全文获取类型
收费全文 | 7332篇 |
免费 | 305篇 |
国内免费 | 52篇 |
专业分类
化学 | 5441篇 |
晶体学 | 71篇 |
力学 | 191篇 |
综合类 | 1篇 |
数学 | 936篇 |
物理学 | 1049篇 |
出版年
2023年 | 52篇 |
2022年 | 36篇 |
2021年 | 140篇 |
2020年 | 142篇 |
2019年 | 125篇 |
2018年 | 101篇 |
2017年 | 86篇 |
2016年 | 208篇 |
2015年 | 184篇 |
2014年 | 225篇 |
2013年 | 381篇 |
2012年 | 533篇 |
2011年 | 582篇 |
2010年 | 328篇 |
2009年 | 241篇 |
2008年 | 488篇 |
2007年 | 510篇 |
2006年 | 517篇 |
2005年 | 508篇 |
2004年 | 425篇 |
2003年 | 350篇 |
2002年 | 278篇 |
2001年 | 100篇 |
2000年 | 78篇 |
1999年 | 47篇 |
1998年 | 45篇 |
1997年 | 58篇 |
1996年 | 93篇 |
1995年 | 57篇 |
1994年 | 56篇 |
1993年 | 60篇 |
1992年 | 42篇 |
1991年 | 26篇 |
1990年 | 24篇 |
1989年 | 24篇 |
1988年 | 38篇 |
1987年 | 23篇 |
1986年 | 30篇 |
1985年 | 61篇 |
1984年 | 39篇 |
1983年 | 25篇 |
1982年 | 49篇 |
1981年 | 26篇 |
1980年 | 21篇 |
1979年 | 26篇 |
1978年 | 32篇 |
1977年 | 28篇 |
1976年 | 22篇 |
1975年 | 19篇 |
1974年 | 22篇 |
排序方式: 共有7689条查询结果,搜索用时 31 毫秒
1.
Foundations of Chemistry - 相似文献
2.
Habarurema Gratien Gerber Thomas Mukabagorora Theonille Hosten Eric Ndayambaje Jean Bernard Betz Richard 《Transition Metal Chemistry》2020,45(1):55-63
Transition Metal Chemistry - Rhenium(I) and (VII) complexes with cyclohex-1-enylolonium cation and bridging pyridyl derivatives are reported. Additionally, the CO-bridged pyridyl and their related... 相似文献
3.
Eric Howard 《Contemporary Physics》2019,60(4):328-329
4.
Eric C. Chi Liuyi Hu Arvind K. Saibaba Arvind U. K. Rao 《Journal of computational and graphical statistics》2019,28(1):36-47
We consider the problem of performing matrix completion with side information on row-by-row and column-by-column similarities. We build upon recent proposals for matrix estimation with smoothness constraints with respect to row and column graphs. We present a novel iterative procedure for directly minimizing an information criterion to select an appropriate amount of row and column smoothing, namely, to perform model selection. We also discuss how to exploit the special structure of the problem to scale up the estimation and model selection procedure via the Hutchinson estimator, combined with a stochastic Quasi-Newton approach. Supplementary material for this article is available online. 相似文献
5.
Mueller Eric V. Gallagher Michael R. Skowronski Nicholas Hadden Rory M. 《Transport in Porous Media》2021,138(3):637-660
Transport in Porous Media - Modeling flow in vegetative fuel beds is a key component in any detailed physics-based tool for simulating wildland fire dynamics. Current approaches for drag modeling,... 相似文献
6.
Consistency requirements and pattern methods in cost sharing problems with technological cooperation
Using the discrete cost sharing model with technological cooperation, we investigate the implications of the requirement that demand manipulations must not affect the agents’ shares. In a context where the enforcing authority cannot prevent agents (who seek to reduce their cost shares) from splitting or merging their demands, the cost sharing methods used must make such artifices unprofitable. The paper introduces a family of rules that are immune to these demand manipulations, the pattern methods. Our main result is the characterization of these methods using the above requirement. For each one of these methods, the associated pattern indicates how to combine the technologies in order to meet the agents’ demands. Within this family, two rules stand out: the public Aumann–Shapley rule, which never rewards technological cooperation; and the private Aumann–Shapley rule, which always rewards technology providers. Fairness requirements imposing natural bounds (for the technological rent) allow to further differentiate these two rules. 相似文献
7.
Heorhii V. Humeniuk Giuseppe Licari Eric Vauthey Naomi Sakai 《Supramolecular chemistry》2020,32(2):106-111
ABSTRACTDesign, synthesis and evaluation of push-pull N,N′-diphenyl-dihydrodibenzo[a,c]phenazines are reported. Consistent with theoretical predictions, donors and acceptors attached to the bent mechanophore are shown to shift absorption maxima to either red or blue, depending on their positioning in the chromophore. Redshifted excitation of push-pull fluorophores is reflected in redshifted emission of both bent and planar excited states. The intensity ratios of the dual emission in more and less polar solvents imply that excited-state (ES) planarization decelerates with increasing fluorophore macrodipole, presumably due to attraction between the wings of closed papillons. ES planarization of highly polarisable papillons is not observed in lipid bilayer membranes. All push-pull papillon amphiphiles excel with aggregation-induced emission (AIE) from bent ES as micelles in water and mechanosensitivity in viscous solvents. They are not solvatochromic and only weakly fluorescent (QY < 4%). 相似文献
8.
Copper Causes Regiospecific Formation of C4F8‐Containing Six‐Membered Rings and their Defluorination/Aromatization to C4F4‐Containing Rings in Triphenylene/1,4‐C4F8I2 Reactions 下载免费PDF全文
Kerry C. Rippy Dr. Eric V. Bukovsky Dr. Tyler T. Clikeman Dr. Yu‐Sheng Chen Dr. Gao‐Lei Hou Dr. Xue‐Bin Wang Dr. Alexey A. Popov Dr. Olga V. Boltalina Prof. Steven H. Strauss 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(3):874-877
The presence of Cu in reactions of triphenylene (TRPH) and 1,4‐C4F8I2 at 360 °C led to regiospecific substitution of TRPH ortho C(β) atoms to form C4F8‐containing rings, completely suppressing substitution on C(α) atoms. In addition, Cu caused selective reductive‐defluorination/aromatization (RD/A) to form C4F4‐containing aromatic rings. Without Cu, the reactions of TRPH and 1,4‐C4F8I2 were not regiospecific and no RD/A was observed. These results, supported by DFT calculations, are the first examples of Cu‐promoted 1) regiospecific perfluoroannulation, 2) preparative C?F activation, and 3) RD/A. HPLC‐purified products were characterized by X‐ray diffraction, low‐temperature PES, and 1H/19F NMR. 相似文献
9.
10.
Synthesis and structure–property relationship of carbazole‐alt‐benzothiadiazole copolymers 下载免费PDF全文
Jules Oriou Feifei Ng Georges Hadziioannou Cyril Brochon Eric Cloutet 《Journal of polymer science. Part A, Polymer chemistry》2015,53(17):2059-2068
A series of four π‐conjugated carbazole‐alt‐benzothiadiazole copolymers (PCBT) were prepared by Suzuki cross‐coupling reaction between synthesized dibromocarbazoles as electron‐rich subunits and 4,7‐bis(4,4,5,5‐tetramethyl‐1,3,2‐dioxaborolan‐2‐yl)?2,1,3‐benzothiadiazole as electron‐deficient subunits. The subunits were directly linked through 2,7‐ or 3,6‐ positions of the carbazole. In addition, the carbazole monomers have been N‐substituted by a branched or a linear side‐chain. The chemical structure of the copolymers and their precursors was confirmed by NMR and IR spectroscopies, and their molar masses were estimated by SEC. Thermal analysis under N2 atmosphere showed no weight loss below 329°C, and no glass transition was observed in between 0 and 250°C. The band gaps of all PCBTs evaluated by optical spectroscopies and by cyclic voltammetry analysis were consistent with expectations and ranged between 2.2 and 2.3 eV. Finally, 2,7 and 3,6 linkages were shown to influence optical properties of PCBTs. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 2059–2068 相似文献