全文获取类型
收费全文 | 17401篇 |
免费 | 1210篇 |
国内免费 | 1030篇 |
专业分类
化学 | 7625篇 |
晶体学 | 54篇 |
力学 | 829篇 |
综合类 | 76篇 |
数学 | 373篇 |
物理学 | 2885篇 |
综合类 | 7799篇 |
出版年
2024年 | 58篇 |
2023年 | 167篇 |
2022年 | 376篇 |
2021年 | 383篇 |
2020年 | 475篇 |
2019年 | 392篇 |
2018年 | 423篇 |
2017年 | 532篇 |
2016年 | 622篇 |
2015年 | 662篇 |
2014年 | 779篇 |
2013年 | 988篇 |
2012年 | 1121篇 |
2011年 | 1002篇 |
2010年 | 767篇 |
2009年 | 765篇 |
2008年 | 781篇 |
2007年 | 996篇 |
2006年 | 875篇 |
2005年 | 769篇 |
2004年 | 718篇 |
2003年 | 646篇 |
2002年 | 613篇 |
2001年 | 495篇 |
2000年 | 531篇 |
1999年 | 500篇 |
1998年 | 383篇 |
1997年 | 443篇 |
1996年 | 339篇 |
1995年 | 337篇 |
1994年 | 267篇 |
1993年 | 210篇 |
1992年 | 215篇 |
1991年 | 191篇 |
1990年 | 176篇 |
1989年 | 147篇 |
1988年 | 132篇 |
1987年 | 92篇 |
1986年 | 56篇 |
1985年 | 42篇 |
1984年 | 45篇 |
1983年 | 21篇 |
1982年 | 26篇 |
1981年 | 14篇 |
1980年 | 18篇 |
1979年 | 13篇 |
1978年 | 8篇 |
1977年 | 5篇 |
1976年 | 5篇 |
1974年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
81.
用裂解气相色谱法研究PMR型聚酰亚胺前体在反应中的化学变化过程,以裂解产物醇和环戊二烯的生成率表示酰胺化或酰亚胺化及交联的程度,结果表明,酰胺化或酰亚胺化在50℃以下不发生,在180~220℃完成,降冰片烯端基在150℃以下不发生交联反应,在280℃,10~18小时可完成交联反应。 相似文献
82.
Zhengping Hao Lidun An Junling Zhou Hongli Wang 《Reaction Kinetics and Catalysis Letters》1996,59(2):295-300
Supported gold catalyst for eliminating hydrogen from CO2 feed gas in the production of urea is found to be superior to other industrial catalysts (e.g. Pt/Al2O3 and PdPt/Al2O3) in catalytic activity and resistance to sulfur poisoning. 相似文献
83.
Chun H Dybtsev DN Kim H Kim K 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(12):3521-3529
A systematic modulation of organic ligands connecting dinuclear paddle-wheel motifs leads to a series of isomorphous metal-organic porous materials that have a three-dimensional connectivity and interconnected pores. Aromatic dicarboxylates such as 1,4-benzenedicarboxylate (1,4-bdc), tetramethylterephthalate (tmbdc), 1,4-naphthalenedicarboxylate (1,4-ndc), tetrafluoroterephthalate (tfbdc), or 2,6-naphthalenedicarboxylate (2,6-ndc) are linear linkers that form two-dimensional layers, and diamine ligands, 4-diazabicyclo[2.2.2]octane (dabco) or 4,4'-dipyridyl (bpy), coordinate at both sides of Zn(2) paddle-wheel units to bridge the layers vertically. The resulting open frameworks [Zn(2)(1,4-bdc)(2)(dabco)] (1), [Zn(2)(1,4-bdc)(tmbdc)(dabco)] (2), [Zn(2)(tmbdc)(2)(dabco)] (3), [Zn(2)(1,4-ndc)(2)(dabco)] (4), [Zn(2)(tfbdc)(2)(dabco)] (5), and [Zn(2)(tmbdc)(2)(bpy)] (8) possess varying size of pores and free apertures originating from the side groups of the 1,4-bdc derivatives. [Zn(2)(1,4-bdc)(2)(bpy)] (6) and [Zn(2)(2,6-ndc)(2)(bpy)] (7) have two- and threefold interpenetrating structures, respectively. The non-interpenetrating frameworks (1-5 and 8) possess surface areas in the range of 1450-2090 m(2)g(-1) and hydrogen sorption capacities of 1.7-2.1 wt % at 78 K and 1 atm. A detailed analysis of the sorption data in conjunction with structural similarities and differences concludes that porous materials with straight channels and large openings do not perform better than those with wavy channels and small openings in terms of hydrogen storage through physisorption. 相似文献
84.
J. A. Poulis C. H. Massen E. Robens G. Reichenauer 《Journal of Thermal Analysis and Calorimetry》2004,76(2):583-592
On the basis of a molecular model for adsorption kinetics Jäntti introduced a method to calculate equilibriums shortly after a change of the pressure of the sorptive gas. In the present paper we show that this method is useful in many more situations than those intended originally. 相似文献
85.
A wide variety of liquid streams are generated as
part of the process research and development effort. Frequently these streams
are drummed off, either as intermediates that must be held for processing
or as wastes that must be sent off-site for disposal. Because of the long
times and low concentrations often involved, current thermoanalytical techniques
were inadequate to detect the potential of streams to generate gas. A custom-made
apparatus, the gas evolution test cell (GETC), was developed in the Merck
Research Laboratories to measure the gas generation potential of various streams
under precisely defined conditions, is the key innovation for the development
of a quantitative gas-generation test method. 相似文献
86.
脱蜡剂DF-1是一种含多种有机成分的碳氢化合物,经气相色谱-红外光谱联用分析后,确定了这些组分的组成与含量。 相似文献
87.
Summary Inverse gas chromatography is shown to be suitable for the study of the oxidation of vegetable oils. With air as carrier gas
characteristic plots of retention index versus time are obtained for hydroxylic test solutes that are consistent with the
oxidation behaviour of vegetable oils. Shifts of retention are found to be accompanied by changes of column efficiency due
to the oxidative crosslinking of polyunsaturated vegetable oils. The technique also leads to useful information concerning
the oxidation of antioxidant inhibited systems.
Presented at the 15th International Symposium on Chromatography, Nürnberg, October 1984 相似文献
88.
89.
Dynamic Interfacial Tension Behavior of Water/Oil Systems Containing In situ-Formed Surfactants 总被引:1,自引:0,他引:1
Time-dependent interfacial tension (IFT) has been investigated for an interfacially reactive immiscible system composed of model-acidified oil and alkaline water. The acidified oil was composed of either lauric acid or linoleic acid dissolved in n-dodecane. Drop volume tensiometry was employed to measure the interfacial tension between the two phases. In the case of lauric acid, the IFT value was found to decrease sharply with increasing alkali concentration, even at low drop formation times. In the case of linoleic acid, the IFT decrease with the drop formation time was more gradual, especially at low alkali concentration. The rate of formation of the interfacial area was also found to be dependent on alkali concentration. 相似文献
90.