全文获取类型
收费全文 | 2513篇 |
免费 | 172篇 |
国内免费 | 12篇 |
专业分类
化学 | 1697篇 |
晶体学 | 15篇 |
力学 | 55篇 |
数学 | 401篇 |
物理学 | 529篇 |
出版年
2023年 | 36篇 |
2022年 | 52篇 |
2021年 | 68篇 |
2020年 | 130篇 |
2019年 | 102篇 |
2018年 | 43篇 |
2017年 | 43篇 |
2016年 | 153篇 |
2015年 | 115篇 |
2014年 | 108篇 |
2013年 | 129篇 |
2012年 | 165篇 |
2011年 | 223篇 |
2010年 | 128篇 |
2009年 | 86篇 |
2008年 | 179篇 |
2007年 | 151篇 |
2006年 | 127篇 |
2005年 | 134篇 |
2004年 | 85篇 |
2003年 | 54篇 |
2002年 | 59篇 |
2001年 | 25篇 |
2000年 | 29篇 |
1999年 | 14篇 |
1998年 | 15篇 |
1997年 | 9篇 |
1996年 | 22篇 |
1995年 | 22篇 |
1994年 | 12篇 |
1993年 | 7篇 |
1992年 | 5篇 |
1991年 | 10篇 |
1989年 | 5篇 |
1987年 | 6篇 |
1986年 | 8篇 |
1985年 | 12篇 |
1984年 | 5篇 |
1983年 | 6篇 |
1982年 | 6篇 |
1980年 | 4篇 |
1978年 | 9篇 |
1976年 | 7篇 |
1975年 | 6篇 |
1974年 | 6篇 |
1970年 | 5篇 |
1969年 | 8篇 |
1967年 | 3篇 |
1966年 | 3篇 |
1964年 | 3篇 |
排序方式: 共有2697条查询结果,搜索用时 15 毫秒
71.
72.
Etienne V. Brouillet Alan R. Kennedy Tobias Krämer Robert E. Mulvey Stuart D. Robertson Alexander Stewart Stephen Towie 《无机化学与普通化学杂志》2020,646(13):726-733
Previous studies of different solvates of 2-methylpyridyllithium (2-picolyllithium) have uncovered electronic structures corresponding to aza-allyl and enamido resonance forms of the metallated pyridine-based compounds. Here, we report the synthesis and characterization of [2-CH2Li(THF)2C5H4N], a new THF solvate. X-ray crystallographic studies reveal a dimeric arrangement featuring a non-planar eight-membered [NCCLi]2 ring, in which the primary cation-anion interaction is between the central Li atom and the C atom of the deprotonated methyl group [length, 2.285(2) Å], suggesting a new carbanionic resonance structure for this 2-picolyllithium series. The significant carbanionic character of [2-CH2Li(THF)2C5H4N] was confirmed by gas-phase DFT calculations [B3LYP/6-311+G(d)] with the calculated electron density interrogated by means of quantum theory of atoms in molecules (QTAIM) and natural bond orbital (NBO) analyses. For comparison these computational analyses were also performed on the literature structures of [2-CH2Li(2-Picoline)C5H4N] and [2-CH2Li(PMDETA)C5H4N]. In a reactivity study, [2-CH2Li(THF)2C5H4N] was found to undergo nucleophilic addition to pyridine to generate dipyridylmethane in a good yield. 相似文献
73.
74.
75.
We show that every two-dimensional entire graphical solution of the Willmore equation with square integrable second fundamental form is a plane. 相似文献
76.
Felix Katzsch Tobias Gruber Edwin Weber 《Acta Crystallographica. Section C, Structural Chemistry》2016,72(9):679-684
The syntheses of three bis(benzo[b]thiophen‐2‐yl)methane derivatives, namely bis(benzo[b]thiophen‐2‐yl)methanone, C17H10OS2, (I), 1,1‐bis(benzo[b]thiophen‐2‐yl)‐3‐(trimethylsilyl)prop‐2‐yn‐1‐ol, C22H20OS2Si, (II), and 1,1‐bis(benzo[b]thiophen‐2‐yl)prop‐2‐yn‐1‐ol, C19H12OS2, (III), are described and their crystal structures discussed comparatively. The conformation of ketone (I) and the respective analogues are rather similar for most of the compounds compared. This is true for the interplanar angles, the Caryl—Cbridge—Caryl angles and the dihedral angles. The best resemblance is found for a bioisotere of (I), viz. 2,2′‐dinaphthyl ketone, (VII). By way of interest, the crystal packings also reveal similarities between (I) and (VII). In (I), the edge‐to‐face interactions seen between two napthyl residues in (VII) are substituted by S…π contacts between the benzo[b]thiophen‐2‐yl units in (I). In the structures of the bis(benzo[b]thiophen‐2‐yl)methanols, i.e. (II) and (III), the interplanar angles are also quite similar compared with analogues and related active pharmaceutical ingredients (APIs) containing the dithiophen‐2‐ylmethane scaffold, though the dihedral angles show a larger variability and produce unsymmetrical molecules. 相似文献
77.
78.
79.
Ramona Hoffmann Bertram Taetz Markus Miezal Gabriele Bleser Sigrid Leyendecker 《PAMM》2016,16(1):89-90
This work investigates the combination of optical motion capturing data with optimal control simulations of human motion, which can be important in a wide range of applications in the professional as well as the private sector, ranging from health and ergonomics over human-machine-interaction to sports and games [1–3]. There are methodically very different approaches to include optical measurement data in the simulation of human motion, see e.g. [4–6]. Two different approaches to combine data and simulation are investigated in this work. Either we use a soft constraints approach, where the difference of simulated and measured marker positions is part of the objective function (1), or we formulate an hard constraints approach with nonlinear constraints that set an upper bound on this difference (2), while the objective function is purely physiologically motivated. (© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
80.
For systems that contain slow and fast dynamics, variational multirate integration schemes are used. These schemes split the system into parts which are simulated using two time grids consisting of micro and macro nodes. This formulation can be extended for multi-body systems. The rigid multi-body system is described by the so called director formulation and constraints describing the joints connecting the bodies. With the Lagrange multiplier method, the constraints are introduced into the equations of motion. A way to implement the null space method into the variational multirate framework is shown and the influence on the number of unknowns is investigated. (© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献