全文获取类型
收费全文 | 5128篇 |
免费 | 963篇 |
国内免费 | 751篇 |
专业分类
化学 | 4131篇 |
晶体学 | 76篇 |
力学 | 320篇 |
综合类 | 102篇 |
数学 | 593篇 |
物理学 | 1620篇 |
出版年
2024年 | 15篇 |
2023年 | 119篇 |
2022年 | 155篇 |
2021年 | 205篇 |
2020年 | 267篇 |
2019年 | 255篇 |
2018年 | 224篇 |
2017年 | 208篇 |
2016年 | 280篇 |
2015年 | 313篇 |
2014年 | 361篇 |
2013年 | 434篇 |
2012年 | 490篇 |
2011年 | 480篇 |
2010年 | 401篇 |
2009年 | 375篇 |
2008年 | 352篇 |
2007年 | 310篇 |
2006年 | 273篇 |
2005年 | 190篇 |
2004年 | 151篇 |
2003年 | 128篇 |
2002年 | 120篇 |
2001年 | 88篇 |
2000年 | 78篇 |
1999年 | 62篇 |
1998年 | 48篇 |
1997年 | 38篇 |
1996年 | 36篇 |
1995年 | 43篇 |
1994年 | 24篇 |
1993年 | 39篇 |
1992年 | 39篇 |
1991年 | 17篇 |
1990年 | 27篇 |
1989年 | 22篇 |
1988年 | 13篇 |
1987年 | 15篇 |
1986年 | 14篇 |
1985年 | 20篇 |
1984年 | 12篇 |
1983年 | 12篇 |
1982年 | 7篇 |
1979年 | 6篇 |
1977年 | 6篇 |
1975年 | 9篇 |
1974年 | 8篇 |
1972年 | 11篇 |
1971年 | 6篇 |
1969年 | 5篇 |
排序方式: 共有6842条查询结果,搜索用时 312 毫秒
41.
57Fe Mössbauer effect study has been performed on intercalated compound 2H?Fe0.5TaSe2 over a temperature range between 14K and 500K. The highly concentrated intercalation samples 2H?FexTaSe2 with Fe atoms (x up to 2) are prepared by the electrochemical method for the first time. The Mössbauer measurement shows that iron is in Fe3+ high spin state and with the same probability occupies both octahedral and tetrahedral interstices of the Van der Waals gap. The fact that effective masses of iron ions in both sites are close to 57 amu and characteristic temperatures (ΘM =130K, 107K respectively) are found to be relatively small is attributed to the weak forces on Fe3+. 相似文献
42.
Synthesis and herbicidal activity of O,O-dialkyl phenoxyacetoxyalkylphosphonates containing fluorine
Ting Chen 《Journal of fluorine chemistry》2006,127(2):291-295
A series of substituted phenoxyacetoxyalkylphosphonates bearing fluorine were designed and synthesized. All the new compounds were identified by elemental analysis, IR, 1H NMR and MS and were tested for herbicidal activity in greenhouse at a rate of 1.5 kg/ha. The results of preliminary bioassay showed that fluorine moiety introduced to the core structure could help to improve the herbicidal activity, and compounds with a 3-trifluoromethyl in benzene ring exhibited higher inhibitory activity. 相似文献
43.
InAs/GaSb/AlSb resonant tunneling spin device concepts 总被引:1,自引:0,他引:1
David Z. -Y. Ting Xavier Cartoix 《Physica E: Low-dimensional Systems and Nanostructures》2004,20(3-4):350
We discuss device concepts for creating spin-polarized current sources without external magnetic fields, using non-magnetic 6.1 Å semiconductor resonant tunneling structures. Spin filters, spin pumps, and spin transistors that exploit structural and bulk inversion asymmetries will be examined. 相似文献
44.
1引言令R~(n×m)、OR~(n×n)、SR~(n×n)(SR_0~(n×n))分别表示所有n×m阶实矩阵、n阶实正交阵、n阶实对称矩阵(实对称半正定阵)的全体,A~ 表示A的Moore-Penrose广义逆,I_k表示k阶单位矩阵,S_k表示k阶反序单位矩阵。R(A)表示A的列空间,N(A)表示A的零空间,rank(A)表示矩阵A的秩。对A=(a_(ij)),B=(b_(ij))∈R~(n×m),A*B表示A与 相似文献
45.
Esarey E. Ting A. Sprangle P. Umstadter D. Liu X. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1993,21(1):95-104
A linearly polarized, ultraintense laser field induces transverse plasma currents which are highly relativistic and nonlinear, resulting in the generation of coherent harmonic radiation in the forward direction (i.e., copropagating with the incident laser field). A nonlinear cold fluid model, valid for ultrahigh intensities, is formulated and used to analyze relativistic harmonic generation. The plasma density response is included self-consistently and is shown to significantly reduce the current driving the harmonic radiation. Phase detuning severely limits the growth of the harmonic radiation. The effects of diffraction are considered in the mildly relativistic limit. No third-harmonic signal emerges from a uniform plasma of near-infinite extent. A finite third-harmonic signal requires the use of a semi-infinite or finite slab plasma. For an initially uniform plasma, no second-harmonic radiation is generated. Generation of even harmonics requires transverse gradients in the initial plasma density profile 相似文献
46.
47.
48.
M. Steyer K. A. Stankov H. Mizoguchi B. Ouyang F. P. Schäfer 《Applied physics. B, Lasers and optics》1989,49(4):331-337
An X-ray preionized, discharge-pumped XeCl laser with a variable beam cross-section of up to 6×6 cm2 is described. It uses flat electrodes and the beam width is determined by X-ray collimation. Its operation characteristics concerning reduced electric field strength (E/p) and X-ray dose are discussed in detail. The inductance of the discharge loop is minimized using a water capacitor arrangement. A very high specific optical power (90 MW/l) is achieved in an active volume of 1.2 l. The pulse energy exceeds 5 J in a 45 ns pulse (FWHM). Komatsu Ltd., Manda 1200, Hiratsuka-shi, Kanagawa 254, Japan Institute of Optics and Fine Mechanics, Department of Plasma Physics, Academia Sinica, Shanghai, P.R. China 相似文献
49.
50.
利用四氯合金酸和N-4-甲基苯基2-吡啶甲酰胺(HL)反应,合成得到了一种新的Au(Ⅲ)配合物:二氯(N-4-甲基苯基2-吡啶甲酰胺合金(Ⅲ)[Au(L-N,N′)Cl2]。并通过元素分析、红外光谱、核磁共振谱、质谱及X-射线单晶衍射对其进行了表征。结构分析表明,Au(Ⅲ)由二个氮原子和二个氯原子配位,呈平面四方形结构。质谱研究发现,该化合物与5′-单磷酸鸟苷(5′-GMP)反应生成[Au(L-N,N′)(5′-GMP)2]。 相似文献