全文获取类型
收费全文 | 68980篇 |
免费 | 5297篇 |
国内免费 | 2738篇 |
学科分类
工业技术 | 77015篇 |
出版年
2024年 | 171篇 |
2023年 | 1060篇 |
2022年 | 1566篇 |
2021年 | 2406篇 |
2020年 | 1949篇 |
2019年 | 1724篇 |
2018年 | 1889篇 |
2017年 | 2179篇 |
2016年 | 1963篇 |
2015年 | 2614篇 |
2014年 | 3230篇 |
2013年 | 3875篇 |
2012年 | 4281篇 |
2011年 | 4513篇 |
2010年 | 3933篇 |
2009年 | 3721篇 |
2008年 | 3653篇 |
2007年 | 3644篇 |
2006年 | 3842篇 |
2005年 | 3324篇 |
2004年 | 2294篇 |
2003年 | 2001篇 |
2002年 | 1928篇 |
2001年 | 1753篇 |
2000年 | 1756篇 |
1999年 | 2011篇 |
1998年 | 1807篇 |
1997年 | 1477篇 |
1996年 | 1410篇 |
1995年 | 1077篇 |
1994年 | 1023篇 |
1993年 | 710篇 |
1992年 | 542篇 |
1991年 | 432篇 |
1990年 | 322篇 |
1989年 | 258篇 |
1988年 | 230篇 |
1987年 | 135篇 |
1986年 | 97篇 |
1985年 | 70篇 |
1984年 | 33篇 |
1983年 | 30篇 |
1982年 | 39篇 |
1981年 | 21篇 |
1980年 | 13篇 |
1979年 | 5篇 |
1978年 | 1篇 |
1976年 | 1篇 |
1959年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
利用芬顿(Fenton)试剂的催化氧化性对焦化废水进行初步的处理,使其CODcr值除去率达80%以上,再用活性炭进行深度处理,使其CODcr值<40mg·L-1,总除去率达98%以上. 相似文献
992.
993.
994.
虚拟实验应用日益广泛,而支持虚拟实验的相关技术成为了研究热点。分析了虚拟化学实验及其在未来虚拟现实技术上的发展趋势,综述了U-nity3D技术、增强现实技术和Kinect体感交互技术的理论基础以及在虚拟化学实验中的应用与发展,以虚拟技术融合的方法为导向,仿真化学实验的实时环境,使虚拟实验简单化、直观化。展望了虚实融合技术在虚拟实验领域的应用前景。虚实融合技术有利于推动虚拟化学实验朝智能化发展,是虚拟实验改革的一个新起点。 相似文献
995.
996.
Hexamethyldisilazane was used as the starting material to synthesize N,N′‐bis(hydroxydiphenylsilanyl)tetraphenylcyclodisilazane (BHPTPC). By condensation polymerization of BHPTPC with α,ω‐bis(dialkylamino)dimethylsiloxane, a series of alternate copolymers containing N,N′‐bis(diphenylsilyl)tetraphenylcyclodisilazane was synthesized. GPC studies show that the highest molecular weight was obtained at a ratio of 1.005 : 1 (BHPTPC: α,ω‐bis(dimethyl amino)dimethylsiloxane). Data of DSC indicate that the temperature of glass transition (Tg) and temperature of melting point (Tm) decreased with the increasing of dimethylsiloxane segments units. Three stages of degradation were found in the thermogravimetric analysis curves. The activation energy of the copolymer (with m = 2, 3, and 7) was calculated by using Flynn–Wall–Ozawa method. The activation energy of the copolymer with m = 2, 3, and 7 at second stage is 214, 211, and 184 kJ/mol, respectively. Isothermal gravimetric analysis shows that for the same temperature and the same time, the weight loss of the alternate copolymer was greatly less than that of common polydimethylsiloxane. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 611–617, 2007 相似文献
997.
Lijin Xie Junfeng Ma Jun Zhou Zhongqiang Zhao Hua Tian Yonggang Wang Jiantao Tao Xiaoyi Zhu 《Journal of the American Ceramic Society》2006,89(5):1717-1720
Well-crystallized bismuth tungstate (Bi2 WO6 ) powders with different morphologies were successfully synthesized via a low-temperature molten salt method. The powders were characterized by X-ray diffraction, transmission electron microscopy, and UV-Vis, respectively. It was found that the variation of morphology of the obtained Bi2 WO6 powder mainly depends on the different reaction temperatures and the weight ratio of LiNO3 –NaNO3 salt to precursor. In addition, the UV-Visible absorption spectra showed that the synthesized powders had strong light absorption properties not only in the ultraviolet light but also in the visible light region. 相似文献
998.
The service mashup programming paradigm is a blooming faction of service oriented Architecture for developing web applications. A mashup application constructs its functionality by combining data, presentation and functionalities obtained from online services published by service providers such as Google and Amazon. This paradigm significantly facilitates the implementation of application and reduces the workload. But it also makes the application rely on the availability and qualities of the online services which beyond its control in which case the robustness of the system requires more concern. This paper proposes a formal model to specify and analyze the behavior and robustness of service mashups under a certain environment where some services may become unavailable. The specification contains both system specification and environment situation. Refinement theory are employed to specify the correctness of dynamic service selection. The framework realizes the service selection by allowing virtual service requests to be handled by any online service having consistent interface and refined functionality. The framework provides a clear definition of the robustness of mashup systems and proposes several rules as well as approaches to preserve the robustness during the development and maintenance of the system. 相似文献
999.
Ji-Hong Zhu Jie Hou Wei-Hong Zhang Yu Li 《Structural and Multidisciplinary Optimization》2014,50(4):561-571
This paper addresses an important problem of design constraints on fastener joint loads that are well recognized in the design of assembled aircraft structures. To avoid the failure of fastener joints, standard topology optimization is extended not only to minimize the structural compliance but also to control shear loads intensities over fasteners. It is shown that the underlying design scheme is to ameliorate the stiffness distribution over the structure in accordance with the control of load distributions over fastener joints. Typical examples are studied by means of topology optimization with joint load constraints and the standard compliance design. The effects of joint load constraints are highlighted by comparing numerical optimization results obtained by both methods. Meanwhile, resin models of optimized designs are fabricated by rapid prototyping process for loading test experiments to make sure the effectiveness of the proposed method. 相似文献
1000.
Guang-yu Zhu Gao-na Lu Chen-Guang Yang Peng Zhang 《Personal and Ubiquitous Computing》2014,18(8):1955-1961
Unified judgment standards and methods are often adopted to identify traffic state in certain road network based on traffic flow parameters. However, drivers often have different perceptions about the traffic state on different road sections, since their expectations on traffic state vary more or less from each other on different road sections. In particular, under the vehicle networking, out of considerations for safety and other relevant factors, requirements for the correlation and coordination of running vehicles have also raised significantly. Therefore, it is necessary to take driver’s perception about the driving conditions of certain road sections into consideration to adjust the release of traffic state. This paper has provided a comprehensive traffic state evaluation model linked with driver’s perception under the vehicle networking. The authors first establish an ANFIS model based on the T–S model and then conduct statistical analysis on drivers’ perceptions about certain traffic state. At last, the authors use the results of statistical analysis as regulatory factors to amend the parameters input through ANFIS. Through simulation, this paper has demonstrated that the model established has a high rate of convergence, a high identification precision and the generalization ability to conduct researches on the identification of traffic state. 相似文献