全文获取类型
收费全文 | 83080篇 |
免费 | 6644篇 |
国内免费 | 5380篇 |
专业分类
化学 | 25421篇 |
晶体学 | 1819篇 |
力学 | 3536篇 |
综合类 | 356篇 |
数学 | 20502篇 |
物理学 | 43470篇 |
出版年
2023年 | 206篇 |
2022年 | 222篇 |
2021年 | 407篇 |
2020年 | 731篇 |
2019年 | 1041篇 |
2018年 | 995篇 |
2017年 | 681篇 |
2016年 | 495篇 |
2015年 | 483篇 |
2014年 | 1177篇 |
2013年 | 2180篇 |
2012年 | 1238篇 |
2011年 | 1821篇 |
2010年 | 2391篇 |
2009年 | 6982篇 |
2008年 | 8076篇 |
2007年 | 6556篇 |
2006年 | 5986篇 |
2005年 | 4132篇 |
2004年 | 3957篇 |
2003年 | 4151篇 |
2002年 | 5363篇 |
2001年 | 3873篇 |
2000年 | 3641篇 |
1999年 | 3426篇 |
1998年 | 2841篇 |
1997年 | 1996篇 |
1996年 | 1779篇 |
1995年 | 2235篇 |
1994年 | 2167篇 |
1993年 | 1623篇 |
1992年 | 1131篇 |
1991年 | 844篇 |
1990年 | 685篇 |
1989年 | 617篇 |
1988年 | 577篇 |
1987年 | 407篇 |
1985年 | 960篇 |
1984年 | 629篇 |
1983年 | 491篇 |
1982年 | 643篇 |
1981年 | 797篇 |
1980年 | 724篇 |
1979年 | 559篇 |
1978年 | 585篇 |
1977年 | 539篇 |
1976年 | 543篇 |
1975年 | 318篇 |
1974年 | 356篇 |
1973年 | 464篇 |
排序方式: 共有10000条查询结果,搜索用时 625 毫秒
991.
In this paper the sufficient conditions for the existence of positive solutions of the neutral difference equations with positive and negative coefficients are established. The results improve some known conclusions in the literature 相似文献
992.
Automorphisms of groups acting faithfully on rooted trees are studied. We find conditions under which every automorphism of such a group is induced by a conjugation from the full automorphism group of the rooted tree. These results are applied to known examples such as Grigorchuk groups, Gupta–Sidki group, etc. 相似文献
993.
王同科 《高等学校计算数学学报(英文版)》2002,11(2):213-225
1 IntroductionFinitevolumeelementmethodorFVEMusesavolumeintegralformulationofthedif ferentialequationwithafinitepartitioningsetofvolumetodiscretizetheequation ,thenre strictstheadmissiblefunctionstoalinearfiniteelementspacetodiscretizethesolution ([1 -4 ] ) .… 相似文献
994.
§ 1 IntroductionA triple system of order v and indexλ,denoted by TS(v,λ) ,is a collection of3- ele-mentsubsets Aof a v- set X,so thatevery 2 - subsetof X appears in preciselyλ subsets of A.L etλ≥ 2 and (X,A) be a TS(v,λ) .If Acan be partitioned into t(≥ 2 ) parts A1,A2 ,...,Atsuch that each (X,Ai) is a TS(v,λi) for 1≤ i≤ t,then (X,A) is called de-composable.Otherwise it is indecomposable.If t=λ,λi=1for 1≤ i≤ t,the TS(v,λ) (X,A) is called completely decomposable.It … 相似文献
995.
In this paper, we give a convergence theorem and error estimates for an iteration method under new Kantorovitch-Ostrowski type condition using the information of higher derivatives at initial points. Compared with the corresponding study in [3],the convergence determination is established under one global condition, instead of two , on the function. 相似文献
996.
We report the temperature dependence of electrical resistance (R) and thermopower (S) of clathrate Cs8Sn44 under high pressure up to 1.2 GPa. We observe a reversible gap widening, prominent relaxation effect of R, irreversible increase of |S| under high pressure. We also find that the power factor S2σ (σ: electrical conductivity) reaches a maximum at pressure of 0.3 GPa. Comparison of the experimental results with band structure calculations suggests that the intrinsic vacancy in the clathrate structure of Cs8Sn44 plays an important role in transport properties under high pressure. Measurements on Cs8Zn4Sn42, a clathrate which has defects other than vacancies, are compared with Cs8Sn44. The results indicate that replacing Sn by Zn has similar effect as the intrinsic vacancy on S. 相似文献
997.
Organically modified solid-state silicates (ORMOSILS) doped with a new laser dye 1,3,5,7,8-pentamethylpyrromethene-2,6-disulfonate-BF2 complex (pyrromethene 556) have been synthesized by a sol-gel method and the compositional effects on pore characteristics, fluorescence and lasing properties have been investigated. It is found that the use of dimethylsulfoxide and γ-glycidoxypropyltrimethoxysilane could greatly change the structure properties of sol-gel derived ORMOSILS cage, and thus the fluorescence and lasing properties of the materials could improve significantly. A successful laser oscillation from this dye-doped ORMOSILS sample has been achieved upon pumping with a Q-switched frequency-doubled Nd:YAG laser at 532 nm. A slope efficiency of 54% with a useful lifetime greater than 10,000 shots has been demonstrated at a pump repetition rate of 1 Hz and a pump intensity of 1 J/cm2 by using the new ORMOSILS cage on our newly designed laser system. Our results have shown that it is possible to obtain a high-efficiency with a long-lifetime for a compact new laser device by low cost dye-doped solid-state ORMOSILS. 相似文献
998.
崔霞 《高等学校计算数学学报(英文版)》2002,11(1):76-88
A new alternating direction (AD) finite element (FE) scheme for 3-dimensional nonlinear parabolic equation and parabolic integro-differential equation is studied. By using AD, the 3-dimensional problem is reduced to a family of single space variable problems, calculation work is simplified; by using FE, high accuracy is kept; by using various techniques for priori estimate for differential equations such as inductive hypothesis reasoning, the difficulty arising from the nonlinearity is treated. For both FE and ADFE schemes, the convergence properties are rigorously demonstrated, the optimal H1-and L2-norm space estimates and the 0((△t)2) estimate for time variable are obtained. 相似文献
999.
In a recent paper [17] we proposed a stochastic algorithm which generates optimal probabilities for the decompression of
an image represented by the fixed point of an IFS system (SAOP). We show here that such an algorithm is in fact a non trivial
example of Generalized Random System with Complete Connections. We also exhibit a generalization which could represent the
solution to the inverse problem for an image with grey levels, if a fixed set of contraction maps is available.
Received: 1 July 2002 相似文献
1000.
箱覆盖问题是NP困难问题中的经典问题,得到了广泛地研究,九十年代以来,半定松驰策略被用来求解组合优化问题,取得了很好的结果[13],本文首次给箱覆盖问题的半定松驰算法,算法的理论分析结果表明它适合于求解大规模的箱覆盖问题。 相似文献