全文获取类型
收费全文 | 2752篇 |
免费 | 115篇 |
国内免费 | 5篇 |
专业分类
化学 | 1980篇 |
晶体学 | 7篇 |
力学 | 61篇 |
数学 | 460篇 |
物理学 | 364篇 |
出版年
2021年 | 17篇 |
2020年 | 43篇 |
2019年 | 45篇 |
2018年 | 29篇 |
2017年 | 26篇 |
2016年 | 71篇 |
2015年 | 64篇 |
2014年 | 91篇 |
2013年 | 123篇 |
2012年 | 138篇 |
2011年 | 184篇 |
2010年 | 93篇 |
2009年 | 80篇 |
2008年 | 138篇 |
2007年 | 156篇 |
2006年 | 140篇 |
2005年 | 146篇 |
2004年 | 136篇 |
2003年 | 87篇 |
2002年 | 48篇 |
2001年 | 25篇 |
2000年 | 26篇 |
1999年 | 25篇 |
1998年 | 17篇 |
1997年 | 47篇 |
1996年 | 45篇 |
1995年 | 31篇 |
1994年 | 45篇 |
1993年 | 37篇 |
1992年 | 22篇 |
1991年 | 31篇 |
1990年 | 29篇 |
1989年 | 31篇 |
1988年 | 29篇 |
1987年 | 31篇 |
1986年 | 42篇 |
1985年 | 47篇 |
1984年 | 49篇 |
1983年 | 40篇 |
1982年 | 45篇 |
1981年 | 26篇 |
1980年 | 37篇 |
1979年 | 36篇 |
1978年 | 29篇 |
1977年 | 34篇 |
1976年 | 24篇 |
1974年 | 14篇 |
1973年 | 16篇 |
1972年 | 19篇 |
1971年 | 16篇 |
排序方式: 共有2872条查询结果,搜索用时 15 毫秒
31.
Comparison of CCD,CMOS and intensified cameras 总被引:2,自引:0,他引:2
The properties of digital cameras are often important to obtain accurate results with image based measurement techniques.
Unfortunately, a detailed comparison of the sensor specifications and performance is not accessible as this information is
normally not provided by the manufacturers and no generally accepted comparison standard exists. Therefore, a detailed quantitative
comparison was performed to evaluate and assess the characteristics of state-of-the-art CCD, CMOS and intensified CMOS sensors.
These results may be of assistance when selecting the appropriate sensor for a desired application. 相似文献
32.
Rainer Mandel 《Annals of Global Analysis and Geometry》2018,54(2):187-236
In this paper, we prove explicit formulas for all Willmore surfaces of revolution and demonstrate their use in the discussion of the associated Dirichlet boundary value problems. It is shown by an explicit example that symmetric Dirichlet boundary conditions do in general not entail the symmetry of the surface. In addition, we prove a symmetry result for a subclass of Willmore surfaces satisfying symmetric Dirichlet boundary data. 相似文献
33.
On Copper(I) Fluorides,the Cuprophilic Interaction,the Preparation of Copper Nitride at Room Temperature,and the Formation Mechanism at Elevated Temperatures 下载免费PDF全文
Dipl.‐Chem. Patrick Woidy Dr. Antti J. Karttunen Dr. Marc Widenmeyer Prof. Dr. Rainer Niewa Prof. Dr. Florian Kraus 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(8):3290-3303
Our attempts to synthesize the hitherto unknown binary copper(I) fluoride have led to first successes and a serendipitious result: By conproportionation of elemental copper and copper(II) fluoride in anhydrous liquid ammonia, two copper(I) fluorides were obtained as simple NH3 complexes. One of them presents an example of ligand‐unsupported “cuprophilic” interactions in an infinite [Cu2(NH3)4]2+ chain with alternating Cu–Cu distances. We discovered that both copper(I) fluorides can easily be converted into Cu3N at room temperature, just by applying a vacuum. Additionally, we investigated the formation mechanism of the classical synthesis route of Cu3N that starts with CuF2 and flowing NH3 in the temperature range between ambient and 290 °C by means of thermal analysis and in situ neutron diffraction. The reaction proceeds at elevated temperatures through the formation of a blue and amorphous ammoniate Cu(NH3)2F2, the reformation of CuF2, and finally the redox reaction to form Cu3N. 相似文献
34.
Aggregation‐Induced‐Emission‐Active Macrocycle Exhibiting Analogous Triply and Singly Twisted Möbius Topologies 下载免费PDF全文
Engui Zhao Luming Meng Christian Schütt Jacky W. Y. Lam Herman H. Y. Sung Prof. Dr. Ian D. Williams Prof. Xuhui Huang Prof. Rainer Herges Prof. Ben Zhong Tang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(33):11707-11711
Molecules with Möbius topology have drawn increasing attention from scientists in a variety of fields, such as organic chemistry, inorganic chemistry, and material science. However, synthetic difficulties and the lack of functionality impede their fundamental understanding and practical applications. Here, we report the facile synthesis of an aggregation‐induced‐emission (AIE)‐active macrocycle (TPE‐ET) and investigate its analogous triply and singly twisted Möbius topologies. Because of the twisted and flexible nature of the tetraphenylethene units, the macrocycle adjusts its conformations so as to accommodate different guest molecules in its crystals. Moreover, theoretical studies including topological and electronic calculations reveal the energetically favorable interconversion process between triply and singly twisted topologies. 相似文献
35.
José Manuel Villalba Franco Dr. Gregor Schnakenburg Prof. Dr. Arturo Espinosa Ferao Prof. Dr. Rainer Streubel 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(9):3727-3735
The novel N,P,C‐cage complexes 5 a – f and 6 a – f have been obtained by the reaction of the P‐pentamethylcyclopentadienylphosphinidene complex 2 , generated thermally from 2H‐azaphosphirene complex 1 , with N‐methyl‐C‐arylcarbaldimines 3 a – f . Li/Cl phosphinidenoid complex 8 reacted with 3 a , b to give N,P,C‐cage complexes 6 a , b , whereas with 3 c – f , complexes 6 c – f were obtained in negligible amounts only. Both types of ligand N,P,C‐cage structures 5 and 6 were found to be in an unprecedented equilibrium, with 5 a , f as the predominant species. Transient electrophilic terminal phosphinidene complexes 10 a – f serve as intermediates in both ligand interconversions ( 5 a , f ? 6 a , f ), as evidenced through trapping reactions with phenylacetylene and N‐methyl‐C‐phenylcarbaldimine, thus leading to the novel N,P,C‐cage complexes 13 b and 15 . DFT calculations predicted a small difference in the relative energies of the two types of N,P,C‐cage ligands, and a remarkable stabilisation of the aminophosphinidene complex 10 as the common precursor, thereby providing an insight into this surprising 5‐ring–3‐ring interconversion. In depth analysis of intermediate 10 revealed the occurrence of both through‐bond (conventional inductive/mesomeric effects) and through‐space (non‐covalent interactions) mechanisms, which amount to 67.8 and 14.4 kcal mol?1, respectively, and account for the remarkable stabilisation of this intermediate. 相似文献
36.
37.
38.
39.
Chu Rainer Kwang-Hua 《Journal of Experimental and Theoretical Physics》2016,123(5):822-826
We illustrate the possible acceleration of cosmic rays passing through a kind of amplification channel (via diffusion modes of propagating plane-wave fronts) induced by a rotating system. Our analysis is mainly based on the quantum discrete kinetic model (considering a discrete Uehling-Uhlenbeck collision term), which has been used to study the propagation of plane (e.g., acoustic) waves in a system of rotating gases. 相似文献
40.