全文获取类型
收费全文 | 29761篇 |
免费 | 6258篇 |
国内免费 | 11451篇 |
专业分类
化学 | 22101篇 |
晶体学 | 1193篇 |
力学 | 2333篇 |
综合类 | 1492篇 |
数学 | 4999篇 |
物理学 | 15352篇 |
出版年
2024年 | 76篇 |
2023年 | 288篇 |
2022年 | 1004篇 |
2021年 | 1054篇 |
2020年 | 1021篇 |
2019年 | 943篇 |
2018年 | 914篇 |
2017年 | 1362篇 |
2016年 | 989篇 |
2015年 | 1458篇 |
2014年 | 1759篇 |
2013年 | 2361篇 |
2012年 | 2197篇 |
2011年 | 2570篇 |
2010年 | 2502篇 |
2009年 | 2838篇 |
2008年 | 2957篇 |
2007年 | 2710篇 |
2006年 | 2780篇 |
2005年 | 2410篇 |
2004年 | 1926篇 |
2003年 | 1361篇 |
2002年 | 1359篇 |
2001年 | 1557篇 |
2000年 | 1673篇 |
1999年 | 969篇 |
1998年 | 472篇 |
1997年 | 396篇 |
1996年 | 359篇 |
1995年 | 303篇 |
1994年 | 331篇 |
1993年 | 344篇 |
1992年 | 280篇 |
1991年 | 220篇 |
1990年 | 231篇 |
1989年 | 242篇 |
1988年 | 196篇 |
1987年 | 161篇 |
1986年 | 147篇 |
1985年 | 94篇 |
1984年 | 115篇 |
1983年 | 108篇 |
1982年 | 74篇 |
1981年 | 83篇 |
1980年 | 64篇 |
1979年 | 48篇 |
1978年 | 30篇 |
1977年 | 14篇 |
1965年 | 21篇 |
1959年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
971.
用荧光光谱法研究了在生理条件下,3-对氯苯基-2-(4-叔丁基苯氧基)-3'-氧环己烷并噻吩并[2,3-d]嘧啶-4(3H)-酮(PTP)与牛血清白蛋白(BSA)的相互作用.实验表明,PTP主要以静态猝灭方式使BSA荧光强度显著降低.计算了不同温度下二者的结合常数和结合位点数,并根据热力学参数确定了PTP与BSA之间的作用力主要为氢键或范德华力.根据F(o)rster非辐射能量转移机理,测定了PTP与BSA相互结合时的作用距离,并用同步荧光技术讨论了其衍生物对BSA构象的影响. 相似文献
972.
HUANG HouBing MA XingQiao YUE Tao XIAO ZhiHua SHI SanQiang & CHEN LongQing 《中国科学:物理学 力学 天文学(英文版)》2011,(7)
The current-induced magnetic switching is studied in Co/Cu/Co nanopillar with an in-plane magnetization traversed under the perpendicular-to-plane external field.Magnetization switching is found to take place when the current density exceeds a threshold.By analyzing precessional trajectories,evolutions of domain walls and magnetization switching times under the perpendicular magnetic field,there are two different magnetization switching modes:nucleation and domain wall motion reversal;uniform magnetization ... 相似文献
973.
松花粉中16种常量和微量元素的TXRF对比分析 总被引:1,自引:0,他引:1
采用微波消解前处理,全反射X射线荧光分析法(TXRF)同时测定松花粉中16种元素,并对马尾松、云南松、油松、黑松、赤松等五种松花粉中16种元素含量进行了测定与比较。结果表明:五种松花粉中都含有这16种元素;Ca,Ti,Mn,Zn和Rb等五种元素平均含量在不同树种间均存在极显著性差异(p≤0.01);K,V,Fe,Co,Cu和Sr等六种元素平均含量在不同树种间均存在显著性差异(p≤0.05);Cr,Ni,As,Pb和Se等五种元素平均含量在不同树种间不存在显著性差异(p>0.05);研究还表明松花粉具有温性或偏寒凉性药的元素谱征。研究结果可以初步断定,松花粉中这16种元素的含量和树种有关,和生长环境、地域等密切相关。 相似文献
974.
975.
Evolution from Diffuse Ferroelectric to Relaxor Ferroelectric in Pb1-xBax(Fe1/2Nb1/2)O3 Solid Solutions 下载免费PDF全文
Dielectric and ferroelectric characteristics for Pb1-xBax(Fe1/2Nh/2)O3 (x = 0,0.05,0.1,0.15, and 0.2) ceramics are determined together with their structures. X-ray diffraction (XRD) analysis confirms the solid solutions with the cubic structure. The dielectric nature changes from diffuse ferroelectric to relaxor ferroelectric with increasing x, while the phase transition temperature Tc (or Tm) decreases monotonously. The diffuse ferroelectric phase transition is observed in the solid solutions with 0≤x ≤0.05. For Pbl-xBax(Fe1/2Nb1/2)O3 with 0.1≤ x≤0.2, relaxor ferroelectric behavior is determined, and the Vogel-Fulcher equation is used to describe the relaxor behavior. The 1/ε versus T plots reveal the diffusion dielectric characteristics in both diffuse and relaxor ferroelectrics. 相似文献
976.
本文分别用混酸水热法(HT)和混酸冷凝回流法(RF)对Vulcan XC-72R碳黑进行预处理,并进一步研究其作为Pt/C催化剂载体的性能。循环伏安实验发现,采用HT法、RF法和未预处理的碳黑作为载体的Pt/C催化剂电催化甲醇氧化的比质量活性(正扫峰电流)分别为1055、704和395 mA/mgpt,即采用HT法预处理碳载体的Pt/C催化剂具有最高的电催化活性,而且计时电流实验也表现出最好的稳定性。实验结果表明,碳载体的预处理方法对制得的Pt/C催化剂的性能具有关键性的影响,且水热法是一种效果较好的预处理碳载体的方法。 相似文献
977.
978.
�� ������ �ƣ�¬ ������ �أ�������� ���������� 《核聚变与等离子体物理》2017,37(4):418-421
The power measurement method for 3.7GHz LHCD system on HL-2A was introduced. It is found by HFSS simulation that the impact of backward wave phase on the measurement of forward power may be suppressed if the isolation of directional coupler is more than 30dB. After improving the system, the total transmission line efficiency of the LHCD system can reach 89% with maximum power 1.5MW in 2016 experiment campaign. 相似文献
979.
Surfaces of three types of CuZr-based bulk metallic glasses (BMGs) were modified by laser surface treatment (LST), and the influence of the treatment on structure and mechanical properties of these alloys was investigated. The phase structure of as-cast and laser-treated samples was characterized by XRD and the morphology of the alloys after fracture was examined by SEM. The compressive plasticity of treated Cu47.5Zr47.5Al5 and Cu46.5Zr47.5Al5Co1 BMGs can be improved from 0.5% to 2.0% and from 1.2% to 5.7% respectively compared with the as-cast ones, while (Cu0.55Zr0.40Al0.05)99Er1 BMG shows insignificant change of plasticity. The improvement in plasticity is attributed to induced crystallization of B2 CuZr phase in the treated surface zone of selected metallic glasses. 相似文献
980.
Recently much attention has been paid to the application of metal hybrid nanoparticles in industrial catalytic fields because of their super-efficient catalytic activity and attractive properties. We explored a novel strategy to prepare GSH-capped Pt–Au–Ag-hybrid nanoclusters through the synergistic effect between ascorbic acid(VC) and glutathione(GSH) with chloroplatinic acid, chloroauric acid, and silver nitrate as precursors. The potential utilization of as-prepared GSH-capped Pt–Au–Aghybrid nanoclusters for catalytic applications has been evaluated through the reduction of 4-nitrophenol(4-NP) with NaBH4; we obtained the kinetic data by monitoring with UV-Vis spectroscopy. Our results illustrate that GSH-capped Pt–Au– Ag-hybrid nanoclusters could facilitate the process of reduction of 4-NP in a way that is unprecedented. This approach may offer a novel, non-cytotoxicity, efficient catalyst for industry. 相似文献