全文获取类型
收费全文 | 6058篇 |
免费 | 829篇 |
国内免费 | 596篇 |
专业分类
化学 | 3362篇 |
晶体学 | 39篇 |
力学 | 182篇 |
综合类 | 81篇 |
数学 | 2728篇 |
物理学 | 1091篇 |
出版年
2024年 | 5篇 |
2023年 | 38篇 |
2022年 | 108篇 |
2021年 | 172篇 |
2020年 | 177篇 |
2019年 | 201篇 |
2018年 | 147篇 |
2017年 | 252篇 |
2016年 | 286篇 |
2015年 | 242篇 |
2014年 | 373篇 |
2013年 | 580篇 |
2012年 | 418篇 |
2011年 | 408篇 |
2010年 | 382篇 |
2009年 | 405篇 |
2008年 | 448篇 |
2007年 | 460篇 |
2006年 | 331篇 |
2005年 | 304篇 |
2004年 | 215篇 |
2003年 | 213篇 |
2002年 | 178篇 |
2001年 | 187篇 |
2000年 | 147篇 |
1999年 | 111篇 |
1998年 | 70篇 |
1997年 | 69篇 |
1996年 | 63篇 |
1995年 | 80篇 |
1994年 | 65篇 |
1993年 | 64篇 |
1992年 | 64篇 |
1991年 | 45篇 |
1990年 | 18篇 |
1989年 | 24篇 |
1988年 | 22篇 |
1987年 | 16篇 |
1986年 | 15篇 |
1985年 | 18篇 |
1984年 | 6篇 |
1983年 | 7篇 |
1982年 | 19篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1979年 | 8篇 |
1978年 | 4篇 |
1973年 | 6篇 |
1972年 | 2篇 |
1971年 | 1篇 |
排序方式: 共有7483条查询结果,搜索用时 15 毫秒
21.
Per B. Zetterlund Kazuki Miyake Kunihiro Goto Bunichiro Yamada 《Journal of polymer science. Part A, Polymer chemistry》2004,42(11):2640-2650
A detailed investigation of addition–fragmentation chain transfer (AFCT) in the free‐radical polymerization of methyl methacrylate (MMA) in the presence of methyl α‐(bromomethyl)acrylate (MBMA) was carried out to elucidate mechanistic details with efficient macromonomer synthesis as an underlying goal. Advanced modeling techniques were used in connection with the experimental work. Curve fitting of simulated and experimental molecular weight distributions with respect to the rate coefficient for addition of propagating radicals to MBMA (kadd) over 60–120 °C resulted in Eadd = 21.7 kJ mol?1 and Aadd = 2.18 × 106 M?1 s?1 and a very weak temperature dependence of the chain‐transfer constant (Eadd ≈ Ep). The rate coefficient for fragmentation of adduct radicals at 60 °C was estimated as kf ≈ 39 s?1 on the basis of experimental data of the MMA conversion and the concentration of 2‐carbomethoxy‐2‐propenyl end groups. The approach developed is generic and can be applied to any AFCT system in which copolymerization does not occur and in which the resulting unsaturated end groups do not undergo further reactions. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2640–2650, 2004 相似文献
22.
Defining speed of diffusion as the amount of time it takes to get from one penetration level to a higher one, we introduce a dynamic model in which we study the link between pricing policy, speed of diffusion, and number of competitors in the market. Our analysis shows that, in the case of strategic (oligopolistic) competition, the speed of diffusion has an important influence on the optimal pricing policy. In particular, we find that higher speeds of diffusion create an incentive to strategically interacting firms to lower their prices. 相似文献
23.
胡迪鹤 《数学物理学报(B辑英文版)》2005,25(1):23-29
This paper is a continuation of [8]. In Section 1, three kinds of communication are introdnced for two states and the relations among them are investigated. In Section 2, two kinds of period of a state are introdnced and it is obtained that the period is a “class property” ,i.e. two states x and y belong to same class implies the period of x is equal to the period of y. 相似文献
24.
25.
The knowledge of hydrocarbon/water phase equilibria is important in the design and operation of equipment for petroleum transport and refining and petrochemical plants. The presence of water in a hydrocarbon mixture can affect the product quality and damage the operation equipment due to corrosion and formation of gas hydrates. Tracing the concentration of hydrocarbons in aqueous media is also important for technical purposes like preventing oil spills and for ecological concerns such as predicting the fate of these organic pollutants in the environment. 相似文献
26.
Marco Sangermano Mehmet Atilla Tasdelen Yusuf Yagci 《Journal of polymer science. Part A, Polymer chemistry》2007,45(21):4914-4920
Photoinitiated cationic polymerization of mono‐ and bifunctional epoxy monomers, namely cyclohexeneoxide (CHO), 4‐epoxycyclohexylmethyl‐3′,4′‐epoxycyclohexanecarboxylate (EEC), respectively by using sulphonium salts in the presence of hydroxylbutyl vinyl ether (HBVE) was studied. The real‐time FTIR spectroscopic, gel content determination, and thermal characterization studies revealed that both hydroxyl and vinyl ether functionalities of HBVE take part in the polymerization. During the polymerization, HBVE has the ability to react via both active chain end (ACE) and activated monomer mechanisms through its hydroxyl and vinyl ether functionalities, respectively. Thus, more efficient curing was observed with the addition of HBVE into EEC‐containing formulations. It was also demonstrated that HBVE is effective in facilitating the photoinduced crosslinking of monofunctional epoxy monomer, CHO in the absence of a conventional crosslinker. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4914–4920, 2007 相似文献
27.
E. Mathieu Y. Foucher P. Dellamonica J. P. Daures 《Methodology and Computing in Applied Probability》2007,9(3):389-397
In AIDS control, physicians have a growing need to use pragmatically useful and interpretable tools in their daily medical
taking care of patients. Semi-Markov process seems to be well adapted to model the evolution of HIV-1 infected patients. In
this study, we introduce and define a non homogeneous semi-Markov (NHSM) model in continuous time. Then the problem of finding
the equations that describe the biological evolution of patient is studied and the interval transition probabilities are computed.
A parametric approach is used and the maximum likelihood estimators of the process are given. A Monte Carlo algorithm is presented
for realizing non homogeneous semi-Markov trajectories. As results, interval transition probabilities are computed for distinct
times and follow-up has an impact on the evolution of patients.
相似文献
28.
A highly stereoselective synthesis of the side Chain enantiomers of brassinolide and dolicholide through an aldol reaction of 2-(4-methoxy benzyloxyl) proplonylaldehyde (5) with the anion of 1- ( tert -butyldimethylsiloxy )-3-methyl-2-butanone ( 6 ) is described. 相似文献
29.
关于任意随机变量序列泛函的强极限定理 总被引:1,自引:1,他引:0
本文在k是固定的正整数,{fn}是R^k 1上的Borel可测函数列时,得到了任意随机变量序列{Xrn≥0}的泛函{fn(Xn-k,…,Xn)}的强极限定理,它是Chung的关于独立随机变量序列的强大数律的推广,作为推论,得到了k重非齐次马尔科夫链的一类强极限定理. 相似文献
30.
D. Baleanu 《Czechoslovak Journal of Physics》2003,53(11):971-976
The variational formulation of the Schrödinger field was investigated and the applicability of the chain method was analyzed. Using Batalin-Fradkin-Tyutin formalism a gauge invariant theory was constructed. 相似文献