全文获取类型
收费全文 | 1804篇 |
免费 | 40篇 |
国内免费 | 3篇 |
专业分类
化学 | 1293篇 |
晶体学 | 3篇 |
力学 | 58篇 |
数学 | 243篇 |
物理学 | 250篇 |
出版年
2023年 | 9篇 |
2021年 | 11篇 |
2020年 | 26篇 |
2019年 | 19篇 |
2018年 | 16篇 |
2017年 | 16篇 |
2016年 | 35篇 |
2015年 | 27篇 |
2014年 | 30篇 |
2013年 | 51篇 |
2012年 | 89篇 |
2011年 | 86篇 |
2010年 | 47篇 |
2009年 | 51篇 |
2008年 | 66篇 |
2007年 | 66篇 |
2006年 | 60篇 |
2005年 | 62篇 |
2004年 | 63篇 |
2003年 | 45篇 |
2002年 | 41篇 |
2001年 | 26篇 |
2000年 | 27篇 |
1999年 | 20篇 |
1998年 | 15篇 |
1997年 | 22篇 |
1996年 | 25篇 |
1995年 | 24篇 |
1994年 | 25篇 |
1993年 | 12篇 |
1992年 | 22篇 |
1991年 | 21篇 |
1990年 | 14篇 |
1989年 | 12篇 |
1988年 | 11篇 |
1987年 | 18篇 |
1986年 | 9篇 |
1985年 | 16篇 |
1984年 | 14篇 |
1982年 | 12篇 |
1980年 | 10篇 |
1979年 | 18篇 |
1978年 | 13篇 |
1977年 | 13篇 |
1976年 | 14篇 |
1975年 | 16篇 |
1974年 | 23篇 |
1972年 | 11篇 |
1968年 | 290篇 |
1967年 | 89篇 |
排序方式: 共有1847条查询结果,搜索用时 31 毫秒
181.
182.
Lee JK Gwinner MC Berger R Newby C Zentel R Friend RH Sirringhaus H Ober CK 《Journal of the American Chemical Society》2011,133(26):9949-9951
In this communication, we report that dipotassium aryl bis(trifluoroborate)s make stable and easy-to-purify yet reactive monomers under Suzuki polycondensation reactions. A bis(trifluoroborate) of 2-alkylbenzotriazole was prepared successfully and copolymerized with dibromobenzothiadiazole in the presence of a Pd catalyst and LiOH, yielding high molecular weight conjugated polymers. This polymer (P1) composed of all electron-accepting units shows excellent electron-transport properties (μ(e) = 0.02 cm(2) V(-1) s(-1)), which proves the value of the aryl bis(trifluoroborate) monomers and suggests that many other types of semiconducting polymers that could not be accessed previously can be synthesized using this approach. 相似文献
183.
Lorenz C Hoffmann A Gross G Windhagen H Dellinger P Möhwald K Dempwolf W Menzel H 《Macromolecular bioscience》2011,11(2):234-244
A fast and simple approach for immobilization using copolymers as interlayers is reported. The synthesized copolymers form stable self-assembled layers on implant materials like, e.g., titanium in a simple coating/drying/washing sequence and have functional groups which can bind proteins from an aqueous solution. The copolymer films have been characterized via ellipsometry and contact angle measurements and were tested for biocompatibility. An immunoassay was used to determine the amount of BMP2 and demonstrated an approximately 10-fold increase as compared to previously used self-assembled monolayers. A BMP2-responsive cell line with luciferase detection was used to determine the biological activity of the bound signaling protein. 相似文献
184.
Expansions of abelian categories are introduced. These are certain functors between abelian categories and provide a tool for induction/reduction arguments. Expansions arise naturally in the study of coherent sheaves on weighted projective lines; this is illustrated by various applications. 相似文献
185.
A graph is total domination edge-critical if the addition of any edge decreases the total domination number, while a graph
with minimum degree at least two is total domination vertex-critical if the removal of any vertex decreases the total domination
number. A 3
t
EC graph is a total domination edge-critical graph with total domination number 3 and a 3
t
VC graph is a total domination vertex-critical graph with total domination number 3. A graph G is factor-critical if G − v has a perfect matching for every vertex v in G. In this paper, we show that every 3
t
EC graph of even order has a perfect matching, while every 3
t
EC graph of odd order with no cut-vertex is factor-critical. We also show that every 3
t
VC graph of even order that is K
1,7-free has a perfect matching, while every 3
t
VC graph of odd order that is K
1,6-free is factor-critical. We show that these results are tight in the sense that there exist 3
t
VC graphs of even order with no perfect matching that are K
1,8-free and 3
t
VC graphs of odd order that are K
1,7-free but not factor-critical. 相似文献
186.
A recently developed technique in sum frequency generation spectroscopy, polarization angle null (or PAN-SFG), is applied to two orientations of the prism face of hexagonal ice. It is found that the vibrational modes of the surface are similar in different faces. As in the basal face, the prism face of ice contains five dominant resonances: 3096, 3146, 3205, 3253, and 3386 cm(-1). On the basal face, the reddest resonance occurs at 3098 cm(-1); within the bandwidth, the same as the prism face. On both the prism and basal faces, this mode contains a significant quadrupole component and is assigned to the bilayer stitching hydrogen bonds. The bluest of the resonances, 3386 cm(-1), occurs slightly blue-shifted at 3393 cm(-1) in the basal face. The prism face has two orientations: one with the optic or c axis in the input plane (the plane formed by the surface normal and the interrogating beam propagation) and one with the c axis perpendicular to the input plane. The 3386 cm(-1) mode has significant intensity only with the c axis in the input plane. On the basis of these orientation characteristics, the 3386 cm(-1) mode is assigned to double-donor molecules in either the top half bilayer or in the lower half bilayer. On the basis of frequency considerations, it is assigned to double-donor molecules in the top half bilayer. These are water molecules containing a nonbonded lone pair. In addition to identification of the components of the broad hydrogen-bonded region, PAN-SFG measures the tangential vs longitudinal content of the vibrational modes. In accord with previous suggestions, the lower frequency modes are predominantly tangential, whereas the higher frequency modes are mainly longitudinal. On the prism face, the 3386 cm(-1) mode is entirely longitudinal. 相似文献
187.
Marciniak H Li XQ Würthner F Lochbrunner S 《The journal of physical chemistry. A》2011,115(5):648-654
The dynamics and mobility of excitons in J-aggregates of perylene bisimides are investigated by transient absorption spectroscopy with a time resolution of 50 fs. The transient spectra are compatible with an exciton delocalization length of two monomers and indicate that vibrational and configurational relaxation processes are not relevant for the spectroscopic properties of the aggregates. Increasing the pump pulse energy and in that way the initial exciton density results in an accelerated signal decay and pronounced exciton-exciton annihilation dynamics. Modeling the data by assuming a diffusive exciton motion reveals that the excitons cannot migrate freely in all three directions of space but their mobility is restricted to one dimension. The observed anisotropy supports this picture and points against direct Fo?rster-transfer-mediated annihilation between the excitons. A diffusion constant of 1.29 nm(2)/ps is deduced from the fitting procedure that corresponds to a maximal exciton diffusion length of 96 nm for the measured exciton lifetime of 3.6 ns. The findings indicate that J-aggregates of perylene bisimides are promising building blocks to facilitate directed energy transport in optoelectronic organic devices or artificial light-harvesting systems. 相似文献
188.
Dr. Gaël Rouillé Mathias Steglich Dr. Cornelia Jäger Prof. Dr. Friedrich Huisken Prof. Dr. Thomas Henning Gabriele Theumer Dr. Ingmar Bauer Prof. Dr. Hans‐Joachim Knölker 《Chemphyschem》2011,12(11):2131-2137
We report on the characterization of dibenzo[cde,opq]rubicene (C30H14). The molecule was studied in solution at room temperature with absorption spectroscopy in the visible (vis) and ultraviolet (UV) wavelength ranges, and with emission spectroscopy. The infrared (IR), visible, ultraviolet, and vacuum ultraviolet (VUV) absorption spectra of a thin film were measured also at room temperature. In addition, the UV/vis absorption spectrum was measured at cryogenic temperatures using the matrix isolation spectroscopy technique. The interpretation of spectra was supported by theoretical calculations based on semiempirical and ab initio models, as well as on density functional theory. Finally, the results of the laboratory study were compared with interstellar spectra. 相似文献
189.
190.
We consider the cost of general orthogonal range queries in random quadtrees. The cost of a given query is encoded into a (random) function of four variables which characterize the coordinates of two opposite corners of the query rectangle. We prove that, when suitably shifted and rescaled, the random cost function converges uniformly in probability towards a random field that is characterized as the unique solution to a distributional fixed-point equation. We also state similar results for 2-d trees. Our results imply for instance that the worst case query satisfies the same asymptotic estimates as a typical query, and thereby resolve an open question of Chanzy et al. (2001). 相似文献