全文获取类型
收费全文 | 180001篇 |
免费 | 18937篇 |
国内免费 | 20390篇 |
专业分类
化学 | 81989篇 |
晶体学 | 2981篇 |
力学 | 8604篇 |
综合类 | 1845篇 |
数学 | 18202篇 |
物理学 | 52843篇 |
无线电 | 52864篇 |
出版年
2023年 | 2282篇 |
2022年 | 4546篇 |
2021年 | 5199篇 |
2020年 | 4935篇 |
2019年 | 5002篇 |
2018年 | 5370篇 |
2017年 | 6187篇 |
2016年 | 6212篇 |
2015年 | 6337篇 |
2014年 | 8326篇 |
2013年 | 10762篇 |
2012年 | 11301篇 |
2011年 | 11922篇 |
2010年 | 10618篇 |
2009年 | 10983篇 |
2008年 | 11608篇 |
2007年 | 10797篇 |
2006年 | 10205篇 |
2005年 | 8700篇 |
2004年 | 7137篇 |
2003年 | 5682篇 |
2002年 | 5676篇 |
2001年 | 5264篇 |
2000年 | 4756篇 |
1999年 | 3111篇 |
1998年 | 2346篇 |
1997年 | 1976篇 |
1996年 | 1883篇 |
1995年 | 1529篇 |
1994年 | 1573篇 |
1993年 | 1529篇 |
1992年 | 1421篇 |
1991年 | 1412篇 |
1990年 | 1359篇 |
1989年 | 1253篇 |
1988年 | 1113篇 |
1987年 | 1097篇 |
1986年 | 1005篇 |
1985年 | 1008篇 |
1984年 | 1022篇 |
1983年 | 914篇 |
1982年 | 862篇 |
1981年 | 758篇 |
1979年 | 852篇 |
1978年 | 833篇 |
1977年 | 824篇 |
1976年 | 928篇 |
1975年 | 822篇 |
1974年 | 849篇 |
1973年 | 850篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
41.
A. I. Bril' V. P. Kabashnikov N. V. Kuz'mina Yu. V. Khodyko 《Journal of Applied Spectroscopy》1991,55(3):934-939
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 55, No. 3, pp. 478–484, September, 1991. 相似文献
42.
43.
In this paper, the influence of viewing distance on subjective assessment of the impairment in video sequences is investigated. Subjective tests using the double-stimulus impairment scale variant II (DSIS II) method have been conducted at viewing distances of 5H (where H stands for the screen height) and 3H, respectively. Several statistical measures have been used to analyze the influence, including correlations and ANOVA (analysis of variance) tests. The results reveal that there is a very high correlation between the subjective scores, the variances are similar under the two viewing distances, the means of subjective data at these two viewing distances are the same, and there is no interaction between the viewing distance and the other two factors, i.e., the codec system and the source sequence. Throughout the tests, there is no evidence that a closer viewing distance such as 3H will vary the subjective test result statistically significantly. 相似文献
44.
Xingxing Yu 《Journal of Graph Theory》2006,51(3):175-198
An infinite graph is 2‐indivisible if the deletion of any finite set of vertices from the graph results in exactly one infinite component. Let G be a 4‐connected, 2‐indivisible, infinite, plane graph. It is known that G contains a spanning 1‐way infinite path. In this paper, we prove a stronger result by showing that, for any vertex x and any edge e on a facial cycle of G, there is a spanning 1‐way infinite path in G from x and through e. Results will be used in two forthcoming papers to establish a conjecture of Nash‐Williams. © 2005 Wiley Periodicals, Inc. J Graph Theory 相似文献
45.
Trellis and convolutional precoding for transmitter-based interference presubtraction 总被引:3,自引:0,他引:3
This paper studies the combination of practical trellis and convolution codes with Tomlinson-Harashima precoding (THP) for the presubtraction of multiuser interference that is known at the transmitter but not known at the receiver. It is well known that a straightforward application of THP suffers power, modulo, and shaping losses. This paper proposes generalizations of THP that recover some of these losses. At a high signal-to-noise ratio (SNR), the precoding loss is dominated by the shaping loss, which is about 1.53 dB. To recover shaping loss, a trellis-shaping technique is developed that takes into account the knowledge of a noncausal interfering sequence, rather than just the instantaneous interference. At rates of 2 and 3 bits per transmission, trellis shaping is shown to be able to recover almost all of the 1.53-dB shaping loss. At a low SNR, the precoding loss is dominated by power and modulo losses, which can be as large as 3-4 dB. To recover these losses, a technique that incorporates partial interference presubtraction (PIP) within convolutional decoding is developed. At rates of 0.5 and 0.25 bits per transmission, PIP is able to recover 1-1.5 dB of the power loss. For intermediate SNR channels, a combination of the two schemes is shown to recover both power and shaping losses. 相似文献
46.
Yu. A. Chaplygin E. A. Artamonova A. Yu. Krasyukov T. Yu. Krupkina 《Semiconductors》2008,42(13):1522-1526
Heat removal problems, thermal effects, and self-heating phenomena occurring during operation of planar power SOI MOS transistors are considered. Using device-technological simulating methods, the transistor characteristics and safe operation range were studied. It was shown that limitations of the safe operation range are mostly associated with structure self-heating rather than with the parasitic bipolar transistor. 相似文献
47.
首先简单回顾了中国铁通成立之初计费管理系统的一期建设和二期扩容后支撑能力的明显不足,以及信息化建设初期各部门独立IT系统运行中的问题,然后较详细介绍了企业信息化规划的整体思路.包括业务系统和流程、组织和业务流程重组、信息技术战略和架构等.并在实践的基础上,列举了信息化系统实施过程中应避免的做法和应注意的事项. 相似文献
48.
Belov V. V. Dobrokhotov S. Yu. Maksimov V. A. 《Theoretical and Mathematical Physics》2003,135(3):765-791
Different versions of the Darboux–Weinstein theorem guarantee the existence of action–angle-type variables and the harmonic-oscillator variables in a neighborhood of isotropic tori in the phase space. The procedure for constructing these variables is reduced to solving a rather complicated system of partial differential equations. We show that this system can be integrated in quadratures, which permits reducing the problem of constructing these variables to solving a system of quadratic equations. We discuss several applications of this purely geometric fact in problems of classical and quantum mechanics. 相似文献
49.
Yu. M. Dyukarev 《Mathematical Notes》2004,75(1-2):66-82
In this paper, we obtain criteria for the indeterminacy of the Stieltjes matrix moment problem. We obtain explicit formulas for Stieltjes parameters and study the multiplicative structure of the resolvent matrix. In the indeterminate case, we study the analytic properties of the resolvent matrix of the moment problem. We describe the set of all matrix functions associated with the indeterminate Stieltjes moment problem in terms of linear fractional transformations over Stieltjes pairs. 相似文献
50.
Yu. P. Kalmykov 《Radiophysics and Quantum Electronics》1989,32(9):826-835
Radio Engineering and Electronics Institute, Academy of Sciences of the USSR. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 32, No. 9, pp. 1113–1124, September, 1989. 相似文献