全文获取类型
收费全文 | 402篇 |
免费 | 4篇 |
专业分类
化学 | 332篇 |
晶体学 | 9篇 |
力学 | 7篇 |
数学 | 22篇 |
物理学 | 36篇 |
出版年
2023年 | 2篇 |
2022年 | 32篇 |
2021年 | 30篇 |
2020年 | 9篇 |
2019年 | 6篇 |
2018年 | 3篇 |
2017年 | 8篇 |
2016年 | 11篇 |
2015年 | 11篇 |
2014年 | 10篇 |
2013年 | 25篇 |
2012年 | 18篇 |
2011年 | 22篇 |
2010年 | 18篇 |
2009年 | 18篇 |
2008年 | 25篇 |
2007年 | 22篇 |
2006年 | 24篇 |
2005年 | 22篇 |
2004年 | 17篇 |
2003年 | 12篇 |
2002年 | 17篇 |
2001年 | 16篇 |
2000年 | 2篇 |
1999年 | 1篇 |
1998年 | 3篇 |
1997年 | 3篇 |
1995年 | 1篇 |
1994年 | 2篇 |
1993年 | 1篇 |
1992年 | 2篇 |
1991年 | 1篇 |
1990年 | 2篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1981年 | 1篇 |
1978年 | 1篇 |
1975年 | 1篇 |
1968年 | 1篇 |
排序方式: 共有406条查询结果,搜索用时 15 毫秒
111.
Jolanta Poplawska Ashraf Labib Deborah M Reed 《The Journal of the Operational Research Society》2015,66(9):1491-1505
Integration of corporate social responsibility (CSR) into a company’s mainstream strategy is a complex task. Practical implementation of CSR requires analysis of both the external and internal environments to determine the prospects and challenges significantly influencing integration of sustainability into business strategy. In order to overcome limitations of single multiple-criteria decision analysis models, this paper proposes a hybrid integrated framework combining cognitive mapping and analytic networks process (ANP) to determine, prioritise and select CSR programmes for implementation. The strategic cognitive map serves as a foundation to build the ANP network and identify the importance of CSR programmes. A knapsack optimisation method is then used to optimally assign resources to CSR alternatives. We demonstrate the usefulness of the framework through a case study in the extractive sector. The framework was empirically tested with 61 respondents using postal and online surveys, MBA workshops, and conference networking. 相似文献
112.
Single‐component self‐assembled monolayers (SAMs) of mercaptoethanesulfonate (MES) on Ag surfaces were studied with surface‐enhanced resonance Raman scattering (SERRS) spectroscopy with a view to their application to immobilize (ferro)cytochrome c (cyt c). SERS studies revealed that MES molecules adopt primarily trans (T) conformation even at early stages of the SAM growth and over wide range of pH values. High accessibility of the negatively charged groups for (bio)molecules in solution makes single‐component MES SAMs suitable linkage monolayers for electrostatic attachment of cyt c, which was verified with SERRS. Cyt c was successfully anchored to MES‐coated Ag at natural (∼5), neutral, and isoelectric point (10.6) pH. At pH = 7.0 and 10.6, SERRS bands characteristic of native six‐coordinated low‐spin (6cLS) heme iron configuration were detected. Lack of buffering resulted in additional appearance of five‐coordinated high‐spin (5cHS) SERRS markers and the presence of bands indicating ferric ion. An electrostatic attraction between protein and SAM was confirmed to exclude the hydrophobic interactions involved in cyt c binding. Cyt c attached to MES SAM on Ag was found to be electroactive at neutral pH, and protein oxidation was assisted with reversible conversion of 6cLS to the non‐native 5cHS state. Alteration of heme orientation deduced from SERRS spectra upon change of redox state allowed us to propose the protein dynamics as the electron transfer rate‐limiting step. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
113.
The interaction of Cibacron blue F3G-A with two therapeutic proteins, recombinant human growth hormone and recombinant human interferon-alpha2b, has been examined by applying gel-permeation chromatography in combination with the absorption difference spectroscopy. The complexes of these proteins with Cibacron blue F3G-A have been isolated, and their absorbance spectra have been registered. The influence of Cibacron blue F3G-A on the oligomeric state of proteins has been investigated. It was found that Cibacron blue F3G-A promotes the generation of interferon-alpha2b dimers at pH 5.0. 相似文献
114.
A reversed-phase high-performance liquid chromatography method with gradient elution was developed for the determination of the caffeic, p-coumaric, and ferulic acids in propolis concentrates. Solid-phase extraction on an RP18 column was applied for preliminary purification, and chromatographic separation was performed on 100 RP18e Lichrospher column of particle size 5 microm. The mobile phase was obtained by mixing in appropriate ratios 0.03 mM NaH2PO4, acidified with H3PO4 up to pH = 3.0, with acetonitrile to obtain a gradient in the elution process. Spectrophotometric detection was conducted at 320 nm. Under the established conditions, the method featured high sensitivity, good precision, and comparability of results, as proven by method validation and statistical analysis of the obtained results. The limits of detection were 0.315, 0.325, and 0.695 microg/mL for caffeic, p-coumaric, and ferulic acids, respectively. The corresponding recovery values were 98.14, 101.05, and 99.42% and the linearity ranges from 1.31 to 99.18 microg/mL, 1.52 to 119.16 microg/mL, and 2.42 to 184.14 microg/mL. The precision of the method was expresed by relative standard deviation values that did not exceed 3%. It was also shown that the propolis concentrates under examination had similar antibacterial activity against Staphylococcus aureus ranging from 119.8 to 124.3 microg/mL, contrary to model mixtures that showed no antibacterial activity. 相似文献
115.
Getautis V Daskeviciene M Malinauskas T Stanisauskaite A Stumbraite J 《Molecules (Basel, Switzerland)》2006,11(1):64-71
A series of mono and di-N-2,3-epoxypropyl N-phenylhydrazones have been prepared on a large scale by reaction of the corresponding N-phenylhydrazones of 9-ethyl-3-carbazolecarbaldehyde, 9-ethyl-3,6-carbazoledicarbaldehyde, 4-dimethyl-amino-, 4-diethylamino-, 4-benzylethylamino-, 4-(diphenylamino)-, 4-(4,4-4'-dimethyl-diphenylamino)-, 4-(4-formyldiphenylamino)- and 4-(4-formyl-4'-methyldiphenyl-amino)benzaldehyde with epichlorohydrin in the presence of KOH and anhydrous Na(2)SO(4). 相似文献
116.
A series of molecular homo and heteroleptic zinc and magnesium compounds with aminophenolate ligands [(µ,η2-L2)ZnEt]2 ( 1 ), [(η2-L2)Zn(µ-BnO)]2 ( 2 ), [Zn(η2-L2)2] ( 3 ), [Zn(η2-L3)2] ( 4 ), [Mg(η2-L3)2] ( 5 ) (L2-H = N-[methylene(2-hydroxy-3,5-di-tert-butylphenyl)]-N-methyl-N-cyclohexylamine, L3-H = N-[methylene(2-hydroxy-3,5-di-tert-butylphenyl)]-N-methyl-N-methyl-1,3-dioxolaneamine) have been prepared and characterized. The homoleptic complexes 3–5 are most probably a mixture of diastereoisomers that in solution show an interesting dynamics which plays an important role in their catalytic behavior. The complexes 2 – 5 are efficient initiators in ring-opening polymerization (ROP) of lactides to produce polymers with desired molecular weight and narrow polydispersity. 相似文献
117.
Marta Ziegler-Borowska Jolanta Kutkowska Bo?ena Modzelewska-Banachiewicz Anna Kaczmarek-K?dziera 《Tetrahedron letters》2010,51(22):2951-2955
An analysis of the products of the reaction of N3-phenylbenzamidrazone with cis-1,2-cyclohexanedicarboxylic anhydride at various temperatures is presented. The identification of the reaction products is carried on with the support of computational techniques. The most stable conformers of the isoindole and triazole derivatives are found within the DFT approach. The theoretical calculations reveal the possible structure of a triazole derivative not available experimentally because of the presence of two diastereoisomers of equal energy. 相似文献
118.
Kapturowska AU Stolarzewicz IA Krzyczkowska J Białecka-Florjańczyk E 《Ultrasonics sonochemistry》2012,19(1):186-191
The aim of this study was to evaluate the efficiency of sonication in releasing protein from a widespread lipase-producing yeast, Yarrowia lipolytica KKP 379, and to examine the impact of ultrasound waves generated in a horn-type sonicator on the lipolytic activity of Y. lipolytica in the hydrolysis of p-nitrophenyl laurate. In this paper, we focused on a few parameters of ultrasound cell disruption, such as the time of sonication, acoustic power, storage time of the frozen yeast biomass used in sonication and the solvent used to suspend the yeast cells which were considered as the most important part in the process of obtaining a biocatalyst from Y. lipolytica for organic synthesis. The most effective additive in protein release proved to be 2% Tween 80; other ideal parameters of the process were ultrasonic power at 150 W for 15 min and 9 weeks of frozen biomass storage time. The sonication parameters, which were the best for protein release, did not seem to be the most effective for obtaining high lipolytic activity due to denaturation as an effect of cavitation. 相似文献
119.
In this paper, the derivation of macroscopic transport equations for this cases of simultaneous heat and water, chemical and water or electrical and water fluxes in porous media is presented. Based on themicro-macro passage using the method of homogenization of periodic structures, it is shown that the resulting macroscopic equations reveal zero-valued cross-coupling effects for the case of heat and water transport as well as chemical and water transport. In the case of electrical and water transport, a nonsymmetrical coupling was found.Notations
b
mobility
-
c
concentration of a chemical
-
D
rate of deformation tensor
-
D
molecular diffusion coefficient
-
D
ij
eff
macroscopic (or effective) diffusion tensor
-
electric field
-
E
0
initial electric field
-
k
ij
molecular tensor
-
j, j
*,
current densities
-
K
ij
macroscopic permeability tensor
-
l
characteristic length of the ERV or the periodic cell
-
L
characteristic macroscopic length
-
L
ijkl
coupled flows coefficients
-
n
i
unit outward vector normal to
-
p
pressure
-
q
t
,q
t
+
,
heat fluxes
-
q
c
,q
c
+
,
chemical fluxes
-
s
specific entropy or the entropy density
-
S
entropy per unit volume
-
t
time variable
-
t
ij
local tensor
-
T
absolute temperature
-
v
i
velocity
-
V
0
initial electric potential
-
V
electric potential
-
x
macroscopic (or slow) space variable
-
y
microscopic (or fast) space variable
-
i
local vectorial field
-
i
local vectorial field
-
electric charge density on the solid surface
-
,
bulk and shear viscosities of the fluid
-
ij
local tensor
-
ij
local tensor
-
i
local vector
-
ij
molecular conductivity tensor
-
ij
eff
effective conductivity tensor
-
homogenization parameter
-
fluid density
-
0
ion-conductivity of fluid
-
ij
dielectric tensor
-
i
1
,
i
2
,
i
3
local vectors
- 4
local scalar
-
S
solid volume in the periodic cell
-
L
volume of pores in the periodic cell
-
boundary between
S
and
L
-
s
rate of entropy production per unit volume
-
total volume of the periodic cell
-
l
volume of pores in the cell
On leave from the Politechnika Gdanska; ul. Majakowskiego 11/12, 80-952, Gdask, Poland. 相似文献
120.
Ślęzak Andrzej Ślęzak-Prochazka Izabella Grzegorczyn Sławomir Jasik-Ślęzak Jolanta 《Transport in Porous Media》2017,116(2):941-957
Transport in Porous Media - S-entropy source of membrane system was described based on linear non-equilibrium thermodynamics. The volume and diffusive fluxes of non-electrolyte solutions and... 相似文献