全文获取类型
收费全文 | 11213篇 |
免费 | 821篇 |
国内免费 | 645篇 |
专业分类
化学 | 4489篇 |
晶体学 | 172篇 |
力学 | 322篇 |
综合类 | 48篇 |
数学 | 4756篇 |
物理学 | 2892篇 |
出版年
2023年 | 52篇 |
2022年 | 146篇 |
2021年 | 160篇 |
2020年 | 146篇 |
2019年 | 245篇 |
2018年 | 268篇 |
2017年 | 241篇 |
2016年 | 224篇 |
2015年 | 211篇 |
2014年 | 345篇 |
2013年 | 772篇 |
2012年 | 511篇 |
2011年 | 742篇 |
2010年 | 582篇 |
2009年 | 885篇 |
2008年 | 838篇 |
2007年 | 679篇 |
2006年 | 673篇 |
2005年 | 509篇 |
2004年 | 504篇 |
2003年 | 435篇 |
2002年 | 435篇 |
2001年 | 312篇 |
2000年 | 276篇 |
1999年 | 310篇 |
1998年 | 251篇 |
1997年 | 209篇 |
1996年 | 222篇 |
1995年 | 172篇 |
1994年 | 201篇 |
1993年 | 153篇 |
1992年 | 129篇 |
1991年 | 78篇 |
1990年 | 77篇 |
1989年 | 62篇 |
1988年 | 53篇 |
1987年 | 50篇 |
1986年 | 29篇 |
1985年 | 42篇 |
1984年 | 51篇 |
1983年 | 33篇 |
1982年 | 48篇 |
1981年 | 74篇 |
1980年 | 58篇 |
1979年 | 75篇 |
1978年 | 44篇 |
1977年 | 11篇 |
1976年 | 10篇 |
1974年 | 11篇 |
1973年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 750 毫秒
51.
In this paper we obtain some metrics results about large partial quotients in the continued fraction expansion. 相似文献
52.
C. Vaca‐Garcia G. Gozzelino W. G. Glasser M. E. Borredon 《Journal of Polymer Science.Polymer Physics》2003,41(3):281-288
The main transitions of cellulose fatty esters with different degrees of substitution (DSs) were investigated with dynamic mechanical thermal analysis. Two distinct main relaxations were observed in partially substituted cellulose esters (PSCEs). They were attributed to the glass‐transition temperature and to the chain local motion of the aliphatic substituents. The temperatures of both transitions decreased when DS or the number of carbon atoms (n) of the acyl substituent increased. Conversely, all the transitions of fully substituted cellulose esters occurred within a narrow temperature range, and they did not vary significantly with n. This phenomenon was explained by the formation of a crystalline phase of the fatty substituents. The presence of few residual OH groups in PSCEs was responsible for a large increase in the storage bending modulus, and it eliminated the effect of n on damping. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 281–288, 2003 相似文献
53.
Rong-Seng Chang Jin-Yi Sheu Ching-Huang Lin He-Chiang Liu 《Optics & Laser Technology》2003,35(1):43-47
A new approach based on the moiré theory and wavelet transform (WT) is proposed for measuring the micro-range distance between a charge-couple-device (CCD) camera and a two-dimensional reference grating. The micro-range distance is determined by measuring the pitch of the moiré pattern image, which is digitized by a CCD camera. A one-dimensional WT algorithm is applied to estimate the pitch of the moiré pattern. Experimental results prove that this technique is very efficient and highly accurate. The moiré range finder is an economic technique for measuring a micro-range distance. 相似文献
54.
Aji P. Mathew Gabriel Groeninckx G. H. Michler H. J. Radusch Sabu Thomas 《Journal of Polymer Science.Polymer Physics》2003,41(14):1680-1696
The effects of the blend ratio and initiating system on the viscoelastic properties of nanostructured natural rubber/polystyrene‐based interpenetrating polymer networks (IPNs) were investigated in the temperature range of ?80 to 150 °C. The studies were carried out at different frequencies (100, 50, 10, 1, and 0.1 Hz), and their effects on the damping and storage and loss moduli were analyzed. In all cases, tan δ and the storage and loss moduli showed two distinct transitions corresponding to natural rubber and polystyrene phases, which indicated that the system was not miscible on the molecular level. However, a slight inward shift was observed in the IPNs, with respect to the glass‐transition temperatures (Tg's) of the virgin polymers, showing a certain degree of miscibility or intermixing between the two phases. When the frequency increased from 0.1 to 100 Hz, the Tg values showed a positive shift in all cases. In a comparison of the three initiating systems (dicumyl peroxide, benzoyl peroxide, and azobisisobutyronitrile), the dicumyl peroxide system showed the highest modulus. The morphology of the IPNs was analyzed with transmission electron microscopy. The micrographs indicated that the system was nanostructured. An attempt was made to relate the viscoelastic behavior to the morphology of the IPNs. Various models, such as the series, parallel, Halpin–Tsai, Kerner, Coran, Takayanagi, and Davies models, were used to model the viscoelastic data. The area under the linear loss modulus curve was larger than that obtained by group contribution analysis; this showed that the damping was influenced by the phase morphology, dual‐phase continuity, and crosslinking of the phases. Finally, the homogeneity of the system was further evaluated with Cole–Cole analysis. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1680–1696, 2003 相似文献
55.
56.
57.
We present a general risk model where the aggregate claims, as well as the premium function, evolve by jumps. This is achieved by incorporating a Lévy process into the model. This seeks to account for the discrete nature of claims and asset prices. We give several explicit examples of Lévy processes that can be used to drive a risk model. This allows us to incorporate aggregate claims and premium fluctuations in the same process. We discuss important features of such processes and their relevance to risk modeling. We also extend classical results on ruin probabilities to this model. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
58.
Huimin Xie Biao Li Robert Geer Bai Xu James Castracane 《Optics and Lasers in Engineering》2003,40(3):163-177
A focused ion beam (FIB) Moiré method is proposed to measure the in-plane deformation of object in a micrometer scale. The FIB Moiré is generated by the interference between a prepared specimen grating and FIB raster scan lines. The principle of the FIB Moiré is described. The sensitivity and accuracy of deformation measurement are discussed in detail. Several specimen gratings with 0.14 and 0.20 μm spacing are used to generate FIB Moiré patterns. The FIB Moiré method is successfully used to measure the residual deformation in a micro-electro-mechanical system structure after removing the SiO2 sacrificial layer with a 5000 lines/mm grating. The results demonstrate the feasibility of this method. 相似文献
59.
S.BOUZID Z.AZARI 《宁波大学学报(理工版)》2003,16(4):354-362
冲蚀过程是一个与颗粒反复冲击物体表面而移除物质相关的表面现象.本文研究了玻璃的冲蚀坑的几何尺寸和体积,给出了冲蚀移除物质如何依赖于颗粒流动速度、颗粒尺寸和冲击角的理论关系.通过理论与实验结果相比较,定义了一定冲蚀坑尺度的有效域. 相似文献
60.