全文获取类型
收费全文 | 655篇 |
免费 | 24篇 |
国内免费 | 4篇 |
专业分类
化学 | 397篇 |
晶体学 | 6篇 |
力学 | 9篇 |
数学 | 45篇 |
物理学 | 226篇 |
出版年
2023年 | 2篇 |
2021年 | 15篇 |
2020年 | 9篇 |
2019年 | 13篇 |
2018年 | 14篇 |
2017年 | 11篇 |
2016年 | 26篇 |
2015年 | 17篇 |
2014年 | 14篇 |
2013年 | 31篇 |
2012年 | 36篇 |
2011年 | 41篇 |
2010年 | 23篇 |
2009年 | 20篇 |
2008年 | 31篇 |
2007年 | 34篇 |
2006年 | 20篇 |
2005年 | 25篇 |
2004年 | 23篇 |
2003年 | 22篇 |
2002年 | 30篇 |
2001年 | 15篇 |
2000年 | 25篇 |
1999年 | 7篇 |
1998年 | 5篇 |
1997年 | 10篇 |
1996年 | 10篇 |
1995年 | 4篇 |
1994年 | 12篇 |
1993年 | 14篇 |
1992年 | 14篇 |
1991年 | 8篇 |
1990年 | 20篇 |
1989年 | 9篇 |
1988年 | 14篇 |
1987年 | 10篇 |
1986年 | 11篇 |
1985年 | 4篇 |
1984年 | 2篇 |
1983年 | 4篇 |
1982年 | 5篇 |
1981年 | 5篇 |
1979年 | 4篇 |
1978年 | 2篇 |
1977年 | 1篇 |
1976年 | 4篇 |
1974年 | 2篇 |
1973年 | 2篇 |
1970年 | 1篇 |
1935年 | 1篇 |
排序方式: 共有683条查询结果,搜索用时 15 毫秒
61.
62.
63.
Summary A recently improved model capable of extracting the wind field from SAR imagery without the aid of ?sea truth? is applied
to ERS-1 SAR data for the Mediterranean Sea. The model is based on the properties of the relationship between the first two
moments of the probabilistic distribution function of SAR signals as well as on spectral analysis of the SAR signal itself. 相似文献
64.
E. Ramos T. Lopez P. Bosch M. Asomoza R. Gomez 《Journal of Sol-Gel Science and Technology》1997,8(1-3):437-442
Sol-Gel Hydrotalcites were synthesized using magnesium ethoxide and variable aluminum sources: aluminum acetilacetonate, aluminum
chloride, aluminum nitrate and aluminum sulfate; in all cases, the gelation was done at pH 10. X-ray diffraction studies show
that the crystallinity depends on the aluminum precursor used. The crystallinity was found in the order aluminum acetylcetonate>aluminum
chloride>aluminum nitrate>aluminum sulfate. The precursor determines the sintering behavior as well. 相似文献
65.
Shneor R Monaghan P Subedi R Anderson BD Aniol K Annand J Arrington J Benaoum H Benmokhtar F Bertin P Bertozzi W Boeglin W Chen JP Choi S Chudakov E Cisbani E Craver B de Jager CW Feuerbach RJ Frullani S Garibaldi F Gayou O Gilad S Gilman R Glamazdin O Gomez J Hansen JO Higinbotham DW Holmstrom T Ibrahim H Igarashi R Jans E Jiang X Jiang Y Kaufman L Kelleher A Kolarkar A Kuchina E Kumbartzki G LeRose JJ Lindgren R Liyanage N Margaziotis DJ Markowitz P Marrone S Mazouz M Meekins D Michaels R 《Physical review letters》2007,99(7):072501
We investigated simultaneously the 12C(e,e'p) and 12C(e,e'pp) reactions at Q2=2 (GeV/c)2, xB=1.2, and in an (e, e'p) missing-momentum range from 300 to 600 MeV/c. At these kinematics, with a missing momentum greater than the Fermi momentum of nucleons in a nucleus and far from the delta excitation, short-range nucleon-nucleon correlations are predicted to dominate the reaction. For (9.5+/-2)% of the 12C(e,e'p) events, a recoiling partner proton was observed back-to-back to the 12C(e,e'p) missing-momentum vector, an experimental signature of correlations. 相似文献
66.
A Bioinspired Molybdenum Complex as a Catalyst for the Photo‐ and Electroreduction of Protons 下载免费PDF全文
Jean‐Philippe Porcher Thibault Fogeron Dr. Maria Gomez‐Mingot Dr. Etienne Derat Lise‐Marie Chamoreau Dr. Yun Li Prof. Marc Fontecave 《Angewandte Chemie (International ed. in English)》2015,54(47):14090-14093
A molybdenum–dithiolene–oxo complex was prepared as a model of some active sites of Mo/W‐dependent enzymes. The ligand, a quinoxaline–pyran‐fused dithiolene, mimics molybdopterin present in these active sites. For the first time, this type of complex was shown to be active as a catalyst for the photoreduction of protons with excellent turnover numbers (500) and good stability in aqueous/organic media and for the electroreduction of protons in acetonitrile with remarkable rate constants (1030 s?1 at ?1.3 V versus Ag/AgCl). DFT calculations provided insight into the catalytic cycle of the reaction, suggesting that the oxo ligand plays a key role in proton exchange. These results provide a basis to optimize this new class of H2‐evolving catalysts. 相似文献
67.
Dr. Desmond MacLeod Carey Dr. Tatiana Gomez Dr. Cesar Morales-Verdejo Dr. Alvaro Muñoz-Castro 《ChemistryOpen》2015,4(5):651-655
The complexation of metal cations into a host–guest situation is particularly well exemplified by [2.2.2]paracyclophane and AgI, which leads to a strong cation–π interaction with a specific face of the host molecule. Through this study we sought a deeper understanding of the effects the metal center has on the NMR spectroscopic properties of the prototypical organic host, generating theoretical reasons for the observed experimental results with an aim to determine the role of the cation–π interaction in a host–guest scenario. From an analysis of certain components of the induced magnetic field and the 13C NMR shielding tensor under its own principal axis system (PAS), the local and overall magnetic behavior can be clearly described. Interestingly, the magnetic response of such a complex exhibits a large axis-dependent behavior, which leads to an overall shielding effect for the coordinating carbon atoms and a deshielding effect for the respective uncoordinated counterparts, evidence that complements previous experimental results. This proposed approach can be useful to gain further insight into the local and overall variation of NMR shifts for host–guest pairs involving both inorganic and organic hosts. 相似文献
68.
Jonas Nilsson Fredrik Noborn Alejandro Gomez Toledo Waqas Nasir Carina Sihlbom Göran Larson 《Journal of the American Society for Mass Spectrometry》2017,28(2):229-241
Purification and liquid chromatography-tandem mass spectrometry (LC-MS/MS) characterization of glycopeptides, originating from protease digests of glycoproteins, enables site-specific analysis of protein N- and O-glycosylations. We have described a protocol to enrich, hydrolyze by chondroitinase ABC, and characterize chondroitin sulfate-containing glycopeptides (CS-glycopeptides) using positive mode LC-MS/MS. The CS-glycopeptides, originating from the Bikunin proteoglycan of human urine samples, had ΔHexAGalNAcGlcAGalGalXyl-O-Ser hexasaccharide structure and were further substituted with 0-3 sulfate and 0-1 phosphate groups. However, it was not possible to exactly pinpoint sulfate attachment residues, for protonated precursors, due to extensive fragmentation of sulfate groups using high-energy collision induced dissociation (HCD). To circumvent the well-recognized sulfate instability, we now introduced Na+ ions to form sodiated precursors, which protected sulfate groups from decomposition and facilitated the assignment of sulfate modifications. Sulfate groups were pinpointed to both Gal residues and to the GalNAc of the hexasaccharide structure. The intensities of protonated and sodiated saccharide oxonium ions were very prominent in the HCD-MS2 spectra, which provided complementary structural analysis of sulfate substituents of CS-glycopeptides. We have demonstrated a considerable heterogeneity of the bikunin CS linkage region. The realization of these structural variants should be beneficial in studies aimed at investigating the importance of the CS linkage region with regards to the biosynthesis of CS and potential interactions to CS binding proteins. Also, the combined use of protonated and sodiated precursors for positive mode HCD fragmentation analysis will likely become useful for additional classes of sulfated glycopeptides. 相似文献
69.
The ability to accurately inject small volumes of sample into microfluidic channels is of great importance in electrophoretic separations. While electrokinetic injection of nanoliter scale volumes is commonly utilized in microchip capillary electrophoresis (MCE), mobility and matrix bias makes quantitation difficult. Herein, we describe a new injection method based on the simple patterning of the crossing of channels that does not require sophisticated instrumentation. The sample volume injected into the separation channel is dependent on the ratio of the widths of the crossing channels. This injection method is capable of introducing, into a separation channel, multiple plugs of sample on a large scale. This injection technique is tested for zone electrophoresis in native and surface modified poly(dimethylsiloxane) (PDMS) chips. 相似文献
70.
Acosta-Gutiérrez S Hernández-Rojas J Bretón J Llorente JM Wales DJ 《The Journal of chemical physics》2011,135(12):124303
Likely candidates for the lowest minima of water clusters (H(2)O)(N) for N ≤ 20 interacting with a uniform electric field strength in the range E ≤ 0.6 V/? have been identified using basin-hopping global optimization. Two water-water model potentials were considered, namely TIP4P and the polarizable Dang-Chang potential. The two models produce some consistent results but also exhibit significant differences. The cluster internal energy and dipole moment indicate two varieties of topological transition in the structure of the global minimum as the field strength is increased. The first takes place at low field strengths (0.1 V/? 10) usually forming helical structures. 相似文献