全文获取类型
收费全文 | 40778篇 |
免费 | 2299篇 |
国内免费 | 1925篇 |
专业分类
化学 | 23147篇 |
晶体学 | 280篇 |
力学 | 3925篇 |
综合类 | 539篇 |
数学 | 8105篇 |
物理学 | 9006篇 |
出版年
2024年 | 66篇 |
2023年 | 379篇 |
2022年 | 1057篇 |
2021年 | 1064篇 |
2020年 | 1014篇 |
2019年 | 981篇 |
2018年 | 876篇 |
2017年 | 1107篇 |
2016年 | 1488篇 |
2015年 | 1128篇 |
2014年 | 1596篇 |
2013年 | 2790篇 |
2012年 | 2284篇 |
2011年 | 2055篇 |
2010年 | 1769篇 |
2009年 | 2298篇 |
2008年 | 2298篇 |
2007年 | 2599篇 |
2006年 | 2128篇 |
2005年 | 1937篇 |
2004年 | 1903篇 |
2003年 | 1580篇 |
2002年 | 1218篇 |
2001年 | 1020篇 |
2000年 | 979篇 |
1999年 | 899篇 |
1998年 | 814篇 |
1997年 | 736篇 |
1996年 | 665篇 |
1995年 | 657篇 |
1994年 | 588篇 |
1993年 | 479篇 |
1992年 | 445篇 |
1991年 | 364篇 |
1990年 | 328篇 |
1989年 | 217篇 |
1988年 | 219篇 |
1987年 | 136篇 |
1986年 | 117篇 |
1985年 | 141篇 |
1984年 | 112篇 |
1983年 | 58篇 |
1982年 | 94篇 |
1981年 | 54篇 |
1980年 | 44篇 |
1979年 | 75篇 |
1978年 | 35篇 |
1977年 | 21篇 |
1976年 | 25篇 |
1973年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
221.
I. V. Korol’kov A. I. Gubanov K. V. Yusenko I. A. Baidina S. A. Gromilov 《Journal of Structural Chemistry》2007,48(3):486-493
Several non-equilibrium solid solutions belonging to the platinum-osmium systems Os0.9Pt0.1, Os0.8Pt0.2, Os0.5Pt0.5, Os0.7Pt0.3, Os0.75Pt0.25 are prepared and studied. The thermal decomposition of [Pt(NH3)4][OsCl6] in the hydrogen and helium atmosphere is investigated. It is found that the Pt0.5Os0.5 solid solution develops through the formation of (NH4)2[OsCl6] and a metallic phase based on Pt. The crystal structure of a double complex salt [Pt(NH3)4][OsCl6] is studied (X8-APEX Bruker, 1508 independent reflections, R = 2.04%). Crystal data for PtOsN4Cl6H12 are: a = 11.6216(5) Å, b = 11.0016(5) Å, c = 10.3819(5) Å, V = 1327.4(1) Å3, space group Cmca, Z = 4, d x = 3.333 g/cm3. The coordination polyhedron around Os is octahedral: 〈Os-Cl〉 2.357 Å, ∠Cl-Os-Cl 89.5–90.5°, while around Pt it is square-planar: Pt-N 2.046 Å, ∠ N-Pt-N 89.59° and 90.41°. 相似文献
222.
223.
Villar-Rodil S. Paredes J. I. Martínez-Alonso A. Tascón J.M.D. 《Journal of Thermal Analysis and Calorimetry》2002,70(1):37-43
The pyrolysis behaviour of Nomex, poly(m-phenylene isophthalamide) fibres under argon has been investigated up to a temperature of 1173 K with different methods to
get direct information on the progressive changes taking place in the solid material and its carbon fibre residues. The main
stages of the pyrolytic degradation of the fibres were determined by thermal analysis (TG and DTA) and their chemical and
morphological evolution through the different steps was subsequently followed by Fourier transform infrared spectroscopy (FTIR)
and atomic force microscopy (AFM) measurements, respectively, on samples treated to various temperatures.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
224.
Raman spectroscopy was applied for the direct non-destructive analysis of amiodarone hydrochloride (ADH), the active ingredient of the liquid formulation Angoron®. The FT-Raman spectra were obtained through the un-broken as-received ampoules of Angoron®. Using the most intense vibration of the active pharmaceutical ingredient (API) at 1568 cm−1, a calibration model, based on solutions with known concentrations, was developed. The model was applied to the Raman spectra recorded from three as-purchased commercial formulations of Angoron® having nominal strength of 50 mg ml−1 ADH. The average value of the API in these samples was found to be 48.56 ± 0.64 mg ml−1 while the detection limit of the proposed technique was found to be 2.11 mg ml−1. The results were compared to those obtained from the application of HPLC using the methodology described in the European Pharmacopoeia and found to be in excellent agreement. The proposed analytical methodology was also validated by evaluating the linearity of the calibration line as well as its accuracy and precision. The main advantage of Raman spectroscopy over HPLC method during routine analysis is that it is considerably faster and no solvent consuming. Furthermore, Raman spectroscopy is non-destructive for the sample. However, the detection limit for Raman spectroscopy is much higher than the corresponding for the HPLC methodology. 相似文献
225.
This research presents the results of an experimental study on the determination of pyrolysis behaviour and kinetics of six
crude oils by differential scanning calorimetry (DSC) and thermogravimetry (TG/DTG). Crude oil pyrolysis indicated two main
temperature ranges where loss of mass was observed. The first region between ambient to 400°C was distillation. The second
region between 400 and 600°C was visbreaking and thermal cracking. Arrhenius-type kinetic model is used to determine the kinetic
parameters of crude oils studied. It was observed that as crude oils gets heavier (°API decreases) cracking activation energy
increases. Activation energy of cracking also show a general trend with asphaltene content.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
226.
Non-destructive in situ determination of pigments in 15th century wall paintings by Raman microscopy
Raman microscopy has been applied to the study of 15th century wall paintings in a chapel of St. Orso Priory palace (Aosta, Italy) in view of their restoration. The use of a transportable instrument has made it possible to work non-destructively in situ without sampling. The main inorganic pigments used by the unknown artist, namely mercury sulphide, azurite, white lead, red and yellow ochre, carbon black and lead tin yellow type I have been identified, and the presence of organic substances and of some decay products (calcium sulphate and oxalate) has been observed. 相似文献
227.
O. V. Shishkin A. S. Polyakova S. N. Desenko D. V. Orlov S. V. Lindeman Yu. T. Struchkov 《Russian Chemical Bulletin》1995,44(3):470-474
The equilibrium geometry and inversion barriers of 5,6-dihydropyrimidine, 6,7-dihydroazolopyrimidines with node nitrogen atoms and their alkyl (Me, Et, Pri, But) and phenyl derivatives were calculated using a molecular mechanics approach. Annelation with azole cycles and the introduction of substituents have a slight effect on the equilibrium conformation of the dihydrocycle (distorted sofa). Alkyl substutuents at saturated carbons have an essentially equatorial orientation in 5,6-dihydropyridimine derivatives and are axial in the annelated analogs. On the other hand, the equatorial conformers are more stable in phenyl derivatives of dihydroazolopyrimidines. Factors determining the relative stability of conformers were analyzed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 487–491, March, 1995. 相似文献
228.
《Electroanalysis》2004,16(9):697-711
Voltammetric approaches for the determination of arsenic and speciation at trace levels are critically appraised in a review covering the literature from 1970 to 2002. Special attention is devoted to stripping modes and to issues related to the choice of working material and supporting electrolyte. A section is dedicated to the management of real samples and aspects of sample preparation. An extensive compilation, organized by real sample type, gathers essential experimental conditions. Potentiometric stripping analysis is introduced for sake of comparison. The coupling of voltammetric detection or preaccumulation with FIA, chromatography, capillary electrophoresis and ICP techniques is also addressed. 相似文献
229.
流动注射电化学发光测定维生素B1的研究 总被引:2,自引:0,他引:2
基于发现在强碱性介质维生素 B1对电生BrO-氧化Luminol的强化学发光有很强的抑制作用, 将在线恒电流电解产生BrO-与流动注射技术结合,建立了流动注射电化学发光测定维生素B1的新方法.该方法测定维生素B1的线性范围为1.0×10-8~6.0×10-6g·ml-1,检出限为3.2×10-9g·ml-1,相对标准偏差为1.2%(n=11).该法具有灵敏度高,可控性强等优点,用于片剂中的维生素B1含量测定,结果满意. 相似文献
230.
Solubility of lanthanum oxide was measured by thermal analysis. The solubility in alkali cryolites is rather high, because of chemical reactions between lanthanum oxide and cryolites. In Li3AlF6-La2O3, alumina precipitates, in the other systems the mixed oxide LaAlO3 is formed. In La2O3-Li3AlF6 the eutectic point is at 9.5 mol% La2O3 and 755 °C. The eutectic points in La2O3-Na3AlF6 and La2O3-K3AlF6 are at 11.5 mol% La2O3, and at 937 and 934 °C, respectively. 相似文献