全文获取类型
收费全文 | 8099篇 |
免费 | 460篇 |
国内免费 | 423篇 |
专业分类
化学 | 4014篇 |
晶体学 | 33篇 |
力学 | 318篇 |
综合类 | 118篇 |
数学 | 2427篇 |
物理学 | 2072篇 |
出版年
2023年 | 59篇 |
2022年 | 109篇 |
2021年 | 117篇 |
2020年 | 110篇 |
2019年 | 181篇 |
2018年 | 125篇 |
2017年 | 179篇 |
2016年 | 182篇 |
2015年 | 148篇 |
2014年 | 224篇 |
2013年 | 362篇 |
2012年 | 274篇 |
2011年 | 445篇 |
2010年 | 417篇 |
2009年 | 562篇 |
2008年 | 465篇 |
2007年 | 413篇 |
2006年 | 397篇 |
2005年 | 259篇 |
2004年 | 203篇 |
2003年 | 204篇 |
2002年 | 202篇 |
2001年 | 168篇 |
2000年 | 173篇 |
1999年 | 151篇 |
1998年 | 125篇 |
1997年 | 105篇 |
1996年 | 97篇 |
1995年 | 65篇 |
1994年 | 52篇 |
1993年 | 46篇 |
1992年 | 43篇 |
1991年 | 40篇 |
1990年 | 28篇 |
1989年 | 30篇 |
1987年 | 19篇 |
1986年 | 21篇 |
1985年 | 417篇 |
1984年 | 292篇 |
1983年 | 234篇 |
1982年 | 209篇 |
1981年 | 152篇 |
1980年 | 119篇 |
1979年 | 142篇 |
1978年 | 80篇 |
1977年 | 86篇 |
1976年 | 88篇 |
1975年 | 89篇 |
1974年 | 116篇 |
1973年 | 130篇 |
排序方式: 共有8982条查询结果,搜索用时 15 毫秒
1.
《Arabian Journal of Chemistry》2021,14(11):103421
Processing of Carapa guianensis seeds to obtain oil on an industrial scale generates a significant amount of by-product, approximately 66% w/w, which is called cake and is a potential source of biomolecules, including simple phenolic structures. For this reason, studies were carried out on the chemical profiles of hydrolyzed extract from this agro-industrial by-product through High Performance Thin-Layer Chromatography (HPTLC) and Gas Chromatography coupled to Mass Spectrometry (GC–MS). These techniques were used to detect metabolic classes and/or groups, and to identify, for the first time, thirteen simple phenolic acids in this by-product. The sample antioxidant capacity was determined by methods of 2,2-diphenyl-1-picrylhydrazyl (DPPH)and 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS+) radicals direct sequestration. The hydrolyzed fraction showed a total of 63.47% in the relative abundance of the total of compounds, standing out: p-hydroxybenzoic acid (39.19%) and protocatechuic acid (3,4-dihydroxybenzoic acid) (5.62%), both from hydroxybenzoic acids and 3-(3,4-dihydroxyphenyl)lactic acid, (7.76%) hydroxycinnamic acids derivatives. In these results, the fraction rich in simple phenolic acids was obtained, attributing the prominent behavior of this matrix antioxidant activity, expressed by (IC50: of 16.42 µg/mL and 6.52 µg/mL for DPPH and ABTS+ radicals, respectively). The research demonstrated an alternative to applicability that involves sustainability from agro-industrial. These techniques were used to detect metabolic classes and/or groups, and to identify, for the first time, thirteen simple phenolic acids in this by-product, generating a process capable of converting biomass into a bioproduct, consisting of bioactive compounds, in addition to adding value to the industrial chain. 相似文献
2.
数据包络分析(DEA)是评价供应链系统(Supply chain system)间相对有效性的一种重要的工具,但是传统的DEA不考虑供应链的内部结构,对系统效率评价偏高;而本文所研究两阶段串联供应链系统,考虑把部分中间产品作为最终产品输出,增加额外中间投入的情形.基于所提出的供应链系统结构,本文建立相应的串联结构下的网络DEA模型,并针对所建立模型进行相关理论的研究,给出了串联结构下的生产可能集和规模收益情况判定方法.最后,进行数值实验,以验证我们提出的结论. 相似文献
3.
4.
Necessary conditions for the Gâteaux differentiability of the distance function to a set are considered. A series of characterizing results is obtained. 相似文献
5.
Mathematical Notes - 相似文献
6.
Mean value in invexity analysis 总被引:1,自引:0,他引:1
In this paper, a generalization of the mean value theorem is considered in the case of functions defined on an invex set with respect to η (which is not necessarily connected). 相似文献
7.
Biswarup Mukhopadhyaya 《Pramana》1998,51(1-2):181-190
The observable consequences of gauge-mediated supersymmetry breaking (GMSB) are reviewed here. Implications of scenarios both
with a neutralino and a slepton as the next lightest supersymmetric particle (NLSP) are surveyed in relation to hadronic ande
+
e
- colliders. We also discuss the phenomenological consequences of the NLSP decaying slowly, giving rise to delayed events in
the detectors.The importance of distinguishing signals of GMSB models from those of the commonly discussed supergravity-type
theories is emphasized. 相似文献
8.
P. De Maesschalck 《Journal of Differential Equations》2007,238(2):338-365
By applying geometric techniques to real analytic singularly perturbed vector fields on the plane, we develop a way to give a bound on the Gevrey type of the Taylor development of canard manifolds at degenerate planar turning points. By blowing up the phase space at the turning point, we find asymptotic estimates even when such expansions w.r.t. traditional phase space variables do not exist. The asymptotic estimates are then used to give a sufficient and necessary condition on the existence of (local) canard solutions. 相似文献
9.
10.
We study the asymptotic distribution of the fill‐up level in a binary trie built over n independent strings generated by a biased memoryless source. The fill‐up level is the number of full levels in a tree. A level is full if it contains the maximum allowable number of nodes (e.g., in a binary tree level k can have up to 2k nodes). The fill‐up level finds many interesting applications, e.g., in the internet IP lookup problem and in the analysis of level compressed tries (LC tries). In this paper, we present a complete asymptotic characterization of the fill‐up distribution. In particular, we prove that this distribution concentrates on one or two points around the most probably value k = ?log1/qn ? log log log n + 1 + log log(p/q)?, where p > q = 1 ? p is the probability of generating the more likely symbol (while q = 1 ? p is the probability of the less likely symbol). We derive our results by analytic methods such as generating functions, Mellin transform, the saddle point method, and analytic depoissonization. We also present some numerical verification of our results. © 2004 Wiley Periodicals, Inc. Random Struct. Alg., 2004 相似文献