全文获取类型
收费全文 | 14374篇 |
免费 | 2337篇 |
国内免费 | 1869篇 |
专业分类
化学 | 10726篇 |
晶体学 | 175篇 |
力学 | 791篇 |
综合类 | 138篇 |
数学 | 1851篇 |
物理学 | 4899篇 |
出版年
2024年 | 34篇 |
2023年 | 309篇 |
2022年 | 505篇 |
2021年 | 468篇 |
2020年 | 591篇 |
2019年 | 577篇 |
2018年 | 456篇 |
2017年 | 364篇 |
2016年 | 650篇 |
2015年 | 646篇 |
2014年 | 814篇 |
2013年 | 1042篇 |
2012年 | 1251篇 |
2011年 | 1275篇 |
2010年 | 923篇 |
2009年 | 784篇 |
2008年 | 901篇 |
2007年 | 866篇 |
2006年 | 785篇 |
2005年 | 717篇 |
2004年 | 523篇 |
2003年 | 471篇 |
2002年 | 498篇 |
2001年 | 434篇 |
2000年 | 306篇 |
1999年 | 297篇 |
1998年 | 269篇 |
1997年 | 238篇 |
1996年 | 253篇 |
1995年 | 210篇 |
1994年 | 197篇 |
1993年 | 167篇 |
1992年 | 137篇 |
1991年 | 127篇 |
1990年 | 89篇 |
1989年 | 94篇 |
1988年 | 64篇 |
1987年 | 42篇 |
1986年 | 33篇 |
1985年 | 44篇 |
1984年 | 44篇 |
1983年 | 22篇 |
1982年 | 20篇 |
1981年 | 13篇 |
1980年 | 13篇 |
1979年 | 2篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1976年 | 2篇 |
1957年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
251.
提出了用于计算实际体系熵相关性质的Monte Carlo多级取样分子模拟方法. 应用这一方法, 对硬球流体的化学势及Helmholtz自由能进行了估算, 得到了满意的结果. 计算化学势时, 不存在通常试验粒子方法所遇到的高密度问题. 该方法特别适合规律性的系统研究, 较之普通模拟方法要有效得多. 模拟得到的硬球体系无限稀释组份的超额化学势与对比直径的关系, 在相变区域为一条双凹曲线; 无论是在相变区还是在单相区, Carnahan-Starling公式对这一关系的描述均有较大偏差. 相似文献
252.
以CAB高分子为膜材料,研究了铸膜液的溶剂体生添加剂对膜形态及选择性渗透N2、O2、CH4、CO2等气体的影响。溶剂体系以丙酮为基本组分,混合甲酰胺或乙酸,可得到具有好的气体渗透性或气体选择性的非对称膜,通过溶剂的红外光谱羰基吸收峰的偏移,认为溶剂体系有可能存在Lewis酸;碱络合物。 相似文献
253.
254.
255.
Jing Li Huayi Shi Runzhi Chen Xiaofeng Wu Jiayi Cheng Fenglin Dong Houyu Wang Yao He 《Chemical science》2021,12(3):896
Synthesis of programmable atom-like nanoparticles (PANs) with high valences and high yields remains a grand challenge. Here, a novel synthetic strategy of microfluidic galvanic displacement (μ-GD) coupled with microfluidic DNA nanoassembly is advanced for synthesis of single-stranded DNA encoder (SSE)-encoded PANs for reliable surface-enhanced Raman scattering (SERS) sensing. Notably, PANs with high valences (e.g., n-valence, n = 12) are synthesized with high yields (e.g., >80%) owing to the effective control of interfacial reactions sequentially occurring in the microfluidic system. On the basis of this, we present the first demonstration of a PAN-based automatic analytical platform, in which sensor construction, sample loading and on-line monitoring are carried out in the microfluidic system, thus guaranteeing reliable quantitative measurement. In the proof-of-concept demonstration, accurate determination of tetracycline (TET) in serum and milk samples with a high recovery close to 100% and a low relative standard deviation (RSD) less than 5.0% is achieved by using this integrated analytical platform.A novel synthetic strategy is presented for microfluidic preparation of programmable atom-like nanoparticles with high valences and high yields. 相似文献
256.
Novel adsorbents which can concentrate Th(IV) in aqueous solution were prepared by immobilizingMyrica rubra tannin and larch tannin onto collagen fibre matrices. The adsorption capacities of the immobilized tannins to Th(IV) are
related to temperature and pH value of the adsorption process. For example, when the initial concentration of Th(IV) was 116.0
mg·l-1 and the immobilized tannin was 100 mg, the adsorption capacities of immobilized Myrica rubra tannin and larch tannin were 55.98 mg Th(IV)·g-1 and 13.19 mg Th(IV)·g-1, respectively at 303 K, and 73.67 mg Th(IV)·g-1 and 18.19 mg Th(IV)·g-1 at 323 K. It was also found that the higher adsorption capacity was obtained at higher pH value. The adsorption equilibrium
data of the immobilized tannins for Th(IV) can be well fitted by the Langmuir model and the mechanism of the adsorption was
found to be a chemical adsorption. In general, the adsorption capacity of immobilized Myrica rubra tannin to Th(IV) is significantly higher than that of immobilized larch tannin, probably due to the fact that the B ring
of Myrica rubra tannin has a pyrogallol structure which has higher reaction activity with metal ions. The breakthrough point of the adsorption
column of immobilized Myrica rubra tannin was at 33 bed volumes for the experimental system. The mass transfer coefficient of adsorption column determined by
Adams-Bohart equation was 1.61·10-4 l·mg-1.min-1. The adsorption column can be easily regenerated by 0.1 mol·l-1 HNO3 solution, showing outstanding ability of concentrating Th(IV).
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
257.
The hydrothermal reactions of AgNO(3), 4,4'-bipy, and carboxylate ligands gave rise to three supramolecular architectures, namely [Ag(bipy)].H(2)SIPA.1/2bipy.H(2)O (1), [Ag(bipy)].1/2H(2)btec.H(2)O (2), and [Ag(bipy)](2).H(2)dpstc.2H(2)O (3) (H(3)SIPA = 5-sulfoisophthalic acid, bipy = 4,4'-bipyridine, H(4)btec = 1,2,4,5-benzenetetracarboxylic acid, H(4)dpstc = 3,3',4,4'-tetracarboxydiphenyl sulfone). All complexes are extended from Ag-bipy linear chains by the combination of coordination bonds and supramolecular interactions in two different approaches. Complexes 1 and 3 comprise two-dimensional frameworks. In the two complexes, a one-dimensional ladderlike structure is first formed by the connection of a Ag-bipy chain through hydrogen bonding between a free carboxylate/bipy ligand and weak coordinative interactions between a free carboxylate ligand and silver ion. The ladderlike structure is then extended to a two-dimensional layer architecture by pi...pi interactions between bipy ligands of the Ag-bipy chains. Complex 2 possesses a three-dimensional framework. The free H(2)btec(2)(-) ligands form a two-dimensional layer network by hydrogen-bonding interactions between protonated and deprotonated carboxylate groups; meanwhile, pi.pi interactions between bipy ligands of Ag-bipy chains also result in a two-dimensional layer. The two layers are further connected by weak Ag-O interactions to generate a three-dimensional supramolecular structure. 相似文献
258.
有限群G的子群H称为G的BNA子群,若对任意的x∈G有H^(x)=H或x∈.若有限群G的所有素数阶和4阶循环子群都是G的BNA子群,则称G为CBNA群.本文主要刻画CBNA群的结构,并且给出所有真子群都是CBNA群的完全分类. 相似文献
259.
The Turán number of a k-uniform hypergraph H,denoted by exk(n;H),is the maximum number of edges in any k-uniform hypergraph F on n vertices which does not contain H as a subgraph.Let Cl~((k)) denote the family of all k-uniform minimal cycles of length l;S(?1,…,?r) denote the family of hypergraphs consisting of unions of r vertex disjoint minimal cycles of length ?1,…?r,respectively,and Cl~((k))denote a k-uniform linear ... 相似文献
260.