全文获取类型
收费全文 | 155852篇 |
免费 | 17534篇 |
国内免费 | 12360篇 |
专业分类
电工技术 | 13715篇 |
技术理论 | 3篇 |
综合类 | 18028篇 |
化学工业 | 20934篇 |
金属工艺 | 10356篇 |
机械仪表 | 11305篇 |
建筑科学 | 11480篇 |
矿业工程 | 6506篇 |
能源动力 | 4227篇 |
轻工业 | 15700篇 |
水利工程 | 4476篇 |
石油天然气 | 6513篇 |
武器工业 | 2047篇 |
无线电 | 15962篇 |
一般工业技术 | 13914篇 |
冶金工业 | 6079篇 |
原子能技术 | 2392篇 |
自动化技术 | 22109篇 |
出版年
2024年 | 737篇 |
2023年 | 2308篇 |
2022年 | 5543篇 |
2021年 | 7299篇 |
2020年 | 5187篇 |
2019年 | 3824篇 |
2018年 | 4198篇 |
2017年 | 4712篇 |
2016年 | 4366篇 |
2015年 | 6670篇 |
2014年 | 8218篇 |
2013年 | 9934篇 |
2012年 | 12026篇 |
2011年 | 12379篇 |
2010年 | 11576篇 |
2009年 | 11293篇 |
2008年 | 11364篇 |
2007年 | 11660篇 |
2006年 | 10596篇 |
2005年 | 8518篇 |
2004年 | 6678篇 |
2003年 | 5893篇 |
2002年 | 5713篇 |
2001年 | 4995篇 |
2000年 | 3639篇 |
1999年 | 1785篇 |
1998年 | 918篇 |
1997年 | 695篇 |
1996年 | 515篇 |
1995年 | 483篇 |
1994年 | 344篇 |
1993年 | 273篇 |
1992年 | 240篇 |
1991年 | 206篇 |
1990年 | 153篇 |
1989年 | 142篇 |
1988年 | 124篇 |
1987年 | 70篇 |
1986年 | 63篇 |
1985年 | 55篇 |
1984年 | 34篇 |
1983年 | 42篇 |
1982年 | 24篇 |
1981年 | 39篇 |
1980年 | 62篇 |
1979年 | 30篇 |
1978年 | 8篇 |
1977年 | 9篇 |
1959年 | 35篇 |
1951年 | 33篇 |
排序方式: 共有10000条查询结果,搜索用时 125 毫秒
51.
52.
Metamerism phenomenon can be used in illuminant detection to ensure the accuracy of light source. A method based on Long‐, Middle‐, Short‐ wavelength cones(LMS) weighting algorithm to evaluate metamerism degree is proposed. The chromatic relationship between the degree of metamerism mismatch and the light source is studied. Herein, the consistency between the metameric indices (MIs) and CIE1976 L*a*b* color difference ranking is analyzed by SRCC, KRCC, PLCC and RMSE. A statistically sampling method to obtain practical LMS cone fundamentals to evaluate metamerism degree is employed. The analysis results obtained show that the method based on LMS weighting algorithm has good evaluation ability and stability in simulation experiments and statistically sampling experiments, which are in line with visual characteristics of human. Proposed method meets the requirements of selecting metameric pairs used in light source detection. The analysis results have certain guiding significance. 相似文献
53.
Research funding has been seen as one of the most important resource in the reward system of science. And usage of publications denotes an interesting perspective of user behavior in scientific communication. This study aims to address the relationship between funding and Usage Count, which is a new metrics item established on the platform of Web of Science. Full records of 300,010 articles published in 2013 were downloaded in October 2015, and divided into six disciplines, including information science library science, education educational research, economics, computer science, materials science, and chemistry. Seven indicators were proposed to measure the impact, including Funding rate, Citation per paper, Usage rate, Usage per paper, Citation difference, Usage difference, and Conversion rate. It concluded funding has impact on usage and citation, and funded papers attract more usage, but varying in different disciplines. Usage Count can be used in the extension of citation metrics but with limits. This study originally engages with usage metrics and detected that there is positive correlation between usage and funding. 相似文献
54.
磷石膏堆场的渗流及稳定性分析结果的可靠度取决于磷石膏物理力学参数的准确性,因此开展磷石膏工程特性研究十分必要。根据我国不同磷石膏堆场的试验数据,分别对磷石膏的物理性质、击实特性、渗透特性、固结特性和强度特性进行了分析。结果表明:磷石膏强度、压缩、渗透特性均与其压实程度密切相关,相同压实程度不同堆场磷石膏的物理力学性质相近;磷石膏渗透特性与其晶体形态有关;磷石膏在荷载作用下具有长期蠕变变形特性,磷石膏堆场封场后仍会发生较大沉降;深部磷石膏破坏时的应变大于浅层磷石膏;磷石膏剪切破坏时产生负孔隙水压力,实际工程中可通过测试孔压的变化了解堆场坝体的安全程度。 相似文献
55.
56.
地质特征认识对煤层气开发效果起着重要作用。在资源特征相差不大的情况下,发现煤层气相邻井的产量差异仍较大。排除工程因素后,通过选取8类地质参数,细致比对了保德区块低产井与邻井的参数特征,筛查出其关键因素为煤层微幅构造与顶板封盖条件,其中以微幅构造为主。据此,重新认识并划分出区块新的次生褶皱背斜单元、向斜单元和斜坡单元,获得了不同次生褶皱构造单元的开发特征。结果表明,高、低产井分布与次生褶皱背斜、向斜相关性高达92%。其中:高产井主要分布在次生褶皱背斜变化较缓、呈隆起状的“平台”,且煤层顶板以泥岩、碳质泥岩为主,封盖性较好;低产井主要分布在次生褶皱向斜,同一井台各井开发效果差异表现为从向斜条带轴部—向斜条带内—向斜条带外的煤层气井平均单井产量不断增加,到向斜轴部的距离大于向斜曲率半径73.5%的范围为主力产气区,小于向斜曲率半径40.0%范围为产水主力区。这对煤层气新井部署、生产管理、开发调整等,具有一定的指导意义。 相似文献
57.
58.
59.
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
60.
A novel dual-rotation bobbin tool friction stir welding (DBT-FSW) was developed, in which the upper shoulder (US) and lower shoulder (LS) have different rotational speeds. This process was tried to weld 3.2 mm thick aluminum-lithium alloy sheets. The metallographic analysis and torque measurement were carried out to characterize the weld formability. Experimental results show that compared to conventional bobbin tool friction stir welding, the DBT-FSW has an excellent process stability, and can produce the defect-free joints in a wider range of welding parameters. These can be attributed to the significant improvement of material flow caused by the formation of a staggered layer structure and the unbalanced force between the US and LS during the DBT-FSW process. 相似文献