全文获取类型
收费全文 | 818篇 |
免费 | 27篇 |
国内免费 | 93篇 |
专业分类
化学 | 647篇 |
晶体学 | 4篇 |
力学 | 36篇 |
数学 | 82篇 |
物理学 | 169篇 |
出版年
2024年 | 3篇 |
2023年 | 100篇 |
2022年 | 10篇 |
2021年 | 11篇 |
2020年 | 13篇 |
2019年 | 14篇 |
2018年 | 14篇 |
2017年 | 12篇 |
2016年 | 15篇 |
2015年 | 18篇 |
2014年 | 17篇 |
2013年 | 57篇 |
2012年 | 31篇 |
2011年 | 38篇 |
2010年 | 37篇 |
2009年 | 47篇 |
2008年 | 47篇 |
2007年 | 57篇 |
2006年 | 41篇 |
2005年 | 30篇 |
2004年 | 25篇 |
2003年 | 22篇 |
2002年 | 19篇 |
2001年 | 20篇 |
2000年 | 23篇 |
1999年 | 23篇 |
1998年 | 24篇 |
1997年 | 12篇 |
1996年 | 10篇 |
1995年 | 7篇 |
1994年 | 9篇 |
1993年 | 12篇 |
1992年 | 9篇 |
1991年 | 14篇 |
1990年 | 3篇 |
1989年 | 12篇 |
1988年 | 4篇 |
1987年 | 7篇 |
1985年 | 11篇 |
1984年 | 6篇 |
1982年 | 3篇 |
1981年 | 7篇 |
1980年 | 4篇 |
1979年 | 9篇 |
1978年 | 4篇 |
1977年 | 6篇 |
1973年 | 3篇 |
1971年 | 4篇 |
1970年 | 2篇 |
1969年 | 2篇 |
排序方式: 共有938条查询结果,搜索用时 15 毫秒
51.
Egbert Hahn Johanna Fruwert und Heinz Böhlig 《Monatshefte für Chemie / Chemical Monthly》1984,115(8-9):935-942
Comparable force fields for HCOO–, HFCO, HClCO and HDCO have been calculated on the basis of internal coordinates. Linear relations between (i) the carbonyl bond order and the carbonyl stretching force constant, (ii) the sum of the three in-plane bending force constants and the hydrogen out-of-plane force constantf
, (iii) a combination of orbital electronegativities andf
, have been obtained. The observed in-plane vibrational frequencies have been calculated with an average error of 6.3 cm–1 or 0.4%. 相似文献
52.
53.
Zvonimir B. Maksić Krešimir Kovačević Andrea Moguš 《Theoretical chemistry accounts》1980,55(2):127-132
A comparative study of the structural parameters in some strained spirohydrocarbons is presented. The theoretical values provided by the STO-3G, MINDO/3 and IMOA methods are in reasonable agreement with each other and with available experimental data offering thus a posteriori justification of the employed approximate schemes. 相似文献
54.
55.
56.
应用键轨道连接矩阵方法提取结构参数PX1CC和PX1CH, 并用于建立预测烷烃折光率的QSPR模型.该模型不仅预测精度较高(其误差仅为0.0048),而且模型中采用的参数表达了直接与分子的折光能力相关的结构信息(即烷烃分子中电子被极化的能力).此参数提取简单,既具备拓扑指数简单、易算,物理意义明确. 相似文献
57.
A hierarchical approach bridging the atomistic and nanometric scales is used to compute the elastic properties of boron nitride nanosheets and nanoribbons, examining the effect of sheet size, aspect ratio and anisotropy. The approach consists in obtaining the bond force (force field) constants by dedicated computations based on density functional theory (DFT) and using such constants as input for larger scale structural models solved by finite element analysis (FEA). The bond force constants calculated by DFT are 616.9 N/m for stretching, 6.27×10−19 Nm/rad2 for in-plane rotation and 1.32×10−19 Nm/rad2 for dihedral rotation. Using these constants, the elastic properties of boron nitride nanosheets and nanoribbons predicted by FEA are almost independent of the sheet size, but strongly dependent on their aspect ratio. The sheet anisotropy increases with increased aspect ratio, with nanoribbons of aspect ratios of 10 exhibiting a ratio of elastic moduli along both in-plane directions of 1.7. 相似文献
58.
John P. Boyd Maria Schlangen Andreas Grohmann Helmut Schwarz 《Helvetica chimica acta》2008,91(8):1430-1434
An unprecedented alkyne–nitrile metathesis takes place when the high‐valent iron‐nitrido dication [Fe(L)N]2+, with L=2,6‐bis(2‐methyl‐1,3‐diaminopropan‐2‐yl)pyridine, is reacted with alkynes in the gas phase under thermal conditions. While the detailed role of the alkyne substrate with respect to relative rates, regioselectivities, and branching ratios remains to be elucidated, the very existence of this novel metathesis reaction provides additional experimental evidence of a genuine, long‐lived, formal iron(V)‐nitrido dication. 相似文献
59.
Burkhard Butschke Maria Schlangen Detlef Schröder Helmut Schwarz 《Helvetica chimica acta》2008,91(10):1902-1915
Mechanistic details for the formation of methane from the title compound as well as the combined elimination of (CH3)2S/CH4 are derived from various mass‐spectrometric experiments including deuterium‐labeling studies and DFT calculations. For the first process, i.e., methane formation, we have identified three competing pathways in which the intact, Pt‐bonded methyl group combines with a H‐atom that originates from a phenyl substituent (ca. 7%), the dimethyl sulfide ligand (ca. 41%), and a methyl group of the diazabutadiene backbone (ca. 52%). In contrast, in the combined (CH3)2S/CH4 elimination, the methane is specifically formed from the Pt‐bound CH3 group and a H‐atom provided by one of the phenyl groups (‘cyclometalation’). 相似文献
60.
C. Zhang 《Mathematische Nachrichten》2009,282(9):1342-1353
Let S be a Riemann sphere with n ≥ 4 points deleted. In this article we investigate certain filling closed geodesics of S and give quantitative common lower bounds for the hyperbolic lengths of those geodesics with respect to any hyperbolic structure on S (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献