全文获取类型
收费全文 | 100437篇 |
免费 | 9059篇 |
国内免费 | 9665篇 |
专业分类
化学 | 32507篇 |
晶体学 | 432篇 |
力学 | 7203篇 |
综合类 | 1480篇 |
数学 | 26732篇 |
物理学 | 24872篇 |
无线电 | 25935篇 |
出版年
2024年 | 244篇 |
2023年 | 1195篇 |
2022年 | 2165篇 |
2021年 | 2530篇 |
2020年 | 2536篇 |
2019年 | 2404篇 |
2018年 | 2015篇 |
2017年 | 2612篇 |
2016年 | 3142篇 |
2015年 | 2967篇 |
2014年 | 4585篇 |
2013年 | 6430篇 |
2012年 | 4976篇 |
2011年 | 5276篇 |
2010年 | 4369篇 |
2009年 | 5430篇 |
2008年 | 6052篇 |
2007年 | 6439篇 |
2006年 | 5960篇 |
2005年 | 5183篇 |
2004年 | 4667篇 |
2003年 | 4616篇 |
2002年 | 4022篇 |
2001年 | 3329篇 |
2000年 | 3235篇 |
1999年 | 2733篇 |
1998年 | 2524篇 |
1997年 | 2108篇 |
1996年 | 1948篇 |
1995年 | 1725篇 |
1994年 | 1598篇 |
1993年 | 1353篇 |
1992年 | 1272篇 |
1991年 | 987篇 |
1990年 | 814篇 |
1989年 | 693篇 |
1988年 | 619篇 |
1987年 | 458篇 |
1986年 | 380篇 |
1985年 | 462篇 |
1984年 | 456篇 |
1983年 | 236篇 |
1982年 | 360篇 |
1981年 | 409篇 |
1980年 | 309篇 |
1979年 | 300篇 |
1978年 | 228篇 |
1977年 | 211篇 |
1976年 | 160篇 |
1974年 | 112篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
3.
如何在互联网时代打造一个信息化的管理模式,已经成为广大学校图书管理发展过程中亟待处理的问题。文章就互联网时代下的高职图书管理信息化建设进行了详细探讨,以期能够给广大同仁提供一些借鉴参考,共同为图书管理工作的现代化改革和发展贡献力量。 相似文献
4.
文章首先对智能化电子信息技术进行了深入的研究,而后分析了该技术在应用过程中出现的问题,最后结合该技术的相关特点给出了相应的问题解决措施,希望能够对智能化电子信息技术的发展提供帮助。 相似文献
5.
6.
《Operations Research Letters》2022,50(2):137-144
In mine planning problems, cutoff grade optimization defines a threshold at every time period such that material above this value is processed, and the rest is considered waste. In orebodies with multiple minerals, which occur in practice, the natural extension is to consider a cutoff surface. We show that in two dimensions the optimal solution is a line, and in n dimensions it is a hyperplane. 相似文献
7.
Manik Chandra Biswas Samit Chakraborty Abhishek Bhattacharjee Zaheeruddin Mohammed 《Advanced functional materials》2021,31(19):2100257
Shape memory materials (SMMs) in 3D printing (3DP) technology garnered much attention due to their ability to respond to external stimuli, which direct this technology toward an emerging area of research, “4D printing (4DP) technology.” In contrast to classical 3D printed objects, the fourth dimension, time, allows printed objects to undergo significant changes in shape, size, or color when subjected to external stimuli. Highly precise and calibrated 4D materials, which can perform together to achieve robust 4D objects, are in great demand in various fields such as military applications, space suits, robotic systems, apparel, healthcare, sports, etc. This review, for the first time, to the best of the authors’ knowledge, focuses on recent advances in SMMs (e.g., polymers, metals, etc.) based wearable smart textiles and fashion goods. This review integrates the basic overview of 3DP technology, fabrication methods, the transition of 3DP to 4DP, the chemistry behind the fundamental working principles of 4D printed objects, materials selection for smart textiles and fashion goods. The central part summarizes the effect of major external stimuli on 4D textile materials followed by the major applications. Lastly, prospects and challenges are discussed, so that future researchers can continue the progress of this technology. 相似文献
8.
This paper infers from a generalized Picone identity the uniqueness of the stable positive solution for a class of semilinear equations of superlinear indefinite type, as well as the uniqueness and global attractivity of the coexistence state in two generalized diffusive prototypes of the symbiotic and competing species models of Lotka–Volterra. The optimality of these uniqueness theorems reveals the tremendous strength of the Picone identity. 相似文献
9.
The effect of the emergency perception of bystanders of cyberbullying victims on helping behaviors is often neglected in research on cyberbullying. In this study, we explored the influence of this cognitive factor on cyber-bystanders’ helping tendencies as well as elucidated possible underlying processes. The results of two studies were reported. In Study 1, 150 undergraduates read a true case of a girl experiencing cyberbullying. The results indicated that when the participants perceived the victim’s situation to be more critical (i.e., higher emergency perception), their helping tendencies were stronger, partly through increased state empathy followed by feelings of responsibility to help. In Study 2, we randomly assigned 300 undergraduates to two groups. The low emergency group read the same cyberbullying case as Study 1, whereas the cyberbullying case read by the high emergency group contained additional emergency information of the victim. The results indicated that the high emergency group expressed stronger helping tendencies than did the low emergency group. This effect was caused by a stronger perception that the victim was in an emergency situation, which not only strengthened the participants’ helping tendencies directly but also indirectly through increasing their state empathy and feelings of responsibility to help. 相似文献
10.
《Annales de l'Institut Henri Poincaré (C) Analyse Non Linéaire》2021,38(5):1337-1371
In this paper we consider minimizers of the functional where is a bounded open set and where are the first k eigenvalues on Ω of an operator in divergence form with Dirichlet boundary condition and with Hölder continuous coefficients. We prove that the optimal sets have finite perimeter and that their free boundary is composed of a regular part, which is locally the graph of a -regular function, and a singular part, which is empty if , discrete if and of Hausdorff dimension at most if , for some . 相似文献