全文获取类型
收费全文 | 80994篇 |
免费 | 6693篇 |
国内免费 | 8880篇 |
专业分类
化学 | 33593篇 |
晶体学 | 718篇 |
力学 | 7173篇 |
综合类 | 1292篇 |
数学 | 25240篇 |
物理学 | 28551篇 |
出版年
2023年 | 649篇 |
2022年 | 1274篇 |
2021年 | 1429篇 |
2020年 | 1517篇 |
2019年 | 1744篇 |
2018年 | 1506篇 |
2017年 | 1895篇 |
2016年 | 2195篇 |
2015年 | 1974篇 |
2014年 | 2838篇 |
2013年 | 5124篇 |
2012年 | 3370篇 |
2011年 | 4113篇 |
2010年 | 3552篇 |
2009年 | 4845篇 |
2008年 | 5078篇 |
2007年 | 5566篇 |
2006年 | 5241篇 |
2005年 | 4223篇 |
2004年 | 3947篇 |
2003年 | 3860篇 |
2002年 | 3441篇 |
2001年 | 2933篇 |
2000年 | 2821篇 |
1999年 | 2556篇 |
1998年 | 2367篇 |
1997年 | 1982篇 |
1996年 | 1781篇 |
1995年 | 1607篇 |
1994年 | 1446篇 |
1993年 | 1212篇 |
1992年 | 1182篇 |
1991年 | 912篇 |
1990年 | 762篇 |
1989年 | 631篇 |
1988年 | 588篇 |
1987年 | 457篇 |
1986年 | 383篇 |
1985年 | 448篇 |
1984年 | 434篇 |
1983年 | 215篇 |
1982年 | 354篇 |
1981年 | 410篇 |
1980年 | 305篇 |
1979年 | 294篇 |
1978年 | 224篇 |
1977年 | 207篇 |
1976年 | 158篇 |
1974年 | 112篇 |
1973年 | 110篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
21.
Thalia Tsiaka Panagiotis Zoumpoulakis Vassilia J. Sinanoglou Constantinos Makris Georgios A. Heropoulos Antony C. Calokerinos 《Analytica chimica acta》2015
High-energy assisted extraction techniques, like ultrasound assisted extraction (UAE) and microwave assisted extraction (MAE), are widely applied over the last years for the recovery of bioactive compounds such as carotenoids, antioxidants and phenols from foods, animals and herbal natural sources. Especially for the case of xanthophylls, the main carotenoid group of crustaceans, they can be extracted in a rapid and quantitative way with the use of UAE and MAE. 相似文献
22.
23.
24.
25.
《Comptes Rendus Physique》2015,16(2):193-203
The field of multiferroics has experienced a rapid progress resulting in the discovery of many new physical phenomena. BiFeO3 (BFO) compound, which is one of the few room-temperature single-phase multiferroics, has contributed subsequently to this progress. As a result, significant review articles have been devoted specifically to this famous system. This chapter is dedicated to the strain effects on the structure stability and property changes of BFO thin films. It is a short and non-exhaustive topical overview that may be seen as an invitation for interested readers to go beyond. There is a very active and prolific research in this field and we apologize to the authors whose relevant work is not cited here. After a short introduction, we will thus review the effect of strain on BFO films by describing the consequences on the structure and the phase transitions as well as on polar, magnetic and magnetoelectric properties. 相似文献
26.
Synthesis of diisocyanides with phenolic groups and their polymerization to helically chiral poly(quinoxaline‐2,3‐diyl)s 下载免费PDF全文
Johannes Scholz Michael Reggelin 《Journal of polymer science. Part A, Polymer chemistry》2015,53(11):1320-1329
The development of synthetic routes which lead to five new diisocyanide monomers with one or two phenolic groups is described. Their polymerization behavior is studied with Pd‐ and Ni‐based initiators, as well as under microwave irradiation. The polymerizability is mainly dominated by steric effects as is concluded from experiments using different protecting groups. Chiroptical properties of these new polymers are studied by CD‐spectroscopy. After deprotection, helically chiral poly(quinoxalin‐2,3‐diyl)s are obtained which display a Brønsted function attached to a stereolabile biaryl axis whose configuration should be influenced by the chiral polymer backbone. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1320–1329 相似文献
27.
Chao Liu Liying Wang Lin Yang Famei Wang Chunhong Xu Jingwei Lv Guanglai Fu Xianli Li Qiang Liu Haiwei Mu Tao Sun Paul K. Chu 《Physics letters. A》2019,383(25):3200-3206
A single-polarization filter comprising a gold-coated photonic crystal fiber based on surface plasmon resonance is designed and investigated. The pattern matching and coupled polarization characteristics analyzed by the full-vector finite element method (FEM) and losses at 1,540 nm are achieved to 1,016.01739 dB/cm (x-pol core mode) and 33.81917 dB/cm (y-pol core mode). The crosstalk (CT) value of the 1,540 nm band is ?853.12653 dB for fiber length and the bandwidth is 850 nm. The working wavelength of the filter ranges from 1,280 nm to 1,540 nm by varying the diameter of outer air holes (), the diameter of inner air holes (), the metal film thickness (t), as well as the liquid refractive index (n). 相似文献
28.
29.
Inflation of balloons provides a straightforward way of achieving large biaxial deformations. Previous studies have shown that when a balloon bursts, crack propagation occurs at very high speed – much higher than would be expected from the low strain modulus and elastic wave velocity of the rubber. The present paper is concerned with studies of the deformation and fracture of cylindrical balloons. On inflation, the deformations of such a balloon pass through an unstable region but subsequently increase monotonically with pressure. In this relatively high pressure region, the ratio of the longitudinal and circumferential extension ratios is broadly in accord with expectations from high-strain elasticity theory when the ratio of the corresponding stresses is taken into account. On bursting, crack speeds up to around 300 m/s in this region. It is shown that these speeds are in accord with large increase in incremental moduli for the highly-strained rubber. Marked changes in crack tip profile observed at very high crack speeds are consistent with control of the rate of growth by inertia rather than by the viscoelastic properties of the rubber (as is believed to be the case at lower speeds). Consistent with this, various elastomers having different glass transition temperatures show similar crack growth behaviour in the very high speed region. 相似文献
30.
Accuracy arguments are the en vogue route in epistemic justifications of probabilism and further norms governing rational belief. These arguments often depend on the fact that the employed inaccuracy measure is strictly proper. I argue controversially that it is ill-advised to assume that the employed inaccuracy measures are strictly proper and that strictly proper statistical scoring rules are a more natural class of measures of inaccuracy. Building on work in belief elicitation I show how strictly proper statistical scoring rules can be used to give an epistemic justification of probabilism.An agent's evidence does not play any role in these justifications of probabilism. Principles demanding the maximisation of a generalised entropy depend on the agent's evidence. In the second part of the paper I show how to simultaneously justify probabilism and such a principle. I also investigate scoring rules which have traditionally been linked with entropies. 相似文献