全文获取类型
收费全文 | 44760篇 |
免费 | 7184篇 |
国内免费 | 8171篇 |
专业分类
化学 | 22132篇 |
晶体学 | 833篇 |
力学 | 1607篇 |
综合类 | 950篇 |
数学 | 3634篇 |
物理学 | 11589篇 |
无线电 | 19370篇 |
出版年
2024年 | 185篇 |
2023年 | 622篇 |
2022年 | 1195篇 |
2021年 | 1319篇 |
2020年 | 1212篇 |
2019年 | 1264篇 |
2018年 | 1239篇 |
2017年 | 1430篇 |
2016年 | 1532篇 |
2015年 | 1975篇 |
2014年 | 2366篇 |
2013年 | 3220篇 |
2012年 | 3432篇 |
2011年 | 3576篇 |
2010年 | 3209篇 |
2009年 | 3340篇 |
2008年 | 3714篇 |
2007年 | 3627篇 |
2006年 | 3350篇 |
2005年 | 2889篇 |
2004年 | 2408篇 |
2003年 | 1961篇 |
2002年 | 2098篇 |
2001年 | 1872篇 |
2000年 | 1590篇 |
1999年 | 1049篇 |
1998年 | 610篇 |
1997年 | 521篇 |
1996年 | 477篇 |
1995年 | 426篇 |
1994年 | 366篇 |
1993年 | 369篇 |
1992年 | 311篇 |
1991年 | 223篇 |
1990年 | 206篇 |
1989年 | 184篇 |
1988年 | 134篇 |
1987年 | 116篇 |
1986年 | 87篇 |
1985年 | 81篇 |
1984年 | 69篇 |
1983年 | 55篇 |
1982年 | 39篇 |
1981年 | 39篇 |
1980年 | 19篇 |
1979年 | 21篇 |
1978年 | 15篇 |
1977年 | 10篇 |
1976年 | 12篇 |
1974年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
101.
Various 2-substituted indoles were prepared by heteroannulation of o-iodoanilines and terminal alkynes in a one-pot reaction with a Pd(II)-NaY zeolite catalyst. The product formation largely depended on the solvent, base, and reaction temperature. The recycled catalyst showed good reusability in the heteroannulation reaction. 相似文献
102.
103.
The authors study the singular integrals under the Hormander condition and the measure not satisfying the doubling condition. At first, if the corresponding singular integral is bounded from L2 to itself, it is proved that the maximal singular integral is bounded from L∞to RBMO except that it is infinite μ-a.e. on Rd. A sufficient condition and a necessary condition such that the maximal singular integral is bounded from L2 to itself are also obtained. There is a small gap between the two conditions. 相似文献
104.
105.
Jong-Hwan Kim Yeon-Chan Hong Sung-Jun Lee Keh-Kun Choi 《Industrial Electronics, IEEE Transactions on》1989,36(3):361-364
A direct adaptive control scheme is proposed for nonminimum-phase systems in which controller parameters are estimated from the recursive least-squares algorithm and additional auxiliary parameters are obtained from the proposed polynomial identity. A local convergence is guaranteed without any extra condition. Integral action is incorporated into the adaptive controller to eliminate the steady-state error and to satisfy a condition of the unique solution for the polynomial identity. The control law used in this scheme is based on the set-point-on-I-only proportional-integral-derivative (PID) structure 相似文献
106.
A graph G is N2‐locally connected if for every vertex ν in G, the edges not incident with ν but having at least one end adjacent to ν in G induce a connected graph. In 1990, Ryjá?ek conjectured that every 3‐connected N2‐locally connected claw‐free graph is Hamiltonian. This conjecture is proved in this note. © 2004 Wiley Periodicals, Inc. J Graph Theory 48: 142–146, 2005 相似文献
107.
In the ever fusion experiments in SWIP, pellet forming process was carried out through adjusting relative devices by staff member in site, which will make every pellet-forming process slight distinction and will result in pellet difference in shape, size and intensity. In the intervals of HL-2A discharges, staff member have to go site to accomplish the pellet-forming process, this wastes human power and increase the potential danger. So it is necessary to develop a remote control system to perform the pellet-forming process. The control system needs have the features of real-time, reliability and be easy to operate and maintain. 相似文献
108.
ZHU Yabin ZHOU Yueliang LIU Zhen WANG Shufang CHEN Zhenghao U Huibin YANG Guozhen XlAO Ling Ren Hongtao JIAO Yulei Zheng Minghui 《中国科学G辑(英文版)》2004,47(2):165-172
The irreversibility field (Hirr) of Y-based superconductor is much higher than that of Bi-based superconductor. Y-based superconductor is capable of maintaining stable electrical currents in high magnetic field and electric field, so it is a better suited mate-rial for electric-current applications. Commonly, the Y-based tapes comprise a YBCO thick film deposited on a flexible substrate, typically with an intermediate buffer layer, and an overcoat of noble metal. In this process, the interm… 相似文献
109.
110.
通过重离子核反应与在束γ谱的实验技术, 对A=130缺中子核区的双奇核136La的高自旋态进行了研究, 所用核反应为130Te(11B,5n). 实验结果扩展了136La的能级纲图, 包括3个集体转动带, 最高自旋态达20h. 对于\uppi h_{11/2}\otimes \upnu h_{11/2}$~带, 观测到了旋称反转与集体回弯现象. 通过系统学比较, 对旋称反转特性进行了讨论. 由推转壳模型的计算指出, 此集体回弯是由一对中子的角动量顺排引起的. 另外两个集体带为具有~$\gamma\approx -60^\circ$~的扁椭形变带, 其可能的组态为: $\uppi h_{11/2}\otimes \upnu g_{7/2}h_{11/2}^2$~与~$\uppi g_{7/2}\otimes\upnu g_{7/2}^2 d_{5/2} h_{11/2}^2$. 相似文献