全文获取类型
收费全文 | 447篇 |
免费 | 13篇 |
国内免费 | 4篇 |
专业分类
化学 | 277篇 |
晶体学 | 1篇 |
力学 | 8篇 |
数学 | 33篇 |
物理学 | 145篇 |
出版年
2023年 | 9篇 |
2022年 | 16篇 |
2021年 | 34篇 |
2020年 | 14篇 |
2019年 | 26篇 |
2018年 | 17篇 |
2017年 | 13篇 |
2016年 | 20篇 |
2015年 | 9篇 |
2014年 | 15篇 |
2013年 | 34篇 |
2012年 | 23篇 |
2011年 | 30篇 |
2010年 | 22篇 |
2009年 | 18篇 |
2008年 | 22篇 |
2007年 | 15篇 |
2006年 | 14篇 |
2005年 | 18篇 |
2004年 | 13篇 |
2003年 | 19篇 |
2002年 | 7篇 |
2001年 | 10篇 |
2000年 | 10篇 |
1999年 | 7篇 |
1998年 | 2篇 |
1997年 | 2篇 |
1996年 | 4篇 |
1995年 | 2篇 |
1994年 | 1篇 |
1992年 | 5篇 |
1991年 | 2篇 |
1990年 | 2篇 |
1987年 | 1篇 |
1985年 | 1篇 |
1984年 | 2篇 |
1982年 | 1篇 |
1975年 | 1篇 |
1970年 | 2篇 |
1938年 | 1篇 |
排序方式: 共有464条查询结果,搜索用时 343 毫秒
401.
V. F. Ur’yash A. E. Gruzdeva A. V. Ur’yash A. A. Silkin N. Yu. Kokurina 《Russian Journal of Physical Chemistry B, Focus on Physics》2010,4(7):1097-1102
The radioprotective properties of a substance from pine shoots prepared by supercritical fluid extraction with carbon dioxide
were studied for a model of an experimental bone-marrow radiation sickness form. Experiments were performed for white nonlinear
mice. The CO2 extract of pine shoots was shown to possess radioprotective properties. The extract was subjected to pre-clinical tests for
Wistar line male rats with respect to its antiatherogenic and antioxidative action in the creation of experimental hyperlipemia. 相似文献
402.
Ziaur Rahman Shakeel ur Rehman Sikander M. Mirza Waheed Arshed Nasir M. Mirza Muhammad Masood 《Radiation measurements》2012,47(6):406-409
Due to worldwide use of I-131 for the treatment of benign and malignant thyroid diseases, reliable dose estimation for various thyroid mass values is necessary. In this study computation of the radiation absorbed dose due to β- and γ-activity of I-131 to thyroid has been carried out using the GEANT4 code for water, ICRP and ICRU soft tissues simulating thyroid tissue. The results are validated by comparison with the MIRD calculations. The effect of size and shape of thyroid on absorbed dose has also been studied by varying the volume of thyroid in 10–150 cm3 range and by using spherical and cylindrical models for thyroid. Experimental measurements have also been performed using a group of 20 patients, who were treated for thyro-toxicosis with I-131. Dose equivalent was measured with a portable ionization chamber after the administration of 405–851 MBq of I-131. Comparison of peak energy and effective energy per transformation with the MIRD has been performed yielding only 0.5% relative differences between these two energies. For spherical model, the relative difference of peak and effective energies with the MIRD is 5.2% and 4.7% respectively and very similar for cylindrical models. Spherical model shows 0.45% increase as compared to that of cylindrical model. The use of water, ICRP or ICRU materials only implies negligible difference. Total energy deposition per decay of I-131 increases with volume for both models. The estimated results of spherical and cylindrical thyroid models show an excellent agreement with the corresponding the MIRD results. Simulated results for ambient dose equivalent rate show a good agreement with our experiment and corresponding errors remain less than 13% in the case of dose at 1 m, and are less than 8% for doses at the neck surface. 相似文献
403.
A. Rauf F. Ahmed A. M. Qureshi Aziz‐ur‐Rehman A. Khan M. I. Qadir M. I. Choudhary Z. H. Chohan M. H. Youssoufid T. Ben Haddad 《中国化学会会志》2011,58(4):528-537
Various novel barbituric and thiobarbituric acid derived sulphonamides were synthesized in excellent yield via three components single pot reaction; and these were screened for in vitro urease inhibition studies against jack bean urease. The compounds 1‐7 were found to exhibit a low to moderate activity whereas compounds 8‐14 showed a significant activity (88.3‐99.9% inhibition determined at 500 μM concentration). Structures of the synthesized compounds were confirmed by 1H‐NMR, 13C‐NMR, mass spectrometry and elemental analysis data. 相似文献
404.
405.
In this paper, we discuss various techniques for solving the system of linear equations that arise from the discretization of the incompressible Stokes equations by the finite‐element method. The proposed solution methods, based on a suitable approximation of the Schur‐complement matrix, are shown to be very effective for a variety of problems. In this paper, we discuss three types of iterative methods. Two of these approaches use the pressure mass matrix as preconditioner (or an approximation) to the Schur complement, whereas the third uses an approximation based on the ideas of least‐squares commutators (LSC). We observe that the approximation based on the pressure mass matrix gives h‐independent convergence, for both constant and variable viscosity. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
406.
This note sets out to counter the view that goal programming applied to diet planning offers little improvement over conventional linear programming techniques. 相似文献
407.
S. M. Hasany F. Rashid A. Rashid H. Rehman 《Journal of Radioanalytical and Nuclear Chemistry》1990,142(2):505-514
An accurate and precise wavelength dispersive X-ray fluorescence spectrometric method is described for the quantitative analysis of hafnium impurities in zirconium oxide matrix in the range from 6.8 to 1004 g/g, using the HfL1 line on 8420+ XRF Quantometer (ARL) with LiF (220) crystal and scintillation detector. The practical limit of measurement is 6.8 g/g. The precision is between 1 to 6% for higher and lower concentrations of hafnium, whereas accuracy in most cases is <5%. 相似文献
408.
Abstract This article reviews some of the recent advances on FTIR spectroscopy in areas related to natural tissues and cell biology. It is the second review publication resulting from a detailed study on the applications of spectroscopic methods in biological studies and summarizes some of the most widely used peak frequencies and their assignments. The aim of these studies is to prepare a database of molecular fingerprints, which will help researchers in defining the chemical structure of the biological tissues introducing most of the important peaks present in the natural tissues. In spite of applying different methods, there seems to be a considerable similarity in defining the peaks of identical areas of the FTIR spectra. As a result, it is believed that preparing a unique collection of the frequencies encountered in FTIR spectroscopic studies can lead to significant improvements both in the quantity and quality of research and their outcomes. This article is the first review of its kind that provides a precise database on the most important FTIR characteristic peak frequencies for researchers aiming to analyze natural tissues by FTIR spectroscopy and will be of considerable assistance to those who are focusing on the analysis of cancerous tissues by FTIR spectroscopy. 相似文献
409.
Rehman, Z.U. and Lee, L.L., 1985. Self consistent equations for calculating ideal gas heat capacity, enthalpy and entropy. III. Coal chemicals. Fluid Phase Equilibria, 22: 21–31.Heat capacity, enthalpy and entropy correlations presented in previous studies (Aly and Lee, and Fakeeha et al.) are generalized here to include 37 coal chemicals and 29 additional hydrocarbons. We take into account one additional vibrational contribution in the formulae. The temperature range tested extends from 298.15 to 1000 K. The ideal heat capacity is predicted to within 0.07% for most substances. 相似文献
410.
Heavy metals were investigated in the medicinal plant Withania somnifera as well as of the soil it was grown in using atomic absorption spectrophotometer. The plant samples were collected from three different locations of N.W.F.P, Pakistan. The plant parts including roots, stem, leaves and fruits were found to have the quantity of heavy metals corresponding to their content in the soil. The purpose of the study is to create awareness among people about the proper use and collection of medicinal plants containing high levels of heavy metals and their adverse health affects. 相似文献