全文获取类型
收费全文 | 20521篇 |
免费 | 3537篇 |
国内免费 | 2289篇 |
专业分类
化学 | 14682篇 |
晶体学 | 260篇 |
力学 | 1250篇 |
综合类 | 186篇 |
数学 | 2059篇 |
物理学 | 7910篇 |
出版年
2024年 | 75篇 |
2023年 | 468篇 |
2022年 | 669篇 |
2021年 | 731篇 |
2020年 | 817篇 |
2019年 | 788篇 |
2018年 | 662篇 |
2017年 | 624篇 |
2016年 | 974篇 |
2015年 | 978篇 |
2014年 | 1106篇 |
2013年 | 1442篇 |
2012年 | 1859篇 |
2011年 | 1890篇 |
2010年 | 1247篇 |
2009年 | 1106篇 |
2008年 | 1293篇 |
2007年 | 1279篇 |
2006年 | 1130篇 |
2005年 | 1006篇 |
2004年 | 720篇 |
2003年 | 628篇 |
2002年 | 570篇 |
2001年 | 432篇 |
2000年 | 410篇 |
1999年 | 470篇 |
1998年 | 355篇 |
1997年 | 369篇 |
1996年 | 309篇 |
1995年 | 298篇 |
1994年 | 302篇 |
1993年 | 246篇 |
1992年 | 197篇 |
1991年 | 198篇 |
1990年 | 177篇 |
1989年 | 112篇 |
1988年 | 86篇 |
1987年 | 89篇 |
1986年 | 60篇 |
1985年 | 44篇 |
1984年 | 43篇 |
1983年 | 24篇 |
1982年 | 25篇 |
1981年 | 18篇 |
1980年 | 14篇 |
1975年 | 2篇 |
1957年 | 4篇 |
1936年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
51.
52.
53.
54.
The structural stability of heat-treated CoN/CN soft X-ray multilayers fabricated by dual-facing-target sputtering has been investigated by using complementary measurement techniques. The high temperature annealing results imply that the destructive threshold of the Co/C multilayers is improved by 100–200 degrees centigrade through doping with N. The low-angle X-ray diffraction of CoN/CN soft X-ray multilayers indicates that the period expansion of the multilayers is only 4 % at 400°C, and the interface pattern still exists even if they were annealed at 700°C. The Raman spectra analyses give the evidence that the formation of the sp3 bonding in the CN sublayers can be suppressed effectively by doping N with atoms, and thus the period expansion resulting from the changes in the density of CN layers can be decreased considerably. The X-ray photoelectron spectra analyses present the information of the existence of the strong covalent bonding betweenC andN atoms, and the ionic bonding between Co and N atoms, which can slow down the tendency of the structural relaxation. The interstitial N atoms decrease the mobility of Co atoms, and thus the fcc-Co and hcp-Co coexist even though the annealing temperature is much higher than the phase transformation temperature of 420°C, leading to the suppression of the grain growth. 相似文献
55.
56.
A method for determining accurate relative molecular masses and elemental compositions of several non-volatile and thermally labile organic compounds in the source cell was established. The experimental sequence included laser desorption/electron impact Fourier transform mass spectrometry and direct-mode observation over a narrow mass range. Perfluorotributylamine was used as internal calibrant. Errors were about 1 ppm. 相似文献
57.
采用固源Si分子束外延,在较高的生长温度于Si(100)衬底上制备出Si1-xGex/Si量子阱发光材料。发光样品的质量和特性通过卢瑟福背散射、X射线双晶衍射及光致发光评估。背散射实验中观察到应变超晶格的反常沟道效应;X射线分析表明材料的生长是共度的、无应力释放的,结晶完整性好。低温光致发光主要是外延合金量子阱中带边激子的无声发射和横光学声子参与的激子复合。并讨论了生长温度对量于阱发光的影响。 相似文献
58.
Yi Jiang Chuan-Lei Jia Xue-Lin Wang Ke-Ming Wang Hong-Ji Ma 《Applied Surface Science》2006,253(5):2674-2677
A planar optical waveguide has been formed in a LiB3O5 crystal using 6.0 MeV Cu+-ions with a dose of 1 × 1015 ions/cm2 at room temperature. Possible propagating modes were measured at a wavelength of 633 nm using the prism-coupling method. The refractive index profiles of the waveguide were reconstructed by an effective refractive index method and the beam propagation method was used to investigate the properties of the propagation modes in the formed waveguide. The results suggest that the fundamental TE0 and TM0 modes may be well-confined and propagate a longer distance inside the waveguide. The implantation process was also simulated using the transport of ions in matter code (TRIM), which indicates that the nuclear energy deposition may be the main factor for the refractive index change. 相似文献
59.
Jiang Tongsong Liu Yonghui Wei Musheng 《高校应用数学学报(英文版)》2006,21(1):113-118
This paper derives a theorem of generalized singular value decomposition of quaternion matrices (QGSVD),studies the solution of general quaternion matrix equation AXB -CYD= E,and obtains quaternionic Roth's theorem. This paper also suggests sufficient and necessary conditions for the existence and uniqueness of solutions and explicit forms of the solutions of the equation. 相似文献
60.
Tao Jin Feng-Xian Jiang Xiao-Li Li Fang Wang Xiao-Hua Shen Rui-Qiang Zhang Hai-Shun Wu 《Applied Surface Science》2006,253(5):2708-2712
CoPt/Ag and [C/CoPt]n/Ag thin films have been prepared onto the glass substrates by magnetron sputtering. We investigated the evolution of texture and magnetic properties of CoPt/Ag and [C/CoPt]n/Ag films. The results show that C-doping plays an important role in improving (0 0 1) texture, improving the order parameter S, reducing the intergrain interactions, and making the magnetization reversal mechanism more close to Stoner-Wolfarth rotational mechanism. The growth mechanism of (0 0 1) texture also seems to be related strongly to the films thickness. Our results show that the highly (0 0 1)-oriented films with ordered fct phase have a significant potential for the perpendicular media of extremely high-density recording. 相似文献