全文获取类型
收费全文 | 37278篇 |
免费 | 5493篇 |
国内免费 | 3658篇 |
专业分类
化学 | 25779篇 |
晶体学 | 358篇 |
力学 | 2227篇 |
综合类 | 241篇 |
数学 | 4280篇 |
物理学 | 13544篇 |
出版年
2024年 | 111篇 |
2023年 | 759篇 |
2022年 | 1224篇 |
2021年 | 1401篇 |
2020年 | 1443篇 |
2019年 | 1329篇 |
2018年 | 1151篇 |
2017年 | 1068篇 |
2016年 | 1610篇 |
2015年 | 1634篇 |
2014年 | 2005篇 |
2013年 | 2579篇 |
2012年 | 3253篇 |
2011年 | 3210篇 |
2010年 | 2180篇 |
2009年 | 2050篇 |
2008年 | 2203篇 |
2007年 | 1961篇 |
2006年 | 1842篇 |
2005年 | 1539篇 |
2004年 | 1301篇 |
2003年 | 984篇 |
2002年 | 894篇 |
2001年 | 738篇 |
2000年 | 691篇 |
1999年 | 829篇 |
1998年 | 693篇 |
1997年 | 636篇 |
1996年 | 705篇 |
1995年 | 603篇 |
1994年 | 551篇 |
1993年 | 470篇 |
1992年 | 449篇 |
1991年 | 364篇 |
1990年 | 324篇 |
1989年 | 236篇 |
1988年 | 216篇 |
1987年 | 198篇 |
1986年 | 141篇 |
1985年 | 157篇 |
1984年 | 135篇 |
1983年 | 116篇 |
1982年 | 80篇 |
1981年 | 59篇 |
1980年 | 49篇 |
1979年 | 33篇 |
1978年 | 26篇 |
1976年 | 27篇 |
1975年 | 31篇 |
1974年 | 23篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Controllable Goos–Hänchen shift of a light beam reflected from the colloidal ferrofluids is investigated by using the stationary-phase method. It is found that the Goos–Hänchen shift can be easily controlled by the local He factor and the volume factor. Using this scheme, the peak value, the peak position and the width of the Goos–Hänchen shift can all be controlled by adjusting the external magnetic field for a fixed configuration, which also provides a possibility for obtaining larger negative Goos–Hänchen shift by changing the external controlling field. Our results have potential applications in optical devices. 相似文献
992.
这里从泛系观引入一种新型的哲学与数学研究,包括在泛系框架下发展哲学七论与数学和一些第二第三哲学以及对事理、物理、技理、医理与战理的某些应用. 相似文献
993.
A theoretical study of a structural transition of secondary phase oxide nanorods in epitaxial YBa2Cu3O7?δ films on vicinal SrTiO3 substrates is presented. Two possible types of film/substrate interface are considered, with one assuming complete coherence, while the other is defective as manifested by the presence of antiphase grain boundaries. Only in the former case does the increase of the vicinal angle of the substrate lead to a substantial change of the strain field in the film, resulting in a transition of the nanorod orientation from the normal to the in-plane direction of the film. The calculated threshold vicinal angle for the onset of the transition and lattice deformation of the YBa2Cu3O7?δ film due to the inclusion of the nanorods is in very good agreement with experimental observations. This result sheds lights on the understanding of the role of the film/substrate lattice mismatch in controlling self-assembly of dopant nanostructures in matrix films. 相似文献
994.
Yueh-Heng Li Guan-Bang Chen Fang-Hsien Wu Tsarng-Sheng Cheng Yei-Chin Chao 《Proceedings of the Combustion Institute》2013,34(2):2253-2259
Hydrogen–air combustion characteristics of a small-scale reactor with different catalyst layouts and configurations are experimentally and numerically investigated. Four different platinum catalyst layouts are used to investigate the effect of catalyst segmentation on combustion performance. It is found that combustion phenomena are strongly related to the variations of inflow velocity, equivalence ratio, and length of catalyst segment. The existence of hetero- and homogeneous reactions in the combustor relies on sufficient catalytically induced exothermicity as well as sufficient hydrogen in the remaining mixture. Besides, the multi-segment catalyst with cavities appreciably extends the stable operating range of catalytic combustion in a small-scale combustor for a wide range of inflow velocities. Nevertheless, gas-phase reaction can be sustained and anchored by the existence of cavity in a small-scale system. The reactor with proposed mechanisms can be applied to various small-scale power, heat generation, and propulsion systems. 相似文献
995.
Chang Wen Minghou Xu Dunxi Yu Changdong Sheng Hongwei Wu Ping’an Zhang Yu Qiao Hong Yao 《Proceedings of the Combustion Institute》2013,34(2):2383-2392
The formation of PM10 (particles less than or equal to 10 μm in aerodynamic diameter) during char combustion in both air-firing and oxy-firing was investigated. Three Chinese coals of different ranks (i.e., DT bituminous coal, CF lignite, and YQ anthracite) were devolatilized at 1300 °C in N2 and CO2 atmosphere, respectively, in a drop tube furnace (DTF). The resulting N2-chars and CO2-chars were burned at 1300 °C in both air-firing (O2/N2 = 21/79) and oxy-firing (O2/CO2 = 21/79). The effects of char properties and combustion conditions on PM10 formation during char combustion were studied. It was found that the formation modes and particle size distribution of PM10 from char combustion whether in air-firing or in oxy-firing were similar to those from pulverized coal combustion. The significant amounts of PM0.5 (particles less than or equal to 0.5 μm in aerodynamic diameter) generated from combustion of various chars suggested that the mineral matter left in the chars after coal devolatilization still had great contributions to the formation of ultrafine particles even during the char combustion stage. The concentration of PM10 from char combustion in oxy-firing was generally less than that in air-firing. The properties of the CO2-chars were different from those of the N2-chars, which was likely due to gasification reactions coal particles experienced during devolatilization in CO2 atmosphere. Regardless of the combustion modes, PM10 formation in combustion of N2-char and CO2-char from the same coal was found to be significantly dependent on char properties. The difference in the PM10 formation behavior between the N2-char and CO2-char was coal-type dependent. 相似文献
996.
无挠左(右)Artin环是拟Frobenius环乌成伟(吉林工学院基础部,长春130012)关键词内积,左(右)内零化子,自内射环.分类号AMS(1991)16D50/CCLO153.3设R为有1的左(右)Artin环,如果对于任一整数洲与r∈R,m... 相似文献
997.
998.
LiuYanyan WuJun 《分析论及其应用》2003,19(4):342-354
A set is called regular if its Hausdorff dimension and upper box-counting dimension coincide. In this paper, we prove that the random self-con formal set is regular almost surely. Also we determine the dimen-sions for a class of random self-con formal sets. 相似文献
999.
将等离子焊接(PAW)电弧和钨极氩弧焊(TIG)电弧串接,相对作用于工件的正反面形成双面电弧焊接(DSAW)系统,可以引导焊接电流沿工件厚度方向流过小孔,补偿等离子电弧穿透工件时消耗的能量,以有效地提高等离子弧的穿透能力.综合考虑影响双面电弧焊接正反面熔池几何形状的力学因素,建立了熔池表面变形的控制方程,以此为基础并采用帖体曲线坐标系建立了DSAW焊接传热的数学模型,分析了DSAW,PAW焊接传热的差异,从传热的角度解释了DSAW焊接熔深增加的原因.焊接工艺实验表明,计算结果与实测结果吻合良好.
关键词:
双面电弧焊接(DSAW)
传热模型
熔池表面变形模型 相似文献
1000.
利用脉宽约为50ps的类镍银139nm软X射线激光作为探针,探测由脉宽80ps的驱动激光打C8H8靶产生的等离子体在1ns后的电子密度分布信息,获得了清晰的莫尔条纹图像.对结果的处理,给出了峰值电子密度为11×1021cm-3,并对在靶面附近莫尔条纹的消失现象作了初步解释
关键词:
软X射线激光探针 莫尔条纹 等离子体电子密度 相似文献