全文获取类型
收费全文 | 278篇 |
免费 | 18篇 |
国内免费 | 1篇 |
专业分类
化学 | 183篇 |
晶体学 | 3篇 |
力学 | 15篇 |
数学 | 40篇 |
物理学 | 56篇 |
出版年
2021年 | 1篇 |
2020年 | 4篇 |
2019年 | 6篇 |
2018年 | 3篇 |
2017年 | 2篇 |
2016年 | 9篇 |
2015年 | 12篇 |
2014年 | 9篇 |
2013年 | 19篇 |
2012年 | 12篇 |
2011年 | 21篇 |
2010年 | 8篇 |
2009年 | 6篇 |
2008年 | 14篇 |
2007年 | 12篇 |
2006年 | 12篇 |
2005年 | 17篇 |
2004年 | 11篇 |
2003年 | 9篇 |
2002年 | 12篇 |
2001年 | 7篇 |
2000年 | 6篇 |
1999年 | 3篇 |
1998年 | 2篇 |
1997年 | 4篇 |
1996年 | 3篇 |
1995年 | 5篇 |
1994年 | 5篇 |
1993年 | 2篇 |
1992年 | 4篇 |
1991年 | 1篇 |
1990年 | 4篇 |
1989年 | 3篇 |
1988年 | 2篇 |
1987年 | 5篇 |
1986年 | 2篇 |
1985年 | 3篇 |
1984年 | 6篇 |
1983年 | 4篇 |
1982年 | 4篇 |
1981年 | 1篇 |
1980年 | 3篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 3篇 |
1976年 | 1篇 |
1975年 | 3篇 |
1974年 | 4篇 |
1973年 | 4篇 |
1967年 | 1篇 |
排序方式: 共有297条查询结果,搜索用时 15 毫秒
11.
Greco MN Hawkins MJ Powell ET Almond HR Corcoran TW de Garavilla L Kauffman JA Recacha R Chattopadhyay D Andrade-Gordon P Maryanoff BE 《Journal of the American Chemical Society》2002,124(15):3810-3811
The serine protease cathepsin G (EC 3.4.21.20; Cat G), which is stored in the azurophilic granules of neutrophils (polymorphonuclear leukocytes) and released on degranulation, has been implicated in various pathological conditions associated with inflammation. By employing high-throughput screening, we identified beta-ketophosphonic acid 1 as a moderate inhibitor of Cat G (IC(50) = 4.1 microM). We were fortunate to obtain a cocrystal of 1 with Cat G and solve its structure by X-ray crystallography (3.5 A). Structural details from the X-ray analysis of 1.Cat G served as a platform for optimization of this lead compound by structure-based drug design. With the aid of molecular modeling, substituents were attached to the 3-position of the 2-naphthyl ring of 1, which occupies the S1 pocket of Cat G, to provide an extension into the hydrophobic S3 region. Thus, we arrived at analogue 7 with an 80-fold potency improvement over 1 (IC(50) = 53 nM). From these results, it is evident that the beta-ketophosphonic acid unit can form the basis for a novel class of serine protease inhibitors. 相似文献
12.
13.
Maverick AW Laxman RK Hawkins MA Martone DP Fronczek FR 《Dalton transactions (Cambridge, England : 2003)》2005,(1):200-206
The tetradentate Schiff-base ligand SIXH2 (alpha,alpha-bis(salicylimino)-m-xylene), prepared from salicylaldehyde and m-xylylenediamine, forms cofacial binuclear complexes with Pd and Cu. Of the two isomers possible (trans-syn and trans-anti) for M2(SIX)2, these complexes crystallize exclusively as the trans-anti isomer. In ansolvous Pd2(SIX)2, the metal-containing planes are approximately parallel, with PdPd 4.416(1) A. Pd2(SIX)2 also forms a crystalline solvate, in which the molecules adopt a more open conformation with longer metal-metal distances (5.109(1) and 5.112(1) A). The M...M distance is significantly longer in Cu2(SIX)2 (6.653(1) A), because of conformational changes in the m-xylylene moieties and substantial tetrahedral distortion about Cu. 相似文献
14.
M. A. Desando Y. P. Handa R. E. Hawkins C. I. Ratcliffe J. A. Ripmeester 《Journal of inclusion phenomena and macrocyclic chemistry》1990,8(1-2):3-16
The structure I clathrate hydrate of carbon monoxide has been studied using dielectric measurements and13C NMR spectroscopy. Broad, weak dielectric absorption curves with maxima at 2.2–3.8 K yieldE
a
= 0.14 kJ mol–1 for the average Arrhenius activation energy associated with the reorientation of the low polarity guest. Except for H2S this represents the fastest reorienting polar guest known among the clathrate hydrates. The low temperature dielectric absorption curves can best be fitted with a Cole-Davidson asymmetric distribution of relaxation times and activation energies (with = 0.06 at 4 × 106 Hz), which at 107 Hz has been resolved into a double symmetric distribution of discrete relaxation times for CO in the small and large cages. The cross-polarization magic angle spinning13C NMR spectra indicate identical chemical shifts for CO in the small and large cages, in contrast to other hydrates. The static spectra show that the CO molecules undergo anisotropic reorientation in the large cages and that there is still considerable mobility at 77 K. One possible model for the anisotropic motion has the CO rapidly moving among sites over each of the 14 faces of the cage with the CO axis orientated towards the cage centre. The cage occupancy ratio at 220 K,
s/
L = 1.11, indicates slightly greater preference of CO for the small cage.Dedicated to Dr D. W. Davidson in honor of his great contributions to the sciences of inclusion phenomena. 相似文献
15.
For every irrational number [0, 1) which is not of constant type we construct aC
2-diffeomorphism of the circle with rotation number which is of type III1. This diffeomorphism can be chosen arbitrarily close to the rotationR
. Our methods also allow us to construct, for every Liouville number [0, 1), aC
-diffeomorphism of the circle with rotation number which is of type III1. 相似文献
16.
6MAP is a fluorescent analogue of adenine that undergoes Watson-Crick base pairing and base stacking in double-stranded DNA. The one-photon absorption spectrum of 6MAP is characterized by a maximum around 330 nm with moderate quantum yield fluorescence centered at about 420 nm. To take advantage of this probe for confocal and single-molecule microscopy, it would be advantageous to be able to excite the analogue via two photons. We report the first determination of the two-photon excitation cross section and spectrum for 6MAP from 614 to 700 nm. The power dependence of the fluorescence indicates that emission results from the absorption of two photons. The one-photon and two-photon emission line shapes are identical within experimental error. A study of the concentration dependence of the fluorescence yield for one-photon excitation shows no measurable quenching up to about 5 microM. The maximum in the two-photon excitation spectrum gives a two-photon cross section, delta(TPE), of 3.4 +/- 0.1 Goeppert-Mayer (G.M.) at 659 nm, which correlates well with the one-photon absorption maximum. This compares quite favorably with cross sections of various naturally fluorescent biological molecules such as flavins and nicotiamide. In addition, we have also obtained the two-photon-induced fluorescence emission spectrum of quinine sulfate. It is approximately the same as that for one-photon excitation, suggesting that two-photon excitation of quinine sulfate may be used for calibration purposes. 相似文献
17.
18.
Low-angle X-ray diffraction measurements of the distance between myosin filaments comprising the smectic B1 liquid crystal found in skinned crayfish striated muscle were made. The interfilament distanceas a function of applied compressive osmotic pressure wasdetermined and the bulk modulus of this myofilament liquid crystal ascertained. Under compression the behavior of this myosin filament lattice is shown to be predicted well by the Murnaghan equation of state. The isothermal bulk modulus, B o, of this myosin filament liquid crystal is 1.51 × 105 dynes/cm2 at 2°C and at 46% actin overlap. 相似文献
19.
Chao Huang Steven M. Santana He Liu Neil H. Bander Benjamin G. Hawkins Brian J. Kirby 《Electrophoresis》2013,34(20-21):2970-2979
The capture of circulating tumor cells (CTCs) from cancer patient blood enables early clinical assessment as well as genetic and pharmacological evaluation of cancer and metastasis. Although there have been many microfluidic immunocapture and electrokinetic techniques developed for isolating rare cancer cells, these techniques are often limited by a capture performance tradeoff between high efficiency and high purity. We present the characterization of shear‐dependent cancer cell capture in a novel hybrid DEP–immunocapture system consisting of interdigitated electrodes fabricated in a Hele‐Shaw flow cell that was functionalized with a monoclonal antibody, J591, which is highly specific to prostate‐specific membrane antigen expressing prostate cancer cells. We measured the positive and negative DEP response of a prostate cancer cell line, LNCaP, as a function of applied electric field frequency, and showed that DEP can control capture performance by promoting or preventing cell interactions with immunocapture surfaces, depending on the sign and magnitude of the applied DEP force, as well as on the local shear stress experienced by cells flowing in the device. This work demonstrates that DEP and immunocapture techniques can work synergistically to improve cell capture performance, and it will aid in the design of future hybrid DEP–immunocapture systems for high‐efficiency CTC capture with enhanced purity. 相似文献
20.
Hyojin Lee Chi P. Huynh Stephen C. Hawkins Mustafa Musameh Dae Hyung Kim 《Liquid crystals》2013,40(3):322-327
We investigated the orientational and electro-optical properties of a nematic liquid crystal (LC) aligned with a directly spinnable carbon nanotube (CNT) web functioning both as an electrode and as an alignment layer. The LC molecules were uniformly oriented along the drawing direction of the CNT web and the spatially averaged birefringence was comparable to a rubbed polyimide sample. The CNT web sample also showed smaller residual DC and hysteresis compared to the polyimide sample. 相似文献