首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   620篇
  免费   27篇
  国内免费   3篇
化学   375篇
晶体学   1篇
力学   24篇
数学   43篇
物理学   207篇
  2024年   2篇
  2023年   6篇
  2022年   21篇
  2021年   10篇
  2020年   17篇
  2019年   18篇
  2018年   20篇
  2017年   18篇
  2016年   43篇
  2015年   27篇
  2014年   35篇
  2013年   78篇
  2012年   41篇
  2011年   61篇
  2010年   32篇
  2009年   32篇
  2008年   26篇
  2007年   23篇
  2006年   13篇
  2005年   15篇
  2004年   13篇
  2003年   6篇
  2001年   8篇
  2000年   4篇
  1999年   5篇
  1998年   3篇
  1997年   9篇
  1996年   5篇
  1995年   7篇
  1993年   4篇
  1992年   5篇
  1991年   2篇
  1990年   3篇
  1988年   2篇
  1987年   3篇
  1986年   2篇
  1984年   3篇
  1983年   3篇
  1981年   3篇
  1980年   3篇
  1979年   2篇
  1978年   1篇
  1977年   3篇
  1976年   1篇
  1975年   1篇
  1974年   2篇
  1973年   1篇
  1971年   1篇
  1970年   2篇
  1968年   1篇
排序方式: 共有650条查询结果,搜索用时 812 毫秒
1.
Plasma Chemistry and Plasma Processing - The present study has been carried to investigate the interaction and effect of plasma activated water (PAW) on pea seeds. PAW is produced with the...  相似文献   
2.
Trabecular bone fracture is closely related to the trabecular architecture, microdamage accumulation, and bone tissue properties. Primary constituents of trabecular tissue are hydroxyapatite (HA) mineralized type-I collagen fibers. In this research, dynamic fracture in two dimensional (2-D) micrographs of ovine (sheep) trabecular bone is modeled using the mesoscale cohesive finite element method (CFEM). The bone tissue fracture properties are obtained based on the atomistic strength analyses of a type-I collagen + HA interfacial arrangement using molecular dynamics (MD). Analyses show that the presented framework is capable of analyzing the architecture dependent fracture in 2-D micrographs of trabecular bone.  相似文献   
3.
Why chaos is rarely observed in natural populations   总被引:2,自引:0,他引:2  
An attempt has been made to understand why chaotic dynamics have received poor evidential support from field studies. Our study opens up the possibility that the cause of failure might not be poor quality of data, as pointed out by earlier authors, but an ecological reality. We have designed two model food chains to examine whether there is a biological basis for the crisis. This investigation is effected with the help of a new method which we introduce at an appropriate place in the text. The fact that chaos exists in a narrow range of parametric values in both the model systems suggests that the crisis indeed has a biological origin.  相似文献   
4.
Photon induced modifications in Triafol-TN and Triafol-BN polymers have been studied in the dose range of 101–106 Gy at room temperature using a 60Co source. To monitor the chemical and structural changes induced by gamma rays, UV, IR, and ESR studies were carried out. Thermal studies were also conducted for understanding the effects of gamma irradiations on these polymers. Variation of track etching characteristics and activation energy for bulk etching have been studied at different gamma rays doses. The experimental results are presented and discussed.  相似文献   
5.
Thin carbon films were deposited on silicon substrates at room temperature using a 0.355 μm Nd:YAG laser wavelength at low irradiance in the presence of argon gas. Various techniques including scanning electron microscopy, X-ray diffraction and Raman spectroscopy were used to analyze the film quality. The influence of the argon gas pressure on the properties of the films is demonstrated and a correlation with the optical emission data is presented.  相似文献   
6.
A rapid, sensitive and specific method to quantify pregabalin in human plasma using metaxalone as the internal standard is described. Sample preparation involved simple protein precipitation by using acetronitrile as solvent. The extract was analyzed by high-performance liquid chromatography coupled to electrospray tandem mass spectrometry (LC-MS–MS). Chromatography was performed isocratically on Thermo Hypurity C18 5 μm analytical column, (50 mm × 4.6 mm i.d.). The assay of pegabalin was linear calibration curve over the range 10.000–10000.000 ng mL?1. The lower limit of quantification was 10.000 ng mL?1 in plasma. The method was successfully applied to the bioequivalence study of pregabalin capsules (150.0 mg) administered as a single oral dose.  相似文献   
7.
8.
Parametric excitation of the electron-acoustic wave (EAW) has been analysed using a hydrodynamical model. The plasma has been assumed to consist of multiply charged ions. The ratio (α) of the hotter ion concentration to that of the electrons is a sensitive parameter. The condition for the occurrence of the EAW is well satisfied for the smaller values of α. The growth rate of the instability gets enhanced by increasing α and the charge state of the hotter ions. The values of α can be varied within short range only.  相似文献   
9.
A procedure for the complete chemical analysis of magnesium or sodium diuranate (yellow cake) sample is reported. Uranium is determined gravimetrically after peroxide precipitation. Optimum parameters, such as pH, quantity of hydrogen peroxide, volume of sample, temperature and complexing agent for quantitave precipitation of uranium, and effective separation of other elements were studied. Aluminum, Ca, Cd, Co, Cr, Cu, Fe, K, Mg, Mn, Na, Ni, Pb, and Zn were determined by flame atomic absorption spectrometer and B, Mo, SO4, REEs and Y by inductively coupled plasma atomic emission spectrometer in the filtrates of hydroxide and peroxide precipitation separation. The proposed method is accurate and the precision is characterized by an RSD of ~0.2% for U; 2 to 6% for Mg, Na, K, Ca, Fe, SiO2, Al, Cd, Co, Cr, Fe, Mn, Ni, Pb, and Zn and 3 to7% for REEs, Y, Mo and B  相似文献   
10.
An experimental investigation of laser-induced breakdown using Nd:YAG laser harmonics for argon, nitrogen and oxygen gases is reported. Pressure dependence as well as wavelength dependence of the breakdown threshold irradianceI th is investigated. The experimental observations for 1.064 and 0.532 m laser wavelengths are in agreement with theoretical calculations which include the effects of multiphoton ionization and cascade ionization.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号