全文获取类型
收费全文 | 880篇 |
免费 | 22篇 |
国内免费 | 11篇 |
专业分类
化学 | 581篇 |
晶体学 | 3篇 |
力学 | 36篇 |
数学 | 103篇 |
物理学 | 190篇 |
出版年
2023年 | 8篇 |
2022年 | 14篇 |
2021年 | 12篇 |
2020年 | 14篇 |
2019年 | 11篇 |
2018年 | 10篇 |
2017年 | 7篇 |
2016年 | 18篇 |
2015年 | 19篇 |
2014年 | 26篇 |
2013年 | 36篇 |
2012年 | 62篇 |
2011年 | 91篇 |
2010年 | 38篇 |
2009年 | 39篇 |
2008年 | 55篇 |
2007年 | 40篇 |
2006年 | 49篇 |
2005年 | 47篇 |
2004年 | 43篇 |
2003年 | 30篇 |
2002年 | 26篇 |
2001年 | 21篇 |
2000年 | 34篇 |
1999年 | 19篇 |
1998年 | 8篇 |
1997年 | 6篇 |
1996年 | 8篇 |
1995年 | 7篇 |
1994年 | 4篇 |
1993年 | 12篇 |
1992年 | 9篇 |
1991年 | 8篇 |
1990年 | 7篇 |
1989年 | 3篇 |
1988年 | 7篇 |
1987年 | 3篇 |
1986年 | 4篇 |
1985年 | 6篇 |
1984年 | 7篇 |
1983年 | 2篇 |
1982年 | 4篇 |
1981年 | 4篇 |
1980年 | 3篇 |
1979年 | 5篇 |
1978年 | 6篇 |
1977年 | 5篇 |
1976年 | 2篇 |
1974年 | 2篇 |
1935年 | 4篇 |
排序方式: 共有913条查询结果,搜索用时 15 毫秒
101.
In this study, through the extension of an one-dimensional, dissimilarly charged protrusions surface model set up in our previous work, a novel dissimilarly charged protrusion array (DCPA) model immersed in an electrolyte solution, which could simulate realistically both the surface morphology and the surface charged condition profoundly concerned on a biological cell membrane, or on the surface of a micro-scale, modified particle used in biomedical engineering and water treatment, is proposed. Considering the condition of small protrusions, the electrical potential field due to the electrical double layer (EDL) on DCPA model is solved semi-analytically using both the double Fourier series and the perturbation method. The analysis from the numerical result reveals that, a small, dissimilarly charged protrusion can lead to a steep variation in the local EDL configuration, especially compared with that in the condition when the charged surface is taken roughly as a flat surface using a lumped, mean surface charge density. 相似文献
102.
Chi HW Chien YC Liu CY Tseng CJ Lee YJ Chan JL Chu YR Chin DH 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(5):1493-1506
The antibiotic neocarzinostatin comprises a carrier protein with a well-defined cavity for accommodating an active enediyne chromophore. The protein has two disulfides, one (Cys(37)-Cys(47)) lies on the cavity bottom and the other (Cys(88)-Cys(93)) in a constrained short loop. When the chromophore is not bound to the protein, a thiol-induced cycloaromatization of the enediyne into a tetrahydroindacene derivative is responsible for the potent antitumor activity. When it is protein-bound, the protein diverts the cycloaromatization pathway to form a distinct hydroxyisochromene-type product. How the protein directs the enediyne chemistry is an interesting puzzle, and various suggestions have been proposed in the past. We screened more than fifty thiols and manipulated conditions to locate reaction features and search for factors that could influence the protein directing strength. Thiol- and oxygen-concentration-dependence studies suggested that disulfides, which maintain the steric rigidity of the protein, could play a key role in diverting the cycloaromatization pathway. For direct proofs, we made mutations at each of the two disulfides by replacing sulfur atoms with oxygen. Circular dichroism and two-dimensional NMR spectroscopy studies suggested that the mutations changed neither the protein conformation nor the ligand interactions. Analyses of the thiol-induced cycloaromatization revealed that rupture of Cys(37)-Cys(47) made the protein almost completely lose its chemical directing ability, whereas rupture of Cys(88)-Cys(93) had only a minor influence. The results demonstrated that the steric rigidity of the binding cavity, but not necessary the whole protein, played an important role in the protein-directed mechanism. 相似文献
103.
This study describes a simple, rapid method for sensing Cr(vi) using 5-thio-(2-nitrobenzoic acid) modified gold nanoparticles (TNBA-AuNPs) as a remover for Cr(iii) and as a sensor for Cr(vi). We discovered that TNBA-AuNPs were dispersed in the presence of Cr(vi), whereas Cr(iii) induced the aggregation of TNBA-AuNPs. Due to this phenomenon, TNBA-AuNPs can be used as a sorbent material for the removal of >90% Cr(iii), without removing Cr(vi). After centrifuging a solution containing Cr(iii), Cr(vi), and TNBA-AuNPs, Cr(iii) and Cr(vi) were separately present in the precipitate and supernatant. In other words, TNBA-AuNPs are capable of separating a mixture of Cr(iii) and Cr(vi). The addition of ascorbic acid to the supernatant resulted in a reduction of Cr(vi) to Cr(iii), driving the aggregation of TNBA-AuNPs. The selectivity of this approach is more than 1000-fold for Cr(vi) over other metal ions. The minimum detectable concentration of Cr(vi) was 1 μM using this approach. Inductively coupled plasma mass spectrometry provided an alternative for the quantification of Cr(iii) and Cr(vi) after a mixture of Cr(iii) and Cr(vi) had been separated by TNBA-AuNPs. The applicability of this approach was validated through the analysis of Cr(vi) in environmental water samples. 相似文献
104.
Stroke is one of the leading causes of mortality, with a high incidence of severe morbidity in survivors. The treatment to minimize tissue injury after stroke is still unsatisfactory and it is mandatory to develop effective treatment strategies for stroke. The pathophysiology of ischemic stroke is complex and involves many processes including energy failure, loss of ion homeostasis, increased intracellular calcium level, platelet aggregation, production of reactive oxygen species, disruption of blood brain barrier, and inflammation and leukocyte infiltration, etc. Tetrandrine, a bisbenzylisoquinoline alkaloid, has many pharmacologic effects including anti-inflammatory and cytoprotective effects. In addition, tetrandrine has been found to protect the liver, heart, small bowel and brain from ischemia/reperfusion injury. It is a calcium channel blocker, and can inhibit lipid peroxidation, reduce generation of reactive oxygen species, suppress the production of cytokines and inflammatory mediators, inhibit neutrophil recruitment and platelet aggregation, which are all devastating factors during ischemia/reperfusion injury of the brain. Because tetrandrine can counteract these important pathophysiological processes of ischemic stroke, it has the potential to be a protective agent for ischemic stroke. 相似文献
105.
Compared to conventional molecular solvents, the ionic liquid [b-3C-im][NTf(2)] was found to promote transimination reactions with up to ~100-fold rate enhancement. This rate effect observed at ambient temperature might be explained by the fact that the ionic liquid displays weak Lewis acidity with very low, if any, nucleophilicity and its imidazolium cation is expected to interact by associating with, and thus electrophilically activating, the C=N bond of the starting imine, leading to increased stabilization of the polar, charged intermediate species and ultimately, rapid product formation. Moreover, the presence of 1 mol% Sc(OTf)(3) in [b-3C-im][NTf(2)] further facilitates the transimination reactions studied. 相似文献
106.
We consider a class of unconstrained nonsmooth convex optimization problems, in which the objective function is the sum of
a convex smooth function on an open subset of matrices and a separable convex function on a set of matrices. This problem
includes the covariance selection problem that can be expressed as an ℓ
1-penalized maximum likelihood estimation problem. In this paper, we propose a block coordinate gradient descent method (abbreviated
as BCGD) for solving this class of nonsmooth separable problems with the coordinate block chosen by a Gauss-Seidel rule. The
method is simple, highly parallelizable, and suited for large-scale problems. We establish global convergence and, under a
local Lipschizian error bound assumption, linear rate of convergence for this method. For the covariance selection problem,
the method can terminate in O(n3/e){O(n^3/\epsilon)} iterations with an e{\epsilon}-optimal solution. We compare the performance of the BCGD method with the first-order methods proposed by Lu (SIAM J Optim
19:1807–1827, 2009; SIAM J Matrix Anal Appl 31:2000–2016, 2010) for solving the covariance selection problem on randomly generated instances. Our numerical experience suggests that the
BCGD method can be efficient for large-scale covariance selection problems with constraints. 相似文献
107.
Chen LY Chen CH Tseng CH Lai FL Hwang BJ 《Chemical communications (Cambridge, England)》2011,47(5):1592-1594
The photoluminescence quantum yield (PL-QY) of ternary colloidal CdSe(x)S(1-x) quantum dots (QDs), which were prepared by a one-injection method, enhances with increasing S content. The possible enhancement mechanism was explored by structural analysis via X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS). Both found that the enhancement of PL-QY of ternary CdSe(x)S(1-x) QDs strongly correlated with self-formed core/shell conformation in the non-coordination solution. 相似文献
108.
Ho CL Hsu KP Tseng YH Wang EI Liao PC Chou JC Lin CN Su YC 《Natural product communications》2011,6(2):267-270
The hydrodistillated leaf essential oil of Machilus kusanoi was analyzed to determine its composition and yield. Twenty-three compounds were identified, the main components being beta-caryophyllene (23.3%), beta-eudesmol (17.1%), alpha-terpineol (16.0%), n-dodecanal (14.2%), and n-decanal (10.4%). Sesquiterpene hydrocarbons (28.1%) and non-terpenoids (25.0%) were the predominant groups of compounds. The leaf oil exhibited excellent antimicrobial and anti-wood-decay fungal activities. 相似文献
109.
Yu-Liang Lin Yu-Hsuan Tseng Jhih-Hao Ho Yi-Fan Chen Prof. Jiun-Tai Chen 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(60):14981-14988
Composite polymer electrolytes (CPEs) with smart, stimuli-responsive characteristics have gained considerable attention owing to their noninvasive manipulation and applications in future technologies. To address this potential, in this work, we demonstrate photoresponsive composite polymer electrolytes, consisting of gel polymer electrolyte (GPE) and spiropyran-immobilized nanoporous anodic aluminum oxide (SP-AAO) templates. Under UV irradiation, the close SP form isomerizes to the open merocyanine (MC) form, creating extremely polarized AAO surfaces; whereas, under visible light irradiation, the MC form reverts to the SP form, creating neutral surface conditions. The electrostatic interactions between ions and AAO surfaces are investigated by attenuated total reflection Fourier-transform infrared (ATR-FTIR) spectroscopy. Moreover, the behavior of ionic conductivity of the GPE@SP-AAO is found to be consistent with the kinetics of isomerization tracked by UV-Vis spectroscopy. This work provides a promising platform for developing next-generation photoelectronic smart devices. 相似文献
110.
Dr. Hong‐Jay Lo M. Sc. Chin‐Yin Lin Dr. Mei‐Chun Tseng Prof. Rong‐Jie Chein 《Angewandte Chemie (International ed. in English)》2014,53(34):9026-9029
A hydroxy‐directed alkylation of an N,N‐diethylarylamide using CIPE‐assisted α‐silyl carbanions (CIPE=complex‐induced proximity effect) has been developed using a simple reagent combination of LDA (lithium diisopropylamide) and chlorosilane. A study of the mechanism, and the application of the procedure to an anionic Snieckus–Fries rearrangement for a highly efficient synthesis of the potent phosphatidylinositol 3‐kinase (PI3K) inhibitor LY294002, are reported. 相似文献