全文获取类型
收费全文 | 593篇 |
免费 | 31篇 |
专业分类
化学 | 499篇 |
力学 | 8篇 |
数学 | 48篇 |
物理学 | 69篇 |
出版年
2023年 | 10篇 |
2022年 | 11篇 |
2021年 | 32篇 |
2020年 | 25篇 |
2019年 | 14篇 |
2018年 | 10篇 |
2017年 | 10篇 |
2016年 | 28篇 |
2015年 | 25篇 |
2014年 | 26篇 |
2013年 | 31篇 |
2012年 | 70篇 |
2011年 | 63篇 |
2010年 | 20篇 |
2009年 | 21篇 |
2008年 | 39篇 |
2007年 | 46篇 |
2006年 | 36篇 |
2005年 | 24篇 |
2004年 | 22篇 |
2003年 | 9篇 |
2002年 | 21篇 |
2001年 | 2篇 |
2000年 | 4篇 |
1999年 | 2篇 |
1998年 | 2篇 |
1995年 | 2篇 |
1994年 | 1篇 |
1993年 | 2篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1987年 | 3篇 |
1986年 | 3篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1976年 | 2篇 |
1973年 | 1篇 |
1967年 | 1篇 |
排序方式: 共有624条查询结果,搜索用时 15 毫秒
1.
João Marcos G. Barbosa Milenna K. Fernandes Rodrigues Lurian C. David Taynara C. e Silva Danielly A. Fortuna Lima Naiara Z. Pereira Emmanuel B. D'Alessandro Anselmo E. de Oliveira Paulo H. Jorge da Cunha Maria Clorinda S. Fioravanti Nelson R. Antoniosi Filho 《Biomedical chromatography : BMC》2020,34(11):e4935
An innovative volatolomic approach employs the detection of biomarkers present in cerumen (earwax) to identify cattle intoxication by Stryphnodendron rotundifolium Mart., Fabaceae (popularly known as barbatimão). S. rotundifolium is a poisonous plant with the toxic compound undefined and widely distributed throughout the Brazilian territory. Cerumen samples from cattle of two local Brazilian breeds (‘Curraleiro Pé-Duro’ and ‘Pantaneiro’) were collected during an experimental intoxication protocol and analyzed using headspace (HS)/GC–MS followed by multivariate analysis (genetic algorithm for a partial least squares, cluster analysis, and classification and regression trees). A total of 106 volatile organic metabolites were identified in the cerumen samples of bovines. The intoxication by S. rotundifolium influenced the cerumen volatolomic profile of the bovines throughout the intoxication protocol. In this way, it was possible to detect biomarkers for cattle intoxication. Among the biomarkers, 2-octyldecanol and 9-tetradecen-1-ol were able to discriminate all samples between intoxicated and nonintoxicated bovines. The cattle intoxication diagnosis by S. rotundifolium was accomplished by applying the cerumen analysis using HS/GC–MS, in an easy, accurate, and noninvasive way. Thus, the proposed bioanalytical chromatography protocol is a useful tool in veterinary applications to determine this kind of intoxication. 相似文献
2.
In this paper we determine which vanishing order of a holomorphic map f at a point of the (non necessarily regular) boundary of a very generic domain of
is required for f to be constant. In particular this vanishing order is 1 if the boundary is Dini-smooth whereas it is at least β/α if f locally maps a Dini-smooth corner of opening πα into a Dini-smooth corner of opening πβ. Finally an analogous result is stated for the case of a holomorphic map f which maps a cusp into a cusp. 相似文献
3.
4.
The incorporation of explicit ions to mimic the effect of ionic strength or to neutralize the overall charge on a system in free energy calculations using molecular dynamics simulations is investigated. The difference in the free energy of hydration between two triosephosphate isomerase inhibitors calculated at five different ion concentrations is used as an example. We show that the free energy difference can be highly sensitive to the presence of explicit ions even in cases where the mutation itself does not involve a change in the overall charge. The effect is most significant if the molecule carries a net charge close to the site mutated. Furthermore, it is shown that the introduction of a small number of ions can lead to very severe sampling problems suggesting that in practical calculations convergence can best be achieved by incorporating either no counterions or by simulating at high ionic strength to ensure sufficient sampling of the ion distribution. 相似文献
5.
Byrne SJ Corr SA Gun'ko YK Kelly JM Brougham DF Ghosh S 《Chemical communications (Cambridge, England)》2004,(22):2560-2561
Denatured (substantially single-stranded) herring sperm DNA acts as a template for the preparation of magnetic nanowires, forming stable aqueous suspensions, which exhibit unprecedentedly high relaxivity at low field, suggesting that the material may be a potentially useful reagent for MRI. 相似文献
6.
Michelangelo Gruttadauria Renato Noto Serena Riela 《Journal of heterocyclic chemistry》1998,35(4):865-869
The stereoselective synthesis of a 2-substituted tetrahydropyran with adjacent alkoxy-bearing stereogenic centre is described. The key steps of this synthesis were the stereoselective epoxidation of an allylic alcohol and the regioselective epoxide ring opening by lithium aluminum hydride. The regio and stereoselective synthesis of a trihydroxyselenide and a trihydroxysulfide is also described. The latter compounds are not suitable for cyclization to tetrahydrofuran ring. 相似文献
7.
Several methodologies were employed to calculate the Gibbs standard free energy of binding for a collection of protein-ligand complexes, where the ligand is a peptide and the protein is representative for various protein families. Almost 40 protein-ligand complexes were employed for a continuum approach, which considers the protein and the peptide at the atomic level, but includes solvent as a polarizable continuum. Five protein-ligand complexes were employed for an all-atom approach that relies on a combination of the double decoupling method with thermodynamic integration and molecular dynamics. These affinities were also computed by means of the linear interaction energy method. Although it generally proved rather difficult to predict the absolute free energies correctly, for some protein families the experimental ranking order was correctly reproduced by the continuum and all-atom approach. Considerable attention has also been given to correctly analyze the affinities of charged peptides, where it is required to judge the effect of one or more ions that are being decoupled in an all-atom approach to preserve electroneutrality. The various methods are further judged upon their merits. 相似文献
8.
Serum estradiol measurement by solid-phase chemiluminescence immunoassay and direct radioimmunoassay
Jozef de Boever Fortuna Kohen Marc Dhont Dirk Vandekerchkhove Georges van Maele 《Analytica chimica acta》1985
Estradiol017β is determined in serum extracts by solid-phase chemiluminescence immunoassay. The results are compared with those obtained from unextracted serum in routine conditions with a commercial radioimmunoassay (r.i.a.) kit. For the chemiluminescence procedure, a purified monoclonal antibody to estradiol-6-carboxymethyloxime/bovine serum albumin and the homologous chemiluminescent marker conjugate estradiol-6-carboxymethyloxime aminobutylethylisoluminol are used. Bound and free ligand are separated by washing and simple centrifugation. Results obtained by the chemiluminescence assay (y) and by r.i.a. (x) on 170 serum specimens from women during ovulation induction showed good correlation (y = 1.01x ? 16 with r = 0.95). The methods are similar in selectivity, detection limit (ca. 10 ng l?1) and precision (interassay relative standard deviation, 8–13%). 相似文献
9.
A method to synthesize 2-phenylselenenyl-1,3-anti-diols and 2-phenyl- selenenyl-1,3-anti-azidoalcohols via hydroxy- or azido-selenenylation of trans-allylic alcohols is reported. Moreover, the first example of hydroxyl-selenenylation of an allylic azide is presented. Yields ranging from moderate to good and diastereomeric ratios up to 95:5 are achieved. 相似文献
10.
The accurate determination of E,E-2,4-hexadiendioic acid (t,t-muconic acid), an important urinary biomarker of benzene exposure, is directly performed in human urine by a new two-dimensional liquid chromatographic method. After a first partial separation of urine components by a reversed-phase mechanism and the focalisation of the anionic analytes on a small anion-chromatographic column, a conventional ion-chromatographic analysis with UV detection is carried out. The analytical procedure is fully controlled by the HPLC instrumentation software using an eight-port switch valve. If compared with conventional one-dimensional procedures, the new method produces chromatograms containing a limited number of well resolved peaks and consequently allows better analytical performances: no interfering peaks, absence of bias, repeatability better than 5% in the concentration range 0.09-5 mg dm-3 and a detection limit of 4.0 micrograms dm-3 (alpha = beta = 0.05) for the analysis of real samples. 相似文献