全文获取类型
收费全文 | 15690篇 |
免费 | 1937篇 |
国内免费 | 1484篇 |
专业分类
电工技术 | 676篇 |
技术理论 | 5篇 |
综合类 | 2106篇 |
化学工业 | 912篇 |
金属工艺 | 492篇 |
机械仪表 | 787篇 |
建筑科学 | 1399篇 |
矿业工程 | 402篇 |
能源动力 | 302篇 |
轻工业 | 949篇 |
水利工程 | 536篇 |
石油天然气 | 1391篇 |
武器工业 | 116篇 |
无线电 | 1946篇 |
一般工业技术 | 1078篇 |
冶金工业 | 368篇 |
原子能技术 | 155篇 |
自动化技术 | 5491篇 |
出版年
2024年 | 67篇 |
2023年 | 196篇 |
2022年 | 376篇 |
2021年 | 403篇 |
2020年 | 455篇 |
2019年 | 382篇 |
2018年 | 386篇 |
2017年 | 482篇 |
2016年 | 522篇 |
2015年 | 614篇 |
2014年 | 853篇 |
2013年 | 876篇 |
2012年 | 1030篇 |
2011年 | 1229篇 |
2010年 | 998篇 |
2009年 | 1047篇 |
2008年 | 1109篇 |
2007年 | 1299篇 |
2006年 | 1144篇 |
2005年 | 936篇 |
2004年 | 836篇 |
2003年 | 669篇 |
2002年 | 557篇 |
2001年 | 410篇 |
2000年 | 346篇 |
1999年 | 309篇 |
1998年 | 265篇 |
1997年 | 188篇 |
1996年 | 183篇 |
1995年 | 172篇 |
1994年 | 169篇 |
1993年 | 110篇 |
1992年 | 90篇 |
1991年 | 62篇 |
1990年 | 51篇 |
1989年 | 52篇 |
1988年 | 25篇 |
1987年 | 21篇 |
1986年 | 17篇 |
1985年 | 32篇 |
1984年 | 24篇 |
1983年 | 19篇 |
1982年 | 17篇 |
1981年 | 14篇 |
1980年 | 11篇 |
1979年 | 11篇 |
1978年 | 8篇 |
1977年 | 10篇 |
1975年 | 5篇 |
1973年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
2.
Sama Rezasoltani Reza Ghanbari Mehdi Azizmohammad Looha Ehsan Nazemalhosseini Mojarad Abbas Yadegar Delisha Stewart Hamid Asadzadeh Aghdaei Mohammad Reza Zali 《International journal of molecular sciences》2020,21(23)
Abnormal activation of Toll-like receptor (TLRs) signaling can result in colon cancer development. The aim of this study was to investigate the expression of important TLRs in different histological types of colorectal polyps and evaluate their relationship with intestinal microbiota. The expression levels of TLR2, 3, 4, and 5 were analyzed in intestinal biopsy specimens of 21 hyperplastic polyp (HP), 16 sessile serrated adenoma (SSA), 29 tubular adenoma (TA), 21 villous/tubulovillous (VP/TVP) cases, and 31 normal controls. In addition, selected gut bacteria including Streptococcus bovis, Enterococcus faecalis, Enterotoxigenic Bacteroides fragilis (ETBF), Fusobacterium nucleatum, Porphyromonas spp., Lactobacillus spp., Roseburia spp., and Bifidobacterium spp. were quantified in fecal samples using absolute qRT PCR, and, finally, the association between TLRs and these gut microbiota- was evaluated by Spearman’s correlation coefficient. Higher expression of TLR2 and TLR4 in VP/TVP and TA, and lower expression levels of TLR3 and TLR5 in all type of polyps were observed. The differences in TLR expression patterns was not only dependent on the histology, location, size, and dysplasia grade of polyps but also related to the intestinal microbiota patterns. TLR2 and TLR4 expression was directly associated with the F. nucleatum, E. faecalis, S. bovis, Porphyromonas, and inversely to Bifidobacterium, Lactobacillus, and Roseburia quantity. Furthermore, TLR3 and TLR5 expression was directly associated with Bifidobacterium, Roseburia, and Lactobacillus quantity. Our results suggest a possible critical role of TLRs during colorectal polyp progression. An abnormal regulation of TLRs in relation to gut microbial quantity may contribute to carcinogenesis. 相似文献
3.
Ivonne Sgura Amos S. Lawless Benedetto Bozzini 《Inverse Problems in Science & Engineering》2019,27(5):618-647
The process of electrodeposition can be described in terms of a reaction-diffusion partial differential equation (PDE) system that models the dynamics of the morphology profile and the chemical composition. Here we fit such a model to the different patterns present in a range of electrodeposited and electrochemically modified alloys using PDE constrained optimization. Experiments with simulated data show how the parameter space of the model can be divided into zones corresponding to the different physical patterns by examining the structure of an appropriate cost function. We then use real data to demonstrate how numerical optimization of the cost function can allow the model to fit the rich variety of patterns arising in experiments. The computational technique developed provides a potential tool for tuning experimental parameters to produce desired patterns. 相似文献
4.
《材料科学技术学报》2019,35(7):1309-1314
Degenerate pattern is a seemingly disordered morphology but it exhibits the inherently ordered crystal connected with tip-splitting and limited stability which makes it difficult to observe in the metallic system. Here we employ (100)[011] orientated planar-front seeds using directional solidification and reveal the fundamental origins of the degenerate pattern growth in an Al-4.5 wt% Cu alloy. We find that the spacing of the tip-splitting (λ) in the degenerate of the alloys followed a power law, λ∝V−0.5, and the frequency (f) of the splitting was related to the growth velocity (V) by ƒ∝V1.5. The dimensionless growth direction (θ/θ0) increased monotonously and approached 0.6 with faster velocity, attributed to its anisotropy in the interface kinetics. Once growth velocity exceeded a threshold, two types of pattern transitions from degenerate to regular dendrites were proposed. One of them exhibited a random and chaotic mode and the other underwent a rotation in growth direction. 相似文献
5.
The simultaneous flow of gas, oil, and water forms various flow patterns due to the complex interfacial relationships. Three-phase flow patterns are classified as the gas-liquid and liquid-liquid flow patterns. Pressure drop, void fraction, liquid holdup, and phase distribution are important characteristics of the three-phase flow. These characteristics are generally associated with the three-phase flow patterns. Hence, the knowledge about flow patterns can help to predict the overall behavior of the three-phase flow. Studies have been conducted to identify three-phase flow pattern and their characteristics at various superficial velocities of gas, oil, and water. The major purpose of the studies is to gather information about the three-phase co-current flow and use it for improvement of the efficiency of the flow systems. Therefore, the accuracy of the measurement technique is critical. Several types of flow pattern identification and measurement techniques have been developed to improve accuracy and provide high-quality results. In this article, classical and advanced techniques used for the three-phase flow identification and measurement have been reviewed. The survey will help the researchers working in the area of multiphase flow to choose the right technique based on the objectives of the studies. 相似文献
6.
7.
8.
9.
湖南出土的楚汉丝织品,以马王堆一、三号汉墓所出为代表,其色彩反映了我国当时印染工艺技术所达到的高度水平,其纹饰则显示了鲜明的时代特征,表现了运动、气势和古拙的艺术风格,充满着神奇浪漫的色彩。 相似文献
10.