全文获取类型
收费全文 | 197724篇 |
免费 | 19485篇 |
国内免费 | 12729篇 |
专业分类
化学 | 83402篇 |
晶体学 | 1631篇 |
力学 | 11999篇 |
综合类 | 512篇 |
数学 | 41108篇 |
物理学 | 51305篇 |
无线电 | 39981篇 |
出版年
2024年 | 503篇 |
2023年 | 3057篇 |
2022年 | 3683篇 |
2021年 | 4676篇 |
2020年 | 4759篇 |
2019年 | 4180篇 |
2018年 | 14729篇 |
2017年 | 14231篇 |
2016年 | 11624篇 |
2015年 | 6310篇 |
2014年 | 6847篇 |
2013年 | 8601篇 |
2012年 | 13863篇 |
2011年 | 20976篇 |
2010年 | 13404篇 |
2009年 | 13364篇 |
2008年 | 14286篇 |
2007年 | 15832篇 |
2006年 | 6599篇 |
2005年 | 6816篇 |
2004年 | 5404篇 |
2003年 | 5190篇 |
2002年 | 3883篇 |
2001年 | 2702篇 |
2000年 | 2596篇 |
1999年 | 2797篇 |
1998年 | 2487篇 |
1997年 | 2267篇 |
1996年 | 2269篇 |
1995年 | 1877篇 |
1994年 | 1636篇 |
1993年 | 1385篇 |
1992年 | 1218篇 |
1991年 | 1038篇 |
1990年 | 805篇 |
1989年 | 628篇 |
1988年 | 504篇 |
1987年 | 409篇 |
1986年 | 411篇 |
1985年 | 336篇 |
1984年 | 223篇 |
1983年 | 166篇 |
1982年 | 153篇 |
1981年 | 104篇 |
1980年 | 95篇 |
1979年 | 65篇 |
1914年 | 45篇 |
1912年 | 40篇 |
1909年 | 41篇 |
1908年 | 40篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Incomplete LU factorization preconditioning techniques often have difficulty on indefinite sparse matrices. We present hybrid reordering strategies to deal with such matrices, which include new diagonal reorderings that are in conjunction with a symmetric nondecreasing degree algorithm. We first use the diagonal reorderings to efficiently search for entries of single element rows and columns and/or the maximum absolute value to be placed on the diagonal for computing a nonsymmetric permutation. To augment the effectiveness of the diagonal reorderings, a nondecreasing degree algorithm is applied to reduce the amount of fill-in during the ILU factorization. With the reordered matrices, we achieve a noticeable improvement in enhancing the stability of incomplete LU factorizations. Consequently, we reduce the convergence cost of the preconditioned Krylov subspace methods on solving the reordered indefinite matrices. 相似文献
92.
93.
色散及光信噪比对DWDM组网的影响 总被引:2,自引:0,他引:2
介绍了色散受限距离及光信噪比对DWDM组网的影响,其中提出了网络设计时的应考虑的问题和减少影响的方法。 相似文献
94.
A pressure sensitive paint (PSP) measurement has been known as a pressure field measurement technique based on the oxygen quenching phenomenon of luminescence of specific luminophores. A PSP measurement was applied for pressure field measurement in a low-solidity circular cascade diffuser of a single-stage transonic centrifugal compressor with 5 in pressure ratio for HFC134a gas. The oxygen concentration was about 500 ppm. Ru (bath-phen) was adsorbed on a silica-gel thinlayer chromatography sheet, and the sheet was pasted onto the side-wall between the cascade vanes. A drastic change in luminescent intensity was recognized during a surge condition. Also the pressure variations based on luminescent intensity agreed well with the pressure fluctuations measured using a semiconductor pressure sensor with high-frequency-response. It was shown that a PSP measurement worked well to investigate the unsteady pressure fields in a circular cascade diffuser of a transonic centrifugal compressor. Moreover, the time response of PSP becomes clear as a problem to be overcome for the present. 相似文献
95.
Fractional factorial split-plot (FFSP) designs have an important value of investigation for their special structures. There are two types of factors in an FFSP design: the whole-plot (WP) factors and sub-plot (SP) factors, which can form three types of two-factor interactions: WP2fi, WS2fi and SP2fi. This paper considers FFSP designs with resolution III or IV under the clear effects criterion. It derives the upper and lower bounds on the maximum numbers of clear WP2fis and WS2fis for FFSP designs, and gives some methods for constructing the desired FFSP designs. It further examines the performance of the construction methods. 相似文献
96.
97.
Chong-Guang Cao Zhong-Peng Yang Xian Zhang 《Journal of Applied Mathematics and Computing》2002,10(1-2):101-109
We extend two inequalities involving Hadamard products of positive definite Hermitian matrices to positive semi-definite Hermitian matrices. Simultaneously, we also show the sufficient conditions for equalities to hold. Moreover, some other matrix inequalities are also obtained. Our results and methods are different from those which are obtained by S. Liu in [J. Math. Anal. Appl. 243:458–463(2000)] and B.-Y. Wang et al. in [Lin. Alg. Appl. 302–303: 163–172(1999)]. 相似文献
98.
Yasuyuki Kawahigashi 《Communications in Mathematical Physics》2002,226(2):269-287
We study the recent construction of subfactors by Rehren which generalizes the Longo–Rehren subfactors. We prove that if
we apply this construction to a non-degenerately braided subfactor N⊂M and α±-induction, then the resulting subfactor is dual to the Longo–Rehren subfactor M⊗M
opp⊂R arising from the entire system of irreducible endomorphisms of M resulting from αplusmn;-induction. As a corollary, we solve a problem on existence of braiding raised by Rehren negatively. Furthermore, we generalize
our previous study with Longo and Müger on multi-interval subfactors arising from a completely rational conformal net of factors
on S
1 to a net of subfactors and show that the (generalized) Longo–Rehren subfactors and α-induction naturally appear in this context.
Received: 11 September 2001 / Accepted: 7 October 2001 相似文献
99.
Julio Castellanos 《Mathematische Zeitschrift》2002,239(4):777-802
We consider complete ideals supported on finite sequences of infinitely near points, in regular local rings with dimensions
greater than two. We study properties of factorizations in Lipman special *-simple complete ideals. We relate it to a type
of proximity, linear proximity, of the points, and give conditions in order to have unique factorization. Several examples
are presented.
Received: 2 February 2000 / in final form: 14 March 2001 / Published online: 18 January 2002 相似文献
100.