全文获取类型
收费全文 | 16394篇 |
免费 | 3751篇 |
国内免费 | 1947篇 |
专业分类
化学 | 11170篇 |
晶体学 | 159篇 |
力学 | 895篇 |
综合类 | 135篇 |
数学 | 2807篇 |
物理学 | 6926篇 |
出版年
2024年 | 52篇 |
2023年 | 235篇 |
2022年 | 350篇 |
2021年 | 526篇 |
2020年 | 686篇 |
2019年 | 646篇 |
2018年 | 547篇 |
2017年 | 620篇 |
2016年 | 964篇 |
2015年 | 900篇 |
2014年 | 1090篇 |
2013年 | 1720篇 |
2012年 | 1183篇 |
2011年 | 1151篇 |
2010年 | 1008篇 |
2009年 | 1078篇 |
2008年 | 1170篇 |
2007年 | 1191篇 |
2006年 | 1016篇 |
2005年 | 966篇 |
2004年 | 782篇 |
2003年 | 680篇 |
2002年 | 498篇 |
2001年 | 402篇 |
2000年 | 402篇 |
1999年 | 341篇 |
1998年 | 308篇 |
1997年 | 243篇 |
1996年 | 183篇 |
1995年 | 176篇 |
1994年 | 144篇 |
1993年 | 107篇 |
1992年 | 101篇 |
1991年 | 69篇 |
1990年 | 63篇 |
1989年 | 63篇 |
1988年 | 70篇 |
1987年 | 45篇 |
1986年 | 45篇 |
1985年 | 53篇 |
1984年 | 39篇 |
1983年 | 13篇 |
1982年 | 32篇 |
1981年 | 34篇 |
1980年 | 16篇 |
1979年 | 15篇 |
1978年 | 15篇 |
1977年 | 14篇 |
1976年 | 8篇 |
1974年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 156 毫秒
71.
本研究应用聚类分析的方法,对人离休髁突×片进行数字图像技术处理所获得的影像密度数值做了详细分析,取得人髁突不同区的骨密度分布及不同年龄阶段髁突密度变化的情况。该方法避免了人为因素的影响,其结果较客观地反映了髁突的骨质密度;为研究病理状态时髁突骨密度的改变提供参考。 相似文献
72.
本文介绍了多路逆磁测量方法及利用这一方法在HER装置上测量热电子环沿轴向的长度与晃荡电子密度的轴向分布的实验结果。 相似文献
73.
In this work two non-local problems for the parabolic-hyperbolic type equation with non-characteristic line of changing type
are considered. Unique solvability of these problems is proven. The uniqueness of the solution is proven by the method of
energy integrals and the existence is proven by the method of integral equations. 相似文献
74.
For approximate wave functions, we prove the theorem that there is a one‐to‐one correspondence between the constraints of normalization and of the Fermi–Coulomb and Coulomb hole charge sum rules at each electron position. This correspondence is surprising in light of the fact that normalization depends on the probability of finding an electron at some position. In contrast, the Fermi–Coulomb hole sum rule depends on the probability of two electrons staying apart because of correlations due to the Pauli exclusion principle and Coulomb repulsion, while the Coulomb hole sum rule depends on Coulomb repulsion. We demonstrate the theorem for the ground state of the He atom by the use of two different approximate wave functions that are functionals rather than functions. The first of these wave function functionals is constructed to satisfy the constraint of normalization, and the second that of the Coulomb hole sum rule for each electron position. Each is then shown to satisfy the other corresponding sum rule. The significance of the theorem for the construction of approximate “exchange‐correlation” and “correlation” energy functionals of density functional theory is also discussed. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 相似文献
75.
One influential parameter which mediates interactions between many types of molecules and biological membranes stems from
the lumped contributions of the transmembrane potential, dipole potential and the difference in the surface potentials on
both sides of a membrane. With relevance to cell physiology, such electrical features of a biomembrane are prone to undergoing
changes as a result of interactions with the aqueous surrounding. Among the most useful tools devoted to exploring changes
of electrical parameters of a lipid membrane induced by certain extracellular ions, lipid composition, and embedded membrane
peptides and proteins, are spectroscopic imaging and the inner field compensation (IFC) method. In this work we layout the
principles of a fully computerized version of the IFC method, which makes it more readily available to users. As a direct
application, we deployed this improved version of the IFC method to time-resolve changes induced by alamethicin monomers upon
membrane dipole potential, following their aggregation within an artificial lipid membrane. Intriguingly, even prior crossing
the membrane core, the membrane-bound alamethicin monomers are shown to significantly increase the dipole potential of the
monolayer they reside in. Such data further emphasize the yet less-explored interplay between membrane-based protein and peptides,
and the membrane dipole potential. 相似文献
76.
An investigation of BELENE Nuclear Power Plant (NPP) free field signal is presented in the current study. An SH wave propagation trough multilayer geological media in the region is considered. An original structural model of the geological column has been developed. The investigated layers are isotropic, with constant depth and skyline parallel. The SH rays are with an arbitrary angle as far as the layers are concerned. The seismic SH waves have been generated by a special detonation device. The main results of the study are graphically illustrated. A comparison between the original BELENE NPP experimental and the numerical surface (free field) signals (obtained by the formulated direct problem) for the investigated geological column has been carried out and its results are hereby shown. 相似文献
77.
Frank H.G.M. Wijnands Charles G. Crookes Paul M. Charles Richard M. Ash Ian F. Lealman Michael J. Robertson Anthony E. Kelly Kevin A. Williams Aeneas B. Massara Richard V. Penty Ian H. White 《Optical and Quantum Electronics》2002,34(10):959-973
An anomalous modulation in the wavelength spectrum has been observed in lasers with spot-size converters. This intensity modulation is shown to be caused by beating between the fundamental lasing mode and radiation modes in the taper. This results in a periodic modulation in the net gain spectrum, which causes wavelength jumps between adjacent net gain maxima, and a drive current dependent spectral width that is expected to affect system performance. The amplitude of this spectral modulation is reduced significantly by either using an angled rear-facet which reflects the beating radiation modes away from the laser axis, or by using a nonlinear, adiabatic taper. 相似文献
78.
79.
Devin Kilminster David Allingham Alistair Mees 《Annals of the Institute of Statistical Mathematics》2002,54(1):224-233
Knowing a probability density (ideally, an invariant density) for the trajectories of a dynamical system allows many significant estimates to be made, from the well-known dynamical invariants such as Lyapunov exponents and mutual information to conditional probabilities which are potentially more suitable for prediction than the single number produced by most predictors. Densities on typical attractors have properties, such as singularity with respect to Lebesgue measure, which make standard density estimators less useful than one would hope. In this paper we present a new method of estimating densities which can smooth in a way that tends to preserve fractal structure down to some level, and that also maintains invariance. We demonstrate with applications to real and artificial data. 相似文献
80.