全文获取类型
收费全文 | 569篇 |
免费 | 11篇 |
国内免费 | 6篇 |
专业分类
化学 | 424篇 |
晶体学 | 5篇 |
力学 | 10篇 |
数学 | 84篇 |
物理学 | 63篇 |
出版年
2022年 | 7篇 |
2021年 | 9篇 |
2020年 | 9篇 |
2019年 | 9篇 |
2018年 | 4篇 |
2017年 | 7篇 |
2016年 | 14篇 |
2015年 | 11篇 |
2014年 | 10篇 |
2013年 | 32篇 |
2012年 | 28篇 |
2011年 | 43篇 |
2010年 | 26篇 |
2009年 | 11篇 |
2008年 | 31篇 |
2007年 | 42篇 |
2006年 | 27篇 |
2005年 | 50篇 |
2004年 | 39篇 |
2003年 | 24篇 |
2002年 | 13篇 |
2001年 | 7篇 |
2000年 | 11篇 |
1999年 | 11篇 |
1998年 | 5篇 |
1997年 | 8篇 |
1996年 | 8篇 |
1995年 | 5篇 |
1994年 | 5篇 |
1993年 | 4篇 |
1992年 | 2篇 |
1990年 | 2篇 |
1989年 | 3篇 |
1988年 | 4篇 |
1987年 | 3篇 |
1986年 | 4篇 |
1985年 | 5篇 |
1984年 | 6篇 |
1982年 | 5篇 |
1981年 | 3篇 |
1980年 | 12篇 |
1979年 | 2篇 |
1978年 | 4篇 |
1977年 | 2篇 |
1976年 | 3篇 |
1974年 | 2篇 |
1973年 | 2篇 |
1972年 | 2篇 |
1968年 | 3篇 |
1930年 | 1篇 |
排序方式: 共有586条查询结果,搜索用时 15 毫秒
151.
OBJECTIVE: To examine the role of the practitioner, informed consent, and genetic counseling in genetic testing decisions and to assess their relative influence on women's decision to have clinical BRCA1/2 testing. METHODS: Qualitative study using in-depth open-ended interviews with 68 women who had considered clinical BRCA1/2 testing. RESULTS: Slightly less than half of the women who had considered BRCA1/2 testing were found to have had a clear and preexisting desire to test or not to test, irrespective of practitioner attitude or advice. CONCLUSION: The decision to accept or decline genetic testing is the result of a complex process that goes beyond interactions between health care providers and patients, indicating a caution against exclusive reliance on informed consent or counseling encounters. 相似文献
152.
Diaz-Marrero AR Austin P Van Soest R Matainaho T Roskelley CD Roberge M Andersen RJ 《Organic letters》2006,8(17):3749-3752
[structure: see text] The new meroterpenoids avinosol (1), 3'-aminoavarone (2), and 3'-phenethylaminoavarone (3) have been isolated from the marine sponge Dysidea sp. collected in Papua New Guinea, and their structures were elucidated by analysis of spectroscopic data. Avinosol (1), which is apparently the first example of a naturally occurring meroterpenoid-nucleoside conjugate, showed antiinvasion activity in a cell-based assay. 相似文献
153.
We present a new nonlocal updating scheme for quantum Monte Carlo simulations, which conserves particle number and other symmetries. It allows exact symmetry projection and direct evaluation of the equal-time Green's function and other observables in the canonical ensemble. The method is applicable to a wide variety of systems. We show results for bosonic atoms in optical lattices, neutron pairs in atomic nuclei, and electron pairs in ultrasmall superconducting grains. 相似文献
154.
Romani A Vignolini P Tanini A Pampaloni B Heimler D 《Natural product communications》2010,5(11):1775-1780
Isoflavones are polyphenolic compounds found mainly in legumes the benefits of which have been widely studied and attributed in particular to their phytoestrogenic activity. The aim of this study was to evaluate the quali-quantitative composition of food supplements based on soy isoflavones (Glycine max L.) and red clover (Trifolium pratense). Six commercial food supplements (five soy-based and one red clover-based) were analyzed by HPLC/DAD/MS. Genistein, daidzein, glycitein, biochanin A and formononetin derivatives (glycosides and acylglycosides) were identified in the analyzed samples. Also the antiradical activities (towards the DPPH* radical) and Fe2+ chelating abilities were compared. 相似文献
155.
Sañudo EC Smith AA Mason PV Helliwell M Aromí G Winpenny RE 《Dalton transactions (Cambridge, England : 2003)》2006,(16):1981-1987
Solid-state decomposition of [V3O(O2CPh)6(H2O)3]Cl at 300 degrees C followed by alcoholysis of the product gives the new vanadium complexes [V6O6(PhCO2)6(CH3O)6(CH3OH)3] (1), [V6O6(PhCO2)6(C2H5O)6(C2H5OH)3] (2), [V6O6(PhCO2)6(C3H7O)6(C3H7OH)3] (3), [V6O6(PhCO2)6(C4H9O)6(C4H9OH)3] (4) and [V4O4(OCH3)6(O2CPh)2(HOCH3)2] (5). Complexes 2, 3 and 5 have been crystallographically characterised. DC magnetic susceptibility studies on complex shows antiferromagnetic coupling leading to a S = 0 spin ground state. 相似文献
156.
157.
158.
Conradson SD Begg BD Clark DL Den Auwer C Espinosa-Faller FJ Gordon PL Hess NJ Hess R Keogh DW Morales LA Neu MP Runde W Tait CD Veirs DK Villella PM 《Inorganic chemistry》2003,42(12):3715-3717
Pu L(3) XAFS measurements show that the excess oxygen in single phase PuO(2+)(x)() occurs as oxo groups with Pu-O distances of 1.83-1.91 A. This distance and the energy of the edge (via comparison with a large number of related compounds) are more consistent with a Pu(IV/V) than a Pu(IV/VI) mixture. Analogous to Pu(IV) colloids, although the Pu-Pu pair distribution remains single site even when it shows substantial disorder, the Pu-O distribution can display a number of additional shells at specific distances up to 3.4 A even in high fired materials when no oxo groups are present, implying intrinsic H(+)/OH(-)(/H(2)O). The number of oxo atoms increases when samples are equilibrated with humid air at ambient temperature, indicating that the Pu reactivity in this solid system differs notably from that of isolated complexes and demonstrating the importance of nanoscale cooperative phenomena and total free energy in determining its chemical properties. 相似文献
159.
Federiconi F Ausili P Fragneto G Ferrero C Mariani P 《The journal of physical chemistry. B》2005,109(21):11037-11045
Guanosine, one of the primary components of nucleic acids, self-associates in water to form G-quadruplexes, four-stranded helicoidal aggregates, made by stacked planar tetramers, consisting of four planar guanine molecules. Essential for the stability of these supramolecular aggregates is the presence of monovalent cations. As G-quadruplexes show a lyotropic polymorphism, neutron diffraction, in combination with the H2O/D2O contrast variation technique, has been applied to study the cation structural features of quadruplexes in hexagonal phase at different hydrations and counterion concentrations. The guanosine 5'-monophosphate, dipotassium salt, was considered and G-quadruplexes in hexagonal phase were prepared in the different experimental conditions (contrast, hydration and KCl solution concentration) by using the osmotic stress technique. The calculated scattering length density distribution maps show that counterions fill the helix inner cavity and that atmospheric cations are bound to a second site, close to the external phosphate groups. The site occupancy turned out to be very high: we found on the inner site 0.87 K ions per tetramer in G-quadruplexes prepared in pure water and 0.97 K ions per tetramer in G-quadruplexes prepared in KCl 0.5 M, while in all cases 6 ions per unit cell were detected to occupy the outer sites, partially neutralizing the two formal negative charges per phosphate group. The very large K ions concentration difference between the binding sites and the bulk solution demonstrates that counterions are structurally involved in the formation and in the stabilization of the helices. 相似文献
160.
Viville P Lazzaroni R Pollet E Alexandre M Dubois P 《Journal of the American Chemical Society》2004,126(29):9007-9012
We report on the controlled chemical grafting of well-defined polymer chains onto individual montmorillonite-type clay nanoplatelets and the direct visualization of the formed hybrid material at the nanoscale level. Our approach is based on the use of a surfactant mixture that contains varying proportions of hydroxyl-substituted alkylammonium and unsubstituted alkylammonium cations to exchange the initial Na(+) counterions of the natural montmorillonite. This allows for the exchange of Na(+) by a tunable amount of hydroxyl functions at the surface of the clays. Those functions are then derivatized into aluminum alkoxides in order to initiate the ring-opening polymerization of epsilon-caprolactone directly from the clay surface that was swollen in an organic solvent. Atomic force microscopy measurements on the resulting polymer-grafted nanoplatelets demonstrate the strong dependence of the coating of the individual clay particles with the composition of the surfactant mixture used for the cationic exchange. This allows for the generation of a range of morphologies varying from polymer islands distributed over the clay surface to homogeneous polymer layers thoroughly coating the platelets. Finally, the control that is achievable over the synthesis of this new family of organic-inorganic nanohybrid materials has been extended to the surface grafting of semicrystalline poly(epsilon-caprolactone)-poly(lactic acid) diblock copolymers with defined compositions. 相似文献