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31.
CE-MS has evolved into a strong alternative to LC-MS. Most of CE-MS applications deal with characterization and identification. However, quantitative aspects have gained importance in, e.g., pharmaceutical and biotechnological applications. Here we summarize and evaluate various methodological aspects in order to achieve sensitive and reproducible results. Similar to LC-MS, aspects of matrix influence on the electrospray process need to be carefully addressed when quantitative results are intended by CE-MS. Due to a more complicated coupling special emphasis needs to be put on the CE-MS interface. Generally linearity over more than three orders of magnitude can be achieved by CE-ESI-MS. Furthermore, a literature survey has been performed in order to give an overview over quantitative measurements performed by CE-MS. The precision can be doubled when changing from a structural related to an isotopically labeled internal standard. Thus a level of precision better than 5% RSD can be achieved. 相似文献
32.
This paper presents an in-depth look at the use of capillary electrophoretic (CE) techniques for the fingerprinting and characterization of humic substances and natural organic matter. These materials are highly heterogeneous in structure and show all characteristics of mixtures unliked in analytical chemistry. The electrophoretic approach, however, allows the determination of mobility distributions in different solution conditions, representative of the effective charge and size distribution status of the components present. A tabulated review covers over 50 references on the subject and highlights the possibilities and problems encountered in the analysis of such polydisperse materials with CE methods. In a second part of the article the consequences of experimental and buffer parameters on the behavior of humic materials in CE are presented. 相似文献
33.
Jens Schwaiger 《Aequationes Mathematicae》1994,48(2-3):317-323
Summary We consider the functional equationf[x
1,x
2,, x
n
] =h(x
1 + +x
n
) (x
1,,x
n
K, x
j
x
k
forj k), (D) wheref[x
1,x
2,,x
n
] denotes the (n – 1)-st divided difference off and prove
Theorem. Let n be an integer, n 2, let K be a field, char(K) 2, with # K 8(n – 2) + 2. Let, furthermore, f, h: K K be functions. Then we have that f, h fulfil (D) if, and only if, there are constants aj K, 0 j n (a := an, b := an – 1) such thatf = ax
n
+bx
n – 1 + +a
0
and h = ax + b. 相似文献
34.
Summary The calculation of the effects of temperature and isotopic composition on the energy weighted moments of the dipole oscillator strength distribution of H2 in the random phase approximation to the polarization propagator are reported. It is seen that the effect of isotopic composition is small, while that of temperature is of an order accessible to experiment. We find that all the mean excitation energiesI
, for =–1, 0, 1, decrease with temperature as does the dipole oscillator strength momentS() for >0, while the opposite is true for <0. These effects are interpreted in terms of the bond length dependence of the excitation energies. 相似文献
35.
Mg(AlH(4))(2) was produced as a nanocrystalline powder by metathesis of NaAlH(4) and MgCl(2). Starting with a structure estimation which was developed from an evaluation of FTIR data and comparison of structural properties of two solvent adducts, quantum chemical calculations were performed on the density functional theory (DFT) level. The calculated atomic positions were used to simulate an X-ray powder diffraction pattern, based on a trigonal unit cell. The simulated pattern was congruent to experimental data. Thus, magnesium alanate exhibits a CdI(2) layer structure, the layers being formed by Mg atoms occupying the Cd sites and AlH(4) tedrahedra occupying the sites of the iodine atoms in CdI(2). 相似文献
36.
On Na2PrO3 and Na2TbO3 Using an exchange reaction of Na2O with Li8TbO6 (Na : Tb = 2.1 : 1; au-tube; 750°C, 30 d) yellow-orange colored single crystals of Na2TbO3 could be prepared for the first time. Na2TbO3 crystallizes monoclinic in C2/c (Z = 8; a = 576.92(6), b = 1001.27(9), c = 1117.91(14) pm, β = 99.98(1)°). According to four-circle data the Li2SnO3-type of structure is adopted (PW 1100, MoKα , 1935 I0 (hkl), R = 4.86%, Rw = 3.63% for all 928 unique reflexions). By a similar exchange reaction of Na2O with Li8PrO6 for the first time single crystals of Na2PrO3 could be prepared, too (Na : Pr = 2.2 : 1; au-tube; 700°C; 23 d). The structure determination reveils that there is a variant of the NaCl-type of structure, which ressembles to the Li2SnO3-type of structure (PW 1100, MoKα , 2199 I0 (hkl)), R = 8.88%, Rw = 5.21% for all 947 unique reflexions; C2/c, Z = 8, a = 678.78(5), b = 977.47(7), c = 1080.38(9) pm, β = 108,4(1)°. In contrast to Na2TbO3 there are no layers according to NaO(Na1/3Tb2/3)O. All octahedral intersticies are occupied systematically with Pr4+ and Na+ : (Na2/3Pr1/3)O(Na2/3Pr1/3)O. 相似文献
37.
Herein we report our investigation on the oxidation of solid-support-bound amino alcohols to their corresponding aldehydes. These aldehydes were converted into diastereomerically pure (>10:1) 2,4-cis-2-aminoalkyl-3-sulfonyl-1,3-oxazolidines using optically pure 1,2-amino alcohols. The relative configuration was determined using the nuclear Overhauser effect (NOE). The synthesized oxazolidines, which were obtained in high purities, represent a new, diverse scaffold for the solid-phase synthesis of libraries directed toward a pharmacological target. 相似文献
38.
Two New Metatitanates with Five-coordinated Titanium: CsNaTiO3 and RbNaTiO3 [1] The new oxides CsNaTiO3 (I) and RbNaTiO3 (II) are obtained by heating well grounded mixtures of the binary oxides in Ni-tubes as colourless platelike crystals. I: CsO0.56, NaO0.48 and TiO2, Cs:Na:Ti = 1.1:1.1:1.0; 600°C, 61 d as well as CsO0.97, NaO0.48 and Ti2O3, Cs:Na:Ti = 1.5:3.0:1.0; 760°C, 27 d. II: RbO0.52, NaO0.48 and TiO2, Rb:Na:Ti = 1.1:1.1:1.0; 750°C, 14 d as well as RbO0.98, NaO0.48 and Ti2O3, Rb:Na:Ti = 1.5:3.1:1.0; 760°C, 27 d. CsNaTiO3 (orthorhombic, Cmcm) is nearly isostructural with KNaTiO3 [2]; a = 601.4(1) pm, b = 1 120.3(1) pm, c = 563.4(1) pm (Guinier-Simon-Data, Z = 4). RbNaTiO3 (monoclinic, C2/c) is isostructural with KNaTiO3; a = 590.3(1) pm, b = 1 098.4(1) pm, c = 555.1(0) pm, β = 92.15° (Guinier-Simon-Data, Z = 4). Both structures are determined by using four-circle diffractometer data (CsNaTiO3: Siemens AED2, 2 896Io(hkl), MoKα , R = 2.4%, Rw = 2.3%; RbNaTiO3: Philips PW 1 100, 2 743Io(hkl), AgKα , R = 9.9%, Rw = 8.9%; additional data see text). The Madelung Part of Lattice Energy (MAPLE), Effective Coordination Numbers (ECoN), Mean Fictive Ionic Radii (MEFIR) and the Charge Distribution in Solids are calculated and discussed. 相似文献
39.
On Oxorhodates of Alkali Metals: β-LiRhO2 We prepared hitherto unknown β-LiRhO2 in form of black, cubic single crystals, O4–F4132, a = 841.27(6) pm, Z = 16. For a first time in case of such metal oxides we find one of the possible variants of order between the NaCl-type with random distribution and the complete ordered types like α-NaFeO2 as a single crystal (four-circle-diffractometer PW 1100, AgKα, 100 von 109 I0(hkl), R = 9.10%, Rw = 5.46%). The Madelung Part of Lattice Energy, MAPLE, and Effective Coordination Numbers, ECoN, these via Mean Fictive Ionic Radii, MEFIR, were calculated and discussed. 相似文献
40.
Palladium[0]-mediated Ullmann cross-coupling of 1-bromo-2-nitrobenzene (1 R = H) and its derivatives with a range of beta-halo-enals, -enones, or -esters readily affords the corresponding beta-aryl derivatives, which are converted into the corresponding quinolines, 2-quinolones, phenanthridines, or 6(5H)-phenanthridinones on reaction with dihydrogen in the presence of Pd on C or with TiCl(3) in aqueous acetone. [reaction: see text] 相似文献