全文获取类型
收费全文 | 14201篇 |
免费 | 2202篇 |
国内免费 | 2226篇 |
专业分类
化学 | 10835篇 |
晶体学 | 141篇 |
力学 | 908篇 |
综合类 | 162篇 |
数学 | 1481篇 |
物理学 | 5102篇 |
出版年
2024年 | 48篇 |
2023年 | 259篇 |
2022年 | 447篇 |
2021年 | 502篇 |
2020年 | 512篇 |
2019年 | 541篇 |
2018年 | 407篇 |
2017年 | 414篇 |
2016年 | 629篇 |
2015年 | 610篇 |
2014年 | 803篇 |
2013年 | 1011篇 |
2012年 | 1177篇 |
2011年 | 1274篇 |
2010年 | 911篇 |
2009年 | 866篇 |
2008年 | 998篇 |
2007年 | 849篇 |
2006年 | 742篇 |
2005年 | 735篇 |
2004年 | 523篇 |
2003年 | 480篇 |
2002年 | 570篇 |
2001年 | 481篇 |
2000年 | 391篇 |
1999年 | 336篇 |
1998年 | 295篇 |
1997年 | 244篇 |
1996年 | 208篇 |
1995年 | 179篇 |
1994年 | 203篇 |
1993年 | 147篇 |
1992年 | 167篇 |
1991年 | 150篇 |
1990年 | 99篇 |
1989年 | 97篇 |
1988年 | 60篇 |
1987年 | 37篇 |
1986年 | 47篇 |
1985年 | 36篇 |
1984年 | 22篇 |
1983年 | 26篇 |
1982年 | 17篇 |
1981年 | 11篇 |
1980年 | 9篇 |
1978年 | 8篇 |
1977年 | 7篇 |
1976年 | 7篇 |
1975年 | 5篇 |
1974年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
Subdifferential representation of homogeneous functions and extension of smoothness in Banach spaces
In this paper, we mainly consider proximal subdifferentials of lower semicontinuous functions defined on real Hilbert space and Clarke's subdifferentials of locally Lipschitzian functions defined on Banach space respectively, and obtain the generalized Euler identity of homogenous functions. Then, by introducing a multifunction F, we extend the smoothness of sphere and differentiability of norm function in Banach space. 相似文献
122.
在反转恢复测试中磁化矢量的演化特征:辐射阻尼效应 总被引:1,自引:0,他引:1
在强辐射阻尼存在下,水样(90% H2O in D2O)的反转恢复实验表明:当两脉冲的相位相差180°且反转脉冲角<180°时,或两脉冲相位一致但反转脉冲角>180°时,在检测期观测到的信号强度将不发生从负极大值到正极大值的突变;在同样的条件下,如果存在频率偏置,信号强度存在波动,即beating效应.只有当两脉冲的相位一致而反转脉冲角<180°时,或两脉冲的相位相差180°但反转脉冲角>180°时,在检测期信号强度才发生突变,即jumping效应.这些现象都可通过辐射阻尼理论予以合理地解释.另外,在检测期当磁化矢量运动到-z轴附近(对应于τ=Trdln{tan[(π±δ)/2]}),信号强度与理论预计的偏差实际上与T1弛豫效应有关. 相似文献
123.
Effect of stimulation rate on phoneme recognition by nucleus-22 cochlear implant listeners 总被引:3,自引:0,他引:3
This study investigated the effect of pulsatile stimulation rate on medial vowel and consonant recognition in cochlear implant listeners. Experiment 1 measured phoneme recognition as a function of stimulation rate in six Nucleus-22 cochlear implant listeners using an experimental four-channel continuous interleaved sampler (CIS) speech processing strategy. Results showed that all stimulation rates from 150 to 500 pulses/s/electrode produced equally good performance, while stimulation rates lower than 150 pulses/s/electrode produced significantly poorer performance. Experiment 2 measured phoneme recognition by implant listeners and normal-hearing listeners as a function of the low-pass cutoff frequency for envelope information. Results from both acoustic and electric hearing showed no significant difference in performance for all cutoff frequencies higher than 20 Hz. Both vowel and consonant scores dropped significantly when the cutoff frequency was reduced from 20 Hz to 2 Hz. The results of these two experiments suggest that temporal envelope information can be conveyed by relatively low stimulation rates. The pattern of results for both electrical and acoustic hearing is consistent with a simple model of temporal integration with an equivalent rectangular duration (ERD) of the temporal integrator of about 7 ms. 相似文献
124.
125.
The Hirota method for generating Hirota’s bilinear equation and constructing soliton solutions of nonlinear evolution equations is discussed and illustrated. Two Maple programs Bilinearization and Multisoliton are presented to automatically calculate Hirota’s bilinear equations for nonlinear evolution equations and to compute their N-soliton solutions for N = 1, 2 or 3, respectively. Different kinds of examples are used to demonstrate the effectiveness of the packages. 相似文献
126.
Dejian Fu Keeyoon Sung Chris D. Boone Kaley A. Walker Peter F. Bernath 《Journal of Quantitative Spectroscopy & Radiative Transfer》2008,109(12-13):2219-2243
Carbon cycle science by Fourier transform spectroscopy (CC-FTS) is an advanced study for a future satellite mission. The goal of the mission is to obtain a better understanding of the carbon cycle in the Earth's atmosphere by monitoring total and partial columns of CO2, CH4, N2O, and CO in the near infrared. CO2, CH4, and N2O are important greenhouse gases, and CO is produced by incomplete combustion. The molecular O2 column is also needed to obtain the effective optical path of the reflected sunlight and is used to normalize the column densities of the other gases. As part of this advanced study, ground-based Fourier transform spectra are used to evaluate the spectral region and resolution needed. Spectra in the 3950–7140 cm?1 region with a spectral resolution of 0.0042 cm?1 recorded at Kiruna (67.84°N, 20.41°E, and 419 m above sea level), Sweden, on 1 April 1998, were degraded to the resolutions of 0.01, 0.1, and 0.3 cm?1. The effect of spectral resolution on the retrievals has been investigated with these four Kiruna spectra. To obtain further information on the spectral resolution, optical components and spectroscopic parameters required by the future mission, high-resolution solar absorption spectra between 2000 and 15000 cm?1 were recorded using Fourier transform spectrometers at Kitt Peak (31.9°N, 111.6°W, and 2.1 km above sea level), Arizona, on 25 July 2005 and Waterloo (43.5°N, 80.6°W, and 0.3 km above sea level), Ontario, on 22 November 2006 with spectral resolutions of 0.01 and 0.1 cm?1, respectively. Dry air volume mixing ratios (VMRs) of CO2 and CH4 were retrieved from these ground-based observations. The HITRAN 2004 spectroscopic parameters are used with the SFIT2 package for the spectral analysis. The measurement precisions for CO2 and CH4 total columns are better than 1.07% and 1.13%, respectively, for our observations. Based on these results, a Fourier transform spectrometer (maximum spectral resolution of 0.1 cm?1 or 5 cm maximum optical path difference (MOPD)) operating between 2000 and 15000 cm?1 is suggested as the primary instrument for the mission. Further progress in improving the atmospheric retrievals for CO2, CH4, and O2 requires new laboratory measurements of the spectroscopic line parameters. 相似文献
127.
We study the evolutionary Prisoner's dilemma game on scale-free networks, focusing on the influence of different initial distributions for cooperators and defectors on the evolution of cooperation. To address this issue, we consider three types of initial distributions for defectors: uniform distribution at random, occupying the most connected nodes, and occupying the lowest-degree nodes, respectively. It is shown that initial configurations for defectors can crucially influence the cooperation level and the evolution speed of cooperation. Interestingly, the situation where defectors initially occupy the lowest-degree vertices can exhibit the most robust cooperation, compared with two other distributions. That is, the cooperation level is least affected by the initial percentage of defectors. Moreover, in this situation, the whole system evolves fastest to the prevalent cooperation. Besides, we obtain the critical values of initial frequency of defectors above which the extinction of cooperators occurs for the respective initial distributions. Our results might be helpful in explaining the maintenance of high cooperation in scale-free networks. 相似文献
128.
129.
ZhengJun Xi 《中国科学:物理学 力学 天文学(英文版)》2018,61(1):010321
正Channel capacity is a core problem in information theory[1,2].The capacity of a classical channel is essentially characterized by maximum transmission rate of classical information[1].However,in quantum information theory,several capacities can be defined for a quantum channel based on the type of information being sent.Currently,classical capacity[3,4],entanglement-assisted classical capacity[5],quantum capacity[6,7],and private capacity[7]are used to define 相似文献
130.
Lyu Jiahui Han Huibin Wu Qiong Ma Hongchao Ma Chun Dong Xiaoli Fu Yinghuan 《Journal of Solid State Electrochemistry》2019,23(3):847-859
Journal of Solid State Electrochemistry - Rational hydrophobic anode has been considered as a promising approach for water pollution remediation. However, the construction method of the hydrophobic... 相似文献