全文获取类型
收费全文 | 55256篇 |
免费 | 4588篇 |
国内免费 | 5703篇 |
专业分类
化学 | 36020篇 |
晶体学 | 770篇 |
力学 | 3166篇 |
综合类 | 314篇 |
数学 | 14206篇 |
物理学 | 11071篇 |
出版年
2023年 | 726篇 |
2022年 | 817篇 |
2021年 | 1273篇 |
2020年 | 1651篇 |
2019年 | 1700篇 |
2018年 | 1501篇 |
2017年 | 1683篇 |
2016年 | 1872篇 |
2015年 | 1785篇 |
2014年 | 2359篇 |
2013年 | 3842篇 |
2012年 | 2757篇 |
2011年 | 3647篇 |
2010年 | 2860篇 |
2009年 | 3602篇 |
2008年 | 3654篇 |
2007年 | 3525篇 |
2006年 | 3024篇 |
2005年 | 2674篇 |
2004年 | 2615篇 |
2003年 | 2130篇 |
2002年 | 2614篇 |
2001年 | 1564篇 |
2000年 | 1344篇 |
1999年 | 1229篇 |
1998年 | 997篇 |
1997年 | 874篇 |
1996年 | 914篇 |
1995年 | 884篇 |
1994年 | 821篇 |
1993年 | 596篇 |
1992年 | 559篇 |
1991年 | 393篇 |
1990年 | 313篇 |
1989年 | 322篇 |
1988年 | 275篇 |
1987年 | 246篇 |
1986年 | 202篇 |
1985年 | 211篇 |
1984年 | 193篇 |
1983年 | 90篇 |
1982年 | 175篇 |
1981年 | 199篇 |
1980年 | 162篇 |
1979年 | 154篇 |
1978年 | 126篇 |
1977年 | 115篇 |
1976年 | 96篇 |
1974年 | 30篇 |
1973年 | 38篇 |
排序方式: 共有10000条查询结果,搜索用时 281 毫秒
71.
Volker Elling. 《Mathematics of Computation》2006,75(256):1721-1733
A particular case of initial data for the two-dimensional Euler equations is studied numerically. The results show that the Godunov method does not always converge to the physical solution, at least not on feasible grids. Moreover, they suggest that entropy solutions (in the weak entropy inequality sense) are not well posed.
72.
通过固相反应法制备了Er3+/Yb3+共掺杂ZrO2-Al2O3粉末的样品,并对样品在980nm激光激发下的上转换发光特性进行了研究.从发射光谱可以发现,在可见光范围内有3个强的发光带,一个位于654nm附近的红光带和两个分别位于545nm、525nm附近的绿光带,分别对应于Er3+离子的以下辐射跃迁:4F9/2→4I15/2、4S3/2→4I15/2、2H11/2→4I15/2.其中又以Er3+离子的4F9/2→4I15/2跃迁产生的红色荧光辐射最强.对其上转换发光机制进行了分析,发现这三个发光过程都是双光子过程.对样品粉末进行了XRD检测,发现ZrO2主要以立方相为主,并且计算得到了这种立方结构的晶格常数.Al2O3固溶于ZrO2中,Al3+嵌入ZrO2后产生氧空位,导致ZrO2晶体的对称性降低,这种结构变化更有利于提高上转换效率,即上转换发光强度增强. 相似文献
73.
74.
M. Brokate D. Rachinskii 《NoDEA : Nonlinear Differential Equations and Applications》2006,13(4):385-411
The paper is concerned with the study of plasticity models described by differential equations with stop and play operators.
We suggest sufficient conditions for the global stability of a unique periodic solution for the scalar models and for the
vector models with biaxial inputs of a particular form, namely the sum of a uniaxial function and a constant term. For another
class of simple biaxial inputs, we present an example of the existence of unstable periodic solutions.
The paper was written during the research stay of D. Rachinskii at the Technical University Munich supported by the research
fellowship from the Alexander von Humboldt Foundation. His work was partially supported by the Russian Science Support Foundation, Russian Foundation for Basic Research (Grant No. 01-01-00146, 03-01-00258), and the Grants of the President of Russia (Grant No. MD-87.2003.01, NS-1532.2003.1). The support is gratefully acknowledged. 相似文献
75.
In this paper we give a realization of some symmetric space G/K as a closed submanifold P of G. We also give several equivalent representations of the submanifold P. Some properties of the set gK∩P are also discussed, where gK is a coset space in G. 相似文献
76.
J. Carlos Díaz-Ramos Ramón Vázquez-Lorenzo 《Differential Geometry and its Applications》2006,24(4):433-442
Explicit examples of Osserman 4-manifolds with exactly two distinct eigenvalues of the Jacobi operators, α and β=4α≠0, are given. The former has multiplicity two and is a double root of the minimal polynomial of the Jacobi operators. 相似文献
77.
The structural properties of polycrystalline silicon films, prepared by plasma enhanced chemical vapor deposition system, with different flow rates of SiH4/SiF4 mixtures at 300 °C were investigated. This study indicates that the low hydrogen coverage on the growing surface, under optimum fluorine radicals, will be leaded to an improvement of crystallized area as compared with case of high hydrogen coverage surface. Moreover, the studies of the role of SiH4 and SiF4 radicals show that the SiH4 radicals are important in the nucleation and growth of grains. However, SiF4 radicals are effective in the structural change of grain boundaries regions and by this way, in the present system, establish the growth of grains under the dominant 〈1 1 0〉 direction. The stress investigation indicates that addition of high flow rate of SiF4 in amorphous film, results in the nearly stress free films. Finally, we found that the changes in g-value reflect the changes in the intrinsic compressive and tensile stress in the both polycrystalline and amorphous silicon films. 相似文献
78.
以金属钇和异丙醇为原料,以HgCl2/I2为复合催化剂,通过对金属钇的机械加工以增加其比表面,并将异丙醇脱水使其含水量降低至0.05%,体系在82℃回流5h,经过滤、减压蒸馏,得到了白色海绵状异丙醇钇,其产率高达83%,合成时间比文献报道的缩短了19h,产率提高了8%。文章确定了催化剂的最佳用量为20gY加入60mg HgCl2/I2,研究了合成产率与HgCl2/I2催化剂和HgCl2催化剂的依赖关系及异丙醇中含水量对合成产率的影响,并对HgCl2/I2的催化作用机理进行了初步探讨。 相似文献
79.
P Vincent A BrioudeC Journet S RabasteS.T Purcell J Le BrusqJ.C Plenet 《Journal of Non》2002,311(2):130-137
We report here the successful inclusion of carbon nanotubes (CNs) into a TiO2 matrix prepared by a sol-gel method. The presence of CNs in the sol-gel matrix and the structure of the film were analyzed principally by transmission electron microscopy. Complementary information about the behavior of embedded carbon nanotubes versus heat treatment and ion irradiation were obtained by X-ray photoelectron spectroscopy. The elaboration of an inorganic matrix containing embedded carbon nanotubes leads to a new nanocomposite. The possible applications of this nanocomposite are discussed. 相似文献
80.
Balázs Szendröi 《Mathematische Zeitschrift》2002,240(2):233-241
This note shows that a certain toric quotient of the quintic Calabi-Yau threefold in provides a counterexample to a recent conjecture of Cox and Katz concerning nef cones of toric hypersurfaces.
Received: 8 February 2001; in final form: 17 September 2001 / Published online: 1 February 2002 相似文献