全文获取类型
收费全文 | 3760篇 |
免费 | 130篇 |
国内免费 | 18篇 |
专业分类
化学 | 2949篇 |
晶体学 | 55篇 |
力学 | 50篇 |
数学 | 216篇 |
物理学 | 638篇 |
出版年
2022年 | 29篇 |
2021年 | 26篇 |
2020年 | 46篇 |
2019年 | 74篇 |
2018年 | 30篇 |
2017年 | 37篇 |
2016年 | 66篇 |
2015年 | 65篇 |
2014年 | 78篇 |
2013年 | 192篇 |
2012年 | 201篇 |
2011年 | 228篇 |
2010年 | 106篇 |
2009年 | 123篇 |
2008年 | 222篇 |
2007年 | 217篇 |
2006年 | 225篇 |
2005年 | 216篇 |
2004年 | 156篇 |
2003年 | 160篇 |
2002年 | 159篇 |
2001年 | 68篇 |
2000年 | 51篇 |
1999年 | 43篇 |
1998年 | 38篇 |
1997年 | 33篇 |
1996年 | 33篇 |
1995年 | 29篇 |
1994年 | 25篇 |
1993年 | 33篇 |
1992年 | 38篇 |
1991年 | 31篇 |
1990年 | 47篇 |
1989年 | 36篇 |
1988年 | 33篇 |
1987年 | 28篇 |
1986年 | 39篇 |
1985年 | 46篇 |
1984年 | 59篇 |
1983年 | 40篇 |
1982年 | 44篇 |
1981年 | 47篇 |
1980年 | 40篇 |
1979年 | 40篇 |
1978年 | 46篇 |
1977年 | 40篇 |
1976年 | 31篇 |
1975年 | 27篇 |
1974年 | 32篇 |
1973年 | 27篇 |
排序方式: 共有3908条查询结果,搜索用时 31 毫秒
991.
A.-H. Sato T. Hayashi 《The European Physical Journal B - Condensed Matter and Complex Systems》2010,76(4):529-535
We investigate an association between a power-law
relationship of constituents’ flows (mean versus standard deviation) and their
covariance matrix on a directed bipartite network.
We propose a Poisson mixture
model and a method to infer states of the constituents’ flows on such a
bipartite network from empirical observation without a priori
knowledge on the network structure. By using a proposed parameter estimation
method with high frequency financial data we found that the scaling
exponent and simultaneous cross-correlation matrix have a positive
correspondence relationship. Consequently we conclude that the scaling
exponent tends to be 1/2 in the case of desynchronous (specific
dynamics is dominant), and to be 1 in the case of synchronous (common
dynamics is dominant). 相似文献
992.
Guuske F. Busscher Laurent Lefort Jozef G.O. Cremers Marco Mottinelli Roel W. Wiertz Ben de Lange Yutaka Okamura Yukinori Yusa Kazuhiko Matsumura Hideo Shimizu Johannes G. de Vries André H.M. de Vries 《Tetrahedron: Asymmetry》2010,21(13-14):1709-1714
Two routes for the preparation of an N-aryl β-amino acid, an important precursor for the cholesterol-lowering drug Ezetimibe, were investigated. The first pathway proceeds via an Rh- or Ir-catalyzed asymmetric hydrogenation of N-aryl enamine giving the desired product with up to 82% ee. The other pathway involves a direct asymmetric reductive amination (DARA) of the β-keto ester which yielded the β-amino ester in high yield and 97% ee. Subsequent copper-catalyzed N-arylation gave the target compound. 相似文献
993.
Wei Wei Zhaolin Gu Sheng Wang Takeshi Fukuda Kiwamu Kase Jungmyoung Ju Yutaka Yamagata Yusuke Tajima 《中国颗粒学报》2013,11(1):20-24
Electrospray deposition(ESD) as a patterning method of nanoparticles deposited on a substrate has attracted much attention due to several advantages over other methods.However,obtaining an optimum ESD processing condition for nanoparticle pattern relies much on trial experiments because of the lack of reliable numerical simulation.In this study,the deposition characteristics of nanoparticle generated by electrospray were investigated by using a three-dimensional Lagrangian model.Three important process parameters,including solution dielectric constant,applied voltage and surface charge density on mask were considered by fixing the geometrical parameters of the ESD device.Simulation result showed that under the condition of without a mask,the spray diameter increases with increasing solvent dielectric constant,and higher applied voltage makes the spray area wider.Controllability of focusing by changing surface charge density on the mask was confirmed:higher surface charge density on the mask results in more focused deposition.Validity of the numerical simulation developed in this study was verified by comparison with experimental data. 相似文献
994.
Yoichi Ogata Takeshi Mogi Yutaka Makita 《Journal of Polymer Science.Polymer Physics》2010,48(5):588-594
Solution property of hydrogenated polystyrene‐b‐poly(ethylene/butylene)‐b‐polystyrene triblock copolymer (SEBS copolymer) was studied by using static light scattering and dynamic light scattering for cyclohexane and N‐methylpyrrolidone (NMP) solutions. From the values of dimensionless parameters ρ, defined as the ratio of radius of gyration 〈S2〉1/2 to hydrodynamic radius RH, and solubility parameters, SEBS copolymer proved to exist as single chain close to random coil in nonpolar cyclohexane, whereas aggregate into the core‐shell micelle consisting of poly(ethylene/butylene) (PEB) core surrounded by PS shell in polar NMP. The core‐shell micelle formed in NMP is composed of 65 polymer chains, having three times larger average chain density (d = 0.12 g cm?3) than a single polymer chain (d = 0.04 g cm?3) in cyclohexane. The comparison with the aggregation behaviors in other solvents demonstrated that the aggregate compactness of the copolymer depended largely on solvent polarity, resulting in formation of the highly dense PEB core (Rc = 4.5 nm) and the thick PS shell (ΔR = 22.9 nm) in high‐polar NMP. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 588–594, 2010 相似文献
995.
Changes in the surface chemical state of a nearly equiatomic nickel–titanium (NiTi) alloy caused by immersion in aqueous solutions of HNO3 and H2SO4 as well as subsequent heating in air at 723 K were analyzed using X-ray photoelectron spectroscopy (XPS). An XPS analysis using angle-resolved technique and a mathematical deconvolution technique revealed that a passive layer formed in an ambient atmosphere contained TiO2 as a major state and Ni(OH)2 and NiO as minor states. The Ni(OH)2 on the alloy remained in the region even when heated in air at 723 K. Therefore, the resulting layer became a Ti-oxide layer with Ni segregated region at the surface, which was NiO formed via dehydration of Ni(OH)2. However, immersion in an aqueous solution of HNO3 or H2SO4 enables Ni(OH)2 state to dissolve in the passive layer of a NiTi alloy; thereby, the Ni segregated region rarely appeared in the oxide layer by heating. The Ni segregated region at the surface becomes an obstacle for the inward diffusion of oxygen; thus, the annihilation of such a segregated region results in an increase in the thickness of the oxide layer. 相似文献
996.
Koichi Machida Akira Kotani Yuzuru Hayashi Hideki Hakamata 《Journal of mass spectrometry : JMS》2022,57(8):e4877
ISO 11843 part 7 (ISO 11843-7) can provide a standard deviation (SD) of area measurements of a target peak through the stochastic behaviors of instrumental noises. The purpose of this study is to demonstrate that ISO 11843-7 can be applied to assess repeatability in an isocratic liquid chromatography–tandem mass spectrometry (LC–MS/MS) system without repetitive measurements. The relative standard deviation (RSD) of the peak area of ergosterol picolinyl ester, which was used as an example, on a multiple reaction monitoring (MRM) chromatogram was determined by ISO 11843-7. The RSD by ISO 11843-7 (N = 1) was within a 95% confidence band of the RSD by repetitive measurements (N = 6). Moreover, the effects of digital smoothing, such as moving average, were also examined on the repeatability assessment in LC–MS/MS by ISO 11843-7. From the results of the comparisons of the RSDs obtained by ISO 11843-7 and the repetitive measurements, it was shown that suitable RSDs of the peak area were obtained from the smoothed MRM chromatograms by the moving average for narrow data point windows (e.g., one-sixth of the peak width). In conclusion, the utility of repeatability assessment based on ISO 11843-7 has been expanded for the validation of an LC–MS/MS system. 相似文献
997.
Hiroyuki Hayashi Shota Katayama Rong Huang Kosuke Kurushima Isao Tanaka 《固体物理学:研究快报》2015,9(3):192-196
Undoped n‐ and p‐type tin monoxide (SnO) films have been selectively fabricated by pulsed laser deposition with a Sn target and careful control of oxygen partial pressure. The films are epitaxially grown in optimal growth conditions on yttria‐stabilized zirconia (YSZ) substrates with out‐of‐plane and in‐plane orientation relationships of (001)SnO//(001)YSZ and [110]SnO//[100]YSZ, respectively. Both Seebeck and Hall measurements show consistent results on the carrier types of the films. The electron Hall mobility is approximately 11 cm2/Vs at room temperature and the carrier activation energy is 0.14 eV for the n‐type film. The growth at increased oxygen partial pressure yields p‐type films, demonstrating the selective fabrication of both n‐ and p‐type SnO films without doping. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim) 相似文献
998.
999.
1000.