全文获取类型
收费全文 | 21066篇 |
免费 | 3804篇 |
国内免费 | 3353篇 |
专业分类
化学 | 16168篇 |
晶体学 | 489篇 |
力学 | 1112篇 |
综合类 | 297篇 |
数学 | 2222篇 |
物理学 | 7935篇 |
出版年
2024年 | 33篇 |
2023年 | 305篇 |
2022年 | 473篇 |
2021年 | 608篇 |
2020年 | 735篇 |
2019年 | 858篇 |
2018年 | 652篇 |
2017年 | 680篇 |
2016年 | 929篇 |
2015年 | 1016篇 |
2014年 | 1144篇 |
2013年 | 1548篇 |
2012年 | 1978篇 |
2011年 | 1951篇 |
2010年 | 1566篇 |
2009年 | 1524篇 |
2008年 | 1717篇 |
2007年 | 1451篇 |
2006年 | 1468篇 |
2005年 | 1317篇 |
2004年 | 1065篇 |
2003年 | 832篇 |
2002年 | 884篇 |
2001年 | 682篇 |
2000年 | 563篇 |
1999年 | 434篇 |
1998年 | 271篇 |
1997年 | 205篇 |
1996年 | 183篇 |
1995年 | 167篇 |
1994年 | 179篇 |
1993年 | 141篇 |
1992年 | 86篇 |
1991年 | 105篇 |
1990年 | 69篇 |
1989年 | 54篇 |
1988年 | 50篇 |
1987年 | 29篇 |
1986年 | 39篇 |
1985年 | 45篇 |
1984年 | 20篇 |
1983年 | 18篇 |
1982年 | 15篇 |
1981年 | 21篇 |
1980年 | 17篇 |
1979年 | 17篇 |
1978年 | 14篇 |
1977年 | 12篇 |
1975年 | 8篇 |
1974年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
161.
Spirals generated from the excitable media within the Barkley model is investigated under the gradient electric fields by a numerical simulation. The spiral drift and spiral break up are observed when the amplitude of the electric fields is modulated by a constant signal or a chaotic signal. It is also verified that, even in the presence of the white noise, the whole system can reach homogeneous states after the spiral breakup, by using an adaptive strategy. 相似文献
162.
Zhigang Yin Nuofu Chen Shulin Song Jun Zhong Kurash Ibrahim 《Solid State Communications》2005,135(7):430-433
Nickel-doped ZnO (Zn1−xNixO) have been produced using rf magnetron sputtering. X-ray diffraction measurements revealed that nickel atoms were successfully incorporated into ZnO host matrix without forming any detectable secondary phase. Ni 2p core-level photoemission spectroscopy confirmed this result and suggested Ni has a chemical valence of 2+. According to the magnetization measurements, no ferromagnetic but paramagnetic behavior was found for Zn0.86Ni0.14O. We studied the electronic structure of Zn0.86Ni0.14O by valence-band photoemission spectroscopy. The spectra demonstrate a structure at ∼2 eV below the Fermi energy EF, which is of Ni 3d origin. No emission was found at EF, suggesting the insulating nature of the film. 相似文献
163.
164.
165.
166.
利用2~8 MeV的Naq+、Clq+(q=2,3,4,5)轰击氦原子,对碰撞的直接多重电离过程进行研究.实验采用反冲离子-散射离子飞行时间符合技术,通过反冲离子飞行时间谱区分不同价态反冲离子;利用静电偏转和位置灵敏探测技术区分不同电荷态散射离子;结合CAMAC-PC多参数获取系统得到一定价态散射离子所对应的反冲离子电荷态分布谱;经分析该谱得到直接多重电离截面与直接单电离截面之比R21.讨论了R21随入射离子速度和电荷态的变化关系. 相似文献
167.
年龄相关的种群扩散系统的最优分布控制 总被引:5,自引:1,他引:4
本文讨论年龄相关的种群扩散系统的最优分布控制 ,证明了最优分布控制的存在性 ,得到了分布控制为最优的充分必要条件及确定最优控制的最优性组 . 相似文献
168.
Applying the approximate Fokker-Planck equation we derived, we obtain the analytic expression of thestationary laser intensity distribution Pst(Ⅰ) by studying the single-mode laser cubic model subject to colored cross-correlation additive and multiplicative noise, each of which is colored. Based on it, we discuss the effects on the stationarylaser intensity distribution Pst(Ⅰ) by cross-correlation between noises and “color“ of noises (non-Markovian effect) whenthe laser system is above the threshold. In detail, we analyze two cases: One is that the three correlation-times (i.e.the self-correlation and cross-correlation times of the additive and multiplicative noise) are chosen to be the same value(τ1 = τ2 = τ3 = τ). For this case, the effect of noise cross-correlation is investigated emphatically, and we detect thatonly when λ≠ 0 can the noise-induced transition occur in the Pst(Ⅰ) curve, and only when τ≠ 0 and λ≠ 0, can the“reentrant noise-induced transition“ occur. The other case is that the three correlation times are not the same value,τ1 ≠τ2 ≠τ3. For this case, we find that the noise-induced transition occurring in the Pst (Ⅰ) curve is entirely differentwhen the values of τ1, τ2, and τ3 are changed respectively. In particular, when τ2 (self-correlation time of additivenoise) is changing, the ratio of the two maximums of the Pst(Ⅰ) curve R exhibits an interesting phenomenon, “reentrantnoise-induced transition“, which demonstrates the effect of noise “color“ (non-Markovian effect). 相似文献
169.
O-Glycosylations using thiomethyl glycosides as donors were compared under both frozen and unfrozen conditions. In the presence of MeOTf as a promoter, enormous rate acceleration was observed when the glycosylation was conducted in p-xylene below its freezing point. 相似文献
170.