全文获取类型
收费全文 | 1619篇 |
免费 | 36篇 |
国内免费 | 3篇 |
专业分类
化学 | 996篇 |
晶体学 | 28篇 |
力学 | 114篇 |
数学 | 151篇 |
物理学 | 369篇 |
出版年
2022年 | 12篇 |
2021年 | 22篇 |
2020年 | 18篇 |
2019年 | 18篇 |
2018年 | 15篇 |
2017年 | 13篇 |
2016年 | 29篇 |
2015年 | 36篇 |
2014年 | 41篇 |
2013年 | 76篇 |
2012年 | 79篇 |
2011年 | 79篇 |
2010年 | 65篇 |
2009年 | 56篇 |
2008年 | 83篇 |
2007年 | 105篇 |
2006年 | 87篇 |
2005年 | 79篇 |
2004年 | 60篇 |
2003年 | 61篇 |
2002年 | 40篇 |
2001年 | 31篇 |
2000年 | 20篇 |
1999年 | 20篇 |
1998年 | 17篇 |
1997年 | 22篇 |
1996年 | 38篇 |
1995年 | 20篇 |
1994年 | 14篇 |
1993年 | 31篇 |
1992年 | 19篇 |
1991年 | 11篇 |
1990年 | 17篇 |
1989年 | 14篇 |
1988年 | 17篇 |
1987年 | 15篇 |
1986年 | 18篇 |
1985年 | 19篇 |
1984年 | 20篇 |
1983年 | 15篇 |
1982年 | 13篇 |
1981年 | 12篇 |
1980年 | 19篇 |
1979年 | 22篇 |
1978年 | 16篇 |
1977年 | 17篇 |
1976年 | 17篇 |
1975年 | 17篇 |
1974年 | 10篇 |
1972年 | 6篇 |
排序方式: 共有1658条查询结果,搜索用时 24 毫秒
1.
2.
3.
Julien Ferrari Christian Terreaux Tibor Kurtn Attila Szikszai‐Kiss Sndor Antus JeromeD. Msonthi Kurt Hostettmann 《Helvetica chimica acta》2003,86(8):2768-2778
Investigation of the methanol extract of the roots of Gnidia involucrata (Thymelaeaceae) led to the isolation and characterization of two new 3,8″‐biflavonoid diastereoisomers, named GB‐4 ( 6a ) and GB‐4a ( 6b ). Their absolute configurations were determined in mixture by on‐line LC/CD measurements, which also allowed the revision of absolute configurations of the biflavanoids GB‐1 and GB‐2, and the configurational assignment of GB‐3. 相似文献
4.
DAndrea A. Tomassini N. Ferrari L. Righini M. Selci S. Bruni M. R. Simeoni G. 《Il Nuovo Cimento D》1995,17(11):1423-1427
Il Nuovo Cimento D - Normalized reflection spectra in GaInAs/GaAs quantum wells are shown for two sets of samples with different alloy concentration (x=9% and 18.5%) and well thickness ranging from... 相似文献
5.
Guido Consonni Piero Veronese Eduardo Gutirrez-Pea 《Journal of multivariate analysis》2004,88(2):335-364
Reference analysis is one of the most successful general methods to derive noninformative prior distributions. In practice, however, reference priors are often difficult to obtain. Recently developed theory for conditionally reducible natural exponential families identifies an attractive reparameterization which allows one, among other things, to construct an enriched conjugate prior. In this paper, under the assumption that the variance function is simple quadratic, the order-invariant group reference prior for the above parameter is found. Furthermore, group reference priors for the mean- and natural parameter of the families are obtained. A brief discussion of the frequentist coverage properties is also presented. The theory is illustrated for the multinomial and negative-multinomial family. Posterior computations are especially straightforward due to the fact that the resulting reference distributions belong to the corresponding enriched conjugate family. A substantive application of the theory relates to the construction of reference priors for the Bayesian analysis of two-way contingency tables with respect to two alternative parameterizations. 相似文献
6.
7.
José A. Ferrari 《General Relativity and Gravitation》1990,22(1):19-32
In this paper we investigate the (static) solution of the Kaluza-Klein equations for a cylindrically symmetric current distribution. Specifically, we are interested in the fields generated by a long, cylindrical solenoid. We shall examine in some detail the concept of effective mass of a charged test particle. We shall show that, for a certain charge-to(rest)mass ratio of the test particle, the effective mass becomes imaginary at a certain distance from the axis of our solenoid. 相似文献
8.
Giampiero Bettinetti Milena Sorrenti Laura Catenacci Franca Ferrari Silvia Rossi Ilaria Salvadeo Paolo Carraro 《Journal of inclusion phenomena and macrocyclic chemistry》2007,57(1-4):329-332
Triacetyl α-cyclodextrin, triacetyl β-cyclodextrin and triacetyl γ-cyclodextrin were tested as possible hydrophobic carriers
to prolong the release of hydrophilic teicoplanin (TCP). Physical–chemical characterization of individual components, drug-carrier
physical mixtures at 0.5, 0.67 and 0.75 mass fraction of carrier, and the respective interaction products by kneading or evaporative
crystallization under microwave irradiation was carried out using differential scanning calorimetry (DSC) and thermogravimetric
analysis (TGA). In vitro drug release in pH 7.4 phosphate buffer at 37 °C was determined by intrinsic dissolution rate (IDR)
measurements on non disintegrating compressed discs. Solid-state interactions of TCP with triacetyl α-cyclodextrin by evaporative
crystallization and kneading and with triacetyl β-cyclodextrin by evaporative crystallization (probably resulting in carrier
amorphization) were demonstrated. The role of carrier hydrophobicity, carrier mass fraction and preparation method of solid
drug-carrier combinations on solid-state drug-carrier interactions and slowing down of TCP release was assessed. Modulation
of drug release can be achieved using TCP-triacetyl γ-cyclodextrin combinations at 0.5 mass fraction of carrier. 相似文献
9.
Franco Piacenti Mario Bianchi Piero Frediani Ugo Matteoli 《Journal of organometallic chemistry》1975,87(3):C54-C55
Both normal and secondary alkylcobalt carbonyls are shown not to undergo isomerization under catalytic “oxo” conditions, and the relevance of this obervation for the mechanism of the “oxo” reaction is discussed. 相似文献
10.
G. Del Piero G. Perego S. Cucinella M. Cesari A. Mazzei 《Journal of organometallic chemistry》1977,136(1):13-18
The crystall and molecular structures of (ClAlN-i-Pr)6 (I), and of (Me0.83H0.17AlN-i-Pr)6(MeAlN-i-Pr)6 have been determined by single crystal three-dimensional X-ray analysis. Block-matrix least-squares refinements led to conventional R factor of 0.039 for I and 0.037 for II. The compounds are isostructural, as the cage molecules consist of a prismatic hexagonal framework, (AlN)6, similar to that observed for the parent hydrogenated analogue (HAlN-i-Pr)6.Some differences in bond distances and angles are discussed, in connection with the different Al-bonded substituents. Crystal data: I, trigonal space group R; a = 17.083(2), c = 9.652(1); Z = 3; Dc 1.46 g cm?3; II, trigonal space group R, a = 17.378(3), c = 9.706(3) »; Z = 3; Dc 1.15 g cm?3. 相似文献