全文获取类型
收费全文 | 283249篇 |
免费 | 4419篇 |
国内免费 | 1036篇 |
专业分类
化学 | 153830篇 |
晶体学 | 3869篇 |
力学 | 10966篇 |
综合类 | 7篇 |
数学 | 34378篇 |
物理学 | 85654篇 |
出版年
2021年 | 1959篇 |
2020年 | 2379篇 |
2019年 | 2535篇 |
2018年 | 3054篇 |
2017年 | 2952篇 |
2016年 | 5116篇 |
2015年 | 3632篇 |
2014年 | 5054篇 |
2013年 | 13237篇 |
2012年 | 10168篇 |
2011年 | 12192篇 |
2010年 | 8105篇 |
2009年 | 7742篇 |
2008年 | 11017篇 |
2007年 | 11016篇 |
2006年 | 10150篇 |
2005年 | 9476篇 |
2004年 | 8405篇 |
2003年 | 7324篇 |
2002年 | 7141篇 |
2001年 | 7963篇 |
2000年 | 6015篇 |
1999年 | 4754篇 |
1998年 | 3977篇 |
1997年 | 4038篇 |
1996年 | 3799篇 |
1995年 | 3604篇 |
1994年 | 3449篇 |
1993年 | 3518篇 |
1992年 | 3824篇 |
1991年 | 3663篇 |
1990年 | 3482篇 |
1989年 | 3446篇 |
1988年 | 3472篇 |
1987年 | 3329篇 |
1986年 | 3195篇 |
1985年 | 4436篇 |
1984年 | 4561篇 |
1983年 | 3754篇 |
1982年 | 4123篇 |
1981年 | 4008篇 |
1980年 | 3872篇 |
1979年 | 3895篇 |
1978年 | 4097篇 |
1977年 | 3928篇 |
1976年 | 4110篇 |
1975年 | 3689篇 |
1974年 | 3819篇 |
1973年 | 4067篇 |
1972年 | 2462篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
861.
Grafov B. M. Davydov A. D. Damaskin B. B. Lazorenko-Manevich R. M. 《Russian Journal of Electrochemistry》2003,39(4):439-440
Russian Journal of Electrochemistry - 相似文献
862.
L. G. Smirnova Yu. B. Grunin S. V. Krasil'nikova M. A. Zaverkina D. R. Bakieva E. V. Smirnov 《Colloid Journal》2003,65(6):778-781
The pulsed NMR, isopiestic and pycnometric methods are applied to investigate the physicochemical properties of softwood [GOST (State Standard) 9571-89] and hardwood [GOST 28172-89] celluloses, as well as flax cellulose [GOST 10330-76, 9394-76], both in the initial state and subjected to chemical treatment. Possible changes occurring in the supramolecular structure of a polymer are analyzed. The structural and sorption characteristics of the investigated samples are calculated. Their water absorption capacities are determined. 相似文献
863.
S. D. Gunapala S. V. Bandara J. K. Liu S. B. Rafol J. M. Mumolo C. A. Shott R. Jones J. Woolaway II J. M. Fastenau A. K. Liu M. Jhabvala K. K. Choi 《Infrared Physics & Technology》2003,44(5-6):411-425
A 9 μm cutoff 640 × 512 pixel hand-held quantum well infrared photodetector (QWIP) camera has been demonstrated with excellent imagery. A noise equivalent differential temperature (NEDT) of 10.6 mK is expected at a 65 K operating temperature with f/2 optics at a 300 K background. This focal plane array has shown background limited performance at a 72 K operating temperature with the same optics and background conditions. In this paper, we discuss the development of this very sensitive long-wavelength infrared camera based on a GaAs/AlGaAs QWIP focal plane array and its performance in quantum efficiency, NEDT, uniformity, and operability. In the second section of this paper, we discuss the first demonstration of a monolithic spatially separated four-band 640 × 512 pixel QWIP focal plane array and its performance. The four spectral bands cover 4–5.5, 8.5–10, 10–12, and 13.5–15 μm spectral regions with 640 × 128 pixels in each band. In the last section, we discuss the array performance of a 640 × 512 pixel broad-band (10–16 μm full-width at half-maximum) QWIP focal plane. 相似文献
864.
Tanos Elfouhaily Maminirina Joelson Stephan Guignard Donald R. Thompson 《Waves in Random and Complex Media》2003,13(3):165-176
This paper is the third in a series discussing a new approximate bistatic model for electromagnetic scattering from perfectly conducting rough surfaces. Our previous approach supplemented the Kirchhoff model through the addition of new terms involving linear orders in slope and surface elevation differences that arise naturally from a second iteration of the surface current integral equation. This completion of the Kirchhoff was shown to provide the correct first-order small perturbation method (SPM-1) in the general bistatic context. The agreement with SPM-1 was achieved because differences of surface heights are no longer expanded in powers of surface slope. While consistent with SPM, our previous formulation fails to reconverge toward the Kirchhoff model, at some incidence and scattered angles, when the illuminated surface satisfies the high frequency roughness condition. This weakness is also shared with the first-order small slope approximation (SSA-1) which is structurally equivalent to our previous formulation where the polarization is independent of surface roughness. The second-order small slope approximation (SSA-2), which satisfies the SPM-1 and second-order small perturbation method (SPM-2) limits by construction, was shown by Voronovich to converge toward the tangent plane approximation of the Kirchhoff model under high frequency conditions. In the present paper, we show that, in addition to the linear orders in our previous model, one must now include cross-terms between slope and surface elevation to ensure convergence toward both high frequency and small perturbation limits. With the inclusion of these terms, our new formulation becomes comparable to the SSA-2 (second-order kernel) without the need to evaluate all the quadratic order slope and elevations terms. SSA-2 is more complete, however, in the sense that it guarantees convergence toward the second-order Bragg limit (SPM-2) in the fully dielectric case in addition to both SPM-1 and Kirchhoff. Our new generalization is shown to explain correctly extra depolarization in specular conditions to be caused by surface curvature and surface autocorrelation for incoherent and coherent scattering, respectively. This result will have large repercussions on the interpretation of bistatically reflected signals such as those from GPS. 相似文献
865.
R. S. Srivastava 《Zeitschrift für Angewandte Mathematik und Physik (ZAMP)》2007,58(5):832-842
The diffraction of normal shock with yawed wedges of small angles have been considered in this paper. Vorticity distribution
of the fluid particle over the diffracted shock has been determined for several Mach numbers of the shock wave. The Mach reflection
effects have also been investigated when the bend is concave to the flow. 相似文献
866.
This article introduces and analyzes a p-version FEM for variational inequalities resulting from obstacle problems for some quasi-linear elliptic partial differential
operators. We approximate the solution by controlling the obstacle condition in images of the Gauss–Lobatto points. We show
existence and uniqueness for the discrete solution u
p
from the p-version for the obstacle problem. We prove the convergence of u
p
towards the solution with respect to the energy norm, and assuming some additional regularity for the solution we derive
an a priori error estimate. In numerical experiments the p-version turns out to be superior to the h-version concerning the convergence rate and the number of unknowns needed to achieve a certain exactness of the approximation. 相似文献
867.
S. R. Tuikina 《Computational Mathematics and Modeling》2007,18(1):10-18
We consider a mathematical model of sorption that allows for external diffusion kinetics and a redox reaction. Two inverse
problems are considered for this model, uniqueness is proved, and numerical solution methods are proposed. The efficiency
of the numerical methods is investigated by computer experiments.
__________
Translated from Prikladnaya Matematika i Informatika, No. 23, pp. 15–23, 2006. 相似文献
868.
869.
R. Percacci A. Vespignani 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,32(4):411-414
Measurements and data analysis have proved very effective in the study of the Internet's physical fabric and have shown heterogeneities
and statistical fluctuations extending over several orders of magnitude. Here we focus on the relationship between the Round-Trip-Time
(RTT) and the geographical distance. We define dimensionless variables that contain information on the quality of Internet
connections finding that their probability distributions are characterized by a slow power-law decay signalling the presence
of scale-free features. These results point out the extreme heterogeneity of Internet delay since the transmission speed between
different points of the network exhibits very large fluctuations. The associated scaling exponents appear to have fairly stable
values in different data sets and thus define an invariant characteristic of the Internet that might be used in the future
as a benchmark of the overall state of “health” of the Internet.
Received 25 January 2003 Published online 7 May 2003 相似文献
870.
R. Uribe-Vargas 《Functional Analysis and Its Applications》2003,37(3):236-240
On a smooth surface in Euclidean 3-space, we consider vanishing curves whose projections on a given plane are small circles centered at the origin. The bifurcations diagram of a parameter-dependent surface is the set of parameters and radii of the circles corresponding to curves with degenerate flattening points. Solving a problem due to Arnold, we find a normal form of the first nontrivial example of a flattening bifurcation diagram, which contains one continuous invariant. 相似文献