全文获取类型
收费全文 | 24972篇 |
免费 | 4514篇 |
国内免费 | 3244篇 |
专业分类
化学 | 17673篇 |
晶体学 | 361篇 |
力学 | 1466篇 |
综合类 | 216篇 |
数学 | 3384篇 |
物理学 | 9630篇 |
出版年
2024年 | 67篇 |
2023年 | 506篇 |
2022年 | 596篇 |
2021年 | 860篇 |
2020年 | 1143篇 |
2019年 | 1083篇 |
2018年 | 934篇 |
2017年 | 936篇 |
2016年 | 1323篇 |
2015年 | 1290篇 |
2014年 | 1493篇 |
2013年 | 2015篇 |
2012年 | 2317篇 |
2011年 | 2358篇 |
2010年 | 1710篇 |
2009年 | 1566篇 |
2008年 | 1696篇 |
2007年 | 1464篇 |
2006年 | 1268篇 |
2005年 | 1146篇 |
2004年 | 913篇 |
2003年 | 765篇 |
2002年 | 817篇 |
2001年 | 643篇 |
2000年 | 503篇 |
1999年 | 505篇 |
1998年 | 374篇 |
1997年 | 353篇 |
1996年 | 374篇 |
1995年 | 337篇 |
1994年 | 251篇 |
1993年 | 186篇 |
1992年 | 177篇 |
1991年 | 172篇 |
1990年 | 134篇 |
1989年 | 102篇 |
1988年 | 56篇 |
1987年 | 57篇 |
1986年 | 74篇 |
1985年 | 54篇 |
1984年 | 33篇 |
1983年 | 31篇 |
1982年 | 17篇 |
1981年 | 11篇 |
1980年 | 8篇 |
1975年 | 2篇 |
1974年 | 1篇 |
1969年 | 1篇 |
1957年 | 4篇 |
1936年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 312 毫秒
101.
102.
The solid-liquid interface motion of NaBi(WO4)2 (NBWO) melt crystal growth is observed in an in situ system, in which the whole processes of interface transition from fiat interface and cellular to dendrite are visualized. The spacing of the dendrite under smaller temperature gradient turns out to be larger than that under larger temperature gradient, which is found to be sensitive to the temperature distribution. The mechanism of dendrite growth of NBWO is studied based on the model of the growth units of anion coordination polyhedra. The { 001} face has two apex links, so it shows higher stability and has high growth rate and forms the arm of dendrite, whereas the {010} face has only one apex link, and thus shows relative slower growth rate and firstly forms the branches. 相似文献
103.
On the third largest Laplacian eigenvalue of a graph 总被引:1,自引:0,他引:1
Ji-Ming Guo 《Linear and Multilinear Algebra》2007,55(1):93-102
In this article, a sharp lower bound for the third largest Laplacian eigenvalue of a graph is given in terms of the third largest degree of the graph. 相似文献
104.
105.
On Polynomial Functions over Finite Commutative Rings 总被引:1,自引:0,他引:1
Jian Jun JIANG Guo Hua PENG Qi SUN Qi Fan ZHANG 《数学学报(英文版)》2006,22(4):1047-1050
Let R be an arbitrary finite commutative local ring. In this paper, we obtain a necessary and sufficient condition for a function over R to be a polynomial function. Before this paper, necessary and sufficient conditions for a function to be a polynomial function over some special finite commutative local rings were obtained. 相似文献
106.
Jin Hu Gang Liu Jixiu Zhang Lingchao Kong Weidong Fei 《Applied Surface Science》2006,253(5):2792-2795
The microstructure of a laser treated Al18B4O33w/2024Al composite has been investigated using transmission electron microscope (TEM), low-angle (glancing angle) X-ray diffraction (XRD) techniques. Various surface microstructures were observed in the laser treated composite. The Al18B4O33 whisker on the surface of the composite was decomposed during laser surface melting, various decomposition products were studied in the laser treated composite. Eutectic phases and the precipitation in the matrix of the composite with laser-treated were observed. The main phases detected in the molten zone were aluminum and decomposition products Al2O3. The effect of laser treatment on the hardness of the composite was also examined. A surface hardness of 400 Hv was noted. 相似文献
107.
Pingan Zeng Jiaquan Liu Yuxia Guo 《Journal of Mathematical Analysis and Applications》2004,300(1):102-128
In this paper, by using the Morse index theory for strongly indefinite functionals developed in [Nonlinear Anal. TMA, in press], we compute precisely the critical groups at the origin and at infinity, respectively. The abstract theorems are used to study the existence (multiplicity) of nontrivial periodical solutions for asymptotically wave equation and beam equation with resonance both at infinity and at zero. 相似文献
108.
109.
Shu Fen Wang Wen Guo Zou Su Wen Liu Dong Xu Duo Rong Yuan Guang Jun Zhou 《Journal of Physics and Chemistry of Solids》2004,65(7):1243-1245
The photoluminescence properties of the Bi3+ in sol-gel derived ZnTiO3 nanocrystals have been investigated. An ultra-violet emission at 360 nm and a visible emission band at 506 nm have been observed, originating from two kinds of emission centers. The former is ascribed to the 3P1-1S0 transition of Bi3+ and the latter to the recombination of the electrons with the photo-generated holes trapped in the zinc vacancies. In all cases the latter contribution is predominant. 相似文献
110.
明确从地胆草中分离得到的两对牦牛儿内酯型的立体异构体即地胆草种内酯(scabertopin)、异地胆草种内酯(isoscabertopin)、异去氧地胆草内酯(isodeoxyelephantopin)和去氧地胆草内酯(deoxyelephantopin)的C-2相对构型;方法 NOESY技术,并结合这4个化合物的1H NMR,13C NMR,HMQC谱;结果 两对立体异构体的NOESY谱有明显差异;结论 通过分析NOESY谱,找寻H-1相关信息,若发现H-1与H-8,H-9β和14-CH3有NOE相关,可以判断化合物的C-2为α构型,若H-1与H-5,H-7,H-3α及H-9α之间有NOE相关,则化合物的C-2为β构型. 相似文献