全文获取类型
收费全文 | 53180篇 |
免费 | 1616篇 |
国内免费 | 319篇 |
专业分类
化学 | 35792篇 |
晶体学 | 469篇 |
力学 | 1597篇 |
综合类 | 2篇 |
数学 | 6757篇 |
物理学 | 10498篇 |
出版年
2022年 | 551篇 |
2021年 | 672篇 |
2020年 | 648篇 |
2019年 | 739篇 |
2018年 | 574篇 |
2017年 | 527篇 |
2016年 | 1192篇 |
2015年 | 977篇 |
2014年 | 1264篇 |
2013年 | 2824篇 |
2012年 | 3164篇 |
2011年 | 3663篇 |
2010年 | 2100篇 |
2009年 | 1781篇 |
2008年 | 3115篇 |
2007年 | 3055篇 |
2006年 | 2933篇 |
2005年 | 2820篇 |
2004年 | 2495篇 |
2003年 | 2026篇 |
2002年 | 1987篇 |
2001年 | 1042篇 |
2000年 | 880篇 |
1999年 | 585篇 |
1998年 | 539篇 |
1997年 | 601篇 |
1996年 | 719篇 |
1995年 | 549篇 |
1994年 | 557篇 |
1993年 | 564篇 |
1992年 | 536篇 |
1991年 | 441篇 |
1990年 | 376篇 |
1989年 | 375篇 |
1988年 | 408篇 |
1987年 | 366篇 |
1986年 | 336篇 |
1985年 | 551篇 |
1984年 | 544篇 |
1983年 | 413篇 |
1982年 | 545篇 |
1981年 | 487篇 |
1980年 | 419篇 |
1979年 | 391篇 |
1978年 | 425篇 |
1977年 | 410篇 |
1976年 | 365篇 |
1975年 | 366篇 |
1974年 | 336篇 |
1973年 | 341篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
11.
Quantitative analysis of polyhexamethylene guanidine (PHMG) oligomers via matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry with an ionic‐liquid matrix
下载免费PDF全文
![点击此处可从《Rapid communications in mass spectrometry : RCM》网站下载免费的PDF全文](/ch/ext_images/free.gif)
12.
Elsye Agustina Jeungchoon Goak Suntae Lee Youngho Seo Jun-Young Park Naesung Lee 《ChemistryOpen》2015,4(5):613-619
Iron catalysts have been used widely for the mass production of carbon nanotubes (CNTs) with high yield. In this study, UV/visible spectroscopy was used to determine the Fe catalyst content in CNTs using a colorimetric technique. Fe ions in solution form red–orange complexes with 1,10-phenanthroline, producing an absorption peak at λ=510 nm, the intensity of which is proportional to the solution Fe concentration. A series of standard Fe solutions were formulated to establish the relationship between optical absorbance and Fe concentration. Many Fe catalysts were microscopically observed to be encased by graphitic layers, thus preventing their extraction. Fe catalyst dissolution from CNTs was investigated with various single and mixed acids, and Fe concentration was found to be highest with CNTs being held at reflux in HClO4/HNO3 and H2SO4/HNO3 mixtures. This novel colorimetric method to measure Fe concentrations by UV/Vis spectroscopy was validated by inductively coupled plasma optical emission spectroscopy, indicating its reliability and applicability to asses Fe content in CNTs. 相似文献
13.
14.
Algebras and Representation Theory - We would like to correct two errors in our paper Involutions of type G2 over a field of characteristic 2 [2]. 相似文献
15.
16.
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
17.
18.
A set of exact conditions is compiled for the purpose of developing and testing approximations for the exchange-correlation energy as a functional of the electron density. Special emphasis is placed upon recently developed density-scaling relationships. Commonly used generalized gradient approximations are compared against several of these conditions. A direct tabular comparison of these functionals (not of calculated properties) with one another is also made. © 1994 John Wiley & Sons, Inc. 相似文献
19.
Using the continuous shape space formalism, we develop an immune system model involving both B lymphocytes and antibody molecules. The binding and cross-linking of receptors on B cells stimulates the cells to divide and, with a lag, to secrete antibody. Using the method of multiple scales, we show how to correctly formulate long-time-scale equations for the population dynamics of B cells, the total antibody concentration, and rate of antibody secretion. We compare our model with previous phenomenological formulations. 相似文献
20.
Aidan Mooney John G. Keating Daniel M. Heffernan 《Chaos, solitons, and fractals》2006,30(5):1088-1097
A digital watermark is a visible, or preferably invisible, identification code that is permanently embedded in digital media, to prove owner authentication and provide protection for documents. Given the interest in watermark generation using chaotic functions a detailed study of one chaotic function for this purpose is performed. In this paper, we present an approach for the generation of watermarks using the logistic map. Using this function, in conjunction with seed management, it is possible to generate chaotic sequences that may be used to create highpass or lowpass digital watermarks. In this paper we provide a detailed study on the generation of optically detectable watermarks and we provide some guidelines on successful chaotic watermark generation using the logistic map, and show using a recently published scheme, how care must be taken in the selection of the function seed. 相似文献