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   30441篇
  免费   5617篇
  国内免费   3297篇
化学   21877篇
晶体学   351篇
力学   1800篇
综合类   143篇
数学   3015篇
物理学   12169篇
  2024年   93篇
  2023年   668篇
  2022年   920篇
  2021年   1191篇
  2020年   1392篇
  2019年   1352篇
  2018年   1133篇
  2017年   1007篇
  2016年   1567篇
  2015年   1457篇
  2014年   1889篇
  2013年   2327篇
  2012年   2840篇
  2011年   2891篇
  2010年   1898篇
  2009年   1801篇
  2008年   2013篇
  2007年   1781篇
  2006年   1656篇
  2005年   1295篇
  2004年   993篇
  2003年   769篇
  2002年   771篇
  2001年   606篇
  2000年   479篇
  1999年   603篇
  1998年   517篇
  1997年   507篇
  1996年   499篇
  1995年   435篇
  1994年   349篇
  1993年   287篇
  1992年   287篇
  1991年   229篇
  1990年   204篇
  1989年   152篇
  1988年   93篇
  1987年   79篇
  1986年   104篇
  1985年   73篇
  1984年   37篇
  1983年   45篇
  1982年   28篇
  1981年   22篇
  1980年   7篇
  1979年   2篇
  1976年   1篇
  1975年   1篇
  1957年   4篇
  1923年   1篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
Based on the quantum fluctuations, we adopt the method of generalized V1 criterion to investigate multipartite entanglement characteristics in an optical parametric amplification system with the consideration of dispersion. The nonlinear interaction becomes strong because of the existence of dispersion coefficient σ. Considering the influence of dispersion factor σ, with increasing the pump parameter μ, the value of minimum variance V1 decreases and the squeezing curve nearly equals 1/(1 + μ). The larger particle number N results in a smaller variance and higher entanglement.  相似文献   
32.
Guided by the self-penetrating features can improve the stability of metal organic frameworks (MOFs), an unprecedented 3D self-penetrated framework, {[Zn (tptc)0.5(bimb)]·H2O}n ( NUC-6 , here NUC corresponding to North University of China), with 3D (4,4)-c {86} net, was designed. Benefit from the high chemical stability and excellent luminescent property, NUC-6 can be act as an efficient multi-response chemo-sensor in detecting dichloronitroaniline pesticide and nitrofuran antibiotics in water with the detection limits are 116 ppb for DCN pesticide, 16 ppb for NFT antibiotic, and 12 ppb for NTZ antibiotic. Besides, the mechanisms of luminescence quenching were revealed from the viewpoint of internal filter effect (IFE) and photo-induced electron transfer (PET), implied by the optical spectroscopy and quantum chemical calculation. This work provides a promising strategy to design stable MOFs by improving the self-penetrating features and to expand their practical applications in the detection of organic pollutants in aqueous medium.  相似文献   
33.
Huang  Jian  Cen  Zhongdi  Xu  Aimin  Liu  Li-Bin 《Numerical Algorithms》2020,83(2):549-563
Numerical Algorithms - A singularly perturbed Volterra integro-differential equation with an integrable singularity in the integral term is considered. The upwind difference method is used to...  相似文献   
34.
35.
36.
37.
Shi  D.  Feng  J.  Wang  J.  Zhao  W.  Li  X. 《Kinetics and Catalysis》2020,61(5):750-757
Kinetics and Catalysis - A series of Cu-SSZ-13@CeO2 catalysts with surface modification with CeO2 was prepared by the modified self-resemble method based on the one-pot synthesized Cu-SSZ-13...  相似文献   
38.
The intermolecular interaction determines the photophysical properties of the organic aggregates, which are critical to the performance of organic photovoltaics. Here, excitonic coupling, an important intermolecular interaction in organic aggregates, between the π-stacking graphene quantum dots is studied by using transient absorption spectroscopy. We find that the spectral evolution of the ground state bleach arises from the dynamic variation of the excitonic coupling in the excited π-stacks. According to the spectral simulations, we demonstrate that the kinetics of the vibronic peak can be exploited as a probe to measure the dynamics of excitonic coupling in the excited π-stacks.  相似文献   
39.
Eucommia ulmoides Oliv. (E. ulmoides) is a valuable and nourishing medicinal herb in China that has been used in the treatment of hypertension. Given the fact that most traditional Chinese medicine is mainly used to treat disease, investigating the pharmacokinetics of traditional Chinese medicines in the pathological state is more useful than that in the normal state. However, the differences in the absorption kinetics of active ingredients of E. ulmoides extract between pathological and physiological conditions have not been reported. Therefore, in this study, the rat intestinal in situ circulatory perfusion model was used to investigate the differences in absorption kinetics of seven active ingredients of E. ulmoides extract in normal and spontaneously hypertensive rats, namely, genipinic acid, protocatechuic acid, neochlorogenic acid, chlorogenic acid, cryptochlorogenic acid, (+)-pinoresinol di-O-β-D -glucopyranoside and (+)-pinoresinol 4′-O-β-D -glucopyranoside. Our results indicate that the pathological state of spontaneous hypertension may change the absorption of active components of E. ulmoides extracts, and these findings may provide a reference for improving the rational use of E. ulmoides in the clinic.  相似文献   
40.
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