全文获取类型
收费全文 | 9841篇 |
免费 | 265篇 |
国内免费 | 20篇 |
专业分类
化学 | 5828篇 |
晶体学 | 163篇 |
力学 | 268篇 |
数学 | 740篇 |
物理学 | 3127篇 |
出版年
2023年 | 92篇 |
2022年 | 173篇 |
2021年 | 164篇 |
2020年 | 181篇 |
2019年 | 245篇 |
2018年 | 209篇 |
2017年 | 237篇 |
2016年 | 318篇 |
2015年 | 215篇 |
2014年 | 402篇 |
2013年 | 801篇 |
2012年 | 556篇 |
2011年 | 663篇 |
2010年 | 420篇 |
2009年 | 411篇 |
2008年 | 460篇 |
2007年 | 441篇 |
2006年 | 335篇 |
2005年 | 282篇 |
2004年 | 229篇 |
2003年 | 163篇 |
2002年 | 184篇 |
2001年 | 117篇 |
2000年 | 125篇 |
1999年 | 86篇 |
1998年 | 56篇 |
1997年 | 56篇 |
1996年 | 92篇 |
1995年 | 104篇 |
1994年 | 98篇 |
1993年 | 92篇 |
1992年 | 120篇 |
1991年 | 86篇 |
1990年 | 80篇 |
1989年 | 92篇 |
1988年 | 88篇 |
1987年 | 90篇 |
1986年 | 74篇 |
1985年 | 104篇 |
1984年 | 120篇 |
1983年 | 82篇 |
1982年 | 98篇 |
1981年 | 97篇 |
1980年 | 102篇 |
1979年 | 90篇 |
1978年 | 102篇 |
1977年 | 84篇 |
1976年 | 56篇 |
1975年 | 62篇 |
1974年 | 74篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
911.
912.
Pawan Kumar R. PrasadR.K. Dwivedi H.K. Singh 《Journal of magnetism and magnetic materials》2011,323(21):2564-2568
A comparative study of the out-of-plane anisotropic magnetoresistance (AMR) in single crystalline and polycrystalline thin films of phase separated manganite Nd0.51Sr0.49MnO3 has been carried out. On-axis DC magnetron sputtering was used to deposit the single crystalline films (30 and 100 nm in thickness) on single crystal (0 0 1) LaAlO3 (LAO) and polycrystalline films (100 nm) on (1 0 0) Yttrium-stabilized ZrO2 (YSZ) substrates. The in-plane and out-of-plane magnetotransport properties of these films differ significantly. A large low field AMR is observed in all the films. AMR shows a peak below the insulator-metal transition temperature in the single crystalline films, while the same increases monotonically in the polycrystalline film. Relatively larger low field AMR (∼20% at T=78 K and H=1.7 kOe) in the polycrystalline films suggests the dominance of the shape anisotropy. 相似文献
913.
Dattatray J. Late Mahendra A. More Sucharita Sinha K. Dasgupta Pankaj Misra B. N. Singh Lalit M. Kukreja Sudha V. Bhoraskar Dilip S. Joag 《Applied Physics A: Materials Science & Processing》2011,104(2):677-685
The paper deals with the comparative study of nanocrystalline Lanthanum hexaboride (LaB6) thin films grown on various substrates by Pulsed laser deposition and Arc plasma method. Field emission studies were carried
out on LaB6 films deposited on various substrates show metallic behavior of the emitters. The high value of field enhancement factors,
indicating that the electron emission from LaB6 nanoscale protrusions deposited on emitter surface. The post field emission surface morphology of the emitters showed no
significant erosion of the films during continuous operation. The observed behavior indicates that it is linked with the growth
of LaB6 films on substrate crystal structure. The LaB6 nanocrystallites/nanowires films were synthesized using arc plasma method shows good emission current stability. The LaB6 micro/nanocrystallites were also obtained by picosecond laser irradiation which gives high enhancement β factor, and good emission current stability along with high current density. The results reveal that nanocrystalline LaB6 films, exhibit high resistance to ion bombardment and excellent structural stability and are more promising emitters for
practical applications in field emission based new generation devices. 相似文献
914.
Philipp Bader Arieh Iserles Karolina Kropielnicka Pranav Singh 《Foundations of Computational Mathematics》2014,14(4):689-720
The computation of the semiclassical Schrödinger equation presents major challenges because of the presence of a small parameter. Assuming periodic boundary conditions, the standard approach consists of semi-discretisation with a spectral method, followed by an exponential splitting. In this paper we sketch an alternative strategy. Our analysis commences with the investigation of the free Lie algebra generated by differentiation and by multiplication with the interaction potential: it turns out that this algebra possesses a structure which renders it amenable to a very effective form of asymptotic splitting: exponential splitting where consecutive terms are scaled by increasing powers of the small parameter. This leads to methods which attain high spatial and temporal accuracy and whose cost scales as \({\mathcal {O}}\!\left( M\log M\right) \) , where \(M\) is the number of degrees of freedom in the discretisation. 相似文献
915.
Construction X and its variants are known from the theory of classical error control codes. We present instances of these constructions that produce binary stabilizer quantum error control codes from arbitrary quaternary linear codes. Our construction does not require the classical linear code \(C\) that is used as the ingredient to satisfy the dual containment condition, or, equivalently, \(C^{\perp _h}\) is not required to satisfy the self-orthogonality condition. We prove lower bounds on the minimum distance of quantum codes obtained from our construction. We give examples of record breaking quantum codes produced from our construction. In these examples, the ingredient code \(C\) is nearly dual containing, or, equivalently, \(C^{\perp _h}\) is nearly self-orthogonal, by which we mean that \(\dim (C^{\perp _h})-\dim (C^{\perp _h}\cap C)\) is positive but small. 相似文献
916.
K. D. Singh 《Zeitschrift für Angewandte Mathematik und Physik (ZAMP)》2004,55(5):894-902
A three dimensional steady fully developed MHD Couette flow of a viscous incompressible electrically conducting fluid is analysed. The lower stationary porous plate is subjected to a periodic injection velocity and the upper porous plate in uniform motion to a constant suction velocity. A magnetic field of uniform strength applied normal to the planes of the plates is fixed with the moving plate. Neglecting the induced magnetic field, an approximate solution for the flow field is obtained and discussed with the help of graphs. 相似文献
917.
Fateh V. Singh 《Tetrahedron letters》2010,51(5):863-6886
An ultrasound-assisted synthesis of functionalized symmetrical biaryls with electron-withdrawing or electron-donating substituents is described and illustrated by the palladium-catalyzed detelluration of 1,2-diarylditellanes. This procedure offers easy access to symmetrical biaryls in short reaction time and the products are achieved in good to excellent yields. 相似文献
918.
The preparation and NMR analysis of 2,3-di-O-benzyl arabinofuranosides have been described. In DMSO-d6, the sugar adopts a conformation in which the hydroxyl groups are in an equatorial position; the equilibrium composition is determined by steric factors. In CDCl3, the sugar adopts a conformation in which the intramolecular hydrogen bonding plays an important role in determining the equilibrium composition. The use of 2,3-di-O-benzyl arabinose in the synthesis of oligoarabinofuranosides enabled the synthesis of α- or β-linked furanosides. 相似文献
919.
Gowravaram Sabitha Gajangi Chandrashekhar Kurra Yadagiri Jhillu Singh Yadav 《Tetrahedron: Asymmetry》2011,22(18-19):1729-1735
The total syntheses of the first examples of diarylheptanoid natural products (5S)-5-acetoxy-1,7-bis(4-hydroxy-3-methoxyphenyl)-3-heptanone 1, and (3S,5S)-3,5-diacetoxy-1,7-bis(4-hydroxy-3-methoxyphenyl)heptane 2 isolated from the rhizomes of Zingiber officinale were accomplished using Sharpless epoxidation and cross-metathesis reactions as the key steps. 相似文献