全文获取类型
收费全文 | 988篇 |
免费 | 215篇 |
国内免费 | 96篇 |
专业分类
化学 | 286篇 |
晶体学 | 18篇 |
力学 | 77篇 |
综合类 | 17篇 |
数学 | 156篇 |
物理学 | 745篇 |
出版年
2024年 | 1篇 |
2023年 | 15篇 |
2022年 | 26篇 |
2021年 | 22篇 |
2020年 | 22篇 |
2019年 | 28篇 |
2018年 | 18篇 |
2017年 | 30篇 |
2016年 | 38篇 |
2015年 | 31篇 |
2014年 | 62篇 |
2013年 | 82篇 |
2012年 | 62篇 |
2011年 | 76篇 |
2010年 | 62篇 |
2009年 | 94篇 |
2008年 | 74篇 |
2007年 | 61篇 |
2006年 | 77篇 |
2005年 | 57篇 |
2004年 | 43篇 |
2003年 | 39篇 |
2002年 | 34篇 |
2001年 | 30篇 |
2000年 | 29篇 |
1999年 | 26篇 |
1998年 | 20篇 |
1997年 | 20篇 |
1996年 | 19篇 |
1995年 | 17篇 |
1994年 | 13篇 |
1993年 | 15篇 |
1992年 | 8篇 |
1991年 | 9篇 |
1990年 | 8篇 |
1989年 | 1篇 |
1988年 | 9篇 |
1987年 | 5篇 |
1986年 | 1篇 |
1985年 | 3篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 3篇 |
1974年 | 1篇 |
1970年 | 1篇 |
排序方式: 共有1299条查询结果,搜索用时 15 毫秒
51.
This paper presents the analytical and simulation responses of the closed orbit distortion in the SSRF storage ring to random and plane wave like magnet vibrations respectively. It is shown that the use of girder is very beneficial in the view of suppressing this response function. Effect of the independently supported gradient bending magnets to the closed orbit response is given. An analytic formula is written to give a rough estimate of the closed orbit distortion due to ground motion, taking into account the closed orbit response function and girder transfer function. As an example, the result of SSRF case is given. 相似文献
52.
The Fourier transform gas-phase infrared spectrum of pyrrole, C4H5N, has been recorded with a resolution of ca. 0.003 cm−1 in the 900-1500 cm−1 spectral region. Four fundamental bands, ν8(A1; 1016.9 cm−1), ν23(B2; 1049.1 cm−1), ν7(A1; 1074.6 cm−1), ν20(B2; 1424.4 cm−1) and the overtone band 2ν16(A1; 962.7 cm−1) have been analysed using the Watson model. The ν8 and 2ν16 bands are unperturbed; the ν7 and ν23 bands are locally perturbed, while the ν20 band is globally perturbed by weak c-Coriolis resonance. Upper state vibrational term values, and rotational and centrifugal distortion constants, have been obtained from fits using S-reduction and Ir-representation as well as A-reduction and IIIr-representation. A set of ground state rotational and centrifugal distortion constants using A-reduction was obtained from a simultaneous fit of ground state combination differences from all five bands and previous microwave and millimetre-wave data. 相似文献
53.
Songting YIN 《Frontiers of Mathematics in China》2018,13(2):435-448
We obtain the Laplacian comparison theorem and the Bishop-Gromov comparison theorem on a Finsler manifold with the weighted Ricci curvature Ric∞ bounded below. As applications, we prove that if the weighted Ricci curvature Ric∞ is bounded below by a positive number, then the manifold must have finite fundamental group, and must be compact if the distortion is also bounded. Moreover, we give the Calabi-Yau linear volume growth theorem on a Finsler manifold with nonnegative weighted Ricci curvature. 相似文献
54.
A lot of work has focused on compensating nonlinear distortions of the microspeaker under large excitation, yet it is unclear at which level the effect of nonlinear distortion is imperceptible or not annoying. In this study virtual listening tests were performed to evaluate the deterioration of sound quality in music signals with different levels of nonlinear distortion by a microspeaker. Binaural recordings of the music played by the microspeaker were made at different voltage levels, adjusted to the same RMS power, and afterwards reproduced by a low distortion reference headphone. The “double-blind triple-stimulus with hidden reference” method was used in the listening tests. Listeners were required to not only discern the distortion, but also rank the severity of the distortion. The effects of several factors including subject, program material and distortion level on the perceived distortion are discussed. 相似文献
55.
JPEG图像是最流行的隐写载体之一,但隐写分析的最新进展表明,如何设计安全的JPEG隐写算法仍是一个困难的问题.本文提出了一种新的JPEG自适应隐写方法.自适应隐写难点在于设计失真函数合理反应修改量化DCT系数造成的嵌入失真.由于量化DCT系数绝对值的大小能够反应JPEG图像主要统计特性,本文根据DCT系数大小关系设计失真函数,结合STC(Syndrome Trellis Codes)编码,分别给出了使用nsF5修改方式的单层嵌入方法以及使用加减一修改方式的双层嵌入方法.实验表明,本文单层嵌入方法比nsF5安全性高,双层嵌入方法比nsF5以及Filler’s Method抵抗多种检测的能力更强. 相似文献
56.
57.
58.
59.
Walter Stcklein 《Chemie in Unserer Zeit》2006,40(1):32-40
Biosensors are analytical devices incorporating biological material (receptor) intimately associated with or integrated within a physicochemical transducer. Advantages are the high selectivity for analyte detection. Examples given comprise the very successful commercial blood glucose biosensors made for the self‐control by the diabetic patients. Other biosensors are part of an analytic system, including the sensor chips of surface plasmon resonance or interferometry based devices, piezoelectric or reflectometric sensors capable of direct measurement of mass changes, and thermometric and other reagentless sensors. The development of nanotubes‐based devices allows for significant enhancment of the signal‐tonoise ratio of the biosensors. A milestone on the way towards miniaturization and parallelization of biosensors is the recently developed and prize‐winning electronic DNA chip. 相似文献
60.
At least two bunchers are needed in the 3 MeV H- Medium Energy Beam Transport(MEBT)line located between RFQ and DTL for the CSNS(China Spallation Neutron Source).A nose-cone geometry has been adopted as the type of buncher cavity for its simplicity,higher impedance and lower risk of multipacting.By making use of the results got from the simulations on the buncher with two-dimension code SUPERFISH,the thermal and structural analyses have been carried out,the process and results to determine the resulting frequency shift due to thermal and structural distortion of the cavity are presented,the water-cooling channel position and the optimum cooling water temperature as well as the tuning method by adjusting the cooling water temperature when the cavity is out of resonance are also determined through the analyses. 相似文献