全文获取类型
收费全文 | 412篇 |
免费 | 59篇 |
国内免费 | 140篇 |
专业分类
化学 | 321篇 |
晶体学 | 19篇 |
力学 | 33篇 |
综合类 | 23篇 |
数学 | 47篇 |
物理学 | 168篇 |
出版年
2023年 | 4篇 |
2022年 | 16篇 |
2021年 | 12篇 |
2020年 | 17篇 |
2019年 | 16篇 |
2018年 | 12篇 |
2017年 | 24篇 |
2016年 | 11篇 |
2015年 | 27篇 |
2014年 | 28篇 |
2013年 | 24篇 |
2012年 | 26篇 |
2011年 | 35篇 |
2010年 | 41篇 |
2009年 | 29篇 |
2008年 | 45篇 |
2007年 | 39篇 |
2006年 | 46篇 |
2005年 | 34篇 |
2004年 | 22篇 |
2003年 | 19篇 |
2002年 | 17篇 |
2001年 | 22篇 |
2000年 | 15篇 |
1999年 | 8篇 |
1998年 | 5篇 |
1997年 | 1篇 |
1996年 | 2篇 |
1994年 | 2篇 |
1993年 | 3篇 |
1992年 | 1篇 |
1986年 | 2篇 |
1984年 | 2篇 |
1983年 | 3篇 |
1971年 | 1篇 |
排序方式: 共有611条查询结果,搜索用时 12 毫秒
561.
562.
三种不同磷源在超声作用下制备磷酸铋,磷酸氢二钠为磷源制备棒状磷酸铋,咪唑磷酸盐离子液为磷源制备梭状磷酸铋,三乙烯四胺磷酸盐离子液为磷源制备颗粒状磷酸铋.XRD表征分析表明三乙烯四胺磷酸离子液为磷源制备的磷酸铋衍射峰最高,咪唑磷酸盐离子液制备磷酸铋次之,磷酸二氢钠制备的磷酸铋衍射峰最低.紫外-可见分析表明离子液中合成的磷酸铋向低波数发生移动.BET分析表明在磷酸二氢钠、咪唑磷酸盐、三乙烯四胺磷酸盐中合成的磷酸铋的比表面积分别为3.9472 m2/g,11.548 m2/g和24.063 m2/g.三种磷酸铋在紫外光下对亚甲基蓝匀有光催化作用,其中三乙烯四胺磷酸盐离子液为磷源制备的磷酸铋光催化性能最佳,同时考察了三乙基四胺磷酸盐离子液制备磷酸铋以及光催化的条件. 相似文献
563.
The population growth of small harmful rats in grassland subjected to environment fluctuation has been modelled in a logistic equation. Two correlated random variables responsible to the fluctuation of the genetic factor and the suppression factor are used. A two-peak structure of the steady probability distribution of rate population is observed in the large fluctuation regime of the genetic factor. With the increase of correlation constant A, the steady probability distribution can change from two peaks to a single peak. The suppression factor μ and its fluctuation also affect the steady probability distribution and can push it toward a small population. 相似文献
564.
Syringe-shaped GaN nanorods are synthesized on Si(111) substrates by annealing sputtered Ga2O3/BN films under flowing ammonia at temperature of 950℃. Most of the nanorods consist of a main rod and a top needle, looking like a syringe. X-ray diffraction and selected-area electron diffraction confirm that the syringe-shaped nanorods are hexagonal wurtzite GaN. Scanning electron microscopy and high-resolution transmission electron microscopy reveal that these nanorods are as long as several micrometres, with diameters ranging from 100 to 300nm. In addition to the BN intermediate layer, the proper annealing temperature has been demonstrated to be a crucial factor for the growth of syringe-shaped nanorods by this method. 相似文献
565.
566.
We study the steady state properties of a logistic growth model in the presence of Gaussian white noise.Based on the corresponding Fokker-Planck equation the steady state solution of the probability distribution functionand its extrema have been investigated. It is found that the fluctuation of the tumor birth rate reduces the populationof the cells while the fluctuation of predation rate can prevent the population of tumor cells from going into extinction.Noise in the system can induce the phase transition. 相似文献
567.
568.
569.
为满足国内油田石油测井的迫切需要, 对小直径测井中子发生器进行了研发。 该发生器离子源采用微型化冷阴极Penning离子源, 离子光学采用结构简单的单极加速系统。 经实验室测试和用户现场刻度及测井表明, 研制的中子发生器具有耐高温、 产额高、 稳定性好等特点, 是目前国内研制的最小直径的工业测井中子发生器。 所测数据与其它测井方法相比较, 地质资料符合性好, 满足了用户测井要求, 现已用于油田生产测井。 A small neutron generator has been developed for meeting the need of well logging in oil fields. The miniature cold cathode Penning ion source and single electrode ion optics system are used in neutron generator. The good performance of the generator has been proved in the laboratory test and well logging in oil field. The generator has good characteristics, such as small diameter, high temperature resistant,high neutron output and good stability. At present, the neutron generator is the smallest logging generator in China, which has been used in oil field generally for conforming the geological data. 相似文献
570.