全文获取类型
收费全文 | 20960篇 |
免费 | 5360篇 |
国内免费 | 2000篇 |
专业分类
化学 | 10213篇 |
晶体学 | 357篇 |
力学 | 2268篇 |
综合类 | 235篇 |
数学 | 928篇 |
物理学 | 14319篇 |
出版年
2024年 | 50篇 |
2023年 | 173篇 |
2022年 | 544篇 |
2021年 | 563篇 |
2020年 | 786篇 |
2019年 | 730篇 |
2018年 | 745篇 |
2017年 | 880篇 |
2016年 | 1053篇 |
2015年 | 958篇 |
2014年 | 1368篇 |
2013年 | 1875篇 |
2012年 | 1457篇 |
2011年 | 1583篇 |
2010年 | 1349篇 |
2009年 | 1355篇 |
2008年 | 1282篇 |
2007年 | 1337篇 |
2006年 | 1302篇 |
2005年 | 1141篇 |
2004年 | 1059篇 |
2003年 | 875篇 |
2002年 | 818篇 |
2001年 | 799篇 |
2000年 | 716篇 |
1999年 | 529篇 |
1998年 | 490篇 |
1997年 | 430篇 |
1996年 | 366篇 |
1995年 | 303篇 |
1994年 | 257篇 |
1993年 | 205篇 |
1992年 | 183篇 |
1991年 | 128篇 |
1990年 | 102篇 |
1989年 | 94篇 |
1988年 | 98篇 |
1987年 | 59篇 |
1986年 | 54篇 |
1985年 | 30篇 |
1984年 | 35篇 |
1983年 | 15篇 |
1982年 | 26篇 |
1981年 | 27篇 |
1980年 | 16篇 |
1979年 | 21篇 |
1978年 | 8篇 |
1977年 | 12篇 |
1976年 | 8篇 |
1974年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
82.
83.
Recent X-ray diffraction studies on α-quartz (SiO2) by Kingmaet al [1], have shown the occurrence of a reversible, crystalline-to-crystalline, phase transition just prior to amorphization
at ≈ 21 GPa. This precursor transition has also been confirmed by our recent molecular dynamics simulation study [2]. In order
to investigate the possibility of a similar behaviour in other isostructural compounds, which also undergo pressure induced
amorphization, α-GeO2 and α-AlPO4 (berlinite form) were studied using energy dispersive X-ray diffraction. In either of these materials, no such phase transition
is detected prior to amorphization. The onset of amorphization and its reversal is found to be time dependent in GeO2. 相似文献
84.
In this paper, we discuss the detailed optical design of a beam line that is under construction on the synchrotron radiation source, Indus-1. Toroidal mirrors are used as pre-and post- focusing elements and a toroidal grating monochromator as a dispersing element. Using three interchangeable gratings, this monochromator will give, at a moderate resolution, a good throughput on the sample in the wavelength range 40 to 1000 Å. Effect of various parameters and their optimization on the resolution and throughput characteristics have been studied by ray tracing calculations, and presented. 相似文献
85.
The fabrication of a periodic domain inversion in LiTaO3 and LiNbO3 using direct ion-beam writing is presented. The polarization of these materials can be reversed at room temperature by irradiating Si2+ ions into +c faces. A first-order periodic domain inversion with a 50% duty cycle, a depth of 300μ, and an interaction length of 1 mm was realized in LiTaO3. Using this structure, 300μW of blue light was generated for a conversion efficiency of 0.25%/W. 相似文献
86.
Thermal expansion measurements have been carried out on Fe substituted superconducting compounds Y1Ba2(Cu1−x
Fe
x
)3O
y
(0<x<4%) using a high resolution dilatometer employing the three terminal capacitance technique. The experimental set up is sensitive
enough to detect changes in α of less than 10−8K−1. Results show that the jump Δα in the coefficient of linear thermal expansion at the superconducting transition temperature,T
c, increases almost linearly with Fe concentration. The normal state thermal expansion coefficient α first decreases, attains
a minimum value aroundx=1% and then increases for higher Fe concentrations. The oxygen content per unit formula is almost constant up tox=1% and then increases rapidly withx. It has also been observed that the anomalous behaviour of α around 260 K observed by Meingastet al [22] for Fe concentrationx=5% is due to inadequate annealing of the sample. 相似文献
87.
Mieko Tanaka-Yamawaki 《Annals of the Institute of Statistical Mathematics》2003,55(2):437-446
Contrary to the common sense in economics and financial engineering, price fluctuations at very fine level of motion exhibit
various evidences against the efficient market hypothesis. We attempt to investigate this issue by studying extensive amount
of foreign currency exchange data for over five years at the finest level of resolution. We specifically focus on the proposed
stability in binomial conditional probabilities originally found in much smaller examples of financial time series. In order
to handle very large data, we have written an efficient program in C that automatically generates those conditional probabilities.
It is found that the stability is maintained for extremely large time duration that covers almost the entire period. Based
on the length of conditions for which the conditional probabilities are distinguishable each other, we identify the length
of memory being less than 3 movements. 相似文献
88.
A monotone dependence of the critical buckling load of a simplysupported TimoshenkoMindlin beam both on the shear correctionfactor and on the stiffness of foundation is proved. Then theworst-scenario method is employed to find the most dangerousinput data. 相似文献
89.
Qing-xuYan Hui-chaoZou De-xingFeng 《应用数学学报(英文版)》2003,19(2):239-246
In this paper, the stabilization problem of nonuniform Timoshenko beam by some nonlinear boundary feedback controls is considered. By virtue of nonlinear semigroup theory, energy-perturbed approach and exponential multiplier method, it is shown that the vibration of the beam under the proposed control actiondecays exponentially or in negative power of time t as t→∞. 相似文献
90.
在本文中提出一个新方法——阶梯折算法来研究在任意载荷下任意非均匀和任意变厚度伯努利-欧拉梁的动力响应问题.研究了自由振动和强迫振动.新方法需要将区间离散为一定数目的元素,每个元素可看作是均匀和等厚度的.因此均匀、等厚度梁的一般解可在每个元素上应用.然后用初参数表示的整个梁的一般解使之满足相邻二元素间的物理和几何连续条件,这样就可以得到解析形式的自由振动的频率方程和解析形式的强迫振动的最终解,它化为求解二元线性代数方程,与离散元素的数目无关.现在的方法可推广应用至任意非均匀及任意变厚度有粘滞性和其他种类的梁以及其他结构元件问题上去. 相似文献