全文获取类型
收费全文 | 284篇 |
免费 | 16篇 |
专业分类
化学 | 220篇 |
晶体学 | 4篇 |
数学 | 31篇 |
物理学 | 45篇 |
出版年
2024年 | 1篇 |
2023年 | 1篇 |
2022年 | 6篇 |
2021年 | 4篇 |
2020年 | 4篇 |
2019年 | 5篇 |
2018年 | 4篇 |
2017年 | 4篇 |
2016年 | 8篇 |
2015年 | 6篇 |
2014年 | 10篇 |
2013年 | 27篇 |
2012年 | 16篇 |
2011年 | 19篇 |
2010年 | 16篇 |
2009年 | 11篇 |
2008年 | 16篇 |
2007年 | 19篇 |
2006年 | 14篇 |
2005年 | 18篇 |
2004年 | 17篇 |
2003年 | 9篇 |
2002年 | 9篇 |
2001年 | 4篇 |
2000年 | 4篇 |
1999年 | 2篇 |
1998年 | 2篇 |
1996年 | 1篇 |
1995年 | 2篇 |
1994年 | 8篇 |
1993年 | 4篇 |
1992年 | 5篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1985年 | 3篇 |
1984年 | 1篇 |
1982年 | 2篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1973年 | 2篇 |
1971年 | 1篇 |
1968年 | 1篇 |
1939年 | 1篇 |
1938年 | 1篇 |
1935年 | 2篇 |
1909年 | 1篇 |
排序方式: 共有300条查询结果,搜索用时 234 毫秒
51.
Sotelo E Fraiz N Yáñez M Laguna R Cano E Raviña E 《Chemical & pharmaceutical bulletin》2002,50(12):1574-1577
This paper describes the synthesis and the antiplatelet activity of a series of 4,5-disubstituted-6-phenyl-3(2H)-pyridazinones. Some of these compounds show a dose-dependent activity and were found to be more active than their 5-substituted analogues. 相似文献
52.
M.A. Mastro S. Maximenko M. Gowda B.S. Simpkins P.E. Pehrsson J.P. Long A.J. Makinen J.A. Freitas Jr. J.K. Hite C.R. Eddy Jr. J. Kim 《Journal of Crystal Growth》2009,311(10):2982-2986
Photo- and cathodo-luminescence measurements of a variable-diameter ensemble of GaN nanowires revealed a diameter-dependent, spectral emission distribution between 350 nm and 850 nm. Spectral analysis indicated that wires with a diameter less than 400 nm were dominated by a yellow luminescence with a weaker near UV/violet emission also present. Examination of this ensemble showed that there was a general trend in the ratio of near-UV-to-yellow emission intensities with increasing nanowire diameter. Additionally, a broad green emission appears in the nanowires with a diameter above approximately 200 nm. A calculation based on the nanoheteroepitaxy model indicates that this diameter represents a transitional thickness where strain is relieved by defect formation mechanisms with a characteristic green emission. 相似文献
53.
Frédéric Dumur Eddy Dumas Jérôme Marrot Francis Sécheresse 《Tetrahedron letters》2007,48(23):4143-4146
Efficient strategies for the synthesis of three building-blocks 4′-(functionalized)-2,2′:6′,2″-terpyridine have been developed for the convergent synthesis of metallodendrons; these strategies provide a practical approach for the rational design of highly conjugated metallodendrimers. 相似文献
54.
Anton Lishchynskyi Fedor M. Miloserdov Eddy Martin Jordi Benet‐Buchholz Eduardo C. Escudero‐Adn Andrey I. Konovalov Vladimir V. Grushin 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2015,127(50):15504-15508
First evidence for the existence of free trifluoromethyl anion CF3− has been obtained. The 3D‐caged potassium cation in [K(crypt‐222)]+ is inaccessible to CF3−, thus rendering it uncoordinated (“naked”). Ionic [K(crypt‐222)]+ CF3− has been characterized by single‐crystal X‐ray diffraction, solution NMR spectroscopy, DFT calculations, and reactivity toward electrophiles. 相似文献
55.
13C-labeled compounds are often employed as surrogate or internal standards to monitor the performance of extraction and instrumental analysis procedures for their unlabeled counterparts. However, labeled and unlabeled counterparts most often coelute chromatographically with overlapping mass ion fragments, posing a challenge to the accurate quantification of these compounds. In the present study, an analytical scheme, using coeluting unlabeled and 13C-labeled polychlorinated biphenyl (PCB) congeners as the model compounds, was developed with a low-resolution tandem mass spectrometer (MS/MS) to determine the appropriate ranges of PCB congener concentrations that satisfy the no-interference condition. Interferences from unlabeled PCBs to quantitation of labeled counterparts could be minimized when 13C-labeled PCB congeners were quantified in the MS/MS mode within a certain concentration range. In addition, good agreements between the measured and theoretically predicted quantitation errors were observed for all labeled PCB congeners except PCB 180. The exception with labeled PCB 180 was mainly attributed to the occurrence of instrumental analytical uncertainty, as analytical error was also observed with absence of unlabeled PCB 180. These results indicate that MS/MS techniques can serve as a useful tool to minimize interferences with quantitation of isotopically labeled compounds from their unlabeled counterparts, which possess partially overlapping ion fragment profiles. 相似文献
56.
We provide combinatorial as well as probabilistic interpretations for the q-analogue of the Pochhammer k-symbol introduced by Díaz and Teruel. We introduce q-analogues of the Mellin transform in order to study the q-analogue of the k-gamma distribution. 相似文献
57.
Terence C. W. Poon Irene L. Ang Man‐Ki Law Kiwi Y. W. Chan Eddy W. Y. Ng Sai‐Ming Ngai Joseph J. Y. Sung Henry L. Y. Chan 《Electrophoresis》2010,31(10):1721-1730
ProteinChip surface‐enhanced laser desorption/ionization technology and magnetic beads‐based ClinProt system are commonly used for semi‐quantitative profiling of plasma proteome in biomarker discovery. Unfortunately, the proteins/peptides detected by MS are non‐recoverable. To obtain the protein identity of a MS peak, additional time‐consuming and material‐consuming purification steps have to be done. In this study, we developed a magnetic beads‐based proteomic fingerprinting method that allowed semi‐quantitative proteomic profiling and micropreparative purification of the profiled proteins in parallel. The use of different chromatographic magnetic beads allowed us to obtain different proteomic profiles, which were comparable to those obtained by the ProteinChip surface‐enhanced laser desorption/ionization technology. Our assays were semi‐quantitative. The normalized peak intensity was proportional to concentration measured by immunoassay. Both intra‐assay and inter‐assay coefficients of variation of the normalized peak intensities were in the range of 4–30%. Our method only required 2 μL of serum or plasma for generating enough proteins for semi‐quantitative profiling by MALDI‐TOF‐MS as well as for gel electrophoresis and subsequent protein identification. The protein peaks and corresponding gel spots could be easily matched by comparing their intensities and masses. Because of its high efficiency and reproducibility, our method has great potentials in clinical research, especially in biomarker discovery. 相似文献
58.
A highly divergent, flexible, and conceptually simple sequence allowing the parallel solution-phase assembly of functionalized azinone libraries has been developed in a one-pot consecutive fashion. Structural decoration of in situ-generated heterocyclic aza-Michael adducts AB was accomplished by exploiting the diversity potential of Heck, Suzuki, Sonogashira, and Stille reactions. 相似文献
59.
We find an explicit expression for the cross-covariance between stochastic integral processes with respect to a -dimensional fractional Brownian motion (fBm) with Hurst parameter , where the integrands are vector fields applied to . It provides, for example, a direct alternative proof of Y. Hu and D. Nualart’s result that the stochastic integral component in the fractional Bessel process decomposition is not itself a fractional Brownian motion. 相似文献
60.
Hilal M Parrado MF Rosa M Gallardo M Orce L Massa EM González JA Prado FE 《Photochemistry and photobiology》2004,79(2):205-210
UV-B radiation (280-320 nm) is harmful to living organisms and has detrimental effects on plant growth, development and physiology. In this work we examined some mechanisms involved in plant responses to UV-B radiation. Seedlings of quinoa (Chenopodium quinoa Willd.) were exposed to variable numbers of UV-B radiation doses, and the effect on cotyledons was studied. We analyzed (1) cotyledons anatomy and chloroplasts ultrastructure; (2) peroxidase activity involved in the lignification processes; and (3) content of photosynthetic pigments, phenolic compounds and carbohydrates. Exposure to two UV-B doses induced an increase in the wall thickness of epidermal cells, which was associated with lignin deposition and higher activity of the peroxidase. The chloroplast ultrastructure showed an appearance typical of plants under shade conditions, likely in response to reduced light penetration into the mesophyll cells due to the screening effect of epidermal lignin deposition. Exposure to UV-B radiation also led to (1) enhancement in the level of phenolics, which may serve a protective function; (2) strong increase in the fructose content, a fact that might be related to higher requirement of erythrose-4P as a substrate for the synthesis of lignin and phenolics; and (3) reduction in the chlorophyll concentration, evidencing alteration in the photosynthetic system. We propose that the observed lignin deposition in epidermal tissues of quinoa is a resistance mechanism against UV-B radiation, which allows growing of this species in Andean highlands. 相似文献