全文获取类型
收费全文 | 6441篇 |
免费 | 329篇 |
国内免费 | 641篇 |
专业分类
化学 | 2015篇 |
晶体学 | 70篇 |
力学 | 679篇 |
综合类 | 35篇 |
数学 | 2890篇 |
物理学 | 1722篇 |
出版年
2023年 | 93篇 |
2022年 | 120篇 |
2021年 | 118篇 |
2020年 | 112篇 |
2019年 | 179篇 |
2018年 | 139篇 |
2017年 | 191篇 |
2016年 | 170篇 |
2015年 | 200篇 |
2014年 | 315篇 |
2013年 | 593篇 |
2012年 | 338篇 |
2011年 | 401篇 |
2010年 | 407篇 |
2009年 | 510篇 |
2008年 | 459篇 |
2007年 | 443篇 |
2006年 | 333篇 |
2005年 | 263篇 |
2004年 | 266篇 |
2003年 | 181篇 |
2002年 | 183篇 |
2001年 | 162篇 |
2000年 | 127篇 |
1999年 | 118篇 |
1998年 | 108篇 |
1997年 | 116篇 |
1996年 | 94篇 |
1995年 | 67篇 |
1994年 | 80篇 |
1993年 | 49篇 |
1992年 | 57篇 |
1991年 | 28篇 |
1990年 | 34篇 |
1989年 | 36篇 |
1988年 | 28篇 |
1987年 | 12篇 |
1986年 | 11篇 |
1985年 | 30篇 |
1984年 | 24篇 |
1983年 | 14篇 |
1982年 | 30篇 |
1981年 | 32篇 |
1980年 | 30篇 |
1979年 | 27篇 |
1978年 | 18篇 |
1977年 | 17篇 |
1976年 | 18篇 |
1975年 | 8篇 |
1973年 | 8篇 |
排序方式: 共有7411条查询结果,搜索用时 15 毫秒
1.
2.
《Physics letters. A》2019,383(23):2784-2788
By modifying the conventional one-electron hopping behavior, we study effects of an occupation-dependent hopping on the ground state of the half-filled one-dimensional pair-hopping model. At weak coupling, the use of bosonization and renormalization-group analysis techniques helps to derive the phase diagram. Such unusual hopping is shown to drive a spin-gap transition and to introduce a new region where the triplet superconducting instability dominates for positively small pair-hopping interaction. 相似文献
3.
Florence Drui Emmanuel Franck Philippe Helluy Laurent Navoret 《Comptes Rendus Mecanique》2019,347(3):259-269
The over-relaxation approach is an alternative to the Jin–Xin relaxation method in order to apply the equilibrium source term in a more precise way. This is also a key ingredient of the lattice Boltzmann method for achieving second-order accuracy. In this work, we provide an analysis of the over-relaxation kinetic scheme. We compute its equivalent equation, which is particularly useful for devising stable boundary conditions for the hidden kinetic variables. 相似文献
4.
电路过渡过程所列方程是微分方程,本文中采用的是方框图模型分析法,即将微分方程的复杂示解分解成最基本的加(减)、乘(除)、积分(微分)、增益等运算,采用VB设计用户界面产进行计算,并给出了一算例。 相似文献
5.
本文给出了混合型多项式Hammerstein积分方程正解的迭代求法,并将所得结果应用到二阶非线性常微分方程的边值问题 相似文献
6.
在不同激光脉宽下的高次谐波 总被引:3,自引:2,他引:1
用数值计算方法计算了不同强激光脉冲宽度下高次谐波的产生.我们发现对于激光场强度不高,不能有效电离初态的激光场,长脉冲宽度可以更有效产生高次谐波;而对于高场强的激光场,由于它能够在几个光学周期之内把原子的初态全部电离,所以短脉冲的激光场能够更有效产生高次谐波. 相似文献
7.
Leif Schrder Christian Schmitz Peter Bachert 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2004,171(2):87
Proton NMR resonances of the endogenous metabolites creatine and phosphocreatine ((P)Cr), taurine (Tau), and carnosine (Cs, β-alanyl-l-histidine) were studied with regard to residual dipolar couplings and molecular mobility. We present an analysis of the direct 1H–1H interaction that provides information on motional reorientation of subgroups in these molecules in vivo. For this purpose, localized 1H NMR experiments were performed on m. gastrocnemius of healthy volunteers using a 1.5-T clinical whole-body MR scanner. We evaluated the observable dipolar coupling strength SD0 (S = order parameter) of the (P)Cr-methyl triplet and the Tau-methylene doublet by means of the apparent line splitting. These were compared to the dipolar coupling strength of the (P)Cr-methylene doublet. In contrast to the aliphatic protons of (P)Cr and Tau, the aromatic H2 (δ = 8 ppm) and H4 (δ = 7 ppm) protons of the imidazole ring of Cs exhibit second-order spectra at 1.5 T. This effect is the consequence of incomplete transition from Zeeman to Paschen-Back regime and allows a determination of SD0 from H2 and H4 of Cs as an alternative to evaluating the multiplet splitting which can be measured directly in high-resolution 1H NMR spectra. Experimental data showed striking differences in the mobility of the metabolites when the dipolar coupling constant D0 (calculated with the internuclear distance known from molecular geometry in the case of complete absence of molecular dynamics and motion) is used for comparison. The aliphatic signals involve very small order parameters S ≈ (1.4 − 3) × 10−4 indicating rapid reorientation of the corresponding subgroups in these metabolites. In contrast, analysis of the Cs resonances yielded S ≈ (113 − 137) × 10−4. Thus, the immobilization of the Cs imidazole ring owing to an anisotropic cellular substructure in human m. gastrocnemius is much more effective than for (P)Cr and Tau subgroups. Furthermore, 1H NMR experiments on aqueous model solutions of histidine and N-acetyl-l-aspartate (NAA) enabled the assignment of an additional signal component at δ = 8 ppm of Cs in vivo to the amide group at the peptide bond. The visibility of this proton could result from hydrogen bonding which would agree with the anticipated stronger motional restriction of Cs. Referring to the observation that all dipolar-coupled multiplets resolved in localized in vivo 1H NMR spectra of human m. gastrocnemius collapse simultaneously when the fibre structure is tilted towards the magic angle (θ ≈ 55°), a common model for molecular confinement in muscle tissue is proposed on the basis of an interaction of the studied metabolites with myocellular membrane phospholipids. 相似文献
8.
Yao Ping HOU 《数学学报(英文版)》2005,21(4):955-960
A signed graph is a graph with a sign attached to each edge. This paper extends some fundamental concepts of the Laplacian matrices from graphs to signed graphs. In particular, the relationships between the least Laplacian eigenvalue and the unbalancedness of a signed graph are investigated. 相似文献
9.
时滞种群模型的正周期解对所有正解的吸引性 总被引:5,自引:0,他引:5
李永昆 《高校应用数学学报(A辑)》1997,(3)
建立了对数种群模型N′(t)=N(t){r(t)-a1(t)ln[N(t)]-a2(t)ln[N(t-τ(t))]}的周期正解的存在性,并得到了正周期解对所有正解的吸引性. 相似文献
10.
本文讨论一类具有奇异性的超线性边值问题.我们证明,解集存在无界连通分支.作为推论,我们在一定程度上改进了文[1]的主要结果,去掉了其主要条件. 相似文献