全文获取类型
收费全文 | 1439篇 |
免费 | 31篇 |
国内免费 | 1篇 |
专业分类
化学 | 883篇 |
晶体学 | 15篇 |
力学 | 37篇 |
数学 | 133篇 |
物理学 | 403篇 |
出版年
2020年 | 14篇 |
2019年 | 11篇 |
2018年 | 7篇 |
2017年 | 8篇 |
2016年 | 17篇 |
2015年 | 13篇 |
2014年 | 23篇 |
2013年 | 66篇 |
2012年 | 56篇 |
2011年 | 80篇 |
2010年 | 46篇 |
2009年 | 29篇 |
2008年 | 59篇 |
2007年 | 67篇 |
2006年 | 68篇 |
2005年 | 61篇 |
2004年 | 83篇 |
2003年 | 45篇 |
2002年 | 49篇 |
2001年 | 42篇 |
2000年 | 46篇 |
1999年 | 27篇 |
1998年 | 26篇 |
1997年 | 12篇 |
1996年 | 21篇 |
1995年 | 21篇 |
1994年 | 25篇 |
1993年 | 42篇 |
1992年 | 27篇 |
1991年 | 18篇 |
1990年 | 15篇 |
1989年 | 12篇 |
1988年 | 16篇 |
1987年 | 8篇 |
1986年 | 19篇 |
1985年 | 18篇 |
1984年 | 15篇 |
1983年 | 11篇 |
1982年 | 16篇 |
1981年 | 10篇 |
1980年 | 10篇 |
1979年 | 16篇 |
1978年 | 20篇 |
1977年 | 13篇 |
1976年 | 22篇 |
1975年 | 15篇 |
1974年 | 11篇 |
1973年 | 10篇 |
1972年 | 8篇 |
1971年 | 10篇 |
排序方式: 共有1471条查询结果,搜索用时 15 毫秒
61.
The Caldeira-Leggett master equation, expressed in Lindblad form, has been used in the numerical study of the effect of a thermal environment on the dynamics of the scattering of a wave packet from a repulsive Eckart barrier. The dynamics are studied in terms of phase space trajectories associated with the distribution function, W(q,p,t). The equations of motion for the trajectories include quantum terms that introduce nonlocality into the motion, which imply that an ensemble of correlated trajectories needs to be propagated. However, use of the derivative propagation method (DPM) allows each trajectory to be propagated individually. This is achieved by deriving equations of motion for the partial derivatives of W(q,p,t) that appear in the master equation. The effects of dissipation on the trajectories are studied and results are shown for the transmission probability. On short time scales, decoherence is demonstrated by a swelling of trajectories into momentum space. For a nondissipative system, a comparison is made of the DPM with the "exact" transmission probability calculated from a fixed grid calculation. 相似文献
62.
The complexes [Ru(salen)(NO)Cl] and [Ru(salen)(NO)(H(2)O)](+) were shown to release the nitrosyl ligand as nitric oxide upon exposure to visible light in organic and aqueous solutions respectively, by means of UV-visible, EPR, and FTIR spectroscopies. The former was prepared by a new synthetic route and had its structure determined by single-crystal X-ray diffraction. A crystal of the dichloromethane solvate is orthorhombic, space group Fdd2 (No. 43) and formula C(16)H(14)ClN(3)O(3)Ru.CH(2)Cl(2), with Z = 16 and cell parameters a = 25.489(4), b = 33.435(4), and c = 9.3716(9) A. The electronic absorption spectra of the complexes were calculated using the INDO/S method. The water-soluble complex is a potential drug for antitumoral phototreatment. 相似文献
63.
Marcantonio KM Frey LF Liu Y Chen Y Strine J Phenix B Wallace DJ Chen CY 《Organic letters》2004,6(21):3723-3725
[reaction: see text] The palladium-catalyzed cyanation reaction is known to be sensitive to dissolved cyanide. Investigation into some causes of high levels of dissolved cyanide is presented here, along with a robust solution to this problem. 相似文献
64.
Capillary electrophoretic approach to screen for enzyme inhibitors in natural extracts 总被引:2,自引:0,他引:2
This paper demonstrates development of electrophoretically mediated micro analysis (EMMA), for screening protein tyrosine phosphatase (PTP) inhibitors in natural extracts. It is demonstrated that capillary electrophoresis (CE) separation of the substrate and the product allows for using the assay in an on-column format to monitor the reaction without typically used fluorogenic substrates. Michaelis-Menten kinetics parameters calculated based on the EMMA results (Km = 1.2-1.5 microM) were in a good agreement (Km = 1.0-1.5 microM) obtained using an off-line CE functional assay (CE FA). EMMA of PTP titrated with different concentrations of ligand demonstrated the peak-shift phenomenon normally seen in affinity capillary electrophoresis. This feature of EMMA gives an indication of the binding affinity of the ligand in addition to its functional activity, providing another dimension in characterization of the protein-inhibitor interaction. It was demonstrated that simultaneous screening of the primary PTP target and a secondary, counter target (PTP-C) using the EMMA format can be used to prioritize hits based on their specificity. 相似文献
65.
Long JW Logan MS Rhodes CP Carpenter EE Stroud RM Rolison DR 《Journal of the American Chemical Society》2004,126(51):16879-16889
We have developed crystalline nanoarchitectures of iron oxide that exhibit superparamagnetic behavior while still retaining the desirable bicontinuous pore-solid networks and monolithic nature of an aerogel. Iron oxide aerogels are initially produced in an X-ray-amorphous, high-surface-area form, by adapting recently established sol-gel methods using Fe(III) salts and epoxide-based proton scavengers. Controlled temperature/atmosphere treatments convert the as-prepared iron oxide aerogels into nanocrystalline forms with the inverse spinel structure. As a function of the bathing gas, treatment temperature, and treatment history, these nanocrystalline forms can be reversibly tuned to predominantly exhibit either Fe(3)O(4) (magnetite) or gamma-Fe(2)O(3) (maghemite) phases, as verified by electron microscopy, X-ray and electron diffraction, microprobe Raman spectroscopy, and magnetic analysis. Peak deconvolution of the Raman-active Fe-O bands yields valuable information on the local structure and vacancy content of the various aerogel forms, and facilitates the differentiation of Fe(3)O(4) and gamma-Fe(2)O(3) components, which are difficult to assign using only diffraction methods. These nanocrystalline, magnetic forms retain the inherent characteristics of aerogels, including high surface area (>140 m(2) g(-1)), through-connected porosity concentrated in the mesopore size range (2-50 nm), and nanoscale particle sizes (7-18 nm). On the basis of this synthetic and processing protocol, we produce multifunctional nanostructured materials with effective control of the pore-solid architecture, the nanocrystalline phase, and subsequent magnetic properties. 相似文献
66.
Brian Mckittrick Amedeo Failli Robert J. Steffan Richard M. Soll Philip Hughes Jean Schmid Andre A. Asselin C. C. Shaw R. Noureldin G. Gavin 《Journal of heterocyclic chemistry》1990,27(7):2151-2163
Three practical synthetic entries of functionalized 6-fluoro-7-substituted indole derivatives were developed in connection with the preparation of 7-fluoro-8-substituted-1,3,4,9-tetrahydropyrano[3,4-b]indole-1-acetic acid derivatives 11 . The first route, which permits group modification about position 8 of the pyranoindole skeleton, employs 2-bromo-3-fluoroaniline ( 18 ) as a key intermediate, the preparation of which was achieved by either a novel ortho metalation of 15 or via the intermediacy of 22 . The second route utilizes 32 to append a terminally functionalized three carbon side chain onto the indole template and in addition leads to 43 from 40 . The third route to the 7-fluoro-8-substituted-pyranoindole skeleton complements route two in that the synthetic pathway exploits 32 in a nucleophilic fashion to construct a terminally functionalized two carbon appendage onto the indole nucleus. 相似文献
67.
Leslie W. Deady Andrew B. Hughes Indumathy B. Mahadevan Nurul H. Quazi Leann M. Tilley 《合成通讯》2013,43(5):803-820
The synthesis of fluorescent 2,10-derivatives of the title chromophore are described. The substituents contain amino-reactive N-hydroxysuccinimde ester and thiol-reactive iodoacetamide groups for attachment to biomolecules. A phosphate derivative was also prepared as an enzyme substrate. 相似文献
68.
69.
Simon Maher Sarfaraz U. Syed David M. Hughes John R. Gibson Stephen Taylor 《Journal of the American Society for Mass Spectrometry》2013,24(8):1307-1314
Previous experimental and theoretical work identified that the application of a static magnetic (B) field can improve the resolution of a quadrupole mass spectrometer (QMS) and this simple method of performance enhancement offers advantages for field deployment. Presented here are further data showing the effect of the transverse magnetic field upon the QMS performance. For the first time, the asymmetry in QMS operation with B x and B y is considered and explained in terms of operation in the fourth quadrant of the stability diagram. The results may be explained by considering the additional Lorentz force (v x B) experienced by the ion trajectories in each case. Using our numerical approach, we model not only the individual ion trajectories for a transverse B field applied in x and y but also the mass spectra and the effect of the magnetic field upon the stability diagram. Our theoretical findings, confirmed by experiment, show an improvement in resolution and ion transmission by application of magnetic field for certain operating conditions. Figure
? 相似文献
70.
Thomas W. Gero Larry W. Jaques Richard P. Mays Debra H. Reid Dwight A. Shamblee Young S. Lo 《合成通讯》2013,43(3-4):553-559
A convenient method to prepare 5-halo-2-hydroxy-nicotinic acid is described. 相似文献