全文获取类型
收费全文 | 14237篇 |
免费 | 2244篇 |
国内免费 | 2917篇 |
专业分类
化学 | 11746篇 |
晶体学 | 353篇 |
力学 | 604篇 |
综合类 | 216篇 |
数学 | 1641篇 |
物理学 | 4838篇 |
出版年
2024年 | 22篇 |
2023年 | 164篇 |
2022年 | 342篇 |
2021年 | 454篇 |
2020年 | 504篇 |
2019年 | 556篇 |
2018年 | 431篇 |
2017年 | 521篇 |
2016年 | 626篇 |
2015年 | 728篇 |
2014年 | 926篇 |
2013年 | 1152篇 |
2012年 | 1285篇 |
2011年 | 1322篇 |
2010年 | 1121篇 |
2009年 | 1055篇 |
2008年 | 1264篇 |
2007年 | 1066篇 |
2006年 | 980篇 |
2005年 | 810篇 |
2004年 | 656篇 |
2003年 | 533篇 |
2002年 | 617篇 |
2001年 | 440篇 |
2000年 | 354篇 |
1999年 | 272篇 |
1998年 | 197篇 |
1997年 | 117篇 |
1996年 | 128篇 |
1995年 | 97篇 |
1994年 | 86篇 |
1993年 | 101篇 |
1992年 | 71篇 |
1991年 | 76篇 |
1990年 | 42篇 |
1989年 | 59篇 |
1988年 | 22篇 |
1987年 | 37篇 |
1986年 | 25篇 |
1985年 | 26篇 |
1984年 | 21篇 |
1983年 | 16篇 |
1982年 | 11篇 |
1981年 | 11篇 |
1980年 | 9篇 |
1979年 | 12篇 |
1978年 | 10篇 |
1977年 | 7篇 |
1976年 | 5篇 |
1966年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 906 毫秒
61.
养殖池塘沉积物的重金属分布及污染特征 总被引:3,自引:0,他引:3
浙江省淅西北地区淡水养殖池塘沉积物重金属调查研究表明,养殖池塘沉积物中7种重金属元素分布不均衡,差异也较大,除Hg和Cr元素外,其余重金属元素已大大超过土壤本底值.虽然其实测含量都未超出国家规定的标准值范围,但沉积物中重金属元素对养殖水环境、养殖品种存在的潜在污染与危害值得关注.污染指数评价显示,养殖池塘沉积物中主要污染物质为Cu和Cr,而Hg、Pb污染程度相对较轻. 相似文献
62.
A novel measurement method of temperature based on the phenomena that the phase difference between principle polarization states in the optical retarder is function of temperature is described. The polarization state of optical beam is changed as it passes through the optical retarder, which depends on the temperature. The temperature of optical retarder is determined by comparison of the power difference between principal polarization states. We demonstrate successfully the temperature measurement by using a polarization maintaining fiber as the optical retarder. With a 100 mm length of the fiber optic retarder, the change rate of phase difference on temperature was 0.236 rad/°C and the measurement error was ±0.038°C over the temperature range of −2.6 – +3.4°C. With a 11.5 mm length of the fiber optic retarder, the change rate of phase difference on temperature was 0.021 rad/°C and the measurement error was ±0.79°C over the temperature range of −8.5 – +86.5°C. 相似文献
63.
64.
A new constant-pressure molecular dynamics (MD) method is developed to simulate the dynamic behavior and structure transition of finite system under external pressure. In this method, no artificial parameter is introduced and the computation overheads are very small. As an application, a hard-soft transition of single wall carbon nanotube (SWCNT) under external pressure is found, which is in agreement with the experiments.
相似文献65.
5‐Methylene‐2‐oxazolidinone (1) and 5‐methylene‐1,3‐thiazolidine‐2‐thione (4) react with various isocyanates to give the corresponding urethanes 3 and 5 in high yields in the presence of palladium(0) or palladium(II) catalyst under mild reaction conditions. A mechanism is proposed. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
66.
Hyun Chul Choi Min Kyu Lee Hyun Joon Shin Seung Bin Kim 《Journal of Electron Spectroscopy and Related Phenomena》2003,130(1-3):85-96
To investigate the formation of a solid electrolyte interface (SEI) on the Li1+xV3O8 electrode surface in the thermodynamic stability range of the organic electrolyte, we applied scanning photoelectron microscopy (SPEM) to a pristine electrode and to an electrode after ten cycles. The F K-edge absorption spectrum of the cycled electrode showed that LiF forms on the electrode surface during the lithium insertion–extraction process in the Li1+xV3O8/Li cell. The photoelectron spectrum for the cycled electrode showed intense spectral features corresponding to Li 1s, F 2s, F 2p, and P 2p electron signals, whereas these spectral features were of negligible intensity for the pristine electrode. The above results give strong support for the formation of an SEI that consists of LiF and compounds containing phosphorus during operation of the battery. The SPEM images also revealed that the fluorine distribution on the surface of the cycled electrode was inhomogeneous. 相似文献
67.
Hong‐Qing Wang Zhao‐Jie Liu Li‐Min Yang Ming‐Wu Ding 《Journal of heterocyclic chemistry》2004,41(3):393-397
A series of new 1H‐pyrazolo[3,4‐d]pyrimidin‐4(5H)‐one Derivatives 5 has been designed and regio‐selectively synthesized via a tandem aza‐Wittig reaction. The structures of all compounds prepared have been confirmed by 1H NMR, IR, EI‐MS spectroscopy and elemental analyses. The results of preliminary bioassay indicate that most compounds 5 possess an inhibition effect against Botrytis cinereapers and Pyricularia oryzae at the concentration of 50 mg/L. 相似文献
68.
By making use of a light gas gun, a specially designed target is impacted by the LY12 flyer, and the pressure is taken in the range of 0.6-3 GPa. Based on the stress profiles measured in the buffer materials by manganese gauges, the Hugoniot curve and release curves of LY12 aluminium alloy are obtained. Meanwhile, the release curves from different initial shocked states are described in both the pressure-particle velocity plane and the pressure-specific volume plane. 相似文献
69.
70.
Yong Joon Park Min Gyu KimYoung-Sik Hong Xianglan WuKwang Sun Ryu Soon Ho Chang 《Solid State Communications》2003,127(7):509-514
Li[NixLi(1/3−2x/3)Mn(2/3−x/3)]O2 (X=0.17, 0.25, 0.33, 0.5) compounds are prepared by a simple combustion method. The Rietvelt analysis shows that these compounds could be classified as having the α-NaFeO2 structure. The initial charge-discharge and irreversible capacity increases with the decrease of x in Li[NixLi(1/3−2x/3)Mn(2/3−x/3)]O2. Indeed, Li[Ni0.50Mn0.50]O2 compound shows relatively low initial discharge capacity of 200 mAh/g and large capacity loss during cycling, with Li[Ni0.17Li0.22Mn0.61]O2 and Li[Ni0.25Li0.17Mn0.58]O2 compounds exhibit high initial discharge capacity over 245 mAh/g and stable cycle performance in the voltage range of 4.8 -2.0 V. On the other hand, XANES analysis shows that the oxidation state of Ni ion reversibly changes between Ni2+ and about Ni3+, while the oxidation state of Mn ion sustains Mn4+ during charge-discharge process. This result does not agree with the previously reported ‘electrochemistry model’ of Li[NixLi(1/3−2x/3)Mn(2/3−x/3)]O2, in which Ni ion changes between Ni2+ and NI4+. Based on these results, we modified oxidation-state change of Mn and Ni ion during charge-discharge process. 相似文献