全文获取类型
收费全文 | 403篇 |
免费 | 30篇 |
国内免费 | 26篇 |
专业分类
化学 | 144篇 |
力学 | 105篇 |
综合类 | 6篇 |
数学 | 34篇 |
物理学 | 170篇 |
出版年
2023年 | 4篇 |
2022年 | 11篇 |
2021年 | 11篇 |
2020年 | 11篇 |
2019年 | 12篇 |
2018年 | 8篇 |
2017年 | 20篇 |
2016年 | 14篇 |
2015年 | 13篇 |
2014年 | 17篇 |
2013年 | 26篇 |
2012年 | 17篇 |
2011年 | 22篇 |
2010年 | 22篇 |
2009年 | 29篇 |
2008年 | 23篇 |
2007年 | 12篇 |
2006年 | 26篇 |
2005年 | 26篇 |
2004年 | 14篇 |
2003年 | 19篇 |
2002年 | 8篇 |
2001年 | 12篇 |
2000年 | 4篇 |
1999年 | 4篇 |
1998年 | 8篇 |
1997年 | 10篇 |
1996年 | 3篇 |
1995年 | 9篇 |
1994年 | 5篇 |
1993年 | 10篇 |
1992年 | 3篇 |
1991年 | 8篇 |
1989年 | 3篇 |
1988年 | 5篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 2篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1977年 | 1篇 |
排序方式: 共有459条查询结果,搜索用时 9 毫秒
61.
用色质联用的方法分析不同温度下柴油蒸汽的组成,确定正烷烃在油蒸汽中的分布;并结合勒夏特列原理计算出各个温度下的蒸汽可燃性指数,计算结果接近于实际情况。 相似文献
62.
Yannick Weesepoel Jean‐Paul Vincken Raluca Maria Pop Kun Liu Harry Gruppen 《Journal of mass spectrometry : JMS》2013,48(7):862-874
The microalga Haematococcus pluvialis produces the pigment astaxanthin mainly in esterified form with a multitude of fatty acids, which results in a complex mixture of carotenol mono‐ and diesters. For rapid fingerprinting of these esters, matrix‐assisted laser desorption ionization time of flight mass spectrometry (MALDI‐TOF/TOF‐MS) might be an alternative to traditional chromatographic separation combined with MS. Investigation of ionization and fragmentation of astaxanthin mono‐ and diester palmitate standards in MALDI‐TOF/TOF‐MS showed that sodium adduct parent masses [M + Na]+ gave much simpler MS2 spectra than radical / protonated [M]+● / [M + H]+ parents. [M + Na]+ fragments yielded diagnostic polyene‐specific eliminations and fatty acid neutral losses, whereas [M]+● / [M + H]+ fragmentation resulted in a multitude of non‐diagnostic daughters. For diesters, a benzonium fragment, formed by polyene elimination, was required for identification of the second fatty acid attached to the astaxanthin backbone. Parents were forced into [M + Na]+ ionization by addition of sodium acetate, and best signal‐to‐noise ratios were obtained in the 0.1 to 1.0 mM range. This method was applied to fingerprinting astaxanthin esters in a crude H. pluvialis extract. Prior to MALDI‐TOF/TOF‐MS, the extract was fractionated by normal phase Flash chromatography to obtain fractions enriched in mono‐ and diesters and to remove pheophytin a, which compromised monoester signals. All 12 types of all‐trans esterified esters found in LC were identified with MALDI‐TOF/TOF‐MS, with the exception of two minor monoesters. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
63.
The flow structure in a flat plate integrated collector storage device, with recirculation of the storage water, is studied experimentally and theoretically. To facilitate flow visualization, an experimental device was constructed by transparent material (Plexiglas). Flow velocities and fluctuations are measured, using a LDV system. A three-dimensional CFD-model was developed using the FLUENT code. The standard k–ω model is selected as the most appropriate. The model is validated, with good agreement, against experimental measurements. Furthermore, copper tubes, in the form of embedded heat exchanger, are placed inside the device and another similar 3D model was developed. The model was used to examine the behavior of the system, when the service water enters the heat exchanger, thus being indirectly heated by the stored hot water. It is shown that the outlet temperature of the service water is enough higher, when recirculation occurs. 相似文献
64.
Zhang Shu-hui Liang Guo-zheng Zhang Wei Zeng Jin-fang 《Mechanics of Composite Materials》2006,42(6):507-512
The surface of aramid fibers was modified with a polymer coating — a surface treatment reagent containing epoxy resin. The
resulting fibers were examined by using NOL tests, hydroburst tests, and the scanning electron microscopy. The modified fibers
had a rougher surface than the untreated ones. The interlaminar shear strength of an aramid-fiber-reinforced epoxy composite
was highest when the concentration of polymer coating system was 5%. The translation of fiber strength in an aramid/epoxy
composite vessel was improved by 8%. The mechanism of the surface treatment of fibers in improving the mechanical properties
of aramid/epoxy composites is discussed.
Russian translation publeshed in Mekhanika Kompozitnykh Materialov, Vol. 42, No. 6, pp. 729–738, November–December, 2006. 相似文献
65.
A zero-curvature criterion is proposed to determine the practical collapse load. Six tests have been carried out on spherical pressure vessels with cylindrical nozzle. Results of these tests and other experimental data quoted from different references are discussed in order to compare the new criterion with various previously proposed criteria. It is concluded that: (1) the zero-curvature point is a characteristic point of the experimental curve and that the new criterion is an objective criterion without any artificial coefficient. (2) the deviation of the collapse load estimated by the new criterion is smaller than that estimated by other criteria.Supported by the Chinese National Foundation of Natural Science. 相似文献
66.
朱锡雄 《宁波大学学报(理工版)》1988,(1)
本文结合我国核动力反应堆的实例,首先介绍了设计规范中采用的断裂分析图的评定方法,然后着重讨论一种新的断裂力学的评定方法。结合对容器材料断裂韧性的实验测定,给出了计算结果,绘制了全寿期的安全运行工况图,并对两种方法的结果作了比较讨论。 相似文献
67.
本文利用解析方法,建立了球形容器角变形的一些几何关系式与局部应力的分析表达式;求得了一个简明而且实用的应力集中系数公式,表明应力集中不仅依赖于角变形量,而且随径厚比的平方根的增加而增加。 相似文献
68.
在外杜瓦系统上设置了爆破片装置,借助大型有限元分析程序ANSYS,对爆破片和托架进行了分析,所得结果与实验结果良好吻合,为同类装置的过压泄放提供了有益的参考。 相似文献
69.
Chao Deng Fengfu Li May Griffith Marc Ruel Erik J Suuronen 《Macromolecular Symposia》2010,297(1):138-146
Summary: Vascular diseases are the leading cause of morbidity and mortality in the western world. Autologous vessels remain the standard for coronary grafting and peripheral bypass surgery; however, their availability in patients can be limited. Therapeutic angiogenesis using growth factors, genes, or progenitor cells has been given considerable scientific attention over the last decade, but has not yet provided a definitive clinical benefit. Biomaterials could be developed to protect protein, DNA and cells against hostile conditions. Chitosan, a natural polymer of glucosamine and N-acetyl glucosamine, has been widely studied in tissue engineering due to its biocompatibility, biodegradability, and muco-adhesive and antimicrobial properties. Notably, the application of chitosan has been gaining attention in the vascular field due to its structural similarity to glycosaminoglycans, which are components of a tissue's extracellular matrix. In this review, chitosan-based materials, and their use in tissue engineered blood vessels, and as protein, gene and cell vectors for angiogenic therapy are discussed. 相似文献
70.
E. Weźranowski A. Kalicki A. Lutze-Birk S. Myczkowski 《Isotopes in environmental and health studies》2013,49(4):155-156
Es wurde eine X-X-Fluoreszensmethode (mit einer 30-mCi-238 Pu-Anregungsquelle und einem Proportionalzähler) zur Bestimmung von eisenhaltigen Verschleiβteilchen in Schmierölen für Schiffsmotoren erarbeitet. Die Methode ermöglicht eine schnelle Abschātzung des Verschleiβes von Miotorteilen. Die Empfindlichkeit der Methode beträgt ca. 0,005% Fe, der mittlere Fehler (nach dem Student-Test bei einer Zuverlässigkeit von 0,95) ca. ±5%. 相似文献