全文获取类型
收费全文 | 10763篇 |
免费 | 1659篇 |
国内免费 | 1464篇 |
专业分类
化学 | 8154篇 |
晶体学 | 194篇 |
力学 | 582篇 |
综合类 | 123篇 |
数学 | 1218篇 |
物理学 | 3615篇 |
出版年
2024年 | 29篇 |
2023年 | 239篇 |
2022年 | 309篇 |
2021年 | 446篇 |
2020年 | 515篇 |
2019年 | 518篇 |
2018年 | 418篇 |
2017年 | 427篇 |
2016年 | 575篇 |
2015年 | 559篇 |
2014年 | 694篇 |
2013年 | 871篇 |
2012年 | 931篇 |
2011年 | 960篇 |
2010年 | 687篇 |
2009年 | 659篇 |
2008年 | 703篇 |
2007年 | 623篇 |
2006年 | 587篇 |
2005年 | 419篇 |
2004年 | 378篇 |
2003年 | 271篇 |
2002年 | 353篇 |
2001年 | 276篇 |
2000年 | 224篇 |
1999年 | 196篇 |
1998年 | 157篇 |
1997年 | 117篇 |
1996年 | 83篇 |
1995年 | 91篇 |
1994年 | 90篇 |
1993年 | 64篇 |
1992年 | 61篇 |
1991年 | 51篇 |
1990年 | 47篇 |
1989年 | 20篇 |
1988年 | 21篇 |
1987年 | 16篇 |
1986年 | 27篇 |
1985年 | 31篇 |
1984年 | 20篇 |
1983年 | 17篇 |
1982年 | 14篇 |
1981年 | 14篇 |
1980年 | 7篇 |
1979年 | 11篇 |
1977年 | 7篇 |
1974年 | 11篇 |
1973年 | 7篇 |
1971年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
61.
In this article a new technique was developed to fabricate scaffolds with a unique microstructure by solid–liquid separation in combination with particulate-leaching. Firstly, the effects of polymer concentration, quenching temperature on the porous morphology and the mechanical property of obtained scaffolds during solid–liquid separation have been investigated. Then, salt granules as porogen were introduced into the solid–liquid phase separation to produce the unique pore structure of the scaffold. The pore diameter of the scaffold could be controlled with the particulate size and the wall of pores possessed special microstructure, which enhanced the pore interconnectivity. The cell culture results confirmed that a good interconnectivity of the scaffold prepared by the improved solid–liquid separation was useful for nutrition transportation and cell proliferation. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
62.
Chongyi Wan Shiming Liu Rongqing Tan Jin Wu Jinwen Zhou Yan Lv Yanning Yu Hua Yang 《Optics & Laser Technology》2004,36(8):2389-649
A high average power, high-repetition-rate TEA CO2 laser employing printed-circuit-board preionizer is described. The power scaling of this preionization configuration has been demonstrated. The average output power reaches 3.6 kW at pulse repetition rate of 180 pps. Furthermore, the scaling-up ability of the rotating spark gap as high-voltage switch for high-average-power gas laser has been validated. 相似文献
63.
We demonstrate a 511 W laser diode pumped composite Nd:YAG ceramic laser. The optical pumping system is consisted of five laser diode stacked arrays arranged in a pentagonal shape around the ceramic rod whose size is φ6.35×144mm. When the pumping power is 1600 W, the cw laser output up to 511 W at 1064nm can be obtained with a linear piano-piano cavity, and the optical-to-optical efficiency is 31.9%. To our knowledge, this is the highest value of laser output by using a newly invented composite Nd:YAG ceramic rod as the gain medium. 相似文献
64.
Wenping Deng Gang Xu Lei Wan Anwen Liu Bo Gao Junhe Du Shuiming Hu Yang Chen 《Acta Physico》2008,24(8):1329-1334
Apparatus integrating a Fourier transform-infrared (FT-IR) spectrometer and a mid-infrared difference frequency generation (DFG) laser spectrometer was built for the study of the matrix isolation spectrum in solid molecular hydrogen. A 3-cm-long molecular hydrogen crystal was grown in a liquid-helium Dewar, and its infrared absorption spectrum in the 1-5 μm region was recorded to test the system. The W0(0) (ν=0←0, J=6←0) line around 2410 cm−1 of solid hydrogen was investigated with the DFG laser spectroscopy. High-resolution matrix isolation spectrum of CO2 co-deposited with hydrogen on a BaF2 cold plate at liquid-helium temperature was studied. 相似文献
65.
66.
It is well known that the non-stationary wideband noise is the most difficult to be removed in speech enhancement. In this paper a novel speech enhancement algorithm based on the dyadic wavelet transform and the simplified Karhunen-Loeve transform (KLT) is proposed to suppress the non-stationary wideband noise. The noisy speech is decomposed into components by the wavelet space and KLT-based vector space, and the components are processed and reconstructed, respectively, by distinguishing between voiced speech and unvoiced speech. There are no requirements of noise whitening and SNR pre-calculating. In order to evaluate the performance of this algorithm in more detail, a three-dimensional spectral distortion measure is introduced. Experiments and comparison between different speech enhancement systems by means of the distortion measure show that the proposed method has no drawbacks existing in the previous methods and performs better shaping and suppressing of the non-stationary wideband noise for speech enhancement. 相似文献
67.
本文简要介绍线性代数学习网站的系统研究与开发设计.涉及到网络数据库、ASP、界面设计等多种技术.该线性代数网上学习系统为老师和学生提供了交流平台,其界面美观、操作简便.具有良好的应用前景. 相似文献
68.
An enantioselective Michael addition of malonate to nitroalkenes is efficiently catalyzed by low loading demethylquinine salts in water; the yield range from 49% to 93% and the ee up to 90%. 相似文献
69.
Hebing Rui 《Proceedings of the American Mathematical Society》2006,134(10):2873-2880
In this note, we use generalized Tchebychev polynomials to define a trace function which satisfies certain conditions. Such a trace will be called the Markov trace. In particular, we obtain formulae for the weights of the Markov trace. As a corollary, we get a combinatorial identity. This generalizes Jones's 1983 result on Temperley-Lieb algebras.
70.
Wei‐Lie Xiao Jian‐Xin Pu Rui‐Rui Wang Liu‐Meng Yang Xiao‐Li Li Sheng‐Hong Li Rong‐Tao Li Sheng‐Xiong Huang Yong‐Tang Zheng Han‐Dong Sun 《Helvetica chimica acta》2007,90(8):1505-1513
Seven new highly oxygenated nortriterpenoids, rubriflorins D–J ( 1 – 7 ), were isolated from the leaves and stems of Schisandra rubriflora, and their structures were elucidated on the basis of extensive analysis of spectroscopic data. These new compounds feature the opening of ring A compared with related known nortriterpenoids isolated from the genus Schisandra and showed weak activity against HIV‐1. 相似文献