全文获取类型
收费全文 | 435368篇 |
免费 | 5526篇 |
国内免费 | 1228篇 |
专业分类
化学 | 233759篇 |
晶体学 | 6489篇 |
力学 | 18765篇 |
综合类 | 13篇 |
数学 | 49929篇 |
物理学 | 133167篇 |
出版年
2021年 | 3760篇 |
2020年 | 4185篇 |
2019年 | 4519篇 |
2018年 | 5855篇 |
2017年 | 5744篇 |
2016年 | 8831篇 |
2015年 | 5561篇 |
2014年 | 8542篇 |
2013年 | 20183篇 |
2012年 | 15649篇 |
2011年 | 19263篇 |
2010年 | 13497篇 |
2009年 | 13350篇 |
2008年 | 17648篇 |
2007年 | 17541篇 |
2006年 | 16253篇 |
2005年 | 14550篇 |
2004年 | 13524篇 |
2003年 | 11892篇 |
2002年 | 11728篇 |
2001年 | 13429篇 |
2000年 | 10085篇 |
1999年 | 7916篇 |
1998年 | 6569篇 |
1997年 | 6314篇 |
1996年 | 6081篇 |
1995年 | 5470篇 |
1994年 | 5392篇 |
1993年 | 5197篇 |
1992年 | 5828篇 |
1991年 | 5924篇 |
1990年 | 5664篇 |
1989年 | 5472篇 |
1988年 | 5493篇 |
1987年 | 5374篇 |
1986年 | 5091篇 |
1985年 | 6560篇 |
1984年 | 6694篇 |
1983年 | 5301篇 |
1982年 | 5387篇 |
1981年 | 5367篇 |
1980年 | 4955篇 |
1979年 | 5352篇 |
1978年 | 5491篇 |
1977年 | 5385篇 |
1976年 | 5328篇 |
1975年 | 4914篇 |
1974年 | 4885篇 |
1973年 | 4880篇 |
1972年 | 3455篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
901.
ALEPH Collaboration D. Buskulic D. Casper I. De Bonis D. Decamp P. Ghez C. Goy J. -P. Lees A. Lucotte M. -N. Minard et al. 《Zeitschrift fur Physik C Particles and Fields》1995,69(1):379-392
A data sample of about 3.0 million hadronicZ decays collected by the ALEPH experiment at LEP in the years 1991 through 1994 is used to make an inclusive selection of
B hadron events. In this event sample 4227±140±252B* mesons in the decayB*→Bγ and 1944±108±161B**
u,d
mesons decaying into a B meson and a charged pion are reconstructed. Here and in the followingB**
u,d
denotes the eightL=1(bū) and (bd) states and their charge conjugate.
For the well establishedB* meson the following quantities are obtained:ΔM=M
B*−MB=(45.30±0.35±0.87) MeV/c2 andN
B*/(N
B+N
B*)=(77.1±2.6±7.0)%. The angular distribution of the photons in theB* rest frame is used to measure the relative contribution of longitudinalB* polarization states to beσ
L/(σ
L+σ
T)=(33±6±5)%. 相似文献
902.
N. M. Borodachev 《International Applied Mechanics》2002,38(5):556-561
The general solution to the spatial stress problem for an elastic layer is given in a new form. A layer compressed by normal forces uniformly distributed over a square is considered as an example. 相似文献
903.
JOSEF MÁLEK JINDŘICH NEČAS K. R. RAJAGOPAL 《Archive for Rational Mechanics and Analysis》2002,165(3):243-269
To describe the flows of fluids over a wide range of pressures, it is necessary to take into account the fact that the viscosity
of the fluid depends on the pressure. That the viscosity depends on the pressure has been verified by numerous careful experiments.
While the existence of solutions local-in-time to the equations governing the flows of such fluids are available for small,
special data and rather unrealistic dependence of the viscosity on the pressure, no global existence results are in place.
Our interest here is to establish the existence of weak solutions for spatially periodic three-dimensional flows that are
global in time, for a large class of physically meaningful viscosity-pressure relationships.
(Accepted May 1, 2002) Published online November 15, 2002
Communicated by S. S. ANTMAN 相似文献
904.
A generalization of strong regularity around a vertex subset C of a graph Γ, which makes sense even if Γis non-regular, is studied. Such a structure appears, together with a kind of distance-regularity around C , when an spectral bound concerning the so-called predistance polynomial of C is attained. As a main consequence of these results, it is shown that a regular (connected) graph Γwith d + 1 distinct eigenvalues is distance-regular, and its distance- d graph Γ d is strongly regular with parameters a = c , if and only if the number of vertices at distance d from each vertex satisfies an expression which depends only on the order of Γand the different eigenvalues of Γ. 相似文献
905.
B. MacMillan M. Halse M. Schneider L. Fardy Y. H. Chui B. J. Balcom 《Applied magnetic resonance》2002,22(2):247-256
Magnetic resonance imaging has rarely been applied to rigid polymeric materials, due primarily to the strong dipolar coupling and short signal lifetimes inherent in these materials. SPRITE (single point ramped imaging withT 1 enhancement) (B. J. Balcom, R. P. MacGregor, S. D. Beyea, D. P. Green, R. L. Armstrong, T. W. Bremner: J. Magn. Reson. A123, 131–134, 1996) is particularly well suited to imaging solid materials. With SPRITE, the only requirement is thatT 2* be long enough so that the signal can be phase-encoded. The minimum phase encoding time is limited by the maximum gradient strength available and by the instrument deadtime. At present this is usually tens of microseconds and will only improve with refinements in technology. We have used the SPRITE sequence in conjunction with raising the sample temperature to obtain images of rigid polymers that have largely frustrated conventional imaging methods. This approach provides a straightforward and reliable method for imaging a class of samples that, up until now, have been very difficult to image. 相似文献
906.
S. Kwieciński M. Weychert A. Jasiński P. Kulinowski I. Wawer E. Sieradzki 《Applied magnetic resonance》2002,22(1):23-29
The disintegration of bromhexin tablets was monitored by magnetic resonance imaging. The fast imaging method FLASH with spoiling
gradients was used to obtain images of the tablets in short time intervals. The rate of the disintegration depends on the
preparation method, kind and percentage of the carrier (polyethylene glycol, lactose). Solid dispersion with slow evaporation
of solvent yields materials with decreased dissolution rate. Increasing molecular mass of polyethylene glycol and its percentage
content also hampers disintegration. 相似文献
907.
B. Pignataro L. Chi S. Gao B. Anczykowski C. Niemeyer M. Adler H. Fuchs 《Applied Physics A: Materials Science & Processing》2002,74(3):447-452
Self-assembled oligomeric nanostructures consisting of bisbiotinylated DNA fragments connected by the protein streptavidin
(STV) are studied by dynamic scanning force microscopy (SFM) operating in air. A comparison of the images taken in repulsive
and attractive regimes is systematically made on DNA and STV structures. Stable and reproducible SFM images are obtained in
the attractive regime by using a special feedback circuit, called Q-control. On the other hand, when SFM is operating in the
repulsive regime, deformation of the structures that reduce the resolution and the image quality are clearly observable. The
heights of both DNA and STV have been measured as a function of the tip/molecule interaction forces. This study offers the
possibility to suggest a different mechanical behavior of DNA with respect to STV.
Received: 24 July 2001 / Accepted: 3 December 2001 / Published online: 4 March 2002 相似文献
908.
P. Kratzer E. Penev M. Scheffler 《Applied Physics A: Materials Science & Processing》2002,75(1):79-88
We demonstrate how first-principles calculations using density-functional theory (DFT) can be applied to gain insight into
the molecular processes that rule the physics of materials processing. Specifically, we study the molecular beam epitaxy (MBE)
of arsenic compound semiconductors. For homoepitaxy of GaAs on GaAs (001), a growth model is presented that builds on results
of DFT calculations for molecular processes on the β2-reconstructed GaAs (001) surface, including adsorption, desorption,
surface diffusion, and nucleation. Kinetic Monte Carlo simulations on the basis of the calculated energetics enable us to
model MBE growth of GaAs from beams of Ga and As2 in atomistic detail. The simulations show that island nucleation is controlled by the reaction of As2 molecules with Ga adatoms on the surface. The analysis reveals that the scaling laws of standard nucleation theory for the
island density as a function of growth temperature are not applicable to GaAs epitaxy. We also discuss heteroepitaxy of InAs
on GaAs (001), and report first-principles DFT calculations for In diffusion on the strained GaAs substrate. In particular,
we address the effect of heteroepitaxial strain on the growth kinetics of coherently strained InAs islands. The strain field
around an island is found to cause a slowing down of material transport from the substrate towards the island, and thus helps
to achieve more homogeneous island sizes.
Received: 2 May 2001 / Accepted: 23 July 2001 / Published online: 3 April 2002 相似文献
909.
910.
T. Ishii M. Asai A. Makishima I. Hossain P. Kleinheinz M. Ogawa M. Matsuda S. Ichikawa 《The European Physical Journal A - Hadrons and Nuclei》2002,13(1-2):15-19
Nuclei in the neutron-rich Ni region have been studied by γ-ray spectroscopy. Gamma-rays emitted from isomers, with T
1/2 > 1 ns, produced in heavy-ion deep-inelastic collisions were measured with an isomer-scope. The nuclear structure of the
doubly magic 68Ni and its neighbor 69,71Cu is discussed on the basis of the shell model. Future experiments for more neutron-rich Ni nuclei are also viewed.
Received: 1 May 2001 / Accepted: 4 December 2001 相似文献