全文获取类型
收费全文 | 161912篇 |
免费 | 24702篇 |
国内免费 | 17535篇 |
专业分类
化学 | 83907篇 |
晶体学 | 1518篇 |
力学 | 8012篇 |
综合类 | 882篇 |
数学 | 14437篇 |
物理学 | 48258篇 |
无线电 | 47135篇 |
出版年
2024年 | 615篇 |
2023年 | 3643篇 |
2022年 | 4711篇 |
2021年 | 5956篇 |
2020年 | 5967篇 |
2019年 | 5659篇 |
2018年 | 4871篇 |
2017年 | 4838篇 |
2016年 | 6920篇 |
2015年 | 7387篇 |
2014年 | 8986篇 |
2013年 | 11553篇 |
2012年 | 13543篇 |
2011年 | 13924篇 |
2010年 | 10304篇 |
2009年 | 10158篇 |
2008年 | 10720篇 |
2007年 | 9842篇 |
2006年 | 9261篇 |
2005年 | 7897篇 |
2004年 | 5636篇 |
2003年 | 4727篇 |
2002年 | 4260篇 |
2001年 | 3541篇 |
2000年 | 3219篇 |
1999年 | 3467篇 |
1998年 | 2956篇 |
1997年 | 2537篇 |
1996年 | 2765篇 |
1995年 | 2233篇 |
1994年 | 2089篇 |
1993年 | 1684篇 |
1992年 | 1548篇 |
1991年 | 1361篇 |
1990年 | 1065篇 |
1989年 | 745篇 |
1988年 | 628篇 |
1987年 | 472篇 |
1986年 | 467篇 |
1985年 | 401篇 |
1984年 | 295篇 |
1983年 | 224篇 |
1982年 | 183篇 |
1981年 | 124篇 |
1980年 | 106篇 |
1979年 | 71篇 |
1978年 | 63篇 |
1977年 | 51篇 |
1976年 | 49篇 |
1974年 | 57篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
941.
Shih-Chang Hsia Szu-Hong Wang 《Very Large Scale Integration (VLSI) Systems, IEEE Transactions on》2007,15(6):725-728
This paper presents a cost-effective 2-D-discrete cosine transform (DCT) architecture based on the fast row/column decomposition algorithm. We propose a new schedule for 2-D-DCT computing to reduce the hardware cost. With this approach, the transposed memory can be simplified using shift-registers for the data transposition between two 1-D-DCT units. A special shift cell with MOS circuit is designed by using the energy transferring methodology. The memory size can be greatly reduced, and the address generator and its READ/WRITE control all can be saved. For an 8 times 8-block transformation, the number of transistors is only 4 k for the shift-register array. The maximum frequency of shift-operation can achieve about 120 MHz, when implemented by 0.35-mum technology. 相似文献
942.
The stagnation slip flow on an axially moving cylinder is studied.The NavierStokes and energy equations reduce to nonlinearordinary differential equations under a similarity transform.For large slip, the flow field decays exponentially into potentialflow. The heat transfer can be expressed as an incomplete gammafunction. In general, the heat transfer increases with slip,Prandtl number and Reynolds number. 相似文献
943.
燃气汽车规模化发展是解决城市环境污染的一个主要途径.以西安市燃气出租车发展问卷调查结果为依据,利用因子分析法对影响燃气出租车发展的变量进行分类.总结出影响燃气出租车发展的八个重要指标,覆涵了政府、加气站、司机个人等方面. 相似文献
944.
Writing-induced nano-deformation of slider body becomes a big concern when the mechanical spacing between the head and disk is continuously reduced to achieve higher magnetic recording areal density. Reduced head–disk spacing increases the risk of head/disk contact and causes the thermal instability in head–disk interface (HDI). This paper reports authors’ efforts towards exploration of interface solutions for writing-induced instability in ultra-low head–disk spacing magnetic system. Multi-shallow step structure with optimized rail position is analyzed and a new femto slider with such structure is explored. The results of numerical simulation indicate that the multi-shallow step structure is an effective approach in reducing the flying height change caused by the writing-induced nano-deformation of the slider body. 相似文献
945.
The synthesis of the title compounds has been achieved in concise, highly regiocontrolled fashion from commercially available (+)-sclareolide. In addition, we offer evidence that the structure of a newly reported natural product from Zingiber ottensii is incorrect. 相似文献
946.
947.
A route to the total synthesis of koumine has been suggested. Five 4-substituted 1, 2-d hydropyridine derivatives, which are supposed to be a conjugated diene of Diels-Alder reaction to produce the isoquinuclidine ring of koumine, have been synthesized. Only two of them were found to be able to undergo the Diels-Alder reaction. The stereochemistry of the reaction product has also been examined. 相似文献
948.
J. Mass M. Avella J. Jimnez M. Callahan E. Grant K. Rakes D. Bliss B. Wang 《Superlattices and Microstructures》2007,42(1-6):306
Understanding the luminescence of ZnO is very important for some applications. In spite of the many studies carried out, there are still some points concerning the origin of some of the luminescence emissions in ZnO crystals that require additional study; in particular, the role of extended defects remains to be a matter of controversy. We present here a cathodoluminescence analysis of the defects generated by Vickers indentation in hydrothermal HTT crystals. Special emphasis was paid to the luminescence band peaking around 3.3 eV. The origin of this band is a matter of controversy, since it has been related to different causes, extended defects being one of the candidates for this emission. The CL images were acquired around crystal defects. It is observed that the 3.3 eV emission is enhanced around the crystal defects; though it is also observed, but weaker, out of the defect regions, which suggests that there exist two luminescence emissions peaking very close to 3.3 eV. The two emissions, one related to structural defects and the other to the LO phonon replica of the free excitonic band, appear very close each other and their relative intensity should determine the shape of the spectrum. 相似文献
949.
950.
王登银 《数学物理学报(B辑英文版)》2007,27(2):317-328
All parabolic subgroups and Borel subgroups of PΩ(2m 1, F) over a linear-able field F of characteristic 0 are shown to be complete groups, provided m > 3. 相似文献