全文获取类型
收费全文 | 2326篇 |
免费 | 53篇 |
国内免费 | 9篇 |
专业分类
化学 | 1414篇 |
晶体学 | 10篇 |
力学 | 37篇 |
数学 | 391篇 |
物理学 | 336篇 |
无线电 | 200篇 |
出版年
2022年 | 17篇 |
2021年 | 31篇 |
2020年 | 23篇 |
2019年 | 24篇 |
2018年 | 21篇 |
2017年 | 21篇 |
2016年 | 39篇 |
2015年 | 31篇 |
2014年 | 35篇 |
2013年 | 123篇 |
2012年 | 96篇 |
2011年 | 117篇 |
2010年 | 71篇 |
2009年 | 51篇 |
2008年 | 100篇 |
2007年 | 101篇 |
2006年 | 112篇 |
2005年 | 123篇 |
2004年 | 93篇 |
2003年 | 79篇 |
2002年 | 68篇 |
2001年 | 32篇 |
2000年 | 32篇 |
1999年 | 24篇 |
1998年 | 26篇 |
1997年 | 27篇 |
1996年 | 33篇 |
1995年 | 31篇 |
1994年 | 27篇 |
1993年 | 24篇 |
1992年 | 35篇 |
1991年 | 28篇 |
1990年 | 19篇 |
1989年 | 19篇 |
1988年 | 29篇 |
1986年 | 20篇 |
1985年 | 48篇 |
1984年 | 46篇 |
1983年 | 38篇 |
1982年 | 45篇 |
1981年 | 43篇 |
1980年 | 50篇 |
1979年 | 31篇 |
1978年 | 41篇 |
1977年 | 39篇 |
1976年 | 28篇 |
1975年 | 30篇 |
1974年 | 28篇 |
1973年 | 22篇 |
1969年 | 16篇 |
排序方式: 共有2388条查询结果,搜索用时 15 毫秒
201.
Commentary on “Caged Phosphate and the Slips and Misses in Determination of Quantum Yields for Ultraviolet‐A‐Induced Photouncaging” by G. Gasser and Co‐Workers 下载免费PDF全文
202.
Retsek JL Drain CM Kirmaier C Nurco DJ Medforth CJ Smith KM Sazanovich IV Chirvony VS Fajer J Holten D 《Journal of the American Chemical Society》2003,125(32):9787-9800
The ground- and excited-state metal-ligand dynamics of nonplanar nickel(II) 2,3,5,7,8,10,12,13,15,17,18,20-dodecaphenylporphyrin (NiDPP) and two fluorinated analogues (NiF(20)DPP and NiF(28)DPP) have been investigated using static and time-resolved absorption spectroscopy in toluene and in ligating media that differ in basicity, aromaticity, and steric encumbrance. Because of the electronic and steric consequences of nonplanarity, NiDPP does not bind axial ligands in the ground state, but metal coordination does occur after photoexcitation with multistep dynamics that depend on the properties of the ligand. Following the structural relaxations that occur in all nickel porphyrins within approximately 10 ps, ligand binding to photoexcited NiDPP is progressively longer in pyridine, piperidine, and 3,5-lutidine (25-100 ps) but does not occur at all in 2,6-lutidine in which the ligating nitrogen is sterically encumbered. The transient intermediate that is formed, which nominally could be either a five- or six-coordinate species, also has a ligand-dependent lifetime (200-550 ps). Decay of this intermediate occurs partially via ligand release to re-form the uncoordinated species, in competition with binding of the second axial ligand and/or conformational/electronic relaxations (of a six-coordinate intermediate) to give the ground state of the bis-ligated photoproduct. The finding that the photoproduct channel principally depends on ligand characteristics along with the time-evolving spectra suggests that the transient intermediate may involve a five-coordinate species. In contrast to NiDPP, the fluorinated analogues NiF(20)DPP and NiF(28)DPP do coordinate axial ligands in the ground state but eject them after photoexcitation. Collectively, these results demonstrate the sensitivity with which the electronic and structural characteristics of the macrocycle, substituents, and solvent (ligands) can govern the photophysical and photochemical properties of nonplanar porphyrins and open new avenues for exploring photoinduced ligand association and dissociation behavior. 相似文献
203.
Self-organization of ZnO nanoparticles into various superstructures (sheet, platelet, ring) has been achieved with the assistance of micelles formed by surfactant cetyltrimethylammonium bromide (CTAB) under one-pot condition. The CTAB-modified zinc hydroxy double salt (Zn-HDS) mesocrystals act as intermediates to form ZnO hexagonal superstructures at temperatures as low as 50 degrees C. The decomposition temperature of Zn-HDS mesocrystals is much lower than that of the corresponding bulk crystals because the organic additive CTAB effectively decreases the degree of crystallinity. Taking advantage of temperature-induced phase transformation of micelles, two-stage self-organization can form ZnO platelets and ring mesocrystals, that is, ZnO ellipsoidal superstructures formed through vertical attachment on (0001) facets of basic units can further assemble to form ZnO platelets and rings through vertical attachment on (0001) facets of ZnO ellipsoidal superstructures. The structural transformation of micelles as shape templates can offer a new route for self-assembly of nonspherical colloids into three-dimensional photonic crystals. ZnO sheet, ring, and platelet mesocrystals with a high population of polar Zn-(0001) plane are expected to have high photocatalytic activity. 相似文献
204.
205.
Jack Murray 《中国电子商情》2010,(8):25-25
在全球最火热的电子设备增长领域当属医疗电子。世界卫生组织估计,目前卫生保健消费达到了5.3万亿美元,而这个数字将在下一个5年到10年的时间内快速增长。 相似文献
206.
Abstract In the present study, the two compressibility moduli of a zinc single crystal were measured at room temperature up to 18 GPa. The results are compared with those obtained by Bridgman from a different experimental method. This study required a gaseous hydrostatic confining pressure, and then it has been necessary to develop an original diamond anvil cell with a large optical aperture allowing the use of sophisticated video imaging and image analysis techniques. A model is proposed for the zinc volume-pressure relation. 相似文献
207.
208.
Jeevan Jaisingh Jack Barron Shailendra Mehta Alok Chaturvedi 《European Journal of Operational Research》2008
The issues we address here are – How should a firm (e.g. Internet service provider (ISP)) that is capable of collecting personal information (browsing information, purchase history, etc.) about consumers, price its service, given that consumers vary in their valuation for privacy, and also vary in terms of the value of their personal information to a third party (firms that need consumer information)? Should the firm have a blanket policy of never collecting, or a policy of always collecting and revealing information? Surprisingly we find that in some cases the collector of information may be no worse off in the asymmetric information case than in the full information case. The paper provides a justification for the strategy of some firms such as ISP’s which never collect information and also for the strategy of other firms, like grocery stores that do. We also find that it is non-optimal for the firm to design contracts where the consumer can choose an intermediate level of privacy. 相似文献
209.
Jack Grahl 《Journal of Mathematical Analysis and Applications》2008,340(1):358-365
We construct an integral of a measurable real function using randomly chosen Riemann sums and show that it converges in probability to the Lebesgue integral where this exists. We then prove some conditions for the almost sure convergence of this integral. 相似文献
210.
In hyperconvex metric spaces we consider best approximation, invariant approximation and best proximity pair problems for multivalued mappings that are condensing or nonexpansive. 相似文献