全文获取类型
收费全文 | 11559篇 |
免费 | 691篇 |
国内免费 | 63篇 |
专业分类
化学 | 8389篇 |
晶体学 | 45篇 |
力学 | 365篇 |
综合类 | 1篇 |
数学 | 2020篇 |
物理学 | 1493篇 |
出版年
2022年 | 67篇 |
2021年 | 112篇 |
2020年 | 125篇 |
2019年 | 180篇 |
2018年 | 147篇 |
2017年 | 131篇 |
2016年 | 328篇 |
2015年 | 344篇 |
2014年 | 370篇 |
2013年 | 608篇 |
2012年 | 595篇 |
2011年 | 647篇 |
2010年 | 489篇 |
2009年 | 472篇 |
2008年 | 616篇 |
2007年 | 556篇 |
2006年 | 569篇 |
2005年 | 518篇 |
2004年 | 511篇 |
2003年 | 437篇 |
2002年 | 519篇 |
2001年 | 232篇 |
2000年 | 216篇 |
1999年 | 124篇 |
1998年 | 119篇 |
1997年 | 135篇 |
1996年 | 159篇 |
1995年 | 109篇 |
1994年 | 129篇 |
1993年 | 115篇 |
1992年 | 116篇 |
1991年 | 99篇 |
1990年 | 89篇 |
1989年 | 89篇 |
1988年 | 80篇 |
1987年 | 83篇 |
1986年 | 74篇 |
1985年 | 126篇 |
1984年 | 140篇 |
1983年 | 100篇 |
1982年 | 149篇 |
1981年 | 123篇 |
1980年 | 146篇 |
1979年 | 133篇 |
1978年 | 145篇 |
1977年 | 124篇 |
1976年 | 127篇 |
1975年 | 107篇 |
1974年 | 115篇 |
1973年 | 84篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
101.
Costas Courcoubetis Panagiotis Konstantopoulos Jean Walrand Richard R. Weber 《Queueing Systems》1989,5(1-3):37-54
Consider a production system that consists ofm machines each of which can produce parts ofn types. When machinek is used, it produces a part of typei with probabilityp
ki
. Requests arrive for parts, one at a time. With probability
i
an arriving request is for a part of typei. The requests must be served without waiting. Thus, if a requested part is not available, it must be produced. We find necessary and sufficient conditions for the existence of a strategy (a choice of the machines to be used) which makes the inventory of parts stable and we provide such a strategy.Two variations of this model are also considered: the case of batch arrivals of requests, and that of a system where the requests can be queued. 相似文献
102.
103.
The improved algorithm surface irradiance derived from a range of satellite-based sensors (SIDES) is presented in this article. It calculates various types of surface UV intensities, such as biologically weighted or unweighted UV spectra, integrated doses or irradiance at specific wavelengths, using data from satellite instruments. These surface UV data are mainly useful for environmental impact or process studies where high accuracy or a high temporal resolution is required. In contrast to several previous studies, SIDES has been validated with spectral measurements. By this method an averaging of positive or negative deviations over the complete wavelength range is avoided. This is especially important for UV wavelengths around 300 nm where biological effectiveness is highest. The results of SIDES deviate less than 7% from ground-based observations for wavelengths between 295 and 400 nm. In contrast, the corresponding deviations of the joint research center algorithm escalate for shorter wavelengths, reaching 35% at 295 nm. This large deviation is due to an inaccurate interpolation procedure that has been detected by spectral analysis. Thus, spectral validation is demonstrated to be an appropriate tool to detect weaknesses in such an algorithm and provides information essential for improvement. 相似文献
104.
Abstract—Applying criteria used for higher plants, phytochrome mediation of uredospore germination in the stem-rust fungus, Puccinia graminis f. sp. tritici (Eriks & Henn) Guyot is established. A 1 min red irradiation at 660 nm promotes uredospore germination and this potentiation of promotion is photoreversible by a 1 min far-red irradiation at 730 nm. 相似文献
105.
Jean Ravez Re´gnault Von Der Mu¨hll Paul Hagenmuller 《Journal of solid state chemistry》1975,14(1):20-24
Au sein d'un re´seau de type BaFeF5 des chai?nes d'octae`dres fluore´sa`sommets communs peuvent disparai?tre en donnant naissance a des canaux dont l'occupation partielle ou totale par des files de cations Sr2+ et de couples d'anions F?, conduit respectivement aux phases Sr3(FeF6)2 ou Sr5T3F19 (T = Cr, Co, Ga). Une discussion cristallochimique permet d'expliquer l'existence d'un domaine de solutions solides au sein du diagramme ternaire SrF2BaF2FeF3. 相似文献
106.
Tran Quang Minh Léon Christiaens Pierre Grandclaudon Alain Lablache-Combier 《Tetrahedron》1977,33(17):2225-2229
Photoirradiated in presence of acetophenone, benzo[b]selenophene and its 3-methyl derivative add to dimethyl acetylenedicarboxylate. In each ease, the primary reaction product is unstable and has not been isolated. Photoexeited in its triplet state (the energy of which is in the neighbourhood of 69 ) benzo[b]selenophene and its 2- and 3-methyl, 2,3 dimethyl, 3 acetoxy and 2-methyl-3-acetoxy derivatives add to 1,2 dichloroethylene leading to cyclobutanes. Neither cyclo-addition occurs in absence of photosensitiser. Single-crystal X-ray analysis gave the structures of the two adducts of 3-acetoxybenzo[b]selenophene with trans-1,2-dichloroethylene. In both compounds the chlorine atoms are trans. 相似文献
107.
108.
109.
110.