全文获取类型
收费全文 | 1212篇 |
免费 | 51篇 |
国内免费 | 21篇 |
专业分类
化学 | 663篇 |
晶体学 | 9篇 |
力学 | 58篇 |
数学 | 259篇 |
物理学 | 295篇 |
出版年
2023年 | 5篇 |
2022年 | 13篇 |
2021年 | 5篇 |
2020年 | 24篇 |
2019年 | 11篇 |
2018年 | 13篇 |
2017年 | 5篇 |
2016年 | 17篇 |
2015年 | 20篇 |
2014年 | 43篇 |
2013年 | 63篇 |
2012年 | 85篇 |
2011年 | 68篇 |
2010年 | 59篇 |
2009年 | 55篇 |
2008年 | 70篇 |
2007年 | 61篇 |
2006年 | 75篇 |
2005年 | 56篇 |
2004年 | 50篇 |
2003年 | 51篇 |
2002年 | 32篇 |
2001年 | 35篇 |
2000年 | 33篇 |
1999年 | 14篇 |
1998年 | 18篇 |
1997年 | 12篇 |
1996年 | 16篇 |
1995年 | 23篇 |
1994年 | 10篇 |
1993年 | 19篇 |
1992年 | 9篇 |
1991年 | 17篇 |
1990年 | 13篇 |
1989年 | 11篇 |
1988年 | 10篇 |
1987年 | 9篇 |
1986年 | 8篇 |
1985年 | 20篇 |
1984年 | 11篇 |
1983年 | 10篇 |
1982年 | 9篇 |
1981年 | 9篇 |
1980年 | 12篇 |
1979年 | 11篇 |
1978年 | 7篇 |
1977年 | 14篇 |
1976年 | 15篇 |
1975年 | 14篇 |
1973年 | 4篇 |
排序方式: 共有1284条查询结果,搜索用时 15 毫秒
111.
Zou L Cheong WL Chung WH Leung YC Wong KY Wong MK Chan PH 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(45):13367-13371
Herein is described the development of a novel switch-on fluorescence assay for detecting β-lactamases. The fluorescence assay comprises two components: solid beads coated with a β-lactam antibiotic, which is linked to an environment-sensitive fluorophore (dansylaminothiophenol, DTA), and amyloid fibrils of hen lysozyme (acting as fluorescence enhancer and visual tool). In the presence of the clinically significant TEM-1 β-lactamase, the DTA-antibiotic complex on the solid beads is hydrolyzed, thus releasing the DTA dye into solution. The DTA dye is only weakly fluorescent in solution but gives strong green fluorescence upon binding to lysozyme fibrils. These strongly fluorescent DTA-bound fibrils can be easily visualized by the naked eye upon illumination of the sample with a simple UV lamp. The fluorescence assay can detect TEM-1 at low concentration (0.01 nM). In contrast, no observable fluorescence appears when the fluorescence assay is performed on samples without the TEM-1 β-lactamase. 相似文献
112.
The multi-technique analytical approach has proved to be a very effective tool for the analysis of artwork, as demonstrated by various studies. In this work, four micro-analysis methods were used to analyze the wall painting fragments in Kaiping Diaolou, a world cultural heritage enlisted in 2007. Field-emission scanning electron microscopy (FE-SEM), energy dispersive X-ray micro-analysis (EDX), combined with micro Raman and Fourier transform infrared (FT-IR) spectroscopy, provided a vast amount of information concerning the raw materials present in the pigments, organic binder, plasters and mortars of the wall painting. Four types of pigments (goethite, lazurite, chromium green and calcite) were identified on the surface layer of the wall paintings. The substrate under the pigment layer was found to be composed of cubic-like calcite (CaCO3), micro-rod bundle-shaped syngenite (K2Ca(SO4)2·H2O), gypsum (CaSO4·2H2O) and silica (SiO2). The organic binder can be attributed to animal glue (such as egg) and drying oil by micro FT-IR spectroscopy. These analysis results can provide important information for the conservation and restoration of the Kaiping Diaolou. 相似文献
113.
The first example of a polystyrene bearing two distinct reagent groups has been prepared. This phosphine and amine functionalized material was used in one-pot Wittig reactions with an aldehyde and either an α-halo-ester, -ketone, or -amide. Due to the heterogeneous nature of the polymer, the desired alkene product of these reactions could be isolated in excellent yield in essentially pure form after only filtration and solvent removal. 相似文献
114.
Tradition- and science-based quality control of Chinese medicines--introducing the Phyto-True system
Leung AY 《Journal of AOAC International》2010,93(5):1355-1366
The current QC practice of quantifying presumed active chemicals or arbitrarily selected chemical markers is of doubtful value in assessing multicomponent complex traditional Chinese medicines (CMs) and often leads to an inconsistent or irreproducible research and clinical outcome. Consequently, the first and most important step in the QC of CMs (or other botanical medicines) whose exact active chemical components are unknown is to use analytical techniques that can comprehensively define the totality of the components/attributes making up their identity and quality. One of the most versatile techniques is HPTLC. Using HPTLC, along with other simple techniques such as FTIR spectroscopy and UV-Vis spectroscopy combined with complementary gene expression profiling, we have been able to correctly identify CM materials, detect adulterants, and differentiate closely related materials and botanical species. Our research has resulted in the introduction of the concept and specimens of Phyto-True Reference Material (PTRM), aka Representative Botanical Reference/Research Material (RBRM), now commercially available, and a novel patent-pending technology (Phyto-True system) that can serve as a starting point for the meaningful QC of traditional CMs so far not possible for these complex materials. Examples will be highlighted to demonstrate this new concept. 相似文献
115.
High‐affinity aptamers for important signal transduction proteins, i.e. Cdc42‐GTP, p21‐activated kinase1 (PAK1) and MRCK (myotonic dystrophy kinase‐related Cdc42‐binding kinase) α were successfully selected in the low micro‐ to nanomolar range using non‐systematic evolution of ligands by exponential enrichment (SELEX) with at least three orders of magnitude enhancement from their respective bulk affinity of naïve DNA library. In the non‐SELEX procedure, CE was used as a highly efficient affinity method to select aptamers for the desired molecular target through a process that involved repetitive steps of partitioning, known as non‐equilibrium CE of equilibrium mixtures with no PCR amplification between successive steps. Various non‐SELEX conditions including the type, concentration and pH of the run buffer were optimized. Other considerations such as salt composition of selection buffer, protein concentration and sample injection size were also studied for high stringency during selection. After identifying the best enriched aptamer pool, randomly selected clones from the aptamer pool were sequenced to obtain the individual DNA sequences. The dissociation constants (Kd) of these sequences were in the low micromolar to nanomolar range, indicating high affinity to the respective proteins. The best binders were also subjected to sequence alignment to generate a phylogenetic tree. No significant consensus region based on approximately 50 sequences for each protein was observed, suggesting the high efficiency of non‐SELEX for the selection of numerous unique sequences with high selectivity. 相似文献
116.
This paper investigates a revenue-sharing contract for coordinating a supply chain comprising one manufacturer and two competing retailers. The manufacturer, as a Stackelberg leader, offers a revenue-sharing contract to two competing retailers who face stochastic demand before the selling season. Under the offered contract terms, the competing retailers are to determine the quantities to be ordered from the manufacturer, prior to the season, and the retail price at which to sell the items during the season. The process of pricing and ordering is expected to result in an equilibrium as in the Bayesian Nash game. On the basis of anticipated responses and actions of the retailers, the manufacturer designs the revenue-sharing contract. Adopting the classic newsvendor problem model framework and using numerical methods, the study finds that the provision of revenue-sharing in the contract can obtain better performance than a price-only contract. However, the benefits earned under the revenue-sharing contract by different supply chain partners differ because of the impact of demand variability and price-sensitivity factors. The paper also analyses the impact of demand variability on decisions about optimal retail price, order quantity and profit sharing between the manufacturer and the retailers. Lastly, it investigates how the competition (between retailers) factor influences the decision-making of supply chain members in response to uncertain demand and profit variability. 相似文献
117.
Pheophorbide a (PhA) was identified as a photosensitizer to exert cytotoxicity on tumor cells. However, the efficacy of this
compound on the treatment of prostate cancer remains unknown. The aim of this study was to evaluate the photodynamic effect
of PhA on prostate cancer cells. Cellular uptake of PhA and cell viability after photo-activation was studied in LNCaP prostate
cancer cells. The corresponding production of reactive oxygen species within cells was determined after photodynamic therapy
(PDT). Our results showed that the uptake of PhA into LNCaP cells was in a time-dependent manner and the cytotoxicity of PhA-PDT
was photosensitizer dose- and light dose-dependent. The intracellular reactive oxygen species was remarkably induced after
PDT treatment, which was responsible for the inhibition effect on prostate cancer cells. This is the first report to evaluate
the photodynamic effect of PhA on prostate cancer. Our findings demonstrate that PhA-PDT may be a potentially promising treatment
for localized prostate cancer, which can be a therapeutic option after the failures of radiotherapy and hormone therapy. 相似文献
118.
Shingyu Leung 《Journal of computational physics》2011,230(9):3500-3524
We propose efficient Eulerian methods for approximating the finite-time Lyapunov exponent (FTLE). The idea is to compute the related flow map using the Level Set Method and the Liouville equation. There are several advantages of the proposed approach. Unlike the usual Lagrangian-type computations, the resulting method requires the velocity field defined only at discrete locations. No interpolation of the velocity field is needed. Also, the method automatically stops a particle trajectory in the case when the ray hits the boundary of the computational domain. The computational complexity of the algorithm is O(Δx?(d+1)) with d the dimension of the physical space. Since there are the same number of mesh points in the x–t space, the computational complexity of the proposed Eulerian approach is optimal in the sense that each grid point is visited for only O(1) time. We also extend the algorithm to compute the FTLE on a co-dimension one manifold. The resulting algorithm does not require computation on any local coordinate system and is simple to implement even for an evolving manifold. 相似文献
119.
We develop numerical methods for solving partial differential equations (PDE) defined on an evolving interface represented by the grid based particle method (GBPM) recently proposed in [S. Leung, H.K. Zhao, A grid based particle method for moving interface problems, J. Comput. Phys. 228 (2009) 7706–7728]. In particular, we develop implicit time discretization methods for the advection–diffusion equation where the time step is restricted solely by the advection part of the equation. We also generalize the GBPM to solve high order geometrical flows including surface diffusion and Willmore-type flows. The resulting algorithm can be easily implemented since the method is based on meshless particles quasi-uniformly sampled on the interface. Furthermore, without any computational mesh or triangulation defined on the interface, we do not require remeshing or reparametrization in the case of highly distorted motion or when there are topological changes. As an interesting application, we study locally inextensible flows governed by energy minimization. We introduce tension force via a Lagrange multiplier determined by the solution to a Helmholtz equation defined on the evolving interface. Extensive numerical examples are also given to demonstrate the efficiency of the proposed approach. 相似文献
120.
Current–voltage (J–V) characteristics of epitaxial hetero-junctions composed of Pr0.7Ca0.3MnO3 and Nb:SrTiO3 were studied under forward and reversed bias conditions. Detailed analysis showed that the J–V characteristics of these heterojunctions can be well-fitted by the thermally-assisted tunnelling model. While the dielectric constant of Nb:SrTiO3 extracted under the forward bias was about one order of magnitude smaller than that of bulk SrTiO3, the value obtained under reverse bias was very close to that of the bulk SrTiO3. The result can be explained by the existence of an interface layer on the Nb:SrTiO3 substrate with a smaller effective dielectric constant. The current finding suggested that the properties of interface layer should be taken into account in order to accurately simulate the J–V characteristics of such heterojunctions. 相似文献