首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   528篇
  免费   12篇
  国内免费   12篇
化学   264篇
晶体学   14篇
力学   22篇
数学   121篇
物理学   131篇
  2023年   7篇
  2022年   20篇
  2021年   18篇
  2020年   13篇
  2019年   20篇
  2018年   8篇
  2017年   10篇
  2016年   17篇
  2015年   17篇
  2014年   19篇
  2013年   100篇
  2012年   15篇
  2011年   16篇
  2010年   18篇
  2009年   12篇
  2008年   13篇
  2007年   10篇
  2006年   15篇
  2005年   7篇
  2004年   7篇
  2003年   7篇
  2002年   5篇
  2001年   9篇
  2000年   6篇
  1999年   6篇
  1998年   7篇
  1997年   14篇
  1996年   7篇
  1995年   6篇
  1994年   8篇
  1993年   4篇
  1991年   3篇
  1987年   3篇
  1978年   3篇
  1977年   4篇
  1973年   4篇
  1969年   3篇
  1967年   6篇
  1966年   5篇
  1965年   7篇
  1964年   4篇
  1962年   9篇
  1960年   4篇
  1959年   3篇
  1956年   3篇
  1955年   4篇
  1934年   2篇
  1933年   4篇
  1927年   2篇
  1923年   2篇
排序方式: 共有552条查询结果,搜索用时 31 毫秒
51.
In recent years, a sufficient condition for determining chaotic behaviours of the non-linear systems has been characterized by the negative Schwarzian derivative (Hac?bekiro?lu et al, Nonlinear Anal.: Real World Appl. 10, 1270 (2009)). In this work, the Schwarzian derivative has been calculated for investigating the quantum chaotic transition points in the high-temperature superconducting frame of reference, which is known as a nonlinear dynamical system that displays some macroscopic quantum effects. In our previous works, two quantum chaotic transition points of the critical transition temperature, T c, and paramagnetic Meissner transition temperature, T PME, have been phenomenologically predicted for the mercury-based high-temperature superconductors (Onba?l? et al, Chaos, Solitons and Fractals 42, 1980 (2009); Aslan et al, J. Phys.: Conf. Ser. 153, 012002 (2009); Çataltepe, Superconductor (Sciyo Company, India, 2010)). The T c, at which the one-dimensional global gauge symmetry is spontaneously broken, refers to the second-order phase transition, whereas the T PME, at which time reversal symmetry is broken, indicates the change in the direction of orbital current in the system (Onba?l? et al, Chaos, Solitons and Fractals 42, 1980 (2009)). In this context, the chaotic behaviour of the mercury-based high-temperature superconductors has been investigated by means of the Schwarzian derivative of the magnetic moment versus temperature. In all calculations, the Schwarzian derivatives have been found to be negative at both T c and T PME which are in agreement with the chaotic behaviour of the system.  相似文献   
52.
In data mining, binary classification has a wide range of applications. Cutting Decision Tree (CDT) induction is an efficient mathematical programming based method that tries to discretize the data set on hand by using multiple separating hyperplanes. A new improvement to CDT model is proposed in this study by incorporating the second goal of maximizing the distance of the correctly classified instances to the misclassification region. Computational results show that developed model achieves better classification accuracy for Wisconsin Breast Cancer database and Japanese Banks data set when compared to existing piecewise-linear models in literature. Furthermore, remarkable results are obtained for the well-known benchmarking data sets (Buba Liver Disorders, Blood Tranfusion and Pima Indian Diabetes) when compared to the original CDT model.  相似文献   
53.
54.
Nonlinear Dynamics - Substitution Box (S-Box) is one of the most significant structures used to create an encryption which is strong and resistant against attacks in block encryption algorithms....  相似文献   
55.
In this study, poly(vinylbenzylchloride) (PVBC) was produced by free‐radical polymerization of 4‐vinylbenzylchloride, and then it was functionalized with 3‐amino‐1,2,4‐triazole (ATri) and 1H‐1,2,4‐triazole (Tri). The composition of the polymers was verified by elemental analysis, and the structure was characterized by Fourier transform infrared and 13C‐nuclear magnetic resonance spectra. PVBC was modified by ATri with 68% and Tri with 50% yield. The polymers were doped with trifluoromethanesulfonic acid (TA) at various molar ratios, X = 0.5, 1, 2, and 3 with respect to aminotriazole and triazole units. Proton transfer from TA to the triazole rings was proved with Fourier transform infrared spectroscopy. Thermogravimetric analysis showed that the samples are thermally stable up to approximately 200 °C. Differential scanning calorimetry results illustrated the homogeneity of the materials. Under anhydrous conditions, PVBCATri3TA and PVBCTri3TA showed highest proton conductivity of 0.086 and 0.042 S/cm, respectively. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010  相似文献   
56.
A mixture of benzimidazole salts (2–7), Pd(OAc)2 and K2CO3 in DMF–H2O catalyzes the Suzuki–Miyaura cross‐coupling reactions promoted by microwave irradiation resulting in high yield within a short time. In particular, the yield of the Suzuki–Miyaura reactions with aryl bromides was found to be nearly quantitative. The synthesized benzimidazole salts (2–7) were identified by 1H‐13C, NMR, IR spectroscopic methods and microanalysis. The molecular structure of 1 was determined by X‐ray crystallography. The antibacterial and antifungal activities of the novel benzimidazole derivatives (1–7) were also tested against standard strains. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   
57.
Plasma samples from 60 transplant patients on mycophenolate mofetil therapy were analysed using validated capillary electrophoresis (CE) method to determine mycophenolic acid (MPA) and its main metabolite mycophenolic acid glucuronide. Enzyme multiplied immunoassay technique (EMIT) values were available for the same samples. The differences between the results from the two methods was clarified by using Bland–Altman analysis and further statistical analysis. More than 90% of the results showed a positive bias, with EMIT giving higher levels than CE.  相似文献   
58.
Aniline-mustard and its glucuronide conjugate were radioiodinated with 131I. The preliminary dynamic tests were carried out on rabbits. The scintigrams showed clearly that the glucuronide conjugate of aniline-mustard was very quickly cleared from the metabolism, accumulating in the bladder in about 15 minutes. The clearance time of radioiodinated aniline-mustard-glucuronide was considerably longer (about 45 min.). The results obtained from the biodistributional studies have represented interesting differences between the metabolic details of radioiodinated compounds, and indicated that the glucuronide conjugate of aniline-mustard may be a promising radioiodinated prodrug, if verification of its selective accumulation in some kinds of tumor cells can be obtained.  相似文献   
59.
The system of inequalities is transformed to the least squares problem on the positive ortant. This problem is solved using orthogonal transformations which are memorized as products. Author’s previous paper presented a method where at each step all the coefficients of the system were transformed. This paper describes a method applicable also to large matrices. Like in revised simplex method, in this method an auxiliary matrix is used for the computations. The algorithm is suitable for unstable and degenerate problems primarily.   相似文献   
60.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号