全文获取类型
收费全文 | 22848篇 |
免费 | 4573篇 |
国内免费 | 7921篇 |
专业分类
化学 | 17350篇 |
晶体学 | 1058篇 |
力学 | 1550篇 |
综合类 | 943篇 |
数学 | 3910篇 |
物理学 | 10531篇 |
出版年
2024年 | 44篇 |
2023年 | 243篇 |
2022年 | 736篇 |
2021年 | 772篇 |
2020年 | 796篇 |
2019年 | 785篇 |
2018年 | 718篇 |
2017年 | 994篇 |
2016年 | 813篇 |
2015年 | 1181篇 |
2014年 | 1339篇 |
2013年 | 1922篇 |
2012年 | 1868篇 |
2011年 | 1982篇 |
2010年 | 1886篇 |
2009年 | 2018篇 |
2008年 | 2378篇 |
2007年 | 2044篇 |
2006年 | 1982篇 |
2005年 | 1635篇 |
2004年 | 1337篇 |
2003年 | 982篇 |
2002年 | 933篇 |
2001年 | 964篇 |
2000年 | 1029篇 |
1999年 | 651篇 |
1998年 | 353篇 |
1997年 | 289篇 |
1996年 | 304篇 |
1995年 | 263篇 |
1994年 | 253篇 |
1993年 | 243篇 |
1992年 | 192篇 |
1991年 | 152篇 |
1990年 | 161篇 |
1989年 | 165篇 |
1988年 | 143篇 |
1987年 | 116篇 |
1986年 | 88篇 |
1985年 | 66篇 |
1984年 | 90篇 |
1983年 | 84篇 |
1982年 | 72篇 |
1981年 | 56篇 |
1980年 | 51篇 |
1979年 | 38篇 |
1978年 | 31篇 |
1977年 | 18篇 |
1976年 | 17篇 |
1975年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 203 毫秒
101.
The photoionization of H atoms irradiated by few-cycle laser pulses is studied numerically. The variations of the total ionization, the partial ionizations in opposite directions, and the corresponding asymmetry with the carrier-envelope phase in several pulse durations are obtained. We find that besides a stronger modulation on the partial ionizations, the change of pulse duration leads to a shift along carrier-envelope (CE) phase in the calculated signals. The phase shift arises from the nonlinear property of ionization and relates closely to the Coulomb attraction of the parent ion to the ionized electron. Our calculations show good agreement with the experimental observation under similar conditions. 相似文献
102.
The nonradiative recombination effect on carrier dynamics in GalnNAs/GaAs quantum wells is studied by timeresolved photoluminescence (TRPL) and polarization-dependent TRPL at various excitation intensities. It is found that both recombination dynamics and spin relaxation dynamics strongly depend on the excitation intensity. Under moderate excitation intensities the PL decay curves exhibit unusual non-exponential behaviour. This result is well simulated by a rate equation involving both the radiative and non-radiative recombinations via the introduction of a new parameter of the effective concentration of nonradiative recombination centres in the rate equation. In the spin dynamics study, the spin relaxation also shows strong excitation power dependence. Under the high excitation power an increase of spin polarization degree with time is observed. This new finding provides a useful hint that the spin process can be controlled by excitation power in GaInNAs systems. 相似文献
103.
江汉平原上空QTEC变化特征的统计分析 总被引:1,自引:0,他引:1
提出了一种观测台网用多接收机性能一致性的标定方法,并利用江汉平原GPS接收台网的观测数据,分析了该地区上空QTEC的日变化、季节变化、年变化和逐年变化的统计特征.标定结果表明,不同接收机之间的仪器偏差是从双频GPS卫星信标推算QTEC的主要误差来源之一,必须校正.统计分析证实,江汉平原上空QTEC的日变化特征同时受电离层和等离子层控制,其年变化以半年周期为主,峰值和谷值分别出现在两分点和两至点附近,QTEC值的逐年变化从太阳活动峰年到低年逐年下降,与以太阳黑子数为代表的太阳活动密切相关. 相似文献
104.
对具有消息恢复的数字签名方案提出了两种攻击方法.此外,对原方案进行了改进,通过对改进方案的安全性分析得出结论:改进方案比原方案更安全,并且消息恢复过程只需要计算一次大数模幂乘和两次单向函数. 相似文献
105.
Banach空间二阶周期边值问题解的存在性 总被引:2,自引:0,他引:2
利用一些比较结果,讨论了Banach空间中二阶周期边值问题解的存在性,获得了若干解的存在性与唯一性结果。 相似文献
106.
Let G be a finite group. A complete Sylow product of G is a product of Sylow subgroups of G, one for each prime divisor of |G|. We shall call G a Sylow factorizable group if it is equal to at least one of its complete Sylow products. We prove that if G is a Sylow factorizable group then the
intersection of all complete Sylow products of G is equal to the solvable radical of G. We generalize the concepts and the result to Sylow products which involve an arbitrary subset of the prime divisors of |G|.
Received: 26 January 2005 相似文献
107.
Dan Popovici 《Comptes Rendus Mathematique》2004,338(1):59-64
Let (X,ω) be a compact complex Hermitian manifold, and let T?γ be a d-closed (1,1) almost positive current on X. A variant of Demailly's regularization-of-currents theorem states that T is the weak limit of a sequence of (1,1)-currents Tm with analytic singularities of coefficient 1/m, lying in the same cohomology class as T, whose Lelong numbers converge to those of T, and with a loss of positivity decaying to zero. We prove that if the (1,1)-form γ is assumed to be closed and C∞, the regularizing currents Tm can be chosen such that for a constant C>0 independent of m. To cite this article: D. Popovici, C. R. Acad. Sci. Paris, Ser. I 338 (2004). 相似文献
108.
In this paper, we have developed an analytical model to study the temperature distributions in IR optical materials heated by laser pulses. Our model takes into account the two-photon absorption (TPA). The calculations are based on a three-dimensional model of heat diffusion in solids using the integral transform method. We find out the rigorous analytical expression of the thermal field when one considers both one- and two-photon absorption. The model is valid for any laser–solid system whose interaction can be described by the generalized Beer–Lambert law. Specific results are presented for an application of the model to ZnSe sample. We find out that TPA can produce detectable temperature variation. 相似文献
109.
将稀土配合物Eu(asprin)_3phen掺杂到导电聚合物PVK中,制成结构分别为ITO/PVK:RE配合物/LiF/AI(1),ITO/PVK:RE配合物/PBD/LiF/AI(2)的电致发光(EL)器件。发现二者的电致发光谱存在着较大的差别:在器件(1)中,来自Eu~(3 )的位于594nm(~5D_0→~7F_1)和614nm(~5D_0→~7F_2)处的发光强度大致相当,而在器件(2)中,EL主要来自Eu~(3 )位于614nm的发光,594nm处的发光很弱,与薄膜状态下的光致发光谱(PL)一致。并针对此现象进行了初步讨论。 相似文献
110.