全文获取类型
收费全文 | 1851篇 |
免费 | 31篇 |
国内免费 | 9篇 |
专业分类
化学 | 983篇 |
晶体学 | 18篇 |
力学 | 59篇 |
数学 | 206篇 |
物理学 | 625篇 |
出版年
2020年 | 13篇 |
2019年 | 10篇 |
2016年 | 15篇 |
2015年 | 20篇 |
2014年 | 15篇 |
2013年 | 62篇 |
2012年 | 80篇 |
2011年 | 83篇 |
2010年 | 37篇 |
2009年 | 38篇 |
2008年 | 80篇 |
2007年 | 84篇 |
2006年 | 75篇 |
2005年 | 81篇 |
2004年 | 65篇 |
2003年 | 40篇 |
2002年 | 44篇 |
2001年 | 42篇 |
2000年 | 42篇 |
1999年 | 24篇 |
1998年 | 33篇 |
1997年 | 21篇 |
1996年 | 32篇 |
1995年 | 32篇 |
1994年 | 52篇 |
1993年 | 54篇 |
1992年 | 43篇 |
1991年 | 37篇 |
1990年 | 26篇 |
1989年 | 36篇 |
1988年 | 28篇 |
1987年 | 24篇 |
1986年 | 21篇 |
1985年 | 35篇 |
1984年 | 22篇 |
1983年 | 27篇 |
1982年 | 20篇 |
1981年 | 29篇 |
1980年 | 24篇 |
1979年 | 28篇 |
1978年 | 27篇 |
1977年 | 27篇 |
1976年 | 27篇 |
1975年 | 28篇 |
1974年 | 31篇 |
1973年 | 35篇 |
1972年 | 22篇 |
1971年 | 12篇 |
1968年 | 11篇 |
1967年 | 10篇 |
排序方式: 共有1891条查询结果,搜索用时 31 毫秒
981.
982.
983.
C. G. Freeman M. J. McEwan R. F. C. Claridge L. F. Phillips 《Chemical physics letters》1971,10(5):530-532
The Xe2 emission band at 168 nm has been observed during irradiation of xenon gas with the 147 nm resonance line. The band is attributed to Xe2 molecules formed by reaction between ground-state and metastable (2u) xenon atoms. 相似文献
984.
Probing the Limits of Ligand Steric Bulk: Backbone CH Activation in a Saturated N‐Heterocyclic Carbene 下载免费PDF全文
Nicholas Phillips Remi Tirfoin Prof. Simon Aldridge 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(13):3825-3830
The consequences of extremely high steric loading have been probed for late transition metal complexes featuring the expanded ring N‐heterocyclic carbene 6‐Dipp. The reluctance of this ligand to form 2:1 complexes with d‐block metals (rationalised on the basis of its percentage buried volume, % Vbur, of 50.8 %) leads to C?H and C?N bond activation processes driven by attack at the backbone β‐CH2 unit. In the presence of IrI (or indeed H+) the net result is the formation of an allyl formamidine fragment, while AuI brings about an additional ring (re‐)closure step via nucleophilic attack at the coordinated alkene. The net transformation of 6‐Dipp in the presence of [(6‐Dipp)Au]+ represents to our knowledge the first example of backbone C?H activation of a saturated N‐heterocyclic carbene, proceeding in this case via a mechanism which involves free carbene in addition to the AuI centre. 相似文献
985.
Expanded‐Ring N‐Heterocyclic Carbenes for the Stabilization of Highly Electrophilic Gold(I) Cations 下载免费PDF全文
Dr. Nicholas Phillips Tristan Dodson Rémi Tirfoin Dr. Joshua I. Bates Prof. Simon Aldridge 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(50):16721-16731
Strategies for the synthesis of highly electrophilic AuI complexes from either hydride‐ or chloride‐containing precursors have been investigated by employing sterically encumbered Dipp‐substituted expanded‐ring NHCs (Dipp=2,6‐iPr2C6H3). Thus, complexes of the type (NHC)AuH have been synthesised (for NHC=6‐Dipp or 7‐Dipp) and shown to feature significantly more electron‐rich hydrides than those based on ancillary imidazolylidene donors. This finding is consistent with the stronger σ‐donor character of these NHCs, and allows for protonation of the hydride ligand. Such chemistry leads to the loss of dihydrogen and to the trapping of the [(NHC)Au]+ fragment within a dinuclear gold cation containing a bridging hydride. Activation of the hydride ligand in (NHC)AuH by B(C6F5)3, by contrast, generates a species (at low temperatures) featuring a [HB(C6F5)3]? fragment with spectroscopic signatures similar to the “free” borate anion. Subsequent rearrangement involves B?C bond cleavage and aryl transfer to the carbophilic metal centre. Under halide abstraction conditions utilizing Na[BArf4] (Arf=C6H3(CF3)2‐3,5), systems of the type [(NHC)AuCl] (NHC=6‐Dipp or 7‐Dipp) generate dinuclear complexes [{(NHC)Au}2(μ‐Cl)]+ that are still electrophilic enough at gold to induce aryl abstraction from the [BArf4]? counterion. 相似文献
986.
Susann K. J. Ludwig Hongying Zhu Stephen Phillips Ashutosh Shiledar Steve Feng Derek Tseng Leendert A. van Ginkel Michel W. F. Nielen Aydogan Ozcan 《Analytical and bioanalytical chemistry》2014,406(27):6857-6866
Current contaminant and residue monitoring throughout the food chain is based on sampling, transport, administration, and analysis in specialized control laboratories. This is a highly inefficient and costly process since typically more than 99 % of the samples are found to be compliant. On-site simplified prescreening may provide a scenario in which only samples that are suspect are transported and further processed. Such a prescreening can be performed using a small attachment on a cellphone. To this end, a cellphone-based imaging platform for a microsphere fluorescence immunoassay that detects the presence of anti-recombinant bovine somatotropin (rbST) antibodies in milk extracts was developed. RbST administration to cows increases their milk production, but is illegal in the EU and a public health concern in the USA. The cellphone monitors the presence of anti-rbST antibodies (rbST biomarker), which are endogenously produced upon administration of rbST and excreted in milk. The rbST biomarker present in milk extracts was captured by rbST covalently coupled to paramagnetic microspheres and labeled by quantum dot (QD)-coupled detection antibodies. The emitted fluorescence light from these captured QDs was then imaged using the cellphone camera. Additionally, a dark-field image was taken in which all microspheres present were visible. The fluorescence and dark-field microimages were analyzed using a custom-developed Android application running on the same cellphone. With this setup, the microsphere fluorescence immunoassay and cellphone-based detection were successfully applied to milk sample extracts from rbST-treated and untreated cows. An 80 % true-positive rate and 95 % true-negative rate were achieved using this setup. Next, the cellphone-based detection platform was benchmarked against a newly developed planar imaging array alternative and found to be equally performing versus the much more sophisticated alternative. Using cellphone-based on-site analysis in future residue monitoring can limit the number of samples for laboratory analysis already at an early stage. Therewith, the entire monitoring process can become much more efficient and economical. Figure
Cellphone-based detection platform for rbST biomarker analysis in milk extracts using a microsphere fluorescence immunoassay 相似文献
987.
Chad A. Snyder Nathan C. Tice Phenahas G. Sriramula James L. Neathery Justin K. Mobley Chad L. Phillips 《合成通讯》2013,43(9):1357-1369
Pyridazines are an important class of heterocyclic compounds as a result of their materials and commercial applications. The synthesis of 5,6-fused ring pyridazines 2a–h from 1,2-diacylcyclopentadienes (fulvenes) 1a–h is described herein. This route was quite general, and features an efficient and convenient two-step synthesis of a series of 5,6-fused ring 1,2-disubstituted pyridazines using enolized 1,2-disubstituted fulvenes in a methanolic solution of hydrazine. Full characterization of newly formed fulvene 1e and pyridazines 2a–h are reported. Single-crystal X-ray analysis confirms the molecular structure of pyridazine 2f, which displayed the expected pyridazine fused to the cyclopentadienyl moiety. Adding to their real world capabilities in electronic devices, compounds 2a–h display reasonably high stability in solution and in air at room temperature.
988.
Mark S. Lowenthal Melissa M. Phillips Catherine A. Rimmer Paul A. Rudnick Yamil Simón-Manso Stephen E. Stein Dmitrii Tchekhovskoi Karen W. Phinney 《Analytical and bioanalytical chemistry》2013,405(13):4451-4465
Standard Reference Materials (SRMs) offer the scientific community a stable and homogenous source of material that holds countless application possibilities. Traditionally, the National Institute of Standards and Technology (NIST) has provided SRMs with associated quantitative information (certified values) for a select group of targeted analytes as measured in a solution or complex matrix. While the current needs of the SRM community are expanding to include non-quantitative data, NIST is attempting to broaden the scope of how and what information is offered to the SRM community by providing qualitative information about biomaterials, such as chromatographic fingerprints and profiles of untargeted identifications. In this work, metabolomic and proteomic profiling efforts were employed to characterize a suite of six Vaccinium berry SRMs. In the discovery phase, liquid chromatography-tandem mass spectrometry (LC-MS/MS) data was matched to mass spectral libraries; a subsequent validation phase based on multiple-reaction monitoring LC-MS/MS relied on both retention time matching of authentic standards along with fragmentation data for a qualitative overview of the most prominent organic compounds present. Definitive and putative identifications were determined for over 70 metabolites based on reporting guidelines set forth by the Metabolomics Standards Initiative (Metabolomics 3(3):211–221, 2007), and the capability of electrospray ionization mass spectrometry (ESI-MS) to profile untargeted metabolites within a complex matrix using mass spectral matching is demonstrated. Bottom-up proteomic analyses were possible using peptide databases translated from expressed sequence tags (ESTs). Homology searches provided identification of novel Vaccinium proteins based on homology to related genera. Chromatographic fingerprints of these berry materials were acquired for supplemental qualitative information to be provided to users of these SRMs. An unbounded set of qualitative data about a biomaterial is a valuable complement to quantitative information traditionally provided in NIST Certificates of Analysis. 相似文献
989.
Qiyao Li Ying Li Tianliang Min Junyi Gong Lili Du David Lee Phillips Junkai Liu Jacky W. Y. Lam Herman H. Y. Sung Ian D. Williams Ryan T. K. Kwok Chun Loong Ho Kai Li Jianguo Wang Ben Zhong Tang 《Angewandte Chemie (International ed. in English)》2020,59(24):9470-9477
Pathogen infections and cancer are two major human health problems. Herein, we report the synthesis of an organic salt photosensitizer (PS), called 4TPA‐BQ, by a one‐step reaction. 4TPA‐BQ presents aggregation‐induced emission features. Owing to the aggregation‐induced reactive oxygen species generated and a sufficiently small ΔEST, 4TPA‐BQ shows a satisfactorily high 1O2 generation efficiency of 97.8 %. In vitro and in vivo experiments confirmed that 4TPA‐BQ exhibited potent photodynamic antibacterial performance against ampicillin‐resistant Escherichia coli with good biocompatibility in a short time (15 minutes). When the incubation duration persisted long enough (12 hours), cancer cells were ablated efficiently, leaving normal cells essentially unaffected. This is the first reported time‐dependent fluorescence‐guided photodynamic therapy in one individual PS, which achieves ordered and multiple targeting simply by varying the external conditions. 4TPA‐BQ reveals new design principles for the implementation of efficient PSs in clinical applications. 相似文献
990.
Mahsa Motshakeri Anthony R. J. Phillips Jadranka Travas‐Sejdic Paul A. Kilmartin 《Electroanalysis》2020,32(9):2101-2111
A gold microelectrode (10 μm diameter) with an electropolymerized layer of poly(3,4‐ethylenedioxythiophene) (PEDOT) was used to quantify uric acid and investigate the antioxidant profile of milk and flavored milks. Comparisons were made with a bare gold microelectrode and a PEDOT‐glassy carbon macroelectrode (3 mm diameter). Two different electropolymerization processes were undertaken in an aqueous and an organic solution, and superior polymer growth was observed for PEDOT polymerized in lithium perchlorate/propylene carbonate. In the presence of a ferri/ferrocyanide redox couple, diffusion‐controlled redox peaks were observed with the PEDOT‐gold microelectrode rather than the plateau current typical of a bare microelectrode. Likewise, an anodic peak for uric acid was observed at the high surface‐area PEDOT‐gold microelectrode, with evidence for pre‐adsorption of uric acid at the electrode. The linear concentration range for uric acid standards was from 6 to 200 μM, and the limit of detection, limit of quantification, and sensitivity were determined to be 7 μM, 24 μM, and 397 μAμM?1cm2, respectively. Cyclic voltammograms of chocolate and espresso flavored milks exhibited significant contributions from the phenolic compounds present. Peak separation was more clearly defined using the PEDOT‐microelectrode compared to a PEDOT‐glassy carbon macroelectrode. 相似文献