全文获取类型
收费全文 | 4904篇 |
免费 | 200篇 |
国内免费 | 2篇 |
专业分类
化学 | 3524篇 |
晶体学 | 43篇 |
力学 | 105篇 |
数学 | 529篇 |
物理学 | 905篇 |
出版年
2023年 | 36篇 |
2022年 | 23篇 |
2021年 | 51篇 |
2020年 | 73篇 |
2019年 | 73篇 |
2018年 | 99篇 |
2017年 | 70篇 |
2016年 | 159篇 |
2015年 | 144篇 |
2014年 | 133篇 |
2013年 | 295篇 |
2012年 | 363篇 |
2011年 | 388篇 |
2010年 | 211篇 |
2009年 | 159篇 |
2008年 | 342篇 |
2007年 | 359篇 |
2006年 | 309篇 |
2005年 | 284篇 |
2004年 | 229篇 |
2003年 | 204篇 |
2002年 | 143篇 |
2001年 | 154篇 |
2000年 | 132篇 |
1999年 | 51篇 |
1998年 | 44篇 |
1997年 | 24篇 |
1996年 | 63篇 |
1995年 | 51篇 |
1994年 | 42篇 |
1993年 | 65篇 |
1992年 | 45篇 |
1991年 | 22篇 |
1990年 | 29篇 |
1989年 | 15篇 |
1988年 | 19篇 |
1987年 | 20篇 |
1986年 | 21篇 |
1985年 | 26篇 |
1984年 | 19篇 |
1983年 | 22篇 |
1982年 | 14篇 |
1981年 | 10篇 |
1980年 | 11篇 |
1979年 | 9篇 |
1978年 | 9篇 |
1977年 | 9篇 |
1976年 | 7篇 |
1975年 | 5篇 |
1973年 | 8篇 |
排序方式: 共有5106条查询结果,搜索用时 15 毫秒
991.
García Ruano JL Torrente E Alonso I Rodriguez M Martín-Castro AM Degl'Innocenti A Frateschi L Capperucci A 《The Journal of organic chemistry》2012,77(4):1974-1982
Phenylselenyl benzylcarbanion stabilized by an (S)-2-p-tolylsulfinyl group evolves in a highly stereoselective way in the reactions with (S)-N-(p-tolylsulfinyl)imines at -98 °C affording diastereomerically pure 1,2-selenoamino derivatives in good yields. The syn or anti relationship of the obtained compounds depends on the alkyl or aryl character of the imine. They are easily transformed into enantiomerically pure (1R,2S)-1-aryl[or (1S,2S)-1-alkyl]-2-(phenylseleno)-2-phenylethylamines by reaction with t-BuLi and subsequent methanolysis of the generated sulfinamide derivatives with TFA. 相似文献
992.
Macrocycle formation by proton-template-induced dimerization of complexes with (alkoxoimino)pyridine
Álvarez CM García-Rodríguez R Martín-Alvarez JM Miguel D Turiel JA 《Inorganic chemistry》2012,51(7):3938-3940
The existence of a strong hydrogen bond between two molecules of an (alkoxoimino)pyridinemanganese(I) complex induces their dimerization and the formation of a metallamacrocycle. The expected intramolecular attack of the alkoxo moiety is disfavored. 相似文献
993.
Do TP Nixon KL Fuss M García G Blanco F Brunger MJ 《The Journal of chemical physics》2012,136(18):184313
We report on differential and integral cross section measurements for the electron impact excitation of the lowest-lying triplet electronic state (a? (3)B(1u)) in ethylene (C(2)H(4)). The energy range of the present experiments was 9 eV-50 eV, with the angular range of the differential cross section measurements being 15°-90°. As the ground electronic state of C(2)H(4) is a (1)A(g) state, this singlet → triplet excitation process is expected to be dominated by exchange scattering. The present angular distributions are found to support that assertion. Comparison, where possible, with previous experimental results from the University of Fribourg group shows very good agreement, to within the uncertainties on the measured cross sections. Agreement with the available theories, however, is generally marginal with the theories typically overestimating the magnitude of the differential cross sections. Notwithstanding that, the shapes of the theoretical angular distributions were in fact found to be in good accord with the corresponding experimental results. 相似文献
994.
Pérez-Díaz JL Álvarez-Valenzuela MA García-Prada JC 《Journal of colloid and interface science》2012,381(1):180-182
Precise measurements of the surface tension of water in air vs. humidity at 5, 10, 15, and 20 °C are shown. For constant temperature, surface tension decreases linearly for increasing humidity in air. These experimental data are in good agreement with a simple model based on Newton's laws here proposed. It is assumed that evaporating molecules of water are ejected from liquid to gas with a mean normal component of the speed of "ejection" greater than zero. A high humidity in the air reduces the net flow of evaporating water molecules lowering the effective surface tension on the drop. Therefore, just steam in air acts as an effective surfactant for the water-air interface. It can partially substitute chemical surfactants helping to reduce their environmental impact. 相似文献
995.
JL García Ruano E Torrente A Parra J Alemán AM Martín-Castro 《The Journal of organic chemistry》2012,77(15):6583-6599
In this work, we report the use of the asymmetric intramolecular Pauson-Khand reactions of 4-aryl-4-cyano-1,6-enynes for obtaining enantiomerically enriched bicyclo[3.3.0]octenones, and the influence of both the quaternary stereocenter and the sulfur functions located at ortho-position of the aryl group, on their stereoselectivity and reactivity. The sulfenyl derivatives bearing substituted or unsubstituted triple bonds and mono- and disubstituted alkene moieties afford bicyclo[3.3.0]octenones in high yields with complete diastereocontrol. These results are explained by assuming the association of the lone electron pair at sulfur to the Co-alkyne complexes. 相似文献
996.
997.
L. Romero A. Ortín B. Monrabal J. R. Torres-Lapasió M. C. García-Álvarez-Coque 《Macromolecular Symposia》2012,312(1):157-166
Summary: CRYSTEX is a fully automated instrument for the determination of Xylene Solubles in polypropylene and ethylene-propylene copolymers, providing an excellent correlation with gravimetric methods. The instrument can be equipped with a dual band infrared (IR) detector to quantify the ethylene weight percentage (C2%) in the amorphous fraction, and in the whole polymer sample. In this work, a new approach based on multiple linear regression (MLR) models is presented, which makes use of two independent IR absorbance signals acquired simultaneously by the detector. A compromise model to predict directly C2% is proposed, which balances good accuracy and reduced experimental effort. MLR models able to predict the total sample concentration were also developed. The results were successfully validated using copolymer standards in a wide chemical composition range. 相似文献
998.
We give a complete characterization for the rational torsion of an elliptic curve in terms of the (non-)existence of integral
solutions of a system of diophantine equations. 相似文献
999.
We show that the lower limit of a sequence of maximal monotone operators on a reflexive Banach space is a representable monotone
operator. As a consequence, we obtain that the variational sum of maximal monotone operators and the variational composition
of a maximal monotone operator with a linear continuous operator are both representable monotone operators. 相似文献
1000.
A novel method for combined particle image velocimetry and laser induced fluorescence is described and results from an experiment
in a stratified flow are presented. A standard two-dimensional, one camera particle image velocimetry configuration is used,
acquiring images of the seeding particles and the dye marking the current simultaneously and separating the two fields digitally.
The implementation of the postprocessing method, its capabilities and the necessary conditions for its use are discussed in
detail. The proposed method is applied to an arrested density current front. The front is made stationary by opposing a uniform
velocity profile, obtained from the combination of a moving floor and the recirculation of fresh water in the channel. To
improve the quality of the images, the current is made optically homogeneous by matching the refractivity index throughout
the domain. Instantaneous and time averaged fields are obtained for both velocity and density. Simultaneous measurements of
these fields provide insight in the mixing processes at the front of the density current. In particular persistent billow
generation, similar to that found in shear layers and associated with Kelvin–Helmholtz instabilities, is observed.
Support for this work was partially provided by the US Office of Naval Research through the Coastal Geosciences Program and
by Exxon Mobil Exploration Company. The authors would like to thank Dr. Wing Lai of TSI, Inc, for loaning part of the PIV
equipment used in this study. 相似文献