全文获取类型
收费全文 | 765篇 |
免费 | 131篇 |
国内免费 | 100篇 |
专业分类
化学 | 236篇 |
晶体学 | 9篇 |
力学 | 157篇 |
综合类 | 139篇 |
数学 | 170篇 |
物理学 | 285篇 |
出版年
2024年 | 1篇 |
2023年 | 32篇 |
2022年 | 45篇 |
2021年 | 68篇 |
2020年 | 51篇 |
2019年 | 34篇 |
2018年 | 33篇 |
2017年 | 49篇 |
2016年 | 32篇 |
2015年 | 31篇 |
2014年 | 68篇 |
2013年 | 67篇 |
2012年 | 59篇 |
2011年 | 65篇 |
2010年 | 63篇 |
2009年 | 48篇 |
2008年 | 30篇 |
2007年 | 42篇 |
2006年 | 39篇 |
2005年 | 25篇 |
2004年 | 11篇 |
2003年 | 13篇 |
2002年 | 14篇 |
2001年 | 27篇 |
2000年 | 9篇 |
1999年 | 19篇 |
1998年 | 3篇 |
1997年 | 1篇 |
1996年 | 5篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1993年 | 3篇 |
1992年 | 2篇 |
1990年 | 2篇 |
1986年 | 1篇 |
1979年 | 2篇 |
排序方式: 共有996条查询结果,搜索用时 15 毫秒
981.
研究冲击波作用下金属微观组织变化对于理解柱壳结构在高应变率下的变形及破坏极为重要。实验通过对20钢金属柱壳在内部爆炸载荷作用下的爆炸回收碎片截面进行微观分析,探讨冲击波作用下材料的组织演化、相变特征,同时使用有限元方法对柱壳膨胀断裂过程中的热力学特征进行分析。研究发现:20钢柱壳近内表面满足α→ε相变热力学条件的有限深度区域内,α晶粒内可见明显的平行滑移线分布特征;电子背散射衍射揭示了平行滑移线区域内组织碎化,且存在{112}<111>和{332}<113>两种孪晶,同时平行滑移线的碎化组织区域中存在密排六方晶格(HCP)的ε相结构,而试样原始组织及爆炸后除试样壁厚内部(0~3.0 mm)区域外均未见ε相结构残留。分析认为:冲击过程中发生了α→ε相变;相变引发的材料性能改变将可能影响断裂破坏过程;考虑冲击波作用下金属材料动态相变对结构变形与破坏的影响,对这类柱壳变形及破坏的精密物理模拟具有重要意义,有必要开展进一步研究。 相似文献
982.
RUAN Hang-Yu 《理论物理通讯》2005,43(1):31-38
A variable separation approach is used to obtain exact solutions
of the (2+1)-dimensional generalized Nizhnik-Novikov-Veselov
equation. Two of these exact solutions are analyzed to study the
interaction between a line soliton and a y-periodic soliton (i.e. the array of the localized structure in the y direction, which propagates in the x direction) and between two dromions. The
interactions between a line soliton and a y-periodic soliton are
classified into several types according to the phase shifts due to
collision. There are two types of singular interactions. One is
the resonant interaction that generates one line soliton while the
other is the extremely repulsive or long-range interaction where
two solitons interchange each other infinitely apart. Some new
phenomena of interaction between two dromions are also reported in
this paper, and detailed behaviors of interactions are illustrated both
analytically and graphically. 相似文献
983.
郑乃峰 《浙江大学学报(理学版)》2012,39(4):367-370
给出了R-交叉积的定义,并给出了R-交叉积代数结构和W-Smash余积余代数结构构成双代数的一个充分必要条件. 相似文献
984.
可变功能机械额功能转换过程设计是该类产品设计开发的一个重要环节,其设计结果不仅决定产品功能的实现与否,还会对诸如安全性、经济性等非技术类问题造成影响,目前还缺少专门针对此过程设计解的分析及评估方法.为解决此问题,结合人失误概率预测技术(Technique for Human Error Rate Prediction, THERP)模型及风险概率与经济性安全评价对功能转换过程进行定量分析.依据THERP模型将功能转换过程划分为一系列子任务,并建立功能转换过程二叉树,同时按照功能转换过程的特点对二叉树进行简化,接着评估各失误路径的发生概率及失误严重度,并将失误严重度量化为经济损失,最后得到功能转换过程的风险值.同时通过角磨机向电锯功能转换的过程定量分析,验证了该方法的可行性. 相似文献
985.
采用分子束外延(MBE)技术外延再生长AlAsSb,对InAs/GaSb Ⅱ类超晶格(T2SLs)长波红外探测器的表面缺陷进行钝化,实现了暗电流的显著降低.首先,研究了湿法腐蚀浅台面的最佳腐蚀液配比,获得了低横向腐蚀、光滑的侧壁以及均匀的腐蚀界面.随后,使用AlAsSb/AlAs/GaAs、AlAsSb/GaSb两种不同的外延再生长组合和单一的SiO2薄层分别对刻蚀后的台面进行钝化,同时保留一个没有钝化的样品作为对照,最后对4种不同钝化条件下探测器的暗电流特性进行了测量.结果发现,使用AlAsSb/GaSb外延再生长钝化层的器件暗电流得到了进一步降低,使用SiO2钝化层的效果次之,而使用AlAsSb/AlAs/GaAs外延再生长钝化层的性能相对较差.上述结果表明,外延再生长钝化技术是降低长波红外探测器暗电流的一种有效方法. 相似文献
986.
自从首个遗传密码子被破译以来, 密码子与所表达的氨基酸之间的关系一直吸引了许多关注. 本研究从氨基酸、核苷和三偏磷酸钠的反应体系出发, 用电子舌检测反应前后体系变化, 考察核苷对氨基酸成肽反应的影响, 试图找到氨基酸与密码子的联系. 结果表明, 大部分氨基酸的密码子或反密码子中间位核苷对反应的促进作用最大, 这种结果可能是因为核苷的碱基与氨基酸的侧链基团之间的某种弱相互作用导致的. 相应地, 亮氨酸和异亮氨酸之间的结果差异更加佐证了上述假设. 这种弱相互作用有望成为研究密码子识别氨基酸的关键突破, 为生命起源的研究提供新方法. 相似文献
987.
《Polymer Gels and Networks》1993,1(2):83-92
1H NMR measurements on spin-lattice relaxation time (T1) and spin-spin relaxation time (T2) were carried out on hydro-swollen crosslinked poly(methacrylic acid) (PMAA) gel to elucidate molecular motion of water molecules contained in the gel as a function of the degree of crosslinking. From these experimental results, it was found that 1H T1 and T2 decrease with an increase of the degree of crosslinking. This shows that molecular motion of water molecules is strongly restrained owing to crosslinking. Further, pulsed-field-gradient spin-echo 1H NMR measurements were carried out to determine the self-diffusion coefficient of water molecules (DH2O contained in the PMAA gel at 300 K as a function of the degree of crosslinking. From these experimental results, it was found that the DH2O value decreases with an increase of the degree of crosslinking. This shows that translational molecular motion of water molecules is restrained by crosslinking. 相似文献
988.
989.
A series of porous S-doped carbon nitride ribbons (PSCN) were prepared by one-pot hydrothermal and sonochemical synthesis techniques. The morphologies and nanostructures of the catalysts were characterized by SEM, XRD and IR, which confirmed the pristine graphitic structures of carbon nitrides retained in the products. Due to sonication treatment, PSCN has porous structures in the thin ribbon and larger specific surface areas (PSCN 43.5 m2/g, SCN 26.6 m2/g and GCN 6.5 m2/g). XPS and elemental mappings verified that sulfur atoms were successfully introduced into the carbon nitride framework. Diffuse reflectance spectroscopy (DRS) results showed S-doping in the carbon nitride reduced the bandgap energy and enhanced their capability of the utilization of visible light, which contributed to higher photo-generated current. Photoluminescence (PL) analysis indicates the recombination of photogenerated carriers was suppressed in PSCN. Moreover, the photocatalytic performance showed that S-doping and porous and thin ribbon nanostructures may effectively boost the CO2 reduction rate (to as much as 5.8 times of GCN) when illuminated by visible light (>420 nm) without the need of sacrificial materials. The preliminary mechanisms of the formation of PSCN and its applications in photocatalytic CO2 reduction are proposed. It highlights the potential of the current technique to produce effective, nonmetal-doped carbon nitride photocatalysts. 相似文献
990.
Ruijia Wang Yi Zhang Prof. Wei Lu Baoyi Wu Shuxin Wei Shuangshuang Wu Prof. Wenqin Wang Prof. Tao Chen 《Angewandte Chemie (International ed. in English)》2023,62(23):e202300417
Many living organisms have the superb structure-editing capacity for better adaptation in dynamic environments over the course of their life cycle. However, it's still challenging to replicate such natural structure-editing capacity into artificial hydrogel actuating systems for enhancing environment-interactive functions. Herein, we learn from the metamorphosis development of glowing octopus to construct proof-of-concept fluorescent hydrogel actuators with life-like structure-editing capacity by developing a universal stepwise inside-out growth strategy. These actuators could perform origami-like 3D shape deformation and also enable the postnatal growth of new structures to adapt additional actuating states for different visual information delivery by using different environment keys (e.g., temperature, pH). This study opens previously unidentified-avenues of bio-inspired hydrogel actuators/robotics and extends the potential uses for environment-interactive information encryption. 相似文献