全文获取类型
收费全文 | 2772篇 |
免费 | 50篇 |
国内免费 | 39篇 |
专业分类
化学 | 1747篇 |
晶体学 | 15篇 |
力学 | 74篇 |
数学 | 339篇 |
物理学 | 686篇 |
出版年
2021年 | 26篇 |
2020年 | 23篇 |
2019年 | 20篇 |
2018年 | 16篇 |
2016年 | 34篇 |
2015年 | 30篇 |
2014年 | 40篇 |
2013年 | 108篇 |
2012年 | 102篇 |
2011年 | 131篇 |
2010年 | 81篇 |
2009年 | 60篇 |
2008年 | 121篇 |
2007年 | 148篇 |
2006年 | 123篇 |
2005年 | 111篇 |
2004年 | 111篇 |
2003年 | 103篇 |
2002年 | 106篇 |
2001年 | 79篇 |
2000年 | 74篇 |
1999年 | 62篇 |
1998年 | 41篇 |
1997年 | 43篇 |
1996年 | 50篇 |
1995年 | 38篇 |
1994年 | 48篇 |
1993年 | 47篇 |
1992年 | 48篇 |
1991年 | 30篇 |
1990年 | 42篇 |
1989年 | 41篇 |
1988年 | 26篇 |
1987年 | 21篇 |
1986年 | 25篇 |
1985年 | 50篇 |
1984年 | 37篇 |
1983年 | 25篇 |
1982年 | 40篇 |
1981年 | 30篇 |
1980年 | 41篇 |
1979年 | 35篇 |
1978年 | 46篇 |
1977年 | 37篇 |
1976年 | 33篇 |
1975年 | 31篇 |
1974年 | 19篇 |
1973年 | 39篇 |
1972年 | 15篇 |
1971年 | 15篇 |
排序方式: 共有2861条查询结果,搜索用时 0 毫秒
41.
In [1], a set of convergent and stable two-point formulae for obtaining the numerical solution of ordinary differential equations having oscillatory solutions was formulated. The derivation of these formulae was based on a non-polynomial interpolant which required the prior analytic evaluation of the higher order derivatives of the system before proceeding to the solution. In this paper, we present a linear multistep scheme of order four which circumvents this (often tedious) initial preparation. The necessary starting values for the integration scheme are generated by an adaptation of the variable order Gragg-Bulirsch-Stoer algorithm as formulated in [2]. 相似文献
42.
William J. Evans 《Journal of organometallic chemistry》1978,154(3):C50-C51
The (Me3Si)3C group causes very large steric hindrance to nucleophilic displacement at a silicon atom to which it is attached, and (Me3Si)3CSiMe2Cl is even less reactive than t-Bu3SiCl towards base. The compounds (Me3Si)3CSiMe2X (X = Cl, Br, or I) are cleaved by MeOH/MeONa to give (Me3Si)2CHSiMe2OMe, possibly via the silaolefin (Me3Si)2 CSiMe2, and the correspondLug (Me3Si)3 CSiPh2X compounds undergo the analogous reaction even more readily. The halides (Me3Si)3CSiR2X (X = Cl or Br) and (Me3Si)3CSiCl3 do not react with boiling alcoholic silver nitrate, but the iodides (Me3Si)3CSiR2I are rapidly attacked. 相似文献
43.
Using single-crystal, automated diffractometer techniques, the linear coefficient of thermal expansion has been determined for La0.62Pb0.38MnO3 from 298 to 627 K. The linear coefficient of thermal expansion is observed to undergo a change from 7.2 × 10?5 Å/K for T < Tc to 10.8 × 10?5 Å/K for T > Tc. It is concluded that while the rhombohedral distortion in the (La, Pb)MnO3 system can be understood qualitatively on the basis of ionic size and polarizability considerations alone, the quantitative systematics of the distortion parameters and the change in the linear thermal expansion coefficient at Tc indicate a significant coupling between the elastic and magnetic exchange forces. 相似文献
44.
D.J. Evans L.A.P. Kane-Maguire D.A. Sweigart 《Journal of organometallic chemistry》1981,215(2):C27-C29
Kinetic results for the addition of OH? to [Mn(CO)3(η-C6H6)]+ (I) in water (eq. 1, X OH) obey the expression kobs kOH[OH?], and give a kOH value of 290 mol?1 dm3 s?1 at 20.0°C and ionic strength of 0.25 mol dm?3. The analogous reaction of NaCN with I in water fits the two-term expression kobs = kOH[OH?] + kCN[CN?], and leads to a kCN value of 0.8 mol?1 dm3 s?1 at 20.0°C and ionic strength of 0.25 mol dm?3. Interestingly, the related reaction (eq. 1, X N3) is too rapid to follow by stopped-flow spectrophotometry, indicating the overall rate trend N3? » OH? » CN?. This unusual nucleophilicity order, unexpected on the basis of both basicity and polarizability, is similar to that previously observed for anion addition to free carbonium ions. 相似文献
45.
M. B. Evans 《Chromatographia》1978,11(4):183-187
Summary The limitations of methods for the characterization of stationary phases, which require the use of a base or reference stationary
phase, are considered. In order to overcome these problems, a new method of column characterization, based upon measurements
of molecular retention index and ΔMe values for selected functional groups, is proposed. ΔMe values are shown to be dependent
upon liquid phase composition, nature of the support and liquid phase loading. 相似文献
46.
Treatment of meso-substituted metalloporphyrins [meso -substituent = OCOCF3, OCOCH3, OMe, CHO, CN, Cl; metal = Zn(II) or Cd(II)] with thallium(III) trifluoroacetate, followed by an acidic work-up, gives the corresponding β-substituted α-oxophlorins which were either characterised as such or else further derivatised. In all cases the major (or only) disubstitution product has the αβ orientation at the meso positions, indicating that the existing meso substituent directs the incoming one (trifluoroacetate) into the flanking, rather than opposite, meso position of the intermediate π-cation radical or π-dication. In contradistinction, meso substituted zinc(II) porphyrins which are able to lose protons (e.g. α-oxophlorins or α-aminoporphyrins) react with thallium(III) trifluoroacetate, and after a work-up with HCl the corresponding γ-chloro-α-oxophlorin or γ-chloro-α-aminoporphyrin is obtained. 相似文献
47.
Summary Inverse gas chromatography with sulphurated olefinic stationary phases and air as carrier gas has been found to yield characteristic
shifts of retention data. The resulting plots of retention index versus reaction time obtained for a range of squalene vulcanizates
have been found to be similar to those given by oxygen absorption measurements. Furthermore the chromatographic oxidation
curves have been found to be consistent with the known oxidation behaviour of the various sulphur networks formed on vulcanization.
This paper is dedicated to the memory of Dr.Graham Moore (1924–1968). 相似文献
48.
49.
50.