全文获取类型
收费全文 | 487篇 |
免费 | 16篇 |
国内免费 | 12篇 |
专业分类
化学 | 361篇 |
晶体学 | 5篇 |
力学 | 7篇 |
数学 | 83篇 |
物理学 | 59篇 |
出版年
2023年 | 3篇 |
2022年 | 2篇 |
2021年 | 6篇 |
2019年 | 11篇 |
2018年 | 5篇 |
2017年 | 5篇 |
2016年 | 13篇 |
2015年 | 10篇 |
2014年 | 14篇 |
2013年 | 29篇 |
2012年 | 40篇 |
2011年 | 47篇 |
2010年 | 21篇 |
2009年 | 15篇 |
2008年 | 32篇 |
2007年 | 34篇 |
2006年 | 23篇 |
2005年 | 31篇 |
2004年 | 29篇 |
2003年 | 34篇 |
2002年 | 16篇 |
2001年 | 6篇 |
2000年 | 6篇 |
1999年 | 3篇 |
1998年 | 4篇 |
1997年 | 10篇 |
1996年 | 2篇 |
1995年 | 4篇 |
1994年 | 5篇 |
1993年 | 3篇 |
1991年 | 4篇 |
1990年 | 3篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1986年 | 3篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1981年 | 2篇 |
1980年 | 3篇 |
1979年 | 3篇 |
1978年 | 5篇 |
1977年 | 4篇 |
1976年 | 1篇 |
1975年 | 2篇 |
1974年 | 3篇 |
1973年 | 3篇 |
1971年 | 1篇 |
1968年 | 2篇 |
1967年 | 1篇 |
排序方式: 共有515条查询结果,搜索用时 31 毫秒
101.
102.
Elemental sulphur, a common constituent of marine sediments, has been shown to give dialkyl sulphides with the Grignard reagents commonly used to derivatize alkyltin species before their determination by gas chromatography with flame photometric detection (GC–FPD). Further, it has been demonstrated that even with the red filter for 610 nm (normally used for organotin compounds) fitted to the detector, sulphur compounds do give rise to an emission signal, which may be mistaken for tin emission from a pentylated or propylated alkyltin compound, as the respective retention times are in some cases quite close. © 1997 by John Wiley & Sons, Ltd. 相似文献
103.
104.
Iain Raeburn 《Acta Appl Math》2009,108(3):509-514
In recent joint work with Nadia Larsen, we gave a new proof of a theorem of Mallat which describes how to construct wavelets
from quadrature mirror filters. Our main innovation was to show how the scaling function associated to the filter can be used
to identify a particular direct limit of Hilbert spaces with L
2(ℝ). Here we show that wavelet-packet bases for L
2(ℝ) also fit naturally into the same direct-limit framework. 相似文献
105.
Benjamin Nabet Naomi E. Leonard Iain D. Couzin Simon A. Levin 《Journal of Nonlinear Science》2009,19(4):399-435
We analyze a continuous-time model of a multi-agent system motivated by simulation studies on dynamics of decision making
in animal groups in motion. Each individual moves at constant speed in the plane and adjusts its heading in response to relative
headings of others in the population. The population includes two subgroups that are “informed” such that individuals in each
subgroup have a preferred direction of motion. The model exhibits fast and slow time scales allowing for a reduction in the
dimension of the problem. The stable solutions for the reduced model correspond to compromise by individuals with conflicting
preferences. We study the global phase space for the proposed reduced model by computing equilibria and exploring stability
and bifurcations.
B. Nabet’s and N.E. Leonard’s work is supported in part by AFOSR grant FA9550-07-1-0-0528 and ONR grants N00014-02-1-0826
and N00014-04-1-0534.
I.D. Couzin’s work was supported by the Royal Society, Balliol College and EPSRC grants GR/S04765/01 and GR/T11234/01, a Searle
Scholar Award and DARPA grant HR001-05-1-0057.
S.A. Levin’s work was supported in part by DARPA grant HR0011-05-1-0057 and NSF grant EF-0434319. 相似文献
106.
A Th(IV) compound, [Th(TFSI)4(HTFSI)].2H2O [where TFSI = N(SO2CF3)2], has been synthesized and characterized using elemental analysis, thermogravimetric analysis, and vibrational spectroscopy. The analysis suggests that the TFSI anion coordinates to the metal center via the sulfonyl oxygens as well as provides evidence for the coordination of HTFSI. The voltammetric behavior of this compound has been studied in the room-temperature ionic liquid [Me3NnBu][TFSI], and results show that Th(IV) is reduced to Th(0) in this ionic liquid in a single reduction step. Analysis of cyclic voltammograms shows that an insoluble product is being formed at the electrode surface, which is attributed to the formation of ThO2 by reaction with water. The E0 value for the reduction of Th(IV) to Th(0) has been determined to be -2.20 V (vs Fc+/Fc; -1.80 V vs SHE). A comparison of this E0 value with those obtained for Th(IV) reduction in a LiCl-KCl eutectic (400 degrees C), water, and nonaqueous solvents shows that the reduction in [Me3NnBu][TFSI] is easier to accomplish than that in these other solvents. 相似文献
107.
Yang J Bremer PJ Lamont IL McQuillan AJ 《Langmuir : the ACS journal of surfaces and colloids》2006,22(24):10109-10117
The adhesion of bacteria to metal oxide and other mineral surfaces may involve bacterial siderophores, many of which contain hydroxamic acid (Ha) ligands. The adsorption behavior of the siderophore-related ligands acetohydroxamic acid, N-methylformohydroxamic acid, N-methylacetohydroxamic acid, and 1-hydroxy-2-piperidone on titanium dioxide thin films has been investigated using in situ ATR-IR spectroscopy with variation of concentration and pH. All the ligands were found to adsorb strongly on the TiO2 surface as hydroxamate ions and form bidentate surface complexes. Vibrational modes involving C=O stretching and N-O stretching of these ligands were assigned by comparing observed IR spectra with those calculated by the density functional method at the B3LYP/6-31+G(d) level. Calculated spectra of the complex [Ti(Ha)(OH)4]-, used to model the TiO2 surface, were compared with observed spectra of adsorbed hydroxamic acids. These results suggest that hydroxamic acid ligands in siderophores would be expected to bind to metal (oxide) and mineral surfaces during bacterial adhesion processes. 相似文献
108.
Perkin S Chai L Kampf N Raviv U Briscoe W Dunlop I Titmuss S Seo M Kumacheva E Klein J 《Langmuir : the ACS journal of surfaces and colloids》2006,22(14):6142-6152
We have measured normal and lateral interactions across a range of different liquids between mica surfaces using a surface force balance (SFB). The mica surfaces were prepared either by melt cutting using Pt wire and standard procedures in our laboratories or by tearing sheets (that had not been exposed to Pt) off from a freshly cleaved sheet of mica. AFM micrographs revealed the substantial absence of Pt nanoparticles on the melt cut and torn-off mica surfaces. Normal-force versus surface-separation (D) profiles and shear force versus D measurements for purified water (no added salt), for concentrated aqueous NaCl solutions, and for cyclohexane revealed that in all cases the behavior of the highly confined liquids between melt-cut and between torn-off mica sheets was identical within experimental scatter. These results demonstrate directly that interactions measured between melt-cut mica surfaces as routinely prepared using established procedures in our laboratories and in other laboratories are free of the effect of any Pt contamination. 相似文献
109.
Hnyk D Bühl M Holub J Hayes SA Wann DA Mackie ID Borisenko KB Robertson HE Rankin DW 《Inorganic chemistry》2006,45(15):6014-6019
The molecular structures of the three heterodecaboranes arachno-6,9-C2B8H14, arachno-6,9-N2B8H12, and arachno-6,9-Se2B8H10 have been determined by ab initio MO theory. In addition, the structure of arachno-6,9-C2B8H14 was experimentally determined using gas-phase electron diffraction (GED). The accuracy of all four of these structures has been confirmed by the good agreement of the (11)B chemical shifts calculated at the GIAO-MP2 level with the experimental values. A comparison of the GIAO-HF and GIAO-MP2 methods shows that for these heteroborane clusters, electron correlation effects on the computed delta((11)B) values are quite substantial and that it is necessary to go beyond the HF level in the NMR computation. 相似文献
110.
Deschamps M Campbell ID 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2006,178(2):206-211
In experiments performed on protonated proteins at high fields, 80% of the NMR spectrometer time is spent waiting for the 1H atoms to recover their polarization after recording the free induction decay. Selective excitation of a fraction of the protons in a large molecule has previously been shown to lead to faster longitudinal relaxation for the selected protons [K. Pervushin, B. Vögeli, A. Eletsky, Longitudinal 1H relaxation optimization in TROSY NMR spectroscopy, J. Am. Chem. Soc. 124 (2002) 12898–12902; P. Schanda, B. Brutscher, Very fast two-dimensional NMR spectroscopy for real-time investigation of dynamic events in proteins on the time scale of seconds, J. Am. Chem. Soc. 127 (2005) 8014–8015; H.S. Attreya, T. Szyperski, G-matrix Fourier transform NMR spectroscopy for complete protein resonance assignment, Proc. Natl. Acad. Sci. USA 101 (2004) 9642–9647]. The pool of non-selected protons acts as a “thermal bath” and spin-diffusion processes (“flip-flop” transitions) channel the excess energy from the excited pool to the non-selected protons in regions of the molecule where other relaxation processes can dissipate the excess energy. We present here a sensitivity enhanced HSQC sequence (COST-HSQC), based on one selective E-BURP pulse, which can be used on protonated 15N enriched proteins (with or without 13C isotopic enrichment). This experiment is compared to a gradient sensitivity enhanced HSQC with a water flip-back pulse (the water flip-back pulse quenches the spin diffusion between 1HN and 1Hα spins). This experiment is shown to have significant advantages in some circumstances. Some observed limitations, namely sample overheating with short recovery delays and complex longitudinal relaxation behaviour are discussed and analysed. 相似文献