全文获取类型
收费全文 | 11553篇 |
免费 | 962篇 |
国内免费 | 1294篇 |
专业分类
化学 | 7603篇 |
晶体学 | 237篇 |
力学 | 77篇 |
综合类 | 49篇 |
数学 | 195篇 |
物理学 | 5648篇 |
出版年
2023年 | 42篇 |
2022年 | 100篇 |
2021年 | 130篇 |
2020年 | 151篇 |
2019年 | 153篇 |
2018年 | 194篇 |
2017年 | 195篇 |
2016年 | 296篇 |
2015年 | 267篇 |
2014年 | 354篇 |
2013年 | 1011篇 |
2012年 | 547篇 |
2011年 | 543篇 |
2010年 | 466篇 |
2009年 | 699篇 |
2008年 | 688篇 |
2007年 | 823篇 |
2006年 | 704篇 |
2005年 | 672篇 |
2004年 | 632篇 |
2003年 | 633篇 |
2002年 | 531篇 |
2001年 | 447篇 |
2000年 | 393篇 |
1999年 | 384篇 |
1998年 | 298篇 |
1997年 | 286篇 |
1996年 | 304篇 |
1995年 | 331篇 |
1994年 | 288篇 |
1993年 | 214篇 |
1992年 | 274篇 |
1991年 | 142篇 |
1990年 | 93篇 |
1989年 | 81篇 |
1988年 | 91篇 |
1987年 | 62篇 |
1986年 | 39篇 |
1985年 | 36篇 |
1984年 | 40篇 |
1983年 | 21篇 |
1982年 | 22篇 |
1981年 | 20篇 |
1980年 | 25篇 |
1979年 | 20篇 |
1978年 | 12篇 |
1977年 | 13篇 |
1976年 | 11篇 |
1974年 | 9篇 |
1973年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Diltiazem is an established cardiovascular drug mainly used for the management of hypertension specifically for the angina pectoris. Fluoroquinolones are widely prescribed against the treatment of severe infections. In vitro relations of diltiazem with fluoroquinolones (ciprofloxacin, levofloxacin, norfloxacin, and ofloxacin) were examined using spectrophotometric and separation techniques, i.e., RP-HPLC. Diltiazem’s availabilities were observed to be predisposed highly in the presence of fluoroquinolones. To investigate the mechanism of interaction in a variety of dissolution environments, i.e., simulating body environments with regard to pH on these interactions has been studied. Moreover, complex of diltiazem–fluoroquinolones were prepared and elucidated through IR spectroscopy and confirmed by computational molecular modeling. 相似文献
102.
Photoacoustic phase is the time delay that occurs from light to acoustic signal. the phase includes two components: one is the time delay that occurs during the process in which light absorbed by a sample converts into heat; the other is the time delay caused from heat to acoustic signal. a modified formula of PA phase is presented based on the R-G theory considering the phase caused by non-radiative relaxation processes. the phase is associated with absorption coefficient (β), thermal diffusion length of sample (μs), the longest lifetime of all excited states (r), and the ratio of rapid to slow heat component (R). When the photoacoustic signal is saturated the phase is associated with only T and R. the effect of different rare earth ions on the PA phase spectra of the ligand (oxine) in the rare earth complexes are reported and are well explained by using the phase formula of PA saturation. 相似文献
103.
The modern intracavity laser method has been applied to study electronic spectra of the hafnium monohalides molecules. Results of new investigation of HfF and HfBr molecules are presented: the bands at 589.3, 590.6, and 593.1 nm observed in intracavity laser spectra of HfF4 have been assigned to the bands of HfF or ionized HfF; new molecular constants of the HfBr molecule have been obtained. Spectroscopic studies of HfCl and Hfl molecules are discussed, and the most reliable molecular constants of HfCl, HfBr, and Hfl molecules are recommended. 相似文献
104.
C-13 and H-1 NMR spectra of some 1-(4′-dimethylaminobenzylideneamino)pyridinium perchlorates show that the angle of twist of the pyridine ring in unsubstituted, 1, and 2-alkyl substituted compounds 2–5 is comparable. However, it is considerably increased in 2,6-dialkyl derivatives. As seen from the spectral data, pyridine and phenyl rings in 2,6-diphenyl derivative 15 are not coplanar. The effect of 4-alkyl substituent is of hyperconjugative chacter. In general, the amount of the positive charge at C-4 in 2,6-dialkyl substituted salts is higher as compared to 2-monosubstituted compounds. 相似文献
105.
O. Auciello 《辐射效应与固体损伤》2013,168(1):11-16
A simple model for blistering mechanism is proposed for energies higher than 20 keV. The model assumes that through the nucleation of smaller bubbles, a critical bubble radius is reached. The planar stress results of Jeffery for a semi-infinite plate with a circular hole subject to a uniform inner normal pressure are roughly taken as valid for the three-dimensional case. Under this assumption, the thickness of the blister's cover and critical ion dose for blister formation are calculated from the knowledge of the mean projected range of ions and blister diameter taken from experimental results. The resulting values are in agreement with the experimental values reported. The model can qualitatively explain breakage at the top of the dome-shaped blisters observed in molybdenum at 1100 K. 相似文献
106.
107.
This review reports a broad overview of the synthetic procedures of 1,8-naphthyridines, dibenzo[b,g][1,8]naphthyridine, dibenzo[c,f][1,8]naphthyridine, 1,8-naphthyridine-3-carboxylic acid, 1,8-naphthyridine-3-carboxamide, and 1,8-naphthyridine-3-carbohydrazide compounds and their reactions. The physical properties, spectral data, and biological importance of naphthyridines are discussed. 相似文献
108.
Luminescence of complex ions is a general phenomenon; the number of such complexes in various electronic configurations found to show emission is increasing rapidly. For some it has been possible to assign the emission as phosphorescence or as fluorescence, for others the proper assignment is as yet not clear. 相似文献
109.
A. M. El-Agramy B. A. Henaish A. A. Shabaka 《Isotopes in environmental and health studies》2013,49(10):479-482
Radiophotolumenescence (RPL) of irradiated and non irradiated thin films of polymethylmethacrylate (PMMA) doped with anthracene (Anth) as a donor, and tetracyanoquinodimethane (TCNQ) as an acceptor, has been investigated. The RPL – glow spectrum was recorded to study the characterizing emission bands from the point of view of glow peak position and intensity and hence the prospective relative sensitivities. RFL – signal fading after one month storage in dark at room temperature post gamma irradiation was also studied. PMMA doped with 6:4 donor to acceptor ratio has been proved to be the most sensitive one with less fading regarding gamma detection. On the other hand 2 Anth: 8 TCNQ was found to be the proper dopant concentration ratio for thermal neutron detection. 相似文献
110.
B. Lorenz R. Kirmse M. Findeisen K. Schmidt 《Isotopes in environmental and health studies》2013,49(1):125-130
Abstract The reaction of 2-pyridine carboxylic acid (Hpic) with (n-Bu4N)[TcNCl4] and (n-Bu4N)[TcOCl4] in ethanol and methanol, respectively, yields the dinuclear μ-oxo complex [(pic)2NTc-O-TcN(pic)(Hpic)Cl] and the monomeric complex [TcO(pic)2Cl]. Visible and infrared spectroscopy, ESR, 1H-NMR and 99Tc-NMR have been used to characterize the new compounds. The most important field of application for the new compounds synthesized is radiodiagnostics. 相似文献