全文获取类型
收费全文 | 3375篇 |
免费 | 185篇 |
国内免费 | 19篇 |
专业分类
化学 | 2601篇 |
晶体学 | 28篇 |
力学 | 82篇 |
数学 | 465篇 |
物理学 | 403篇 |
出版年
2023年 | 26篇 |
2022年 | 43篇 |
2021年 | 67篇 |
2020年 | 89篇 |
2019年 | 90篇 |
2018年 | 57篇 |
2017年 | 57篇 |
2016年 | 124篇 |
2015年 | 82篇 |
2014年 | 121篇 |
2013年 | 147篇 |
2012年 | 249篇 |
2011年 | 302篇 |
2010年 | 111篇 |
2009年 | 86篇 |
2008年 | 234篇 |
2007年 | 201篇 |
2006年 | 211篇 |
2005年 | 192篇 |
2004年 | 150篇 |
2003年 | 124篇 |
2002年 | 118篇 |
2001年 | 30篇 |
2000年 | 32篇 |
1999年 | 21篇 |
1998年 | 29篇 |
1997年 | 26篇 |
1996年 | 28篇 |
1995年 | 33篇 |
1994年 | 21篇 |
1993年 | 28篇 |
1992年 | 28篇 |
1991年 | 27篇 |
1990年 | 15篇 |
1989年 | 19篇 |
1988年 | 18篇 |
1987年 | 21篇 |
1985年 | 31篇 |
1984年 | 30篇 |
1983年 | 18篇 |
1982年 | 37篇 |
1981年 | 24篇 |
1980年 | 24篇 |
1979年 | 20篇 |
1978年 | 23篇 |
1977年 | 23篇 |
1976年 | 19篇 |
1975年 | 12篇 |
1974年 | 10篇 |
1973年 | 10篇 |
排序方式: 共有3579条查询结果,搜索用时 15 毫秒
1.
Nicholas Pippenger 《Random Structures and Algorithms》1991,2(2):121-149
We determine the limiting behavior of the blocking probability for spider-web networks, a class of crossbar switching networks proposed by Ikeno. We use a probabilistic model proposed by the author, in which the busy links always form disjoint routes through the network. We show that if the occupancy probability is below the threshold 2 - √2 = 0.5857…, then the blocking probability tends to zero, whereas above this threshold it tends to one. This provides a theoretical explanation for results observed empirically in simulations by Bassalygo, Neiman, and Vvedenskaya. 相似文献
2.
We show that using ionic liquids as reagents in conjunction with microwave heating it is possible to prepare primary alkyl halides from the corresponding alcohols rapidly. Using ionic liquids as solvents in conjunction with microwave heating it is possible to prepare aryl nitriles from the corresponding aryl bromides or iodides. The scope and limitations of using microwave-promotion as a tool in these reactions is discussed. 相似文献
3.
4.
Tobias P. Kunzler Christoph M. Sprecher Nicholas D. Spencer 《Applied Surface Science》2006,253(4):2148-2153
Gradient surfaces allow rapid, high-throughput investigations and systematic studies in many disparate fields, including biology, tribology and adhesion. We describe a novel method for the fabrication of material-independent morphology gradients, involving a two-step process of particle erosion followed by a chemical polishing procedure that preferentially removes features with a small radius of curvature as a function of time. Gradients are fabricated on aluminium surfaces, but they may be readily transferred to other materials via a replication technique, which allows for the production of identical roughness gradient samples with any chosen surface chemistry. The gradients have been characterized by means of scanning electron microscopy and optical profilometry. Standard roughness parameters (Ra, Rq, Rz, Sm and Sk) were calculated from optical profilometry data. The roughness has also been assessed over different wavelength windows by means of a fast Fourier transformation approach. 相似文献
5.
6.
Using a simulation technique introduced recently, we study winding clusters in percolation on the torus and the Möbius strip for different aspect ratios. The asynchronous parallelization of the simulation makes very large system and sample sizes possible. Our high accuracy results are fully consistent with predictions from conformal field theory. The numerical results for the Möbius strip and the number distribution of winding clusters on the torus await theoretical explanation. To our knowledge, this study is the first of its kind. 相似文献
7.
8.
Emrys A. Jones Nicholas P. Lockyer John C. Vickerman 《International journal of mass spectrometry》2007,260(2-3):146
Recent developments in desorption/ionisation mass spectrometry techniques have made their application to biological analysis a realistic and successful proposition. Developments in primary ion source technology, mainly through the advent of polyatomic ion beams, have meant that the technique of secondary ion mass spectrometry (SIMS) can now access the depths of information required to allow biological imaging to be a viable option.Here the role of the primary ion C60+ is assessed with regard to molecular imaging of lipids and pharmaceuticals within tissue sections. High secondary ion yields and low surface damage accumulation are demonstrated on both model and real biological samples, indicating the high secondary ion efficiency afforded to the analyst by this primary ion when compared to other cluster ion beams used in imaging. The newly developed 40 keV C60+ ion source allows the beam to be focused such that high resolution imaging is demonstrated on a tissue sample, and the greater yields allow the molecular signal from the drug raclopride to be imaged within tissue section following in vivo dosing.The localisation shown for this drug alludes to issues regarding the chemical environment affecting the ionisation probability of the molecule; the importance of this effect is demonstrated with model systems and the possibility of using laser post-ionisation as a method for reducing this consequence of bio-sample complexity is demonstrated and discussed. 相似文献
9.
Blundell Tom L. Bolanos-Garcia Victor Chirgadze Dimitri Y. Harmer Nicholas J. Lo Thomas Pellegrini Luca Sibanda B. Lynn 《Structural chemistry》2002,13(3-4):405-412
Signaling in living systems needs to achieve high specificity, to be reversible, and to achieve high signal to noise. Signaling mediated by multiprotein systems has evolved that avoids the requirement for high-affinity binary complexes that would be difficult to reverse and which, in the overcrowded cell, would lead to excessive noise in the system. Symmetrical structures are only occasionally formed. When they are, it is principally to colocate components, for example, the tyrosyl kinases of growth factors, where dimers form. Symmetry is, however, often broken, presumably to create more sensitivity and specificity in the signaling system by assembling other components, into higher-order multiprotein systems. The binding of a single heparin to two 1:1 FGF:FGFR complexes is an example, as is the binding of a single ligase to the Xrcc4 dimer, perhaps so creating a further DNA-binding site. 相似文献
10.
Mingyang Zhao Warren T. Ford Stefan H. J. Idziak Nicholas C. Maliszewskyj Paul A. Heiney 《Liquid crystals》1994,16(4):583-599
The hexa-4-dodecyloxybenzoyl derivative 1 of azacrown [18]-N6 was originally reported to have a 'tubular' mesophase on the basis of its large central ring and 6-fold symmetry. Starting in the mesophase, annealing of 1 under a cover slip results in formation of a new crystalline phase that melts directly to an isotropic liquid at the temperature previously observed for the mesophase to isotropic transition. Thus the phase behaviour of 1 is kinetically controlled. The analogous hexa-3,4-bisdodecyloxybenzoyl derivative 2 of azacrown [18]-N6 has no kinetic limitations to its phase changes and has an enantiotropic columnar liquid crystalline phase. We have synthesized side chain copolysiloxanes with a (CH2)11 spacer and 75-84 per cent by weight of the same 4-dodecyloxybenzoyl-[18]-N6 mesogen. The polysiloxanes also display a liquid crystalline phase. 相似文献