全文获取类型
收费全文 | 319篇 |
免费 | 12篇 |
国内免费 | 10篇 |
专业分类
化学 | 103篇 |
力学 | 36篇 |
数学 | 34篇 |
物理学 | 33篇 |
综合类 | 135篇 |
出版年
2024年 | 2篇 |
2023年 | 8篇 |
2022年 | 15篇 |
2021年 | 15篇 |
2020年 | 15篇 |
2019年 | 13篇 |
2018年 | 5篇 |
2017年 | 20篇 |
2016年 | 6篇 |
2015年 | 7篇 |
2014年 | 12篇 |
2013年 | 19篇 |
2012年 | 10篇 |
2011年 | 15篇 |
2010年 | 10篇 |
2009年 | 20篇 |
2008年 | 15篇 |
2007年 | 15篇 |
2006年 | 15篇 |
2005年 | 11篇 |
2004年 | 10篇 |
2003年 | 10篇 |
2002年 | 7篇 |
2001年 | 2篇 |
2000年 | 11篇 |
1999年 | 7篇 |
1998年 | 6篇 |
1997年 | 6篇 |
1996年 | 3篇 |
1995年 | 4篇 |
1994年 | 4篇 |
1993年 | 5篇 |
1992年 | 3篇 |
1991年 | 2篇 |
1990年 | 3篇 |
1989年 | 3篇 |
1988年 | 3篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有341条查询结果,搜索用时 15 毫秒
271.
272.
Terramechanics plays an important role in determining the design and control of autonomous robots and other vehicles that move on granular surfaces. Traction capabilities, slippage, and sinkage of a robot are governed by the interaction of a robot’s appendage with the operating terrain. It is important to understand how the terrain flows under this appendage during such an interaction. In this work, dynamics of soil performance and locomotion performance of a lugged wheel travelling on soft soil are numerically investigated. Studies are conducted with a two-dimensional model by using the discrete element method to analyze the interactions between a lugged wheel and the soil. The soil performance is studied by examining the force distribution and evolution of force networks during the course of the wheel travel. For two different control modes, namely, slip-based wheel control and angular velocity-based wheel control, the performance parameters such as, sinkage, traction, traction efficiency, and power consumption of the wheel are compared for various wheel configurations. The findings of this work are expected to be useful for optimal design and control of the lugged wheel travelling on deformable surfaces. 相似文献
273.
A discrete analog of the dressing method is presented and used to derive integrable nonlinear evolution equations, including two infinite families of novel continuous and discrete coupled integrable systems of equations of nonlinear Schrödinger type. First, a demonstration is given of how discrete nonlinear integrable equations can be derived starting from their linear counterparts. Then, starting from two uncoupled, discrete one‐directional linear wave equations, an appropriate matrix Riemann‐Hilbert problem is constructed, and a discrete matrix nonlinear Schrödinger system of equations is derived, together with its Lax pair. The corresponding compatible vector reductions admitted by these systems are also discussed, as well as their continuum limits. Finally, by increasing the size of the problem, three‐component discrete and continuous integrable discrete systems are derived, as well as their generalizations to systems with an arbitrary number of components. 相似文献
274.
For given graphs G and H, the Ramsey numberR(G,H) is the smallest natural number n such that for every graph F of order n: either F contains G or the complement of F contains H. In this paper, we investigate the Ramsey number R(∪G,H), where G is a tree and H is a wheel Wm or a complete graph Km. We show that if n?3, then R(kSn,W4)=(k+1)n for k?2, even n and R(kSn,W4)=(k+1)n-1 for k?1 and odd n. We also show that . 相似文献
275.
276.
Peter A. Clarkson David Gómez-Ullate Yves Grandati Robert Milson 《Studies in Applied Mathematics》2020,144(3):357-385
This paper focuses on the construction of rational solutions for the -Painlevé system, also called the Noumi-Yamada system, which are considered the higher order generalizations of PIV. In this even case, we introduce a method to construct the rational solutions based on cyclic dressing chains of Schrödinger operators with potentials in the class of rational extensions of the harmonic oscillator. Each potential in the chain can be indexed by a single Maya diagram and expressed in terms of a Wronskian determinant whose entries are Hermite polynomials. We introduce the notion of cyclic Maya diagrams and characterize them for any possible period, using the concepts of genus and interlacing. The resulting classes of solutions can be expressed in terms of special polynomials that generalize the families of generalized Hermite, generalized Okamoto, and Umemura polynomials, showing that they are particular cases of a larger family. 相似文献
277.
修整是多层电镀超硬磨粒砂轮精密磨削的关键技术之一.电镀镍钴合金硬度和强度高,是理想的超硬磨料砂轮结合剂;但同时也导致砂轮修整困难.为此对镍钴合金镀层的电解修整机理进行了研究.首先,根据标准电极电位的理论分析了镍钴合金电解修整的可行性;然后,采用电化学分析仪测试了镍钴合金镀层在NaNO3溶液中的极化曲线,表明极化曲线存在钝化区;最后,进行了电解修整镍钴合金镀层CBN砂轮试验,结果表明对于2V和5V的电解修整电压,较高的电解电压有利于电镀镍钴合金超硬磨料砂轮电解修整. 相似文献
278.
徐载熊 《东华大学学报(自然科学版)》1993,(5)
为使超硬砂轮能发挥其优异的性能,应避免堵塞和重视修整。用单颗粒金刚石修整工具是不适宜的。作者对磨削修整法和制动修整法进行了研究,取得了好的效果。 相似文献
279.
Birgit Stubbe Arn Mignon Heidi Declercq Sandra Van Vlierberghe Peter Dubruel 《Macromolecular bioscience》2019,19(8)
Hydrogels are interesting as wound dressing for burn wounds to maintain a moist environment. Especially gelatin and alginate based wound dressings show strong potential. Both polymers are modified by introducing photocrosslinkable functionalities and combined to hydrogel films (gel‐MA/alg‐MA). In one protocol gel‐MA films are incubated in alg‐MA solutions and crosslinked afterward into double networks. Another protocol involves blending both and subsequent photocrosslinking. The introduction of alginate into the gelatin matrix results in phase separation with polysaccharide microdomains in a protein matrix. Addition of alg(‐MA) to gel‐MA leads to an increased swelling compared to 100% gelatin and similar to the commercial Aquacel Ag dressing. In vitro tests show better cell adhesion for films which have a lower alginate content and also have superior mechanical properties. The hydrogel dressings exhibit good biocompatibility with adaptable cell attachment properties. An adequate gelatin‐alginate ratio should allow application of the materials as wound dressings for several days without tissue ingrowth. 相似文献
280.
In order to prepare a novel hemostatic dressing for uncontrolled hemorrhage, a porous chitosan sponge was coated with self-assembled(thrombin/tannic acid)n films, which were based on hydrogen bonding interactions between thrombin and tannic acid at physiologic p H. According to the whole blood clotting test, the coated chitosan sponges showed a significantly high rate of blood clotting due to the addition of thrombin. On the other hand, the storable half-life of immobilized thrombin is extended to 66.9 days at room temperature, which is 8.5 times longer than unfixed thrombin. It is because of the immobilization effect of, not only the porous structure of chitosan sponge but also the interactions between thrombin and tannic acid. In addition, the tannic acid has similar antibacterial effect to chitosan. Therefore, it is an excellent combination of chitosan, thrombin and tannic acid. Besides, all of materials in this research have been approved by the United States Food and Drug Administration(FDA). So the chitosan-based sponge is a promising candidate dressing for uncontrolled hemorrhage due to its storable, bio-safe and highly effective hemostatic properties. 相似文献