全文获取类型
收费全文 | 48597篇 |
免费 | 7501篇 |
国内免费 | 5420篇 |
专业分类
化学 | 34206篇 |
晶体学 | 522篇 |
力学 | 3270篇 |
综合类 | 478篇 |
数学 | 5496篇 |
物理学 | 17546篇 |
出版年
2024年 | 104篇 |
2023年 | 909篇 |
2022年 | 1265篇 |
2021年 | 1482篇 |
2020年 | 1861篇 |
2019年 | 1764篇 |
2018年 | 1499篇 |
2017年 | 1321篇 |
2016年 | 2114篇 |
2015年 | 2053篇 |
2014年 | 2554篇 |
2013年 | 3302篇 |
2012年 | 4247篇 |
2011年 | 4415篇 |
2010年 | 2877篇 |
2009年 | 2773篇 |
2008年 | 3094篇 |
2007年 | 2833篇 |
2006年 | 2696篇 |
2005年 | 2225篇 |
2004年 | 1749篇 |
2003年 | 1486篇 |
2002年 | 1502篇 |
2001年 | 1195篇 |
2000年 | 1034篇 |
1999年 | 1139篇 |
1998年 | 913篇 |
1997年 | 865篇 |
1996年 | 992篇 |
1995年 | 791篇 |
1994年 | 738篇 |
1993年 | 597篇 |
1992年 | 552篇 |
1991年 | 473篇 |
1990年 | 386篇 |
1989年 | 309篇 |
1988年 | 266篇 |
1987年 | 206篇 |
1986年 | 191篇 |
1985年 | 166篇 |
1984年 | 122篇 |
1983年 | 88篇 |
1982年 | 54篇 |
1981年 | 52篇 |
1980年 | 30篇 |
1978年 | 19篇 |
1977年 | 23篇 |
1976年 | 20篇 |
1975年 | 30篇 |
1974年 | 27篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
关于四元数矩阵乘积迹的不等式 总被引:1,自引:0,他引:1
设 H~(m×n)为 m×n 四元数矩阵的集合,σ_1(A)≥…≥σ_n(A)为 A∈H~(mxn)的奇异值。本文证明了:1)设 A∈H~(mxm),B∈H~(mxm),r=min(m,m),则|tr(4B)|≤c r σ_i(A)σ_i(B).2)设 A_i∈H~(mxm),i=1,2,…,n,(A_1A_2…A_n)k为 A_1A_2…A_n 的任一个 k 阶主子阵,则|tr(A_1.A_2…A_n)_k|≤sun form i=1 to k σ_i(A_1)…σ_i(A_n).我们还得到四元数矩阵迹的其它一些不等式。这些结果推广和改进了文[1],[2]中的结果,进一步解决了 Bellman 猜想。 相似文献
72.
Yuxi Zheng 《Communications in Mathematical Physics》1991,135(3):581-594
We show that the weak-L
2 limit of a sequence of solutions of the two dimensional incompressible Euler equation is still a solution, provided that a (strong) concentration set for the reduced defect measure has locally finite one dimensional Hausdorff measure in space and time. 相似文献
73.
74.
The present paper devotes to the long-time behavior of a class of reaction diffusion equations with delays under Dirichlet boundary conditions. The stability and global attractability for the zero solution are provided, and the existence, stability and attractability for the positive stationary solution are also obtained. 相似文献
75.
A design of diode-pumped high-efficiency Nd:YVO4/LBO red laser is reported. Using critical phase-matching (CPM) LBO, 671 nm red laser was obtained from 1342 nm light by intracavity frequency doubling. With an incident pump laser of 800 mW, using type-I and type-II CPM LBO, 97 and 52 mWTEM00 mode red laser outputs were obtained, with optical-to-optical conversion efficiencies of up to 12.1% and 6.5%, respectively. 相似文献
76.
Wen Zhang Hui Huang Yu Ding Margherita Gavagnin Ernesto Mollo Guido Cimino Yue‐Wei Guo 《Helvetica chimica acta》2006,89(4):813-820
Three new polyoxygenated steroids, muricesteroid ( 1 ), and menellsteroids A ( 2 ) and B ( 3 ), were isolated from two species of the South China Sea gorgonian Muricella flexuosa and Menella verrucosa Brundin , respectively. The structures of these new compounds were elucidated on the basis of extensive spectroscopic analysis, chemical methods and comparison with known related compounds. 相似文献
77.
78.
This paper reports that the m-plane GaN layer is grown on (200)-plane LiAlO2 substrate by metal-organic chemical wpour deposition (MOCVD) method. Tetragonal-shaped crystallites appear at the smooth surface. Raman measurement illuminates the compressive stress in the layer which is released with increasing the layer's thickness. The high transmittance (80%), sharp band edge and excitonic absorption peak show that the GaN layer has good optical quality. The donor acceptor pair emission peak located at -3.41 eV with full-width at half maximum of 120 meV and no yellow peaks in the photoluminescence spectra partially show that no Li incorporated into GaN layer from the LiAlO2 substrate. 相似文献
79.
以CF4和C6H6的混合气体作为气源,在微波电子回旋共振化学气相沉积(ECRCVD)装置中制备了氟化非晶碳薄膜(aC:F),并在N2气氛中作了退火处理以考察其热稳定性.通过傅里叶变换红外吸收谱和紫外可见光谱获得了薄膜中CC双键的相对含量和光学带隙,发现膜中CC键含量与光学带隙之间存在着密切的关联,在高微波功率下沉积的氟化非晶碳膜具有低的光学带隙和较好的热稳定性.
关键词:
氟化非晶碳膜
光学带隙
退火温度
热稳定性 相似文献
80.
The results of laser induced deposition of copper on polyimide substrate from copper electrolyte solution are reported. Unlike most work reported in the literatures where CW Ar+ lasers were used, a second harmonic (532 nm wavelength) Q-switch Nd:YAG laser was used for our experiments. The deposition process was conducted by laser-catalyzing of the polyimide surface and subsequent photothermal-accelerated reduction of copper-complex ions in an alkaline reducing environment. The characteristics of the deposited copper line were investigated in terms of laser beam scanning speed, and the number of scans. The surface morphology and chemical composition of the deposited copper were analyzed using field emission scanning electron microscope (FESEM) and energy dispersive spectrometer (EDX). The optimum processing conditions have been identified. The copper deposit was found to adhere well to the substrate. 相似文献