全文获取类型
收费全文 | 21533篇 |
免费 | 3463篇 |
国内免费 | 3659篇 |
专业分类
化学 | 9331篇 |
晶体学 | 469篇 |
力学 | 732篇 |
综合类 | 338篇 |
数学 | 1813篇 |
物理学 | 6252篇 |
无线电 | 9720篇 |
出版年
2024年 | 89篇 |
2023年 | 308篇 |
2022年 | 698篇 |
2021年 | 754篇 |
2020年 | 680篇 |
2019年 | 590篇 |
2018年 | 654篇 |
2017年 | 823篇 |
2016年 | 758篇 |
2015年 | 944篇 |
2014年 | 1229篇 |
2013年 | 1617篇 |
2012年 | 1666篇 |
2011年 | 1800篇 |
2010年 | 1588篇 |
2009年 | 1634篇 |
2008年 | 1818篇 |
2007年 | 1690篇 |
2006年 | 1540篇 |
2005年 | 1354篇 |
2004年 | 1050篇 |
2003年 | 857篇 |
2002年 | 785篇 |
2001年 | 670篇 |
2000年 | 770篇 |
1999年 | 410篇 |
1998年 | 250篇 |
1997年 | 172篇 |
1996年 | 190篇 |
1995年 | 136篇 |
1994年 | 174篇 |
1993年 | 147篇 |
1992年 | 121篇 |
1991年 | 105篇 |
1990年 | 93篇 |
1989年 | 76篇 |
1988年 | 60篇 |
1987年 | 42篇 |
1986年 | 48篇 |
1985年 | 37篇 |
1984年 | 34篇 |
1983年 | 29篇 |
1982年 | 29篇 |
1981年 | 31篇 |
1980年 | 25篇 |
1979年 | 16篇 |
1978年 | 10篇 |
1976年 | 8篇 |
1975年 | 7篇 |
1974年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
62.
63.
Based on the algebraic entanglement measure proposed [G. Vidal et al., Phys. Rev. A 65 (2002) 032314],we study the entanglement evolution of both pure quantum states and mixed ones of 2-qutrit system in a symmetrybroken environment consisting of a fermionic bath. Entanglement of states will decrease or remain constant under the influence of environment, and the class of states which remain unchanged has been found out. 相似文献
64.
Do W. Lee Eun Y. Seo Sung I. Cho Chae S. Yi 《Journal of polymer science. Part A, Polymer chemistry》2004,42(11):2747-2755
Pyridine‐2‐carboximidates [methyl ( 1a ), ethyl ( 1b ), isopropyl ( 1c ), cyclopentyl ( 1d ), cyclohexyl ( 1e ), n‐octyl ( 1f ), and benzyl ( 1g )] were prepared from the reaction of 2‐cyanopyridine with the corresponding alcohols. Cyclopentyl‐substituted 1d was found to be a highly effective ligand for copper‐catalyzed atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA). For example, the observed rate constant for a CuBr/ 1d catalytic system was found to be nearly twice as high as the cyclohexyl‐substituted CuBr/ 1e catalytic system [kobs = (1.19 vs 0.56) × 10?4 s?1). The effects of the solvents, temperature, catalyst/initiator, and solvent/monomer ratio on the ATRP of MMA were studied systematically for the CuBr/ 1d catalytic system. The optimum condition for the ATRP of MMA was found to be a 1:2:1:400 [CuBr]o/[ 1d ]o/[ethyl 2‐bromoisobutyrate]o/[MMA]o ratio at 60 °C in veratrole solution, which yielded well‐defined poly(MMA) with a narrow molecular weight distribution of 1.14. The catalytically active copper complex 2d was isolated from the reaction of CuBr with 1d . Narrow molecular weight distributions as low as 1.06 were achieved for the CuBr/ 1d catalytic system by employing 10% of the deactivator CuBr2. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2747–2755, 2004 相似文献
65.
66.
Jaedong Cho John Blackwell Sergei N. Chvalun Morton Litt Yuan Wang 《Journal of Polymer Science.Polymer Physics》2004,42(13):2576-2585
As‐cast films of poly(2,5‐benzimidazole) exhibit uniplanar orientation in which the planes of the aromatic rings lie parallel to the film surface. Upon doping with phosphoric acid, the original crystalline order is lost, but the doped film can be stretched to produce films with uniaxial orientation. After thermal annealing at 540 °C, nine Bragg reflections are resolved in the fiber diagram, and these are indexed by an orthorhombic unit cell with the dimensions a = 18.1 Å, b = 3.5 Å, and c = 11.4 Å, containing four monomer units of two chains. The absence of odd‐order 00l reflections points to a 21 chain conformation, which is probably planar so that the aromatic units can be stacked along the b axis. The water and phosphoric acid contents of the crystalline structure cannot be determined exactly because of the presence of extensive amorphous regions that probably have different solvation. The best agreement between the observed and calculated intensities is for an idealized structure containing two phosphoric acids and two water molecules per unit cell. However, the phosphoric acid is probably present mainly in the form of pyrophosphoric acid and its higher oligomers. In addition, the X‐ray data are consistent with a more disordered structure containing chains with random (up and down) polarity and a lack of c‐axis registry. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2576–2585, 2004 相似文献
67.
68.
69.
与传统时域有限差分算法相比,采用以伪谱方法离散Maxwell微分方程为基础的时域伪谱(PSTD)算法计算大的电尺度电磁场时域问题,将大大提高计算效率,降低内存需求。为了拓宽PSTD算法的应用,近年来,基于网格插值方法的非均匀时域伪谱算法得到了发展。研究的重点是算法中非均匀网格技术的实现及其在时域瞬态脉冲电磁场模拟和高功率超宽带脉冲技术方面的应用。以高斯脉冲为激励源,用该算法计算了多层介质的反射和透射,并通过超宽带脉冲穿墙实验对这一方法的应用进行了验证。模拟和实验结果具有较好的一致性。 相似文献
70.
近年来,Bridges等人在Hamiltonian力学意义下,直接把有限维Hamiltonian系统推广到无穷维,通过引入新的函数坐标,使得偏微分方程在时间和空间的各个方向上都有各自不同的有限维辛结构,这样原偏微分方程就由各个有限维辛结构以及右端的梯度函数决定,称这样的方程为多辛Hamiltonian系统.多辛Hamiltonian系统满足多辛守恒定律,满足多辛Hamiltonian系统的多辛守恒律的离散算法称为多辛算法.以耦合非线性Schr dinger方程为例,研究无穷维Hamiltonian系统的多辛算法,验证了两孤立子碰撞后会发生相互通过、反射及融合现象. 相似文献