全文获取类型
收费全文 | 14621篇 |
免费 | 2122篇 |
国内免费 | 1602篇 |
专业分类
化学 | 10552篇 |
晶体学 | 81篇 |
力学 | 1366篇 |
综合类 | 247篇 |
数学 | 1583篇 |
物理学 | 4516篇 |
出版年
2024年 | 37篇 |
2023年 | 166篇 |
2022年 | 384篇 |
2021年 | 535篇 |
2020年 | 680篇 |
2019年 | 519篇 |
2018年 | 539篇 |
2017年 | 541篇 |
2016年 | 750篇 |
2015年 | 635篇 |
2014年 | 802篇 |
2013年 | 1433篇 |
2012年 | 936篇 |
2011年 | 898篇 |
2010年 | 679篇 |
2009年 | 819篇 |
2008年 | 761篇 |
2007年 | 863篇 |
2006年 | 780篇 |
2005年 | 690篇 |
2004年 | 651篇 |
2003年 | 527篇 |
2002年 | 521篇 |
2001年 | 403篇 |
2000年 | 389篇 |
1999年 | 332篇 |
1998年 | 337篇 |
1997年 | 275篇 |
1996年 | 233篇 |
1995年 | 210篇 |
1994年 | 124篇 |
1993年 | 151篇 |
1992年 | 127篇 |
1991年 | 97篇 |
1990年 | 77篇 |
1989年 | 51篇 |
1988年 | 55篇 |
1987年 | 50篇 |
1986年 | 45篇 |
1985年 | 40篇 |
1984年 | 37篇 |
1983年 | 12篇 |
1982年 | 25篇 |
1981年 | 22篇 |
1980年 | 22篇 |
1979年 | 20篇 |
1978年 | 13篇 |
1977年 | 10篇 |
1976年 | 12篇 |
1973年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 156 毫秒
61.
62.
Butyltins were analyzed in waters from California river and lake marinas and were detected at the part per trillion (ppt) level in most locations. The tributyltin:dibutyltin (TBT/DBT) ratios in the fresh waters were similar to those in their saline counterparts indicating like rates of degradation in the two salinity regimes. 相似文献
63.
An infinite row of periodically spaced, identical rigid circularcylinders is excited by an acoustic line source which is parallelto the generators of the cylinders. A method for calculatingthe scattered field accurately and efficiently is presented.When the cylinders are sufficiently close together, Rayleigh–Blochsurface waves that propagate energy to infinity along the arrayare excited. An expression is derived which enables the amplitudesof these surface waves to be computed without requiring thesolution to the full scattering problem. 相似文献
64.
65.
66.
The plastic deformation field near the horizontal surface of a half space of perfectly plastic material associated with an indenting rotating rigid tooth is studied using slip line theory. The tooth is one of many on a roll surface and indents first into the half-space material and then rotates about the roll center. A slip line field is proposed for the deforming plastic region and a solution scheme is outlined. The emphasis is on determining the shape of the deforming region, especially that of the free surface. The study has a potential application in roughness transfer in metal forming processing. 相似文献
67.
本文针对一类非饱和土壤水流问题,提出了基于二次插值的特征差分格式,得到了严谨的L2模误差估计.并作了数值试验,指明方法的有效性. 相似文献
68.
J. C. Raines J. P. Schmidt J. P. Burelbach H. K. Fauske 《Journal of Thermal Analysis and Calorimetry》2006,85(1):53-55
Hydrogen
peroxide is a very versatile oxidizing agent, and it is also environmentally
compatible considering that the products of its exothermic decomposition are
oxygen and water.When kept in a clean temperature-controlled environment,
the self-reaction (decomposition) rate is extremely low. However, it is well
known that even a small amount of contamination will dramatically increase
the reaction rate. This paper describes the use of the fast thermal activity
interpreter (FTAI) instrument to examine the chemical reactivity of commercially
available 50% hydrogen peroxide at two different temperatures (30 and 40°C)
both with and without contamination. The results show that at 30°C a small
amount of rust (330 ppm) increases the reaction rate of 50% hydrogen peroxide
by a factor of 50. When the temperature is increased to 40°C, the reaction
rate is further increased by almost a factor of four. The implication for
reactivity management is that at this contamination level most practical vessel
sizes would require emergency venting capability.
An evaluation
was then performed to determine the emergency venting requirement for the
safe transportation or storage of the contaminated hydrogen peroxide. It was
determined that for quantities of the material less than 5 gallons, conventional
breather vents would be sufficient to accommodate the gas evolved. However,
for larger quantities, a safety relief device would be needed. For example,
for a 400-gallon tote bin at 40°C the required minimum vent area is estimated
to be 4.3 in2, corresponding to a minimum vent
diameter of 2.3 inches. 相似文献
69.
Yu. D. Perfiliev V. S. Rusakov L. A. Kulikov A. A. Kamnev K. Alkhatib 《Hyperfine Interactions》2006,167(1-3):881-885
To explain line broadening in emission Mössbauer spectra as compared to the corresponding absorber measurements, the model of trapped electrons has been proposed. Auger electrons (emitted, e.g. after electron capture by 57Co or after the converted isomeric transition of 119mSn), as well as secondary electrons, may be trapped in the proximity to the nucleogenic ion. Electrons captured by lattice traps at different distances from the daughter ion induce an asymmetric distribution of quadrupole splitting in the resulting emission spectra, as shown in a few examples. This model is supported by estimates of quadrupole splitting values which may be caused by such trapped electrons located at specified distances from the nucleogenic atom. 相似文献
70.
功能性丙烯酸/MBAM体系共聚产物的研制 总被引:2,自引:0,他引:2
以丙烯酸和MBAM为主要原料,经聚合,合成了一种高性能的具有良好保水性能的聚合产物,其保水量达到750~1000倍.50℃以下有良好的保水性能,28℃以下有极好的保水性能,并研究了工艺条件对该产品性能的影响因素. 相似文献