V). The galvanostatic charge/discharge profile was studied by sandwiching best performing NPGEs between a LiFePO4 cathode and lithium metal anode. The specific discharge capacity of the cell (Li/NPGE/LiFePO4) room temperature at 0.1C rate is found to be 138 mAh/g. 相似文献
56.
Quantification of response time in poly(vinyl alcohol)–metal complex thermochromic polymeric systems
Thermochromic poly(vinyl alcohol) (PVA)‐based material was synthesized and an extensive study of its thermochromic behavior with respect to response time was carried out. It was observed that it is possible to manipulate the response time by keeping control over chemical and physical parameters. The response time, which is the most important property of a smart material, has in this case been found to be very much influenced by rate of heat transfer into the material. Different compositions of the thermochromic material and their corresponding response time with respect to rate of heat transfer were studied and correlated. First, a theoretical equation was derived and later on it was experimentally verified to quantify the response time in PVA–metal complex‐based thermochromic systems. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4832–4834, 2006 相似文献
57.
Monoj Pramanik Suneel Kumar Srivastava Biswas Kumar Samantaray Anil Kumar Bhowmick 《应用聚合物科学杂志》2003,87(14):2216-2220
Ethylene vinyl acetate rubber (45% vinyl acetate content, EVA‐45) and organomodified clay (12Me‐MMT) composites were prepared by solution blending of the rubber and the clay. A combination of X‐ray diffraction, scanning electron microscopy, and transmission electron microscopy studies showed that the composites obtained are on the nanometer scale. The measurements of the dynamic mechanical properties for different compositions over a temperature range (?100 to +100°C) showed that the storage moduli of these rubber–clay nanocomposites are higher above the glass to rubber transition temperature compared to the neat rubber. The tensile strength of the nanocomposites is about 1.6 times higher than that of the EVA‐45. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 87: 2216–2220, 2003 相似文献
58.
In this study, an attempt has been made to find the correlation between diffusion tensor imaging (DTI) indices of white matter (WM) regions and mini mental state examination (MMSE) score of Alzheimer patients. Diffusion weighted images are obtained from the ADNI database. These are preprocessed for eddy current correction and removal of non-brain tissue. Fractional anisotropy (FA), mean diffusivity (MD), radial diffusivity (RD) and axial diffusivity (DA) indices are computed over significant regions (Fornix left, Splenium of corpus callosum left, Splenium of corpus callosum right, bilateral genu of the corpus callosum) affected by Alzheimer disease (AD) pathology. The correlation is computed between diffusion indices of the significant regions and MMSE score using linear fit technique so as to find the relation between clinical parameters and the image features. Binary classification has been employed using support vector machine, decision stumps and simple logistic classifiers on the extracted DTI indices along with MMSE score to classify Alzheimer patients from healthy controls. It is observed that distinct values of DTI indices exist for the range of MMSE score. However, there is no strong correlation (Pearson's correlation coefficient ‘r’ varies from 0.0383 to −0.1924) between the MMSE score and the diffusion indices over the significant regions. Further, the performance evaluation of classifiers shows 94% accuracy using SVM in differentiating AD and control. In isolation clinical and image features can be used for prescreening and diagnosis of AD but no sub anatomic region correlation exist between these features set. The discussion on the correlation of diffusion indices of WM with MMSE score is presented in this study. 相似文献
59.
An Ni-Mn-Zn alloy has been satisfactorily electrodeposited from a sulphate bath containing nickel sulphate (20–23 g dm−3), manganese sulphate (76–88 g dm−3), zinc sulphate (18–24 g dm−3), ammonium sulphate (30 g dm−3), thiourea (18g dm−3) and ascorbic acid (0.8 g dm−3) under various plating conditions, namely, current density 1.0–3.0 A dm−2; temperature 30–45° C; pH 2.7–4.2 and duration of electrolysis 15–30 min. Semibright, blackish-grey, thin films were generally
deposited with the proportion of nickel and manganese in the deposits increasing with increasing current density, temperature
and duration of electrolysis. However, the amount of zinc increased as the pH of the solution was raised. The cathode efficiency
for alloy deposition increased linearly as the temperature or the pH of the solution was decreased, whereas at any particular
pH and temperature it continuously rose with increasing current density or the time of deposition. The cathode polarization
shifted to more negative values on increasing the current density and to less negative values at higher pH values and temperatures
which consequently lowered the throwing power under the latter conditions. 相似文献
60.
An Experimental Study to Evaluate the Effect of Ambient Temperature during Manual Lifting and Design of Optimal Task Parameters
下载免费PDF全文
![点击此处可从《人机工程学与制造业中的人性因素》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Ravindra Pratap Singh Ajay Batish T. P. Singh Anirban Bhattacharya 《人机工程学与制造业中的人性因素》2014,24(1):54-70
In the present study, the effect of lifting task parameters on the heart rate and oxygen uptake of workers during manual lifting tasks in different ambient conditions was evaluated. The experiments conducted in two different temperature conditions showed a significantly higher oxygen uptake and heart rate in colder conditions as compared to warmer conditions. Three other factors, namely, load, lifting frequency, and vertical distance were found to significant affect the responses. Various combinations of significant factors were used to calculate oxygen uptake and heart rate. These were then compared with the safe limits as per the maximum aerobic capacity of workers. Based on these comparisons, the safe combinations were identified that can be used to design lifting tasks in varied ambient conditions. The study further concluded that lifting tasks performed in winter should have different relaxation or fatigue allowances built into the cycle time of the task to compensate for higher exertion. © 2011 Wiley Periodicals, Inc. 相似文献