全文获取类型
收费全文 | 435472篇 |
免费 | 6681篇 |
国内免费 | 1797篇 |
专业分类
化学 | 244619篇 |
晶体学 | 6620篇 |
力学 | 17550篇 |
综合类 | 72篇 |
数学 | 48968篇 |
物理学 | 126121篇 |
出版年
2020年 | 3831篇 |
2019年 | 4123篇 |
2018年 | 5306篇 |
2017年 | 5241篇 |
2016年 | 8016篇 |
2015年 | 5535篇 |
2014年 | 7846篇 |
2013年 | 19417篇 |
2012年 | 16175篇 |
2011年 | 19197篇 |
2010年 | 13267篇 |
2009年 | 12783篇 |
2008年 | 17409篇 |
2007年 | 17392篇 |
2006年 | 16142篇 |
2005年 | 14816篇 |
2004年 | 13273篇 |
2003年 | 11769篇 |
2002年 | 11327篇 |
2001年 | 12439篇 |
2000年 | 9571篇 |
1999年 | 7149篇 |
1998年 | 5742篇 |
1997年 | 5636篇 |
1996年 | 5645篇 |
1995年 | 4991篇 |
1994年 | 5026篇 |
1993年 | 4787篇 |
1992年 | 5610篇 |
1991年 | 5512篇 |
1990年 | 5268篇 |
1989年 | 5232篇 |
1988年 | 5118篇 |
1987年 | 5068篇 |
1986年 | 4901篇 |
1985年 | 6509篇 |
1984年 | 6592篇 |
1983年 | 5305篇 |
1982年 | 5668篇 |
1981年 | 5487篇 |
1980年 | 5058篇 |
1979年 | 5540篇 |
1978年 | 5694篇 |
1977年 | 5792篇 |
1976年 | 5687篇 |
1975年 | 5187篇 |
1974年 | 5263篇 |
1973年 | 5262篇 |
1972年 | 3835篇 |
1968年 | 3268篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
In this paper, we study the local linear convergence properties of a versatile class of Primal–Dual splitting methods for minimizing composite non-smooth convex optimization problems. Under the assumption that the non-smooth components of the problem are partly smooth relative to smooth manifolds, we present a unified local convergence analysis framework for these methods. More precisely, in our framework, we first show that (i) the sequences generated by Primal–Dual splitting methods identify a pair of primal and dual smooth manifolds in a finite number of iterations, and then (ii) enter a local linear convergence regime, which is characterized based on the structure of the underlying active smooth manifolds. We also show how our results for Primal–Dual splitting can be specialized to cover existing ones on Forward–Backward splitting and Douglas–Rachford splitting/ADMM (alternating direction methods of multipliers). Moreover, based on these obtained local convergence analysis result, several practical acceleration techniques are discussed. To exemplify the usefulness of the obtained result, we consider several concrete numerical experiments arising from fields including signal/image processing, inverse problems and machine learning. The demonstration not only verifies the local linear convergence behaviour of Primal–Dual splitting methods, but also the insights on how to accelerate them in practice. 相似文献
72.
M. Kroon E. Andreasson E. Persson Jutemar V. Petersson L. Persson M. Dorn P.A.T. Olsson 《Experimental Mechanics》2018,58(1):75-86
Injection-moulding is one of the most common manufacturing processes used for polymers. In many applications, the mechanical properties of the product is of great importance. Injection-moulding of thin-walled polymer products tends to leave the polymer structure in a state where the mechanical properties are anisotropic, due to alignment of polymer chains along the melt flow direction. The anisotropic elastic-viscoplastic properties of low-density polyethylene, that has undergone an injection-moulding process, are therefore examined in the present work. Test specimens were punched out from injection-moulded plates and tested in uniaxial tension. Three in-plane material directions were investigated. Because of the small thickness of the plates, only the in-plane properties could be determined. Tensile tests with both monotonic and cyclic loading were performed, and the local strains on the surface of the test specimens were measured using image analysis. True stress vs. true strain diagrams were constructed, and the material response was evaluated using an elastic-viscoplasticity law. The components of the anisotropic compliance matrix were determined together with the direction-specific plastic hardening parameters. 相似文献
73.
Indermeet Kohli Taylor L. Braunberger Amanda F. Nahhas Fatima N. Mirza Mohsen Mokhtari Alexis B. Lyons Nikiforos Kollias Eduardo Ruvolo Henry W. Lim Iltefat H. Hamzavi 《Photochemistry and photobiology》2020,96(1):208-214
Human skin is exposed to visible light (VL; 400–700 nm) and long-wavelength ultraviolet A1 (UVA1) radiation (370–400 nm) after the application of organic broad-spectrum sunscreens. The biologic effects of these wavelengths have been demonstrated; however, a dose–response has not been investigated. Ten subjects with Fitzpatrick skin phototype IV-VI were enrolled. Subjects were irradiated with 2 light sources (80–480 J cm−2): one comprising VL with less than 0.5% UVA1 (VL+UVA1) and the other pure VL. Skin responses were evaluated for 2 weeks using clinical and spectroscopic assessments. 4-mm punch biopsies were obtained from nonirradiated skin and sites irradiated with 480 J cm−2 of VL+UVA1 and pure VL 24 h after irradiation. Clinical and spectroscopic assessments demonstrated a robust response at VL+UVA1 sites compared with pure VL. Histology findings demonstrated a statistically significant increase in the marker of inflammation (P < 0.05) and proliferation (P < 0.05) at the irradiated sites compared with nonirradiated control. Threshold doses of VL+UVA1 resulting in biologic responses were calculated. Results indicate that approximately 2 h of sun exposure, which equates to VL+UVA1 dose (~400 J cm−2), is capable of inducing inflammation, immediate erythema and delayed tanning. These findings reinforce the need of photoprotection beyond the UV range. 相似文献
74.
75.
76.
S. Q. Hou W. Wang Z. Y. Wang Z. W. Hu K. Liu 《Journal of Applied Mechanics and Technical Physics》2018,59(1):153-162
In order to investigate the characteristics of force chains in a granular flow system, a parallel plate shear cell is constructed to simulate the shear movement of an infinite parallel plate and observe variations in relevant parameters. The shear dilatancy process is divided into three stages, namely, plastic strain, macroscopic failure, and granular recombination. The stickslip phenomenon is highly connected with the evolution of force chains during the shear dilatancy process. The load–distribution rate curves and patterns of the force chains are utilized to describe the load-carrying behaviors and morphologic changes of force chains separately. Force chains, namely, “diagonal gridding,” “tadpole-shaped,” and “pinnate” are defined according to the form of the force chains in the corresponding three stages. 相似文献
77.
78.
79.
80.
V. V. Sagaradze N. V. Kataeva V. A. Zavalishin K. A. Kozlov V. V. Makarov A. R. Kuznetsov 《哲学杂志》2020,100(14):1868-1879
ABSTRACT The authors present the results of an investigation in Fe–Ni-Cr austenitic alloys of the low-temperature deformation-induced segregations of nickel that form in the micro regions being (i) located close to grain- and subgrain boundaries and (ii) characteristic of the concentration and magnetic inhomogeneities indicated by the appearance of a dark diffraction contrast at the electron diffraction patterns taken from these regions typical (at the same time) of an enhanced value of Curie temperature. The observed effects were connected with the micro distortions caused by the local change of lattice parameter because of an increase in nickel concentration, as well as in the result of a magnetostriction dilatation. Using methods of the X-ray energy dispersive spectroscopy (XEDS) and atomic-probe body-section radiography (tomography – APT) has made it possible to determine the borders of those regions of austenite that were characteristic of an enhanced concentration of nickel in the fields of the localisation of a deformation-induced segregation of nickel in the vicinity of grain (subgrain) boundaries of austenitic alloys of the types Fe–13Cr–30Ni and Fe–37Ni–3Ti. 相似文献