全文获取类型
收费全文 | 1694篇 |
免费 | 76篇 |
国内免费 | 3篇 |
专业分类
化学 | 1425篇 |
晶体学 | 9篇 |
力学 | 12篇 |
数学 | 143篇 |
物理学 | 184篇 |
出版年
2024年 | 2篇 |
2023年 | 32篇 |
2022年 | 99篇 |
2021年 | 107篇 |
2020年 | 66篇 |
2019年 | 56篇 |
2018年 | 60篇 |
2017年 | 31篇 |
2016年 | 99篇 |
2015年 | 56篇 |
2014年 | 80篇 |
2013年 | 114篇 |
2012年 | 113篇 |
2011年 | 133篇 |
2010年 | 79篇 |
2009年 | 67篇 |
2008年 | 110篇 |
2007年 | 83篇 |
2006年 | 81篇 |
2005年 | 77篇 |
2004年 | 62篇 |
2003年 | 39篇 |
2002年 | 26篇 |
2001年 | 13篇 |
2000年 | 6篇 |
1999年 | 15篇 |
1998年 | 8篇 |
1997年 | 7篇 |
1996年 | 13篇 |
1995年 | 3篇 |
1993年 | 3篇 |
1992年 | 4篇 |
1991年 | 2篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1984年 | 3篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1979年 | 1篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1975年 | 1篇 |
1971年 | 1篇 |
1969年 | 1篇 |
1966年 | 1篇 |
1964年 | 1篇 |
1961年 | 1篇 |
1960年 | 2篇 |
排序方式: 共有1773条查询结果,搜索用时 15 毫秒
991.
Marina V. Chirskaya Natalia L. Sergovskaya Sergey I. Sviridov 《Tetrahedron letters》2004,45(48):8811-8813
Substituted 3-bromotetrahydrofurans were prepared from homoallylic alcohols via bromination and cyclization in methanol in the presence of potassium carbonate. 相似文献
992.
Natalia Berruti Onesti 《Annali di Matematica Pura ed Applicata》1960,52(1):79-106
Sunto Nel presente lavoro l' A. stabilisce le equazioni di Eulero relative agli integrali curvilinei
e rileva alcune proprietà delle estremali relative alla funzione F, occupandosi in particolare dell'esistenza delle derivate
successive delle funzioni da cui le estremali sono definite. 相似文献
993.
The focus of this article is the investigation of the electrical behavior of the normal myocardium following the delivery of high-strength defibrillation shocks. To achieve its goal, the study employs a complex three-dimensional defibrillation model of a slice of the canine heart characterized with realistic geometry and fiber architecture. Defibrillation shocks of various strengths and electrode configurations are delivered to the model preparation in which a sustained ventricular tachycardia is induced. Instead of analyzing the post-shock electrical events as progressions of transmembrane potential maps, the study examines the evolution of the postshock phase singularities (PSs) which represent the organizing centers of reentry. The simulation results demonstrate that the shock induces numerous PSs the majority of which vanish before the reentrant wavefronts associated with them complete half of a single rotation. Failed shocks are characterized with one or more PSs that survive the initial period of PS annihilation to establish a new postshock arrhythmia. The increase in shock strength results in an overall decrease of the number of PSs that survive over 200 ms after the end of the shock; however, the exact behavior of the PSs is strongly dependent on the shock electrode configuration. (c) 2002 American Institute of Physics. 相似文献
994.
Propranolol was imprinted using noncovalent interactions in the shell of core-shell nanoparticles prepared by aqueous emulsion polymerization in the presence and absence of toluene. The imprinted particles were characterized, and their capacity to rebind propranolol from both organic and aqueous media was analyzed. Results showed that the amount of template incorporated into the polymer and the presence of toluene as a "porogenic" agent influenced the ability of the nanoparticles obtained to rebind propranolol. The presence of toluene during imprinting increased rebinding by about 2-fold in buffer and by 3-fold in toluene, compared with similar materials made in the absence of toluene during imprinting. It also influenced the final surface area of the particles. Binding site affinity, assessed by radioligand displacement, was measured as IC50 values of about 1-10 microM. This compares with about 3 microM for bulk polymer made with a similar composition. Finally, to demonstrate the advantages of structured particles for analytical applications a new property, fluorescence, was incorporated into the core of the particles without interfering with the imprinted shell and its ability to rebind propranolol. 相似文献
995.
996.
997.
Controlled incorporation of water molecules into carboxy hydrogen-bond networks: a designed approach
Pérez C Rodríguez ML Foces-Foces C Pérez-Hernández N Pérez R Martín JD 《Organic letters》2003,5(5):641-644
The incorporation of water molecules into the hydrogen-bonded pattern of condensed organic materials implies an unfavorable entropic tradeoff resulting from water ordering. Here we show for a family of diacids of general structure (+/-)-1 that extended chains of anhydrous or hydrated structures can be prepared by controlling the steric factors that lead to the closest packing of individual components. 相似文献
998.
Vera Mara L. Palacios Camilo J. O. Daz Nieto Csar H. Palacios Noelia A. Di Carlantonio Natalia Luna Franco G. Torres Walter R. Flexer Victoria 《Journal of Solid State Electrochemistry》2022,26(9):1981-1994
Journal of Solid State Electrochemistry - It is expected that lithium sourcing from aqueous sources in the medium term will account for over half of worldwide production, since reserves in brines... 相似文献
999.
Natalia Manousi Adamantia Vlachaki Fotini S. Kika Catherine K. Markopoulou Paraskevas D. Tzanavaras Constantinos K. Zacharis 《Journal of separation science》2022,45(6):1240-1251
A salting-out homogeneous liquid-liquid microextraction was proposed for the quantification of four azole drugs in human urine prior to high-performance liquid chromatography analysis. The procedure involved the mixing of the sample with acetonitrile in appropriate volumes followed by the addition of sodium sulfate solution in order to facilitate phase separation. The parameters influencing the extraction performance were studied and optimized using a two-step experimental design. The analytical procedure was thoroughly validated using the accuracy profiles as a graphical decision-making tool. The β-expectation tolerance intervals did not exceed the acceptance criteria of ±15% meaning that 95% of future results will be included in the defined bias limits. The limits of detection of the procedure were satisfactory, ranging between 0.01 and 0.03 μg/mL. The mean analytical bias in the spiking levels was satisfactory and ranged between –10.3 and 4.2% while the relative standard deviation was lower than 5.6%. Monte-Carlo simulations followed by capability analysis were employed to investigate the ruggedness of the sample preparation protocol. The developed method offers advantages compared to previously reported approaches for the same type of analysis including extraction efficiency and scaling down of the sample volume and extraction time. 相似文献
1000.
A two-point boundary value problem is considered on the interval [0, 1], where the leading term in the differential operator is a Riemann-Liouville fractional derivative of order 2 ? δ with 0 < δ < 1. It is shown that any solution of such a problem can be expressed in terms of solutions to two associated weakly singular Volterra integral equations of the second kind. As a consequence, existence and uniqueness of a solution to the boundary value problem are proved, the structure of this solution is elucidated, and sharp bounds on its derivatives (in terms of the parameter δ) are derived. These results show that in general the first-order derivative of the solution will blow up at x = 0, so accurate numerical solution of this class of problems is not straightforward. The reformulation of the boundary problem in terms of Volterra integral equations enables the construction of two distinct numerical methods for its solution, both based on piecewise-polynomial collocation. Convergence rates for these methods are proved and numerical results are presented to demonstrate their performance. 相似文献