全文获取类型
收费全文 | 16983篇 |
免费 | 2622篇 |
国内免费 | 1831篇 |
专业分类
化学 | 9093篇 |
晶体学 | 122篇 |
力学 | 884篇 |
综合类 | 88篇 |
数学 | 1615篇 |
物理学 | 5047篇 |
无线电 | 4587篇 |
出版年
2024年 | 74篇 |
2023年 | 450篇 |
2022年 | 520篇 |
2021年 | 688篇 |
2020年 | 659篇 |
2019年 | 562篇 |
2018年 | 547篇 |
2017年 | 497篇 |
2016年 | 692篇 |
2015年 | 785篇 |
2014年 | 914篇 |
2013年 | 1215篇 |
2012年 | 1349篇 |
2011年 | 1355篇 |
2010年 | 996篇 |
2009年 | 941篇 |
2008年 | 1047篇 |
2007年 | 989篇 |
2006年 | 917篇 |
2005年 | 751篇 |
2004年 | 524篇 |
2003年 | 444篇 |
2002年 | 428篇 |
2001年 | 388篇 |
2000年 | 344篇 |
1999年 | 406篇 |
1998年 | 357篇 |
1997年 | 286篇 |
1996年 | 334篇 |
1995年 | 297篇 |
1994年 | 258篇 |
1993年 | 209篇 |
1992年 | 183篇 |
1991年 | 184篇 |
1990年 | 166篇 |
1989年 | 123篇 |
1988年 | 108篇 |
1987年 | 82篇 |
1986年 | 65篇 |
1985年 | 65篇 |
1984年 | 33篇 |
1983年 | 36篇 |
1982年 | 35篇 |
1981年 | 25篇 |
1980年 | 14篇 |
1979年 | 14篇 |
1978年 | 9篇 |
1977年 | 12篇 |
1974年 | 9篇 |
1973年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
Bursts consist of a varying number of asynchronous transfer mode cells corresponding to a datagram. Here, we generalized weighted fair queueing to a burst-based algorithm with preemption. The new algorithm enhances the performance of the switch service for real-time applications, and it preserves the quality of service guarantees. We study this algorithm theoretically and via simulations. 相似文献
132.
133.
134.
Applied Biochemistry and Biotechnology - A novel, anaerobic fermentation process is developed to produce calcium magnesium acetate (CMA) from cheese whey. CMA can be used as a noncorrosive road... 相似文献
135.
136.
HAO Wei-Fang Tang Hui ZHU Xiao-Qing CHENG Jin-Pei 《有机化学》2003,23(Z1):172-172
Great interests have been accumulated in recent years in the chemistry and biochemistry of nitric oxide (NO) since the remarkable discoveries of its key roles in a wide range of human physiological processes. To elucidate the mechanistic details of NO migration from its donor to its acceptor, it is necessary to determine the Y-NO bind energy that registers the thermodynamic driving force for NO release and capture. In this paper the heterolytic and homolytic N-NO bond dissociation energies [ i. e., △Hhet(N-NO) and △Hhomo(N-NO)] for ten N-nitroso-p-substituted-benzensulfonyl methylamines in acetonitrile are offered, which were obtained from titration calorimetry and thermodynamic cycles, respectively (Scheme 1). 相似文献
137.
138.
工程上对片筏的力学分析,通常采用温克勒地基模型,且假定床基系数是常量。本则认为床基系数是坐标的函数,考虑了具有线性变化床基系数的地基上的片筏,利用伽辽金法求得周边固支片筏在均布荷载作用下的挠度。所得结果颇具一般性且实用价值更高。 相似文献
139.
For improved mechanical and water‐swelling properties of chitosan films, a series of transparent films were prepared with dialdehyde starch as a crosslinking agent. Fourier transform infrared and X‐ray analysis results demonstrated that the formation of Schiff's base disturbed the crystallization of chitosan. The mechanical properties and water‐swelling properties of the films were significantly improved. The best values of the tensile strength and breaking elongation were 113.1 MPa and 27.0%, respectively, when the dialdehyde starch content was 5%. All the crosslinked films still retained obvious antimicrobial effects toward S. aureus and E. coli, and they showed potential for biomedical applications. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 993–997, 2003 相似文献
140.
Yuxin Leng Lihuang Lin Wenyao Wang Yunhua Jiang Bin Tang Zhizhan Xu 《Optics & Laser Technology》2003,35(6):425-429
A birefringent crystal quartz plate of known thickness has been used as a spectral filter for spectral shaping in a Ti:sapphire regenerative amplifier. The spectral profile of the amplified pulse ejected from the regenerative amplifier was observed while adjusting the birefringent crystal plate in the cavity. By altering the gain spectrum, the bandwidth of the regeneratively amplified pulse was increased from 18 to 35 nm by using a 0.34-mm thick birefringent plate. The output pulse spectrum from the regenerative amplifier neared the bandwidth of the seed pulse. As a comparison, we used a coated filter outside the regenerative amplifier cavity, and the bandwidth of the regeneratively amplified pulse was stretched to 28 nm. When the bandwidth was stretched to 35 nm, the pulse was compressed to 35 fs. 相似文献