全文获取类型
收费全文 | 21494篇 |
免费 | 2619篇 |
国内免费 | 1469篇 |
专业分类
化学 | 14934篇 |
晶体学 | 254篇 |
力学 | 1306篇 |
综合类 | 108篇 |
数学 | 2521篇 |
物理学 | 6459篇 |
出版年
2024年 | 39篇 |
2023年 | 352篇 |
2022年 | 561篇 |
2021年 | 892篇 |
2020年 | 845篇 |
2019年 | 936篇 |
2018年 | 857篇 |
2017年 | 739篇 |
2016年 | 1202篇 |
2015年 | 979篇 |
2014年 | 1244篇 |
2013年 | 1876篇 |
2012年 | 1869篇 |
2011年 | 1798篇 |
2010年 | 1357篇 |
2009年 | 1181篇 |
2008年 | 1209篇 |
2007年 | 1070篇 |
2006年 | 958篇 |
2005年 | 882篇 |
2004年 | 561篇 |
2003年 | 500篇 |
2002年 | 471篇 |
2001年 | 314篇 |
2000年 | 266篇 |
1999年 | 275篇 |
1998年 | 218篇 |
1997年 | 254篇 |
1996年 | 228篇 |
1995年 | 197篇 |
1994年 | 177篇 |
1993年 | 117篇 |
1992年 | 125篇 |
1991年 | 112篇 |
1990年 | 108篇 |
1989年 | 105篇 |
1988年 | 86篇 |
1987年 | 63篇 |
1986年 | 74篇 |
1985年 | 69篇 |
1984年 | 52篇 |
1983年 | 33篇 |
1982年 | 41篇 |
1981年 | 26篇 |
1980年 | 32篇 |
1979年 | 22篇 |
1978年 | 21篇 |
1975年 | 19篇 |
1974年 | 18篇 |
1972年 | 19篇 |
排序方式: 共有10000条查询结果,搜索用时 531 毫秒
51.
The H-point standard addition method (HPSAM), based on a spectrophotometric measurement for the simultaneous determination of hydrazine and acetylhydrazine, is described. This method is based on the difference between the rates of their reactions with N,N-dimethylaminobenzaldehyde (DAB) in the presence of sodium dodecyl sulfate (SDS) in acidic media. The results showed that hydrazine and acetylhydrazine could be determined simultaneously in the range of 0.020 - 0.70 and 0.20 - 5.0 mg L(-1), respectively. Under the working conditions, the proposed method was successfully applied to the simultaneous determination of hydrazine and acetylhydrazine in several synthetic mixtures and plasma and water samples. 相似文献
52.
53.
The aim of this article is to give some property of continued fraction with matrices arguments, about their convergence and
others applications. At the end of this work, we present a resolution of the Algebraic Riccati Equation by giving an explicit
continued fraction development of its solution.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
54.
本文报道了在Zn0.76Cd0.24Se/ZnSe多量子阱(MQWs)中,用不同的Ar+激光线激发,观察到了共振增强的喇曼散射。首次在室温和77K的条件下,用Ar+的457.9nm谱线激发,观察到分别来自ZnSe垒层和Zn0.76Cd0.24Se阱层的限制纵光学声子模(LO)的喇曼散射,并对上述不同的光学模的起因进行了分析。 相似文献
55.
ELSO is an environment for the solution oflarge-scale optimization problems. With ELSO the user is required to provide only code for the evaluation of a partially separable function. ELSO exploits the partialseparability structure of the function to computethe gradient efficiently using automatic differentiation.We demonstrate ELSO's efficiency by comparing thevarious options available in ELSO.Our conclusion is that the hybrid option in ELSOprovides performance comparable to the hand-coded option, while having the significantadvantage of not requiring a hand-coded gradient orthe sparsity pattern of the partially separable function.In our test problems, which have carefully coded gradients,the computing time for the hybrid AD option is within a factor of two of thehand-coded option. 相似文献
56.
57.
The stability of Ochratoxin A during its extraction using different extraction techniques has been evaluated. Microwave-assisted extraction and pressurised liquid extraction, in addition to two other reference methods of extraction, i.e. ultrasound-assisted and magnetic stirring-assisted extraction, were evaluated. The effect of extraction temperature using the cited techniques was checked.The results show that Ochratoxin A can be extracted using microwave-assisted extraction at temperatures up to 150 °C without degradation. Pressurised liquid extraction can be used at temperatures up to 100 °C, for extraction times of less than 30 min. Further, both ultrasound-assisted extraction and magnetic stirring extraction can be applied at temperatures up to 65 °C.High-performance liquid chromatography combined with fluorescence detection using a Chromolith RP-18e column at a flow rate of 5 mL min−1 was used to quantify the Ochratoxin A. The retention time for the Ochratoxin A was 1.3 min. The limits of detection (LOD) and of quantification (LOQ) were 0.03 and 0.10 μg L−1, respectively. 相似文献
58.
59.
A nanoscale
multivalent platinum drug based on a poly(amidoamine) [PAMAM] dendrimer (generation
4.5, carboxylate surface) has been synthesized and fully characterized using
a variety of spectroscopic, chromatographic and thermal methods. Treatment
of the dendrimer with an aqueous solution containing an excess diaquo(cis-1,2-diaminocyclohexane)platinum(II) produces
a conjugate containing approximately forty (diaminocyclohexane)platinum(II)
moieties at the surface of the dendrimer. This material undergoes smooth two-stage
thermal decomposition to provide residual platinum oxide reflecting the platinum
loading in the drug. 相似文献
60.
On Polynomial Functions over Finite Commutative Rings 总被引:1,自引:0,他引:1
Jian Jun JIANG Guo Hua PENG Qi SUN Qi Fan ZHANG 《数学学报(英文版)》2006,22(4):1047-1050
Let R be an arbitrary finite commutative local ring. In this paper, we obtain a necessary and sufficient condition for a function over R to be a polynomial function. Before this paper, necessary and sufficient conditions for a function to be a polynomial function over some special finite commutative local rings were obtained. 相似文献