全文获取类型
收费全文 | 16962篇 |
免费 | 3278篇 |
国内免费 | 4146篇 |
学科分类
数理化 | 24386篇 |
出版年
2024年 | 46篇 |
2023年 | 189篇 |
2022年 | 519篇 |
2021年 | 565篇 |
2020年 | 744篇 |
2019年 | 691篇 |
2018年 | 658篇 |
2017年 | 827篇 |
2016年 | 1037篇 |
2015年 | 782篇 |
2014年 | 1025篇 |
2013年 | 1692篇 |
2012年 | 1505篇 |
2011年 | 1493篇 |
2010年 | 1276篇 |
2009年 | 1220篇 |
2008年 | 1185篇 |
2007年 | 1171篇 |
2006年 | 1050篇 |
2005年 | 895篇 |
2004年 | 813篇 |
2003年 | 686篇 |
2002年 | 738篇 |
2001年 | 587篇 |
2000年 | 489篇 |
1999年 | 401篇 |
1998年 | 341篇 |
1997年 | 267篇 |
1996年 | 253篇 |
1995年 | 217篇 |
1994年 | 188篇 |
1993年 | 128篇 |
1992年 | 124篇 |
1991年 | 83篇 |
1990年 | 85篇 |
1989年 | 57篇 |
1988年 | 58篇 |
1987年 | 34篇 |
1986年 | 34篇 |
1985年 | 41篇 |
1984年 | 36篇 |
1983年 | 25篇 |
1982年 | 31篇 |
1981年 | 15篇 |
1980年 | 15篇 |
1979年 | 8篇 |
1978年 | 16篇 |
1976年 | 12篇 |
1975年 | 7篇 |
1973年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
51.
Koichi Itoh Takeji Takui 《Proceedings of the Japan Academy. Series B, Physical and biological sciences》2004,80(2):29
This review paper deals with an overview of molecule-based magnetism as a rapidly developing interdisciplinary field, topological symmetry rule as the first principle of spin alignment in organic open-shell systems in the ground state, the proposal of organic through-bond 1D and 2D ferro- and superparamagnets and the detection of the first organic high-spin molecule, m-phenylenebis(phenylmethylene) in the quintet ground state (S = 2), followed by extended organic high-spin systems with π-conjugation such as aromatic hydrocarbons having S = 3, 4, 5. The paper also describes a theoretical approach to the understanding of electronic spin structures of organic high-spin molecules by invoking both Heisenberg and Hubbard model Hamiltonians, weakly interacting intramolecular high-spin systems from both experimental and theoretical sides, the spin density distribution of the first organic high-spin molecule in terms of electron- nuclear multiple resonance spectroscopy and the detection and characterization of ionic high-spin hydrocarbons, emphasizing the establishment of high spin chemistry underlying organic molecular magnetism. 相似文献
52.
L. Saloff-Coste 《Potential Analysis》1995,4(4):429-467
Old and recent results concerning Harnack inequalities for divergence form operators are reviewed. In particular, the characterization of the parabolic Harnack principle by simple geometric properties -Poincaré inequality and doubling property- is discussed at length. It is shown that these two properties suffice to apply Moser's iterative technique. 相似文献
53.
H-空间与拟向量变分不等式 总被引:2,自引:0,他引:2
本在Hausdorff locally convex H-空间上建立了一个新的不动点定理;利用局部交性质,在Hausdorff locally convex H-空间上建立了相应的拟向量变分不等式. 相似文献
54.
Hubert Kalf 《Journal of Differential Equations》2004,205(2):408-423
We show that the point spectrum of the standard Coulomb-Dirac operator H0 is the limit of the point spectrum of the Dirac operator with anomalous magnetic moment Ha as the anomaly parameter tends to 0. For negative angular momentum quantum number κ, this holds for all Coulomb coupling constants c for which H0 has a distinguished self-adjoint realisation. For positive κ, however, there are some exceptional values for c, and in general an index shift between the eigenvalues of H0 and the limits of eigenvalues of Ha appears, accompanied with additional oscillations of the eigenfunctions of Ha very close to the origin. 相似文献
55.
The propagation properties of decentered twisted Gaussian Schell-model (DTGSM) beams passing through a misaligned first-order optical system are studied. The explicit expressions for the cross-spectral density function and Wigner distribution function of the output beam are derived, which retain their form unchanged. It is shown that the DTGSM beams preserve their closed property. The second-order moments matrix and the Wigner distribution function evolve with the usual laws, whereas the first-order moments matrix varies, as if a ray passes through such system. The propagation of DTGSM beams through an aligned first-order optical system is treated as the limiting case that corresponds to the vanishing misalignment parameters. 相似文献
56.
旋转带电体磁矩计算的若干法则与算例 总被引:2,自引:0,他引:2
本文在文献 [1]、[2 ]等的基础上给出关于旋转带电体的磁矩计算的若干法则 ,均以定理形式表达 ,并列表枚举其相关算例 相似文献
57.
The reactions of bis(trimethylstannyl)ethyne, Me3Sn–C?C–SnMe3 ( 4 ), with trimethylsilyl‐ or dimethylsilyl‐dialkylboryl‐substituted alkenes 1 – 3 afford organometallic‐substituted allenes 5 , 6 and 8 , 9 in high yield. In the case of (E)‐2‐trimethylsilyl‐3‐diethylboryl‐2‐pentene ( 1) , a butadiene derivative 7 could be detected as an intermediate prior to rearrangement into the allene. All reactions were monitored by 29Si and 119Sn NMR, and the products were characterized by an extensive NMR data set (1H, 11B, 13C, 29Si, 119Sn NMR). Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
58.
Thi Thi Nge Naruhito Hori Akio Takemura Hirokuni Ono Tsunehisa Kimura 《Journal of Polymer Science.Polymer Physics》2003,41(7):711-714
A high magnetic field of 5 T was used to fabricate a magnetically aligned, optically anisotropic, liquid‐crystalline chitin/poly(acrylic acid) composite. The aligned mesophase was fixed by photoinitiated free‐radical polymerization. From an examination of polarized optical micrographs and an X‐ray diffraction study, a high degree of orientation of 0.70 was observed for the composite with a higher liquid‐crystalline chitin concentration (10.70 wt %); the orientation was reduced with a decreased chitin concentration at a given acrylic acid concentration. The X‐ray data for the developed composite showed a uniplanar orientation for the chitin crystallites, with its molecular long axes perpendicular to the direction of the magnetic field. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 711–714, 2003 相似文献
59.
60.
求解非对称线性方程组的QMRGCGS方法 总被引:2,自引:1,他引:1
1 引言 求解非对称线性方程组Ax=b的双共轭梯度方法(BCG)[3]和它的变形共轭梯度平方方法(CGS)[6]都有典型的不规则收敛行为,后来Freund和Nachtigal提出一种BCG类方法,即拟极小剩余方法(QMR)[7],用来补救BCG方法的收敛性并且产生了光滑的收敛曲线。然而,象BCG方法一样,QMR方法要用到系数矩阵A及其转置A~T与向量的乘积,为了解决这一问题,Freund提出TFQMR方法,此方法具有拟极小剩余性,同时不需用到A~T与向量的乘积。 相似文献