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   7245篇
  免费   1112篇
  国内免费   1575篇
化学   3010篇
晶体学   59篇
力学   615篇
综合类   7篇
数学   2595篇
物理学   3646篇
  2023年   10篇
  2022年   12篇
  2021年   15篇
  2020年   18篇
  2019年   9篇
  2018年   4篇
  2017年   13篇
  2016年   17篇
  2015年   22篇
  2014年   39篇
  2013年   127篇
  2012年   96篇
  2011年   141篇
  2010年   174篇
  2009年   368篇
  2008年   762篇
  2007年   1225篇
  2006年   1228篇
  2005年   868篇
  2004年   719篇
  2003年   569篇
  2002年   515篇
  2001年   470篇
  2000年   447篇
  1999年   348篇
  1998年   303篇
  1997年   282篇
  1996年   250篇
  1995年   217篇
  1994年   164篇
  1993年   153篇
  1992年   154篇
  1991年   119篇
  1990年   31篇
  1989年   20篇
  1988年   11篇
  1987年   7篇
  1985年   1篇
  1984年   1篇
  1983年   1篇
  1982年   1篇
  1976年   1篇
排序方式: 共有9932条查询结果,搜索用时 16 毫秒
1.
吴承康 《力学学报》2018,50(6):1279-1282
郭永怀先生是我国著名的力学家和应用数学家. 在美国留学和工作期间, 他耕耘在空气动力学前沿, 为跨声速流与应用数学做出贡献. 在回国工作的12 年间, 他积极参加规划我国力学发展蓝图, 培育力学人才, 是我国近代力学的奠基人; 他为我国原子弹、氢弹的研制贡献了全部心血乃至生命, 是我国核武器事业的先驱. 郭永怀先生热爱祖国、艰苦奋斗、谦虚质朴、无私奉献, 他学识渊博, 治学严谨, 是我国科技工作者的楷模.
郭永怀先生是《力学学报》第二任主编. 在他的主持下,《力学学报》从创刊初期就具有很高的学术起点和公正、严谨、求实的学术声誉. 这里我们向广大读者介绍郭先生的光辉一生, 并刊出他的学生们的一些论文, 以表达我们对这位主编的怀念和崇敬.   相似文献   
2.
Squaraines (SQs) with tunable emission in the solid state is of great importance for various demands; however a remaining challenge is emission quenching upon aggregation. Herein, a unique SQ, named as CIEE-SQ, is designed to exhibit strong emission in crystal, undergoing crystallization-induced reverse from dark 1(n+σ,π*) to bright 1(π,π*) excited states. Such an excited state of CIEE-SQ can be subtly tuned by molecular conformation changes during the unexpected temperature-triggered single-crystal to single-crystal (SCSC) reversible transformation. Furthermore, co-crystallization between CIEE-SQ and chloroform largely stabilize the 1(π,π*) state, enhancing the transition dipole moment and decreasing the reorganization energy to boost the fluorescence, which is promising in data encryption and decryption.  相似文献   
3.
An on-line solid phase extraction-high performance liquid chromatography-tandemmass spectrometry method for the analysis of perfluoroalkyl substances (PFASs) in water samples was developed. The optimal analytical conditions were obtained through the optimization of the extraction efficiency of online solid phase extraction column, sample loading rate and loading volume, and the concentration of ammonium acetate in mobile phase. Under the optimal condition, the analytical method displayed good linearity (r2 > 0.99) for 12 PFASs (C5-C14 perfluoroalkyl carboxylic acids and C6/C8 perfluoroalkyl sulfonic acids) over a concentration range of 0.5-100 ng/L. The limits of quantitation for samples were between 0.025 ng/L and 0.5 ng/L and the relative standard deviations (RSD) of five consecutive analyses were less than 10% for 1 ng/L standard solution. Satisfactory results were obtained using this analytical method for the analysis of perfluoroalkyl substances in Antarctic ice core samples. The recoveries of all perfluoroalkyl substances were in a range of 73%-117% when the sampleswere spiked with standards at the concentrations of 2.5 ng/L and 25 ng/L.  相似文献   
4.
滕旭东  郭霞生  章东 《声学学报》2019,44(6):1053-1059
弹性体材料在早期退化阶段会出现一些长度不同,且分布不均匀的介观尺度微裂纹,声波在这些裂纹聚集区(或裂纹群)传播会激发较强的非经典非线性。文中以缓变截面的锥棒为研究对象,在Preisach-Mayergoyz (PM)空间模型下研究了声波通过微裂纹聚集区激发的非经典非线性谐波传播特性,实验验证了三次谐波位移幅度与缺陷位置、宽度的反演关系。理论计算和实验结果表明:微裂纹群激发了较强的奇次谐波,引起非经典非线性传播;其谐波幅度与微裂纹聚集区域位置、宽度及非经典非线性参数紧密相关,利用三次或五次谐波位移幅度能够准确定位缺陷的区域。   相似文献   
5.
Cuprous chloride was coordinated by diazabutadiene (DAB‐R) ligands to form Cu(I)‐(DAB‐R) complexes, most of which have a 1:1 ratio of Cu to DAB‐R as reported. In the case of a special DAB‐iPP, N,N′‐bis(2,6‐diisopropylphenyl)‐1,4‐diaza‐1,3‐butadiene, an unexpected composition of complex was found with the formula Cu(I)Cl(DAB)2. When employed as catalyst for triarylamine synthesis from the coupling of aryl halides with primary and secondary arylamines, the new Cu(I)‐(DAB‐iPP) complex displayed high efficiency.  相似文献   
6.
主动隔振下固支薄板基础振动抑制的参数多目标优化   总被引:1,自引:0,他引:1  
考虑动力设备-隔振器-薄板基础为复合主动隔振体系,并将薄板视为固支形式;以传递力作用在薄板基础上某点导纳为中间变量,在传递力、导纳、薄板振动峰值位移及峰值点距离影响因素分析的基础上,进行了系统耦联参数的多目标优化研究。优化算法采用较新的强度Pareto进化算法(SPEA2),该算法具有参数设置少、收敛速度快、寻优能力强及Pareto最优解分布均匀等优点。目标函数考虑为薄板振动的位移峰值及峰值点间的距离,目的是在有效控制薄板振动的同时,尽可能地使薄板趋于单峰值点振动,这对于板上附属操作设备及工作人员是有利的;最后,在最优参数的基础上对隔振器的安装位置进行讨论研究。数值计算结果表明,本文方法可有效地计算出隔振系统的最优参数,并为工业建筑及其他工程振动的最优隔振设计提供新思路。  相似文献   
7.
刘少轩  彭实 《化学教育》2020,41(7):72-75
对中学化学学生实验活动中产生的气体污染物进行测试,得到不同通风条件下化学实验室内部空气污染物的数据。结果表明,中学化学学生分组实验产生的主要气体污染物有苯、甲苯、甲醛、氨气等,实验过程中如不采取任何通风措施,实验室气体污染物的浓度短时间内会急剧升高,所以采取有效措施对实验室内部空气污染物进行消除是非常必要的。目前中学化学实验室配备的通风设备以桌面排风设备为主,相比于自然通风的环境,学生实验时开启桌面排风设备,能够有效降低实验产生的气体污染物浓度。  相似文献   
8.
Journal of Thermal Analysis and Calorimetry - Sublimator offers effective heat rejection for the spacecraft, which work in warm environments or with peak heat loads, by evaporating or sublimating...  相似文献   
9.
The analytical infinite series solution of submicron particle transport in a circular tube bounded by a porous wall, such as a pinhole, is determined under the slip velocity boundary condition, and the solution is verified by using the experimental data in the previous studies for the specific cases. The results show that particle penetration rate increases with the increase of the porous parameter, the axial pressure drop, and the pinhole radius, whereas it decreases with increasing the pinhole length. The penetration rate of nano-particles are more sensitive to the variation of these parameters. However, the differences between the penetrations of particles ranging from 0.3 μm to 1 μm are not evident because the diffusion becomes weak gradually in this size range. In addition, a further comparison is performed between the analytical solution and the existing studies, and approximate expressions are presented for accurate calculation of particle penetration rate through pinholes appearing in porous materials including filter devices and masks.  相似文献   
10.
Using the characteristic of small energy difference between two high Rydberg states, we theoretically investigate the carrier envelope phase (CEP) effect in a bound-bound transition of an atom in a low-frequency long laser pulse with tens of optical cycles. Particularly, we first prepare a Rydberg state of a hydrogen-like atom by a laser field with the resonant frequency between this state and the ground state. Then by using a low-frequency long laser pulse interacting with this Rydberg atom, we calculate the population of another Rydberg state nearby this Rydberg state at the end of the laser pulse and find that the population changes dramatically with the CEP of the low-frequency pulse. This CEP effect is attributed to the interference between the positive-frequency and negative-frequency components in one-photon transition. These results may provide a method to measure the CEP value of a long laser pulse with low frequency.  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