全文获取类型
收费全文 | 277篇 |
免费 | 13篇 |
国内免费 | 1篇 |
专业分类
化学 | 181篇 |
晶体学 | 3篇 |
力学 | 13篇 |
数学 | 39篇 |
物理学 | 55篇 |
出版年
2022年 | 2篇 |
2020年 | 4篇 |
2019年 | 6篇 |
2018年 | 3篇 |
2017年 | 2篇 |
2016年 | 9篇 |
2015年 | 11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 | 13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 | 5篇 |
1999年 | 3篇 |
1998年 | 2篇 |
1997年 | 3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 | 3篇 |
1986年 | 1篇 |
1985年 | 3篇 |
1984年 | 6篇 |
1983年 | 3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291条查询结果,搜索用时 0 毫秒
91.
Chris Holland Nicholas Hawkins Martin Frydrych Peter Laity David Porter Fritz Vollrath 《Macromolecular bioscience》2019,19(3)
Native silk proteins, extracted directly from the silk gland prior to spinning, offer access to a naturally hydrated protein that has undergone little to no processing. Combined with differential scanning calorimetry (DSC), it is possible to probe the thermal stability and hydration status of silk and thus investigate its denaturation and solidification, echoing that of the natural spinning process. It is found that native silk is stable between ?10 °C and 55 °C, and both the high‐temperature enthalpy of denaturation (measured via modulated temperature DSC) and a newly reported low‐temperature ice‐melting transition may serve as useful quality indicators in the future for artificial silks. Finally, compared to albumin, silk's denaturation enthalpy is much lower than expected, which is interpreted within a recently proposed entropic desolvation framework which can serve to unveil the low‐energy aquamelt processing pathway. 相似文献
92.
Peter Wonneberger Nils Knig Fabian B. Kraft Menyhrt B. Srosi Evamarie Hey‐Hawkins 《Angewandte Chemie (International ed. in English)》2019,58(10):3208-3211
The unprecedented phospha‐aza‐Diels–Alder reaction between an activated electron‐poor imine and 2H‐phospholes yields 1‐phospha‐2‐azanorbornenes in a highly chemoselective and moderately diastereoselective reaction. The intermediate 2H‐phospholes, which act as dienes, are formed in situ from the corresponding 1H‐phospholes. Theoretical calculations confirm that the phospha‐aza‐Diels–Alder reaction is of normal electron demand. The reactive P?N bond in 1‐phospha‐2‐azanorbornenes can be cleaved by nucleophiles leading to the formation of 2,3‐dihydrophospholes. 相似文献
93.
Assessing model fit by cross-validation 总被引:8,自引:0,他引:8
Hawkins DM Basak SC Mills D 《Journal of chemical information and computer sciences》2003,43(2):579-586
When QSAR models are fitted, it is important to validate any fitted model-to check that it is plausible that its predictions will carry over to fresh data not used in the model fitting exercise. There are two standard ways of doing this-using a separate hold-out test sample and the computationally much more burdensome leave-one-out cross-validation in which the entire pool of available compounds is used both to fit the model and to assess its validity. We show by theoretical argument and empiric study of a large QSAR data set that when the available sample size is small-in the dozens or scores rather than the hundreds, holding a portion of it back for testing is wasteful, and that it is much better to use cross-validation, but ensure that this is done properly. 相似文献
94.
Gahan LR Grillo VA Hambley TW Hanson GR Hawkins CJ Proudfoot EM Moubaraki B Murray KS Wang D 《Inorganic chemistry》1996,35(4):1039-1044
Reaction of manganese(II) perchlorate hexahydrate with a methanol solution of 1-thia-4,7-diazacyclononane ([9]aneN(2)S) resulted in the isolation of the manganese(II) complex [Mn([9]aneN(2)S)(2)](ClO(4))(2). The X-ray structure of this complex is reported: crystal system orthorhombic, space group Pbam, No. 55, a = 7.937(2) ?,b = 8.811(2) ?, c = 15.531(3) ?, Z = 2, R = 0.0579. The complex is high spin (S = (5)/(2)) with an effective magnetic moment (&mgr;(eff)) 5.82 &mgr;(B) at 298 K and 5.65 &mgr;(B) at 4.2 K. Computer simulation of the Q-band EPR spectrum of [Mn([9]aneN(2)S)(2)](ClO(4))(2) yields g = 1.99 +/- 0.01, |D| = 0.19 +/- 0.005 cm(-)(1), and E/D = 0.04 +/- 0.02. For the analogous hexaamine complex [Mn([9]aneN(3))(2)](ClO(4))(2) ([9]aneN(3) = 1,4,7-triazacyclononane) analysis of the EPR spectra produced the following values: g = 1.98 +/- 0.01, |D| = 0.09 +/- 0.003 cm(-)(1), and E/D = 0.1 +/- 0.01. The spin Hamiltonian parameters for [Mn([9]aneN(2)S)(2)](ClO(4))(2) derived from the EPR spectra produced a good fit to the magnetic susceptibility data. 相似文献
95.
96.
Ribière P Bravo-Altamirano K Antczak MI Hawkins JD Montchamp JL 《The Journal of organic chemistry》2005,70(10):4064-4072
[reaction: see text] A new nickel-based catalytic system has been developed for phosphorus-carbon bond formation. The addition of alkyl phosphinates to alkynes is catalyzed by nickel chloride in the absence of added ligand. The reaction generally proceeds in high yields, even with internal alkynes, which were poor substrates in our previously reported palladium-catalyzed hydrophosphinylation of alkyl phosphinates. The method is useful for the preparation of H-phosphinate esters and their derivatives. The one-pot synthesis of various important organophosphorus compounds is also demonstrated. The reaction can be conducted with microwave heating. 相似文献
97.
Cold preservation of endothelial cells was studied, comparing primary endothelial cells (human umbilical vein endothelial cells - HUVECs) and a continuously growing cell line (ECV304 cells). Viability at the end of 24h cold preservation was measured by dye exclusion, whilst metabolism was assessed by Alamar blue conversion. Two preservation solutions were studied (UW solution) and sucrose-based (SbS) in both cell types. The response was similar in both cell types to preservation under normoxic conditions (with percentage dye exclusion maintained at about 80 percent in both preservation solutions) whereas under hypoxic conditions ECV304 were more sensitive to preservation in UW solution (dye exclusion reduced to 43.5+/-1.4 percent versus 73.6+/-14 percent (P<0.01). Metabolism assessed by Alamar blue conversion after cold preservation and rewarming was similar in both ECV304 and HUVECs after storage under normoxic conditions in UW solution, but in both cell types, metabolism was higher in SbS (P<0.05 and p<0.01) than in UW solution. Under hypoxic conditions, both cell types showed similar recovery of metabolism after storage in either UW or SbS. If the cells (in this case ECV304 under aerobic conditions) were stored for 24h and then allowed to rewarm in either of the respective preservation solutions (UW or SbS for 1h) before the Alamar blue test, metabolism was higher (p less than 0.01) in those exposed to SbS. UW solution and SbS provide similar protection for endothelial cells under hypoxic conditions, but SbS has some advantages under normoxic storage or if the cells experience variable temperatures in the presence of residual preservation solution at the end of cold preservation period. 相似文献
98.
99.
100.
This paper presents a theoretical model for dealing with uncertainity in capital investment. Utilizing the problem of recurring capital replacement, an optimum strategy is derived under variable discounting. A linear approximation to the variable discount function is given as an illustration. 相似文献