全文获取类型
收费全文 | 2385篇 |
免费 | 39篇 |
国内免费 | 26篇 |
专业分类
化学 | 1380篇 |
晶体学 | 42篇 |
力学 | 68篇 |
数学 | 515篇 |
物理学 | 445篇 |
出版年
2022年 | 34篇 |
2021年 | 51篇 |
2020年 | 26篇 |
2019年 | 28篇 |
2018年 | 31篇 |
2017年 | 25篇 |
2016年 | 60篇 |
2015年 | 38篇 |
2014年 | 63篇 |
2013年 | 112篇 |
2012年 | 114篇 |
2011年 | 101篇 |
2010年 | 88篇 |
2009年 | 98篇 |
2008年 | 125篇 |
2007年 | 145篇 |
2006年 | 131篇 |
2005年 | 110篇 |
2004年 | 93篇 |
2003年 | 68篇 |
2002年 | 65篇 |
2001年 | 46篇 |
2000年 | 48篇 |
1999年 | 36篇 |
1998年 | 34篇 |
1997年 | 28篇 |
1996年 | 42篇 |
1995年 | 30篇 |
1994年 | 29篇 |
1993年 | 33篇 |
1992年 | 29篇 |
1991年 | 21篇 |
1990年 | 27篇 |
1989年 | 25篇 |
1988年 | 30篇 |
1987年 | 25篇 |
1986年 | 31篇 |
1985年 | 31篇 |
1984年 | 34篇 |
1983年 | 20篇 |
1982年 | 32篇 |
1981年 | 21篇 |
1980年 | 26篇 |
1979年 | 11篇 |
1978年 | 20篇 |
1977年 | 21篇 |
1976年 | 13篇 |
1975年 | 7篇 |
1974年 | 12篇 |
1965年 | 8篇 |
排序方式: 共有2450条查询结果,搜索用时 15 毫秒
61.
Ali Jabalameli Andrzej Nowek Richard H. Sullivan Jerzy Leszczyński 《Structural chemistry》1997,8(4):245-256
Ab initio studies (LCAO-MO method) on conformers of three seleno derivatives of the biuret molecules diselenobiuret [I], selenobiuret [II], and selenothiobiuret [III] were carried out at the Hartree-Fock (HF) and MP2 levels. The molecular geometries of these species were fully optimized at the HF level and characterized by analysis of the harmonic vibrational frequencies using a split-valence triple-zeta basis set augmented by a set ofd polarization functions on heavy atoms andp polarization functions on hydrogen atoms [TZP(d, p)]. The total energies of the HF-optimized structures were calculated at the MP2 (frozen core) level using a larger TZP (2df, 2pd) basis set. The potential energy searches revealed a total of 11 minimum-energy conformers (assigned astrans-trans, trans-cis, cis-trans, andcis-cis) and seven transition-state species for the title molecules. The two predicted conformers for diselenobiuret (Ia=trans-trans andIc=cis-cis) are characterized byC
2 and the third byC
s symmetry. For selenothiobiuret two forms (IIIa=trans-trans andIIId=cis-cis) possessC
1 and two (IIIb=trans-cis andIIIc=cis-trans) possessC
s symmetries, respectively. For selenobiuret, four formsIIa=trans-trans (C1),IIb=trans-cis (C
s),IIc=cis-trans (C
1), andIId=cis-cis (C1), were obtained as a result of gradient optimization. Comparison of the relative energies for the considered species indicated that thecis-trans forms are the most stable conformations for all three systems at both the HF and MP2 levels of theory. 相似文献
62.
Exchange interactions in copper(II) complexes with tridentate Schiff bases: EPR and magnetic studies
Bogusława Jeżowska-Trzebiatowska Julia Jezierska Jerzy Baranowski 《Chemical physics letters》1977,52(3):590-594
The influence of the nature of ligands upon the magnetic and EPR properties was investigated for the series of polynuclear Cu(II) complexes with tridentate Schiff bases. A similar tendency of changes in the |J| and D parameters was found for binuclear Cu(II) complexes with ligands derived from condensation of 3-amino-1-propanol with 2-hydroxyaldehydes and acetylacetone as well as for Cu(II) complexes with condensation products of o-aminophenol and β-diketones. The Cu(II) complex with Schiff base of 1-amino-2-propanol and acetylacetone exhibits ferromagnetic behaviour suggesting tetrameric structure. 相似文献
63.
Werner Georg Nowak 《Journal of Number Theory》1984,19(2):254-262
It is proved that (for every ε > 0) (where {·} denotes the fractional part and Bk the Bernoulli polynomial of order k) under the suppositions that k ≥ 2 and 2a ? 1 ≥ b ≥ 1. If (1) were true for k = 1, a = b = 0, then Piltz' divisor problem (for n = 3) would be readily solved. This is an analog to a conjecture formulated by S. Chowla and H. Walum in 1963 and settled in the affirmative (under suitable suppositions) quite recently by S. Kanemitsu and R. Sita Rama Chandra Rao. 相似文献
64.
Microcalorimetry and measurement of culture turbidity using a Bioscreen C Analyzer System were applied to study the toxic effect of phenanthrene on Cunninghamella elegans IM 1785/21Gp spore germination. The results of C. elegans spore incubation in Bioscreen C microbiology reader showed the inhibition of spore germination by 70% (with 25 mg l−1 of phenanthrene) and total inhibition of the fungus growth with a higher content of the xenobiotic (50-100 mg l−1). The microcalorimetric technique showed to be useful for the estimation of metabolic activity of C. elegans spores in growth medium up to xenobiotic concentrations of 90 mg l−1. These data corresponded with the microscopic observations. The obtained results showed that the microcalorimetry method could be a valuable supplement in the study on the mechanism of PAHs detoxification by fungi. 相似文献
65.
66.
D. S. Baranov N. Y. Chabrov V. A. Filipov A. A. Ivanilov P. V. Ivanov V. I. Konyushko V. M. Korablev V. A. Korotkov V. A. Krupnov V. V. Makeev A. G. Myagkov A. Yu. Polyarush A. A. Sokolov E. P. Kuznetsov H. -J. Grabosch H. H. Kaufmann U. Krecker R. Nahnhauer S. Nowak H. Vogt 《Zeitschrift fur Physik C Particles and Fields》1984,21(3):189-196
We present data on the multiplicity structure of inclusive charged hadron production in charged current neutrino and antineutrino freon interactions in the energy range 3–30 GeV resulting from an experiment with the bubble chamber SKAT. Average multiplicities, dispersions and correlation coefficients are investigated. Furthermore, KNO-scaling is studied and average net charges are calculated in different kinematical regions. Our data are compared with results from \(\begin{array}{*{20}c} {( - )} \\ v \\ \end{array} \) -interactions on an isoscalar target of “free” nucleons to study the influence of nuclear effects. 相似文献
67.
The fabrication and application of an end-column amperometric detection (AD) system with a carbon electrode for capillary-column liquid chromatography (CLC) were described. This new amperometric detector showed good sensitivity and stability in detecting the thiocompounds and other analytes with CLC. In order to obtain the better separation and detection performance for analytes, several operational parameters had been investigated: the working potentials, pH and flow rate. Under the optimum conditions, the method could effectively separate and determine cysteine (Cys), glutathione (GSH), dopamine (DA) and 6-thiopurine (6-TP). Good repeatability for retention time was obtained with a relative standard deviation (R.S.D.) value of 0.5%. The linear range covered over three orders of magnitude and the limits of detection were 8 fmol for cysteine, 20 fmol for glutathione, 8 fmol for dopamine and 20 fmol for 6-thiopurine. This method was successfully applied in determination of urinary sample with characteristics of simplicity, high sensitivity and good repeatability. 相似文献
68.
Werner Georg Nowak 《manuscripta mathematica》1984,49(2):195-205
Let A(x) denote the number of lattice points in the circle u2+v2x and define as the infimum of all reals for which
. The objective of this paper is to show that 35/108 which improves upon all previously known results. This estimate is an immediate consequence of a surprisingly easy generalization of KOLESNIK's work on Dirichlet's divisor problem to divisor functions with respect to arithmetic progressions. 相似文献
69.
Jerzy Kijowski 《General Relativity and Gravitation》1978,9(10):857-877
A new variational principle based on the affine connection in space-time is proposed. This leads to a new formulation of general relativity. The gravitational field is a field of inertial frames in space-time. The metricg appears as a momentum canonically conjugate to the gravitational field. In the case of simple matter fields, e.g., scalar fields, electromagnetic fields, Proca fields, or hydrodynamical matter, the new formulation is equivalent to the traditional one. A new formulation of conservation laws is proposed. 相似文献
70.
James P. Kutney Peter Grice Krystyna Piotrowska Steven J. Rettig Jerzy Szykula James Trotter Loc Van Chu 《Helvetica chimica acta》1983,66(6):1820-1826
The thujone-derived enone 1 , upon base-catalyzed reaction with 2-methyl-6-vinylpyridine is converted to the pyridine analogue 5 (Scheme 1). Catalytic reduction of the latter to 6 generates two new centers of chirality which eventually become C(8) and C(14) in the ultimate synthetic steroid analogue 12 . An X-ray analysis of 6 establishes the structure and absolute configuration so as to determine its suitability in subsequent synthetic studies. The acetal derivative 7 , via Birch reduction, hydrolysis, and internal aldol cyclization, is converted into the cyclohexenone analogue 10 (Scheme 2). This ‘one-pot’ process affords an efficient conversion of the pyridine ring into a cyclohexenone system required for A-ring construction of the steroid skeleton. Finally, conversion of 10 , via the unsaturated diketone 11 , provides the chiral steroid analogue 12 . 相似文献