全文获取类型
收费全文 | 4611篇 |
免费 | 451篇 |
国内免费 | 422篇 |
专业分类
化学 | 993篇 |
晶体学 | 17篇 |
力学 | 1596篇 |
综合类 | 83篇 |
数学 | 1317篇 |
物理学 | 1478篇 |
出版年
2024年 | 6篇 |
2023年 | 36篇 |
2022年 | 66篇 |
2021年 | 139篇 |
2020年 | 138篇 |
2019年 | 97篇 |
2018年 | 108篇 |
2017年 | 171篇 |
2016年 | 261篇 |
2015年 | 180篇 |
2014年 | 223篇 |
2013年 | 283篇 |
2012年 | 226篇 |
2011年 | 257篇 |
2010年 | 226篇 |
2009年 | 267篇 |
2008年 | 277篇 |
2007年 | 278篇 |
2006年 | 277篇 |
2005年 | 255篇 |
2004年 | 227篇 |
2003年 | 207篇 |
2002年 | 152篇 |
2001年 | 137篇 |
2000年 | 114篇 |
1999年 | 114篇 |
1998年 | 110篇 |
1997年 | 99篇 |
1996年 | 72篇 |
1995年 | 81篇 |
1994年 | 67篇 |
1993年 | 42篇 |
1992年 | 42篇 |
1991年 | 35篇 |
1990年 | 40篇 |
1989年 | 18篇 |
1988年 | 25篇 |
1987年 | 23篇 |
1986年 | 17篇 |
1985年 | 19篇 |
1984年 | 13篇 |
1982年 | 13篇 |
1981年 | 5篇 |
1980年 | 5篇 |
1979年 | 10篇 |
1978年 | 9篇 |
1977年 | 4篇 |
1974年 | 4篇 |
1973年 | 2篇 |
1957年 | 2篇 |
排序方式: 共有5484条查询结果,搜索用时 15 毫秒
61.
A test statistic is developed that checks the validity of the extreme value conditions without specifiying the shape parameter of the limiting extreme value distribution. 相似文献
62.
为了考虑金属材料表面微凸结构对模具与工件接触区域上的非局部摩擦效应,在锥形模圆柱体超塑性挤压加工分析中,采用Oden等提出的非局部摩擦定律代替经典的库仑摩擦定律,利用主应力法或工程法建立了相应问题的积微分形式的力平衡方程.在简化的情况下,采用摄动法求得所论问题的近似解,并分析了影响应力的非局部效应的相关因素. 相似文献
63.
生产函数有着相应的经济理论背景,是以科学的数据为样本,反复拟合、检验、修正后得到的,揭示产出量与生产要素资本和劳动之间内在的必然的统计相关关系,是科学的结论。本文就此与余斌、程立茹先生进行探讨和商榷。 相似文献
64.
65.
对薄层柱壳爆炸膨胀断裂过程的研究 总被引:10,自引:2,他引:8
本文提出了一个用于描述动态破坏发展过程的损伤度函数。从这个损伤度函数出发,把材料特征性方程取为强化粘塑性本构方程形式,导出了薄层柱壳爆炸膨胀运动在两种近似下(恒定膨胀速度近似合恒定应变速率近似)断裂判据的解析表达式。结果分析表明,在上述条件下,存在着一个动态断裂“塑性峰”,在这个峰值条件的应变率下,柱壳出现贯穿断裂时刻的应变最大。以软钢为算例,本断裂判据可以比较好地解释Иванов和陈大年等给出的实验结果。这时,动态断裂“塑性峰”对应的应变率为4×104 s-1,相应的应变约为60%~80%。 相似文献
66.
燮理阴阳胶囊的制备与质量标准研究 总被引:1,自引:0,他引:1
为研制燮理阴阳胶囊生产工艺,并建立相应的质量标准,采用正交实验法进行了工艺研究,采用薄层色谱法进行了鉴定,确立了水煎提取的工艺条件,建立了知母、熟地黄、淫羊藿的鉴别方法。该制剂的制备工艺简单易行,质量检定方法可行,质量稳定。 相似文献
67.
Thermoanalytical characterization of carbon/carbon hybrid material, Apple Woodceramics 总被引:3,自引:0,他引:3
Woodceramics, a carbon/carbon composite of plant-originated carbon reinforced by glassy carbon from phenolic resin, was prepared from apple pomace at carbonizing temperatures of 1073 K (AWC800) and 1473 K (AWC1200), and characterized by thermoanalytical methods and X-ray diffraction (XRD). Simultaneous differential scanning calorimetry (DSC) and thermogravimetric (TG) showed complicated overlapping reactions similar to those of coal. The initial temperature of pyrolysis was obtained by fitting logistic functions to observed TG data. The results suggested that AWC1200 contained more volatile matter than AWC800. In an inert atmosphere, complicated devolatilization takes place. In an oxidizing atmosphere, thermal change occurs roughly in four steps: desorption of physically adsorbed matter; pyrolysis into aliphatic and aromatic fragments; ignition; combustion of char. The oxidation resistance of AWC1200 was superior to AWC800. 相似文献
68.
Recent developments in quantitative surface analysis by Auger (AES) and x-ray photoelectron (XPS) spectroscopies are reviewed and problems relating to a more accurate quantitative interpretation of AES/XPS experimental data are discussed. Special attention is paid to consideration of elementary physical processes involved and influence of multiple scattering effects on signal line intensities. In particular, the major features of core-shell ionization by electron impact, Auger transitions and photoionization are considered qualitatively and rigorous approaches used to calculate the respective transition probabilities are analysed. It is shown that, in amorphous and polycrystalline targets, incoherent scattering of primary and signal Auger and photoelectrons can be described by solving analytically a kinetic equation with appropriate boundary conditions. The analytical results for the angular and energy distribution, the mean escape depth, and the escape probability as a function of depth of origin of signal electrons as well as that for the backscattering factor in AES are in good agreement with the corresponding Mote Carlo simulation data. Methods for inelastic background subtraction, surface composition determination and depth-profile reconstructions by angle-resolved AES/XPS are discussed. Examples of novel techniques based on x-ray induced photoemission are considered. 相似文献
69.
A three-dimensional pharmacophore model was developed from a series of inhibitors of Aurora A kinase to discover new potent anti-cancer agents using the HypoGen module in the Catalyst software. The pharmacophore model was developed based on the structure of 20 currently available inhibitors, which were carefully selected from the literature. The best hypothesis (Hypo 1) was defined by four features: one hydrogen-bond donor and three hy- drophobic points, with the best correlation coefficient of 0.909, the lowest rms deviation of 1.563, and the highest cost difference of 99.075. The Hypo 1 was then validated by a test set consisting of 24 compounds and by a cross-validation of 95% confidence level through randomizing the data using the CatScramble program, which suggested that a predictive pharmacophore model had been successfully obtained. 相似文献
70.