全文获取类型
收费全文 | 202065篇 |
免费 | 2240篇 |
国内免费 | 501篇 |
专业分类
化学 | 110571篇 |
晶体学 | 3647篇 |
力学 | 7996篇 |
综合类 | 11篇 |
数学 | 19207篇 |
物理学 | 63374篇 |
出版年
2020年 | 1726篇 |
2019年 | 1919篇 |
2018年 | 2237篇 |
2017年 | 2356篇 |
2016年 | 3518篇 |
2015年 | 2193篇 |
2014年 | 3546篇 |
2013年 | 9080篇 |
2012年 | 6513篇 |
2011年 | 8013篇 |
2010年 | 5698篇 |
2009年 | 5656篇 |
2008年 | 7156篇 |
2007年 | 7066篇 |
2006年 | 6693篇 |
2005年 | 6050篇 |
2004年 | 5523篇 |
2003年 | 5103篇 |
2002年 | 4868篇 |
2001年 | 6144篇 |
2000年 | 4626篇 |
1999年 | 3518篇 |
1998年 | 2746篇 |
1997年 | 2702篇 |
1996年 | 2591篇 |
1995年 | 2442篇 |
1994年 | 2331篇 |
1993年 | 2166篇 |
1992年 | 2828篇 |
1991年 | 2730篇 |
1990年 | 2675篇 |
1989年 | 2693篇 |
1988年 | 2717篇 |
1987年 | 2722篇 |
1986年 | 2593篇 |
1985年 | 3305篇 |
1984年 | 3314篇 |
1983年 | 2598篇 |
1982年 | 2710篇 |
1981年 | 2766篇 |
1980年 | 2538篇 |
1979年 | 2878篇 |
1978年 | 2865篇 |
1977年 | 2981篇 |
1976年 | 2819篇 |
1975年 | 2557篇 |
1974年 | 2510篇 |
1973年 | 2467篇 |
1972年 | 1704篇 |
1968年 | 1703篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
12.
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
13.
14.
15.
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
16.
17.
18.
Mathematical Notes - 相似文献
19.
Mohammad Azam Saud I. Al-Resayes Agata Trzesowska-Kruszynska Rafal Kruszynski S.F. Adil N.K. Lokanath 《Journal of Saudi Chemical Society》2019,23(5):636-641
A new derivative of dioxouranium(VI) salen complex, [UO2(L)(pyridine)], where [L = N,N′-Bis(2-hydroxybenzylidene)-2,2-dimethyl-1,3-propanediamine] is synthesized and characterized by elemental analysis (C, H, N), FT-IR, ESI-MS spectrometry, UV/Vis, fluorescence, 1H and 13C NMR spectroscopy and thermal gravimetric (TG) study. Furthermore, the single crystal X-ray diffraction measurements of the complex were carried out at 100 and 273 K. The crystal structure measurements revealed that the complex has distorted pentagonal bipyramidal geometry with uranium atom located at the centre and bonded to two phenoxy oxygen and two azomethine nitrogen in tetradenate fashion and one nitrogen from pyridine making it seven coordinated. In addition, the photoluminescence property of the complex was also recorded. 相似文献
20.
In the present work, the use of cylindrical turbulators in a double pipe heat exchanger has been investigated. Cylindrical fin type of turbulators has been placed circumferentially separated by 90° on the outer side of an inner pipe at a regular pitch. Experimental studies were undertaken for different air flow rates in a turbulent regime whose Reynolds number range between 2500 and 10000. Heat transfer characteristics like Nu and friction factor have been experimentally determined. Parametric studies were conducted by changing the pitch and also the orientation of the turbulators. Nu and friction factor were found to increase as the pitch is reduced. A model with alternatively changed orientation outperformed others by exhibiting highest Nu and reduced friction factor. 相似文献