全文获取类型
收费全文 | 88573篇 |
免费 | 834篇 |
国内免费 | 524篇 |
专业分类
化学 | 31700篇 |
晶体学 | 862篇 |
力学 | 7197篇 |
综合类 | 3篇 |
数学 | 33242篇 |
物理学 | 16927篇 |
出版年
2023年 | 103篇 |
2022年 | 518篇 |
2021年 | 474篇 |
2020年 | 428篇 |
2019年 | 488篇 |
2018年 | 10721篇 |
2017年 | 10465篇 |
2016年 | 6638篇 |
2015年 | 1312篇 |
2014年 | 937篇 |
2013年 | 1469篇 |
2012年 | 4631篇 |
2011年 | 11268篇 |
2010年 | 6203篇 |
2009年 | 6494篇 |
2008年 | 7064篇 |
2007年 | 9192篇 |
2006年 | 578篇 |
2005年 | 1630篇 |
2004年 | 1745篇 |
2003年 | 2177篇 |
2002年 | 1186篇 |
2001年 | 342篇 |
2000年 | 347篇 |
1999年 | 216篇 |
1998年 | 235篇 |
1997年 | 199篇 |
1996年 | 251篇 |
1995年 | 150篇 |
1994年 | 118篇 |
1993年 | 114篇 |
1992年 | 93篇 |
1991年 | 99篇 |
1990年 | 79篇 |
1989年 | 95篇 |
1988年 | 91篇 |
1987年 | 93篇 |
1986年 | 89篇 |
1985年 | 84篇 |
1984年 | 82篇 |
1983年 | 59篇 |
1982年 | 69篇 |
1981年 | 59篇 |
1980年 | 71篇 |
1979年 | 64篇 |
1978年 | 56篇 |
1914年 | 45篇 |
1912年 | 40篇 |
1909年 | 41篇 |
1908年 | 40篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
21.
It is shown that time-dependent temperatures in a transient, conductive system can be approximately modeled by a fractional-order
differential equation, the order of which depends on the Biot number. This approximation is particularly suitable for complex
shapes for which a first-principles approach is too difficult or computationally time-consuming. Analytical solutions of these
equations can be written in terms of the Mittag-Leffler function. The approximation is especially useful if a suitable fractional-order
controller is to be designed for the system. 相似文献
22.
This paper presents the applications of digital image correlation technique to the mesoscopic damage and fracture study of
some granular based composite materials including steelfiber reinforced concrete, sandstone and crystal-polymer composite.
The deformation fields of the composite materials resulted from stress localization were obtained by the correlation computation
of the surface images with loading steps and thus the related damage prediction and fracture parameters were evaluated. The
correlation searching could be performed either directly based on the gray levels of the digital images or from the wavelet
transform (WT) coefficients of the transform spectrum. The latter was developed by the authors and showed higher resolution
and sensitivity to the singularity detection. Because the displacement components came from the rough surfaces of the composite
materials without any coats of gratings or fringes of optical interferometry, both surface profiles and the deformation fields
of the composites were visualized which was helpful to compare each other to analyze the damage of those heterogeneous materials.
The project supported by the National Natural Science Foundation of China (10125211 and 10072002), the Scientific Committee
of Yunnan Province for the Program of Steel Fiber Reinforced Concrete, and the Institute of Chemical Materials, CAEP at Mianyang 相似文献
23.
The reactions of bis(trimethylstannyl)ethyne, Me3Sn–C?C–SnMe3 ( 4 ), with trimethylsilyl‐ or dimethylsilyl‐dialkylboryl‐substituted alkenes 1 – 3 afford organometallic‐substituted allenes 5 , 6 and 8 , 9 in high yield. In the case of (E)‐2‐trimethylsilyl‐3‐diethylboryl‐2‐pentene ( 1) , a butadiene derivative 7 could be detected as an intermediate prior to rearrangement into the allene. All reactions were monitored by 29Si and 119Sn NMR, and the products were characterized by an extensive NMR data set (1H, 11B, 13C, 29Si, 119Sn NMR). Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
24.
25.
26.
DEBACHE Abdelmadjid BOULCINA Raouf TAFER Radia BELFAITAH Ali RHOUATI Salah CARBONI Bertrand 《中国化学》2008,26(11):2112-2116
The synthesis of 1,2,3,4-dihydropyrimidinone/thione derivatives was achieved in good to excellent yields using calcium(II) nitrate as catalyst to promote the Biginelli three-component condensation reaction from a diversity of aromatic aldehydes, β-keto compounds and urea or thiourea. The reaction was carried out under solvent-free conditions. 相似文献
27.
28.
29.
30.