全文获取类型
收费全文 | 3558篇 |
免费 | 641篇 |
国内免费 | 418篇 |
专业分类
化学 | 2740篇 |
晶体学 | 39篇 |
力学 | 396篇 |
综合类 | 41篇 |
数学 | 477篇 |
物理学 | 924篇 |
出版年
2024年 | 12篇 |
2023年 | 57篇 |
2022年 | 126篇 |
2021年 | 160篇 |
2020年 | 195篇 |
2019年 | 175篇 |
2018年 | 137篇 |
2017年 | 162篇 |
2016年 | 208篇 |
2015年 | 165篇 |
2014年 | 217篇 |
2013年 | 306篇 |
2012年 | 253篇 |
2011年 | 258篇 |
2010年 | 211篇 |
2009年 | 209篇 |
2008年 | 202篇 |
2007年 | 203篇 |
2006年 | 187篇 |
2005年 | 170篇 |
2004年 | 162篇 |
2003年 | 185篇 |
2002年 | 120篇 |
2001年 | 88篇 |
2000年 | 75篇 |
1999年 | 51篇 |
1998年 | 50篇 |
1997年 | 58篇 |
1996年 | 31篇 |
1995年 | 39篇 |
1994年 | 31篇 |
1993年 | 14篇 |
1992年 | 13篇 |
1991年 | 16篇 |
1990年 | 14篇 |
1989年 | 9篇 |
1988年 | 11篇 |
1987年 | 6篇 |
1986年 | 6篇 |
1985年 | 4篇 |
1984年 | 4篇 |
1983年 | 5篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1963年 | 1篇 |
1959年 | 1篇 |
1936年 | 1篇 |
排序方式: 共有4617条查询结果,搜索用时 15 毫秒
111.
Thomas J. Gedemer 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(1):95-104
It is difficult to estimate the degree of thermal degradation which has taken place in complex parts composed of cellulosics and polymeric insulation unless complete failure has occurred. There is a definite need for a parameter which can quickly and easily measure the relative degree of thermal attack on organic insulation subjected to various known environmental and processing conditions. This paper reports preliminary work using derivative thermogravimetry to perform this function. Derivative thermogravimetric analysis (TGA) was used to produce a value, TGA Index, related to the peak height of the major TGA derivative signal. This TGA Index was found to correlate with the copper number of insulating paper measured after thermal degradation. The application of TGA Index to evaluation of polymer degradation after thermal shock, water absorption, and accelerated UV attack is also discussed. Finally, preliminary studies on the use of derivative TGA to evaluate coatings exposed to various outdoor environments around the country are reported. 相似文献
112.
Polymer-bound alkylthiopurine and -pyrimidine bases were prepared and used as the polymeric reagents for the reactions of nitrile, olefin, and enone formation. The corresponding low molecular weight compounds were also prepared for comparison. Differences in the reactivity of these reagents were related to the change in tautomerism of the purine and pyrimidine moieties. 相似文献
113.
Attapulgite grafted with polystyrene via a simultaneous reverse and normal initiation atom transfer radical polymerization
下载免费PDF全文
![点击此处可从《Journal of polymer science. Part A, Polymer chemistry》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Haicun Yang Hongting Pu Fanghong Gong 《Journal of polymer science. Part A, Polymer chemistry》2016,54(11):1508-1516
The surface grafting of attapulgite (ATP) with polystyrene (PS) was established via a simultaneous reverse and normal initiation atom transfer radical polymerization (SR&NIATRP). 4‐(chloromethyl)phenyltrimethoxysilane (CMPTMS) chemical bounded on the surface of ATP (ATP‐Cl, Cl‐I) was prepared via one‐step self‐assembly. SR&NI ATRP of styrene was conducted using CuCl2 complex tris(2‐(dimethylamino)ethyl)amine (Me6‐TREN) as the catalytic system, initiated by 2,2‐azobis(isobutyronitrile) (AIBN) and ATP‐Cl. FT‐IR, XRD, XPS, TGA and TEM data were consistent with the grafting of benzyl chloride groups and PS chains on ATP surface. The controllability of polymerization was investigated by the kinetics behavior under different molar ratio of AIBN and CuCl2. The obtained polymer possessed a uniform distribution of molecular weights with a lower polydispersity index of 1.2~1.4. The relationship between polymerization on the surface of ATP and in solution was discussed in detail based on TGA data of hybrid particles and GPC trace of free polymer in solution. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1508–1516 相似文献
114.
We present novel inorganic–organic hybrid catalyst to accomplish domino multi‐component reaction (MCR) for synthesis of 3‐amino‐2′‐oxospiro[benzo[c]pyrano[3,2‐a]phenazine‐1,3′‐indoline]‐2‐carbonitrile/carboxylate derivatives. This methodology offers remarkable development by easy production of H3PMo12O40/Hyd‐SBA‐15 in regard to solving the problem of using harsh catalysts, also it demonstrates to be impressive and environmentally friendly in term of low reaction times and high yields. 相似文献
115.
P. Glaister 《International Journal of Mathematical Education in Science & Technology》2013,44(1):110-117
Three techniques for determining a straight line fit to data are compared. The methods are applied to a range of datasets containing one or more outliers, and to a specific example from the field of chemistry. For the method which is the most resistant to the presence of outliers, a Microsoft Excel spreadsheet, as well as two Matlab routines, are included which can be used to determine the slope and intercept estimates. 相似文献
116.
《数学季刊》2016,(2):178-188
Statistical inference is developed for the analysis of generalized type-II hybrid censoring data under exponential competing risks model. In order to solve the problem that approximate methods make unsatisfactory performances in the case of small sample size, we establish the exact conditional distributions of estimators for parameters by conditional moment generating function(CMGF). Furthermore, confidence intervals(CIs) are constructed by exact distributions, approximate distributions as well as bootstrap method respectively, and their performances are evaluated by Monte Carlo simulations. And finally, a real data set is analyzed to illustrate all the methods developed here. 相似文献
117.
118.
Dr. Sarvesh K. Srivastava Prof. Dr. Oliver G. Schmidt 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(27):9072-9076
A proof‐of‐concept design for autonomous, self‐propelling motors towards value‐added product synthesis and separation is presented. The hybrid motor design consists of two distinct functional blocks. The first, a sodium borohydride (NaBH4) granule, serves both as a reaction prerequisite for the reduction of vanillin and also as a localized solid‐state fuel in the reaction mixture. The second capping functional block consisting of a graphene–polymer composite serves as a hydrophobic matrix to attract the reaction product vanillyl alcohol (VA), resulting in facile separation of this edible value‐added product. These autonomously propelled motors were fabricated at a length scale down to 400 μm, and once introduced in the reaction environment showed rapid bubble‐propulsion followed by high‐purity separation of the reaction product (VA) by the virtue of the graphene–polymer cap acting as a mesoporous sponge. The concept has excellent potential towards the synthesis/isolation of industrially important compounds, affinity‐based product separation, pollutant remediation (such as heavy metal chelation/adsorption), as well as localized fuel‐gradients as an alternative to external fuel dependency. 相似文献
119.
Elena Akhmatskaya José M. Asua 《Journal of polymer science. Part A, Polymer chemistry》2012,50(7):1383-1393
Modification of the polymer–polymer interfacial tension is a way to tailor‐make particle morphology of waterborne polymer–polymer hybrids. This allows achieving a broader spectrum of application properties and maximizing the synergy of the positive properties of both polymers, avoiding their drawbacks. In situ formation of graft copolymer during polymerization is an efficient way to modify the polymer–polymer interfacial tension. Currently, no dynamic model is available for polymer–polymer hybrids in which a graft copolymer is generated during polymerization. In this article, a novel model based on stochastic dynamics is developed for predicting the dynamics of the development of particle morphology for composite waterborne systems in which a graft copolymer is produced in situ during the process. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012 相似文献
120.
The paper describes the validation of a newly developed very LES (VLES) method for the simulation of turbulent separated flow. The new VLES method is a unified simulation approach that can change seamlessly from Reynolds‐averaged Navier–Stokes to DNS depending on the numerical resolution. Four complex test cases are selected to validate the performance of the new method, that is, the flow past a square cylinder at Re = 3000 confined in a channel (with a blockage ratio of 20%), the turbulent flow over a circular cylinder at Re = 3900 as well as Re = 140,000, and a turbulent backward‐facing step flow with a thick incoming boundary layer at Re = 40,000. The simulation results are compared with available experimental, LES, and detached eddy simulation‐type results. The new VLES model performs well overall, and the predictions are satisfactory compared with previous experimental and numerical results. It is observed that the new VLES method is quite efficient for the turbulent flow simulations; that is, good predictions can be obtained using a quite coarse mesh compared with the previous LES method. Discussions of the implementation of the present VLES modeling are also conducted on the basis of the simulations of turbulent channel flow up to high Reynolds number of Reτ = 4000. The efficiency of the present VLES modeling is also observed in the channel flow simulation. From a practical point of view, this new method has considerable potential for more complex turbulent flow simulations at relative high Reynolds numbers. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献