全文获取类型
收费全文 | 114084篇 |
免费 | 6931篇 |
国内免费 | 5699篇 |
专业分类
化学 | 56314篇 |
晶体学 | 1331篇 |
力学 | 5596篇 |
综合类 | 322篇 |
数学 | 11838篇 |
物理学 | 33820篇 |
无线电 | 17493篇 |
出版年
2023年 | 1253篇 |
2022年 | 1999篇 |
2021年 | 2716篇 |
2020年 | 2800篇 |
2019年 | 2996篇 |
2018年 | 3338篇 |
2017年 | 3331篇 |
2016年 | 4020篇 |
2015年 | 2996篇 |
2014年 | 4291篇 |
2013年 | 5774篇 |
2012年 | 6012篇 |
2011年 | 6244篇 |
2010年 | 5016篇 |
2009年 | 5174篇 |
2008年 | 5418篇 |
2007年 | 5048篇 |
2006年 | 4653篇 |
2005年 | 4167篇 |
2004年 | 3574篇 |
2003年 | 3295篇 |
2002年 | 3356篇 |
2001年 | 2987篇 |
2000年 | 2381篇 |
1999年 | 1977篇 |
1998年 | 1824篇 |
1997年 | 1581篇 |
1996年 | 1491篇 |
1995年 | 1220篇 |
1994年 | 1266篇 |
1993年 | 1201篇 |
1992年 | 1168篇 |
1991年 | 1200篇 |
1990年 | 1170篇 |
1989年 | 1071篇 |
1988年 | 931篇 |
1987年 | 935篇 |
1986年 | 889篇 |
1985年 | 927篇 |
1984年 | 923篇 |
1983年 | 830篇 |
1982年 | 807篇 |
1979年 | 807篇 |
1978年 | 815篇 |
1977年 | 814篇 |
1976年 | 921篇 |
1975年 | 814篇 |
1974年 | 846篇 |
1973年 | 848篇 |
1972年 | 755篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
The excitation of eigen surface waves by tubular electron beams in cylindrical discharge devices is studied. The influence of the wave‐field azimuthal structure on the excitation efficiency and nonlinear stage of the plasmabeam instability is investigated both numerically and analytically. Analytical expressions for the saturation amplitude and excitation efficiency of the wave under study are derived. They are found to agree well with results obtained by numerical modelling of the plasma‐beam interaction presented in this paper. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
12.
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
13.
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
14.
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
15.
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
16.
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
17.
Steensgaard J. Zhiqing Zhang Wenhuan Yu Sarhegyi A. Lucchese L. Dae-Ik Kim Temes G.C. 《IEEE transactions on circuits and systems. I, Regular papers》2008,55(5):1289-1296
Incremental data converters (IDCs) are useful in instrumentation and measurement applications, where low-frequency analog signals need to be converted into digital form with high accuracy and low power dissipation. They are particularly well suited for applications where a single analog-digital converter is multiplexed between many channels. This paper proposes an exact design methodology for IDCs, which optimizes the signal-to-noise ratio of the converter under practical design constraints. The process also allows the designer to apportion the noise budget in an arbitrary manner between thermal and quantization noise. The design process is illustrated by an example which describes the optimization of a third-order multiplexed IDC. 相似文献
18.
Eng Leong Tan Ding Yu Heh 《Microwave and Wireless Components Letters, IEEE》2008,18(5):296-298
This letter presents an unconditionally stable alternating direction implicit finite-difference time-domain (ADI-FDTD) method with fourth order accuracy in time. Analytical proof of unconditional stability and detailed analysis of numerical dispersion are presented. Compared to second order ADI-FDTD and six-steps SS-FDTD, the fourth order ADI-FDTD generally achieves lower phase velocity error for sufficiently fine mesh. Using finer mesh gridding also reduces the phase velocity error floor, which dictates the accuracy limit due to spatial discretization errors when the time step size is reduced further. 相似文献
19.
A lithium(I) coordination polymer has been formed from LiClO4 and the 2,2′‐bipyrimidine (bpym) ligand in which each square pyramidal lithium(I) atom is coordinated in the basal plane by four nitrogen donor atoms derived from two bpym ligands and one water molecule at the apical position. These are connected into a layer structure via hydrogen‐bonding interactions involving the perchlorate anions. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
20.
Some possible errors in determining the gravity anomalies are discussed. Such errors may be caused by an inaccurate calibration of the gravimeter used in an airborne survey system. An approach based on wavelet decompositions is proposed for its additional calibration with the use of flight data obtained during repeated flights. 相似文献