全文获取类型
收费全文 | 2416篇 |
免费 | 76篇 |
国内免费 | 115篇 |
专业分类
化学 | 488篇 |
晶体学 | 6篇 |
力学 | 135篇 |
综合类 | 27篇 |
数学 | 1000篇 |
物理学 | 951篇 |
出版年
2024年 | 3篇 |
2023年 | 61篇 |
2022年 | 27篇 |
2021年 | 39篇 |
2020年 | 41篇 |
2019年 | 40篇 |
2018年 | 45篇 |
2017年 | 62篇 |
2016年 | 68篇 |
2015年 | 63篇 |
2014年 | 84篇 |
2013年 | 223篇 |
2012年 | 94篇 |
2011年 | 95篇 |
2010年 | 93篇 |
2009年 | 156篇 |
2008年 | 123篇 |
2007年 | 140篇 |
2006年 | 135篇 |
2005年 | 86篇 |
2004年 | 82篇 |
2003年 | 71篇 |
2002年 | 88篇 |
2001年 | 75篇 |
2000年 | 70篇 |
1999年 | 93篇 |
1998年 | 55篇 |
1997年 | 62篇 |
1996年 | 44篇 |
1995年 | 50篇 |
1994年 | 30篇 |
1993年 | 39篇 |
1992年 | 14篇 |
1991年 | 9篇 |
1990年 | 12篇 |
1989年 | 16篇 |
1988年 | 21篇 |
1987年 | 16篇 |
1986年 | 13篇 |
1985年 | 10篇 |
1984年 | 6篇 |
1983年 | 5篇 |
1982年 | 9篇 |
1981年 | 13篇 |
1980年 | 5篇 |
1979年 | 8篇 |
1978年 | 5篇 |
1974年 | 2篇 |
1973年 | 3篇 |
1969年 | 1篇 |
排序方式: 共有2607条查询结果,搜索用时 31 毫秒
101.
102.
The torsional vibrations of star molecules are studied with a reduced dimensionality model. In this model, the molecule is described by two equivalent sets of lumped inertial cylinders and vibrational frequencies are predicted by solution of the coupled equations of motion. Force constants are determined by including them as free parameters in the model and fitting the computed frequencies to their analogs as determined using full normal coordinate analysis at the HFSCF level of theory. Best agreement between the methods occurs when torsional force constants are included for the first two layers of the molecule. This reveals that non-bonded torsional interactions are important in the vibrational dynamics of these systems. Further insight is afforded by an analysis of why simple harmonic oscillator models are sufficient for modeling some related systems but fail to reproduce the trend in global mode frequencies for saturated aliphatic star molecules. The analysis reveals that the origin of this failure lies in backbone flexibility in these branched polymeric systems. 相似文献
103.
Here we present a simple yet effective gas chromatography-mass spectrometry (GC-MS) identification approach for the detection of heteroatom-containing compounds (HACCs) in petroleum fractions. The MS/AMDIS (Automated Mass Spectral Deconvolution and Identification System) program was used to identify parts per million (ppm) HACC concentrations in petroleum fractions in place of traditional techniques (extraction and standard injection). Polycyclic aromatic sulfur heterocycles (S-PAHs) were used as model compounds to confirm the validity of the AMDIS identifiers, which were compared with extracted results using the off-line X-calibur software. AMDIS was able to identify ppm concentrations of S-PAHs in oil condensate. There was good agreement between experimental and AMDIS identification results for S-PAHs in oil condensate. AMDIS was also used to detect nitrogen-containing compounds (NCCs) and alkylphenols in oil condensate. Our results confirmed the presence of 2-methylbenzothiazole, carbazole, and 2,4-ditertbutyl phenol. In a crude oil sample, AMDIS identification of m/z=191 biomarkers was consistent with empirical results. Therefore, AMDIS can help to reduce the number of experimental steps in identification protocols. 相似文献
104.
Correlated electron current and temperature dependence of the conductance of a quantum point contact
C. Sloggett A. I. Milstein O. P. Sushkov 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,61(4):427-432
We investigate finite temperature corrections to the Landauer formula
due to electron–electron interaction within the quantum point contact.
When the Fermi level is close to the barrier height, the conducting
wavefunctions become peaked on the barrier, enhancing the
electron–electron interaction. At the same time, away from the contact
the interaction is strongly suppressed by screening. To describe
electron transport we formulate and solve a kinetic equation for the
density matrix of electrons. The correction to the conductance G is
negative and strongly enhanced in the region 0.5 × 2e2/h ≤ G
≤ 1.0 × 2e2/h. Our results for conductance agree with the
so-called “0.7 structure” observed in experiments. 相似文献
105.
Thermal conductance of nanofluids: is the controversy over? 总被引:1,自引:1,他引:1
Over the last decade nanofluids (colloidal suspensions of solid nanoparticles) sparked excitement as well as controversy.
In particular, a number of researches reported dramatic increases of thermal conductivity with small nanoparticle loading,
while others showed moderate increases consistent with the effective medium theories on well-dispersed conductive spheres.
Accordingly, the mechanism of thermal conductivity enhancement is a hotly debated topic. We present a critical analysis of
the experimental data in terms of the potential mechanisms and show that, by accounting for linear particle aggregation, the
well established effective medium theories for composite materials are capable of explaining the vast majority of the reported
data without resorting to novel mechanisms such as Brownian motion induced nanoconvection, liquid layering at the interface,
or near-field radiation. However, particle aggregation required to significantly enhance thermal conductivity, also increases
fluid viscosity rendering the benefit of nanofluids to flow based cooling applications questionable. 相似文献
106.
107.
1.引言考虑非线性代数方程组这里, 为连续的对角映射,二者的导函数均存在,但并不一定连续.这类非线性代数方程组具有丰富的实际背景.譬如,Stefan问题和许多弱非线性椭圆型偏微分方程,就可归结为(1.1)的数值求解问题.根据方程组(1.1)的特殊结构,并利用矩阵多重分裂思想,文tZ]讨论了一类并行非线性Gauss-Seidel型迭代算法.这类算法具有很好的数值性质和较高的并行效率·在此基础上,运用松弛加速技术,文[8]进一步研究了一类并行多分… 相似文献
108.
Pierre-yves Le Gall 《K-Theory》1999,16(4):361-390
Let
be a locally compact topological groupoid, A and B two C*-algebras endowed with a continuous action of
. We define an operator K-theory group K K
(A,B). We describe two basic properties of this theory: the existence of a Kasparov product and functoriality with respect to groupoid cocycles. 相似文献
109.
一类描述混沌映射的符号动力系统 总被引:11,自引:0,他引:11
本文定义了符号空间上的拟移位映射,并用该类映射描述了Cantor集及平面Cantor集上的混沌映射,本文结果可看作Smale马蹄模型的简化。 相似文献
110.
61.Intr0ducti0nInthispaper,wediscussareactionnetinacombusti0nmodel:V={R,,R2},whereR,andR2aredistinctreacti0nprocesses:Rl:A1+A,-A,,R2:A2+A3-P,A,(j=1,2,3)denotesthereactant,andPdenotestheinertproduct.Thesereactionsareexothermicreactions-LetQ,,Q2standforheatenergiesandU=(U,,U,,U,,U,)forstatevariablesdescribingreactions,whereUoisreactiontemporature,andU,(j=1,2,3)isthemolarityofthej-threactant.AssumethatV,(i=1,2)isthereactantvariablefortheithreactionpr0cess:V,=(Q,,1,-l,l)",V2=(Q,,O,-l,-… 相似文献