全文获取类型
收费全文 | 6095篇 |
免费 | 376篇 |
国内免费 | 586篇 |
专业分类
化学 | 5218篇 |
晶体学 | 174篇 |
力学 | 228篇 |
综合类 | 8篇 |
数学 | 62篇 |
物理学 | 1367篇 |
出版年
2024年 | 3篇 |
2023年 | 65篇 |
2022年 | 83篇 |
2021年 | 72篇 |
2020年 | 111篇 |
2019年 | 113篇 |
2018年 | 103篇 |
2017年 | 164篇 |
2016年 | 268篇 |
2015年 | 195篇 |
2014年 | 202篇 |
2013年 | 406篇 |
2012年 | 354篇 |
2011年 | 371篇 |
2010年 | 308篇 |
2009年 | 438篇 |
2008年 | 314篇 |
2007年 | 384篇 |
2006年 | 332篇 |
2005年 | 264篇 |
2004年 | 243篇 |
2003年 | 207篇 |
2002年 | 165篇 |
2001年 | 155篇 |
2000年 | 139篇 |
1999年 | 147篇 |
1998年 | 135篇 |
1997年 | 111篇 |
1996年 | 117篇 |
1995年 | 139篇 |
1994年 | 128篇 |
1993年 | 102篇 |
1992年 | 80篇 |
1991年 | 68篇 |
1990年 | 50篇 |
1989年 | 32篇 |
1988年 | 56篇 |
1987年 | 40篇 |
1986年 | 48篇 |
1985年 | 49篇 |
1984年 | 60篇 |
1983年 | 33篇 |
1982年 | 69篇 |
1981年 | 38篇 |
1980年 | 30篇 |
1979年 | 36篇 |
1978年 | 13篇 |
1976年 | 5篇 |
1973年 | 5篇 |
1966年 | 2篇 |
排序方式: 共有7057条查询结果,搜索用时 343 毫秒
991.
《Arabian Journal of Chemistry》2022,15(11):104208
Dendrobium nobile alkaloids (DNLA) and glycosides are the main active components extracted from Dendrobium nobile Lindl. (D. nobile) used for thousands of years in China. The pharmacological effects of the above chemical components are significantly different. D. nobile is mainly grown at an altitude ranging from 230 to 800 m in Chishui City, Northwest Guizhou Province. However, it is unclear whether the metabolite in D. nobile is influenced by the planting altitude. Hence, to reveal the different metabolite in D. nobile cultivated at the altitude of 336 m, 528 m, and 692 m, ultra-high performance liquid chromatography with Q/TOF-MS couple with multivariate analysis were developed. Using the orthogonal partial least squares-discriminant analysis, 19 different metabolites were discovered and then tentatively assigned their structures as alkaloids and glycosides by comparing mass spectrometry data with in-house database and literature. Moreover, the result of semiquantitative analysis showed the content of dendrobine that was belonged to alkaloids significantly increased at the altitude of 692 m, whereas the content of glycosides demonstrated an accumulation trend at the altitude of 528 m. The results could provide valuable information for the optimal clinical drug therapeutics and provide a reference for quality control. 相似文献
992.
Bi-injection moulding is a widely used process to manufacture engineering products and consumer goods. Typically, a thermoplastic is combined with rubber or another thermoplastic to create colour differences or hard and soft areas, respectively. The aim of this study was to optimise the injection parameters and processing conditions for the moulding of two-component standard peel test specimens with suitable functional properties. In this work, all parameters of thermo-rheo-kinetic behaviour were identified to predict the entire filling stage and the effect of a liquid silicone rubber cross-linking reaction during the injection moulding process. The models of Carreau-Yasuda and Isayev-Deng regarding the thermal dependence assumed by Arrhenius’ law were used. In our study, over-injection moulding is simulated and examined using finite element software (Cadmould 3D) to investigate the thermo-rheo-kinetic behaviour and the adhesion of liquid silicone rubber during the filling mould process in over-moulding. Numerical simulation results were then compared with the experimental results, and good agreement was obtained. 相似文献
993.
Viko Ladelta George Zapsas Yves Gnanou Nikos Hadjichristidis 《Journal of polymer science. Part A, Polymer chemistry》2019,57(24):2450-2456
New tricrystalline triblock terpolymers, polyethylene‐block‐poly(ε‐caprolactone)‐block‐poly(L‐lactide) (PE‐b‐PCL‐b‐PLLA), were synthesized by ROP of ε‐caprolactone (CL) and L‐lactide (LLA) from linear ω‐hydroxyl polyethylene (PE‐OH) macroinitiators. The linear PE‐OH macroinitiators were prepared by C1 polymerization of methylsulfoxonium methylide (polyhomologation). Tin(II) 2‐ethylhexanoate was used as the catalyst for the sequential ROP of CL and LLA in one‐pot polymerization at 85 °C in toluene (PE‐OH macroinitiators are soluble in toluene at 80 °C). 1H NMR spectra confirmed the formation of PE‐b‐PCL‐b‐PLLA triblock terpolymers through the appearance of the characteristic proton peaks of each block. GPC traces showed the increase in the number average molecular weight from PE‐OH macroinitiator to PE‐b‐PCL, and PE‐b‐PCL‐b‐PLLA corroborating the successful synthesis. The existence of three crystalline blocks was proved by DSC and XRD spectroscopy. © 2019 The Authors. Journal of Polymer Science Part A: Polymer Chemistry published by Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 2450–2456 相似文献
994.
M. P. Marsan I. Muller A. Milon W. Warnock Y. Nakatani G. Ourisson J. Jaud 《Journal of chemical crystallography》1995,25(11):783-786
Synthesis of sterols with varying side chains, including deuterium labeled stigmasterol and sitosterol may be performed via the Wittig-Horner coupling of a 22 aldehyde derived from stigmasterol and a suitable sulfoxide derivative of the side chain. The X-ray structure determination of this synthon have been performed since it is a crucial step in order to know the absolute configuration of the chiral carbon atoms. Crystallographic data were as follows:a=7.437(2),b=10.103(4),c=10.274(3)Å, =100.32(6)o,
=759.4 Å3, space group P21 (No.4),Z=2,D
c=1.239 g cm–3. 相似文献
995.
Ju Hwan Lee Eun-Mi Kim Gi-Seok Heo Hae-Chang Jeong Dong Hyun Kim Dong Wook Lee 《Liquid crystals》2018,45(8):1137-1146
We investigated the characteristics of a solution-processed indium-doped zinc oxide (In:ZnO) film formed via ion-beam (IB) irradiation as a liquid crystal (LC) alignment layer. The In:ZnO film was deposited using solution processing and cured at various temperatures. Uniform LC alignment was observed at all curing temperatures in cross-polarised optical microscopy images. A regular pre-tilt angle supported these results and showed homogeneous LC alignment. Several surface analyses were conducted to evaluate the effect of IB irradiation on the In:ZnO film surface. X-ray diffraction analysis showed an amorphous structure both before and after IB irradiation, and physical surface reformation was observed using atomic force microscopy. Root mean square surface roughness was reduced and a smooth surface was achieved after IB irradiation. X-ray photoelectron spectroscopy was used to detect chemical surface reformation. It was found that the IB irradiation broke the metal-oxide bonds and increased the occurrence of oxygen vacancies, which affected the van der Waals forces between the LC molecules and the In:ZnO film surface. Electrical performance was observed to identify the possibility of using the In:ZnO film in LC applications. Enhanced electro-optical performance was measured and zero residual DC voltage which was verified using a capacitance-voltage curve was achieved. 相似文献
996.
Ahmed Jasim M. Al-Karawi Ali Jasim Hammood Adil A. Awad Al-Ameen Bariz OmarAli Saba Riad Khudhaier Dhafir T. A. Al- Heetimi 《Liquid crystals》2018,45(11):1603-1619
The following organic and organic–inorganic hybrid compounds were prepared as photo-luminescent materials following efficient and practical synthetic methods: 1,3-bis[4-(n-alkoxy)phenyl]-2-propen-1-one (where, n-alkoxy: O(CH2)nH, n = 6,7,8,9 or 10); 3,5-bis[4-(n-alkoxy)phenyl]-1H-pyrazole (where, n-alkoxy: O(CH2)nH, n = 6,7,8,9 or 10) (in case of n = 7, a mixture of 3,5-bis(4-heptyloxyphenyl)-1H-pyrazole and 3,5-bis(4-heptyloxyphenyl)-4H-pyrazole was detected) and bis(3,5-bis [4-(n-alkoxy) phenyl]-1H-pyrazole) silver(I) nitrate (where, n-alkoxy: O(CH2)nH, n = 6,7,8,9 or 10). The prepared compounds have been characterised and their structures were elucidated depending upon (FTIR, UV-Vis, 1HNMR, 13CNMR, 2D 1H-1H-COSY, 2D 1H-13C-HSQC and mass spectra) in addition to molar conductivity measurements for silver(I) complexes. The mesomorphism behaviour of the prepared compounds was studied using polarised light optical microscopy and confirmed with differential scanning calorimetry and X-ray powder diffraction techniques. The studies showed that among all of these compounds only the pyrazole derivatives are liquid crystal materials. The luminescent properties of all the prepared compounds were also investigated which confirmed that all of these compounds are photo-luminescent in the crystalline solid state and in the mesophase. 相似文献
997.
Vertical alignment (VA) is a widely applied operation mode for liquid crystal displays. To achieve optimum brightness, the electrode of VA is often patterned with fish-bone fine slits to generate fringe field, so the negative liquid crystal aligns along the fine slits when the electric field is applied. VA is usually simply modelled by the bend geometry along the cell gap. However, defects, domain boundaries and periodical splay induced by the fine slits also exist in real pixels and disturb the liquid crystal alignment. Polymer-stabilised VA test cells with various fine slit pitches which lead to various strength of fringe field were fabricated to observe the deformation of liquid crystal. Then the models of liquid crystal deformation nearby the defects and in the fine slit area were proposed to calculate the electromagnetic (fEM) and elastic free energy (felastic). The results show that the key factor to regulate fEM and felastic is the pitch of the fine slits, and the optimum liquid crystal alignment is obtained when fEM and felastic are equal. The models are useful for further investigation on the dynamics of liquid crystal alignment and applications in industrial products. 相似文献
998.
The effects of the surface polarity of a glass substrate on the orientation of nematic liquid crystals (LCs) were studied using the polarised optical microscope and Fourier-transform infrared spectroscopy. On the surface of oxygen plasma treated glass, a homeotropic alignment of LCs was induced for LCs with negative dielectric anisotropy. This suggests that vertical orientation of LCs could be induced on a polar glass substrate without using an LC alignment layer. Upon cooling towards the isotropic–nematic transition, E7 with positive dielectric anisotropy changes its LC arrangement to isotropic, homeotropic, planar orientations in order. The nematic LC anchoring transition of E7 was interpreted by considering the competition between van der Waals forces and dipole interactions that control the alignment of LC molecules on a polar glass surface. 相似文献
999.
《中国化学会会志》2018,65(2):212-216
To overcome the relatively low resolution in the separation and quantitative analysis of mixtures of nitrite and nitrate, a reversed‐phase ion‐pair liquid chromatographic method is developed with advantages of high accuracy, good selectivity, high efficiency, and low cost. By employing cetyltrimethylammonium bromide (CTAB) as the ion‐pair reagent, this method can work excellently in situations where one component in the mixture is highly in excess (e.g., molar ratio of n( NO2−):n(NO3−) ranging from 1:99 to 95:5). The operation parameters were optimized on a Shim‐pack VP‐ODS(150 L × 4.6) analytical column using a methanol/water ratio of 50:50 (v/v) mobile phase containing 7.0 mmol/L CTAB and 3.1 mmol/L potassium dihydrogen phosphate (KH2PO4).The column works at a temperature of 35 °C with a flow rate of 1.5 mL/min. Such a protocol can be applied to monitor the formation of trace nitrous acid during the oxidative decomposition of nitric acid. 相似文献
1000.
《Electrophoresis》2018,39(12):1460-1465
This work presents a simple, low‐cost method to fabricate semi‐circular channels using solder paste, which can amalgamate the cooper surface to form a half‐cylinder mold using the surface tension of Sn–Pd alloy (the main component in solder paste). This technique enables semi‐circular channels to be manufactured with different dimensions. These semi‐circular channels will then be integrated with a polymethylmethacrylate frame and machine screws to create miniaturized, portable microfluidic valves for sequential liquid delivery and particle synthesis. This approach avoids complicated fabrication processes and expensive facilities and thus has the potential to be a useful tool for lab‐on‐a‐chip applications. 相似文献