全文获取类型
收费全文 | 58050篇 |
免费 | 6452篇 |
国内免费 | 3061篇 |
专业分类
化学 | 16591篇 |
晶体学 | 88篇 |
力学 | 3883篇 |
综合类 | 671篇 |
数学 | 11540篇 |
物理学 | 11642篇 |
无线电 | 23148篇 |
出版年
2024年 | 142篇 |
2023年 | 654篇 |
2022年 | 1240篇 |
2021年 | 1389篇 |
2020年 | 1741篇 |
2019年 | 1323篇 |
2018年 | 1306篇 |
2017年 | 1963篇 |
2016年 | 2379篇 |
2015年 | 2368篇 |
2014年 | 3710篇 |
2013年 | 3782篇 |
2012年 | 4057篇 |
2011年 | 4052篇 |
2010年 | 3121篇 |
2009年 | 3296篇 |
2008年 | 3691篇 |
2007年 | 3770篇 |
2006年 | 3371篇 |
2005年 | 3024篇 |
2004年 | 2753篇 |
2003年 | 2459篇 |
2002年 | 2005篇 |
2001年 | 1531篇 |
2000年 | 1288篇 |
1999年 | 1135篇 |
1998年 | 948篇 |
1997年 | 806篇 |
1996年 | 731篇 |
1995年 | 729篇 |
1994年 | 519篇 |
1993年 | 421篇 |
1992年 | 321篇 |
1991年 | 312篇 |
1990年 | 200篇 |
1989年 | 149篇 |
1988年 | 163篇 |
1987年 | 109篇 |
1986年 | 93篇 |
1985年 | 96篇 |
1984年 | 79篇 |
1983年 | 51篇 |
1982年 | 62篇 |
1981年 | 52篇 |
1980年 | 37篇 |
1979年 | 39篇 |
1978年 | 24篇 |
1977年 | 11篇 |
1976年 | 15篇 |
1957年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
141.
Olga V. Zhukova Evgenia V. Arkhipova Tatiana F. Kovaleva Daria A. Zykova Natalya A. Dubovskaya 《Molecules (Basel, Switzerland)》2022,27(14)
Cancer is a leading cause of mortality globally. Despite remarkable improvements in cancer-treatment approaches, disease recurrence and progression remain major obstacles to therapy. While chemotherapy is still a first-line treatment for a variety of cancers, the focus has shifted to the development and application of new approaches to therapy. Nevertheless, the relationship between immune response, neoplastic diseases and treatment efficiency is not fully understood. Therefore, the aim of the study was to investigate the immunopharmacological effects of methacrylic acid homopolymer in an in vivo tumor model. Materials and methods: Monomeric methacrylic acid was used to synthesize polymers. Methacrylic acid was polymerized in dioxane in the presence of 4-Cyano-4-[(dodecylsulfanylthiocarbonyl)sulfanyl]pentanoic acid. To study the molecular weight characteristics of PMAA by GPC, carboxyl groups were preliminarily methylated with diazomethane. An experimental cancer model was obtained by grafting RMK1 breast cancer cells. The serum levels of IL-6, IL-10, IL-17, transforming growth factor β1 (TGF-β1), and tumor necrosis factor α (TNF-α) were measured by ELISA. Results: The effect of PMAA on the serum concentrations of several cytokines was studied upon its single administration to laboratory animals in early neoplastic process. The IL-6, IL-17 and TGF-β1 concentrations were found to change significantly and reach the level observed in intact rats. The IL-10 concentration tended to normalize. Conclusion: The positive results obtained are the basis for further studies on the effect of methacrylic-acid polymers with different molecular-weight characteristics on the neoplastic process. 相似文献
142.
Yue Sun Aidong Xu Kai Wang Xiufang Zhou Haifeng Guo Xiaojia Han 《Entropy (Basel, Switzerland)》2022,24(7)
One of the biggest challenges for the fault diagnosis research of industrial robots is that the normal data is far more than the fault data; that is, the data is imbalanced. The traditional diagnosis approaches of industrial robots are more biased toward the majority categories, which makes the diagnosis accuracy of the minority categories decrease. To solve the imbalanced problem, the traditional algorithm is improved by using cost-sensitive learning, single-class learning and other approaches. However, these algorithms also have a series of problems. For instance, it is difficult to estimate the true misclassification cost, overfitting, and long computation time. Therefore, a fault diagnosis approach for industrial robots, based on the Multiclass Mahalanobis-Taguchi system (MMTS), is proposed in this article. It can be classified the categories by measuring the deviation degree from the sample to the reference space, which is more suitable for classifying imbalanced data. The accuracy, G-mean and F-measure are used to verify the effectiveness of the proposed approach on an industrial robot platform. The experimental results show that the proposed approach’s accuracy, F-measure and G-mean improves by an average of 20.74%, 12.85% and 21.68%, compared with the other five traditional approaches when the imbalance ratio is 9. With the increase in the imbalance ratio, the proposed approach has better stability than the traditional algorithms. 相似文献
143.
144.
针对高速公路交通拥挤和堵塞问题,提出用模糊诱导的方法,对采集的交通信息进行处理后,通过模糊识别的方法,认定其状态,将交通状态数据通过图形化的方法,发布给司乘人员,以达到交通管理的目的。首先分析了交通流状态的表达方法,然后设计出交通状态模糊识别的判断函数,并给出了交通状态模糊表达的处理方法。 相似文献
145.
印制电路板应变测量用应变片选用方法研究 总被引:2,自引:0,他引:2
应变测量由于它的众多优点在电子产品可靠性领域的应用越来越广泛,但电阻应变片的类型繁多,功能各异,以至于使用者很难找到满足自己测试目的和测试环境的应变片。文章提出的选用方法从应变片种类、敏感栅材料、基底材料、电阻值、尺寸、敏感栅结构型式和测试量境温度等方面,综合考虑并结合生产商的应变片型号编码系统,可以快捷地找到适合的印制电路板应变测量用应变片,同时针对绝大多数电子制造商不具备专业应变片检定设备的现实,介绍了一套简单可行的应变片检定工具,并通过两个实例证明该检定方法的可行性。 相似文献
146.
147.
148.
A mathematical representation is given of the processing performed by the peripheral nervous cells of the human visual system. This representation consists essentially of a set of shift-variant convolutions, implying non-uniform resolutions in both the space and frequency domains. A remarkable property of such “convolutions” is the form-invariance of their outputs with respect to (size) linear scalings of the inputs. It is shown that this latter property is a necessary support of the hypothesis according to which the visual system translates linear scalings of the (retinal) inputs into shifts of the (cortical) outputs. 相似文献
149.
150.
分析并总结了体系工程的概念与定义,阐述了体系工程的内涵,提出了体系工程的主要工程实践:需求与顶层设计工程、集成与构建工程及演化与评价工程。以解决体系的构建与演化问题为目标,提出了体系工程过程,分析了体系工程过程与系统工程过程存在的差异。最后讨论了体系工程研究需要解决的关键理论问题。 相似文献