全文获取类型
收费全文 | 12561篇 |
免费 | 2309篇 |
国内免费 | 3375篇 |
专业分类
化学 | 10031篇 |
晶体学 | 456篇 |
力学 | 767篇 |
综合类 | 284篇 |
数学 | 1727篇 |
物理学 | 4980篇 |
出版年
2024年 | 24篇 |
2023年 | 148篇 |
2022年 | 336篇 |
2021年 | 379篇 |
2020年 | 473篇 |
2019年 | 447篇 |
2018年 | 444篇 |
2017年 | 483篇 |
2016年 | 533篇 |
2015年 | 651篇 |
2014年 | 832篇 |
2013年 | 986篇 |
2012年 | 1074篇 |
2011年 | 1119篇 |
2010年 | 1031篇 |
2009年 | 1012篇 |
2008年 | 1162篇 |
2007年 | 972篇 |
2006年 | 954篇 |
2005年 | 828篇 |
2004年 | 702篇 |
2003年 | 563篇 |
2002年 | 581篇 |
2001年 | 582篇 |
2000年 | 496篇 |
1999年 | 301篇 |
1998年 | 178篇 |
1997年 | 132篇 |
1996年 | 131篇 |
1995年 | 121篇 |
1994年 | 104篇 |
1993年 | 69篇 |
1992年 | 69篇 |
1991年 | 57篇 |
1990年 | 51篇 |
1989年 | 50篇 |
1988年 | 36篇 |
1987年 | 28篇 |
1986年 | 25篇 |
1985年 | 14篇 |
1984年 | 16篇 |
1983年 | 8篇 |
1982年 | 5篇 |
1981年 | 8篇 |
1980年 | 4篇 |
1979年 | 7篇 |
1978年 | 2篇 |
1971年 | 2篇 |
1964年 | 2篇 |
1957年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
991.
992.
In this letter, we investigate the influence of the stress on magnetoelectric (ME) effect in a magnetostrictive-PZT bilayer.
ME voltage coefficient α*E = δE / δH, where δE is the induced electric field for an applied alternating current (ac) magnetic field δH, is obtained by solving the stress-related piezoelectric constitutive equation and the conventional magnetostrictive equation
with appropriate boundary condition. Based on the free-energy density function of the PZT film in stress state, we get the
stress-related piezoelectric charge coefficient p
d*31 and dielectric permittivity pε*33. After taking the cobalt ferrite (CFO) as magnetostrictive phase, it is found that α*E increases with decreasing 2-d compressive stress for CFO-PZT, which not only is qualitatively consistent with previous experimental
measurements, but also provides a possible route to improve the ME effect.
相似文献
993.
Lu‐Feng Zou Kuang Shen Yao Fu Qing‐Xiang Guo 《Journal of Physical Organic Chemistry》2007,20(10):754-763
Experimental studies showed that sulfur radicals play the vital role in petroleum formation. 1 Sulfur‐ centered radicals also exhibit activities in antioxidant functions. Here we conduct a theoretical investigation of their precursor‐disulfides. By investigation into substituent effect on sulfur? sulfur bond dissociation enthalpies (S? S BDEs), we would like to find the most effective provider for sulfur radicals. In the present work, 50 alpha‐substituted disulfides and 16 para‐substituted aryl disulfides are studied systematically, with the general formula XS‐SX or HS‐SX. The substituent effect on S? S BDEs is found to be very eminent, ranging from 33.2 to 75.0 kcal/mol for alpha‐substituted disulfide, and from 43.7 to 59.7 kcal/mol for para‐substituted phenyl disulfides. We also evaluate the performance of 44 density functional methods to get an accurate prediction. A further study indicates that substituents play a major role in radical energies, instead of molecule energies, which is substantiated by the good linearity between XS‐SX bond dissociation enthalpy (BDE) and HS‐SX BDE. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
994.
The polycrystalline Ti/TiNx multilayer films were deposited by magnetron sputtering, and the as-deposited multilayer coatings were annealed at 500-800 °C for 2-4 h in vacuum. We investigated the effects of annealing temperature and annealing time on the microstructural, interfacial, and mechanical properties of the polycrystalline Ti/TiNx multilayer films. It was found that the hardness increased with annealing temperature. This hardness enhancement was probably caused by the preferred crystalline orientation TiN(1 1 1). The X-ray reflectivity measurements showed that the layer structure of the coatings could be maintained after annealing at 500 °C and the addition of the Si3N4 interlayer to Ti/TiNx multilayer could improve the thermal stability to 800 °C. 相似文献
995.
针对电子器件的高效冷却问题,对自然循环回路系统内表面加工有方柱形微结构的硅片上FC-72的强化沸腾换热性能进行了实验研究.测试了两个芯片,其表面上的方柱形微结构的边长均为30μm,但高度分别为60 μm和200 μm.沸腾介质的过冷度设为10 K、25 K和35 K.随着壁面过热度的增加,微结构表面芯片上的热流密度急剧增加且临界热流密度时芯片的表面温度低于芯片回路正常工作的临界上限温度85℃,这与其在池沸腾换热中的特点一样.但临界热流密度值与池沸腾情况相比有所降低. 相似文献
996.
997.
998.
999.
测量了Pr(0.5):ZBLAN非晶的吸收光谱,由此利用Judd-Ofelt理论计算了Pr3 离子在材料中的光谱跃迁强度参量,讨论Judd-Ofelt理论在计算Pr3 离子的强度参数时存在的问题.从所得到的强度参数计算预言了此材料中Pr3 离子的各能级之间的自发辐射跃迁速率、荧光分支比和积分发射截面,由所得结果讨论了该材料作为激光材料的前景及可能存在的光子雪崩上转换机制. 相似文献
1000.