全文获取类型
收费全文 | 66297篇 |
免费 | 13799篇 |
国内免费 | 6412篇 |
专业分类
化学 | 63552篇 |
晶体学 | 869篇 |
力学 | 2241篇 |
综合类 | 477篇 |
数学 | 5645篇 |
物理学 | 13724篇 |
出版年
2024年 | 44篇 |
2023年 | 424篇 |
2022年 | 647篇 |
2021年 | 1090篇 |
2020年 | 2183篇 |
2019年 | 3431篇 |
2018年 | 1834篇 |
2017年 | 1516篇 |
2016年 | 4531篇 |
2015年 | 4696篇 |
2014年 | 4947篇 |
2013年 | 6170篇 |
2012年 | 5596篇 |
2011年 | 5002篇 |
2010年 | 4833篇 |
2009年 | 4725篇 |
2008年 | 4581篇 |
2007年 | 3779篇 |
2006年 | 3418篇 |
2005年 | 3305篇 |
2004年 | 2916篇 |
2003年 | 2657篇 |
2002年 | 3544篇 |
2001年 | 2559篇 |
2000年 | 2225篇 |
1999年 | 1203篇 |
1998年 | 631篇 |
1997年 | 582篇 |
1996年 | 502篇 |
1995年 | 453篇 |
1994年 | 397篇 |
1993年 | 354篇 |
1992年 | 327篇 |
1991年 | 266篇 |
1990年 | 232篇 |
1989年 | 187篇 |
1988年 | 139篇 |
1987年 | 112篇 |
1986年 | 100篇 |
1985年 | 102篇 |
1984年 | 59篇 |
1983年 | 46篇 |
1982年 | 33篇 |
1981年 | 32篇 |
1980年 | 18篇 |
1979年 | 10篇 |
1978年 | 12篇 |
1976年 | 8篇 |
1974年 | 7篇 |
1973年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 125 毫秒
21.
A (di)graph is supereulerian if it contains a spanning eulerian sub(di)graph. This property is a relaxation of hamiltonicity. Inspired by this analogy with hamiltonian cycles and by similar results in supereulerian graph theory, we analyze a number of sufficient Ore type conditions for a digraph to be supereulerian. Furthermore, we study the following conjecture due to Thomassé and the first author: if the arc‐connectivity of a digraph is not smaller than its independence number, then the digraph is supereulerian. As a support for this conjecture we prove it for digraphs that are semicomplete multipartite or quasitransitive and verify the analogous statement for undirected graphs. 相似文献
22.
Unexpected benzimidazole ring formation from a quinoneimide species in the presence of ammonium acetate as supporting electrolyte used in the coupling of electrochemistry with mass spectrometry 下载免费PDF全文
23.
Transport in Porous Media - A macroscopic model that accounts for the effect of momentum dispersion on flows in porous media is proposed. The model is based on the pore scale prevalence hypothesis... 相似文献
24.
The research progress of a novel traffic solution,a submerged floating tunnel(SFT),is reviewed in terms of a study approach and loading scenario.Among existing publications,the buoyancy-weight ratio(BWR) is usually predefined.However,BWR is a critical structural parameter that tremendously affects the dynamic behaviour of not only the tunnel tube itself but also the cable system.In the context of a SFT prototype(SFTP) project in Qiandao Lake(Zhejiang Province,China),the importance of BWR is illustrated by finite element analysis and subsequently,an optimized BWR is proposed within a reasonable range in the present study.In the numerical model,structural damping is identified to be of importance.Rayleigh damping and the corresponding Rayleigh coefficients are attained through a sensitivity study,which shows that the adopted damping ratios are fairly suitable for SFTP.Lastly,the human sense of security is considered by quantifying the comfort index,which helps further optimize BWR in the SFTP structural parameter design. 相似文献
25.
26.
27.
28.
The Effect of the Spacer of Bis(biurea) Ligands on the Structure of A2L3‐type (A=anion) Phosphate Complexes 下载免费PDF全文
Prof. Biao Wu Dr. Shaoguang Li Prof. Yibo Lei Prof. Huaiming Hu Dr. Nader de Sousa Amadeu Prof. Dr. Christoph Janiak Dr. Jennifer S. Mathieson Dr. De‐Liang Long Prof. Leroy Cronin Prof. Xiao‐Juan Yang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(6):2588-2593
By tuning the length and rigidity of the spacer of bis(biurea) ligands L, three structural motifs of the A2L3 complexes (A represents anion, here orthophosphate PO43?), namely helicate, mesocate, and mono‐bridged motif, have been assembled by coordination of the ligand to phosphate anion. Crystal structure analysis indicated that in the three complexes, each of the phosphate ions is coordinated by twelve hydrogen bonds from six surrounding urea groups. The anion coordination properties in solution have also been studied. The results further demonstrate the coordination behavior of phosphate ion, which shows strong tendency for coordination saturation and geometrical preference, thus allowing for the assembly of novel anion coordination‐based structures as in transition‐metal complexes. 相似文献
29.
Star copolymers have attracted significant interest due to their different characteristics compared with diblock copolymers, including higher critical micelle concentration, lower viscosity, unique spatial shape, or morphologies. Development of synthetic skills such as anionic polymerization and controlled radical polymerization have made it possible to make diverse architectures of polymers. Depending on the molecular architecture of the copolymer, numerous morphologies are possible, for instance, Archimedean tiling patterns and cylindrical microdomains at symmetric volume fraction for miktoarm star copolymers as well as asymmetric lamellar microdomains for star‐shaped copolymers, which have not been reported for linear block copolymers. In this review, we focus on morphologies and microphase separations of miktoarm (AmBn and ABC miktoarm) star copolymers and star‐shaped [(A‐b‐B)n] copolymers with nonlinear architecture. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 1–21 相似文献
30.