全文获取类型
收费全文 | 34327篇 |
免费 | 2460篇 |
国内免费 | 946篇 |
专业分类
电工技术 | 1459篇 |
技术理论 | 4篇 |
综合类 | 1548篇 |
化学工业 | 5639篇 |
金属工艺 | 1522篇 |
机械仪表 | 1666篇 |
建筑科学 | 1682篇 |
矿业工程 | 744篇 |
能源动力 | 1187篇 |
轻工业 | 2201篇 |
水利工程 | 446篇 |
石油天然气 | 992篇 |
武器工业 | 146篇 |
无线电 | 5370篇 |
一般工业技术 | 5040篇 |
冶金工业 | 2755篇 |
原子能技术 | 387篇 |
自动化技术 | 4945篇 |
出版年
2023年 | 418篇 |
2022年 | 619篇 |
2021年 | 1117篇 |
2020年 | 905篇 |
2019年 | 785篇 |
2018年 | 887篇 |
2017年 | 928篇 |
2016年 | 855篇 |
2015年 | 1063篇 |
2014年 | 1407篇 |
2013年 | 2117篇 |
2012年 | 1990篇 |
2011年 | 2311篇 |
2010年 | 1839篇 |
2009年 | 1881篇 |
2008年 | 1937篇 |
2007年 | 1741篇 |
2006年 | 1575篇 |
2005年 | 1259篇 |
2004年 | 1110篇 |
2003年 | 1186篇 |
2002年 | 1393篇 |
2001年 | 1156篇 |
2000年 | 773篇 |
1999年 | 638篇 |
1998年 | 972篇 |
1997年 | 672篇 |
1996年 | 554篇 |
1995年 | 472篇 |
1994年 | 391篇 |
1993年 | 334篇 |
1992年 | 241篇 |
1991年 | 222篇 |
1990年 | 224篇 |
1989年 | 199篇 |
1988年 | 170篇 |
1987年 | 149篇 |
1986年 | 127篇 |
1985年 | 125篇 |
1984年 | 107篇 |
1983年 | 75篇 |
1982年 | 70篇 |
1981年 | 62篇 |
1980年 | 81篇 |
1979年 | 49篇 |
1978年 | 60篇 |
1977年 | 60篇 |
1976年 | 78篇 |
1975年 | 43篇 |
1973年 | 38篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
51.
Waste ceramic sands were effectively used to prepare the high-intensity and low-density ceramic proppants, realising the recycling of the waste ceramic sands. The technology involved the pelletising in an intensive mixer, in which the waste ceramic sands and other starting materials were added, and followed by heat-treatment under different sintering conditions. The sintering temperature, holding time and heating rate were optimised by investigating the crystalline phase, microstructure, density and breakage ratio of the obtained proppants. The results showed that the proppants sintered at 1260°C for 2?h with a heating rate of 5°C?min–1 under air atmosphere exhibited high crush resistance and low density, with the breakage ratio of 8.5% under 52?MPa closure pressure and bulk density of 1.65?g?cm–3. The proppants prepared by bauxite, waste ceramic sands and sintering aids are promising candidates as high-intensity and low-density fracturing proppants in future applications. 相似文献
52.
轧辊氧化膜形成及剥落显著影响轧辊的辊耗及钢板的表面质量。为控制轧辊的氧化行为,采用增重法研究离心铸造高铬铸钢轧辊在大气及水蒸气环境中的氧化行为,并采用金相显微镜(OM)、扫描电子显微镜(SEM)、X射线衍射(XRD)等方法研究了高铬铸钢组织及氧化膜的结构。结果表明,高铬铸钢组织为回火马氏体基体和共晶Cr7C3碳化物;氧化过程中基体优先被氧化,粗大碳化物表面几乎不被氧化;温度及环境对氧化膜生长及相结构都有一定的影响,高温及水蒸气环境加速氧化,并促进γ Fe2O3向γ Fe3O3转化。因此,控制轧辊的氧化,关键是控制轧辊的使用温度。 相似文献
53.
目的 高光谱图像波段数目巨大,导致在解译及分类过程中出现“维数灾难”的现象。针对该问题,在K-means聚类算法基础上,考虑各个波段对不同聚类的重要程度,同时顾及类间信息,提出一种基于熵加权K-means全局信息聚类的高光谱图像分类算法。方法 首先,引入波段权重,用来刻画各个波段对不同聚类的重要程度,并定义熵信息测度表达该权重。其次,为避免局部最优聚类,引入类间距离测度实现全局最优聚类。最后,将上述两类测度引入K-means聚类目标函数,通过最小化目标函数得到最优分类结果。结果 为了验证提出的高光谱图像分类方法的有效性,对Salinas高光谱图像和Pavia University高光谱图像标准图中的地物类别根据其光谱反射率差异程度进行合并,将合并后的标准图作为新的标准分类图。分别采用本文算法和传统K-means算法对Salinas高光谱图像和Pavia University高光谱图像进行实验,并定性、定量地评价和分析了实验结果。对于图像中合并后的地物类别,光谱反射率差异程度大,从视觉上看,本文算法较传统K-means算法有更好的分类结果;从分类精度看,本文算法的总精度分别为92.20%和82.96%, K-means算法的总精度分别为83.39%和67.06%,较K-means算法增长8.81%和15.9%。结论 提出一种基于熵加权K-means全局信息聚类的高光谱图像分类算法,实验结果表明,本文算法对高光谱图像中具有不同光谱反射率差异程度的各类地物目标均能取得很好的分类结果。 相似文献
54.
This study assessed the collection efficiency (CE) of two popularly used sampling devices (BioSampler and Coriolis sampler) for fungal aerosols. Phosphate‐buffered saline (PBS) supplemented with or without surfactant (Tween‐20, Tween‐80, or Triton X‐100) and antifoam agent was prepared and used as collection liquids. The agar impactor (BioStage) was simultaneously operated with liquid‐based samplers to collect fungi from seven sites located at a university building, public library, and animal farming. Fungal concentrations determined by liquid samplers were divided by those by BioStage, and the ratio values represented CE. Results indicate that the CE of BioSampler was superior to that of Coriolis (P = 0.0001) and the PBS containing surfactant collected fungi better than that without surfactant (P < 0.0001), whereas antifoam agent showed no influence (P = 0.8). Moreover, fungal concentrations determined by BioSampler with surfactant‐added PBS were statistically indifferent from those by BioStage (P > 0.05) with a Spearman correlation coefficient of 0.81‐0.83 (P < 0.01). In addition to sampler and collection liquid, sampling location was also identified as a significant CE factor (P = 0.006), implying potential influences by fungal genera in the studied fields. Overall, BioSampler with surfactant‐supplemented PBS (eg, Triton X‐100) is recommended considering the great CE and compatibility with a variety of analytical assays. 相似文献
55.
Strength of Materials - The lightweight ceramic/aluminum alloy composite armor design is examined and optimized to get better protective performance. The armor penetrability is simulated via the... 相似文献
56.
Sustainable biocomposites have gained considerable interest as an alternative to conventional composites in recent years due to their cost-effectiveness and environmental friendliness. The aim of this study was to investigate the performance and durability behavior of biocomposites from sustainable biocarbon (BC) as compared to conventional established fillers. The poly(butylene terephthalate) (PBT) and its composites reinforced with BC, talc, and glass fiber (GF) were prepared and the durability performances was investigated. The study showed that BC/PBT biocomposites provided a lighter weight alternative to traditionally used fillers. After undergoes thermo-oxidative aging, the mechanical properties of BC/PBT biocomposite were deteriorated. The GF/PBT showed the most stable in retaining its mechanical properties in comparison to the talc/PBT and BC/PBT. The aging behavior and mechanism of the PBT composites were discussed. This study provides further insight on the durability-related properties progression of biocomposites as compared to traditional used fillers. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47722. 相似文献
57.
Xue Dingchuan Zhu Yichao Li Shaoshuai Liu Chang Zhang Weisheng Guo Xu 《Structural and Multidisciplinary Optimization》2020,61(2):457-474
Structural and Multidisciplinary Optimization - Surrogate modeling is commonly used to replace expensive simulations of engineering problems. Kriging is a popular surrogate for deterministic... 相似文献
58.
Min Wang Jingwen Ma Qingbo Chang Xiaobin Fan Guoliang Zhang Fengbao Zhang Wenchao Peng Yang Li 《Ceramics International》2018,44(5):5250-5256
Herein, a novel nanocomposite of binary ZnO–CoO nanoparticles loaded on the graphene nanosheets (ZnO–CoO/rGO) has been successfully constructed via a facile, economical and two–step process. The obtained ZnO–CoO/rGO hybrids with high electrical conductivity and abundant active sites, could be modified on a glassy carbon electrode to detect glucose and H2O2 multi–functionally. The fabricated biosensor exhibits wide linear range for glucose (10 μM to 11.205 mM) and H2O2 (25 μM to 11.1 mM), and their corresponding sensitivity are 168.7 μA mM?1 cm?2 and 183.3 μA mM?1 cm?2. The limits of detection are 1.3 μM and 0.44 μM for the oxidation of glucose and the reduction of H2O2, respectively. Furthermore, remarkable selectivity, long–term stability and outstanding reproducibility of the non–enzyme biosensor prove that ZnO–CoO/rGO hybrids are the promising candidate in practical applications. 相似文献
59.
Water-lubricated polymer is attracting more and more interest from the industry. Adding nanoparticles is considered to be an effective way to improve the tribological performance. In this work, water-lubricated Polyetheretherketone (PEEK)-steel contacts were employed as the objects of study. A careful comparative study was made by investigating the effect of adding graphene oxide (GO) into water or into PEEK. Results show that adding GO into water can significantly reduce the wear and friction coefficient of pure PEEK, which is much more effective than adding GO into PEEK. Under the lubrication of GO aqueous dispersion, the wear of PEEK remains very low even under a harsh condition where the pressure reaches 50 MPa and the linear sliding speed is 0.7 m/s. Neat PEEK and GO/PEEK composites in pure water exhibit serious wear under this harsh condition. The excellent lubricating properties of GO aqueous dispersion are attributed to GO nanosheets entering into solid contacts, which can not only form a protective layer on steel counterpart repairing the worn surface, but also strongly adhere to the PEEK matrix resulting in an in situ-formed GO coating and prevent the scratch by steel counterpart. 相似文献
60.