全文获取类型
收费全文 | 10606篇 |
免费 | 1371篇 |
国内免费 | 1266篇 |
专业分类
化学 | 5796篇 |
晶体学 | 139篇 |
力学 | 997篇 |
综合类 | 193篇 |
数学 | 2546篇 |
物理学 | 3572篇 |
出版年
2024年 | 18篇 |
2023年 | 96篇 |
2022年 | 212篇 |
2021年 | 302篇 |
2020年 | 338篇 |
2019年 | 292篇 |
2018年 | 273篇 |
2017年 | 358篇 |
2016年 | 429篇 |
2015年 | 375篇 |
2014年 | 532篇 |
2013年 | 927篇 |
2012年 | 616篇 |
2011年 | 692篇 |
2010年 | 558篇 |
2009年 | 708篇 |
2008年 | 701篇 |
2007年 | 654篇 |
2006年 | 647篇 |
2005年 | 576篇 |
2004年 | 480篇 |
2003年 | 486篇 |
2002年 | 392篇 |
2001年 | 320篇 |
2000年 | 308篇 |
1999年 | 274篇 |
1998年 | 238篇 |
1997年 | 210篇 |
1996年 | 199篇 |
1995年 | 191篇 |
1994年 | 125篇 |
1993年 | 114篇 |
1992年 | 99篇 |
1991年 | 73篇 |
1990年 | 73篇 |
1989年 | 66篇 |
1988年 | 59篇 |
1987年 | 34篇 |
1986年 | 33篇 |
1985年 | 31篇 |
1984年 | 40篇 |
1983年 | 10篇 |
1982年 | 24篇 |
1981年 | 16篇 |
1980年 | 3篇 |
1979年 | 13篇 |
1978年 | 5篇 |
1977年 | 6篇 |
1976年 | 5篇 |
1975年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
991.
A general kinetic equation is suggested in order to describe solid state decompositions or, more generally, solid state reactions
and transformations on the basis of some existing general equations. This differential equation can be expressed as: dα/dt=k[(1-α)q]x{[1-(1-α)1−q]/(1-q)}y, where α represents the degree of conversion, k is the rate constant while q, x and y are characteristic parameters for a
given mechanism.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
992.
Tris(2‐aminoethyl)amine‐based ferrocene‐terminated dendrimers as burning rate catalysts for ammonium perchlorate‐based propellant decomposition 下载免费PDF全文
Zain‐ul‐Abdin Li Wang Haojie Yu Rizwan Ullah Khan Raja Summe Ullah Muhammad Haroon 《应用有机金属化学》2018,32(4)
Ferrocene‐based derivatives show potential application as burning rate catalysts (BRCs) for solid composite propellants. However, migration problems of simple ferrocene‐based derivatives limit their application as BRCs in solid composite propellants. To overcome the migration problems of ferrocene‐based BRCs and to enhance the burning rate of ammonium perchlorate (AP)‐based propellants, zero‐ to second‐generation tris(2‐aminoethyl)amine‐based ferrocene‐terminated dendrimers (G0, G1 and G2) were synthesized. The structures of G0, G1 and G2 were confirmed using 1H NMR, Fourier transform infrared and UV–visible spectroscopies. The electrochemical behavior of G0, G1 and G2 was investigated using cyclic voltammetry. It was found that G0, G1 and G2 showed redox behavior due to the presence of ferrocene and this redox behavior was diffusion controlled over the investigated scan range. The burning rate catalytic effect of G0, G1 and G2 on thermal decomposition of AP was investigated using thermogravimetry and differential thermogravimetry. G0, G1 and G2 showed good catalytic effect on the thermal decomposition of AP. Anti‐migration studies showed that migration of G0, G1 and G2 was much slower than that of 2,2‐bis(ethylferrocenyl)propane (catocene) and ferrocene. 相似文献
993.
The halogen/lithium (X/Li) exchange’s usefulness is challenged by the extreme conditions employed during the conversion of a bromo or an iodo substituent to an organolithium intermediate. Our preliminary disclosure reveals that simple X/Li exchanges can be accomplished at ambient temperature and in doped hydrocarbon media using n-BuLi. Use of a continuous reactor featuring brief reaction times (?1 s) and large product throughputs further facilitates the production of a product resulting from a sequential X/Li exchange and nucleophilic addition. 相似文献
994.
XU Mancai OU Zhize SHI Zuoqing XU Mingcheng LI Haitao YU Shanxin HE Binglin 《Chinese Journal of Reactive Polymers》2000,(1)
1. INTRODUCTIONReduction of organic compounds by NaBH, is often used in organic synthesis. The reactiollis only proceeded in the interface between the organic phase and water phase because of the lowsolubility of NaBH. in organic compounds, and this results in the slow reaction rate and lowyield. In order to increase the reaction rate and yield, NaBH, was converted totetraalkylammonium borohydrides II' 'l, and this made the operating process complex and greatamount of quaternary ammon… 相似文献
995.
996.
Recent advances in theoretical models of respiratory mechanics 总被引:1,自引:0,他引:1
As an important branch of biomedical engineering, respiratory mechanics helps to understand the physiology of the respiratory system and provides fundamental data for developing such clinical technologies as ventilators. To solve different clinical problems, researchers have developed numerous models at various scales that describe biological and mechanical properties of the respiratory system. During the past decade, benefiting from the continuous accumulation of clinical data and the dramatic progress of biomedical technologies (e.g. biomedical imaging), the theoretical modeling of respiratory mechanics has made remarkable progress regarding the macroscopic properties of the respiratory process, complexities of the respiratory system, gas exchange within the lungs, and the coupling interaction between lung and heart. The present paper reviews the advances in the above fields and proposes potential future projects. 相似文献
997.
Evaluation for the performance of learning algorithm has been the main thread of theoretical research of machine learning.
The performance of the regularized regression algorithm based on independent and identically distributed(i.i.d.) samples has
been researched by a large number of references. In the present paper we provide the convergence rates for the performance
of regularized regression based on the inputs of p-order Markov chains. 相似文献
998.
With the B3LYP calculation method of density functional theory(DFT)and the 6-31G* basis set,full optimization calculation was made for phenoxathiin10-oxide(PTO)and 135 polybromine phenoxathiin 10-oxides(PBPTOs)with the Gaussian 03 program and molar heat capacity in constant volume(CVθ)value of each molecule in the standard state was obtained.The relation between CVθ and the substitution position and number of bromine atom(NPBS)was studied,and the results indicated good correlation(R2 = 1.000)between CVθ and NPBS of PBPTO compounds.Based on the output file of Gaussian 03 program,molar heat capacity at constant pressure(Cp,m)of PBPTO compounds from 200 to 1,000 K was calculated with the statistical thermodynamics program,and the correlation equation between Cp,m and temperature(T,T-1 and T-2)was obtained with the least-squares method,and the correlation coefficient of the correlation equation(R2)was 1.000.In addition,based on the partition function of each molecule calculated by vibration analysis,the relative rate constant of formation of each molecule was calculated. 相似文献
999.
1000.
A variational approach using a new wave function to ddμ muonic molecular ion is proposed. This approach requires four terms in the total three‐body wave function. The formation and fusion take place by the reason of the existence of the both Coulomb potential and nuclear absorption. The nuclear fusion rates and eigenvalues related to such levels below dμ(1s) + d threshold are calculated with a good accuracy and a short computation time. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008 相似文献