全文获取类型
收费全文 | 36731篇 |
免费 | 5366篇 |
国内免费 | 4321篇 |
专业分类
化学 | 21152篇 |
晶体学 | 446篇 |
力学 | 1267篇 |
综合类 | 218篇 |
数学 | 2856篇 |
物理学 | 9093篇 |
无线电 | 11386篇 |
出版年
2024年 | 114篇 |
2023年 | 792篇 |
2022年 | 981篇 |
2021年 | 1293篇 |
2020年 | 1347篇 |
2019年 | 1348篇 |
2018年 | 1147篇 |
2017年 | 1187篇 |
2016年 | 1565篇 |
2015年 | 1731篇 |
2014年 | 2189篇 |
2013年 | 2656篇 |
2012年 | 3059篇 |
2011年 | 3263篇 |
2010年 | 2469篇 |
2009年 | 2404篇 |
2008年 | 2737篇 |
2007年 | 2440篇 |
2006年 | 2210篇 |
2005年 | 1864篇 |
2004年 | 1439篇 |
2003年 | 1200篇 |
2002年 | 1184篇 |
2001年 | 945篇 |
2000年 | 772篇 |
1999年 | 637篇 |
1998年 | 525篇 |
1997年 | 416篇 |
1996年 | 370篇 |
1995年 | 326篇 |
1994年 | 324篇 |
1993年 | 259篇 |
1992年 | 221篇 |
1991年 | 201篇 |
1990年 | 153篇 |
1989年 | 137篇 |
1988年 | 81篇 |
1987年 | 74篇 |
1986年 | 61篇 |
1985年 | 61篇 |
1984年 | 44篇 |
1983年 | 27篇 |
1982年 | 27篇 |
1981年 | 15篇 |
1980年 | 23篇 |
1979年 | 13篇 |
1978年 | 9篇 |
1976年 | 15篇 |
1975年 | 9篇 |
1974年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 93 毫秒
201.
由于悬空侧壁部分的变形状态是圆锥形零件成形的关键,而径向拉应力是实现悬空部分成形的必要条件,同时也是该部分冲压成形成败的关键为此,经力学分析得出了侧壁部分径向拉应力的解析式和造成圆锥形零件破裂的最大径向拉应力的计算式。同时分析了圆锥形零件的成形载荷。 相似文献
202.
铝酸锶铕的合成与发光的研究 总被引:35,自引:2,他引:33
本文详细报导4(SrEu)O·7Al2O3.磷光体的合成及激活剂Eu2+离子浓度、硼酸、五氧化二磷等对磷光体发光强度,发射光谱和激发光谱的影响.讨论了不同Eu2+离子之间的能量传递.测量了不同Eu2+浓度下磷光体的荧光寿命和长余辉特性. 相似文献
203.
Haishan Bu Yanwan Pang Dandan Song Tongyin Yu T. M. Voll George Czornyj B. Wunderlich 《Journal of Polymer Science.Polymer Physics》1991,29(2):139-152
Various approaches to the preparation and verification of single-molecule single crystals are discussed for polyethylene and poly (oxyethylene). Analytic tools are electron microscopy, electron diffraction, and differential scanning calorimetry. The main difficulty in producing a single-molecule single crystal is to keep crystals from joining during growth. 相似文献
204.
Xiaodong Xu Pingxin Song Guoqing Zhou Jun Xu Peizhen Deng 《Solid State Communications》2004,129(11):717-720
Cr4+:YbAG (Cr4+:Yb3Al5O12) crystal with a size up to Φ24 mm×30 mm was grown by the Czochralski method. In the absorption spectrum, there are two absorption bands at 939 and 969 nm, respectively, which are suitable for InGaAs diode laser pumping, and there is an absorption band at 1030 nm, which is suitable for passive Q-switched laser output at 1.03 μm. A broad emission spectrum from 970 to 1100 nm was exhibited from 940 nm wavelength pumping. This crystal is promising as a self-Q-switched laser crystal used for compact, efficient, highly stable, passive self-Q-switched thin chip solid-state lasers. 相似文献
205.
The intent of this paper is to design a high-frequency transformer that is to be incorporated into the DC/DC pulsewidth-modulated switch-mode power supplies by two different technical approaches: a conventional wound-coil magnetic using copper wires, and a planar magnetic with layered copper tracks on laminated printed circuit board. Comparisons will be made between the two approaches in terms of profile: mounting height and surface area, and performance: power losses and efficiency. Other indicators like temperature rise and leakage inductance that causes electromagnetic interference, and cost, materials, and process fluency are also to be looked into. A sandwiched configuration for primary and secondary windings is proposed for the planar type. Issues arising and typical phenomena encountered will be discussed in detail. Primarily, the dominating factor in performance, cost effectiveness, or circuit compactness that restrains the choice of a particular type is to be evaluated. 相似文献
206.
We demonstrated a unified two-band broadband light source based on erbium-doped fiber. The proposed scheme generates high output power at both bands and saves doped-fiber and pump lasers. 相似文献
207.
208.
209.
This paper deals with a model of time-dependent double diffusive convection in Darcy flow. In particular it is concerned with the spatial decay of solutions when the flow is confined to a semi-infinite cylinder. Decay bounds for an energy expression are derived. 相似文献
210.
We prove some basic properties of Donaldson’s flow of surfaces in a hyperkähler 4-manifold. When the initial submanifold is symplectic with respect to one Kähler form and Lagrangian with respect to another, we show that certain kinds of singularities cannot form, and we prove a convergence result under a condition related to one considered by M.-T. Wang for the mean curvature flow. 相似文献