全文获取类型
收费全文 | 12391篇 |
免费 | 2028篇 |
国内免费 | 1748篇 |
专业分类
化学 | 9091篇 |
晶体学 | 157篇 |
力学 | 738篇 |
综合类 | 127篇 |
数学 | 1603篇 |
物理学 | 4451篇 |
出版年
2024年 | 27篇 |
2023年 | 173篇 |
2022年 | 269篇 |
2021年 | 368篇 |
2020年 | 427篇 |
2019年 | 442篇 |
2018年 | 390篇 |
2017年 | 380篇 |
2016年 | 543篇 |
2015年 | 567篇 |
2014年 | 711篇 |
2013年 | 895篇 |
2012年 | 1065篇 |
2011年 | 1213篇 |
2010年 | 873篇 |
2009年 | 891篇 |
2008年 | 1009篇 |
2007年 | 868篇 |
2006年 | 793篇 |
2005年 | 604篇 |
2004年 | 457篇 |
2003年 | 370篇 |
2002年 | 411篇 |
2001年 | 346篇 |
2000年 | 313篇 |
1999年 | 267篇 |
1998年 | 199篇 |
1997年 | 172篇 |
1996年 | 204篇 |
1995年 | 172篇 |
1994年 | 107篇 |
1993年 | 104篇 |
1992年 | 86篇 |
1991年 | 84篇 |
1990年 | 65篇 |
1989年 | 65篇 |
1988年 | 39篇 |
1987年 | 38篇 |
1986年 | 34篇 |
1985年 | 25篇 |
1984年 | 19篇 |
1983年 | 21篇 |
1982年 | 14篇 |
1981年 | 10篇 |
1980年 | 5篇 |
1979年 | 4篇 |
1974年 | 4篇 |
1972年 | 4篇 |
1971年 | 3篇 |
1957年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 47 毫秒
991.
992.
993.
电感耦合等离子体原子发射光谱法测定电解金属锰中硒、铁、硅 总被引:1,自引:0,他引:1
本文采用稀硫酸溶解试样,ICP-AES法同时测定电解金属锰中硒、铁、硅,通过对溶样酸、锰基体以及背景的研究,确定了分析条件。该方法简便具有良好的精密度和准确性,相对标准偏差不大于2.68%,回收率为98%-105%。经t检验与经典法无显著性差异。 相似文献
994.
995.
L. Xiao Y. Q. Li S. F. Wang Z. Fang G. Z. Qiu 《Journal of Thermal Analysis and Calorimetry》2009,95(2):565-569
The principle for the electro-generative simultaneous leaching (EGSL) is applied to simultaneous leaching of pyrite-MnO2 in this paper. A galvanic system for the bio-electro-generative simultaneous leaching (BEGSL) has been set up. The equation
of electric quantity vs. time is used to study the effect of produced sulfur on electro-generative efficiency and quantity. It has been shown that
the resistance decreased in the presence of Acidithiobacillus thiooxidans (A. thiooxidans) with the increase of electro-generative efficiency. The effects of temperature and grain size on rate of ferrous extraction
from pyrite under the conditions of presence and absence of A. thiooxidans were studied, respectively. The changes in the extraction rate of Fe2+ as particle size in presence of A. thiooxidans were more evident than that in the absence, which indicated that the extraction in bio-electro-generative leaching was affected
by particle size remarkably. Around the optimum culture temperature for A. thiooxidans, the bigger change in the conversion rate of Fe2+ was depending on temperature. The transferred charge in BEGSL including part of S0 to sulfate group in the presence of (A. thiooxidans) which is called as biologic electric quantity, and the ratio of biologic electric quantity reached to 58.10% in 72 h among
the all-transferred charge.
Supported by the major state basic research development program (No. 2004CB619204); the National Science Foundation of China
(No. 50374077); the Education Department Foundation of Hunan Province (No. 07D069). 相似文献
996.
In this paper, hybrid bidirectional associative memory neural networks with discrete delays is considered. By ingeniously importing real parameters di > 0(i = 1,2,···,n) which can be adjusted, we establish some new sufficient conditions for the dynamical characteristics of hybrid bidirectional associative memory neural networks with discrete delays by the method of variation of parameters and some analysis techniques. Our results generalize and improve the related results in [10,11]. Our work is significant... 相似文献
997.
The period interaction on diffraction of the blazed transmission gratings is analyzed with a modified extended scalar theory. For one certain period, the lights reflected from the neighboring structures can be refracted by the grating facets and form two extra fields on the bottom facet of blazed transmission gratings. The effects of this period interaction versus several diffraction orders for a fixed fabrication error of blazed transmission gratings with intermediate structures are discussed for both TE and TM polarizations. The results have been compared with those obtained with finite-difference time-domain method. 相似文献
998.
Chu‐Chang Chen Fuh‐Min Fang Yi‐Chao Li Long‐Ming Huang Cheng‐Yang Chung 《国际流体数值方法杂志》2009,60(1):79-93
The unsteady forces on a square cylinder in sinusoidally oscillating flows with non‐zero‐mean velocities are investigated numerically by using a weakly compressible‐flow method with three‐dimensional large eddy simulations. The major parameters in the analysis are Keulegan–Carpenter number (KC) and the ratio between the amplitude and the mean velocities of the approaching flow (AR). By varying the values of KC and AR the resulting drag and lift of the cylinders are analyzed systematically at two selected approaching‐flow attack angles (0 and 22.5°). In the case of the non‐zero attack angle, results show that both the drag and lift histories can be adequately described by Morison equations. However, Morison equations fail to correctly describing the lift history as the attack angle is zero. In addition, when the ratio of AR/KC is near the Strouhal number of the bluff‐body flow, the resulting drag is promoted due to the occurrence of resonance. Based on the results of systematic analyses, finally, the mean and inertia force coefficients at the two selected attack angles are presented as functions of KC and AR based on the Morison relationships. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
999.
A conductive carbon paste electrode (CPE) comprising a new zinc complex of [Zn(C11H15N3)2Cl2] and carbon powder was fabricated by the direct mixing method. The structure of [Zn(C11H15N3)2Cl2] was characterized by X-ray crystallography and elemental analysis. The electrochemical behavior and electrocatalysis of
the new zinc complex modified CPE (Zn–CPE) have been studied in detail. This bulk-modified Zn–CPE displayed good electrocatalytic
activity toward the reduction of the hydrogen peroxide and nitrite. The results are reproducible with a lower detection limit
than reported currently using other modified electrodes. Also, this bulk-modified CPE exhibits remarkable long-term stability,
simple preparation, and inexpensive material, which is important for practical application on electrochemistry sensors. 相似文献
1000.