全文获取类型
收费全文 | 3067篇 |
免费 | 264篇 |
国内免费 | 47篇 |
专业分类
化学 | 104篇 |
晶体学 | 5篇 |
力学 | 68篇 |
综合类 | 31篇 |
数学 | 874篇 |
物理学 | 291篇 |
无线电 | 2005篇 |
出版年
2024年 | 8篇 |
2023年 | 61篇 |
2022年 | 94篇 |
2021年 | 91篇 |
2020年 | 99篇 |
2019年 | 66篇 |
2018年 | 55篇 |
2017年 | 96篇 |
2016年 | 111篇 |
2015年 | 99篇 |
2014年 | 151篇 |
2013年 | 180篇 |
2012年 | 150篇 |
2011年 | 145篇 |
2010年 | 115篇 |
2009年 | 169篇 |
2008年 | 245篇 |
2007年 | 210篇 |
2006年 | 219篇 |
2005年 | 161篇 |
2004年 | 119篇 |
2003年 | 138篇 |
2002年 | 106篇 |
2001年 | 87篇 |
2000年 | 77篇 |
1999年 | 88篇 |
1998年 | 57篇 |
1997年 | 49篇 |
1996年 | 39篇 |
1995年 | 16篇 |
1994年 | 16篇 |
1993年 | 11篇 |
1992年 | 11篇 |
1991年 | 10篇 |
1990年 | 5篇 |
1989年 | 6篇 |
1988年 | 3篇 |
1987年 | 2篇 |
1985年 | 2篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有3378条查询结果,搜索用时 16 毫秒
131.
132.
The theoretical concept of the computer program is based on the compartment theory for the 3-pool model using single pulse administration of the tracer. The code estimates the model parameters by means of the non-linear method of least squares fit under steady state conditions. Furthermore the parameters of the protein metabolism are calculated. The program works interactively and allows reading and modifying the experimental 15N tracer data via terminal and controlling the program. 相似文献
133.
详细介绍圭亚那乔治敦某五星级酒店空调系统在负荷计算、设备选型、空调系统自控、防排烟设计、LEED认证等设计情况。 相似文献
134.
This article studies the degree distribution property of low density parity check (LDPC) codes by Gaussian approximation (GA) and presents an efficient hybrid automatic repeat quest (HARQ) scheme for LDPC-coded orthogonal frequency division multiplexing (OFDM) system. In the scheme, the important bits with large degrees have high retransmission priorities and are mapped to the sub-carriers with better channel quality indicator (CQI) levels in the OFDM system. The new scheme provides more protection to the bits with large degrees and thus contributes more to the decoding process by offering more transmission power. In this way the system performance would be improved. The statistics and simulation results also prove the new scheme. 相似文献
135.
This article improves results of Hamada, Helleseth and Maekawa on minihypers in projective spaces and linear codes meeting the Griesmer bound.In [10,12],it was shown that any
-minihyper, with
, where
, is the disjoint union of
points,
lines,...,
-dimensional subspaces. For q large, we improve on this result by increasing the upper bound on
non-square, to
non-square,
square,
, and (4) for
square, p prime, p<3, to
. In the case q non-square, the conclusion is the same as written above; the minihyper is the disjoint union of subspaces. When q is square however, the minihyper is either the disjoint union of subspaces, or the disjoint union of subspaces and one subgeometry
. For the coding-theoretical problem, our results classify the corresponding
codes meeting the Griesmer bound. 相似文献
136.
We reinterpret the state space dimension equations for geometric Goppa codes. An easy consequence is that if deg
then the state complexity of
is equal to the Wolf bound. For deg
, we use Clifford's theorem to give a simple lower bound on the state complexity of
. We then derive two further lower bounds on the state space dimensions of
in terms of the gonality sequence of
. (The gonality sequence is known for many of the function fields of interest for defining geometric Goppa codes.) One of the gonality bounds uses previous results on the generalised weight hierarchy of
and one follows in a straightforward way from first principles; often they are equal. For Hermitian codes both gonality bounds are equal to the DLP lower bound on state space dimensions. We conclude by using these results to calculate the DLP lower bound on state complexity for Hermitian codes. 相似文献
137.
By a T
*(2, k, v)-code we mean a perfect4-deletion-correcting code of length 6 over an alphabet of size v, which is capable of correcting anycombination of up to 4 deletions and/or insertions of letters that occur in transmission of codewords. Thethird author (DCC Vol. 23, No. 1) presented a combinatorial construction for such codes and prove thata T
*(2, 6, v)-code exists for all positive integers v 3 (mod 5), with 12 possible exceptions of v. In this paper, the notion of a directedgroup divisible quasidesign is introduced and used to show that a T
*(2, 6,v)-code exists for all positive integers v 3 (mod 5), except possiblyfor v {173, 178, 203, 208}. The 12 missing cases for T
*(2,6, v)-codes with v 3 (mod 5) are also provided, thereby the existenceproblem for T
*(2, 6, v)-codes is almost complete. 相似文献
138.
The structure of linear codes of constant weight 总被引:1,自引:0,他引:1
Jay A. Wood 《Transactions of the American Mathematical Society》2002,354(3):1007-1026
In this paper we determine completely the structure of linear codes over of constant weight. Namely, we determine exactly which modules underlie linear codes of constant weight, and we describe the coordinate functionals involved. The weight functions considered are: Hamming weight, Lee weight, two forms of Euclidean weight, and pre-homogeneous weights. We prove a general uniqueness theorem for virtual linear codes of constant weight. Existence is settled on a case by case basis.
139.
Space–time (ST) coding is a proved technique for achieving high data rates in 3G mobile systems that combines coding, modulation and multiple transmitters and receivers. A novel algorithm is proposed for ST ring trellis‐coded modulation (ST‐RTCM) systems with continuous‐phase modulation (CPM) when the channel coefficients are known to the receiver. This algorithm is based on the CPM decomposed model, which exploits the memory properties of this modulation method, resulting in a straightforward implementation of joint ST coding and CPM, which is particularly suitable for ring codes. This new scheme is used to investigate the performance of the delay diversity code with CPM over slow Rayleigh fading channels, in particular with MSK which is one of the most widely used modulation methods of continuous phase. Furthermore, a feedback version of delay diversity allowed by the decomposition is tested in 1REC and 1RC systems. This feedback configuration is seen to provide good results for low signal‐to‐noise ratios. Simulations results are also provided for multilevel ST‐RTCM codes that achieve a higher throughput than MSK‐coded systems. Additionally the serial concatenation of an outer Reed–Solomon code with an ST‐RTCM code is shown, this combination further reduces the error probability and achieves even more reliable communications. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
140.
JIA Xiao-yun LUO Shou-shan YUAN Chao-wei.School of Continuing Education Beijing University of Posts Telecommunications Beijing P.R. China .School of Software Engineering Beijing University of Posts Telecommunications Beijing P.R. China .National Key Laboratory of Integrated Service Networks Xidian University Xi'an P.R. China 《中国邮电高校学报(英文版)》2006,13(2):66-69
1Introduction Withthedevelopmentofcomputerandnetworkcom municationtechnology,andwiththedifferenceofuser s demands,digitalsignaturetechniquesarebeingexpand edgreatly,fromthesinglesignature,singleverification modetothemulti user sone.Forexample,adocument sy… 相似文献