全文获取类型
收费全文 | 360888篇 |
免费 | 7336篇 |
国内免费 | 3685篇 |
专业分类
化学 | 179662篇 |
晶体学 | 5642篇 |
力学 | 18629篇 |
综合类 | 229篇 |
数学 | 49768篇 |
物理学 | 117979篇 |
出版年
2021年 | 2270篇 |
2020年 | 2492篇 |
2019年 | 2421篇 |
2018年 | 11584篇 |
2017年 | 12401篇 |
2016年 | 8277篇 |
2015年 | 4243篇 |
2014年 | 4666篇 |
2013年 | 11775篇 |
2012年 | 13382篇 |
2011年 | 23398篇 |
2010年 | 14786篇 |
2009年 | 14729篇 |
2008年 | 20142篇 |
2007年 | 23429篇 |
2006年 | 9006篇 |
2005年 | 15150篇 |
2004年 | 10712篇 |
2003年 | 9656篇 |
2002年 | 7435篇 |
2001年 | 8347篇 |
2000年 | 6535篇 |
1999年 | 5178篇 |
1998年 | 4062篇 |
1997年 | 4039篇 |
1996年 | 3971篇 |
1995年 | 3634篇 |
1994年 | 3376篇 |
1993年 | 3170篇 |
1992年 | 3770篇 |
1991年 | 3649篇 |
1990年 | 3494篇 |
1989年 | 3411篇 |
1988年 | 3307篇 |
1987年 | 3324篇 |
1986年 | 3036篇 |
1985年 | 4088篇 |
1984年 | 4060篇 |
1983年 | 3284篇 |
1982年 | 3465篇 |
1981年 | 3378篇 |
1980年 | 3236篇 |
1979年 | 3484篇 |
1978年 | 3774篇 |
1977年 | 3482篇 |
1976年 | 3427篇 |
1975年 | 3188篇 |
1974年 | 3163篇 |
1973年 | 3156篇 |
1967年 | 2283篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
The Ramanujan Journal - Inspired by Andrews and Merca’s recent work on the number of even parts over all partitions into distinct parts, we introduce a new kind of Beck type identities, which... 相似文献
82.
The satisfiability (SAT) problem is a core problem in computer science. Existing studies have shown that most industrial SAT instances can be effectively solved by modern SAT solvers while random SAT instances cannot. It is believed that the structural characteristics of different SAT formula classes are the reasons behind this difference. In this paper, we study the structural properties of propositional formulas in conjunctive normal form (CNF) by the principle of structural entropy of formulas. First, we used structural entropy to measure the complex structure of a formula and found that the difficulty solving the formula is related to the structural entropy of the formula. The smaller the compressing information of a formula, the more difficult it is to solve the formula. Secondly, we proposed a -approximation strategy to approximate the structural entropy of large formulas. The experimental results showed that the proposed strategy can effectively approximate the structural entropy of the original formula and that the approximation ratio is more than 92%. Finally, we analyzed the structural properties of a formula in the solution process and found that a local search solver tends to select variables in different communities to perform the next round of searches during a search and that the structural entropy of a variable affects the probability of the variable being flipped. By using these conclusions, we also proposed an initial candidate solution generation strategy for a local search for SAT, and the experimental results showed that this strategy effectively improves the performance of the solvers CCAsat and Sparrow2011 when incorporated into these two solvers. 相似文献
83.
Acta Mathematica Sinica, English Series - We are interested in the existence and asymptotic behavior for the least energy solutions of the following fractional eigenvalue problem $$\left({\rm{P}}... 相似文献
84.
Sergio Ayala‐Mar Javier Donoso‐Quezada Roberto C. Gallo‐Villanueva Victor H. Perez‐Gonzalez Jos Gonzlez‐Valdez 《Electrophoresis》2019,40(23-24):3036-3049
Exosomes are nanovesicles secreted by most cellular types that carry important biochemical compounds throughout the body with different purposes, playing a preponderant role in cellular communication. Because of their structure, physicochemical properties and stability, recent studies are focusing in their use as nanocarriers for different therapeutic compounds for the treatment of different diseases ranging from cancer to Parkinson's disease. However, current bioseparation protocols and methodologies are selected based on the final exosome application or intended use and present both advantages and disadvantages when compared among them. In this context, this review aims to present the most important technologies available for exosome isolation while discussing their advantages and disadvantages and the possibilities of being combined with other strategies. This is critical since the development of novel exosome‐based therapeutic strategies will be constrained to the effectiveness and yield of the selected downstream purification methodologies for which a thorough understanding of the available technological resources is needed. 相似文献
85.
Transport in Porous Media - The theme of coupling problems for adsorption, absorption and thermochemical transport in porous media is very important for engineering applications. Based on the... 相似文献
86.
Differential Equations - We study a mixed problem for systems of one-dimensional semilinear hyperbolic equations with variable nonlinearity growth rate and nonlinear boundary conditions. Theorems... 相似文献
87.
随着经济的飞速发展,社会对能源的需求日益扩大,对工业废水的无害化处理也提出了更高的要求。光催化燃料电池 (photocatalytic fuel cell, PFC) 在燃料电池中引入半导体光催化材料作为电极,实现了有机污染物高效降解和同步对外产电的双重功能,在废水无害化与资源化利用方面具有潜在的应用价值。半导体光催化电极是PFC系统高效运行的核心组件,增强其可见光响应和光生载流子分离是提高PFC性能的关键策略。反应器结构设计和运行参数优化也有利于改善PFC性能。本文从PFC基本原理和应用入手,综述了PFC在环境污染物资源化处理中的研究进展,并详细阐述了提高PFC的污染控制性能和产电效率的优化手段,为进一步设计高效稳定的PFC系统并实现其在水污染控制和清洁能源生产中的应用提供理论指导。 相似文献
88.
An oriented tetrahedron defined on four vertices is a set of four cyclic triples with the property that any ordered pair of vertices is contained in exactly one of the cyclic triples. A tetrahedral quadruple system of order with index , denoted by , is a pair , where is an ‐set and is a set of oriented tetrahedra (blocks) such that every cyclic triple on is contained in exactly members of . A is pure if there do not exist two blocks with the same vertex set. When , the spectrum of a pure TQS has been completely determined by Ji. In this paper, we show that there exists a pure if and only if and . A corollary is that a simple also exists if and only if and . 相似文献
89.
Monomeric sarcosine oxidase (mSOx) fusion with the silaffin peptide, R5, designed previously for easy protein production in low resource areas, was used in a biosilification process to form an enzyme layer electrode biosensor. mSOx is a low activity enzyme (10–20 U/mg) requiring high amounts of enzyme to obtain an amperometric biosensor signal, in the clinically useful range <1 mM sarcosine, especially since the Km is >10 mM. An amperometric biosensor model was fitted to experimental data to investigate dynamic range. mSOx constructs were designed with 6H (6×histidine) and R5 (silaffin) peptide tags and compared with native mSOx. Glutaraldehyde (GA) cross‐linked proteins retained ~5 % activity for mSOx and mSOx‐6H and only 0.5 % for mSOx‐R5. In contrast R5 catalysed biosilification on (3‐mercaptopropyl) trimethoxysilane (MPTMS) and tetramethyl orthosilicate (TMOS) particles created a ‘self‐immobilisation’ matrix retaining 40 % and 76 % activity respectively. The TMOS matrix produced a thick layer (>500 μm) on a glassy carbon electrode with a mediated current due to sarcosine in the clinical range for sarcosinemia (0–1 mM). The mSOx‐R5 fusion protein was also used to catalyse biosilification in the presence of creatinase and creatininase, entrapping all three enzymes. A mediated GC enzyme linked current was obtained with dynamic range available for creatinine determination of 0.1–2 mM for an enzyme layer ~800 nm. 相似文献
90.
Saleh Z. M. Nasser H. Özkol E. Günöven M. Abak K. Canli S. Bek A. Turan R. 《Journal of nanoparticle research》2015,17(10):1-12
Journal of Nanoparticle Research - Plasmonic interfaces consisting of silver nanoparticles of different sizes (50–100&;nbsp;nm) have been processed by the self-assembled dewetting... 相似文献