全文获取类型
收费全文 | 1626篇 |
免费 | 21篇 |
国内免费 | 18篇 |
专业分类
化学 | 1092篇 |
晶体学 | 25篇 |
力学 | 34篇 |
数学 | 268篇 |
物理学 | 246篇 |
出版年
2023年 | 9篇 |
2022年 | 8篇 |
2021年 | 11篇 |
2020年 | 21篇 |
2019年 | 10篇 |
2018年 | 7篇 |
2017年 | 9篇 |
2016年 | 34篇 |
2015年 | 18篇 |
2014年 | 24篇 |
2013年 | 73篇 |
2012年 | 67篇 |
2011年 | 96篇 |
2010年 | 56篇 |
2009年 | 59篇 |
2008年 | 119篇 |
2007年 | 112篇 |
2006年 | 103篇 |
2005年 | 75篇 |
2004年 | 87篇 |
2003年 | 84篇 |
2002年 | 89篇 |
2001年 | 26篇 |
2000年 | 33篇 |
1999年 | 25篇 |
1998年 | 22篇 |
1997年 | 23篇 |
1996年 | 34篇 |
1995年 | 12篇 |
1994年 | 18篇 |
1993年 | 12篇 |
1992年 | 20篇 |
1991年 | 11篇 |
1989年 | 13篇 |
1988年 | 6篇 |
1987年 | 7篇 |
1986年 | 12篇 |
1985年 | 17篇 |
1984年 | 19篇 |
1983年 | 9篇 |
1982年 | 19篇 |
1981年 | 27篇 |
1980年 | 13篇 |
1979年 | 23篇 |
1978年 | 19篇 |
1977年 | 9篇 |
1976年 | 9篇 |
1975年 | 11篇 |
1974年 | 9篇 |
1972年 | 7篇 |
排序方式: 共有1665条查询结果,搜索用时 15 毫秒
71.
Michael W. Winkley Gerard F. Judd Roland K. Robins 《Journal of heterocyclic chemistry》1971,8(2):237-240
The first synthesis of a purine nucleoside analog containing a bridgehead nitrogen atom is here reported. The direct glycosylation of the trimethylsilyl derivative of s-triazolo[2,3-a] pyrimid-7-one has been shown to give 3-(β-D-ribofuranosyl)-s-triazolo[2,3-a]pyrimid-7-one (V) and 4-(β-D-ribof'uranosyl)-s-lriazolo[2,3-α]pyrimid-7-one (VII). The nueleoside V may he considered a close analog of inosine in which the nitrogen N1 and C5 of inosine have been interchanged. Bro-minalion of the tri-O-acelyl derivative IV gave, after deblocking, 6-bromo-3-(β-D-ribofurnaosyl)-s-triazolo[2,3-a] pyrimid-7-one (IX). Structural assignments of the nucleosides were made on the basis of comparison of the ultraviolet absorption spectral characteristics with 3-methyl-s-triazolo-[2,3-a]pyrimid-7-one (XI) and 4-methyl-s-lriazolo[2,3-a Jpyrimid-7-one (XII) prepared by a standard procedure from 7-methoxy-s-triazolo(2,3-a] pyrimidine (X). 相似文献
72.
J. Serrano V. Bertin S. Bulbulian 《Journal of Radioanalytical and Nuclear Chemistry》2002,254(1):91-94
Calcined hydrotalcite packed columns were utilized to sorb 235U fission products and their decay products. The elution behavior of some radionuclides was studied after washing the columns, either with distilled water or 0.5% NaCl solution. Afterwards, fission products and their decay products were eluted using 0.5% NaCl solution. It was found that no matter the washing process, 99mTc, the b--decay product of 99Mo, was easily separated from 99Mo which was strongly retained on the hydrotalcite. 132I, the b--decay product of 132Te, was eluted slowly and was separated from 132Te which was retained on the column. 131I and 140Ba were eluted together with 99mTc and 132I, although in smaller proportions. 相似文献
73.
Sabine Beernaerts Marie Gerard Philippe Debongnie Jean-Paul Barthelemy Luc Pussemier Alfred Copin 《International journal of environmental analytical chemistry》2013,93(6):469-480
A monitoring study was carried out in 1998-1999 on a medium-sized (c. 4580 km2) watershed of the Dyle (or Dijle) river in central Belgium, composed of both rural and urbanized areas. This watershed may be considered as representative of a large part of the country. Samples were taken each month from seven sites along the course of the river, plus one from its major affluent the Demer. The eight molecules monitored were the main herbicides used on the major crops in the area, plus some used in nonagricultural sectors. The concentrations found were mostly in the 0-3 μg/L range, with some peaks between 3 and 14 μg/L. The averages over all spring and summer samples analyzed ranged from 0.14 (bentazone) to 1.54 μg/L (diuron). Time and space specific patterns could be observed. 相似文献
74.
Yu. A. Pisarenko O. O. Usol’tseva C. A. Cardona O. T. Gerard 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2013,87(9):1433-1441
Linear independent forms of the azeotropy rule applicable to diagrams of distillation (reaction distillation) and their fragments are established and presented as simple polyhedra of arbitrary dimensions. 相似文献
75.
76.
Elisa Maria Alessi Gerard GómezJosep J. Masdemont 《Communications in Nonlinear Science & Numerical Simulation》2012,17(2):854-866
We extend the analysis, started in a previous work [1], concerning the formation of lunar impact craters due to low-energy trajectories. First, we adopt the Circular Restricted Three-Body Problem and consider different choices of initial conditions inside the stable invariant manifold associated with the central invariant one in the neighborhood of the L2 equilibrium point in the Earth-Moon system. Then we move to the Bicircular Restricted Four-Body Problem to study the effect of the Sun on the distribution of impacts on the Moon’s surface. 相似文献
77.
78.
79.
80.
Gerard ’t Hooft 《Foundations of Physics》2016,46(9):1185-1198