全文获取类型
收费全文 | 2325篇 |
免费 | 313篇 |
国内免费 | 192篇 |
专业分类
化学 | 1494篇 |
晶体学 | 43篇 |
力学 | 98篇 |
综合类 | 28篇 |
数学 | 273篇 |
物理学 | 894篇 |
出版年
2024年 | 5篇 |
2023年 | 25篇 |
2022年 | 64篇 |
2021年 | 55篇 |
2020年 | 86篇 |
2019年 | 76篇 |
2018年 | 70篇 |
2017年 | 96篇 |
2016年 | 95篇 |
2015年 | 96篇 |
2014年 | 141篇 |
2013年 | 170篇 |
2012年 | 129篇 |
2011年 | 198篇 |
2010年 | 103篇 |
2009年 | 122篇 |
2008年 | 103篇 |
2007年 | 147篇 |
2006年 | 133篇 |
2005年 | 124篇 |
2004年 | 90篇 |
2003年 | 95篇 |
2002年 | 94篇 |
2001年 | 62篇 |
2000年 | 58篇 |
1999年 | 82篇 |
1998年 | 51篇 |
1997年 | 42篇 |
1996年 | 36篇 |
1995年 | 38篇 |
1994年 | 27篇 |
1993年 | 21篇 |
1992年 | 29篇 |
1991年 | 8篇 |
1990年 | 12篇 |
1989年 | 12篇 |
1988年 | 5篇 |
1987年 | 6篇 |
1986年 | 5篇 |
1985年 | 7篇 |
1984年 | 3篇 |
1983年 | 3篇 |
1981年 | 4篇 |
1980年 | 1篇 |
1966年 | 1篇 |
排序方式: 共有2830条查询结果,搜索用时 15 毫秒
11.
Pyrolysis ammonia chemical ionization (PyCI) mass spectrometry was performed on hy-droxyethyl-, hydroxypropyl-,methyl-, hydroxypropylmethyl-, and ethylhydroxyethyl cel-luloses. The mass peaks in the PyCI mass spectra of these cellulose ethers could be assigned to the ions of pyrolytic dissociation products which form via the [2 + 2 + 2] cycloreversion and the Ei elimination pyrolysis pathway. Structural information about the residual amount of nonderivatized cellulose, the relative chain length distributions of the substituents in hydroxyalkyl celluloses, and the end-capping of hydroxyalkyl substituents by alkyl groups in the mixed cellulose ethers is obtained. Interference of secondary pyrolysis products in the PyCI mass spectra is found to be of minor importance, especially in the lower mass regions. © 1995 John Wiley & Sons, Inc. 相似文献
12.
The mechanism of the slowly opened Q-switch operation was investigated thoroughly. Maximum energy extraction from the resonator
could be optimized, and the smallest output beam divergence could be achieved. In this article, we present a detailed analysis
that has numerically verified the mode-selection mechanism in the slowly opened Q-switch operation, and the degree of the
smaller output laser beam divergence that has been achieved. The mechanism of the slowly opened Q-switch operation is the
inherent advantage of the passive saturable absorber in this operation. We can use the maximum energy extraction and the smallest
output beam divergence results of the slowly opened Q-switch operation to design and optimize various passive saturable absorbers:
plastic dye sheets, LiF:F2− color center crystals, Cr4+: YAG crystals, RG1000 color glass filters, and the single crystal semiconductor saturable absorber wafers that are in developed
in our microchip laser systems. 相似文献
13.
Kozo Matsumoto Junichi Nakashita Hideki Matsuoka 《Journal of polymer science. Part A, Polymer chemistry》2006,44(15):4696-4707
Diblock copolymer poly(1,1,3,N,N′‐pentamethyl‐3‐vinylcyclodisilazane)‐block‐polystyrene (polyVSA‐b‐polySt) and triblock copolymer poly(1,1,3,N,N′‐pentamethyl‐3‐vinylcyclodisilazane)‐block‐polystyrene‐block‐poly(1,1,3,N,N′‐pentamethyl‐3‐vinylcyclodisilazane) (polyVSA‐b‐polySt‐b‐polyVSA), consisting of silazane and nonsilazane segments, were prepared by the living anionic polymerization of 1,1,3,N,N′‐pentamethyl‐3‐vinylcyclodisilazane and styrene. PolyVSA‐b‐polySt formed micelles having a poly(1,1,3,N,N′‐pentamethyl‐3‐vinylcyclodisilazane) (polyVSA) core in N,N‐dimethylformamide, whereas polyVSA‐b‐polySt and polyVSA‐b‐polySt‐b‐polyVSA formed micelles having a polyVSA shell in n‐heptane. The micelles with a polyVSA core were core‐crosslinked by UV irradiation in the presence of diethoxyacetophenone as a photosensitizer, and the micelles with a polyVSA shell were shell‐crosslinked by UV irradiation in the presence of diethoxyacetophenone and 1,6‐hexanedithiol. These crosslinked micelles were pyrolyzed at 600 °C in N2 to give spherical ceramic particles. The pyrolysis process was examined by thermogravimetry and thermogravimetry/mass spectrometry. The morphologies of the particles were analyzed by atomic force microscopy and transmission electron microscopy. The chemical composition of the pyrolysis products was analyzed by X‐ray fluorescence spectroscopy and Raman scattering spectroscopy. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4696–4707, 2006 相似文献
14.
兖州高硫煤的加氢热解脱硫及脱硫动力学 总被引:5,自引:1,他引:5
在加压热天平上,考察了氢气和氮扬气氛下高硫煤的热解脱硫。利用气相色谱在线分析研究了硫化氢氢气的逸出规律。结果表明,加氢热解比氮气下的热解有着更显著的脱友作用,脱硫率可达90%以上。而且加氢热解下65%的脱除硫转化为气相硫化氢,而氮气下热解是有80%的硫转化为液相。 相似文献
15.
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
16.
Pappa A. Kyriakou S. Mikedi K. Tzamtzis N. Statheropoulos M. 《Journal of Thermal Analysis and Calorimetry》2004,78(2):415-426
The design, the abilities and a characteristic application of an in-house made interface for combining thermogravimetry (TG)
with mass spectrometry (MS) are presented. The TG-MS interface consists mainly of three co-axial tubes. The position of the
intermediate tube was determined after calculation of the temperature profile at the TG furnace exit tube. The inner tube
position was determined taking into consideration its protection against condensation of heavy molecules and the time delay
for the transfer of the evolved gases. This interface allows either continuous sampling and transferring of the evolved gases
from the TG to the MS or repetitive introduction of short sampling pulses of TG evolved gases to MS. The interface is capable
of coupling various commercial instruments. In the present work two configurations of this interface are demonstrated. Finally
an example of application of this interface on forest fuel pyrolysis is presented.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
17.
18.
Slow pyrolysis of walnut shell which is a cheap and abundantly available solid waste was carried out using thermogravimetric
analysis. The effects of raw material heating rate on the pyrolysis properties and kinetic parameters were investigated. A
two-step consecutive reaction model were used to simulate the pyrolysis process. The kinetic parameters were established by
using the pattern search method. Comparison between experimental data and the model prediction indicated that the two-step
consecutive reaction model can better describe the slow pyrolysis of walnut shell as the formation of an intermediate during
the pyrolysis process was taken into account. 相似文献
19.
E. A. Chernyshev T. L. Krasnova E. S. Abramova E. A. Abronin A. B. Petrunin A. P. Sergeev 《Russian Chemical Bulletin》1997,46(9):1582-1585
Pyrolysis of trichlorosilane (TCS) and copyrolysis of TCS with 1,3-butadiene were studied. The enthalpies and activation energies
for the reactions of the products of TCS pyrolysis were found by quantum-chemical calculations. A direct study of the pyrolysis
of TCS by mass spectrometry was carried out. Based on the thermochemical parameters found by quantum-chemical calculations
and on the results of GLC and mass spectrometry concerning the composition of the pyrolysis products, it was concluded that
the pyrolysis of TCS follows a scheme that includes formation of radicals and silylenes.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1659–1662, September, 1997. 相似文献
20.
Thermal degradation of wood treated with guanidine compounds in air: Flammability study 总被引:1,自引:0,他引:1
Wood has been treated with guanidine phosphate, guanidine nitrate, guanidine carbonate and guanidine chloride to impart flame retardancy. The samples were subjected to differential thermal analysis (DTA) and thermogravimetry (TG) from ambient temperature to 800°C in air to study their thermal behaviors. From the resulting data, kinetic parameters for different stages of thermal degradation were obtained following the method of Broido. For the decomposition of wood and flame retardant wood, the activation energy was found to decrease from 116 to 54 kJ mol–1; the char yield was found to increase from 5.6 to 34.9%, LOI from 18 to 41.5, which indicated that the flame retardancy of treated wood was improved. Effects of the different compounds on the degradation and flammability of wood have also been proposed.This revised version was published online in November 2005 with corrections to the Cover Date. 相似文献