全文获取类型
收费全文 | 1121篇 |
免费 | 21篇 |
国内免费 | 13篇 |
专业分类
化学 | 662篇 |
晶体学 | 5篇 |
力学 | 36篇 |
数学 | 150篇 |
物理学 | 302篇 |
出版年
2022年 | 9篇 |
2021年 | 14篇 |
2020年 | 15篇 |
2019年 | 14篇 |
2018年 | 9篇 |
2017年 | 9篇 |
2016年 | 9篇 |
2015年 | 12篇 |
2014年 | 25篇 |
2013年 | 36篇 |
2012年 | 49篇 |
2011年 | 57篇 |
2010年 | 30篇 |
2009年 | 23篇 |
2008年 | 43篇 |
2007年 | 48篇 |
2006年 | 43篇 |
2005年 | 43篇 |
2004年 | 39篇 |
2003年 | 43篇 |
2002年 | 36篇 |
2001年 | 23篇 |
2000年 | 22篇 |
1999年 | 22篇 |
1998年 | 13篇 |
1997年 | 18篇 |
1996年 | 21篇 |
1995年 | 16篇 |
1994年 | 21篇 |
1993年 | 13篇 |
1992年 | 21篇 |
1991年 | 20篇 |
1990年 | 13篇 |
1988年 | 10篇 |
1986年 | 9篇 |
1985年 | 16篇 |
1984年 | 14篇 |
1983年 | 9篇 |
1982年 | 14篇 |
1981年 | 14篇 |
1980年 | 21篇 |
1979年 | 12篇 |
1978年 | 11篇 |
1977年 | 13篇 |
1976年 | 16篇 |
1975年 | 9篇 |
1974年 | 13篇 |
1973年 | 20篇 |
1972年 | 10篇 |
1937年 | 8篇 |
排序方式: 共有1155条查询结果,搜索用时 15 毫秒
71.
Yasser M. Loksha Per T. Jrgensen Erik B. Pedersen Mahmoud A. El‐Badawi Ahmed A. El‐Barbary Claus Nielsen 《Journal of heterocyclic chemistry》2002,39(2):375-382
5‐Alkyl‐4‐benzyl‐1,3‐dihydroimidazol‐2‐ones ( 3a‐d ) and 5‐alkyl‐4‐benzyl‐1,3‐dihydroimidazole‐2‐thiones (7a‐d) were prepared via Dakin West reaction on DL‐phenylalanine with the appropriate aliphatic acid anhydrides followed by hydrolysis and reaction with potassium cyanate or potassium thiocyanate. Compounds 3a‐d were alkylated with ethoxymethyl chloride to give the alkylated imidazoles 5a‐d which were considered analogues of Emivirine with deletion of carbonyl group at the 4‐position. Alkylation of 7a‐d afforded the corresponding S‐alkylated derivatives 8a‐p which in a similar way were considered analogues of S‐DABO. However all the imidazole derivatives were devoid of activity against HIV. 相似文献
72.
Monitoring the Transition from Spherical to Polymer‐like Surfactant Micelles Using Small‐Angle X‐Ray Scattering 下载免费PDF全文
Dr. Grethe Vestergaard Jensen Dr. Reidar Lund Dr. Jérémie Gummel Dr. Theyencheri Narayanan Prof. Jan Skov Pedersen 《Angewandte Chemie (International ed. in English)》2014,53(43):11524-11528
Despite over a century of modern surfactant science, the kinetic pathways of morphological transitions in micellar systems are still not well understood. This is mainly as a result of the lack of sufficiently fast methods that can capture the structural changes of such transitions. Herein, a simple surfactant system consisting of sodium dodecyl sulfate (SDS) in aqueous NaCl solutions is investigated. Combining synchrotron radiation small‐angle X‐ray scattering (SAXS) with fast stopped‐flow mixing schemes allows monitoring the process where polymer‐like micelles are formed from globular micelles when the salt concentration is suddenly increased. The results show that “worm‐like” micelles are formed by fusion of globular micelles and short cylinders in a fashion that bears similarities to a step‐like polymerization process. 相似文献
73.
Tuija Jokinen Dr. Mikko Sipilä Stefanie Richters Prof. Veli‐Matti Kerminen Dr. Pauli Paasonen Dr. Frank Stratmann Dr. Douglas Worsnop Prof. Markku Kulmala Dr. Mikael Ehn Prof. Hartmut Herrmann Dr. Torsten Berndt 《Angewandte Chemie (International ed. in English)》2014,53(52):14596-14600
Gas‐phase oxidation routes of biogenic emissions, mainly isoprene and monoterpenes, in the atmosphere are still the subject of intensive research with special attention being paid to the formation of aerosol constituents. This laboratory study shows that the most abundant monoterpenes (limonene and α‐pinene) form highly oxidized RO2 radicals with up to 12 O atoms, along with related closed‐shell products, within a few seconds after the initial attack of ozone or OH radicals. The overall process, an intramolecular ROO→QOOH reaction and subsequent O2 addition generating a next R′OO radical, is similar to the well‐known autoxidation processes in the liquid phase (QOOH stands for a hydroperoxyalkyl radical). Field measurements show the relevance of this process to atmospheric chemistry. Thus, the well‐known reaction principle of autoxidation is also applicable to the atmospheric gas‐phase oxidation of hydrocarbons leading to extremely low‐volatility products which contribute to organic aerosol mass and hence influence the aerosol–cloud–climate system. 相似文献
74.
Kaloustian J. Pauli A. M. Pieroni G. Portugal H. 《Journal of Thermal Analysis and Calorimetry》2002,70(3):959-973
The human urinary calculi are mainly constituted by calcium oxalate, magnesium ammonium phosphate hexahydrate, and uric acid.
The ions or molecules are easily characterized by wet chemical methods. The difficulties appear in the differentiation of
the hydrates of calcium oxalate (monohydrate COM or Whewellite, and dihydrate COD or Weddelite). A high level of COD in the
urinary stones leads, often, inflammation, sharp pain and blood in urine. In the worse cases, they must be extracted by surgical
way. The identification of the main components of urinary calculi, the knowledge of the true number of water molecules bounded
to the calcium oxalate, and the determination of each hydrate in the mixture, are the interests of this memory. The thermal
analysis (simultaneous DTA-TG) was applied on thirty-three urinary calculi. The determination of the calcium oxalate hydrates
was confirmed by calorimetry (DSC).
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
75.
We present a space‐time finite element method capable of dealing with flows in multiple co‐rotating reference frames. Since equal order interpolation is used for all degrees of freedom, Galerkin/least‐squares stabilization is applied. We give a detailed derivation of the equations involved, introduce the variational form, present the stabilization parameters, and also discuss implementation issues. Numerical examples in 2D and 3D show generality and efficiency of the method, if steady‐state behavior of rotating components is sufficient for the CFD analysis. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
76.
The confinement of a nonneutral plasma in a magnetic-surface, or stellarator, configuration is explored. The fluid equilibrium equations are derived and are found to be fundamentally different from previous results. Diocotron modes are predicted to be stable. The collisional confinement time can be very long. Possible applications include positron trapping and confinement of positron-electron plasmas. The basic physics can be addressed experimentally in the simple tabletop stellarator planned for construction at Columbia University. 相似文献
77.
We propose a theoretical model for the recently reported anomalously long decay of a space-charge field that was resonantly excited in a photorefractive sillenite crystal [Phys. Rev. Lett. 79, 67 (1997)]. The model is based on the conventional concept of charge transfer and does not require excessively large values of the quality factor for space-charge waves. The effect in question is qualified as a critical slowing of the relaxation process as the threshold of optical oscillation is approached. 相似文献
78.
We have studied the time distribution of semi-leptonic decays of the neutral K meson produced in a hydrogen bubble chamber in the reaction K+p → Kopπ+ with K+ momenta between 1.2 and 1.7 GeV/c. We have identified 306 πev decays and 74 πμv decays of known lepton charge with proper times between 0.04 and 20 KS lifetimes. 相似文献
79.
Christian L. Pedersen Ole Buchardt Sine Larsen Kenneth J. Watson 《Tetrahedron letters》1973,14(24):2195-2198
80.
Niels Vigand Pedersen 《Journal of Functional Analysis》1981,43(3):368-393
For an arbitrary separable locally compact group G we exhibit a canonical Borel subset of the quasi-dual (with the Mackey Borel structure), such that is a standard Borel space in the induced Borel structure, and such that the canonical measure for the left regular representation λGof G is concentrated on . On the basis of this we discuss the (non-unimodular) “Plancherel theorem.” 相似文献