全文获取类型
收费全文 | 2616篇 |
免费 | 93篇 |
国内免费 | 15篇 |
专业分类
化学 | 1772篇 |
晶体学 | 12篇 |
力学 | 74篇 |
数学 | 391篇 |
物理学 | 475篇 |
出版年
2023年 | 16篇 |
2022年 | 48篇 |
2021年 | 65篇 |
2020年 | 45篇 |
2019年 | 40篇 |
2018年 | 38篇 |
2017年 | 37篇 |
2016年 | 94篇 |
2015年 | 79篇 |
2014年 | 75篇 |
2013年 | 156篇 |
2012年 | 156篇 |
2011年 | 184篇 |
2010年 | 103篇 |
2009年 | 105篇 |
2008年 | 165篇 |
2007年 | 166篇 |
2006年 | 164篇 |
2005年 | 147篇 |
2004年 | 145篇 |
2003年 | 110篇 |
2002年 | 110篇 |
2001年 | 36篇 |
2000年 | 28篇 |
1999年 | 30篇 |
1998年 | 19篇 |
1997年 | 17篇 |
1996年 | 33篇 |
1995年 | 13篇 |
1994年 | 14篇 |
1993年 | 12篇 |
1992年 | 10篇 |
1991年 | 10篇 |
1990年 | 17篇 |
1989年 | 13篇 |
1988年 | 13篇 |
1987年 | 7篇 |
1986年 | 11篇 |
1985年 | 27篇 |
1984年 | 17篇 |
1983年 | 16篇 |
1982年 | 22篇 |
1981年 | 16篇 |
1980年 | 20篇 |
1979年 | 25篇 |
1977年 | 6篇 |
1976年 | 5篇 |
1975年 | 5篇 |
1974年 | 6篇 |
1973年 | 4篇 |
排序方式: 共有2724条查询结果,搜索用时 0 毫秒
991.
Depalo N Carrieri P Comparelli R Striccoli M Agostiano A Bertinetti L Innocenti C Sangregorio C Curri ML 《Langmuir : the ACS journal of surfaces and colloids》2011,27(11):6962-6970
Asymmetric binary nanocrystals (BNCs) formed by a spherical γ-Fe(2)O(3) magnetic domain epitaxially grown onto a lateral facet of a rodlike anatase TiO(2) nanorod have been functionalized with PEG-terminated phospholipids, resulting in a micellar system that enables the BNC dispersion in aqueous solution. The further processability of the obtained water-soluble BNC including PEG lipid micelles and their use in bioconjugation experiments has been successfully demonstrated by covalently binding to bovine serum albumin (BSA). The whole process has also been preliminarily performed on spherical iron oxide nanocrystals (NCs) and TiO(2) nanorods (NRs), which form single structural units in the heterostructures. Each step has been thoroughly monitored by using optical, structural, and electrophoretic techniques. In addition, an investigation of the magnetic behavior of the iron oxide NCs and BNCs, before and after incorporation into PEG lipid micelles and subsequently bioconjugation, has been carried out, revealing that the magnetic characteristics are mostly retained. The proposed approach to achieving water-soluble anisotropic BNCs and their bioconjugates has a large potential in catalysis and biomedicine and offers key functional building blocks for biosensor applications. 相似文献
992.
Funari SS Rebbin V Marzorati L di Vitta C 《Langmuir : the ACS journal of surfaces and colloids》2011,27(13):8257-8262
We synthesize and characterize alkylthiohydroquinones (ATHs) in order to investigate their interactions with lipid model membranes, POPE and POPC. We observe the formation of structures with different morphologies, or curvature of the lipid bilayer, depending on pH and increasing temperature. We attribute their formation to changes in the balance charge/polarity induced by the ATHs. Mixtures of ATHs with POPE at pH 4 form two cubic phases, P4(3)32 and Im3m, that reach a maximum lattice size at 40 °C while under basic conditions these phases only expand upon heating from room temperature. The cubic phases coexist with lamellar or hexagonal phases and are associated with inhomogeneous distribution of the ATH molecules over the lipid matrix. The zwitterionic POPC does not form cubic phases but instead shows lamellar structures with no clear influence of the 2,6-BATH. 相似文献
993.
Direct and competition ligand-based NMR experiments are often used in the screening of chemical fragment libraries against a protein target due to the high relative sensitivity of NMR for protein-binding events. A plethora of NMR methods has been proposed for this purpose. Two of these techniques are the (19)F T(2) filter and the (1)H selective T(2) filter experiments. Modifications of the pulse sequences of these experiments have resulted in a ~2-fold reduction in the experiment time thus allowing an increase in the screening throughput and making NMR an attractive technique for screening large compound collections. 相似文献
994.
Oliveira SR Nogueira LJ Augusti R Stoianoff MA Aguilar CM Rocha WR Donnici CL 《Rapid communications in mass spectrometry : RCM》2012,26(3):377-384
Sodium adducts of six organosulfur‐α,ω‐ditetrazole compounds (Tz‐(CH2)n‐S(O)m‐(CH2)n‐Tz; where Tz = tetrazole ring; n = 2, 3; m = 0, 1, 2) were generated via electrospray ionization (ESI) and their fragmentation pattern assessed via collision‐induced dissociation (CID). Two main dissociation channels were observed: (a) losses of N2 and HN3 from the tetrazole rings; (b) cleavage of the C–S bond. The sulfoxides pass predominantly through the second fragmentation pathway, but for the sulfides and sulfones the tetrazole ring fragmentation occurs. Theoretical calculations at the B3LYP/6‐31 + G(d,p) level indicate that for all the adducts (sulfide, sulfoxide, and sulfone) the dissociation pathway that leads to product ions arising from loss of N2 was the most exothermic. Based on these results and assumptions, it was postulated that the dissociation of the sulfoxide adducts occurs under kinetic control (N2‐loss pathway via a much more energetic transition state). For the sulfide and sulfone adducts, on the other hand, the dissociation process takes place via a thermodynamically controlled process. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
995.
Jan P. Götze Claudio Greco Roland Mitrić Vlasta Bonačić‐Koutecký Peter Saalfrank 《Journal of computational chemistry》2012,33(28):2233-2242
Blue light sensing using flavin (BLUF) protein photoreceptor domains change their hydrogen bond network after photoexcitation. To explore this phenomenon, BLUF domains from R. sphaeroides were simulated using Amber99 molecular dynamics (MD). Five starting configurations were considered, to study different BLUF proteins (AppA/BlrB), Trp conformations (“Win”/“Wout”), structure determination (X‐ray/NMR), and finally, His protonation states. We found dependencies of the hydrogen bonds on almost all parameters. Our data show an especially strong correlation of the Trp position and hydrogen bonds involving Gln63. The latter is in some contradiction to earlier results (Obanayama et al., Photochem. Photobiol. 2008, 84 10031010). Possible origins and implications are discussed. Our calculations support conjectures that Gln63 is more flexible with Trp104 in Win position. Using snapshots from MD and time‐dependent density functional theory, UV/vis spectra for the chromophore were determined, which account for molecular motion of the protein under ambient conditions. In accord with experiment, it is found that the UV/vis spectra of BLUF bound flavin are red‐shifted and thermally broadened for all calculated π → π* transitions, relative to gas phase flavin at T = 0 K. However, differences in the spectra between the various BLUF configurations cannot be resolved with the present approach. © 2012 Wiley Periodicals, Inc. 相似文献
996.
Mohamadreza K. Bakht Mahdi Sadeghi Claudio Tenreiro 《Journal of Radioanalytical and Nuclear Chemistry》2012,292(1):53-59
Application of nanoparticles in nuclear medicine has aimed to develop diagnosis and therapeutic techniques. Cerium oxide nanoparticles
(CNPs) are expected to be useful for protection of healthy tissue from radiation-induced harm and could serve therapeutic
function. Among a variety of cerium radioisotopes, 137mCe (T
1/2 = 34.4 h, IT (99.22%), β+ (0.779%)) could be a novel candidate radionuclide in the field of diagnosis owing to its appropriate half-life, 99.91% natural
abundance of target and its intense gamma line at 254.29 keV. In this study, 137mCe excitation function via the natLa(p,3n) reaction was calculated by TALYS-1.2 and EMPIRE-3 codes. The excitation function calculations demonstrated that the
natLa(p,3n)137mCe reaction leads to the formation of the 136/138Ce isotopic contamination in the 22–35 MeV energy range. Interestingly, the isotopic impurities of 137mCe could serve radio protector function. Overall results indicate that the cyclotron produced 137mCeO2 nanoparticles by irradiation of a target encompassing lanthanum oxide nanoparticles could be a potent alternative for conventional
diagnostic radionuclides with simultaneous radioprotection capacity. 相似文献
997.
998.
999.
MP Serrano C Lorente FE Morán Vieyra CD Borsarelli AH Thomas 《Physical chemistry chemical physics : PCCP》2012,14(33):11657-11665
UV-A radiation (320-400 nm) induces damage to the DNA molecule and its components through photosensitized reactions. Biopterin (Bip) and its photoproducts 6-formylpterin (Fop) and 6-carboxypterin (Cap) accumulate in the skin of human beings suffering from vitiligo, a depigmentation disorder where the protection against UV radiation fails because of the lack of melanin. This study was aimed to evaluate the photosensitizing properties of oxidized pterins present in the skin and to elucidate the mechanisms involved in the photosensitized oxidation of purine nucleotides by pterins in vitro. For this purpose, steady-state and time-resolved experiments in acidic (pH 5.0-5.8) aqueous solution were performed using Bip, Fop and Cap as photosensitizers and the nucleotide 2'-deoxyguanosine 5'-monophosphate (dGMP) as an oxidizable target. The three pterin derivatives are able to photosensitize dGMP, being Fop the most efficient sensitizer. The reactions proceed through two competing pathways: (1) electron transfer from dGMP to triplet excited-state of pterins (type I mechanism) and (2) reaction of dGMP with (1)O(2) produced by pterins (type II mechanism). Kinetic analysis revealed that the electron transfer pathway is the main mechanism and the interaction of dGMP with the triplet excited-state of pterins and the formation of the corresponding dGMP radicals were demonstrated by laser flash photolysis experiments. The biological implications of the results obtained are also discussed. 相似文献
1000.