全文获取类型
收费全文 | 68998篇 |
免费 | 3265篇 |
国内免费 | 1342篇 |
专业分类
电工技术 | 2266篇 |
技术理论 | 9篇 |
综合类 | 7277篇 |
化学工业 | 3880篇 |
金属工艺 | 826篇 |
机械仪表 | 1367篇 |
建筑科学 | 32648篇 |
矿业工程 | 2280篇 |
能源动力 | 908篇 |
轻工业 | 2098篇 |
水利工程 | 4846篇 |
石油天然气 | 1128篇 |
武器工业 | 128篇 |
无线电 | 1800篇 |
一般工业技术 | 3723篇 |
冶金工业 | 2138篇 |
原子能技术 | 196篇 |
自动化技术 | 6087篇 |
出版年
2024年 | 117篇 |
2023年 | 388篇 |
2022年 | 875篇 |
2021年 | 1143篇 |
2020年 | 1137篇 |
2019年 | 788篇 |
2018年 | 797篇 |
2017年 | 1010篇 |
2016年 | 1466篇 |
2015年 | 1748篇 |
2014年 | 7247篇 |
2013年 | 3926篇 |
2012年 | 5369篇 |
2011年 | 5801篇 |
2010年 | 5131篇 |
2009年 | 5351篇 |
2008年 | 4686篇 |
2007年 | 5308篇 |
2006年 | 4027篇 |
2005年 | 3042篇 |
2004年 | 2748篇 |
2003年 | 2463篇 |
2002年 | 1956篇 |
2001年 | 1418篇 |
2000年 | 1151篇 |
1999年 | 834篇 |
1998年 | 619篇 |
1997年 | 523篇 |
1996年 | 398篇 |
1995年 | 376篇 |
1994年 | 264篇 |
1993年 | 205篇 |
1992年 | 161篇 |
1991年 | 99篇 |
1990年 | 103篇 |
1989年 | 112篇 |
1988年 | 96篇 |
1987年 | 61篇 |
1986年 | 63篇 |
1985年 | 80篇 |
1984年 | 96篇 |
1983年 | 104篇 |
1982年 | 95篇 |
1981年 | 30篇 |
1980年 | 33篇 |
1979年 | 22篇 |
1978年 | 22篇 |
1977年 | 17篇 |
1965年 | 7篇 |
1955年 | 15篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
Yong Pan Chen Zhu Wen Bin Zeng Pei Fu Chi Chen Bao Ming Xu Zhong Feng Gao 《Chembiochem : a European journal of chemical biology》2021,22(24):3431-3436
Rapid and sensitive point-of-care testing (POCT) is an extremely critical mission in practical applications, especially for rigorous military medicine, home health care, and in the third world. Here, we report a visual POCT method for adenosine triphosphate (ATP) detection based on Taylor rising in the corner of quadratic geometries between two rod surfaces. We discuss the principle of Taylor rising, demonstrating that it is significantly influenced by contact angle, surface tension, and density of the sample, which are controlled by ATP-dependent rolling circle amplification (RCA). In the presence of ATP, RCA reaction effectively suppresses Taylor-rising behavior, due to the increased contact angle, density, and decreased surface tension. Without addition of ATP, untriggered RCA reaction is favorable for Taylor rising, resulting in a significant height. With this proposed method, visual sensitive detection of ATP without the aid of other instruments is realized with only a 5 μL droplet, which has good selectivity and a low detection limit (17 nM). Importantly, this visual method provides a promising POCT tool for user-friendly molecular diagnostics. 相似文献
22.
The lead-free piezoelectric ceramics (Na.47Bi.47Ba.06)1-xCaxTiO3 (x?=?0, 0.01, 0.02, 0.03, 0.05, and 0.08, abbreviated as BNBTC/0, BNBTC/1, BNBTC/2, BNBTC/3, BNBTC/5, and BNBTC/8, respectively) were obtained using the solid-state reaction method. The structure, electric conductivity, and dielectric, ferroelectric, and piezoelectric properties of the Ca2+-doped (Na.47Bi.47Ba.06)TiO3 ceramics were thoroughly investigated. The ceramics sintered at 1200?°C exhibit dense microstructures, having relative densities higher than 96%. The X-ray diffraction results demonstrate that all ceramics have a pure perovskite structure. The mean grain sizes of the ceramics are related to the Ca2+ quantity. A small quantity of Ca2+ ions (x?≤?0.03) improves the piezoelectric and ferroelectric properties of the samples. The dielectric behavior of the samples is sensitive to the Ca2+ content and electric poling. The results demonstrate that the electrical properties of the (Na.47Bi.47Ba.06)TiO3 lead-free ceramics can be well tuned by varying the Ca2+ quantity. 相似文献
23.
Mohan B. Ponnuchamy G. Mohan Muralikrishna Venkateswara Rao Mannava G. Srinivas Reddy 《Ceramics International》2018,44(13):15019-15023
Nanocrystalline nickel oxide (NiO) was prepared from nickel hydroxide by Spark plasma sintering (SPS) and the mechanisms involved in the densification of NiO were studied. Reverse precipitated nickel hydroxide powders were SPS processed at 400, 600 and 700?°C with 70?MPa pressure. Pure NiO with 12?nm crystallite size formed after 400?°C sintering process. However NiO grains had grown to 18 and 38?nm after 600 and 700?°C sintering respectively. NiO pellets prepared using 600 and 700?°C SPS sintering schedules had relative densities of 83% and 94% respectively. Two displacement rate regimes were observed during densification of NiO in both 600 and 700?°C sintering processes. Decomposition of nickel hydroxide and particle sliding of NiO led to first displacement rate maximum while inverse Hall-Petch based plastic deformation facilitated densification during the constant second displacement rate regime. No densification occurred during sintering holding times indicating the limited role that diffusion played during densification. 相似文献
24.
25.
26.
27.
Seong‐Hee Kim 《Quality and Reliability Engineering International》2015,31(6):923-934
We present a distribution‐free tabular cumulative sum chart for monitoring the variability of an autocorrelated process. A quantity known as the asymptotic variance parameter is employed as a measure of the variability, and a distribution‐free tabular cumulative sum chart is applied to variance estimates calculated from batches of nonoverlapping samples. The proposed chart is applicable to a stationary process with a general marginal distribution and a general autocorrelation structure. It also determines control limits analytically without trial‐and‐error simulations. The performance of the proposed chart is tested on stationary processes with both normal and nonnormal marginals with various autocorrelation structures. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
28.
Numerical dissipation acts as artificial viscosity to make smoke viscous. Reducing numerical dissipation is able to recover visual details smeared out by the numerical dissipation. Great efforts have been devoted to suppress the numerical dissipation in smoke simulation in the past few years. In this paper we investigate methods of combating the numerical dissipation. We describe visual consequences of the numerical dissipation and explore sources that introduce the numerical dissipation into course of smoke simulation. Methods are investigated from various aspects including grid variation, high-order advection, sub-grid compensation, invariant conservation, and particle-based improvement, followed by discussion and comparison in terms of visual quality, computational overhead, ease of implementation, adaptivity, and scalability, which leads to their different applicability to various application scenarios. 相似文献
29.
In the present research, nanostructured Pd–Cd alloy electrocatalysts with different compositions were produced using the electrodeposition process. The morphology of the samples was studied by scanning electron microscopy analysis. Also, the elemental composition of the samples was determined by energy-dispersive X-ray spectroscopy and elemental mapping tests. Tafel polarization and electrochemical impedance spectroscopy methods were employed to determine the electrochemical corrosion properties of the synthesized samples in a solution containing 0.5 M sulfuric acid and 0.1 M formic acid. The linear sweep voltammetry, cyclic voltammetry, and chronoamperometry techniques were also employed to evaluate the electrocatalytic activity of prepared samples toward the oxidation of formic acid. In this respect, the influence of some factors such as formic acid and sulfuric acid concentrations and also potential scan rate was investigated. Compared to the pure Pd sample, the Pd–Cd samples were more reactive for the oxidation of formic acid. Besides, the sample with a lower amount of Pd (Pd1·3Cd) demonstrated much higher electrocatalytic activity than the Pd7·1Cd and Pd2·1Cd samples. The observed high mass activity of 15.06 A mg?1Pd for the Pd1·3Cd sample which is 21.1 times higher than Pd/C is an interesting result of this study. 相似文献
30.
This study addresses the problem of choosing the most suitable probabilistic model selection criterion for unsupervised learning
of visual context of a dynamic scene using mixture models. A rectified Bayesian Information Criterion (BICr) and a Completed
Likelihood Akaike’s Information Criterion (CL-AIC) are formulated to estimate the optimal model order (complexity) for a given
visual scene. Both criteria are designed to overcome poor model selection by existing popular criteria when the data sample
size varies from small to large and the true mixture distribution kernel functions differ from the assumed ones. Extensive
experiments on learning visual context for dynamic scene modelling are carried out to demonstrate the effectiveness of BICr
and CL-AIC, compared to that of existing popular model selection criteria including BIC, AIC and Integrated Completed Likelihood
(ICL). Our study suggests that for learning visual context using a mixture model, BICr is the most appropriate criterion given
sparse data, while CL-AIC should be chosen given moderate or large data sample sizes. 相似文献