全文获取类型
收费全文 | 1998篇 |
免费 | 83篇 |
国内免费 | 5篇 |
专业分类
电工技术 | 17篇 |
综合类 | 2篇 |
化学工业 | 681篇 |
金属工艺 | 62篇 |
机械仪表 | 33篇 |
建筑科学 | 47篇 |
能源动力 | 123篇 |
轻工业 | 138篇 |
水利工程 | 13篇 |
石油天然气 | 7篇 |
无线电 | 134篇 |
一般工业技术 | 403篇 |
冶金工业 | 134篇 |
原子能技术 | 25篇 |
自动化技术 | 267篇 |
出版年
2024年 | 8篇 |
2023年 | 26篇 |
2022年 | 48篇 |
2021年 | 78篇 |
2020年 | 57篇 |
2019年 | 56篇 |
2018年 | 95篇 |
2017年 | 81篇 |
2016年 | 89篇 |
2015年 | 26篇 |
2014年 | 71篇 |
2013年 | 150篇 |
2012年 | 99篇 |
2011年 | 134篇 |
2010年 | 91篇 |
2009年 | 81篇 |
2008年 | 97篇 |
2007年 | 75篇 |
2006年 | 77篇 |
2005年 | 53篇 |
2004年 | 37篇 |
2003年 | 28篇 |
2002年 | 39篇 |
2001年 | 18篇 |
2000年 | 24篇 |
1999年 | 22篇 |
1998年 | 28篇 |
1997年 | 18篇 |
1996年 | 19篇 |
1995年 | 26篇 |
1994年 | 21篇 |
1993年 | 32篇 |
1992年 | 23篇 |
1991年 | 20篇 |
1990年 | 27篇 |
1989年 | 15篇 |
1988年 | 15篇 |
1987年 | 22篇 |
1986年 | 17篇 |
1985年 | 20篇 |
1984年 | 18篇 |
1983年 | 18篇 |
1982年 | 17篇 |
1981年 | 21篇 |
1980年 | 17篇 |
1979年 | 9篇 |
1978年 | 4篇 |
1977年 | 4篇 |
1976年 | 6篇 |
1970年 | 3篇 |
排序方式: 共有2086条查询结果,搜索用时 15 毫秒
161.
In recent years, isokinetic strengths (dynamic strength exertions at constant speed) have almost replaced isometric (static) strengths in laboratory studies as measures of a person's strength exertion capabilities. Many industries are also showing a keen interest in replacing static strength usage with dynamic strength usage. The increasing acceptance of isokinetic strengths as a more valid and accurate measure of people's strength exertion capability has necessitated the development of isokinetic strength databases. This paper presents one-arm isokinetic pull strength profiles of males, engaged in infrequent exertion in a horizontal plane, as a function of posture (sitting and standing), reach distance (25, 40, and 55 cm for the sitting posture; 45, 65, and 85 cm for the standing posture), and angle of the preferred (stronger) arm from the frontal plane (0—frontal plane, 30, 60, 90, 120, and 150 deg). Twenty-five males participated in the study. The results indicated that more strength is exerted while standing. The strength also increases with the reach distance. The strength exertion becomes stronger as the angle of the arm increases to 90° from the frontal plane (i.e., the arm moves to the sagittal plane) and then weakens. 相似文献
162.
Variations in the antibacterial activity of the sponge Ircinia ramosa were evaluated during two collection periods (January and May) against vicinity fouling bacteria (VFB) and sponge surface-associated bacteria (SAB). The density of fouling bacteria in the water column, as well as epibacterial abundance on the sponge surface, was enumerated during both collections, and both increased in the warmer month of May. The extracts obtained from SAB were also tested for their role in antibacterial activity of the host. Sponge-associated bacteria are capable of producing antibacterial metabolites. The antibacterial activity that originated from polar fractions in the cooler month of January shifted towards the nonpolar fractions in May. Nonpolar fractions were more useful for the sponge when threatened with increased bacterial density. Thus, the chemical nature and production of antibacterial compounds produced by sponge or its associated bacteria appears to be governed by the environment. An inverse relationship was observed between the epibacterial abundance over the sponge surface in nature and the antibacterial activity displayed by the sponge extracts in laboratory bioassays. This investigation reveals the importance of collection period as well as the role of associated bacteria in the evaluation of antibacterial activity. 相似文献
163.
Sagar V. Kamarthi Soundarr T. Kumara Francis T. S. Yu Inyong Ham 《Journal of Intelligent Manufacturing》1990,1(2):125-140
Neural networks have gained increased importance in the past few years. One of the basic characteristics of neural networks is the property of associative memory. In this paper we study the possibility of using the ideas of neural networks and associative memory in the manufacturing domain, with specific reference to design data retrieval in group technology. A two-layer feed-forward perceptron with backpropagation is simulated on a Vax-8550 to train example parts. The complete scheme along with the simulation results are explained and future directions indicated. 相似文献
164.
We report thermoelectric power measurements on BiSrCaCuO (2212) superconducting oxide and compare the observed behaviour with
that of the YBaCuO (123) system. The relative importance of phonon drag and diffusion thermopower contributions is evaluated
for the two systems by analysing the data using a generalized expression of the typeS=αT+β/T. The thermopower enhancement effect just aboveT
c
gives parameter values comparable to those of YBa2Cu3O7−x
system. 相似文献
165.
Manzer H. Siddiqui Mutahhar Y. Al-Khaishany Mohammed A. Al-Qutami Mohamed H. Al-Whaibi Anil Grover Hayssam M. Ali Mona S. Al-Wahibi Najat A. Bukhari 《International journal of molecular sciences》2015,16(5):10214-10227
Drought stress is one of the major abiotic stresses that are a threat to crop production worldwide. Drought stress impairs the plants growth and yield. Therefore, the aim of the present experiment was to select the tolerant genotype/s on the basis of moprpho-physiological and biochemical characteristics of 10 Vicia faba genotypes (Zafar 1, Zafar 2, Shebam, Makamora, Espan, Giza Blanka, Giza 3, C4, C5 and G853) under drought stress. We studied the effect of different levels of drought stress i.e., (i) normal irrigation (ii) mild stress (iii) moderate stress, and (iv) severe stress on plant height (PH) plant−1, fresh weight (FW) and dry weight (DW) plant−1, area leaf−1, leaf relative water content (RWC), proline (Pro) content, total chlorophyll (Total Chl) content, electrolyte leakage (EL), malondialdehyde (MDA), hydrogen peroxide (H2O2) content, and activities of catalase (CAT), peroxidase (POD) and superoxide dismutase (SOD) of genotypes of faba bean. Drought stress reduced all growth parameters and Total Chl content of all genotypes. However, the deteriorating effect of drought stress on the growth performance of genotypes “C5” and “Zafar 1” were relatively low due to its better antioxidant enzymes activities (CAT, POD and SOD), and accumulation of Pro and Total Chl, and leaf RWC. In the study, genotype “C5” and “Zafar 1” were found to be relatively tolerant to drought stress and genotypes “G853” and “C4” were sensitive to drought stress. 相似文献
166.
Rheological behavior and spinnability of biodegradable materials based on SPI and PVA were studied for the production of electrospun fibers. pH level, processing temperature, and heating time were adjusted to investigate the effects of denaturing of soy protein on the rheology of SPI/PVA solutions. The results show that zero shear viscosity and degree of shear thinning of the SPI solution can be controlled by adjusting pH level and thermal treatment. The continuous production of uniform SPI/PVA fibers was achieved by electrospinning. The presence and amount of soy protein in the electrospun fibers was determined by EMPA and elemental analysis, confirming that the SPI was well incorporated into the PVA and remained in the electrospun fibers.
167.
Poisson’s ratio of HTPB based composite propellant is estimated at break using double dumbbell specimens as per ASTM D638 Type IV standard and its value obtained by change in the volume of specimens is calculated as approximately 0.25. This major finding contradicts the behaviour of solid rocket propellants in respect of Poisson’s ratio, which is reported to be 0.5. Further, Poisson’s ratio varies almost linearly with strain even in linear portion of stress‐strain curve in uni‐axial tensile testing as per theoretical calculations. It must be noted that no change in volume does not necessarily indicate constant Poisson’s ratio equal to 0.5. SEM scan indicates that the rate of reduction of Poisson’s ratio with longitudinal strain accelerates after dewetting due to the formation of vacuoles. Bilinear variation of Poisson’s ratio with longitudinal strain is observed. One slope is valid in pre‐dewetting region, calculated from close form solution and other slope is valid for post‐dewetting region, which is measured at break. Measurement of Poisson’s ratio at various longitudinal strains indicates uni‐linear variation and not a bilinear variation with a kink. It is also observed that Poisson’s ratio is different along different lateral directions of the propellant specimen. Poisson’s ratio in two orthogonal directions perpendicular to longitudinal axis is calculated as 0.17 and 0.30. As ASTM Specimen has rectangular cross‐section of approximate size 6×4 mm, the directional behavior of Poisson’s ratio may be attributed to initial dimensions. Prismatic propellant specimen with square cross‐section of 115×6×6 mm dimension do not show any variation in respect of Young’s modulus, tensile strength and percentage elongation as compared to ASTM specimen. Directional behavior of Poisson’s ratio with almost similar numerical value is again observed, thus ruling out dependence of this behavior on different initial dimensions of propellant cross‐section. The propellant slurry flow during vacuum casting, directional curing and orientation of specimen with respect to web of the cast propellant are mainly responsible for this directional behaviour of Poisson’s ratio for the composite propellants. Composite propellants behave as compressible material in most of the region and near failure region or at higher strains; Poisson’s ratio is not anywhere close to 0.5, instead it is close to 0.25. 相似文献
168.
Additively manufactured polymeric products for automotive, aerospace, and biomedical applications are usually intended for service in an outdoor environment with high mechanical loading conditions. The strength and sustainability of the products can be significantly degraded due to the outdoor environmental conditions such as UV light, moisture, heat, and so forth. In this research work, a novel weather-resistant polymer (WRP) material, that is, acrylonitrile styrene acrylate (ASA), has been studied. Furthermore, this work aims to study the effect of process parameters and enhance the strength of WRP (ASA) specimens using the FFF process. The optimized process parameters, that is, build orientation (BO), extrusion temperature (ET), layer thickness (LT), and printing speed (PS), were identified based on the tensile and flexural strength using the Taguchi technique and statistical analysis. The best tensile and flexural strengths for the specimen were achieved at both orientations (XYZ and ZXY) TS: 255°C ET, 0.14 mm LT, 50 mm/s PS; and FS: 245°C ET, 0.28 mm LT, 50 mm/s PS, respectively. Regression model was developed to investigate the correlation between the process parameters with tensile and flexural strength. A validation test confirmed the findings, and the error between the actual and predicted values is less than ±10%. 相似文献
169.
Joseph J. Armstrong Adilakshmi G. Robin C. R. Rene Vidhya S. Narukullapati Bharath Kumar Reddy M. Koti Kumar T. Ch. Anil 《SILICON》2023,15(1):127-131
Silicon - We designed a new model tunnel field-effect transistor (TFET) based on Triple Heterojunction Tunnel Field Effect Transistor (THJ-TFET) is investigated and designed in this paper. This... 相似文献
170.
Suprabha Nayar Sharmistha P. Sagar Avijit Guha 《Journal of materials science. Materials in medicine》2010,21(4):1099-1102
Hydroxyapatite-poly (vinyl) alcohol nanocomposite powder was synthesized using varying poly (vinyl) alcohol concentrations. The dried powder was compacted into micro-porous disks at a load of 4 tons. The disks were sintered at 1200°C to evolve porous nanocomposites. Size and shape of the pores observed in the scanning electron micrographs were quantified by using image processing software. Ultrasound velocity measurements were done to evaluate mechanical properties non-destructively. 相似文献