全文获取类型
收费全文 | 2170篇 |
免费 | 49篇 |
国内免费 | 6篇 |
专业分类
化学 | 1599篇 |
晶体学 | 12篇 |
力学 | 38篇 |
数学 | 279篇 |
物理学 | 297篇 |
出版年
2023年 | 19篇 |
2022年 | 75篇 |
2021年 | 68篇 |
2020年 | 57篇 |
2019年 | 52篇 |
2018年 | 33篇 |
2017年 | 33篇 |
2016年 | 66篇 |
2015年 | 57篇 |
2014年 | 56篇 |
2013年 | 124篇 |
2012年 | 120篇 |
2011年 | 164篇 |
2010年 | 110篇 |
2009年 | 99篇 |
2008年 | 135篇 |
2007年 | 144篇 |
2006年 | 116篇 |
2005年 | 144篇 |
2004年 | 101篇 |
2003年 | 53篇 |
2002年 | 48篇 |
2001年 | 32篇 |
2000年 | 32篇 |
1999年 | 29篇 |
1998年 | 14篇 |
1997年 | 16篇 |
1996年 | 23篇 |
1995年 | 13篇 |
1994年 | 14篇 |
1993年 | 9篇 |
1992年 | 11篇 |
1991年 | 10篇 |
1990年 | 16篇 |
1989年 | 9篇 |
1988年 | 7篇 |
1987年 | 7篇 |
1986年 | 5篇 |
1985年 | 9篇 |
1984年 | 5篇 |
1983年 | 9篇 |
1982年 | 6篇 |
1981年 | 14篇 |
1980年 | 11篇 |
1979年 | 8篇 |
1978年 | 4篇 |
1977年 | 4篇 |
1976年 | 8篇 |
1973年 | 6篇 |
1972年 | 4篇 |
排序方式: 共有2225条查询结果,搜索用时 15 毫秒
821.
Carla Cuniberti 《Journal of Polymer Science.Polymer Physics》1970,8(12):2051-2065
The NMR relaxation times T1 and T2 have been measured for fractionated samples of polydimethylsiloxane with different molecular weights in the amorphous state and in tetrachloroethylene solutions. The results are interpreted on the basis of the anisotropic reorientation model proposed by Woessner for small molecules. A correlation time characteristic of the diffusional rotation of chain segments is calculated and shown to be proportional to the square root of the bulk viscosity. 相似文献
822.
We obtain some results on Young diagrams. Based on these results, we construct bases for Young symmetry classes of tensors. Using these bases, we obtain a complete reduction of the representation A ??mA [A∈GL(n,] and irreducible matrix representations of the full linear group. 相似文献
823.
V. V. Pereira R. R. Silva M. H. dos Santos D. F. Dias M. E. C. Moreira J. A. Takahashi 《Natural product research》2016,30(17):1974-1979
Jacaranda oxyphylla Cham. (Bignoniaceae) is a shrub found in the Brazilian cerrado and used in folk medicine to treat microbial infections. The aim of this study was to carry out a phytochemical screening and evaluate antioedematogenic, antimicrobial and antiacetylcholinesterase properties of J. oxyphylla crude extracts. All extracts analysed showed presence of terpenoids, which are potentially active chemical substances. A high AChE inhibitory activity for hexane extract from leaves and for the extracts from twigs was found. Ethanol extract from leaves of J. oxyphylla showed activity against Gram-positive (Staphylococcus aureus and Bacillus cereus) and Gram-negative (Escherichia coli) bacteria. This extract was also effective in inhibiting the stages of inflammation evaluated. Biological investigation and phytochemical screening of J. oxyphylla extracts provided additional evidence of its traditional medicinal value. 相似文献
824.
Chung KC Cao L Dias AV Pickering IJ George GN Zamble DB 《Journal of the American Chemical Society》2008,130(43):14056-14057
The high-affinity nickel-binding site of the Escherichia coli [NiFe]-hydrogenase accessory protein HypB was localized to residues at the immediate N-terminus of the protein. Modification of a metal-binding fusion protein, site-directed mutagenesis experiments, and DFT calculations were used to identify the N-terminal amine as a ligand as well as the three cysteine residues in the CXXCGCXXX motif. This sequence can be removed from the protein and both a synthesized peptide and a protein fusion bind nickel with a similar affinity and the same structure as the parent metalloprotein, indicating the self-sufficiency of this high-affinity nickel-binding sequence. 相似文献
825.
Dias K Nikolaou S De Giovani WF 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2008,70(1):154-161
Al-catechin/beta-cyclodextrin and Al-quercetin/beta-cyclodextrin (beta-CD) inclusion compounds were synthesized and characterized by IR, UV-vis, 1H and 13C NMR and TG and DTA analyses. Because quercetin is sparingly soluble in water, the stability constants of the Al-quercetin/beta-CD and Al-catechin/beta-CD compounds were determined by phase solubility studies. The AL-type diagrams indicated the formation of 1:1 inclusion compounds and allowed calculation of the stability constants. The thermodynamic parameters were obtained from the dependence of the stability constants on temperature and results indicated that the formation of the inclusion compounds is an enthalpically driven process. The thermal decomposition of the solid Al-quercetin/beta-CD and Al-catechin/beta-CD inclusion compounds took place at different stages, compared with the respective precursors, proving that an inclusion complexation process really occurred. 相似文献
826.
V. S. Braga F. A. C. Garcia J. A. Dias Sílvia C. L. Dias 《Journal of Thermal Analysis and Calorimetry》2008,92(3):851-855
Nb2O5 supported on SiO2-Al2O3 were prepared with a wide loading range (2, 5, 10, 15, 20 and 25 mass%) and analyzed by simultaneous thermogravimetric (TG)
and differential thermal analysis (DTA). The materials presented a phase transition close to 1364°C. This phase transition
was studied by XRD, FTIR and Raman spectroscopy. Amixture of orthorhombic (T) andmonoclinic (H andM) crystalline phases was
evidenced in the supported samples, which is coverage dependent, in contrast to the formation of only the monoclinic phase
(H and M) when pure Nb2O5 is heated under the same conditions. These results indicate the stabilization of Nb2O5 on silica-alumina surface. 相似文献
827.
D. dos Santos Dias Marisa Spirandeli Crespi C. A. Ribeiro 《Journal of Thermal Analysis and Calorimetry》2008,94(2):539-543
The recycling of soft drink bottles poly(ethylene terephthalate) (PET) has been used as an additive in varnish containing
alkyd resin. The PET, called to recycled PET (PET-R), was added to the varnish in increasing amounts. Samples of varnish containing
PET-R (VPET-R) were used as a film onto slides and its thermal properties were evaluated using thermogravimetry (TG). Throughout
the visual analysis and thermal behavior of VPET-R it is possible to identify that the maximum amount of PET-R added to the
varnish without changing in the film properties was 2%.
The kinetic parameters, such as activation energy (E) and the pre-exponential factor (A) were calculated by the isoconversional Flynn-Wall-Ozawa method for the samples containing 0.5 to 2.0% PET-R. A decrease
in the values of E was verified for lower amounts of PET-R for the thermal decomposition reaction. A kinetic compensation effect (KCE) represented
by the lnA=−13.42+0.23E equation was observed for all samples. The most suitable kinetic model to describe this decomposition process is the autocatalytic
Šesták-Berggren, being the model applied to heterogeneous systems. 相似文献
828.
Isabella Cravero Carla Manni M. Lucia Sampoli 《Journal of Computational and Applied Mathematics》2008
The aim of this paper is to present a new class of B-spline-like functions with tension properties. The main feature of these basis functions consists in possessing C3 or even C4 continuity and, at the same time, being endowed by shape parameters that can be easily handled. Therefore they constitute a useful tool for the construction of curves satisfying some prescribed shape constraints. The construction is based on a geometric approach which uses parametric curves with piecewise quintic components. 相似文献
829.
830.
The preparation of an enantiomerically enriched beta-diketimine composed of isoquinoline and 2-aminonaphthalene (IAN amine) is described, thereby offering new opportunities in the synthesis of nonracemic beta-diketimine- and pyridine-based chiral catalysts. 相似文献