全文获取类型
收费全文 | 10623篇 |
免费 | 1458篇 |
国内免费 | 883篇 |
专业分类
化学 | 2272篇 |
晶体学 | 114篇 |
力学 | 941篇 |
综合类 | 175篇 |
数学 | 2494篇 |
物理学 | 2602篇 |
无线电 | 4366篇 |
出版年
2024年 | 28篇 |
2023年 | 112篇 |
2022年 | 205篇 |
2021年 | 281篇 |
2020年 | 310篇 |
2019年 | 264篇 |
2018年 | 264篇 |
2017年 | 385篇 |
2016年 | 430篇 |
2015年 | 446篇 |
2014年 | 649篇 |
2013年 | 816篇 |
2012年 | 695篇 |
2011年 | 705篇 |
2010年 | 591篇 |
2009年 | 683篇 |
2008年 | 714篇 |
2007年 | 691篇 |
2006年 | 601篇 |
2005年 | 570篇 |
2004年 | 467篇 |
2003年 | 446篇 |
2002年 | 349篇 |
2001年 | 320篇 |
2000年 | 301篇 |
1999年 | 245篇 |
1998年 | 198篇 |
1997年 | 204篇 |
1996年 | 176篇 |
1995年 | 181篇 |
1994年 | 97篇 |
1993年 | 88篇 |
1992年 | 85篇 |
1991年 | 52篇 |
1990年 | 60篇 |
1989年 | 47篇 |
1988年 | 42篇 |
1987年 | 22篇 |
1986年 | 19篇 |
1985年 | 27篇 |
1984年 | 29篇 |
1983年 | 5篇 |
1982年 | 17篇 |
1981年 | 13篇 |
1980年 | 4篇 |
1979年 | 10篇 |
1978年 | 3篇 |
1977年 | 4篇 |
1975年 | 4篇 |
1957年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
71.
本文在Knockout交换结构的基础上,探讨一种新的ATM交换结构,使其本身带有优先权控制功能,以适应不同业务对信元丢失率及时延的不同要求。这种结构既能最大限度地有效利用系统资源,又能满足不同用户对业务质量的不同要求,并能降低交换结构复杂度。 相似文献
72.
128kb/s电视电话系统中数码率缓存器的控制策略研究 总被引:2,自引:0,他引:2
本文探讨了电视电话/会议电视的H,261建议中低码率时(p=2)数码率缓存器的控制问题,提出一种既有宏观预分配又有微观分割的控制策略(简称GALS),并用测试图像序列进行了计算机模拟。将本文方法与RM8中有关策略作了比较,实验结果表明图像的主观质量有所改善。 相似文献
73.
A method for the deposition of BN onto graphite and other substrates is described. Boron trichloride (BCl3) and ammonia (NH3) diluted with Ar were used as reacting gases. The deposition process was carried out at 1300 K as well as lower temperatures in an open system at pressures of 1 atm. The consequences of the introduction of hydrogen to the system were considered. It was demonstrated that the replacement of argon with hydrogen increases the efficiency of the process as well as the theoretical rate of BN deposition. However, the acceleration of the deposition seems to be unprofitable, because the resulting supersaturation leads to the formation of an amorphous phase. The modification of the experimental conditions were proposed.Dedicated to Professor Dr. rer. nat. Dr. h.c. Hubertus Nickel on the occasion of his 65th birthday 相似文献
74.
Monocrystalline 6H-SiC thin films have been epitaxially grown on off-axis 6H-SiC {0001} substrates in the temperature range
of 1623–1873 K via chemical vapor deposition. The growth rate was a strong function of the growth temperature and the reactant
gas concentration. The activation energies for growth were 64 kJ/mole and 55 kJ/mole for the (0001) Si face and the (0001)
C face, respectively. The concentration of growth pits in the films increased as a function of decreasing deposition temperature,
increasing concentration of reactant gases and increasing off-axis orientation. Beta-SiC islands were also observed in the
epilayers when the (SiH4 + C2H4)/H2 ratio was ≥2.5:3000. 相似文献
75.
76.
给出动态随机弹性的概念及运算性质,讨论了动态随机弹性在期权定价模型中的应用.主要结果有:(1)在波动率为常数时,期权价格对的弹性,得到了动态随机弹性服从运动,并给出了相应的经济解释;(2)由于波动率一般不是常数,也是随机过程,因此本文进一步研究了期权价格对波动率的弹性,就股票价格的波动情况给出了数学描述和金融意义上的解释. 相似文献
77.
Q.J. Zhu 《Journal of Mathematical Analysis and Applications》2007,326(1):708-720
Investment systems are studied using a framework that emphasize their profiles (the cumulative probability distribution on all the possible percentage gains of trades) and their log return functions (the expected average return per trade in logarithmic scale as a function of the investment size in terms of the percentage of the available capital). The efficiency index for an investment system, defined as the maximum of the log return function, is proposed as a measure to compare investment systems for their intrinsic merit. This efficiency index can be viewed as a generalization of Shannon's information rate for a communication channel. Applications are illustrated. 相似文献
78.
After taking into account energy conservation and the particle’s self-gravitation interaction, Hawking radiation of the massive
particle as tunneling from Schwarzshild-anti-de Sitter black hole is studied by using Parikh-Wilczek’s semi-classical quantum
tunneling approach. Meanwhile, Hawking radiation as tunneling from the black hole is reexamined by developing Angheben–Nadalini–Vanzo–Zerbini
(ANVZ) covariant method to cover energy conservation and the particle’s self-gravitation interaction. Both the results perfectly
generalize those obtained by Parikh and Wilczek, and show that the tunneling rate is related to the change of Bekenstein-Hawking
entropy, and the factual emission spectrum is not exactly thermal, but satisfies the underlying unitary theory.
PACS: 04.70-s, 9760. Lf. 相似文献
79.
Peng Feng 《Journal of Mathematical Analysis and Applications》2007,329(1):347-356
In this paper we establish the exact blow-up rate of the large solutions of a porous media logistic equation. We consider the carrying capacity function with a general decay rate at the boundary instead of the usual cases when it can be approximated by a distant function. Obtaining the accurate blow-up rate allows us to establish the uniqueness result. Our result covers all previous results on the ball domain and can be further adapted in a more general domain. 相似文献
80.
设Λ={λn}n∞=1为正的实数数列,且当n→∞时,有λn↘0.本文给出了当λn≤Mn-1/2,n=1,2,…,(其中M>0为一正常数)时Müntz系统{xλn}的有理函数在Lp[0,1]空间的逼近速度,主要结论为Rn(f,Λ) Lp≤CMω(f,n-1/2)Lp,1≤p≤∞. 相似文献