全文获取类型
收费全文 | 24824篇 |
免费 | 4038篇 |
国内免费 | 3568篇 |
专业分类
化学 | 19386篇 |
晶体学 | 334篇 |
力学 | 1243篇 |
综合类 | 207篇 |
数学 | 2554篇 |
物理学 | 8706篇 |
出版年
2024年 | 64篇 |
2023年 | 359篇 |
2022年 | 773篇 |
2021年 | 792篇 |
2020年 | 898篇 |
2019年 | 997篇 |
2018年 | 850篇 |
2017年 | 790篇 |
2016年 | 1174篇 |
2015年 | 1227篇 |
2014年 | 1447篇 |
2013年 | 1941篇 |
2012年 | 2249篇 |
2011年 | 2228篇 |
2010年 | 1587篇 |
2009年 | 1606篇 |
2008年 | 1807篇 |
2007年 | 1601篇 |
2006年 | 1437篇 |
2005年 | 1324篇 |
2004年 | 1104篇 |
2003年 | 879篇 |
2002年 | 983篇 |
2001年 | 742篇 |
2000年 | 550篇 |
1999年 | 478篇 |
1998年 | 397篇 |
1997年 | 341篇 |
1996年 | 298篇 |
1995年 | 237篇 |
1994年 | 221篇 |
1993年 | 163篇 |
1992年 | 158篇 |
1991年 | 148篇 |
1990年 | 119篇 |
1989年 | 84篇 |
1988年 | 73篇 |
1987年 | 46篇 |
1986年 | 52篇 |
1985年 | 48篇 |
1984年 | 26篇 |
1983年 | 23篇 |
1982年 | 18篇 |
1981年 | 20篇 |
1980年 | 11篇 |
1975年 | 7篇 |
1974年 | 6篇 |
1973年 | 5篇 |
1971年 | 5篇 |
1936年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
981.
982.
采用基于密度泛函理论的第一性原理研究了钪(Sc)、氧空位(OV)单/共掺杂锐钛矿相TiO2,对晶体结构、形成能以及电子结构进行了对比分析.研究结果表明,Sc-TiO2在富氧环境下缺陷形成能为负值,富钛环境下缺陷形成能为正值,表明Sc-TiO2只能在富氧环境下制备;OV-TiO2、Sc-OV-TiO2在富氧或富钛环境下缺陷形成能均为负值,但富氧环境下形成能更低;OV-TiO2的0/1-缺陷电荷转变能级为深能级,而Sc-TiO2的0/1-缺陷电荷转变能级则属于相对较浅能级;与纯锐钛矿相TiO2相比,Sc-TiO2的禁带宽度略有减小,但OV-TiO2、Sc-OV-TiO2禁带宽度变宽. 相似文献
983.
Ziheng Lu Fan Sui Yue-E Miao Guohua Liu Cheng Li Wei Dong Jiang Cui Tianxi Liu Junxiong Wu Chunlei Yang 《Journal of Energy Chemistry》2021,(7):170-197
Separators are indispensable components of modern electrochemical energy storage devices such as lithium-ion batteries (LIBs).They perform the critical function... 相似文献
984.
Lijun Cai Sarina Macfadyen Baozhen Hua Haochuan Zhang Wei Xu Yonglin Ren 《Molecules (Basel, Switzerland)》2022,27(6)
Monitoring and early detection of stored-grain insect infestation is essential to implement timely and effective pest management decisions to protect stored grains. We report a reliable analytical procedure based on headspace solid-phase microextraction coupled with gas chromatography–mass spectrometry (HS-SPME-GC-MS) to assess stored-grain infestation through the detection of volatile compounds emitted by insects. Four different fibre coatings were assessed; 85 µm CAR/PDMS had optimal efficiency in the extraction of analytes from wheat. The headspace profiles of volatile compounds produced by Tribolium castaneum (Herbst), Rhyzopertha dominica (Fabricius), and Sitophilus granarius (Linnaeus), either alone or with wheat, were compared with those of non-infested wheat grains. Qualitative analysis of chromatograms showed the presence of different volatile compound profiles in wheat with pest infestation compared with the wheat controls. Wheat-specific and insect-specific volatile compounds were identified, including the aggregation pheromones, dominicalure-1 and dominicalure-2, from R. dominica, and benzoquinones homologs from T. castaneum. For the first time, the presence of 3-hydroxy-2-butanone was reported from S. granarius, which might function as an alarm pheromone. These identified candidate biomarker compounds can be utilized in insect surveillance and monitoring in stored grain to safeguard our grain products in future. 相似文献
985.
The temperature and electrical field dependent conductivity of n-type CdSe nanocrystal thin films is investigated. In the low electrical field regime, the conductivity follows sigma approximately exp([-(T(*)/T)(1/2)] in the temperature range 10相似文献
986.
D形光纤Bragg光栅弯曲灵敏度的理论和实验研究 总被引:1,自引:1,他引:1
用材料力学理论分析了D形光纤Bragg光栅(D-shaped fiber Bragg grating,D-FBG)以及常规光纤Bragg光栅由弯曲引起的轴向应变,得到了光栅Bragg波长漂移的弯曲敏感特性.实验结果和理论计算结果基本相符.与常规FBG相比,该D-FBG的弯曲灵敏度要高近80倍.因此D-FBG可以直接应用于弯曲形变的测量,以及间接应用于压力、加速度等物理量的测量.理论分析和实验结果对采用该类型光纤光栅的器件和传感系统的设计具有参考意义. 相似文献
987.
采用Agilent 81910A光子全参量测试仪,首次实验研究了InP/In1-xGaxAs1-yPy-MQW(Multiple-Quantum-Well,MQW)材料与衬底间因应力而产生的M-Z型光调制器的PDL影响以及由此引起的由差分群时延(Differential Group Delay,DGD)表征的偏振模色散(Polarization Mode Dispersion,PMD).研究结果表明,半导体MQW光调制器的PDL与DGD是一致的.因此在半导体光器件的制作过程中,应尽可能地减小衬底与波导芯层之间的因残存应力的存在造成对光器件的高速性能的不利影响. 相似文献
988.
KBA显微镜是一种非轴对称、非共轴的掠入射成像系统。其结构复杂,调节精度要求很高,在实际成像实验操作中难以掌握其成像特性。利用光学设计软件模拟其成像,对系统的调节和成像分析提供有益的参考。利用光学设计软件ZEMAX模拟了KBA显微镜对点源的成像过程,给出了KBA显微镜成像系统的焦深约为1 mm,景深为50 mm左右。并且由模拟可知,掠入射角对成像的影响很大。对像素尺寸约10μm的探测设备,模拟得出KBA成像系统的空间分辨力上限为3μm左右。基于星光Ⅱ装置对周期为20μm的网格靶成像,获得了KBA显微镜较为清晰的X光图像。该项工作为进一步开展掠入射成像系统的研究奠定了基础。 相似文献
989.
Based on Jacobson's molecular free length theory in liquids and the relationship between ultrasonic velocity and the molecular free length in organic liquids, this paper deduces the equations for pressure coefficient and temperature coefficient of ultrasonic velocity and nonlinear acoustic parameter B/A in both of organic liquid and organic liquid binary mixtures. These nonlinear acoustic parameters are evaluated against the measured results and data from other sources. The equations reveal the connections between the nonlinear acoustic parameters and some internal structural of the medium or mixtures e.g. the sizes of molecule, several thermodynamic physical parameters and outside status e.g. condition of pressure and temperature of the liquid or liquid mixture. With the equations the nonlinear acoustic parameter B/A of organic liquid binary mixtures, which is impossible to know without the nonlinear acoustic parameter B/A of the tow components before, can be calculated based on the structural and physical parameters of organic liquid and organic liquid binary mixtures. 相似文献
990.
Nanocrystalline spinel ferrite thin films of CoxFe3−xO4 (x=0.3, 0.5, 0.8, and 1.0) have been prepared by RF sputtering on quartz substrate without a buffer layer at room temperature and annealed at the temperature range from 200 to 600 °C in air. The as-sputtered films exhibit the preferred orientation and the high magnetization and coercivity. After annealing, the preferred orientations become poor, but the magnetization and coercivity increase. The sample with a magnetization of 455 emu/cm3, a coercivity of 2.8 kOe, a remanence ratio of 0.72, and a maximum energy product of 2.4 MGOe has been obtained. The influence of Co ions and annealing temperature on the magnetic properties has been discussed. 相似文献