全文获取类型
收费全文 | 829篇 |
免费 | 22篇 |
专业分类
化学 | 566篇 |
晶体学 | 11篇 |
力学 | 17篇 |
数学 | 87篇 |
物理学 | 170篇 |
出版年
2021年 | 7篇 |
2020年 | 7篇 |
2017年 | 7篇 |
2016年 | 16篇 |
2015年 | 12篇 |
2014年 | 11篇 |
2013年 | 29篇 |
2012年 | 34篇 |
2011年 | 30篇 |
2010年 | 22篇 |
2009年 | 20篇 |
2008年 | 40篇 |
2007年 | 34篇 |
2006年 | 38篇 |
2005年 | 56篇 |
2004年 | 27篇 |
2003年 | 24篇 |
2002年 | 28篇 |
2001年 | 14篇 |
2000年 | 13篇 |
1999年 | 6篇 |
1998年 | 6篇 |
1997年 | 5篇 |
1996年 | 18篇 |
1995年 | 13篇 |
1994年 | 9篇 |
1993年 | 18篇 |
1992年 | 7篇 |
1991年 | 11篇 |
1990年 | 11篇 |
1989年 | 7篇 |
1988年 | 9篇 |
1987年 | 8篇 |
1986年 | 10篇 |
1985年 | 14篇 |
1984年 | 22篇 |
1983年 | 15篇 |
1982年 | 14篇 |
1981年 | 8篇 |
1980年 | 7篇 |
1979年 | 10篇 |
1978年 | 12篇 |
1977年 | 15篇 |
1976年 | 11篇 |
1975年 | 11篇 |
1974年 | 8篇 |
1973年 | 11篇 |
1972年 | 5篇 |
1968年 | 7篇 |
1966年 | 9篇 |
排序方式: 共有851条查询结果,搜索用时 15 毫秒
191.
The mechanism of the OH‐initiated oxidation of isoprene in the presence of NO and O2 has been investigated using a discharge‐flow system at 298 K and 2 torr total pressure. OH radical concentration profiles were measured using laser‐induced fluorescence as a function of reaction time. The rate constant for the reaction of OH + isoprene was measured to be (1.10 ± 0.05) × 10−10 cm3 mol−1 s−1. In the presence of NO and O2, regeneration of OH radicals by the reaction of isoprene‐based peroxy radicals with NO was measured and compared to simulations of the kinetics of this system. The results of these experiments are consistent with an overall rate constant of 9 × 10−12 cm3 mol−1 mol−1 (with an uncertainty factor of 2) for the reaction of isoprene‐based hydroxyalkyl peroxy radicals with NO. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 637–643, 1999 相似文献
192.
Mass spectrometry-based survey of age-associated protein carbonylation in rat brain mitochondria 总被引:1,自引:0,他引:1
Prokai L Yan LJ Vera-Serrano JL Stevens SM Forster MJ 《Journal of mass spectrometry : JMS》2007,42(12):1583-1589
There is a body of evidence lending credence to the idea that oxidative stress may be responsible for age-related deleterious changes in brain function, and that protein carbonylation is a potential marker for such changes. An investigation of oxidative damage to mitochondrial proteins from aged rat brains was done using gel electrophoresis coupled with carbonylation-specific immunostaining. Six proteins that appeared to be susceptible to oxidative modification were identified by in-gel trypsin digestion followed by matrix-assisted laser desorption/ionization mass spectrometry and tandem mass spectrometry. Two subunits of the H(+)-transporting ATP synthase, adenine nucleotide translocator, voltage-dependent anion channel, glutamate oxaloacetate transaminase, and aconitase were identified as likely targets of age-associated carbonylation. 相似文献
193.
Jex AR Whipp M Campbell BE Cacciò SM Stevens M Hogg G Gasser RB 《Electrophoresis》2007,28(21):3875-3883
In the present study, we used a mutation scanning-targeted sequencing approach to assess variation in part (pgp60) of the 60 kDa glycoprotein (gp60) gene among Cryptosporidium samples from humans in Victoria, Australia. Two nuclear ribosomal loci (the small subunit rRNA gene and the second internal transcribed spacer) were used to identify the samples as Cryptosporidium hominis (n = 74), Cryptosporidium parvum (n = 23) or Cryptosporidium meleagridis (n = 1). In total, nine distinct pgp60 sequences were identified (three C. hominis, five C. parvum and one C. meleagridis). Phylogenetic analyses of the pgp60 sequence data, employing well-defined reference sequences for comparison, allowed the genotypic and subgenotypic classification of samples. The C. hominis samples were classified as Ib A10G2R2, Id A15G1R2, and a new genotype, designated Ib2, was identified subgenotypically as A18G1R4. The C. parvum samples were classified as IIa A18G3R1, IIa A20G3R1, IIa A22G3R1, IIa A23G3R1 and IIc A5G3R2. These findings suggested that the C. hominis metapopulation is largely homogeneous, consisting of a single dominant genotype, Ib A10G2R2, whereas the C. parvum metapopulation is considerably more heterogeneous, with no single dominant genotype. The greater level of genetic heterogeneity found among the C. parvum samples, despite the smaller sample size, may relate to the zoonotic infection pattern of this species, which would be reflective of a greater number of possible infection sources. The present mutation scanning approach, coupled with targeted sequencing of genetically distinct representatives, is a practical, cost-effective tool for large-scale population genetic and epidemiological studies of Cryptosporidium and other eukaryotic organisms. 相似文献
194.
Three routes have been explored to synthesise the telomere-targeted agent 3,11-difluoro-6,8,13-trimethyl-8H-quino[4,3,2-kl]acridinium methosulfate . Application of a 6-(2-azidophenyl)phenanthridine precursor gave an entry to the indazolo[2,3-f]phenanthridine ring system not the required quino[4,3,2-kl]acridine. A six step synthesis starting from 2,6-dibromo-4-methylbenzonitrile via a 1-arylacridin-9(10H)-one intermediate, or , gave the required in low overall yield (<10%). The most efficient route entailed the one-pot (five step) conversion of 1,2-dimethyl-6-fluoroquinolinium methosulfate to in 33% yield employing triethylamine as base and nitrobenzene as solvent. 相似文献
195.
Zhang YM Chohnan S Virga KG Stevens RD Ilkayeva OR Wenner BR Bain JR Newgard CB Lee RE Rock CO Jackowski S 《Chemistry & biology》2007,14(3):291-302
Coenzyme A (CoA) is the major acyl group carrier in intermediary metabolism. Hopantenate (HoPan), a competitive inhibitor of the pantothenate kinases, was used to chemically antagonize CoA biosynthesis. HoPan dramatically reduced liver CoA and mice developed severe hypoglycemia. Insulin was reduced, glucagon and corticosterone were elevated, and fasting accelerated hypoglycemia. Metabolic profiling revealed a large increase in acylcarnitines, illustrating the role of carnitine in buffering acyl groups to maintain the nonesterified CoASH level. HoPan triggered significant changes in hepatic gene expression that substantially increased the thioesterases, which liberate CoASH from acyl-CoA, and increased pyruvate dehydrogenase kinase 1, which prevents the conversion of CoASH to acetyl-CoA. These results identify the metabolic rearrangements that maintain the CoASH pool which is critical to mitochondrial functions, including gluconeogenesis, fatty acid oxidation, and the tricarboxylic acid and urea cycles. 相似文献
196.
K F Faull J P Whitelegge J Higginson T To J Johnson A N Krutchinsky K G Standing A J Waring R L Stevens C B Fluharty A L Fluharty 《Journal of mass spectrometry : JMS》1999,34(10):1040-1054
Cerebroside sulfate activator protein is a small, heat-stable protein that is exceptionally resistant to proteolytic attack. This protein is essential for the catabolism of cerebroside sulfate and several other glycosphingolipids. Protein purified from pig kidney and human urine was extensively characterized by reversed-phase liquid chromatography and electrospray mass spectrometry. These two sources revealed 20 and 18 different molecular isoforms of the protein, respectively. Plausible explanations of the structures of the majority of these isoforms can be made on the basis of accurate molecular mass assignments. The reversed-phase chromatographic and electrospray mass spectrometric properties of enzymatically deglycosylated and disulfide-reduced protein were also compared. In addition to a demonstration of the power of electrospray ionization mass spectrometry for revealing a wealth of information on protein microheterogeneity and structural detail, the results also demonstrate the utility of this technique for monitoring spontaneous chemical and enzymatically mediated changes that occur as a result of metabolic processing and protein purification. 相似文献
197.
198.
Matthew P. Stevens Emily Spray Iigo J. Vitorica-Yrezabal Kuldip Singh Vanessa M. Timmermann Lia Sotorrios Fabrizio Ortu 《Molecules (Basel, Switzerland)》2022,27(14)
Herein, we report the synthesis of a series of heteroleptic magnesium complexes stabilized with the scorpionate ligand tris(2-pyridylthio)methanide (Tptm). The compounds of the general formula [Mg(Tptm)(X)] (1-X; X = Cl, Br, I) were obtained via protonolysis reaction between the proligand and selected Grignard reagents. Attempts to isolate the potassium derivative K(Tptm) lead to decomposition of Tptm and formation of the alkene (C5H4N-S)2C=C(C5H4N-S)2, and this degradation was also modelled using DFT methods. Compound 1-I was treated with K(CH2Ph), affording the degradation product [Mg(Bptm)2] (2; Bptm = {CH(S-C5NH3)2}−). We analyzed and quantified the steric properties of the Tptm ligand using the structural information of the compounds obtained in this study paired with buried volume calculations, also adding the structural data of HTptm and its CF3-substituted congener (HTptmCF3). These studies highlight the highly flexible nature of this ligand scaffold and its ability to stabilize various coordination motifs and geometries, which is a highly desirable feature in the design of novel organometallic reagents and catalysts. 相似文献
199.
Tailoring RuII Pyridine/Triazole Oxygenation Catalysts and Using Photoreactivity to Probe their Electronic Properties 下载免费PDF全文
Fritz Weisser Hendrik Stevens Johannes Klein Margarethe van der Meer Dr. Stephan Hohloch Prof. Dr. Biprajit Sarkar 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(24):8926-8938
Tuning of ligand properties is at the heart of influencing chemical reactivity and generating tailor‐made catalysts. Herein, three series of complexes [Ru(L)(Cl)(X)]PF6 (X=DMSO, PPh3, or CD3CN) with tripodal ligands (L1–L5) containing pyridine and triazole arms are presented. Triazole‐for‐pyridine substitution and the substituent at the triazole systematically influence the redox behavior and photoreactivity of the complexes. The mechanism of the light‐driven ligand exchange of the DMSO complexes in CD3CN could be elucidated, and two seven‐coordinate intermediates were identified. Finally, tuning of the ligand framework was applied to the catalytic oxygenation of alkanes, for which the DMSO complexes were the best catalysts and the yield improved with increasing number of triazole arms. These results thus show how click‐derived ligands can be tuned on demand for catalytic processes. 相似文献
200.
Chengxiang Xiang Adam Z. Weber Shane Ardo Alan Berger YiKai Chen Robert Coridan Katherine T. Fountaine Sophia Haussener Shu Hu Rui Liu Nathan S. Lewis Miguel A. Modestino Matthew M. Shaner Meenesh R. Singh John C. Stevens Ke Sun Karl Walczak 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2016,128(42):13168-13183