全文获取类型
收费全文 | 28904篇 |
免费 | 3189篇 |
国内免费 | 3550篇 |
专业分类
化学 | 14031篇 |
晶体学 | 242篇 |
力学 | 1100篇 |
综合类 | 202篇 |
数学 | 2282篇 |
物理学 | 5525篇 |
综合类 | 12261篇 |
出版年
2024年 | 41篇 |
2023年 | 285篇 |
2022年 | 517篇 |
2021年 | 587篇 |
2020年 | 648篇 |
2019年 | 696篇 |
2018年 | 557篇 |
2017年 | 653篇 |
2016年 | 924篇 |
2015年 | 1122篇 |
2014年 | 1405篇 |
2013年 | 1808篇 |
2012年 | 2086篇 |
2011年 | 2177篇 |
2010年 | 1784篇 |
2009年 | 1756篇 |
2008年 | 2059篇 |
2007年 | 1821篇 |
2006年 | 1637篇 |
2005年 | 1605篇 |
2004年 | 1390篇 |
2003年 | 1163篇 |
2002年 | 1454篇 |
2001年 | 1350篇 |
2000年 | 946篇 |
1999年 | 842篇 |
1998年 | 638篇 |
1997年 | 615篇 |
1996年 | 568篇 |
1995年 | 451篇 |
1994年 | 402篇 |
1993年 | 290篇 |
1992年 | 283篇 |
1991年 | 249篇 |
1990年 | 210篇 |
1989年 | 169篇 |
1988年 | 150篇 |
1987年 | 88篇 |
1986年 | 74篇 |
1985年 | 42篇 |
1984年 | 22篇 |
1983年 | 21篇 |
1982年 | 13篇 |
1981年 | 12篇 |
1980年 | 8篇 |
1979年 | 2篇 |
1977年 | 3篇 |
1957年 | 3篇 |
1936年 | 8篇 |
1935年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
121.
微连接用无铅钎料及稀土在钎料中的应用现状 总被引:2,自引:0,他引:2
综述了微连接用无铅钎料的应用研究现状,指出SnAgCu系合金因良好的综合性能将成为最有潜力的锡铅钎料替代品。基于对稀土在钎料中应用研究成果的分析,认为添加微量稀土有望成为改善SnAgCu系无铅钎料蠕变性能的重要途径。充分利用我国丰富的稀土资源开发低Ag的SnAgCuRE系钎料,应当成为中国今后无铅钎料研究开发的重点。 相似文献
122.
Xi Nian FANG Jian Hua WANG 《数学学报(英文版)》2006,22(6):1819-1824
In this paper, we study the extension of isometries between the unit spheres of normed space E and C(Ω). We obtain that any surjective isometry between the unit spheres of normed space E and C(Ω) can be extended to be a linear isometry on the whole space E and give an affirmative answer to the corresponding Tingley's problem (where Ω be a compact metric space). 相似文献
123.
In this paper, we study a micro‐macro model for polymeric fluid. The system involves coupling between the macroscopic momentum equation and a microscopic evolution equation describing the combined effects of the microscopic potential and thermofluctuation. We employ an energetic variation procedure to explore the relation between the macroscopic transport of the particles and the induced elastic stress due to the microscopic structure. For the initial data not far from the equilibrium, we prove the global existence and uniqueness of classical solutions to the system. © 2006 Wiley Periodicals, Inc. 相似文献
124.
A Novel Analytical Approach for Multi-Layer Diaphragm-Based Optical Microelectromechanical-System Pressure Sensors 下载免费PDF全文
An optical microelectromechanical-system (MEMS) pressure sensor based on multi-layer circular diaphragm is described and analysed by using the proposed novel analytical approach and the traditional transfer matrix method. The analytical expressions of the deflection of multi-layer diaphragm and absolute optical reflectance are derived respectively. The influence of residual stress on the deflection of diaphragm is also analysed. Simulation results given by the finite element method are consistent with the ones which are analysed by using the analytical approach. The analytical approach will be helpful to design and fabricate the optical MEMS pressure sensors with multi-layer diaphragm based on Fabry-Perot interferometry. 相似文献
125.
Hua Zhang Nabil A. Amro Robert Elghanian Joseph Fragala 《Applied Surface Science》2006,253(4):1960-1963
A method, combining micro-contact printing (μCP), wet chemical etching and reactive ion etching (RIE), is reported to fabricate microstructures on Si and SiOx. Positive and negative structures were generated based on different stamps used for μCP. The reproducibility of the obtained microstructures shows the methodology reported herein could be useful in Micro-Electro-Mechanical Systems (MEMS), optical and biological sensing applications. 相似文献
126.
127.
根据塑料挤出的特点,在编程实现对型材截面轮廓凸凹性自动判断的基础上,采用射线法与比例间隔法相结合的方法,确定流道入口圆周上型值点的位置.以三次多项式作为流道模腔型曲线的数学模型,依据流线型要求给出的初始、边界条件,得出型曲线的数学方程.构建了挤出模流道的三维参数化曲面模型.有限元分析结果显示,该方法创建的流线型流道模型,其流动稳定性和平顺性都优于直线型流道. 相似文献
128.
Wei Gang SU Huai Jie ZHONG 《数学学报(英文版)》2006,22(2):515-522
This paper introduces the concept of the generalized Riesz operators and the concept of the generalized West decomposition of a general operator which generalizes the definition of the West decomposition of Riesz operators, and proves that the following three statements are equivalent on a general Banach space:
(a) Every generalized Riesz operator has the generalized West decomposition;
(b) Every operator makes strong Stampfli theorem true; Every operator has Apostol's compact correction. 相似文献
129.
We report viscometric data collected in a Couette rheometry on dilute, single‐solvent polystyrene (PS)/dioctyl phthalate (DOP) solutions over a variety of polymer molecular weights (5.5 × 105 ≤ Mw ≤ 3.0 × 106 Da) and system temperatures (288 K ≤ T ≤ 318 K). In view of the essential viscometric features, the current data may be classified into three categories: The first concerns all the investigated solutions at low shear rates, where the solution properties are found to agree excellently with the Zimm model predictions. The second includes all sample solutions, except for high‐molecular‐weight PS samples (Mw ≥ 2.0 × 106 Da), where excellent time–temperature superposition is observed for the steady‐state polymer viscosity at constant polymer molecular weights. No similar superposition applies at a constant temperature but varied polymer molecular weights, however. The third appears to be characteristic of dilute high‐molecular‐weight polymer solutions, for which the effects of temperature on the viscosity curve are further complicated at high shear rates. The implications concerning the relative importance of hydrodynamic interactions, segmental interactions, and chain extensibility with increasing polymer molecular weight, system temperature, and shear rate are discussed. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 787–794, 2006 相似文献
130.