全文获取类型
收费全文 | 98586篇 |
免费 | 5980篇 |
国内免费 | 5245篇 |
专业分类
电工技术 | 5301篇 |
技术理论 | 5篇 |
综合类 | 10083篇 |
化学工业 | 13266篇 |
金属工艺 | 6082篇 |
机械仪表 | 3642篇 |
建筑科学 | 4712篇 |
矿业工程 | 1538篇 |
能源动力 | 3175篇 |
轻工业 | 6053篇 |
水利工程 | 2325篇 |
石油天然气 | 4279篇 |
武器工业 | 830篇 |
无线电 | 7712篇 |
一般工业技术 | 14990篇 |
冶金工业 | 3129篇 |
原子能技术 | 2219篇 |
自动化技术 | 20470篇 |
出版年
2024年 | 107篇 |
2023年 | 530篇 |
2022年 | 819篇 |
2021年 | 1074篇 |
2020年 | 1464篇 |
2019年 | 1367篇 |
2018年 | 1419篇 |
2017年 | 1414篇 |
2016年 | 1924篇 |
2015年 | 2667篇 |
2014年 | 4595篇 |
2013年 | 5316篇 |
2012年 | 4732篇 |
2011年 | 5402篇 |
2010年 | 4521篇 |
2009年 | 5946篇 |
2008年 | 5905篇 |
2007年 | 6265篇 |
2006年 | 5718篇 |
2005年 | 4805篇 |
2004年 | 4121篇 |
2003年 | 4010篇 |
2002年 | 3949篇 |
2001年 | 2961篇 |
2000年 | 3322篇 |
1999年 | 3055篇 |
1998年 | 2558篇 |
1997年 | 2440篇 |
1996年 | 2591篇 |
1995年 | 2720篇 |
1994年 | 2471篇 |
1993年 | 1500篇 |
1992年 | 1536篇 |
1991年 | 1049篇 |
1990年 | 779篇 |
1989年 | 683篇 |
1988年 | 648篇 |
1987年 | 387篇 |
1986年 | 235篇 |
1985年 | 376篇 |
1984年 | 418篇 |
1983年 | 437篇 |
1982年 | 336篇 |
1981年 | 407篇 |
1980年 | 274篇 |
1979年 | 118篇 |
1978年 | 112篇 |
1977年 | 74篇 |
1976年 | 40篇 |
1975年 | 57篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
1.
2.
《Ceramics International》2022,48(3):3544-3553
In this study the effects of thermal shock on the impact damage resistance, damage tolerance and flexural strength of Nextel 610/alumina silicate ceramic matrix composites were experimentally evaluated. Composite laminates with balanced and symmetric layup were gradually heated to 1200°C in an air-based furnace and held for at least 30 min before being removed and immersed in water at room temperature. The laminates were then subjected to low velocity impacts via a hemispherical steel impactor. The resultant damage was characterized non-destructively, following which the laminates were subjected to compression tests. Three-point bend tests were also performed to evaluate the effect of thermal shock on the flexural strength and related failure modes of the laminates. Thermally shocked laminates showed smaller internal damage and larger external damage areas in comparison to their pristine counterparts. For the impact energy and resultant damage size considered, the residual compressive strengths for the thermally shocked and pristine laminates were similar. 相似文献
3.
《中国有色金属学会会刊》2021,31(10):3063-3074
The transient liquid phase (TLP) bonding of CoCuFeMnNi high entropy alloy (HEA) was studied. The TLP bonding was performed using AWS BNi-2 interlayer at 1050 °C with the TLP bonding time of 20, 60, 180 and 240 min. The effect of bonding time on the joint microstructure was characterized by SEM and EDS. Microstructural results confirmed that complete isothermal solidification occurred approximately at 240 min of bonding time. For samples bonded at 20, 60 and 180 min, athermal solidification zone was formed in the bonding area which included Cr-rich boride and Mn3Si intermetallic compound. For all samples, the γ solid solution was formed in the isothermal solidification zone of the bonding zone. To evaluate the effect of TLP bonding time on mechanical properties of joints, the shear strength and micro-hardness of joints were measured. The results indicated a decrement of micro-hardness in the bonding zone and an increment of micro-hardness in the adjacent zone of joints. The minimum and maximum values of shear strength were 100 and 180 MPa for joints with the bonding time of 20 and 240 min, respectively. 相似文献
4.
In Vivo Simultaneous Analysis of Gene Expression by Dual-Color Luciferases in Caenorhabditis elegans
Both fluorescent and luminescent observation are widely used to examine real-time gene expression patterns in living organisms. Several fluuorescent and luminescent proteins with specific optical properties have been developed and applied for simultaneous, multi-color observation of more than two gene expression profiles. Compared to fluorescent proteins, however, the application of multi-color luminescent imaging in living organisms is still limited. In this study, we introduced two-color luciferases into the soil nematode C. elegans and performed simultaneous analysis of two gene expression profiles. Using a green-emitting luciferase Eluc (emerald luciferase) and red-emitting luciferase SLR (stable luciferase red), the expression patterns of two genes were simultaneously observed in single animals from embryonic to adult stages over its whole life span. In addition, dual gene activities were observed at the single embryo level, with the simultaneous observation of morphological changes. These are the first application of a two-color luciferase system into a whole animal and suggest that precise relationship of expression patterns of multiple genes of interest can be analyzed over the whole life of the animal, dependent on the changes in genetic and/or environmental conditions. 相似文献
5.
6.
Weronika Gonciarz ukasz Lechowicz Mariusz Urbaniak Wiesaw Kaca Magdalena Chmiela 《International journal of molecular sciences》2021,22(1)
Infections due to Gram-negative bacteria Helicobacter pylori may result in humans having gastritis, gastric or duodenal ulcer, and even gastric cancer. Investigation of quantitative changes of soluble biomarkers, correlating with H. pylori infection, is a promising tool for monitoring the course of infection and inflammatory response. The aim of this study was to determine, using an experimental model of H. pylori infection in guinea pigs, the specific characteristics of infrared spectra (IR) of sera from H. pylori infected (40) vs. uninfected (20) guinea pigs. The H. pylori status was confirmed by histological, molecular, and serological examination. The IR spectra were measured using a Fourier-transform (FT)-IR spectrometer Spectrum 400 (PerkinElmer) within the range of wavenumbers 3000–750 cm−1 and converted to first derivative spectra. Ten wavenumbers correlated with H. pylori infection, based on the chi-square test, were selected for a K-nearest neighbors (k-NN) algorithm. The wavenumbers correlating with infection were identified in the W2 and W3 windows associated mainly with proteins and in the W4 window related to nucleic acids and hydrocarbons. The k-NN for detection of H. pylori infection has been developed based on chemometric data. Using this model, animals were classified as infected with H. pylori with 100% specificity and 97% sensitivity. To summarize, the IR spectroscopy and k-NN algorithm are useful for monitoring experimental H. pylori infection and related inflammatory response in guinea pig model and may be considered for application in humans. 相似文献
7.
Saerom Lee Ga-Eun Lim Yong-Nyun Kim Hyeon-Sook Koo Jaegal Shim 《International journal of molecular sciences》2021,22(4)
The extracellular matrix (ECM) is important for normal development and disease states, including inflammation and fibrosis. To understand the complex regulation of ECM, we performed a suppressor screening using Caenorhabditis elegans expressing the mutant ROL-6 collagen protein. One cuticle mutant has a mutation in dpy-23 that encodes the μ2 adaptin (AP2M1) of clathrin-associated protein complex II (AP-2). The subsequent suppressor screening for dpy-23 revealed the lon-2 mutation. LON-2 functions to regulate body size through negative regulation of the tumor growth factor-beta (TGF-β) signaling pathway responsible for ECM production. RNA-seq analysis showed a dominant change in the expression of collagen genes and cuticle components. We noted an increase in the cav-1 gene encoding caveolin-1, which functions in clathrin-independent endocytosis. By knockdown of cav-1, the reduced TGF-β signal was significantly restored in the dpy-23 mutant. In conclusion, the dpy-23 mutation upregulated cav-1 expression in the hypodermis, and increased CAV-1 resulted in a decrease of TβRI. Finally, the reduction of collagen expression including rol-6 by the reduced TGF-β signal influenced the cuticle formation of the dpy-23 mutant. These findings could help us to understand the complex process of ECM regulation in organism development and disease conditions. 相似文献
8.
9.
《Journal of the European Ceramic Society》2021,41(13):6290-6301
In this study, monolithic B4C and B4C-based ceramics incorporating FeNiCoCrMo dual-phase (FCC and BCC) high entropy alloys (HEAs) were produced by spark plasma sintering (SPS). The effect of additives on the densification behavior, mechanical properties, microstructures, and phase evaluation of the samples were investigated. X-ray analysis confirmed the existence of FCC structured HEA and depletion of BCC structured HEA, after high-temperature reaction between B4C-HEAs. The addition of HEAs enhanced the densification behavior by liquid phase sintering. Furthermore, hardness and fracture toughness values of the samples increased with increasing HEAs content. Fracture toughness and hardness values for all composites were higher than the monolithic B4C. A combination of the highest density (∼99.22 %) and the best mechanical properties (32.3 GPa hardness and 4.53 MPa m1/2 fracture toughness) was achieved with 2.00 vol.% HEA addition. 相似文献
10.
The mechanical properties of complex concentrated alloys (CCAs) depend on their formed phases and corresponding microstructures.The data-driven prediction of the phase formation and associated mechanical properties is essential to discovering novel CCAs.The present work collects 557 samples of various chemical compositions,comprising 61 amorphous,167 single-phase crystalline,and 329 multi-phases crystalline CCAs.Three classification models are developed with high accuracies to category and understand the formed phases of CCAs.Also,two regression models are constructed to predict the hard-ness and ultimate tensile strength of CCAs,and the correlation coefficient of the random forest regression model is greater than 0.9 for both of two targeted properties.Furthermore,the Shapley additive expla-nation (SHAP) values are calculated,and accordingly four most important features are identified.A significant finding in the SHAP values is that there exists a critical value in each of the top four fea-tures,which provides an easy and fast assessment in the design of improved mechanical properties of CCAs.The present work demonstrates the great potential of machine learning in the design of advanced CCAs. 相似文献