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   512719篇
  免费   4149篇
  国内免费   1166篇
化学   241221篇
晶体学   6414篇
力学   28034篇
综合类   14篇
数学   75257篇
物理学   167094篇
  2021年   4035篇
  2020年   4438篇
  2019年   5145篇
  2018年   12626篇
  2017年   13182篇
  2016年   12477篇
  2015年   5871篇
  2014年   9393篇
  2013年   20812篇
  2012年   18825篇
  2011年   27313篇
  2010年   19239篇
  2009年   19533篇
  2008年   24500篇
  2007年   26765篇
  2006年   16119篇
  2005年   17898篇
  2004年   15102篇
  2003年   14043篇
  2002年   12818篇
  2001年   13565篇
  2000年   10057篇
  1999年   7522篇
  1998年   6413篇
  1997年   6209篇
  1996年   5857篇
  1995年   5354篇
  1994年   5289篇
  1993年   5149篇
  1992年   5533篇
  1991年   5970篇
  1990年   5691篇
  1989年   5667篇
  1988年   5374篇
  1987年   5571篇
  1986年   5209篇
  1985年   6603篇
  1984年   6675篇
  1983年   5626篇
  1982年   5714篇
  1981年   5426篇
  1980年   5229篇
  1979年   5726篇
  1978年   5878篇
  1977年   5855篇
  1976年   5961篇
  1975年   5568篇
  1974年   5514篇
  1973年   5704篇
  1972年   4237篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Physics of Atomic Nuclei - The muon puzzle is an excess of muon bundles generated by primary cosmic rays (PCR) at energies above 10 $${}^{17}$$ eV compared to estimations that assume even a heavy...  相似文献   
72.
Doklady Physical Chemistry - The rheological behavior of a 1 wt % suspension of highly porous chitosan particles in polydimethylsiloxane in a high electric field has been studied as a function of...  相似文献   
73.
Journal of Structural Chemistry - N-cyanomethylanabasine is prepared with an yield of 70% by the interaction of the alkaloid anabasine with glyconitrile. It is shown that the highest yield of the...  相似文献   
74.
Journal of Inclusion Phenomena and Macrocyclic Chemistry - Novel neodymium phthalocyaninates based on template condensation of 4-[(4-benzyloxy)phenoxy]- or...  相似文献   
75.
Ab initio calculations have been performed to investigate some of the spectroscopic properties, like geometry, frequency, electron affinity, ionization potential and finally adiabatic bond dissociation energies (BDEs) of lead monohalides, lead dihalides and their ions viz. PbX, PbX±, PbX2, PbX2± (X ?= ?F, Cl, Br, I) in their ground state at the QCISD(T)//MP2 level of theory using correlation consistent basis sets. For the validation of MP2 optimized geometry and frequency, we further obtained geometry and frequency of all the neutral and ionic systems using QCISD(T) method with the same basis sets. The BDEs of PbX2 molecules are calculated using the BDEs of PbX2± ions and taking ionization potential and electron affinity of various systems. The calculated values are found in good agreement with the available data. Most of the data for ionic systems are reported first time in literature.  相似文献   
76.
A facile biosynthesis route was followed to prepare zinc oxide nanoparticles (ZnO NPs) using Euphorbia milii (E. milii) leaf constituents. The SEM images exhibited presence of spherical ZnO NPs and the corresponding TEM images disclosed monodisperse nature of the ZnO NPs with diameter ranges between 12 and 20 nm. The Brunauer–Emmett–Teller (BET) analysis revealed that the ZnO NPs have specific surface area of 20.46 m2/g with pore diameter of 2 nm–10 nm and pore volume of 0.908 cm3/g. The EDAX spectrum exemplified the existence of Zn and O elements and non-appearance of impurities that confirmed pristine nature of the ZnO NPs. The XRD pattern indicated crystalline peaks corresponding to hexagonal wurtzite structured ZnO with an average crystallite size of 16.11 nm. The FTIR spectrum displayed strong absorption bands at 512 and 534 cm?1 related to ZnO. The photocatalytic action of ZnO NPs exhibited noteworthy degradation of methylene blue dye under natural sunlight illumination. The maximum degradation efficiency achieved was 98.17% at an illumination period of 50 min. The reusability study proved considerable photostability of the ZnO NPs during photocatalytic experiments. These findings suggest that the E. milii leaf constituents can be utilized as suitable biological source to synthesis ZnO NPs for photocatalytic applications.  相似文献   
77.
Atopic dermatitis is characterized by leukocyte migration into the skin dermis and typically driven by excessive chemokine production at the site of inflammation. Conventional topical formulations such as gels, creams, and ointments are insufficient for this treatment because of low penetration of drug molecules into the targeted skin tissues. Herein, using a simple, green, sustainable strategy, we have developed novel primary zein nanoparticles embedded in curcumin (Cur) and coated with silk sericin (ZHSCs) for the topical delivery of Cur to penetrate into the dermis and exercise anti-dermatitis effects on the lesion with minimal side-effects. Transdermal delivery experiments and porcine skin fluorescence imaging indicated that ZHSCs facilitate the penetration of Cur across the epidermis layer of skin to reach deep-seated sites. Notably, ZHSCs = 1:0.25 (zein-to-silk sericin mass ratios of 1:0.25) markedly elevated the skin permeability and cumulative turnover of Cur transferred, which were provided a greater than a 3.8-fold increase relative to free Cur. The special nanoparticles of ZHS = 1:0.25 possessed the deepest localization depth and experience a transition of the particle structure and core-shell separation after penetrating into the dermis of skin. In a cell model of dermatitis induced by tumor necrosis factor α/interferon γ co-stimulation, compared with free Cur, Cur-loaded ZHS nanoparticles down-regulated the generation of inflammatory cytokines and chemokines in keratinocytes through suppression of the nuclear translocation of NF-κBp65 and hence exerted an anti-dermatitis effect. This strategy may provide new avenues and direction for the demanding issues of valid topical delivery systems.  相似文献   
78.
Journal of Applied Mechanics and Technical Physics - The physical grounds of droplet breakup in a flow behind an incident shock wave in accordance with one of possible sheet stripping...  相似文献   
79.
Crystallography Reports - The review is devoted to the current state of affairs and prospects for development in the field of neutron reflectometry on the existing and future neutron sources in the...  相似文献   
80.
Journal of Applied Mechanics and Technical Physics - Theoretical results obtained within the framework of the weakly nonlinear model of a developed boundary layer in a flow past a...  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