全文获取类型
收费全文 | 2519篇 |
免费 | 287篇 |
国内免费 | 162篇 |
专业分类
化学 | 737篇 |
晶体学 | 24篇 |
力学 | 316篇 |
综合类 | 97篇 |
数学 | 447篇 |
物理学 | 1347篇 |
出版年
2024年 | 6篇 |
2023年 | 22篇 |
2022年 | 61篇 |
2021年 | 62篇 |
2020年 | 54篇 |
2019年 | 39篇 |
2018年 | 56篇 |
2017年 | 83篇 |
2016年 | 106篇 |
2015年 | 74篇 |
2014年 | 115篇 |
2013年 | 155篇 |
2012年 | 96篇 |
2011年 | 139篇 |
2010年 | 129篇 |
2009年 | 150篇 |
2008年 | 166篇 |
2007年 | 180篇 |
2006年 | 191篇 |
2005年 | 170篇 |
2004年 | 129篇 |
2003年 | 114篇 |
2002年 | 96篇 |
2001年 | 81篇 |
2000年 | 68篇 |
1999年 | 58篇 |
1998年 | 57篇 |
1997年 | 47篇 |
1996年 | 43篇 |
1995年 | 33篇 |
1994年 | 34篇 |
1993年 | 23篇 |
1992年 | 19篇 |
1991年 | 25篇 |
1990年 | 20篇 |
1989年 | 15篇 |
1988年 | 14篇 |
1987年 | 7篇 |
1986年 | 10篇 |
1985年 | 8篇 |
1984年 | 3篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1979年 | 1篇 |
1977年 | 2篇 |
1969年 | 1篇 |
1959年 | 2篇 |
排序方式: 共有2968条查询结果,搜索用时 15 毫秒
151.
Juan Peng Yuhan Wei Hanfu Wang Binyao Li Yanchun Han 《Macromolecular rapid communications》2005,26(9):738-743
Summary: We follow the time development of the microdomain structure in symmetric polystyrene‐block‐poly(methyl methacrylate) (PS‐b‐PMMA) diblock copolymer thin films during acetone vapor treatment. Besides the highly ordered nanoscopic spheres or stripes as reported previously, a novel so‐called flower‐like pattern, which comprises six PS spheres and each PS sphere belongs to three “flowers” is formed. This finding is very helpful to discuss the highly ordered nanoscopic sphere formation process.
152.
Axel Rußler Thomas Lange Antje Potthast Thomas Rosenau Elena Berger-Nicoletti Herbert Sixta Paul Kosma 《Macromolecular Symposia》2005,223(1):189-200
Analytical monitoring of xanthation in the viscose process along with xanthate group analysis in the viscose material is a long-debated problem in cellulose chemistry. The task is rendered extremely intricate by the lability of the starting material and the harshness of the reaction medium, which adds to a lack of suitable analytical approaches. In a four-years' endeavor in our lab, a method is being developed which allows to analyze the distribution of xanthate groups in viscoses relative to the anhydroglucose units and along the cellulose chain. In a first step the xanthate groups are stabilized by alkylation, which was optimized towards quantitative conversion. In a second step, the remaining free hydroxyl groups are protected by carbanilation, followed by selective removal of the stabilized xanthate groups. Steps two and three thus generate an inverse image of the initial xanthate pattern. In the forth and fifth step, the liberated hydroxyl groups are methylated, and the carbanilates are removed, so that in the overall process the xanthates were replaced by methyl groups. All reaction steps have been comprehensively tested with regard to completeness of conversion and orthogonality of the protecting groups. 相似文献
153.
E. Yu. Mikhteeva E. G. Savchuk E. A. Tararako E. B. Merkulov V. K. Goncharuk 《Journal of Structural Chemistry》2005,46(6):1082-1085
Images of cleaved surfaces were obtained for 53ZrF4-20BaF2-4LaF3-3AlF3-20NaF (ZBLAN) glasses and fused quartz using an NTMDT atomic force microscope. It is shown that the scatter of particle size depends on the cooling rate and is 21–48.5 Å for the cleaved surface of ZBLAN glass obtained by very fast cooling and 68–172 Å for the cleaved surface of ZBLAN after slow cooling. For cleaved fused quartz, the range is 25-18 Å. 相似文献
154.
Anhydrous disodium phosphonate, Na2HPO3, was prepared by dehydration of its pentahydrate. The crystal structure of Na2HPO3 was solved from high resolution X‐ray powder diffraction data (P21/n; Z = 4; a = 9.6987(1), b = 6.9795(1), c = 5.0561(1) Å, β = 92.37(1)°; V = 341.97(1) Å3). The crystal structure consists of two types of sodium‐oxygen polyhedra, which are connected via common edges and vertices forming layers perpendicular to [100]. These Na(1)‐ and Na(2)‐layers are interlinked via common edges, forming in a 3D‐framework. The resulting topology is providing oxygen arrangements that please the coordinative requirement of phosphorus(III). 相似文献
155.
Chemical and physical analyses of malt, the main ingredient of beer, have been used to predict the concentration of certain volatile compounds in the finished beer.The prediction was done by means of the partial least squares regression (PLS2) in SIMCA. The total data set as well as individual malt clusters were submitted to PLS analysis. Best prediction was obtained by separating the total object matrix in classes according to similarity found by fuzzy pattern recognition (FCV). FCV was also used to separate the beer variables in classes and to select the subset of variables to be predicted.A joint approach of fuzzy pattern recognition to identify groups of samples and SIMCA-PLS2 to predict several dependent variables is suggested as a powerful tool in process-analytical chemistry. 相似文献
156.
Anil Kumar 《Journal of Chemical Sciences》1986,97(1):1-7
The distribution of nickel and cobalt species has been computed, based on the pH-dependent model of Zirino and Yamamoto. The
media used in the pH range of 7 to 9 are natural waters like fresh water, sea water and a mixture of them at different compositions,
at 25°C temperature and 1 atm pressure. In fresh water, both nickel and cobalt dominate as free cations at lower pH, and as
carbonato complexes at higher pH. In sea water, chloro complexes are significant. In mixtures of the two kinds of water, as
might be found in a totally mixed estuary, chloro complexes are important, varying slowly with pH. Sea water plays an important
role in complexation. The present results are in excellent agreement with experimental data obtained by the resin exchange
method. 相似文献
157.
The effects of the ball-to-powder diameter ratio (BPDR) and the shape of the powder particles on EDEM simulation results and time in the planetary ball mill was investigated. BPDR was varied from 1 to 40/3 by changing the powder particle diameter from 8 to 0.6 ?mm. The size and shape of the powder particles do not give a significant change in both the ball motion pattern and simulation results when BPDR is over 20/3. It can be assumed that the kinetic energy of the ball has nothing to do with the size and shape of the powder particle. The simulation time and data size increase exponentially as BPDR increases. The effect of change of the powder particle shape on the calculated data size is not significant, but the more complicated its shape, the longer the simulation time, which is linearly related to the number of spheres composing a particle. 相似文献
158.
159.
160.
本文报道了采用自行设计组装的光声光谱(PAS)测量系统,测定(Zn,Cd)(S,Se)粉末固溶体的带隙与组分的关系;观测ZnS:Mn粉末发光材料的光声谱,确定出Mn~(2+)五个激发态能级的位置;利用光声谱的深度剖面分析,对Cu_xS-ZnS:Mn粉末材料进行分析,获得满意的结果。表明光声谱法对凝聚态物质的研究和监测能提供多方面的信息,是一种极有用的新型光谱测量技术。 相似文献