全文获取类型
收费全文 | 160359篇 |
免费 | 12581篇 |
国内免费 | 16649篇 |
专业分类
化学 | 108854篇 |
晶体学 | 1893篇 |
力学 | 5164篇 |
综合类 | 1741篇 |
数学 | 25495篇 |
物理学 | 46442篇 |
出版年
2024年 | 159篇 |
2023年 | 1183篇 |
2022年 | 2377篇 |
2021年 | 4146篇 |
2020年 | 4103篇 |
2019年 | 4057篇 |
2018年 | 3501篇 |
2017年 | 4582篇 |
2016年 | 5497篇 |
2015年 | 4839篇 |
2014年 | 6444篇 |
2013年 | 12074篇 |
2012年 | 9656篇 |
2011年 | 9121篇 |
2010年 | 7859篇 |
2009年 | 10192篇 |
2008年 | 10348篇 |
2007年 | 10965篇 |
2006年 | 9496篇 |
2005年 | 7719篇 |
2004年 | 7150篇 |
2003年 | 6157篇 |
2002年 | 8176篇 |
2001年 | 4809篇 |
2000年 | 4289篇 |
1999年 | 3872篇 |
1998年 | 3436篇 |
1997年 | 2706篇 |
1996年 | 2441篇 |
1995年 | 2222篇 |
1994年 | 1979篇 |
1993年 | 1782篇 |
1992年 | 1706篇 |
1991年 | 1152篇 |
1990年 | 950篇 |
1989年 | 832篇 |
1988年 | 799篇 |
1987年 | 594篇 |
1986年 | 541篇 |
1985年 | 597篇 |
1984年 | 515篇 |
1983年 | 300篇 |
1982年 | 533篇 |
1981年 | 675篇 |
1980年 | 584篇 |
1979年 | 626篇 |
1978年 | 509篇 |
1977年 | 384篇 |
1976年 | 330篇 |
1973年 | 214篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
931.
The mechanism of X-ray waveguide-resonance propagation or the radiation superstream model, which can become the ground of X-ray nanophotonics, is discussed briefly. Some attention is devoted to features consideration of the simplest devices characterized by the waveguide-resonance transportation of X-ray beams. The experimental data showing the user possibilities of a simplest waveguide-resonators application for diffractometry are presented. We discuss the main reasons to improve the metrological characteristics for total reflection X-ray fluorescence (TXRF) analytical method in case when the target exciting beam is formed by a waveguide-resonator. Some problems appearing during the waveguide-resonator application are formulated. 相似文献
932.
采用溶胶-凝胶工艺与原位生长技术,制备了ZnSe/SiO2复合薄膜.X射线衍射分 析表明薄膜中ZnSe晶体呈立方闪锌矿结构.X射线荧光分析结果显示薄膜中Zn与Se摩尔比为1 ∶1.01—1∶1.19.利用场发射扫描电子显微镜观察了复合薄膜的表面形貌,结果表明复合薄 膜表面既存在尺寸约为400nm的ZnSe晶粒,也存在尺寸小于100nm的ZnSe晶粒.利用椭偏仪测 量了薄膜椭偏角Ψ,Δ与波长λ的关系,采用Maxwell-Garnett有效介质理论对薄膜的光学 常数、厚度、气孔率、ZnS
关键词:
2复合薄膜')" href="#">ZnSe/SiO2复合薄膜
光学性质
椭偏光度法
荧光光谱 相似文献
933.
Majid Vaezzadeh Ehsan Noruzifar Ghanati Faezeh Mohsen Salehkotahi Reza Mehdian 《Journal of magnetism and magnetic materials》2006
Experimental results of applying a steady magnetic field (20 and 30 mT) on agricultural plants reveal that their growth is more than that of control plants. Considering that these plants have ferritin cells, and each ferritin cell has 4500 Fe atoms, it is obvious that they have an outstanding role in the plants’ growth. As the last spin magnetic moment (SMM) of the Fe atom posed to an external magnetic field (EMF), the composition of SMM and EMF create an oscillator in the system. Then we have a moment of force on ferritin cells. This oscillator exerts its energy, then damps and finally locates in the field direction. The relaxed energy increased the internal temperature (i.e., the effective temperature of the magnetic spin system of plant) so that it is situated in a proper temperature for growing. This phenomenon (temperature increasing) occurs in the initial minutes of applying the magnetic field. So it depends on the number of times of locating the plant in magnetic field in a day (n). If this number (n) passes the critical value, the plant reaches a burning temperature and growth is perturbed. In this paper, the plant growth rate and critical temperature in a steady magnetic field were investigated and formulated theoretically. An innovative result in this research is as follows: if a plant's environment was in the dormant temperature, we could increase the internal temperature of the plant by applying a magnetic field n times in a day (for growth). 相似文献
934.
Maryam Mirza-Aghayan Rabah Boukherroub Mahshid Rahimifard 《Journal of organometallic chemistry》2007,692(23):5113-5116
The palladium(II) chloride/triethylsilane system has been successfully applied for the selective hydrogenation of the carbon-carbon double bond of α,β-unsaturated ketones to yield the corresponding saturated carbonyl compounds. The reaction takes place under mild conditions and affords high yields. 相似文献
935.
936.
We prove both geometric ergodicity and regular variation of the stationary distribution for a class of nonlinear stochastic recursions that includes nonlinear AR-ARCH models of order 1. The Lyapounov exponent for the model, the index of regular variation and the spectral measure for the regular variation all are characterized by a simple two-state Markov chain. 相似文献
937.
We introduce some relative versions of star selection principles first considered in [5], [11]. Some of the work extends results
from [4], [5] and gives some examples.
相似文献
938.
本篇文章首先定义了向量变分不等式的严格可行点概念,其次在假设了映射是强(D)-伪单调的情况下,证明了向量变分不等式解集非空有界与其严格可行点存在的等价性问题,推广了在数量变分不等式上得到的相应结果. 相似文献
939.
Jing-na Li Xiao-feng Wang Zheng-an Yao 《应用数学学报(英文版)》2007,23(3):421-432
In this paper, we propose a model in studying soft ferromagnetic films, which is readily accessible experimentally. By using penalty approximation and compensated compactness, we prove that the dynamical equation in thin film has a local weak solution. Moreover, the corresponding linear equation is also dealt with in great detail. 相似文献
940.
In this paper, the effect of cubic zinc metaborate Zn4O(BO2)6 on the sintering of MnZn-ferrites for medium frequency power applications is investigated. Zinc metaborate is synthesized in the laboratory using zinc oxide and boric acid as metal precursors. As observed, when zinc metaborate is added to the MnZn-ferrites at an optimum amount of 0.02 wt%, it significantly enhances densification and therefore allows, for a given density, reduction of the firing temperature by almost 200 °C. MnZn-ferrites exhibiting power losses of 70 mW/cm3 (measured at a frequency of 400 kHz, magnetic field 50 mT and temperature of 90 °C) are synthesized from conventionally milled powders with average particle diameter 0.6 μm, compacted and fired at 1100 °C. Identical experiments conducted under the same conditions on specimens without zinc metaborate additions revealed power losses greater than 300 mW/cm3, because of insufficient densification. 相似文献