全文获取类型
收费全文 | 23893篇 |
免费 | 3830篇 |
国内免费 | 2609篇 |
专业分类
化学 | 16841篇 |
晶体学 | 296篇 |
力学 | 1425篇 |
综合类 | 239篇 |
数学 | 2659篇 |
物理学 | 8872篇 |
出版年
2024年 | 41篇 |
2023年 | 491篇 |
2022年 | 800篇 |
2021年 | 774篇 |
2020年 | 974篇 |
2019年 | 890篇 |
2018年 | 741篇 |
2017年 | 711篇 |
2016年 | 1077篇 |
2015年 | 989篇 |
2014年 | 1244篇 |
2013年 | 1625篇 |
2012年 | 2059篇 |
2011年 | 2083篇 |
2010年 | 1424篇 |
2009年 | 1370篇 |
2008年 | 1532篇 |
2007年 | 1406篇 |
2006年 | 1343篇 |
2005年 | 1085篇 |
2004年 | 870篇 |
2003年 | 720篇 |
2002年 | 623篇 |
2001年 | 519篇 |
2000年 | 513篇 |
1999年 | 592篇 |
1998年 | 487篇 |
1997年 | 430篇 |
1996年 | 439篇 |
1995年 | 387篇 |
1994年 | 358篇 |
1993年 | 325篇 |
1992年 | 269篇 |
1991年 | 229篇 |
1990年 | 237篇 |
1989年 | 159篇 |
1988年 | 119篇 |
1987年 | 84篇 |
1986年 | 97篇 |
1985年 | 65篇 |
1984年 | 37篇 |
1983年 | 39篇 |
1982年 | 37篇 |
1981年 | 21篇 |
1980年 | 8篇 |
1979年 | 4篇 |
1976年 | 1篇 |
1957年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
111.
112.
对水热处理后得到的USY沸石作进一步的酸处理以及采用改进的氟硅酸盐溶液骨架富硅工艺,分别得到了经XPS剖面分析证实为铝分布均匀的超稳Y沸石HAY-Ⅰ和HAY-Ⅱ。IR分析表明,在酸处理过程中从USY沸石中去掉的那部分非骨架铝类与3690cm~(-1)处羟基有关,仍残留在HAY-Ⅰ沸石中的那部分非骨架铝类与3670cm~(-1)和3600cm~(-1)处羟基有关。XRD和化学分析表明HAY-Ⅰ沸石仍含有约50%的非骨架铝类,而HAY-Ⅱ沸石则基本上不含非骨架铝类,HAY-Ⅱ沸石还显示更高的结晶保留度。DTA分析表明,HAY-Ⅰ和HAY-Ⅱ两种沸石的热稳定性均高于USY沸石。 相似文献
113.
114.
P. Y. Zhu 《Il Nuovo Cimento C》1991,14(3):263-283
Summary The effective-medium approximation is applied to investigate scattering from a half-space of randomly and densely distributed
discrete scatterers. Starting from vector wave equations, an approximation, called effective-medium Born approximation, a
particular way, treating Green's functions, and special coordinates, of which the origin is set at the field point, are used
to calculate the bistatic- and back-scatterings. An analytic solution of backscattering with closed form is obtained and it
shows a depolarization effect. The theoretical results are in good agreement with the experimental measurements in the cases
of snow, multi- and first-year sea-ice. The root product ratio of polarization to depolarization in backscattering is equal
to 8; this result constitutes a law about polarized scattering phenomena in the nature. 相似文献
115.
稳态锁模产生4ps激光脉冲 总被引:1,自引:0,他引:1
首次利用GaAs光电导开关,控制Nd:YLF激光器腔内Q值,实现稳态锁模,获得脉宽和能量稳定性极高的4ps激光脉冲。 相似文献
116.
117.
Q.J. Zhu 《Journal of Mathematical Analysis and Applications》2007,326(1):708-720
Investment systems are studied using a framework that emphasize their profiles (the cumulative probability distribution on all the possible percentage gains of trades) and their log return functions (the expected average return per trade in logarithmic scale as a function of the investment size in terms of the percentage of the available capital). The efficiency index for an investment system, defined as the maximum of the log return function, is proposed as a measure to compare investment systems for their intrinsic merit. This efficiency index can be viewed as a generalization of Shannon's information rate for a communication channel. Applications are illustrated. 相似文献
118.
Wei Mingjun Zhu Wanzhen 《Annals of Differential Equations》2007,23(4):511-518
In this paper we consider the system of classical particles coupled with a Klein-Gordon field in two dimensions.We establish a-priori-bounds on the solutions of this system with initial data satisfying a size restriction derived from conservation of energy.This result,together with the smoothing of"velocity averaging",yields the existence of global weak solutions to the corresponding restricted initial value problem.The size restriction is necessary since energy of the system is indefinite.Finally,we show that the weak solutions preserve the total mass. 相似文献
119.
Huayang Zhu Robert J. Kee Jeffrey R. Engel David T. Wickham 《Proceedings of the Combustion Institute》2007,31(2):1965-1972
This paper reports the results of experimental and modeling efforts to characterize partial oxidation of methane to produce synthesis gas (H2 and CO) using metal-substituted hexaaluminate catalysts in short-contact-time reactors. Hexaaluminate catalysts offer excellent high-temperature stability compared to the equivalent metal-based catalysts. The hexaaluminates are synthesized by a metal-exchange process using alumoxane precursors that enable a wide range of metal substitutions. Of all the combinations tested, RhSr-substituted hexaaluminates yielded the best performance. The catalysts are supported on alumina porous-foam structures, which are positioned within a tube furnace to control the operating temperature. Two-stage combinations of RhSr- and Ni-substituted hexaaluminates are shown to improve conversion activity and selectivity compared to a single-catalyst system. 相似文献
120.
By using the theory of coincidence degree, we study a kind of periodic solutions to p-Laplacian neutral functional differential equation with multiple deviating arguments, a new result on the existence of periodic solutions is obtained. 相似文献