全文获取类型
收费全文 | 415438篇 |
免费 | 6806篇 |
国内免费 | 1395篇 |
专业分类
电工技术 | 7718篇 |
综合类 | 351篇 |
化学工业 | 62454篇 |
金属工艺 | 14358篇 |
机械仪表 | 11958篇 |
建筑科学 | 11847篇 |
矿业工程 | 877篇 |
能源动力 | 11231篇 |
轻工业 | 44079篇 |
水利工程 | 3339篇 |
石油天然气 | 1850篇 |
武器工业 | 13篇 |
无线电 | 55667篇 |
一般工业技术 | 77480篇 |
冶金工业 | 75479篇 |
原子能技术 | 5577篇 |
自动化技术 | 39361篇 |
出版年
2021年 | 2767篇 |
2019年 | 2547篇 |
2018年 | 3959篇 |
2017年 | 4019篇 |
2016年 | 4279篇 |
2015年 | 3536篇 |
2014年 | 5902篇 |
2013年 | 19542篇 |
2012年 | 10474篇 |
2011年 | 15018篇 |
2010年 | 11495篇 |
2009年 | 13069篇 |
2008年 | 14145篇 |
2007年 | 14501篇 |
2006年 | 12965篇 |
2005年 | 12123篇 |
2004年 | 11704篇 |
2003年 | 11376篇 |
2002年 | 11019篇 |
2001年 | 11202篇 |
2000年 | 10322篇 |
1999年 | 10803篇 |
1998年 | 24049篇 |
1997年 | 17622篇 |
1996年 | 13937篇 |
1995年 | 11005篇 |
1994年 | 9800篇 |
1993年 | 9382篇 |
1992年 | 7142篇 |
1991年 | 6800篇 |
1990年 | 6412篇 |
1989年 | 6117篇 |
1988年 | 5868篇 |
1987年 | 4892篇 |
1986年 | 4840篇 |
1985年 | 5989篇 |
1984年 | 5607篇 |
1983年 | 4836篇 |
1982年 | 4506篇 |
1981年 | 4454篇 |
1980年 | 4212篇 |
1979年 | 4085篇 |
1978年 | 3773篇 |
1977年 | 4558篇 |
1976年 | 6100篇 |
1975年 | 3119篇 |
1974年 | 3013篇 |
1973年 | 2893篇 |
1972年 | 2321篇 |
1971年 | 2004篇 |
排序方式: 共有10000条查询结果,搜索用时 609 毫秒
91.
92.
A Stimulation Method to Assess the Contractile Status of the Lumbar Extensors in a Seated Posture
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)
The purpose of present study was to develop and evaluate methods to assess stimulation responses of the lumbar extensors, as part of a longer‐term goal of detecting fatigue during prolonged sitting. Three stimulation frequencies (2, 5, and 8 Hz) were tested in separate stages, which include 3 stimulation trains and 4 sampling blocks. Repeated measures analyses of variance were used to determine whether any significant differences in mean stimulation responses occurred with respect to stimulation frequency, sampling block, and stimulation train. Reliability of measured stimulation responses was assessed within and between sampling blocks using intraclass correlation coefficients. Stimulation frequencies significantly affected the stimulation responses and time‐to‐potentiation differed between the 3 stimulation frequencies; it was highest for 2 Hz stimulation. All 3 stimulation frequencies resulted in excellent reliability within and between sampling blocks. Use of the current protocol at 2 Hz is recommended as appropriate to measure the lumbar extensors status during prolonged sitting. 相似文献
93.
D. Solís-Cortés E. Navarrete-Astorga J.L. Costa-Krämer J. Salguero-Fernandez R. Schrebler D. Leinen E.A. Dalchiele J.R. Ramos-Barrado F. Martín 《Ceramics International》2019,45(5):5577-5587
C-axis textured thin films of gallium-doped indium zinc oxide (GIZO) with a 2% ratio of Ga/Zn, were obtained via RF-magnetron sputtering with high transparency and electrical conductivity. A Box-Behnken response surface design was used to evaluate the effects of the deposition parameters (In2O3 target power, deposition time, and substrate temperature) on the chemical composition, optical, electrical, and structural properties of the GIZO films. The optical constants and the electrical properties were obtained using optical models. The GIZO stoichiometry, and therefore the In/Zn atomic ratio, affected the crystallinity, crystalline parameters, band gap, and charge carrier mobility of the GIZO films. The charge carrier density was related to the change in the crystalline parameters of the hexagonal structure and the In/Zn atomic ratio. The best electrical conductivity values (1.75?×?103 Ω?1 cm?1) were obtained for GIZO films with In/Zn ratio ≥?1. Several figures of merit (FOM) defined for the visible and solar regions were comparatively used to select the optimal In/Zn atomic ratio that provided the best balance between the conductivity and the transparency. The optimal In/Zn ratio was in a range of 0.85–0.90 for the GIZO films. 相似文献
94.
Titania-based ceramics with adjustable anatase-rutile fractions were obtained by milling of anatase, quartz and corundum precursors, uniaxial pressing and firing at 1100?°C. The influence of silica and alumina, combined with milling time and compaction pressure, was studied by design of experiments. The L9 orthogonal array with a three-level noise factor was employed. Firing of pure titania at 1100?°C yielded complete anatase to rutile transformation (ART), whereas stabilized samples show that an optimum amount of 9% silica and 33% alumina reduces phase transformation to only about 5?wt% rutile. An extended correlation matrix combined with analysis of variance (ANOVA) was applied to assess the combined effects of quartz, alumina, milling time and uniaxial compressing pressure on relative density, and anatase to rutile transformation. Results show absence of ART after milling, and controlled partial conversion of anatase to rutile after firing. Very good fitting was obtained by multivariate analysis on considering first and second order terms for dependence on silica contents and interactions between silica and each of the remaining factors, including milling time. This empirical dependence could be interpreted on a sound physicochemical basis, allowing the prediction of suitable compositions and processing conditions to obtain rutile-free samples by conventional ceramic processing, and to design ceramic samples with controlled fractions of anatase and rutile. 相似文献
95.
Zhuang CHENG Jianfeng WANG Matthew Richard COOP Guanlin YE 《Frontiers of Structural and Civil Engineering》2020,14(2):357
The development of a miniature triaxial apparatus is presented. In conjunction with an X-ray micro-tomography (termed as X-ray μCT hereafter) facility and advanced image processing techniques, this apparatus can be used for in situ investigation of the micro-scale mechanical behavior of granular soils under shear. The apparatus allows for triaxial testing of a miniature dry sample with a size of (diameter height). In situ triaxial testing of a 0.4–0.8 mm Leighton Buzzard sand (LBS) under a constant confining pressure of 500 kPa is presented. The evolutions of local porosities (i.e., the porosities of regions associated with individual particles), particle kinematics (i.e., particle translation and particle rotation) of the sample during the shear are quantitatively studied using image processing and analysis techniques. Meanwhile, a novel method is presented to quantify the volumetric strain distribution of the sample based on the results of local porosities and particle tracking. It is found that the sample, with nearly homogenous initial local porosities, starts to exhibit obvious inhomogeneity of local porosities and localization of particle kinematics and volumetric strain around the peak of deviatoric stress. In the post-peak shear stage, large local porosities and volumetric dilation mainly occur in a localized band. The developed triaxial apparatus, in its combined use of X-ray μCT imaging techniques, is a powerful tool to investigate the micro-scale mechanical behavior of granular soils. 相似文献
96.
97.
98.
Correlation between instrumental texture and colour quality attributes with sensory analysis of selected cheeses as affected by fat contents
下载免费PDF全文
![点击此处可从《International Journal of Food Science & Technology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
A. Półtorak J. Wyrwisz M. Moczkowska M. Marcinkowska‐Lesiak A. Stelmasiak U. Ulanicka M. Zalewska A. Wierzbicka Da‐Wen Sun 《International Journal of Food Science & Technology》2015,50(4):999-1008
This study evaluated several physical and sensory parameters of different types of cheese available in the Polish market. The measurements of textural properties were conducted in an Instron universal testing machine, while the colour properties of cheeses were measured using a Minolta chromameter. The chemical composition was determined by means of the near‐infrared spectroscopy (NIRs). Moreover, a trained sensory panel was invited to assess the cheese texture‐related properties. Generally, cheeses with reduced fat content were characterised by higher hardness, adhesiveness, cohesiveness and elasticity. Texture‐related parameters of cheese with canola oil were comparable to that of most of full‐fat cheeses. The correlation analysis between physical and sensory attributes related to cheese textural properties indicated the potential applications of TPA, shear and penetration tests (r = 0.766, r = 0.75 and r = 0.765, respectively) for the evaluation of sensory properties related to the hardness. Meanwhile, the elasticity of cheese obtained from sensory evaluation was strongly correlated with the elasticity determined from the shear test (r = 0.722) and moderately correlated with the elasticity from penetration test (r = 0.588), indicating a need to refine the method of penetration test. In addition, cheeses exhibited higher meltability during convection heating at 230 °C than microwave heating. The values of meltability for cheese with reduced fat content were lower than those of full‐fat cheese. 相似文献
99.
100.