全文获取类型
收费全文 | 1202篇 |
免费 | 28篇 |
专业分类
化学 | 659篇 |
晶体学 | 10篇 |
力学 | 41篇 |
数学 | 87篇 |
物理学 | 433篇 |
出版年
2022年 | 9篇 |
2021年 | 15篇 |
2020年 | 15篇 |
2019年 | 15篇 |
2018年 | 9篇 |
2016年 | 16篇 |
2015年 | 17篇 |
2014年 | 21篇 |
2013年 | 54篇 |
2012年 | 44篇 |
2011年 | 55篇 |
2010年 | 38篇 |
2009年 | 28篇 |
2008年 | 55篇 |
2007年 | 61篇 |
2006年 | 64篇 |
2005年 | 45篇 |
2004年 | 46篇 |
2003年 | 34篇 |
2002年 | 28篇 |
2001年 | 29篇 |
2000年 | 25篇 |
1999年 | 12篇 |
1998年 | 8篇 |
1997年 | 19篇 |
1996年 | 10篇 |
1995年 | 22篇 |
1994年 | 29篇 |
1993年 | 34篇 |
1992年 | 17篇 |
1991年 | 13篇 |
1990年 | 19篇 |
1989年 | 17篇 |
1988年 | 14篇 |
1987年 | 10篇 |
1986年 | 11篇 |
1985年 | 11篇 |
1984年 | 19篇 |
1983年 | 14篇 |
1982年 | 20篇 |
1981年 | 17篇 |
1980年 | 12篇 |
1979年 | 12篇 |
1978年 | 22篇 |
1977年 | 14篇 |
1976年 | 25篇 |
1975年 | 14篇 |
1974年 | 19篇 |
1973年 | 11篇 |
1972年 | 10篇 |
排序方式: 共有1230条查询结果,搜索用时 15 毫秒
991.
Adam Elliston Samuel R. A. Collins Craig B. Faulds Ian N. Roberts Keith W. Waldron 《Applied biochemistry and biotechnology》2014,172(7):3621-3634
Waste copier paper is a potential substrate for the production of glucose relevant for manufacture of platform chemicals and intermediates, being composed of 51 % glucan. The yield and concentration of glucose arising from the enzymatic saccharification of solid ink-free copier paper as cellulosic substrate was studied using a range of commercial cellulase preparations. The results show that in all cellulase preparations examined, maximum hydrolysis was only achieved with the addition of beta-glucosidase, despite its presence in the enzyme mixtures. With the use of Accellerase® (cellulase), high substrate loading decreased conversion yield. However, this was overcome if the enzyme was added between 12.5 and 20 FPU g substrate?1. Furthermore, this reaction condition facilitated continual stirring and enabled sequential additions (up to 50 % w/v) of paper to be made to the hydrolysis reaction, degrading nearly all (99 %) of the cellulose fibres and increasing the final concentration of glucose whilst simultaneously making high substrate concentrations achievable. Under optimal conditions (50 °C, pH 5.0, 72 h), digestions facilitate the production of glucose to much improved concentrations of up to 1.33 mol l?1. 相似文献
992.
Peter R. Stevenson Bret E. Dunlap Paul S. Powell Brae V. Petersen Christopher J. Hatch Hung Chan Garret I. Still Michael T. Fulton Justin S. McKell David C. Collins 《Analytical and bioanalytical chemistry》2013,405(10):3085-3089
Single-dimension separations are routinely coupled in series to achieve two-dimensional separations, yet little has been done to simultaneously exploit multiple dimensions during separation. In this work, simultaneous chromatography and electrophoresis is introduced and evaluated for its potential to achieve two-dimensional separations. In simultaneous chromatography and electrophoresis, chromatography occurs via capillary action while an orthogonal electric field concurrently promotes electrophoresis in a second dimension. A novel apparatus with a dual solvent reservoir was designed to apply the concurrent electric field. Various compounds were used to characterize the apparatus and technique, i.e., vitamins, amino acids, and dyes. Improved separation is reported with equivalent analysis times in comparison to planar chromatography alone. The feasibility of simultaneously employing chromatography and electrophoresis in two dimensions is discussed. Figure
Separation of eight dyes is improved in comparison to (a) planar chromatography alone when employing (b) simultaneous chromatography and electrophoresis 相似文献
993.
A Comparison of the Stability and Reactivity of Diamido‐ and Diaminocarbene Copper Alkoxide and Hydride Complexes 下载免费PDF全文
Lee R. Collins Dr. Ian M. Riddlestone Dr. Mary F. Mahon Prof. Michael K. Whittlesey 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(40):14075-14084
The mononuclear N‐heterocyclic carbene (NHC) copper alkoxide complexes [(6‐NHC)CuOtBu] (6‐NHC=6‐MesDAC ( 1 ), 6‐Mes ( 2 )) have been prepared by addition of the free carbenes to the tetrameric tert‐butoxide precursor [Cu(OtBu)]4, or by protonolysis of [(6‐NHC)CuMes] (6‐NHC=6‐MesDAC ( 3 ), 6‐Mes ( 4 )) with tBuOH. In contrast to the relatively stable diaminocarbene complex 2 , the diamidocarbene derivative 1 proved susceptible to both thermal and hydrolytic ring‐opening reactions, the latter affording [(6‐MesDAC)Cu(OC(O)CMe2C(O)N(H)Mes)(CNMes)] ( 6 ). The intermediacy of [(6‐MesDAC)Cu(OH)] in this reaction was supported by the generation of Cu2O as an additional product. Attempts to generate an isolable copper hydride complex of the type [(6‐MesDAC)CuH] by reaction of 1 with Et3SiH resulted instead in migratory insertion to generate [(6‐MesDAC‐H)Cu(P(p‐tolyl)3)] ( 9 ) upon trapping by P(p‐tolyl)3. Migratory insertion was also observed during attempts to prepare [(6‐Mes)CuH], with [(6‐Mes‐H)Cu(6‐Mes)] ( 10 ) isolated, following a reaction that was significantly slower than in the 6‐MesDAC case. The longer lifetime of [(6‐Mes)CuH] allowed it to be trapped stoichiometrically by alkyne, and also employed in the catalytic semi‐reduction of alkynes and hydrosilylation of ketones. 相似文献
994.
995.
Corentin Cruch Sayak Gupta Jeremy Kodanko Shawn K. Collins 《Molecules (Basel, Switzerland)》2022,27(12)
A series of copper-based photocatalysts of the type Cu(NN)(BINAP)BF4 were synthesized bearing π-extended diimine ligands. Their behavior in several photocatalytic processes were evaluated and revealed acceptable levels of activity in an SET process, but negligible activity in PCET or ET processes. Suitable activity in ET processes could be restored through modification of the ligand. The BINAP-derived complexes were then evaluated for activity against triple-negative breast cancer cell lines. Controls indicated that copper complexes, and not their ligands, were responsible for activity. Encouraging activity was displayed by a homoleptic complex Cu(dppz)2BF4. 相似文献
996.
The binding of hydrogen in different vacancy complexes in platinum metal was investigated with atomic-scale sensitivity using perturbed angular correlations of gamma rays (PAC). Hydrogen was introduced by cathodic charging. Detrapping was monitored microscopically during desorption at 294 K by changes in site fractions of hydrogen-decorated and undecorated complexes. Analysis of desorption includes effects of retrapping of hydrogen at other sites. Assuming a trap concentration of 10–3, binding enthalpies of 0.23(2), 0.28(1), 0.24(1) and >0.20 eV are obtained for hydrogen atoms in 1V to 4V complexes, respectively. The small differences between the binding enthalpies demonstrate that hydrogen binding is insensitive to the detailed geometrical structure of small vacancy complexes. However, the magnitudes found here are a factor of two smaller than in the literature. 相似文献
997.
Multishell conduction in multiwalled carbon nanotubes 总被引:3,自引:0,他引:3
The full electronic complexity of multiwalled carbon nanotubes may be explored by sequentially removing individual carbon
shells. This technique is employed to directly measure the number of shells contributing to conduction at room temperature,
as well as the contribution of each shell to the overall conductance. By exploring the gate dependence of the conductance,
the random alternation between semiconducting and metallic shells can also be observed.
Received: 31 August 2001 / Accepted: 3 December 2001 / Published online: 4 March 2002 相似文献
998.
D. Gopi J. Indira V. Collins Arun Prakash L. Kavitha 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2009,74(1):282-284
In this paper, we have reported a novel method to synthesize nanoporous hydroxyapatite (HAP) powders by freezing organic–inorganic soft solutions. The formation of porous and crystalline HAP nanopowder was achieved via calcining the samples at 600 °C followed by sintering at temperatures ranging from 900 °C to 1100 °C. The samples were analyzed by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopic (SEM) techniques. The results showed the formation of a carbon free nanoporous hydroxyapatite powders due to the decomposition of organic template enclosing the precipitated HAP. It was also observed that the rapid grain growth with retainment of pores while the crystallinity of the HAP nanopowder increased with the increase in sintering temperature which is substantiated from the XRD and SEM results. Such organized porous materials can act as a better biomaterial for bone tissue engineering. 相似文献
999.
An overview of the experimental approaches to study weak interactions using traps is given. Both charged and neutral weak currents are considered.
相似文献1000.
A review of the techniques and applications of multichannel ellipsometry in the dual-rotating-compensator configuration is given. This ellipsometric approach has been established as the ultimate in real-time, single-spot optical measurement, as it determines the entire 16-element Mueller matrix of a sample over a wide spectral range (up to 1.7-5.3 eV) from raw data collected over a single optical period of 0.25 s. The sequence of optical elements for this ellipsometer is denoted PC1rSC2rA, where P, S, and A represent the polarizer, sample, and analyzer. C1r and C2r represent two MgF2 rotating compensators, either biplates or monoplates that rotate synchronously at frequencies of ω1 = 5ω and ω2 = 3ω, where π/ω is the fundamental optical period. Previous high-speed Mueller matrix measurements with this instrument have been performed on uniform, weakly anisotropic samples such as (110) Si, in which case one can extract the bulk isotropic and near-surface anisotropic optical responses simultaneously. In such an application, the instrument is operated at its precision/accuracy limits. Here, ex situ results on a strongly anisotropic, locally biaxial film are presented that demonstrate instrument capabilities for real-time analysis of such films during fabrication or modification. In addition, the use of the instrument as a real-time probe to extract surface roughness evolution on three different in-plane scales for an isotropic film surface is demonstrated for the first time. 相似文献