全文获取类型
收费全文 | 97289篇 |
免费 | 5323篇 |
国内免费 | 12237篇 |
专业分类
化学 | 77752篇 |
晶体学 | 1197篇 |
力学 | 2409篇 |
综合类 | 932篇 |
数学 | 12737篇 |
物理学 | 19822篇 |
出版年
2024年 | 127篇 |
2023年 | 776篇 |
2022年 | 2340篇 |
2021年 | 2235篇 |
2020年 | 2615篇 |
2019年 | 2406篇 |
2018年 | 2062篇 |
2017年 | 2913篇 |
2016年 | 3180篇 |
2015年 | 2699篇 |
2014年 | 3659篇 |
2013年 | 7076篇 |
2012年 | 6629篇 |
2011年 | 5294篇 |
2010年 | 4527篇 |
2009年 | 6155篇 |
2008年 | 6303篇 |
2007年 | 6498篇 |
2006年 | 5937篇 |
2005年 | 5050篇 |
2004年 | 4689篇 |
2003年 | 3859篇 |
2002年 | 4997篇 |
2001年 | 2896篇 |
2000年 | 2693篇 |
1999年 | 2545篇 |
1998年 | 2210篇 |
1997年 | 1738篇 |
1996年 | 1452篇 |
1995年 | 1383篇 |
1994年 | 1234篇 |
1993年 | 1017篇 |
1992年 | 967篇 |
1991年 | 650篇 |
1990年 | 538篇 |
1989年 | 522篇 |
1988年 | 384篇 |
1987年 | 300篇 |
1986年 | 284篇 |
1985年 | 230篇 |
1984年 | 240篇 |
1983年 | 138篇 |
1982年 | 213篇 |
1981年 | 177篇 |
1980年 | 194篇 |
1979年 | 183篇 |
1978年 | 169篇 |
1977年 | 122篇 |
1976年 | 108篇 |
1973年 | 67篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
921.
J. Escribano R. Masegosa D. Nava M. G. Prolongo Catalina Salom 《Journal of Thermal Analysis and Calorimetry》2006,83(3):675-679
The
mineral sabugalite (HAl)0.5[(UO2)2(PO4)]2⋅8H2O, has been studied using a combination of energy
dispersive X-ray analysis, X-ray diffraction, dynamic and controlled rate
thermal analysis techniques. X-ray diffraction shows that the starting material
in the thermal decomposition is sabugalite and the product of the thermal
treatment is a mixture of aluminium and uranyl phosphates. Four mass loss
steps are observed for the dehydration of sabugalite at 48°C (temperature
range 39 to 59°C), 84°C (temperature range 59 to 109°C), 127°C
(temperature range 109 to 165°C) and around 270°C (temperature range
175 to 525°C) with mass losses of 2.8, 6.5, 2.3 and 4.4%, respectively,
making a total mass loss of water of 16.0%. In the CRTA experiment mass loss
stages were found at 60, 97, 140 and 270°C which correspond to four dehydration
steps involving the loss of 2, 6, 6 and 2 moles of water. These mass losses
result in the formation of four phases namely meta(I)sabugalite, meta(II)sabugalite,
meta(III)sabugalite and finally uranyl phosphate and alumina phosphates. The
use of a combination of dynamic and controlled rate thermal analysis techniques
enabled a definitive study of the thermal decomposition of sabugalite. While
the temperature ranges and the mass losses vary due to the different experimental
conditions, the results of the CRTA analysis should be considered as standard
data due to the quasi-equilibrium nature of the thermal decomposition process.
The online version of the original article can be found at 相似文献
922.
Single crystals of U3+:LaBr3 were grown by the Bridgman-Stockbarger technique. High-resolution polarized absorption spectra of the crystals were recorded at 4.2 K in the 4000-50,000 cm−1 range. Sixty-four experimental crystal-field energy levels of the U3+ ion were fitted to a semiempirical Hamiltonian employing free-ion, one-electron crystal-field as well as two-particle correlation crystal-field (CCF) operators with an r.m.s. deviation of 28 cm−1. The performed analysis of the spectra enabled the determination of crystal-field parameters and assignment of the observed 5f3→5f3 transitions. The effects of selected CCF operators on the splitting of some specific U3+ multiplets have been investigated and the obtained values of Hamiltonian parameters are discussed and compared with those reported in previous analyses. 相似文献
923.
Incorporation of FT-IR spectral data in a computer-assisted prediction of globular protein structure
Currently, much effort is being directed to the determination of the three-dimensional structure of proteins. Two classes of research are of interest; spectrometric techniques which include Fourier transform infrared (FT-IR) spectrometry, and non-spectrometric prediction schemes. The spectra obtained using FT-IR spectrometry, are analyzed to determine the percentages of alpha-helices, beta-pleated sheets, and non-structured coils in a protein. Unfortunately, FT-IR, as well as other spectrometric techniques, cannot be used to determine the exact secondary structure of a protein reliably. Non-spectrometric prediction methods yield information on the exact secondary structure, but are not always accurate. Most prediction methods relate the primary amino acid sequence to the secondary structure of a protein, allowing sequential secondary structure information for the protein examined to be obtained. The goal of this research is to incorporate FT-IR with a prediction method, resulting in an improvement in the accuracy of the prediction. 相似文献
924.
925.
926.
Under various basic solutions and reaction durations, 3-substituted 4-formyIsydnones and nitroalkanes containing α-active hydrogen (e.g. nitromethane and nitroethane) are converted to β-nitroalcohols, nitroalkenes and dinitroalkanes. β-Nitroalcohols are obtained only by electrochemical reaction on an electrogenerated base (EGB). The mechanism of overall reaction steps in particular is discussed. 相似文献
927.
S. H. Kim Eli M. Pearce T. K. Kwei 《Journal of polymer science. Part A, Polymer chemistry》1993,31(13):3167-3180
The precursor of polybenzimidazole (PBI), poly(3,3′-diamino-4,4′-benzidine isophthalamide) (PDABI), was synthesized from poly(3,3′-dinitro-4,4′-benzidine isophthalamide) (PDNBI) by reduction. With increasing temperature, the NH2 moiety which was protected by SnCl5?1 could cyclize and form PBI. Blends with polyamic acid (LaRC-TPI) were prepared. Clear blend films were prepared at up to 400°C. The IR spectra displayed shifts in the NH stretching band, thereby providing evidence for specific interactions related to the miscibility of their cured blends. © 1993 John Wiley & Sons, Inc. 相似文献
928.
The fluorimetric determination of mercury ions with o-vanillin-8-aminoquinoline (OVAQ) in aqueous solutions was investigated. Hg(II) could react with the fluorescent reagent OVAQ
(λex/em = 278/314 nm) to form a nonfluorescent complex in an ethanol-water medium of pH 6.00. The linear range of the proposed method
was from 2.5 to 80 μg/L, and the detection limit was 0.80 μg/L. The interferences of 24 foreign ions were also studied. The
method was successfully applied to the determination of Hg(II) in sludge.
The text was submitted by the authors in English. 相似文献
929.
建立了测定尿液中3种羟基多环芳烃的氮化碳复合材料磁性固相萃取结合高效液相色谱-荧光检测法。所构筑的磁性氮化碳材料,经扫描电子显微镜、X射线衍射仪、振动样品磁强计和比表面积分析仪表征后,用于尿液中3种羟基多环芳烃的富集净化。考察了吸附剂用量、吸附时间、洗脱溶液和洗脱体积(单次洗脱体积×洗脱次数)对萃取效率的影响。结合高效液相色谱-荧光分析,在0.25~250 μg/L范围内线性关系良好(相关系数r=0.999),3种羟基多环芳烃的检出限和定量限分别为0.08和0.25 μg/L,回收率为90.1%~102%,日内和日间精密度分别为1.5%~7.7%和2.2%~8.7%。该本方法简单、快速、高效,可用于尿液中羟基多环芳烃的分析。 相似文献
930.