全文获取类型
收费全文 | 19862篇 |
免费 | 2155篇 |
国内免费 | 2067篇 |
专业分类
化学 | 14473篇 |
晶体学 | 219篇 |
力学 | 906篇 |
综合类 | 178篇 |
数学 | 2305篇 |
物理学 | 6003篇 |
出版年
2024年 | 41篇 |
2023年 | 271篇 |
2022年 | 474篇 |
2021年 | 500篇 |
2020年 | 607篇 |
2019年 | 606篇 |
2018年 | 535篇 |
2017年 | 493篇 |
2016年 | 758篇 |
2015年 | 783篇 |
2014年 | 977篇 |
2013年 | 1261篇 |
2012年 | 1488篇 |
2011年 | 1660篇 |
2010年 | 1190篇 |
2009年 | 1183篇 |
2008年 | 1307篇 |
2007年 | 1183篇 |
2006年 | 1078篇 |
2005年 | 951篇 |
2004年 | 910篇 |
2003年 | 760篇 |
2002年 | 780篇 |
2001年 | 627篇 |
2000年 | 518篇 |
1999年 | 380篇 |
1998年 | 269篇 |
1997年 | 207篇 |
1996年 | 251篇 |
1995年 | 195篇 |
1994年 | 184篇 |
1993年 | 162篇 |
1992年 | 149篇 |
1991年 | 120篇 |
1990年 | 129篇 |
1989年 | 94篇 |
1988年 | 103篇 |
1987年 | 73篇 |
1986年 | 75篇 |
1985年 | 98篇 |
1984年 | 71篇 |
1983年 | 69篇 |
1982年 | 51篇 |
1981年 | 48篇 |
1980年 | 48篇 |
1979年 | 35篇 |
1977年 | 37篇 |
1976年 | 37篇 |
1974年 | 48篇 |
1973年 | 44篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
The mass spectra of saturated monohydric alcohols are used in structure elucidation by means of computer programs of the artificial intelligence type. The structure generator is constrained by a structure predictor to show the sub-group structure in a fairly definite area, and spectral characteristics are also predicted. According to the commands of the structure predictor, sub-groups conforming to the mass spectra studied are then combined into molecular structures which are ranked for output. The system was tested for 218 mass spectra of 115 alcohols from different laboratories: all the correct answers were included in the 6 highest scores, with 78% for the highest score and 91% for the highest 2 scores. 相似文献
992.
D.Y. Lin T.P. Huang Y.C. Kao C.C. Huang H.C. Kuo Li Chang 《Physica E: Low-dimensional Systems and Nanostructures》2011,44(3):659-664
In this study, we present the optical characteristics of A-plane ZnO/ZnMgO multiple quantum wells (MQWs) with different well widths grown on R-plane sapphire substrates by pulsed laser deposition (PLD). The energy gaps of ZnO and ZnMgO have been observed by photoluminescence (PL) and absorption spectra. The electrons confined in the ZnO wells transit from the electron ground sub-band to the heavy-hole ground sub-band (noted as 11H) located at 3.40 and 3.57 eV for the ZnO/ZnMgO MQWs samples with well widths of 5.6 and 1.2 nm, respectively. The strong anisotropic polarization characteristic has been studied by polarization-dependent PL measurements. For comparison, we also calculated the transition energies of different well thicknesses varying from 1 to 6 nm. The theoretical results match quite well with the experimental values and revealing the suitable conduction band offset Qc=0.6. The temperature dependence of PL spectra is being investigated, in the temperature range between 10 and 300 K. 相似文献
993.
Adare A Afanasiev S Aidala C Ajitanand NN Akiba Y Al-Bataineh H Alexander J Al-Jamel A Aoki K Aphecetche L Armendariz R Aronson SH Asai J Atomssa ET Averbeck R Awes TC Azmoun B Babintsev V Baksay G Baksay L Baldisseri A Barish KN Barnes PD Bassalleck B Bathe S Batsouli S Baublis V Bauer F Bazilevsky A Belikov S Bennett R Berdnikov Y Bickley AA Bjorndal MT Boissevain JG Borel H Boyle K Brooks ML Brown DS Bucher D Buesching H Bumazhnov V Bunce G Burward-Hoy JM Butsyk S Campbell S Chai JS Chang BS 《Physical review letters》2007,98(23):232301
The PHENIX experiment at the BNL Relativistic Heavy Ion Collider (RHIC) has measured J/psi production for rapidities -2.2相似文献
994.
基于简单的主振荡功率放大结构,演示了一种高功率窄线宽线性偏振全光纤激光器,其最大输出功率为3.08 kW,3 dB线宽为0.2 nm。在整个功率缩放过程中,偏振消光比约为94%,光束质量M 2约为1.4。这是国内外首次实现3 kW全保偏光纤激光输出,与基于相位调制的窄线宽激光器相比,该激光器可实现近似的线宽,同时具有受激布里渊散射阈值高、系统结构简单、成本低等特点。 相似文献
995.
A high-energy electron beam generator is used to generate a plasma
in atmosphere. Based on a Monte Carlo toolkit named GEANT4, a model
including complete physics processes is established to simulate the
passage of the electron beam in air. Based on the model, the
characteristics of the electron beam air plasma are calculated. The
energy distribution of beam electrons (BEs) indicates that
high-energy electrons almost reside in the centre region of the
beam, but low-energy electrons always live in the fringe area. The
energy deposition is calculated in two cases, i.e., with and without
secondary electrons (SEs). Analysis indicates that the energy
deposition of SEs accounts for a large part of the total energy
deposition. The results of the energy spectrum show that the electrons
in the inlet layer of the low-pressure chamber (LPC) are monoenergetic,
but the energy spectrum of the electrons in the outlet layer is not
pure. The SEs are largely generated at the outlet of the LPC.
Moreover, both the energy distribution of BEs and the magnitude of
the density of SEs are closely related to the pressure of LPC. Thus,
a conclusion is drawn that a low magnitude of LPC pressure is
helpful for reducing the energy loss in the LPC and also useful for
greatly increasing the secondary electron density in dense air. 相似文献
996.
Feature extraction plays an important role in the clustering analysis. In this paper an integrated Autoregressive (AR)/Autoregressive Conditional Heteroscedasticity (ARCH) model is proposed to characterize the vibration signal and the model coefficients are adopted as feature vectors to realize clustering diagnosis of rolling element bearings. The main characteristic is that the AR item and ARCH item are interrelated with each other so that it can depict the excess kurtosis and volatility clustering information in the vibration signal more accurately in comparison with two-stage AR/ARCH model. To testify the correctness, four kinds of bearing signals are adopted for parametric modeling by using the integrated and two-stage AR/ARCH model. The variance analysis of the model coefficients shows that the integrated AR/ARCH model can get more concentrated distribution. Taking these coefficients as feature vectors, K means based clustering is utilized to realize the automatic classification of bearing fault status. The results show that the proposed method can get more accurate results in comparison with two-stage model and discrete wavelet decomposition. 相似文献
997.
998.
A modified variable-coefficient projective Riccati equation mapping method is applied to (2 + 1)-dimensional Wick-type stochastic generalized Broer-Kaup system. With the help of Hermit transformation, we obtain a series of new exact stochastic solutions to the stochastic Broer-Kaup system in the white noise environment. 相似文献
999.
QiuHongLI LinNIU ChangQiaoZHANG FengHuaWEI HuZHANG 《中国化学快报》2004,15(1):115-117
The oxidation of methanol was investigated on platinum-modified polyaniline electrode.Changes in the electrode rotation rates (Ω) during platinum electrodeposition remarkably affect the formation and distribution of platinum in the polymer matrix and consequently lead to different currents of methanol oxidation. The results show that platinum loading is proportional to rotation rates Ω^1/2. 相似文献
1000.
XiGuang Cao Xun Chen YunHua Chen XiangYi Cui DeQing Fang ChangBo Fu Karl L. Giboni HaoWei Gong GuoDong Guo Ming He Jie Hu XingTao Huang XiangDong Ji YongLin Ju ShaoLi Li Qing Lin HuaXuan Liu JiangLai Liu Xiang Liu Wolfgang Lorenzon YuGang Ma YaJun Mao KaiXuan Ni Kirill Pushkin XiangXiang Ren Michael Schubnell ManBing Shen YuJie Shi Scott Stephenson AnDi Tan Greg Tarlé HongWei Wang JiMing Wang Meng Wang XuMing Wang Zhou Wang YueHuan Wei ShiYong Wu MengJiao Xiao Xiang Xiao PengWei Xie Tao Ye YingHui You XiongHui Zen Hua Zhang Tao Zhang HaiYing Zhao Li Zhao XiaoPeng Zhou ZhongHua Zhu 《中国科学:物理学 力学 天文学(英文版)》2014,57(8):1476-1494