全文获取类型
收费全文 | 40053篇 |
免费 | 1091篇 |
国内免费 | 163篇 |
专业分类
化学 | 25865篇 |
晶体学 | 310篇 |
力学 | 667篇 |
综合类 | 4篇 |
数学 | 7030篇 |
物理学 | 7431篇 |
出版年
2023年 | 254篇 |
2022年 | 472篇 |
2021年 | 621篇 |
2020年 | 596篇 |
2019年 | 663篇 |
2018年 | 745篇 |
2017年 | 679篇 |
2016年 | 1361篇 |
2015年 | 1102篇 |
2014年 | 1157篇 |
2013年 | 2411篇 |
2012年 | 2400篇 |
2011年 | 2577篇 |
2010年 | 1636篇 |
2009年 | 1547篇 |
2008年 | 2295篇 |
2007年 | 2246篇 |
2006年 | 2063篇 |
2005年 | 1892篇 |
2004年 | 1621篇 |
2003年 | 1314篇 |
2002年 | 1125篇 |
2001年 | 863篇 |
2000年 | 767篇 |
1999年 | 605篇 |
1998年 | 453篇 |
1997年 | 441篇 |
1996年 | 545篇 |
1995年 | 403篇 |
1994年 | 428篇 |
1993年 | 385篇 |
1992年 | 369篇 |
1991年 | 333篇 |
1990年 | 312篇 |
1989年 | 259篇 |
1988年 | 247篇 |
1987年 | 244篇 |
1986年 | 245篇 |
1985年 | 318篇 |
1984年 | 327篇 |
1983年 | 218篇 |
1982年 | 238篇 |
1981年 | 237篇 |
1980年 | 233篇 |
1979年 | 165篇 |
1978年 | 160篇 |
1977年 | 163篇 |
1976年 | 143篇 |
1975年 | 129篇 |
1973年 | 130篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
121.
122.
G. Martínez J. Milln J. Contreras 《Journal of polymer science. Part A, Polymer chemistry》2003,41(4):508-519
A poly(vinyl chloride) (PVC) sample was chlorinated in solution in the presence of 2,2′‐azobisisobutyronitrile and by the fluid‐bed method. The aim was to evaluate the scope of the stereoselectivity of the chlorination reaction. The quantitative microstructural analysis of the residual PVC with a degree of chlorination was followed by 13C NMR spectroscopy. From the evolution of the content of isotactic (mm), heterotactic (mr), and syndiotactic (rr) triads and of mmmm, mmmr, and rmmr isotactic pentads in the unchlorinated parts of the polymer, it was unambiguously inferred that the chlorination reaction proceeds by a stereoselective mechanism in that the mr heterotactic triads are the most reactive structures followed by the isotactic triad at mmmr and rmmr pentads. This conclusion was confirmed on the basis of the Fourier transform infrared results. The results provide valuable information regarding the effect of tacticity and related local conformations in the chemical reactions of PVC. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 508–519, 2003 相似文献
123.
José M. Arrieta Neus Cónsul Anibal Rodríguez-Bernal 《Zeitschrift für Angewandte Mathematik und Physik (ZAMP)》2004,23(2):1-14
We prove the existence of nonconstant stable stationary
solutions of
an evolution problem with a nonlinear reaction acting on the
boundary. These solutions present layers at certain points of the
boundary. We also study the behavior of these solutions as the small
parameter appearing in the equation approaches zero and show some
stability properties of the profiles given by these equilibrium
solutions. 相似文献
124.
The sound propagation into a courtyard shielded from direct exposure is predicted using an equivalent sources approach. The problem is simplified into that of a two-dimensional city canyon. A set of equivalent sources are used to couple the free half-space above the canyon to the cavity inside the canyon. Atmospheric turbulence causes an increase in the expected value of the sound pressure level compared to a homogeneous case. The level increase is estimated using a von Kármán turbulence model and the mutual coherences of all equivalent sources' contributions. For low frequencies the increase is negligible, but at 1.6 kHz it reaches 2-5 dB for the geometries and turbulence parameters used here. A comparison with a ray-based model shows reasonably good agreement. 相似文献
125.
Summary The potential of liquid chromatography-mass spectrometry (LC-MS) has been studied for the simultaneous determination of sixteen carbamate and organophosphorus pesticides in honeybees using a traditional sample preparation protocol based on acetone extraction and dichloromethane partitioning. The performances of both atmospheric pressure chemical ionization (APCI) and electrospray (ES) interfaces were compared. APCI offered better sensitivity and specificity for a higher range of pesticides. Limits of quantification were from 0.01 to 0.17 mg kg–1, at which recoveries obtained were between 64 and 93%, except for pirimicarb that was at 13%, with relative standard deviations ranging from 7 to 20%. Fenitrothion, fenoxycarb, methiocarb and phoxim were found in bees from Valencian Community beehives at concentrations between 0.03 and 3.75 mg kg–1. 相似文献
126.
The adsorption of six-membered hydrocarbon cycles and cyclopentane and the interaction of hydrogen with the adsorbed layer on polycrystalline Pt-foil have been studied. The work function change (Δφ) was followed by a Kelvin probe and the C/Pt peak ratio was determined by Auger electron spectroscopy. Combining these two techniques made it possible to distinguish between chemisorption via σ-bonds and π-complex formation. Benzene and toluene adsorbed first as π-complex while cyclohexane showed initially a partial aromatization and a π-complex-like bonding to the surface. Excess hydrocarbon or addition of hydrogen transformed the π-complex into σ-bonded species. Cyclopentane adsorbed via σ-bonds and showed no significant hydrogen effect. 相似文献
127.
J. M. Cuevas J. M. Laza M. Correa J. L. Vilas M. Rodríguez L. M. Len 《Journal of Polymer Science.Polymer Physics》2003,41(17):1965-1977
The reticulation process of an epoxy resin using an amine as a cure agent was studied at different temperatures and concentrations of the cure agent with dynamic mechanical thermal analysis. The study was performed under both isothermal and nonisothermal conditions, and a temperature–time–transformation diagram was obtained. The measurements from the two modes gave similar results, although the nonisothermal mode required fewer experiments. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1965–1977, 2003 相似文献
128.
129.
130.
Summary A new gas chromatographic method using an automatic purge-and-trap system coupled to a GC with mass selective detection to analyze styrene at the parts-per-trillions (ng kg–1) level is described. The method shows a good sensitivity and the detection limit is 10 ng kg–1 with a relative standard deviation (RSD) of 4.7% for 164 ng kg–1 styrene in olive oil. This analytical method has been successfully applied to the analysis of styrene in extra-virgin olive oil from the European market. 相似文献