全文获取类型
收费全文 | 29349篇 |
免费 | 3535篇 |
国内免费 | 2492篇 |
专业分类
化学 | 13230篇 |
晶体学 | 599篇 |
力学 | 2905篇 |
综合类 | 276篇 |
数学 | 9482篇 |
物理学 | 8884篇 |
出版年
2024年 | 29篇 |
2023年 | 272篇 |
2022年 | 466篇 |
2021年 | 621篇 |
2020年 | 1074篇 |
2019年 | 834篇 |
2018年 | 767篇 |
2017年 | 881篇 |
2016年 | 1147篇 |
2015年 | 1076篇 |
2014年 | 1308篇 |
2013年 | 2108篇 |
2012年 | 1302篇 |
2011年 | 1611篇 |
2010年 | 1554篇 |
2009年 | 2111篇 |
2008年 | 2282篇 |
2007年 | 2192篇 |
2006年 | 1956篇 |
2005年 | 1513篇 |
2004年 | 1295篇 |
2003年 | 1357篇 |
2002年 | 1192篇 |
2001年 | 942篇 |
2000年 | 764篇 |
1999年 | 649篇 |
1998年 | 648篇 |
1997年 | 474篇 |
1996年 | 438篇 |
1995年 | 337篇 |
1994年 | 328篇 |
1993年 | 250篇 |
1992年 | 217篇 |
1991年 | 194篇 |
1990年 | 128篇 |
1989年 | 118篇 |
1988年 | 109篇 |
1987年 | 101篇 |
1986年 | 94篇 |
1985年 | 103篇 |
1984年 | 86篇 |
1983年 | 60篇 |
1982年 | 87篇 |
1981年 | 71篇 |
1980年 | 47篇 |
1979年 | 52篇 |
1978年 | 34篇 |
1977年 | 23篇 |
1976年 | 26篇 |
1973年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
1.
Jose M. Guisan Gloria Fernandez-Lorente Javier Rocha-Martin Daniel Moreno-Gamero 《Current Opinion in Green and Sustainable Chemistry》2022
Different strategies for the preparation of efficient and robust immobilized biocatalysts are here reviewed. Different physico-chemical approaches are discussed.i.- The stabilization of enzyme by any kind of immobilization on pre-existing porous supports.ii.- The stabilization of enzymes by multipoint covalent attachment on support surfaces.iii.- Additional stabilization of immobilized-stabilized enzyme by physical or chemical modification with polymers.These three strategies can be easily developed when enzymes are immobilized in pre-existing porous supports. In addition to that, these immobilized-stabilized derivatives are optimal to develop enzyme reaction engineering and reactor engineering. Stabilizations ranging between 1000 and 100,000 folds regarding diluted soluble enzymes are here reported. 相似文献
2.
《Arabian Journal of Chemistry》2022,15(1):103536
These days, an important concern in water contamination is the remaining dyes from various sources (for instance, dye and dye intermediates industries, pulp and paper industries, textile industries, craft bleaching industries, tannery, and pharmaceutical industries, etc.), and a broad range of persistent organic contamination has been entered to the wastewater treatment systems or natural water supplies. Indeed, it is extremely hazardous and toxic to the living organism. Therefore, it is necessary to remove these organic pollutants before releasing them into the environment. Photocatalysis is a quickly growing technology for sewage procedures. For this purpose, Cu2HgI4 nanostructures were prepared via facile, and cost-effective sonochemical method. The effect of varied circumstances, such as various surfactants, sonication power, and sonication time was considered on the crystallinity, structure, shape, and particle size of products. Cu2HgI4 possesses a suitable bandgap (2.2 eV) in the visible area. The photocatalytic performance of the Cu2HgI4 was surveyed for the elimination of various organic dyes under visible radiation and exposed that this compound could degrade and remove methyl orange about 94.2% in an acidic medium after 160 min under visible light. Besides, the result showed that various parameters, including, pH, dye concentration, types of dyes, catalyst dosages, and time of irradiation affected the photocatalytic efficiency. 相似文献
3.
4.
5.
6.
Here we propose and analyze a mathematical model that aims to describe the marble sulphation process occurring in a given material. The model accounts for rugosity as well as for damaging effects. This model is characterized by some technical difficulties that seem hard to overcome from a theoretical viewpoint. Therefore, we introduce some physically reasonable modifications in order to establish the existence of a suitable notion of solution on a given time interval. Numerical simulations are presented and discussed, also in view of further research. 相似文献
7.
Kento Nishikibe Keisuke Nishikawa Momochika Kumagai Matsumi Doe Yoshiki Morimoto 《化学:亚洲杂志》2022,17(1):e202101137
There are marine cytotoxic bromotriterpenoids, named the thyrsiferol family that are structurally characterized by some tetrahydropyran (THP) and tetrahydrofuran (THF) rings. The thyrsiferol family belongs to natural products that are often difficult to determine their stereostructures even by the current, highly advanced spectroscopic methods, especially in acyclic systems including stereogenic tetrasubstituted carbon centers. In such cases, it is effective to predict and synthesize the possible stereostructures. Herein, to elucidate ambiguous stereostructures and unassigned absolute configurations of aplysiol B, laurenmariannol, and saiyacenol A, members of the thyrsiferol family, we carried out their asymmetric chemical syntheses featuring 6-exo and 5-exo oxacyclizations of epoxy alcohol precursors and 6-endo bromoetherification of a bishomoallylic alcohol. In this paper, we report total assignments of their stereostructures through their asymmetric chemical syntheses and also their preliminary cytotoxic activities against some tumor cells. These results could not have been achieved without depending on asymmetric total synthesis. 相似文献
8.
利用平面动力系统方法的分支理论,研究了Boussinesq方程,通过对Boussinesq方程进行行波变换,得到了相应行波系统的首次积分和平衡点,给出了不同参数条件下的相图,证实了Boussinesq方程存在孤立波解和周期波解。 相似文献
9.
《中国物理 B》2021,30(10):107304-107304
The field of two-dimensional topological semimetals, which emerged at the intersection of two-dimensional materials and topological materials, has been rapidly developing in recent years. In this article, we briefly review the progress in this field. Our focus is on the basic concepts and notions, in order to convey a coherent overview of the field. Some material examples are discussed to illustrate the concepts. We discuss the outstanding problems in the field that need to be addressed in future research. 相似文献
10.
液流电池是一种安全性高、使用寿命长、可扩展的大规模储能系统,可以协助电网调峰储能,提高能源利用率,发展前景广阔。双极板是液流电池的重要组成部分。功能上起到了分隔、串联电池、传导电流、为电堆提供结构支撑等作用。从成本构成角度看,双极板的价格占电堆成本的比重也较大。开发高性能、低成本的双极板对加快液流电池的商业化应用具有重要意义,也是目前业界的迫切需求。虽然文献上报道了许多针对液流电池双极板开发的工作,但是目前高性能、低成本的液流电池双极板产品仍无法充分满足市场需求。本文着重介绍了石墨基复合双极板的研究现状,介绍了材料选择、工艺流程对关键性能的影响,对相关工作进行了评述,并为液流电池双极板的开发提出了建议。 相似文献