全文获取类型
收费全文 | 22147篇 |
免费 | 3753篇 |
国内免费 | 3138篇 |
专业分类
化学 | 16923篇 |
晶体学 | 259篇 |
力学 | 1307篇 |
综合类 | 198篇 |
数学 | 2793篇 |
物理学 | 7558篇 |
出版年
2024年 | 26篇 |
2023年 | 344篇 |
2022年 | 613篇 |
2021年 | 683篇 |
2020年 | 770篇 |
2019年 | 823篇 |
2018年 | 716篇 |
2017年 | 691篇 |
2016年 | 963篇 |
2015年 | 1096篇 |
2014年 | 1275篇 |
2013年 | 1676篇 |
2012年 | 1957篇 |
2011年 | 2010篇 |
2010年 | 1446篇 |
2009年 | 1415篇 |
2008年 | 1586篇 |
2007年 | 1428篇 |
2006年 | 1275篇 |
2005年 | 1141篇 |
2004年 | 935篇 |
2003年 | 726篇 |
2002年 | 751篇 |
2001年 | 637篇 |
2000年 | 503篇 |
1999年 | 458篇 |
1998年 | 419篇 |
1997年 | 317篇 |
1996年 | 311篇 |
1995年 | 286篇 |
1994年 | 260篇 |
1993年 | 214篇 |
1992年 | 178篇 |
1991年 | 188篇 |
1990年 | 188篇 |
1989年 | 134篇 |
1988年 | 125篇 |
1987年 | 94篇 |
1986年 | 77篇 |
1985年 | 76篇 |
1984年 | 34篇 |
1983年 | 39篇 |
1982年 | 29篇 |
1981年 | 23篇 |
1980年 | 15篇 |
1979年 | 11篇 |
1978年 | 9篇 |
1977年 | 13篇 |
1973年 | 9篇 |
1936年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 125 毫秒
71.
利用已知弹性函数级联上高非线性度多输出布尔函数的方法构造(n,m,t)弹性函数,其非线性度为2^n-1-2^n-l/2-1+2^l/2.nlmax(n-l,m,t),在相同条件下改进了Kurosawa的非线性度2^n-1-2^n-l/2-1.特别地,本文构造了两类具体的向量弹性函数,得到两个不同的非线性度.本文所得函数的非线性度在大多数情况下是比较好的. 相似文献
72.
73.
Jiaqiang Wang Hua Fang Ying Li Junjie Li Zhiying Yan 《Journal of molecular catalysis. A, Chemical》2006,250(1-2):75-79
Cobalt-doped mesoporous titania with a crystalline framework synthesized by surfactant templating method presented highly selective (99%) and reasonable conversion rate (49%) of catalytic oxidation of para-chlorotoluene to para-chlorobenzaldehyde in acetic acid using aqueous hydrogen peroxide as oxidant for the first time. Recycling of the catalyst indicates that the catalyst can be used a number of times without losing its activity to a greater extent. By contrast, cobalt-doped mesoporous titania without a crystalline structure and cobalt doped the commercial titania, Degussa P25 prepared by impregnation method with the similar concentration of cobalt were found inactive. The effects of catalyst concentration, reaction time, reaction temperature, and solvents on the performance of the catalyst were also investigated. 相似文献
74.
On Polynomial Functions over Finite Commutative Rings 总被引:1,自引:0,他引:1
Jian Jun JIANG Guo Hua PENG Qi SUN Qi Fan ZHANG 《数学学报(英文版)》2006,22(4):1047-1050
Let R be an arbitrary finite commutative local ring. In this paper, we obtain a necessary and sufficient condition for a function over R to be a polynomial function. Before this paper, necessary and sufficient conditions for a function to be a polynomial function over some special finite commutative local rings were obtained. 相似文献
75.
岳华 《数学的实践与认识》2003,33(6):96-104
本文证明了可分无穷维 Hilbert空间上每个有界线性算子均可写成两个强不可约算子之和 .这回答了文献 [9]中提出一个公开问题 相似文献
76.
Huazhong Tang Tao Tang Kun Xu 《Zeitschrift für Angewandte Mathematik und Physik (ZAMP)》2004,55(3):365-382
In this paper, the Kinetic Flux Vector Splitting (KFVS)
scheme is extended to solving the shallow water equations with
source terms. To develop a well-balanced scheme between the source
term and the flow convection, the source term effect is accounted
in the flux evaluation across cell interfaces. This leads to a
modified gas-kinetic scheme with particular application to the
shallow water equations with bottom topography. Numerical
experiments show better resolution of the unsteady solution than
conventional finite difference method and KFVS method with little
additional cost. Moreover, some positivity properties of the
gas-kinetic scheme is established. 相似文献
77.
78.
ChunXiaLI YingXiaLI LingBoYU HuaZHANG SiftDongCHU HuaShiGUAN 《中国化学快报》2003,14(8):776-778
A convenient synthetic route was developed for the synthesis of the novel glycolipids: 1,2-di-O-acyl-3-O-(2‘-acylamide-2‘-denxy-ct-D-glucopyranosyl)-sn-glycerols. 10 new compounds of glycolipids with different acyl groups were obtained. 相似文献
79.
Xuyuan GuScott Cowell Jinfa YingXuejun Tang Victor J. Hruby 《Tetrahedron letters》2003,44(31):5863-5866
(2S,3S)- and (2R,3R)-2-amino-3-phenyl-5-hexenoic acids have been synthesized in large scale by using Ni(II)-complexes as a template. The amino acids were used in the synthesis of [4,3,0]-bicyclic β-turn mimetics by a convergent methodology. The unique advantage of this strategy is the convenience of introducing side chain groups with predetermined chiralities on both the five- and six-membered heterocyclic rings. 相似文献
80.
We examine the ferroelectric-relaxor behavior of (Ba0.65Sr0.35)(Zr0.35Ti0.65)O3 (BSZT) ceramics in the temperature range from 80 to 380 K. A broad dielectric maximum, which shifts to higher temperature with increasing frequency, signifies the relaxor-type behavior of these ceramics. The value of the relaxation parameter γ∼2 estimated from the linear fit of the modified Curie-Weiss law, indicates the relaxor nature of the BSZT ceramics. The dielectric relaxation rate follows the Vogel-Fulcher relation with TVF=107 K, Ea=0.121 eV, and ν0=6.83×1014 Hz, further supports such relaxor nature. The slim P-E hysteresis loop and ‘butterfly’ shape dc bias field dependence of permittivity at T>Tm (Tm, the temperature of permittivity maximum) clearly signifies the occurrence of nanopolar clusters, which is the typical characteristic of ferroelectric relaxor. At 300 K and 10 kHz, the dielectric constant and loss tan δ are ∼1100 and 0.0015, respectively. The high tunability (∼25%) and figure of merit (∼130) at room temperature show that the BSZT ceramics could be a promising candidate for tunable capacitor applications. 相似文献