全文获取类型
收费全文 | 467篇 |
免费 | 3篇 |
国内免费 | 4篇 |
专业分类
化学 | 326篇 |
晶体学 | 6篇 |
力学 | 5篇 |
数学 | 40篇 |
物理学 | 97篇 |
出版年
2019年 | 4篇 |
2017年 | 2篇 |
2016年 | 4篇 |
2014年 | 7篇 |
2013年 | 10篇 |
2012年 | 7篇 |
2011年 | 14篇 |
2010年 | 10篇 |
2009年 | 7篇 |
2008年 | 15篇 |
2007年 | 11篇 |
2006年 | 20篇 |
2005年 | 30篇 |
2004年 | 20篇 |
2003年 | 27篇 |
2002年 | 24篇 |
2001年 | 16篇 |
2000年 | 17篇 |
1999年 | 10篇 |
1998年 | 7篇 |
1997年 | 4篇 |
1996年 | 6篇 |
1995年 | 8篇 |
1994年 | 6篇 |
1993年 | 7篇 |
1992年 | 7篇 |
1991年 | 5篇 |
1990年 | 6篇 |
1989年 | 2篇 |
1988年 | 10篇 |
1987年 | 7篇 |
1986年 | 7篇 |
1985年 | 16篇 |
1984年 | 10篇 |
1983年 | 10篇 |
1982年 | 18篇 |
1981年 | 10篇 |
1980年 | 9篇 |
1979年 | 11篇 |
1978年 | 4篇 |
1977年 | 7篇 |
1976年 | 5篇 |
1975年 | 5篇 |
1974年 | 4篇 |
1973年 | 10篇 |
1972年 | 3篇 |
1969年 | 3篇 |
1968年 | 2篇 |
1967年 | 2篇 |
1932年 | 2篇 |
排序方式: 共有474条查询结果,搜索用时 15 毫秒
91.
Although there are a number of existing assays for monitoring the activity of both isopenicillin N synthase (IPNS) and deacetoxycephalosporin C synthase (DAOCS), none have demonstrated the qualities required for screening a mutant library. Hence, enzyme-linked immunosorbent assays (ELISAs) for IPNS and DAOCS were developed based on the detection of the catalytic turnover products isopenicillin N and cephalexin/phenylacetyl-7-aminodeacetoxycephalosporanic acid (G-7-ADCA), respectively. These assays are relatively fast compared to existing assays, such as the hole-plate bioassay, and are amenable with high-throughput screening. Both the IPNS and DAOCS-ELISAs were optimised for use with crude protein extracts rather than purified protein, thereby eliminating any additional time required for purification. The ELISA developed for the detection of cephalexin had an IC50 value of 154 ± 9 ng mL−1 and LOD of 7.2 ± 2.2 ng mL−1 under conditions required for the assay. Good recoveries and correlation was observed for spiked samples when the concentration of crude protein was kept below 1 mg mL−1. The DAOCS-ELISA was found to have increased sensitivity compared to the hole-plate bioassay (10.3 μg mL−1). The IPNS-ELISA did not significantly increase the sensitivity (approximately 5 μg mL−1) compared to that of the hole-plate bioassay (16 μg mL−1) for isopenicillin N. The minimum amount of crude protein extract required for producing detectable amounts of product for both assays was below 0.5% of the maximum amount of protein that the assay could contain without any effect on the ELISA. This suggests that when screening a mutant library, mutants producing low amounts of the product could still be detected using these assays. 相似文献
92.
Cheruzel LE Cecil MR Edison SE Mashuta MS Baldwin MJ Buchanan RM 《Inorganic chemistry》2006,45(8):3191-3202
A new polyimidazole tripod N,N-bis((1-methyl-4-pivalamidoimidazol-2-yl)methyl)-N'-((1-methylimidazol-2-yl)methyl)amine (L2) has been synthesized and shown to form intramolecular hydrogen bonds with different axial ligands bonded to Cu(II) in the solid state. The same hydrogen-bonding property of L2 appears responsible for the stabilization of a Cu(II)-OOH species in solution. The crystal structures of L2 and three of its Cu(II) complexes are reported. The [Cu(L2)X]ClO4 complexes, 4-6 (X- = Cl-, OH-, or N3-) have distorted trigonal bipyramidal geometries in the solid state and have been characterized further by UV-vis absorption, electron paramagnetic resonance (EPR) spectroscopy, and cyclic voltammetry. The reaction of [Cu(L2)OH](ClO4) (5) with H2O2 and tert-butyl hydroperoxide in methanol generates [Cu(L2)OOH](ClO4) (7) and [Cu(L2)OO(t)Bu](ClO4) (8) which have been characterized by different spectroscopic methods. The compound [Cu(L2)OO(t)Bu]+ displays a band at 395 nm (epsilon = 950 M(-1) cm(-1)) assigned to an alkylperoxo pi*(sigma) --> Cu ligand-to-metal charge transfer (LMCT) transition, while [Cu(L2)OOH]+ displays a peroxo pi*(sigma) --> Cu charge-transfer transition at 365 nm with epsilon = 1300 M(-1) cm(-1), a mass ion at m/z 593.4, and nu(O-O) stretch (resonance Raman) at 854 cm(-1) that shifts to lower energy by 46 cm(-1) upon 18O substitution. 相似文献
93.
Zhuang J Amoroso JH Kinloch R Dawson JH Baldwin MJ Gibney BR 《Inorganic chemistry》2006,45(12):4685-4694
Heme a, the metalloporphyrin cofactor unique to cytochrome c oxidases, differs from the more common heme b by two chemical modifications, a C-2 hydroxyethylfarnesyl group and a C-8 formyl group. To elucidate a role of the C-8 formyl group, we compare the heme affinity, spectroscopy, and electrochemistry of a heme a mimic, Fe(diacetyldeuterioporphyrin IX) or Fe(DADPIX), with heme b, Fe(protoporphryrin IX) or Fe(PPIX), incorporated into a designed heme protein. The [Delta7-H3m]2 protein ligand, or maquette, selected for this study contains two equivalent bis-(3-methyl-L-histidine) heme binding sites within a four-alpha-helix bundle scaffold. The spectroscopic data on Fe(PPIX) and Fe(DADPIX) bound to [Delta7-H3m]2 demonstrate that these complexes are excellent synthetic analogues for natural cytochromes b and a, respectively. Comparison of the spectroscopic, electrochemical, and equilibrium thermodynamic data measured for the Fe(PPIX)-[Delta7-H3m]2 maquette with the previously reported Fe(PPIX)-[Delta7-His]2 complex demonstrates that changing the heme axial ligands to 3-methyl-L-histidine from L-histidine does not alter the resulting heme protein properties significantly in either oxidation state. Heme binding studies demonstrate that [Delta7-H3m]2 binds two ferrous Fe(DADPIX) or Fe(PPIX) moieties with similar dissociation constant values. However, in the ferric state, the data show that [Delta7-H3m]2 only binds a single Fe(DADPIX) and that one 2500-fold weaker than oxidized Fe(PPIX). The data demonstrate that the 4.6 kcal mol(-1) weakened affinity of [Delta7-H3m]2 for oxidized Fe(DADPIX) results in the majority of the 160 mV, 3.7 kcal mol(-1), positive shift in the heme reduction potential relative to Fe(PPIX). These data indicate that a role of the formyl group on heme a is to raise the iron reduction potential, thus making it a better electron acceptor, but that it does so by destabilizing the affinity of bis-imidazole sites for the ferric state. 相似文献
94.
E. G. Fu Y. Q. Wang G. F. Zou J. Xiong M. J. Zhuo Q. M. Wei J. K. Baldwin Q. X. Jia L. Shao A. Misra M. Nastasi 《Applied Physics A: Materials Science & Processing》2012,108(1):121-126
We studied the effect of irradiation on small angle grain boundaries in mosaic structured Cu thin films. The films showed a decrease in mosaic spread via a narrowing of the full width at half maximum in XRD rocking curves and a smaller minimum yield of RBS channeling after irradiation. These data indicate the irradiation decreased the misorientation angles between mosaic blocks separated by small angle grain boundaries. Mechanisms involving interactions between grain boundary dislocations and irradiation induced defects are discussed. 相似文献
95.
Manson JL Baldwin AG Scott BL Bendix J Del Sesto RE Goddard PA Kohama Y Tran HE Ghannadzadeh S Singleton J Lancaster T Möller JS Blundell SJ Pratt FL Zapf VS Kang J Lee C Whangbo MH Baines C 《Inorganic chemistry》2012,51(14):7520-7528
[Ni(HF(2))(3-Clpy)(4)]BF(4) (py = pyridine) is a simple one-dimensional (1D) coordination polymer composed of compressed NiN(4)F(2) octahedra that form chains with bridging HF(2)(-) ligands. In spite of significant distortion of the HF(2)(-) bridge, a quasi-1D antiferromagnetic (AFM) behavior was observed with J(FHF) = 4.86 K. 相似文献
96.
Wetting Phase Bridges Establish Capillary Continuity Across Open Fractures and Increase Oil Recovery in Mixed-Wet Fractured Chalk 总被引:1,自引:0,他引:1
Eirik Aspenes Geir Ersland Arne Graue Jim Stevens Bernard A. Baldwin 《Transport in Porous Media》2008,74(1):35-47
The effect of fractures on oil recovery and in situ saturation development in fractured chalk has been determined at near
neutral wettability conditions. Fluid saturation development was monitored both in the matrix and in the fractures and the
mechanisms of fracture crossing were determined using high spatial resolution MRI. Capillary continuity across open oil-filled
fractures was verified by imaging the water bridges established within the fracture. Despite an alternate escape fracture
for the water, separate water bridges were shown to be stable for the entire duration of the experiments. The established
capillary contact resulted in oil recovery exceeding the spontaneous imbibition potential in the outlet-isolated cores by
ca. 10% PV. This is explained by viscous recovery provided by water bridges across open fractures. The size of the bridges
seemed to be controlled by the wettability of the rock and not by the differential pressure applied across the open fracture. 相似文献
97.
98.
Baldwin Rusty O. Davis IV Nathaniel J. Kobza John E. Midkiff Scott F. 《Queueing Systems》2000,35(1-4):1-21
Real-time scheduling, or scheduling with respect to a deadline, is critical in many application areas such as telecommunications,
control systems, and manufacturing. This paper presents a novel approach to real-time scheduling based on a queueing theory
model. Using real-time queueing theory (RTQT), one can analytically determine the distribution of the lead-time profile (i.e.,
the time until the deadline is reached) of customers waiting for service. Emphasis is placed on the development of the equations
used to determine the lead-time profile distribution. The development of the GI/G/1 case is presented and confirmed using
simulation. Simulation results confirm prior research for the M/M/1 and GI/M/1 case. As a practical application, RTQT is used
to implement a packet admission control algorithm for a telecommunications network. Using this algorithm, packet lateness
was reduced by up to 31%.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
99.
Stewart Baldwin 《Journal of Fixed Point Theory and Applications》2010,7(1):201-222
We construct abstract Julia sets homeomorphic to Julia sets for complex polynomials of the form f
c
(z) = z
2 + c, having an associated periodic kneading sequence of the form [`(a*)]{\overline{\alpha\ast}} which is not a period n-tupling. We show that there is a single simply-defined space of “itineraries” which contains homeomorphic copies of all such
Julia sets in a natural combinatorial way, with dynamical properties which are derivable directly from the combinatorics.
This also leads to a natural definition of abstract Julia sets even for those kneading sequences which are not realized by
any polynomial f
c
, with similar dynamical properties. 相似文献
100.
Xia JS Pan W Vicente CL Adams ED Sullivan NS Stormer HL Tsui DC Pfeiffer LN Baldwin KW West KW 《Physical review letters》2004,93(17):176809
At a very low-temperature of 9 mK, electrons in the second Landau level of an extremely high-mobility two-dimensional electron system exhibit a very complex electronic behavior. With a varying filling factor, quantum liquids of different origins compete with several insulating phases leading to an irregular pattern in the transport parameters. We observe a fully developed nu=2+2/5 state separated from the even-denominator nu=2+1/2 state by an insulating phase and a nu=2+2/7 and nu=2+1/5 state surrounded by such phases. A developing plateau at nu=2+3/8 points to the existence of other even-denominator states. 相似文献