全文获取类型
收费全文 | 548篇 |
免费 | 20篇 |
国内免费 | 4篇 |
专业分类
化学 | 326篇 |
晶体学 | 7篇 |
力学 | 10篇 |
数学 | 100篇 |
物理学 | 129篇 |
出版年
2023年 | 3篇 |
2022年 | 8篇 |
2021年 | 8篇 |
2020年 | 12篇 |
2019年 | 16篇 |
2018年 | 12篇 |
2017年 | 17篇 |
2016年 | 23篇 |
2015年 | 16篇 |
2014年 | 21篇 |
2013年 | 42篇 |
2012年 | 39篇 |
2011年 | 48篇 |
2010年 | 21篇 |
2009年 | 25篇 |
2008年 | 31篇 |
2007年 | 35篇 |
2006年 | 17篇 |
2005年 | 24篇 |
2004年 | 23篇 |
2003年 | 11篇 |
2002年 | 14篇 |
2001年 | 7篇 |
2000年 | 13篇 |
1998年 | 5篇 |
1997年 | 10篇 |
1996年 | 3篇 |
1995年 | 7篇 |
1994年 | 2篇 |
1993年 | 6篇 |
1992年 | 4篇 |
1991年 | 4篇 |
1990年 | 2篇 |
1989年 | 4篇 |
1988年 | 3篇 |
1987年 | 3篇 |
1985年 | 2篇 |
1984年 | 5篇 |
1983年 | 1篇 |
1981年 | 4篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1978年 | 3篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1974年 | 3篇 |
1973年 | 1篇 |
1971年 | 1篇 |
1957年 | 1篇 |
1943年 | 1篇 |
排序方式: 共有572条查询结果,搜索用时 703 毫秒
61.
62.
Harshika Agarwal Shweta Yadav Gautam Jaiswar 《Journal of Thermal Analysis and Calorimetry》2017,129(3):1471-1479
The thermal, morphological and optical studies of BaSO4 and MMT (nanoclay) embedded in PVDF were investigated. Nanocomposites samples of PVDF–BaSO4–MMT were prepared by varying the loadings (1–4 mass%) in case of BaSO4 and MMT nanomaterials, respectively. Polyvinylidene fluoride–barium sulfate-montmorillonite (PVDF–BaSO4–MMT) nanocomposites were prepared by solvent-mixing technique. Nanoparticles were synthesized by in situ deposition technique with the help of nonionic polymeric surfactant, and the particle size of nanoparticles was recognized by scanning electron microscopy (SEM) analysis which confirms that the particle has diameter of 80–90 nm. As prepared, nanocomposites films (thickness, 25 μm) were characterized by Fourier transform infrared microscopy (FTIR), SEM and electron diffraction spectroscopy (EDS). FTIR shows that all the chemical constituents were present in the nanocomposites, whereas SEM analysis suggested that the nanofillers dispersed well in polymer matrix and EDS showed the elemental composition of nanocomposite samples. Thermal properties of nanocomposites were studied by using TG/DTA/DTG. TG/DTA studies showed decomposition temperature of pure PVDF is 473.5 °C. The decomposition temperature (T d) of nanocomposites was increased by 93 °C in case of nanocomposites with addition of both BaSO4 and MMT nanomaterials. The difference in the thermal degradation temperature was found to be 1.2% higher in case of addition of BaSO4 nanoparticle as compared to nanoclay. The obtained transparent nanocomposite films were characterized by using UV–Vis spectrophotometer which shows that transparencies of nanocomposites are maintained in visible region, the intensity of absorption band in UV region is increased with the addition of BaSO4 nanoparticles, while in case of addition of nanoclay the UV region does not show drastic changes. Addition of both nanoparticle and nanoclay shows higher absorption in comparison with the individual samples. But further, doubling the amount of nanoparticle and nanoclay shows decrease in UV absorption. Overall, the results of thermal studies show that the incorporation of BaSO4 and MMT could significantly improve the thermal properties of nanocomposites. 相似文献
63.
Gautam Batra 《Journal of Elasticity》1989,21(2):131-146
A principle of virtual work is proposed for thermo-elastic bodies. From it are derived the equations of motion, the Cauchy stress principle and the Gibbs relations. The principle is also used to analyse the response of internally constrained bodies. 相似文献
64.
A series of amino acid-derived enantiomerically pure substituted benzo[d][1,2,3,6]oxatriazocine derivatives and 1-alkyl substituted benzotriazoles has been prepared by the diazotization of amino acid-derived benzo-fused alicycles. The first unprecedented diazo-oxygen bond formation in acidic medium led to an entirely new kind of substituted benzo[d][1,2,3,6]oxatriazocine heterocycles. 相似文献
65.
Epsita?Ghanti Nobel?Tomar Prikshit?Gautam R.?NagarajanEmail author 《Journal of Sol-Gel Science and Technology》2011,57(1):12-15
Al(OPh)3 involving sterically hindered phenyl groups on ultrasonic assisted micro hydrolysis yielded a mixture of boehmite and bayerite
as deduced from the FTIR and powder X-ray diffraction pattern. In the thermogravimetric trace, the complete removal of decomposable
moieties of the hydrolyzed gel occurred around 530 °C. Calcining the gel at temperatures 600, 700, 800 and 900 °C showed crystalline
tetragonal δ-Al2O3 to be the product at 900 °C as deduced from FTIR, 27Al NMR and PXRD techniques. δ-Al2O3 showed a surface area of 135 m2/g with rectangular bar like morphology with the sizes below 50 nm in the TEM images. 相似文献
66.
Die Wasserstoffbrücke ist eine Wechselwirkung, bei der ein Wasserstoffatom von zwei Atomen statt nur einem angezogen wird und als Brücke zwischen den beiden wirkt. Die Anziehung wird mit zunehmender Elektronegativität jedes der beiden Atome stärker. In klassischer Betrachtungsweise sind Wasserstoffbrücken weitgehend elektrostatisch, in manchen Fällen sogar teilkovalent. Das Konzept der Wasserstoffbrücke wurde im Laufe der Zeit immer wieder erweitert, um auch schwächere und dispersivere Wechselwirkungen einzubeziehen, sofern eine gewisse elektrostatische Beschaffenheit der Wechselwirkung gegeben ist. In der Praxis wird eine enorme Vielfalt an sehr starken, starken, mäßig starken, schwachen und sehr schwachen Wasserstoffbrücken beobachtet. Aktuell werden schwache Wasserstoffbrücken mit vielen Fragen der Strukturchemie und der Biologie in Verbindung gebracht. Während starke Wasserstoffbrücken von allen bestehenden Definitionen der Erscheinung erfasst werden, können schwächere zu Problemen bei der Benennung und zu Konflikten mit bestehenden Definitionen führen. Kürzlich wurde der International Union of Pure and Applied Chemistry (IUPAC) eine Empfehlung für eine aktualisierte Definition des Begriffs “Wasserstoffbrücke” vorgelegt. In diesem Essay soll die vorgeschlagene Definition ausführlich erläutert werden. 相似文献
67.
Vargis E Kanter EM Majumder SK Keller MD Beaven RB Rao GG Mahadevan-Jansen A 《The Analyst》2011,136(14):2981-2987
In this paper, we examine how variations in normal tissue can influence disease classification of Raman spectra. Raman spectra from normal areas may be affected by previous disease or proximity to areas of dysplasia. Spectra were acquired in vivo from 172 patients and classified into five tissue categories: true normal (no history of disease), previous disease normal (history of disease, current normal diagnosis), adjacent normal (disease on cervix, spectra acquired from visually normal area), low grade, and high grade. Taking into account the various "normal" states of the tissue before statistical analysis led to a disease classification accuracy of 97%. These results indicate that abnormal changes significantly affect Raman spectra, even when areas are histopathologically normal. The sensitivity of Raman spectroscopy to subtle biochemical differences must be considered in order to successfully implement it in a clinical setting for diagnosing cervical dysplasia and cancer. 相似文献
68.
Desiraju GR 《Angewandte Chemie (International ed. in English)》2011,50(25):5590-5591
69.
Thakur TS Kirchner MT Bläser D Boese R Desiraju GR 《Physical chemistry chemical physics : PCCP》2011,13(31):14076-14091
Structural and electronic properties of C-H···O contacts in compounds containing a formyl group are investigated from the perspective of both hydrogen bonding and dipole-dipole interactions, in a systematic and graded approach. The effects of α-substitution and self-association on the nature of the formyl H-atom are studied with the NBO and AIM methodologies. The relative dipole-dipole contributions in formyl C-H···O interactions are obtained for aldehyde dimers. The stabilities and energies of aldehyde clusters (dimer through octamer) have been examined computationally. Such studies have an implication in crystallization mechanisms. Experimental X-ray crystal structures of formaldehyde, acrolein and N-methylformamide have been determined in order to ascertain the role of C-H···O interactions in the crystal packing of formyl compounds. 相似文献
70.
Gautam Pankaj Sahu Daya Ram Dixit Avinash Som Tanmoy 《Journal of Optimization Theory and Applications》2021,190(2):491-523
Journal of Optimization Theory and Applications - In this paper, the first-order forward–backward–half forward dynamical systems associated with the inclusion problem consisting of... 相似文献