全文获取类型
收费全文 | 478篇 |
免费 | 9篇 |
国内免费 | 2篇 |
专业分类
化学 | 342篇 |
力学 | 6篇 |
数学 | 33篇 |
物理学 | 108篇 |
出版年
2023年 | 4篇 |
2022年 | 2篇 |
2021年 | 2篇 |
2020年 | 5篇 |
2019年 | 4篇 |
2018年 | 4篇 |
2017年 | 3篇 |
2016年 | 5篇 |
2015年 | 3篇 |
2014年 | 6篇 |
2013年 | 26篇 |
2012年 | 14篇 |
2011年 | 26篇 |
2010年 | 8篇 |
2009年 | 7篇 |
2008年 | 23篇 |
2007年 | 33篇 |
2006年 | 17篇 |
2005年 | 25篇 |
2004年 | 11篇 |
2003年 | 17篇 |
2002年 | 10篇 |
2001年 | 16篇 |
2000年 | 10篇 |
1999年 | 7篇 |
1998年 | 15篇 |
1997年 | 9篇 |
1996年 | 17篇 |
1995年 | 14篇 |
1994年 | 5篇 |
1993年 | 12篇 |
1992年 | 12篇 |
1991年 | 9篇 |
1990年 | 12篇 |
1989年 | 6篇 |
1988年 | 11篇 |
1987年 | 8篇 |
1986年 | 10篇 |
1985年 | 13篇 |
1984年 | 10篇 |
1983年 | 5篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1978年 | 6篇 |
1977年 | 5篇 |
1974年 | 2篇 |
1973年 | 2篇 |
1971年 | 2篇 |
1969年 | 2篇 |
1968年 | 2篇 |
排序方式: 共有489条查询结果,搜索用时 0 毫秒
191.
Z. V. I. Zaretskii E. E. Kingston J. H. Beynon M. Guilhaus R. G. Kingston A. G. Brenton J. H. Beynon Michael J. Welch Daniel J. Pereles White V Edward Peter C. Burgers I. L. Aubagnac B. Elamrani F. M. Devienne R. Combarieu Sabatino Nacson Alex G. Harrison Robert G. Gilbert Margaret M. Sheil Peter J. Derrick 《Journal of mass spectrometry : JMS》1985,20(6):422-431
192.
Arlinghaus LR Li X Rahman AR Welch EB Xu L Gore JC Yankeelov TE 《Magnetic resonance imaging》2011,29(5):630-638
MRI techniques have been developed that can noninvasively probe the apparent diffusion coefficient (ADC) of water via diffusion-weighted MRI (DW-MRI). These methods have found much application in cancer where it is often found that the ADC within tumors is inversely correlated with tumor cell density, so that an increase in ADC in response to therapy can be interpreted as an imaging biomarker of positive treatment response. Dynamic contrast enhanced MRI (DCE-MRI) methods have also been developed and can noninvasively report on the extravascular extracellular volume fraction of tissues (denoted by ve). By conventional reasoning, the ADC should therefore also be directly proportional to ve. Here we report measurements of both ADC and ve obtained from breast cancer patients at both 1.5 and 3.0 T. The 1.5-T data were acquired as part of normal standard of care, while the 3.0-T data were obtained from a dedicated research protocol. We found no statistically significant correlation between ADC and ve for the 1.5- or 3.0-T patient sets on either a voxel-by-voxel or a region-of-interest (ROI) basis. These data, combined with similar results from other disease sites in the literature, may indicate that the conventional interpretation of either ADC, ve or their relationship is not sufficient to explain experimental findings. 相似文献
193.
Stephan DW Greenberg S Graham TW Chase P Hastie JJ Geier SJ Farrell JM Brown CC Heiden ZM Welch GC Ullrich M 《Inorganic chemistry》2011,50(24):12338-12348
In 2006, our group reported the first metal-free systems that reversibly activate hydrogen. This finding was extended to the discovery of "frustrated Lewis pair" (FLP) catalysts for hydrogenation. It is this catalysis that is the focal point of this article. The development and applications of such FLP hydrogenation catalysts are reviewed, and some previously unpublished data are reported. The scope of the substrates is expanded. Optimal conditions and functional group tolerance are considered and applied to targets of potential commercial significance. Recent developments in asymmetric FLP hydrogenations are also reviewed. The future of FLP hydrogenation catalysts is considered. 相似文献
194.
Albright A Eddings D Black R Welch CJ Gerasimchuk NN Gawley RE 《The Journal of organic chemistry》2011,76(18):7341-7351
Chiral, C(2)-symmetric imidazolium and imidazolinium ions, as well as the corresponding copper- or silver-bound carbenoids, have been prepared. Structural study of these compounds by X-ray crystallography reveals a chiral pocket that surrounds the putative carbene site or the metal-carbene bond, at carbon 2, in three of the four ligands prepared. Preliminary investigation into the application of these complexes has shown one of them to be highly enantioselective in the hydrosilylation of acetophenone. 相似文献
195.
A novel synthesis of different aromatic and heteroaromatic difluorodioxole derivatives has been developed. The starting materials were catechols, which, after treatment with thiophosgene, formed at 0 °C the respective thiodioxoles. The latter were reacted for a short time with commercially available bromine trifluoride, producing potentially biologically important difluoroaryldioxoles in moderate to high yields. 相似文献
196.
Shim JU Patil SN Hodgkinson JT Bowden SD Spring DR Welch M Huck WT Hollfelder F Abell C 《Lab on a chip》2011,11(6):1132-1137
A microfluidic device capable of exploiting the permeability of small molecules through polydimethylsiloxane (PDMS) has been fabricated in order to control the contents of microdroplets stored in storage wells. We demonstrate that protein precipitation and crystallization can be triggered by delivery of ethanol from a reservoir channel, thus controlling the protein solubility in microdroplets. Likewise quorum sensing in bacteria was triggered by delivery of the auto-inducer N-(3-oxododecanoyl)-l-homoserine lactone (OdDHL) through the PDMS membrane of the device. 相似文献
197.
Henson ZB Welch GC van der Poll T Bazan GC 《Journal of the American Chemical Society》2012,134(8):3766-3779
π-Conjugated materials containing pyridal[2,1,3]thiadiazole (PT) units have recently achieved record power conversion efficiencies of 6.7% in solution-processed, molecular bulk-heterojunction (BHJ) organic photovoltaics. Recognizing the importance of this new class of molecular systems and with the aim of establishing a more concrete path forward to predict improvements in desirable solid-state properties, we set out to systematically alter the molecular framework and evaluate structure-property relationships. Thus, the synthesis and properties of 13 structurally related D(1)-PT-D(2)-PT-D(1) compounds, where D represents a relatively electron-rich aromatic segment compared to PT, are provided. Physical properties were examined using a combination of absorption spectroscopy, cyclic voltammetry, thermal gravimetric analysis, differential scanning calorimetry, and solubility analysis. Changes to end-capping D(1) units allowed for fine control over electronic energy levels both in solution and in the bulk. Substitution of different alkyl chains on D(2) gives rise to controllable melting and crystallization temperatures and tailored solubility. Alterations to the core donor D(2) lead to readily identifiable changes in all properties studied. Finally, the regiochemistry of the pyridal N-atom in the PT heterocycle was investigated. The tailoring of structures via subtle structural modifications in the presented molecular series highlights the simplicity of accessing this chromophore architecture. Examination of the resulting materials properties relevant for device fabrication sets forth which can be readily predicted by consideration of molecular structure and which lack a systematic understanding. Guidelines can be proposed for the design of new molecular frameworks with the possibility of outperforming the current state of the art OPV performance. 相似文献
198.
This personal account describes the pursuit of non‐fullerene acceptors designed from simple and accessible organic pi‐conjugated building blocks and assembled through efficient direct (hetero)arylation cross‐coupling protocols. Initial materials development focused on isoindigo and diketopyrrolopyrrole organic dyes flanked by imide‐based terminal acceptors. Efficiencies in solution‐processed organic solar cells were modest but highlighted the potential of the material design. Materials performance was improved through structural engineering to pair perylene diimide with these organic dyes. Optimization of active layer processing and solar cell device fabrication identified the perylene diimide flanked diketopyrrolopyrrole structure as the best framework, with fullerene‐free organic solar cells achieving power conversion efficiencies above 6 %. This material has met our criteria for a simple wide band gap fullerene alternative for pairing with a range of donor polymers. 相似文献
199.
Customarily, speaking and singing have tended to be regarded as two completely separate sets of behaviors in clinical and educational settings. The treatment of speech and voice disorders has focused on the client's speaking ability, as this is perceived to be the main vocal behavior of concern. However, according to a broader voice-science perspective, given that the same vocal structure is used for speaking and singing, it may be possible to include singing in speech and voice therapy. In this article, a theoretical framework is proposed that indicates possible benefits from the inclusion of singing in such therapeutic settings. Based on a literature review, it is demonstrated theoretically why singing activities can potentially be exploited in the treatment of prepubertal children suffering from speech and voice disorders. Based on this theoretical framework, implications for further empirical research and practice are suggested. 相似文献
200.
In this paper we study the behavior of computable series of computable partial functions with varying domains (but each domain containing all computable points), and prove that the sum of the series exists and is computable exactly on the intersection of the domains when a certain computable Cauchyness criterion is met. In our point‐free approach, we name points via nested sequences of basic open sets, and thus our functions from a topological space into the reals are generated by functions from basic open sets to basic open sets. The construction of a function that produces the sum of a series requires working with an infinite array of pairs of basic open sets, and reconciling the varying domains. We introduce a general technique for using such an array to produce a set function that generates a well‐defined point function and apply the technique to a series to establish our main result. Finally, we use the main finding to construct a computable, and thus continuous, function whose domain is of Lebesgue measure zero and which is nonextendible to a continuous function whose domain properly includes the original domain. (We had established existence of such functions with domains of measure less than ε for any , in an earlier paper.) 相似文献