全文获取类型
收费全文 | 222169篇 |
免费 | 5919篇 |
国内免费 | 3773篇 |
专业分类
化学 | 128084篇 |
晶体学 | 3621篇 |
力学 | 9163篇 |
综合类 | 238篇 |
数学 | 21818篇 |
物理学 | 68937篇 |
出版年
2020年 | 1969篇 |
2019年 | 2034篇 |
2018年 | 2051篇 |
2017年 | 1955篇 |
2016年 | 3385篇 |
2015年 | 2837篇 |
2014年 | 3751篇 |
2013年 | 9738篇 |
2012年 | 7462篇 |
2011年 | 9016篇 |
2010年 | 6115篇 |
2009年 | 6020篇 |
2008年 | 7839篇 |
2007年 | 7840篇 |
2006年 | 7394篇 |
2005年 | 6727篇 |
2004年 | 6005篇 |
2003年 | 5290篇 |
2002年 | 5156篇 |
2001年 | 6436篇 |
2000年 | 4946篇 |
1999年 | 4057篇 |
1998年 | 3218篇 |
1997年 | 3203篇 |
1996年 | 3180篇 |
1995年 | 2888篇 |
1994年 | 2747篇 |
1993年 | 2619篇 |
1992年 | 3090篇 |
1991年 | 2927篇 |
1990年 | 2833篇 |
1989年 | 2811篇 |
1988年 | 2732篇 |
1987年 | 2707篇 |
1986年 | 2534篇 |
1985年 | 3400篇 |
1984年 | 3370篇 |
1983年 | 2768篇 |
1982年 | 2967篇 |
1981年 | 2884篇 |
1980年 | 2798篇 |
1979年 | 2944篇 |
1978年 | 3173篇 |
1977年 | 2983篇 |
1976年 | 2922篇 |
1975年 | 2779篇 |
1974年 | 2734篇 |
1973年 | 2753篇 |
1967年 | 2137篇 |
1966年 | 1931篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
201.
202.
Hellweg T. Schemmel S. Rother G. Brlet A. Eckerlebe H. Findenegg G.H. 《The European physical journal. E, Soft matter》2003,12(1):1-4
The European Physical Journal E - The temperature-induced microphase separation of the binary liquid system iso-butyric acid+heavy water (iBA + D2O) in a mesoporous silica glass (CPG-10-75) of... 相似文献
203.
M Lepère R Gobeille V.Malathy Devi M.A.H Smith B Aoaeh A.W Mantz 《Journal of Molecular Spectroscopy》2004,224(1):7-12
We have analyzed the methyl fluoride RQ(J,0)Q branch lines located near 1475 cm−1 using a simultaneous multi-spectrum fitting technique. In this analysis we have used previously recorded diode-laser data in which we collected many data points covering only one or two Q branch lines in a particular run. The analysis consists of simultaneously fitting 57 spectra collected with numerous pressure and path length conditions for all absorption lines. The data are concatenated to create one continuous spectrum of the Q branch. We have determined the intensity and self-broadened widths at 296 K for 23 RQ(J,0) lines. 相似文献
204.
The crystal structure, magnetic and magnetotransport properties of the variation of B′-site transition metal in Sr2FeMO6 (M=Mo, W) with double perovskites structure have been investigated systematically. Measurements of magnetization vs. temperature at H=5 T show that Sr2FeMoO6 is a ferromagnet and Sr2FeWO6 is an antiferromagnet with TN∼35 K. Additionally, the large magnetoresistance ratio (MR) of ∼22% (H=3 T) at room temperature (RT) was observed in the Sr2FeWO6 compound. However, the Sr2FeMoO6 compound did not show any significant MR even at high fields and RT (MR∼1%; H=3 T and 300 K). The implications of these findings are supported by band structure calculations to explain the interaction between the 4d(Mo) and 5d(W) orbitals of transition metal ions and oxygen ions. 相似文献
205.
We give necessary and sufficient conditions for an operator on a separable Hilbert space to satisfy the hypercyclicity criterion.
This paper is a part of the second author’s Doctoral thesis, written at Shiraz University under the direction of the first
author. 相似文献
206.
A homologous series of azomesogens, 2″-[4-(4′-n-alkoxybenzoyloxy)-2-chlorophenylazo] naphthalenes, with lateral chloro groups was synthesised. All the homologues synthesized
exhibit enantiotropic nematic mesophase. The mesomorphic properties of the present series are compared with other structurally
related series to evaluate the effect of lateral chloro group and its position on mesomorphism
This paper was presented at the 10th National Conference on Liquid Crystals held at Bangalore, India during 9–11 October 2003. 相似文献
207.
G.P. Romanelli D. Bennardi D.M. Ruiz G. Baronetti H.J. Thomas 《Tetrahedron letters》2004,45(48):8935-8939
Substituted coumarins are synthesized from phenols and β-ketoesters by the Pechmann reaction, using a Wells-Dawson heteropolyacid (H6P2W18O62·24H2O) as catalyst by a solvent-free procedure. This one requires low reaction times, 130 °C temperature and as little as 1 mol % of Wells-Dawson acid, obtaining good to excellent yields of coumarins. The catalyst showed to be reusable with no differences in the yields. The results are compared with those of the reactions performed in toluene solution. The presented synthetic procedure is a convenient, clean and fast alternative for synthesizing 4-substituted coumarins (17 examples). 相似文献
208.
We extend the matrix version of Cochran's statistical theorem to outer inverses of a matrix. As applications, we investigate the Wishartness and independence of matrix quadratic forms for Kronecker product covariance structures. 相似文献
209.
Yang Mujie Zhao Jian Li Aibing Shen Zhiquan Zhang Mingjian Lin Senhao 《Journal of polymer science. Part A, Polymer chemistry》1989,27(11):3829-3835
This paper reports that 60Co γ-ray irradiation can convert cis-polyphenylacetylene (cis-PPA) films prepared with rare-earth coordination catalysts to highly photosensitive materials. The dependence of the photosensitivity on irradiation dose, preparation methods, and microstructure of the PPA films has been investigated by means of a potential discharge technique. The photosensitivity was enhanced with increasing irradiation dose. The critical dose to produce a light response was 5 × 103 Gy. The maximum surface potential discharge rate was 618 V/s, and the dark decay was approximately 2 V/s for cis-PPA films irradiated with 60Co γ-ray (dose: 2 × 105 Gy). The cis-transoidal-PPA and an electrophotographic photoreceptor device incorporating cis-PPA showed a higher irradiation effect. The structure and properties of 60Co γ-ray irradiated rare-earth PPA films are similar to the unirradiated films. 相似文献
210.
J E Paanakker J M Thio H M Van den Wildenberg F M Kaspersen 《Journal of chromatography. A》1987,421(2):327-335
An assay has been developed and validated for the routine monitoring of vecuronium in plasma. It consists of solid-phase extraction using C18 disposables as sample pre-treatment, high-performance liquid chromatography and post-column ion-pair extraction with fluorimetric detection. The fluorescent anion 9,10-dimethoxyanthracene-2-sulphonate (DAS) is used as the counter ion. The detection limit is ca. 5 ng/ml in plasma with a signal-to-noise ratio of 10. The assay is also applicable for monitoring vecuronium and its potential metabolites in other biological media, e.g., urine, bile and tissue (liver, kidney) homogenates. 相似文献