全文获取类型
收费全文 | 1602篇 |
免费 | 61篇 |
国内免费 | 6篇 |
专业分类
化学 | 1235篇 |
晶体学 | 8篇 |
力学 | 20篇 |
数学 | 196篇 |
物理学 | 210篇 |
出版年
2024年 | 2篇 |
2023年 | 18篇 |
2022年 | 40篇 |
2021年 | 46篇 |
2020年 | 52篇 |
2019年 | 35篇 |
2018年 | 19篇 |
2017年 | 25篇 |
2016年 | 53篇 |
2015年 | 55篇 |
2014年 | 49篇 |
2013年 | 86篇 |
2012年 | 102篇 |
2011年 | 138篇 |
2010年 | 65篇 |
2009年 | 60篇 |
2008年 | 105篇 |
2007年 | 114篇 |
2006年 | 93篇 |
2005年 | 98篇 |
2004年 | 69篇 |
2003年 | 70篇 |
2002年 | 73篇 |
2001年 | 15篇 |
2000年 | 13篇 |
1999年 | 5篇 |
1998年 | 12篇 |
1997年 | 8篇 |
1996年 | 34篇 |
1995年 | 22篇 |
1994年 | 17篇 |
1993年 | 11篇 |
1992年 | 16篇 |
1991年 | 4篇 |
1990年 | 6篇 |
1989年 | 3篇 |
1988年 | 6篇 |
1987年 | 5篇 |
1986年 | 2篇 |
1985年 | 6篇 |
1984年 | 6篇 |
1983年 | 3篇 |
1982年 | 3篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1977年 | 1篇 |
排序方式: 共有1669条查询结果,搜索用时 15 毫秒
881.
A diastereoselective allylation of N-tert-butane sulfinyl α-iminoesters using allylboronic acids is developed to obtain optically active non-proteinogenic α-amino acid precursors in good yields and diastereoselectivities. Gram-scale synthesis, broad tolerance of functional groups, excellent stereodivergence, post-synthetic modifications, and easy removal of the chiral auxiliary are some of the key highlights. The protocol is applicable to various amino acids and short peptides, resulting in the incorporation of these precursors at the N-terminal position.A diastereoselective allylation of N-tert-butane sulfinyl α-iminoesters using allylboronic acids is developed to obtain optically active non-proteinogenic α-amino acid precursors in good yield and diastereoselectivities. 相似文献
882.
ABSTRACT Grain boundaries of metallic materials subjected to severe plastic deformation exhibit significantly enhanced diffusivity and excess energy compared with their relaxed poly- or bi-crystalline counterparts even when the macroscopic degrees of freedom are the same in both types of grain boundaries. Boundaries of excess energy are/can be relaxed by annealing. As a first step in accounting for this experimentally observed high-energy state of general high-angle grain boundaries subjected to severe plastic deformation, a concept of localised basic shear units and the presence of localised extra free volume in these units situated in different locations in the grain boundaries, which was originally proposed to explain steady-state structural superplastic flow, is made use of. Using MD simulation, the mechanical response of these modified grain boundaries is compared with that of their relaxed state. The results are also compared with a case of a homogeneous distribution of extra free volume within the grain boundary. The localised shear units containing extra free volume introduced in the grain boundaries are found to alter their physical and mechanical features strongly, which, in turn, drastically affect, consistent with experimental results, the mechanical response of the heavily deformed material. 相似文献
883.
Lisa Milchram Anita Fischer Jasmin Huber Regina Soldo Daniela Sieghart Klemens Vierlinger Stephan Blüml Günter Steiner Andreas Weinhusel 《Molecules (Basel, Switzerland)》2022,27(4)
For the identification of antigenic protein biomarkers for rheumatoid arthritis (RA), we conducted IgG profiling on high density protein microarrays. Plasma IgG of 96 human samples (healthy controls, osteoarthritis, seropositive and seronegative RA, n = 24 each) and time-series plasma of a pristane-induced arthritis (PIA) rat model (n = 24 total) were probed on AIT’s 16k protein microarray. To investigate the analogy of underlying disease pathways, differential reactivity analysis was conducted. A total of n = 602 differentially reactive antigens (DIRAGs) at a significance cutoff of p < 0.05 were identified between seropositive and seronegative RA for the human samples. Correlation with the clinical disease activity index revealed an inverse correlation of antibodies against self-proteins found in pathways relevant for antigen presentation and immune regulation. The PIA model showed n = 1291 significant DIRAGs within acute disease. Significant DIRAGs for (I) seropositive, (II) seronegative and (III) PIA were subjected to the Reactome pathway browser which also revealed pathways relevant for antigen presentation and immune regulation; of these, seven overlapping pathways had high significance. We therefore conclude that the PIA model reflects the biological similarities of the disease pathogenesis. Our data show that protein array analysis can elucidate biological differences and pathways relevant in disease as well be a useful additional layer of omics information. 相似文献
884.
A series of C3-symmetric fully substituted benzenes were prepared based on alkyl triamino-benzene-tricarboxylates. Starting with a one step-synthesis, the alkyl triamino-benzene-tricarboxylates were synthesized using the corresponding cyanoacetates. The reactivity of these electronically sophisticated compounds was investigated by the formation of azides, the click reaction of the azides and a Sandmeyer-like reaction. Caused by the low stability of triaminobenzenes, direct N-alkylation was rarely reported. The use of the stable alkyl triamino-benzene-tricarboxylates allowed us total N-alkylation under standard alkylation conditions. The molecular structures of the C3-symmetric structures have been corroborated by an X-ray analysis. 相似文献
885.
Hong Ding Lisa K. Olson Joseph A. Caruso 《Spectrochimica Acta Part B: Atomic Spectroscopy》1996,51(14):1801-1812
Chromium picolinate products have been examined for different forms of chromium, using chromatographic separation and inductively coupled plasma mass spectrometric detection. The brands we evaluated contained no detectable amount of elemental chromium(VI), the toxic form. Since chromium picolinate might have other chromium forms as impurities, different products may contain different forms of chromium species. Compared with ion-exchange, reversed-phase chromatography showed excellent chromium recovery based on the amount stated on the product label. 相似文献
886.
887.
888.
Yong Sun Won Sung Soo Park Young Seok Kim Timothy J. Anderson Lisa McElwee-White 《Journal of Crystal Growth》2009,311(14):3587-3591
DFT calculations were employed to investigate transamination during metalorganic chemical vapor deposition (MOCVD) of transition metal nitrides films, such as titanium nitride (TiN) and tantalum nitride (TaN). The calculated energetics and rate constants for the ligand exchange of tert-butylimidotris(dimethylamido) tantalum (TBTDMT) with NH3 demonstrated that NH3 addition to form the ammonia adduct, TBTDMT·NH3, proton transfer and dissociation of dimethylamine to afford net transamination of the dimethylamido ligand are facile even at low temperature (∼300 °C). The transamination of the tert-butylimido ligand, however, was relatively slow at those temperatures but became facile at temperatures appropriate for CVD growth (∼600 °C). Rapid transamination is consistent with lower temperature for growth of TaN by MOCVD in the presence of NH3, efficient removal of carbon-containing ligands, and incorporation of higher levels of nitrogen in the resulting films. 相似文献
889.
Lisa Eisele Wilaiwan Chaikhan Samar Batool Dr. Alexey Cherevan Prof. Dominik Eder Prof. Katharina Bica-Schröder 《ChemCatChem》2024,16(6):e202301454
Efficiently generating C1 building blocks from environmentally friendly carbon sources, such as through photocatalytic CO2 reduction, is essential for fostering a sustainable circular economy. The pursuit of mild catalytic activation methods has yielded powerful catalysts that can be synergistically employed alongside various reaction media to enhance overall performance. Herein, we elucidate the influence of diverse imidazolium-based ionic liquids as additives for visible-light-driven CO2 reduction with ruthenium(II)- and rhenium(I)-bipyridine complexes. Our investigation reveals that incorporating ionic liquids into traditional solvents at concentrations below 10 % can markedly boost CO production while suppressing H2 generation. The best results were obtained for the highly basic ionic liquid [C2mim][OAc], resulting in a substantial rise in CO formation from 0.3 μmol/h to 5.4 μmol/h and an increase in turnover number from 3 to 59. This study underscores the cooperative influence of imidazolium-based ionic liquids on CO2 photoreduction while circumventing their use as primary solvents, thus offering a promising avenue for sustainable chemical synthesis. 相似文献
890.
Stefan Bucur Marius Niculaua Catalina Ionica Ciobanu Neculai Catalin Lungu Ionel Mangalagiu 《Molecules (Basel, Switzerland)》2021,26(18)
This communication reports a novel synthesis route for the preparation of monofunctionalized β-cyclodextrin in a single stage. The approach involves only the in-situ protection of secondary hydroxyl groups as an excellent alternative to the classical procedure involving a series of five steps of protection and deprotection of hydroxyl groups (both primary and secondary ones) belonging to β-cyclodextrin. 相似文献