全文获取类型
收费全文 | 264486篇 |
免费 | 3263篇 |
国内免费 | 1013篇 |
专业分类
化学 | 144790篇 |
晶体学 | 3849篇 |
力学 | 10450篇 |
综合类 | 3篇 |
数学 | 31026篇 |
物理学 | 78644篇 |
出版年
2020年 | 1942篇 |
2019年 | 2272篇 |
2018年 | 2676篇 |
2017年 | 2584篇 |
2016年 | 4204篇 |
2015年 | 2888篇 |
2014年 | 4281篇 |
2013年 | 12272篇 |
2012年 | 9064篇 |
2011年 | 11250篇 |
2010年 | 7219篇 |
2009年 | 6989篇 |
2008年 | 10129篇 |
2007年 | 10312篇 |
2006年 | 9558篇 |
2005年 | 8977篇 |
2004年 | 8026篇 |
2003年 | 7084篇 |
2002年 | 6987篇 |
2001年 | 7515篇 |
2000年 | 5607篇 |
1999年 | 4429篇 |
1998年 | 3788篇 |
1997年 | 3832篇 |
1996年 | 3623篇 |
1995年 | 3391篇 |
1994年 | 3188篇 |
1993年 | 3246篇 |
1992年 | 3530篇 |
1991年 | 3534篇 |
1990年 | 3337篇 |
1989年 | 3307篇 |
1988年 | 3395篇 |
1987年 | 3247篇 |
1986年 | 3144篇 |
1985年 | 4316篇 |
1984年 | 4518篇 |
1983年 | 3683篇 |
1982年 | 4115篇 |
1981年 | 3973篇 |
1980年 | 3814篇 |
1979年 | 3835篇 |
1978年 | 4071篇 |
1977年 | 3888篇 |
1976年 | 4053篇 |
1975年 | 3626篇 |
1974年 | 3742篇 |
1973年 | 4024篇 |
1972年 | 2454篇 |
1971年 | 1891篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Investigated is the dependency of the crack tip opening displacement (CTOD) on the local microstructure of the heat affected zone in high-strength low-alloy (HSLA) microalloyed steel. Since the initiation of the crack tip location could not be controlled in fatigue, any possible correlation between heat iput in welding and fracture toughness could be smeared. Modified CTOD data are defined; they show that the fracture resistance of the weld joint decreased as the heat input increased. 相似文献
92.
An analysis is made of the conditions of formation and the stability region of static-soliton-type magnetic nonuniformities
in a (001)-crystal plate with combined anisotropy. It is shown that if demagnetizing fields in the plate are taken into account,
static solitons can localize at certain defects for appropriate parameters of the material. The soliton stability region was
found to be bounded by two extreme values of the material parameters, namely, those at which the soliton is unstable against
collapse and at which it expands. It was also found that the soliton stability region differs considerably from that predicted
theoretically in the model disregarding the finite size of the sample and the presence of defects.
Fiz. Tverd. Tela (St. Petersburg) 40, 1498–1502 (August 1998) 相似文献
93.
The barotropic compressible Navier–Stokes equations in an unbounded domain are studied. We prove the unique existence of the solution (u, p) of the system (1.1) in the Sobolev spaceHk + 3 × Hk + 2provided that the derivatives of the data of the problem are sufficiently small, wherek ≥ 0 is any integer. The proof follows from an analysis of the linearized problem, the solvability of the continuity equation, and the Schauder fixed point theory. Similar smoothness results are obtained for a linearized form of (1.1). 相似文献
94.
R. Plaga 《Foundations of Physics》1997,27(4):559-577
The many-worlds interpretation of quantum mechanics predicts the formation of distinct parallel worlds as a result, of a quantum
mechanical measurement. Communication among these parallel worlds would experimentally rule out alternatives to this interpretation.
A possible procedure for “interworld” exchange of information and energy, using only state of the art quantum optical equipement,
is described. A single ion is isolated from its environment in an ion trap. Then a quantum mechanical measurement with two
discrete outcomes is performed on another system, resulting in the formation of two parallel worlds. Depending on the outcome
of this measurement the ion is excited from only one of the parallel worlds before the ion decoheres through its interaction
with the environment. A detection of this excitation in the other parallel world is direct evidence for the many-worlds interpretation.
This method could have important practical applications in physics and beyond. 相似文献
95.
Highly sensitive optical reflectivity measurements are used to investigate the layer-by-layer transition in extremely thin
and thick N-(4-n-hexyloxybenzylidene)-4-n-hexylaniline (6O.6) films. The simple power-law form, N=N
0
t
−1/3, for the penetration of the crystal-B order is found to describe the transitions only near the surface. A deviation from
the power law is observed for the interior layers.
Pis’ma Zh. éksp. Teor. Fiz. 63, No. 4, 266–269 (25 February 1996)
Published in English in the original Russian journal. Edited by Steve Torstveit. 相似文献
96.
Open circuit voltage (OCV) measurements in H2O/air concentration cells at T<580 K using Yb-doped SrCeO3 electrolyte indicate that under these conditions, protons are transported through the electrolyte as -ve ions, possibly as
hydroxyl (OH−) ions. The H+ ionic transport, which is generally reported, becomes the dominant mode for H2O/air concentration cells at temperatures greater than 750 K or when H2O/air electrodes are replaced by H2/Ar, and the anomalous OCV sign disappears. The combination of low temperature and the presence of hydrogen and oxygen as
provided by the H2O/air system appears to be necessary for the postulated hydroxyl ion electrode reactions to take place.
In addition to OCV measurements, results from impedance spectroscopy are used to provide evidence in support of the suggested
hydroxyl ion mode of protonic transport under the specified conditions. These findings are directly relevant in the development
of novel humidity sensors in the temperature range 450–580K and is reported in a separate paper in this conference.
Paper presented at the 3rd Euroconference on Solid State Ionics, Teulada, Sardinia, Italy, Sept. 15–22, 1996 相似文献
97.
C. Fallnich B. Ruffing Th. Herrmann A. Nebel R. Beigang R. Wallenstein 《Applied physics. B, Lasers and optics》1995,60(5):427-436
We report on a cw mode-locked non-critically phase matched KTP optical parametric oscillator synchronously pumped by a picosecond Ti:Sapphire laser. High average signal output power of up to 950 mW over a large tuning range has been achieved. For this OPO the influence of resonator-length detuning on the output power, pulse duration and spectral bandwidth has been investigated. The measured data are in good agreement with the results of a numerical simulation using a split-step Fourier method which considers the group-velocity mismatch, the group-velocity dispersion and the self-phase modulation. The numerical simulation also describes the measured strong pump depletion and its influence on the OPO output and efficiency. 相似文献
98.
99.
Brian R. Hunt 《Proceedings of the American Mathematical Society》1998,126(3):791-800
The Weierstrass nowhere differentiable function, and functions constructed from similar infinite series, have been studied often as examples of functions whose graph is a fractal. Though there is a simple formula for the Hausdorff dimension of the graph which is widely accepted, it has not been rigorously proved to hold. We prove that if arbitrary phases are included in each term of the summation for the Weierstrass function, the Hausdorff dimension of the graph of the function has the conjectured value for almost every sequence of phases. The argument extends to a much wider class of Weierstrass-like functions.
100.
We have recently demonstrated that polarization transfer using an adiabatic passage through the Hartmann-Hahn condition (APHH-CP) by a variation of the radio-frequency amplitude can substantially improve the transfer efficiency over Hartmann-Hahn cross polarization. Here we show that APHH-CP can be combined with fast magic angle sample spinning (MAS). The heteronuclear dipolar order, established in the course of the transfer, can indeed be created and preserved. 相似文献