全文获取类型
收费全文 | 61863篇 |
免费 | 10177篇 |
国内免费 | 1584篇 |
专业分类
化学 | 57736篇 |
晶体学 | 604篇 |
力学 | 1271篇 |
综合类 | 1篇 |
数学 | 4796篇 |
物理学 | 9216篇 |
出版年
2023年 | 160篇 |
2022年 | 347篇 |
2021年 | 787篇 |
2020年 | 1676篇 |
2019年 | 2995篇 |
2018年 | 1433篇 |
2017年 | 1043篇 |
2016年 | 4010篇 |
2015年 | 4092篇 |
2014年 | 4195篇 |
2013年 | 5568篇 |
2012年 | 4778篇 |
2011年 | 4307篇 |
2010年 | 4143篇 |
2009年 | 3903篇 |
2008年 | 4146篇 |
2007年 | 3302篇 |
2006年 | 3080篇 |
2005年 | 3006篇 |
2004年 | 2636篇 |
2003年 | 2352篇 |
2002年 | 2890篇 |
2001年 | 1947篇 |
2000年 | 1804篇 |
1999年 | 741篇 |
1998年 | 302篇 |
1997年 | 304篇 |
1996年 | 371篇 |
1995年 | 264篇 |
1994年 | 268篇 |
1993年 | 280篇 |
1992年 | 222篇 |
1991年 | 177篇 |
1990年 | 190篇 |
1989年 | 165篇 |
1988年 | 120篇 |
1987年 | 116篇 |
1986年 | 97篇 |
1985年 | 142篇 |
1984年 | 95篇 |
1983年 | 77篇 |
1982年 | 104篇 |
1981年 | 111篇 |
1980年 | 67篇 |
1979年 | 94篇 |
1978年 | 73篇 |
1977年 | 76篇 |
1976年 | 82篇 |
1974年 | 67篇 |
1973年 | 72篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
Uhm H.S. Lee P.H. Kim Y.I. Kim J.H. Chang H.Y. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1995,23(4):628-635
A theory is developed for the density profile of low temperature plasmas confined by applied magnetic field and an experiment of the electron-cyclotron-resonance (ECR) plasma is conducted to compare the theoretical prediction and experimental measurements. Due to a large electron mobility along the magnetic field, electrons move quickly out of the system, leaving ions behind and building a space charge potential, which leads to the ambipolar diffusion of ions. In a steady-state condition, the plasma generation by ionization of neutral molecules is in balance with plasma loss due to the diffusion, leading to the electron temperature equation, which is expressed in terms of the plasma size, chamber pressure, and the ionization energy and cross section of neutrals. The power balance condition leads to the plasma density equation, which is also expressed in terms of the electron temperature, the input microwave power and the chamber pressure. It is shown that the plasma density increases, reaches its peak and decreases, as the chamber pressure increases from a small value (0.1 mTorr). These simple expressions of electron temperature and density provide a scaling law of ECR plasma in terms of system parameters. After carrying out an experimental observation, it is concluded that the theoretical predictions of the electron temperature and plasma density agree remarkably well with experimental data 相似文献
62.
Laser welding is one of the most precise welding processes in joining sheet metals. In laser welding, performing real time evaluation of the welding quality is very important to enhance the efficiency of the welding process. In this study, the plasma and spatter, which are generated during laser welding, are measured using UV and IR photodiodes. The factors that influence weld quality are classified into five categories; optimal heat input, slightly low heat input, low heat input, partial joining due to gap mismatch, and nozzle deviation. The data number deviated from reference signals and their standard deviations were also considered to evaluate the qualities. A system was also formulated to perform real time evaluations of the weld quality using a fuzzy multi-feature pattern recognition with the measured signals. 相似文献
63.
64.
65.
66.
Jong Uhn Kim 《Transactions of the American Mathematical Society》2002,354(3):1117-1135
In this paper we discuss an initial-boundary value problem for a stochastic nonlinear equation arising in one-dimensional viscoelasticity. We propose to use a new direct method to obtain a solution. This method is expected to be applicable to a broad class of nonlinear stochastic partial differential equations.
67.
5‐Amino‐4‐methyl‐2‐phenyl‐6‐substitutedfuro[2,3‐d]pyrimidines ( 2a‐c ) were reacted with 2,5‐dimethoxytetrahydrfuran to afford the pyrrolyl derivatives 3a‐c . Compound 3a was chosen as intermediate for the synthesis of poly fused heterocycles incorporated furopyrimidines moiety 4–11 . Some of the synthesized compounds were screened for their antibacterial and antifungal activities. 相似文献
68.
Gauss periods give an exponentiation algorithm that is fast for many finite fields but slow for many other fields. The current paper presents a different method for construction of elements that yield a fast exponentiation algorithm for finite fields where the Gauss period method is slow or does not work. The basic idea is to use elements of low multiplicative order and search for primitive elements that are binomial or trinomial of these elements. Computational experiments indicate that such primitive elements exist, and it is shown that they can be exponentiated fast. 相似文献
69.
Neodymium-substituted Bi4Ti3O12 (BNdT) thin films were prepared by a chemical solution deposition technique on platinum- coated silicon substrates. All of
the samples were annealed at the relatively low temperature of 600 °C by a rapid thermal annealing process in different atmospheres,
such as O2, air, and nitrogen, and vacuum. Irrespective of different annealing atmospheres, all of the BNdT thin films exhibit good
ferroelectric properties, such as a saturated hysteresis loop, good fatigue endurance, and low leakage current density. A
large remanent polarization (Pr) of ∼48 μC/cm2 with an electric field of 240 kV/cm was observed from the BNdT thin film annealed in O2 atmosphere. The BNdT thin films annealed in nitrogen and vacuum, at reduced oxygen partial pressures, exhibit smaller Pr than that annealed in oxygen. The difference of Pr of the BNdT thin films annealed in different atmospheres may originate from differences in the grain sizes and the number
of oxygen vacancies.
PACS 77.55.+f; 77.80.-e; 77.80.Fm; 81.15.-z 相似文献
70.