全文获取类型
收费全文 | 38633篇 |
免费 | 1855篇 |
国内免费 | 4523篇 |
专业分类
化学 | 28284篇 |
晶体学 | 567篇 |
力学 | 228篇 |
综合类 | 160篇 |
数学 | 10669篇 |
物理学 | 5103篇 |
出版年
2024年 | 30篇 |
2023年 | 253篇 |
2022年 | 534篇 |
2021年 | 655篇 |
2020年 | 674篇 |
2019年 | 1761篇 |
2018年 | 940篇 |
2017年 | 1642篇 |
2016年 | 1017篇 |
2015年 | 962篇 |
2014年 | 1336篇 |
2013年 | 3303篇 |
2012年 | 2003篇 |
2011年 | 2610篇 |
2010年 | 1937篇 |
2009年 | 2205篇 |
2008年 | 2592篇 |
2007年 | 2711篇 |
2006年 | 2322篇 |
2005年 | 1888篇 |
2004年 | 1822篇 |
2003年 | 1499篇 |
2002年 | 1253篇 |
2001年 | 1084篇 |
2000年 | 1048篇 |
1999年 | 891篇 |
1998年 | 760篇 |
1997年 | 677篇 |
1996年 | 576篇 |
1995年 | 654篇 |
1994年 | 508篇 |
1993年 | 431篇 |
1992年 | 407篇 |
1991年 | 282篇 |
1990年 | 204篇 |
1989年 | 176篇 |
1988年 | 133篇 |
1987年 | 103篇 |
1986年 | 118篇 |
1985年 | 144篇 |
1984年 | 118篇 |
1983年 | 63篇 |
1982年 | 107篇 |
1981年 | 109篇 |
1980年 | 90篇 |
1979年 | 96篇 |
1978年 | 87篇 |
1977年 | 58篇 |
1976年 | 55篇 |
1975年 | 26篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
31.
Saida Sultanic 《Integral Equations and Operator Theory》2006,55(4):573-595
The central question of this paper is the one of finding the right analogue of the Commutant Lifting Theorem for the Bergman
space La2. We also analyze the analogous problem for weighted Bergman spaces La,α2, − 1 < α < ∞. 相似文献
32.
Michel Hébert 《Archive for Mathematical Logic》1991,31(2):133-143
Summary We give a syntactic characterization of (finitary) theories whose categories of models are closed under the formation of connected limits (respectively the formation of pullbacks and substructures) in the category of all structures. They are also those theories whose consistent extensions by new atomic facts admit in each component an initial structure (respectively an initial term structure), and also thoseT for whichM(T) is locally finitely multi-presentable in a canonical way. We also show that these two properties of theories are nonuniform. 相似文献
33.
Srinivasan G. 《物理学报》2006,55(5):2548-2552
讨论了Ni0.8Zn0.2Fe2O4 (NZFO)与锆钛酸铅(PZT)的双层膜结构样品的磁电(ME)效应.NZFO粉料由溶胶-凝胶法制成,再经900℃热压,并高温烧结.在该双层膜中测量到了很强的磁电相互作用.发现横向的磁电效应比纵向效应大一个数量级,并且随NZFO烧结温度的提高而增加.当烧结温度从950℃上升到1380℃时,横向ME电压系数(αE)的最大值变化范围为25.6 mV Am-2≤αE≤199.6 mV Am-2.理论分析显示NZFO-PZT双层膜样品中ME效应源于NZFO与PZT之间相对良好的磁电耦合.
关键词:
镍铁氧体
PZT
热压法
ME效应 相似文献
34.
A construction for Segal operations for K-theory of categories with cofibrations, weak equivalences and a biexact pairing is given and coherence properties of the operations are studied. The model for K-theory, which is used, allows coherence to be studied by means of (symmetric) monoidal functors. In the case of Waldhausen A-theory it is shown how to recover the operations used in Waldhausen (Lecture Notes in Mathematics, Vol. 967, Springer, Berlin, 1982, pp. 390-409) for the A-theory Kahn-Priddy theorem. The total Segal operation for A-theory, which assembles exterior power operations, is shown to carry a natural infinite loop map structure. The basic input is the un-delooped model for K-theory, which has been developed from a construction by Grayson and Gillet for exact categories in Gunnarsson et al. (J. Pure Appl. Algebra 79 (1992) 255), and Grayson's setup for operations in Grayson (K-theory (1989) 247). The relevant material from these sources is recollected followed by observations on equivariant objects and pairings. Grayson's conditions are then translated to the context of categories with cofibrations and weak equivalences. The power operations are shown to be well behaved w.r.t. suspension and are extended to algebraic K-theory of spaces. Staying close with the philosophy of Waldhausen (1982) Waldhausen's maps are found. The Kahn-Priddy theorem follows from splitting the “free part” off the equivariant theory. The treatment of coherence of the total operation in A-theory involves results from Laplaza (Lecture Notes in Mathematics, Vol. 281, Springer, Berlin, 1972, pp. 29-65) and restriction to spherical objects in the source of the operation. 相似文献
35.
36.
A. P. Vink E. van der Kolk P. Dorenbos C. W. E. van Eijk 《Optics Communications》2002,210(3-6):277-284
The optical properties of Ce3+ in CaSO4, SrSO4 and BaSO4 are reported. The Ce3+ ion shows 4f05d1→2F5/2,2F7/2 luminescence in all three sulphates. Co-doping with Na+ does not change the local surrounding of the Ce3+ ion, but enhances the amount of Ce3+ ions built in. Under optical excitation, besides the typical Ce3+ doublet emission in the ultraviolet spectral region, band emission around 445 nm was observed. This band emission was not assigned to emission from a Ce3+ centre, but to emission from an impurity-trapped exciton. Under X-ray excitation, both Ce3+ emission and an emission band around 380 nm was observed. This band was assigned to emission from a self-trapped exciton. 相似文献
37.
Summary In this paper a Gauss-Jordan algorithm with column interchanges is presented and analysed. We show that, in contrast with Gaussian elimination, the Gauss-Jordan algorithm has essentially differing properties when using column interchanges instead of row interchanges for improving the numerical stability. For solutions obtained by Gauss-Jordan with column interchanges, a more satisfactory bound for the residual norm can be given. The analysis gives theoretical evidence that the algorithm yields numerical solutions as good as those obtained by Gaussian elimination and that, in most practical situations, the residuals are equally small. This is confirmed by numerical experiments. Moreover, timing experiments on a Cyber 205 vector computer show that the algorithm presented has good vectorisation properties. 相似文献
38.
39.
Using Brown's construction (J. Algebra 15 (1970) 103) of an exact 6-term sequence for a fibration of groupoids we show how an exact 9-term sequence can be associated to a fibration of bigroupoids. Applications to topology and algebra are given. 相似文献
40.
主要介绍了一个引理,这个引理奠定了K4-同胚图K4(α,1,1,δ,ε,η)色性研究的基础。 相似文献