全文获取类型
收费全文 | 81828篇 |
免费 | 15982篇 |
国内免费 | 6924篇 |
专业分类
化学 | 72988篇 |
晶体学 | 951篇 |
力学 | 3527篇 |
综合类 | 583篇 |
数学 | 7445篇 |
物理学 | 19240篇 |
出版年
2024年 | 100篇 |
2023年 | 886篇 |
2022年 | 1007篇 |
2021年 | 1598篇 |
2020年 | 2894篇 |
2019年 | 4081篇 |
2018年 | 2376篇 |
2017年 | 1968篇 |
2016年 | 5289篇 |
2015年 | 5307篇 |
2014年 | 5727篇 |
2013年 | 7233篇 |
2012年 | 7066篇 |
2011年 | 6534篇 |
2010年 | 5705篇 |
2009年 | 5495篇 |
2008年 | 5316篇 |
2007年 | 4554篇 |
2006年 | 4088篇 |
2005年 | 3791篇 |
2004年 | 3164篇 |
2003年 | 2771篇 |
2002年 | 3475篇 |
2001年 | 2463篇 |
2000年 | 2288篇 |
1999年 | 1454篇 |
1998年 | 967篇 |
1997年 | 923篇 |
1996年 | 960篇 |
1995年 | 756篇 |
1994年 | 678篇 |
1993年 | 590篇 |
1992年 | 548篇 |
1991年 | 474篇 |
1990年 | 397篇 |
1989年 | 314篇 |
1988年 | 254篇 |
1987年 | 200篇 |
1986年 | 193篇 |
1985年 | 194篇 |
1984年 | 126篇 |
1983年 | 98篇 |
1982年 | 66篇 |
1981年 | 60篇 |
1980年 | 33篇 |
1978年 | 26篇 |
1977年 | 24篇 |
1976年 | 23篇 |
1975年 | 30篇 |
1974年 | 32篇 |
排序方式: 共有10000条查询结果,搜索用时 378 毫秒
31.
32.
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
33.
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
34.
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
35.
36.
37.
在中国科学技术大学夏季学期的研究型实验课程"化学科研基础训练"中开设"壳聚糖的制备与表征"综合实验,以龙虾壳为原料,通过除蛋白、脱盐、脱色、脱乙酰等一系列反应,制备得到目标产物壳聚糖。运用红外光谱、核磁共振仪、黏度法、滴定等对产品的结构及性能进行表征。 相似文献
38.
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
39.
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
40.