全文获取类型
收费全文 | 21045篇 |
免费 | 3609篇 |
国内免费 | 1771篇 |
专业分类
化学 | 4517篇 |
晶体学 | 56篇 |
力学 | 2770篇 |
综合类 | 554篇 |
数学 | 9719篇 |
物理学 | 8809篇 |
出版年
2024年 | 36篇 |
2023年 | 216篇 |
2022年 | 473篇 |
2021年 | 538篇 |
2020年 | 557篇 |
2019年 | 498篇 |
2018年 | 507篇 |
2017年 | 764篇 |
2016年 | 857篇 |
2015年 | 707篇 |
2014年 | 1168篇 |
2013年 | 1454篇 |
2012年 | 1159篇 |
2011年 | 1333篇 |
2010年 | 1183篇 |
2009年 | 1329篇 |
2008年 | 1479篇 |
2007年 | 1555篇 |
2006年 | 1275篇 |
2005年 | 1149篇 |
2004年 | 1112篇 |
2003年 | 926篇 |
2002年 | 887篇 |
2001年 | 718篇 |
2000年 | 625篇 |
1999年 | 589篇 |
1998年 | 506篇 |
1997年 | 441篇 |
1996年 | 388篇 |
1995年 | 381篇 |
1994年 | 243篇 |
1993年 | 222篇 |
1992年 | 163篇 |
1991年 | 197篇 |
1990年 | 126篇 |
1989年 | 83篇 |
1988年 | 111篇 |
1987年 | 74篇 |
1986年 | 61篇 |
1985年 | 65篇 |
1984年 | 46篇 |
1983年 | 31篇 |
1982年 | 33篇 |
1981年 | 38篇 |
1980年 | 27篇 |
1979年 | 27篇 |
1978年 | 16篇 |
1977年 | 11篇 |
1976年 | 8篇 |
1974年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
1.
为提高煤与瓦斯突出矿井瓦斯抽放效果,建立了3个一级指标、14个二级指标的突出矿井瓦斯抽放限制影响因素评价指标体系,利用AHP和熵权法分别确定指标因子主、客观权重.通过实地调研分析和反馈验证了AHP-熵权法的可行性和正确性,利用加权平均法确定评价模型的综合权重.研究表明:封孔方式、钻孔半径、抽放时间、煤体裂隙发育程度和抽放负压是目前影响煤矿瓦斯抽放效果的主控因素. 相似文献
2.
3.
4.
5.
蛋白质-多糖复合体系作为生物活性物质传递系统的壁材,有着人工合成聚合物或无机物等其他材料不可比拟的多重优势。本文就蛋白质和多糖之间的连接方式及蛋白质-多糖复合体系形成传递系统的多种形式进行了综述,以及对此领域的发展趋势进行了展望。结合蛋白质和多糖的结构特点,二者之间的链接方式分为非共价结合的物理共聚,和共价结合的美拉德偶联、化学交联、酶催化交联等方式,文中分别对各种连接方式的原理和机理,以及其影响因素做了深入阐述。以蛋白质-多糖复合体系为壁材对活性物质的传递形式大体上分成乳化系统、胶束、纳米凝胶、分子复合物以及壳核结构等系统。不同的活性物质的特征和传递需求,可针对性地选择合适结构的蛋白质和多糖种类以及二者的连接方式和传递系统的形式。并且,随着研究的逐步发展和推进,此领域的发展趋势朝着智能化和靶向性的方向进行。目前活性物质的蛋白质-多糖复合体系的传递系统,还依然面临着系统设计、评价和应用等多方面的挑战,这就要求我们在更全面更深入了解认识其对活性物质影响和功效的基础上,安全合理地设计和深入细致地评价活性成分的传递系统。 相似文献
6.
7.
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
8.
9.
Rong Yin Jihui Zhang Xudong Shang 《Mathematical Methods in the Applied Sciences》2020,43(15):8736-8752
This paper is dedicated to studying the following Schrödinger–Poisson system Under some different assumptions on functions V(x), K(x), a(x) and f(u), by using the variational approach, we establish the existence of positive ground state solutions. 相似文献
10.
《Comptes Rendus Physique》2019,20(3):204-217
Disaster relief requires many resources. Depending on the circumstances of each event, it is important to rapidly choose the suitable means to respond to the emergency intervention. A brief review of the conditions and means demonstrated the usefulness of an autonomous stand-alone machine for these missions. If many techniques and technologies exist, their relevant combination to achieve such a system presents several challenges. This communication tries to outline the possible achievement of an autonomous vehicle under these particular circumstances. This paper focuses on the specific working conditions and welcomes future contributions from robotics and artificial intelligence.In the necessarily limited scope of this article, the authors focus on a particularly critical aspect: location. Indeed, this machine is intended to evolve in heterogeneous and dangerous environment and without any outside contacts that could last up to several days. This blackout, due to the propagation difficulties of electromagnetic waves in the ground, induces an independence of the localisation process and makes the use of any radio navigation support system (GNSS), most of the time, impossible. The knowledge of the position of the system, both for navigation of the autonomous system (Rover) and location of targets (victims buried under debris) must be able to be estimated without contributions from external systems. Inertial classical techniques, odometer, etc., have to be adapted to these conditions during a long period without external support. These techniques also have to take into account that energy optimisation requests the use of low-power processors. Consequently, only poor computing capacity is available on-board.The article starts with a presentation of the context of a post-disaster situation as well as the main missions of Search and Rescue (SaR). It is followed by the analysis of autonomous navigation located in a post-earthquake situation. We will then discuss means to determine the attitude of the autonomous system and its position. The interest of hybridisation with external systems – whenever possible –, will be evaluated with a view to correcting deviations suffered by the system during its mission. Finally, prospects and future work are presented. 相似文献