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   404231篇
  免费   9021篇
  国内免费   5544篇
化学   208522篇
晶体学   6284篇
力学   20314篇
综合类   329篇
数学   48718篇
物理学   134629篇
  2022年   3802篇
  2021年   4869篇
  2020年   5237篇
  2019年   5753篇
  2018年   7323篇
  2017年   7389篇
  2016年   10000篇
  2015年   6206篇
  2014年   9859篇
  2013年   19919篇
  2012年   16626篇
  2011年   19169篇
  2010年   14379篇
  2009年   14311篇
  2008年   16815篇
  2007年   16487篇
  2006年   15172篇
  2005年   13207篇
  2004年   12234篇
  2003年   10815篇
  2002年   10926篇
  2001年   12390篇
  2000年   9227篇
  1999年   7273篇
  1998年   6239篇
  1997年   5872篇
  1996年   5522篇
  1995年   4741篇
  1994年   4765篇
  1993年   4553篇
  1992年   4891篇
  1991年   5132篇
  1990年   4911篇
  1989年   4744篇
  1988年   4415篇
  1987年   4528篇
  1986年   4323篇
  1985年   5276篇
  1984年   5316篇
  1983年   4445篇
  1982年   4490篇
  1981年   4174篇
  1980年   4100篇
  1979年   4448篇
  1978年   4423篇
  1977年   4418篇
  1976年   4442篇
  1975年   4192篇
  1974年   4210篇
  1973年   4223篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
Plasma Chemistry and Plasma Processing - The hydrocarbons present in diesel exhaust, although treated as minor pollutants, are equivalent to some of the major pollutants in terms of toxicity,...  相似文献   
102.
Physics of Particles and Nuclei Letters - The Silicon Photomultiplier (SiPM) is a novel semiconducting photodetector which can detect single photons. It consists of many microcells (pixels)...  相似文献   
103.
Yu  Tian-Jun  Zhou  Sha  Yang  Xiao-Dong  Zhang  Wei 《Nonlinear dynamics》2018,91(2):1041-1060
Nonlinear Dynamics - Global dynamics of a flexible asymmetrical rotor resting on vibrating supports is investigated. Hamilton’s principle is used to derive the partial differential governing...  相似文献   
104.
Research on Chemical Intermediates - Recorded IR and Raman spectra of 5-fluoro-uracil have been analyzed with the carried out theoretical computation by Gaussian-09 [DFT/B3LYP/6-311?++G**]...  相似文献   
105.
A simple and efficient nitrile-directed meta-C−H olefination, acetoxylation, and iodination of biaryl compounds is reported. Compared to the previous approach of installing a complex U-shaped template to achieve a molecular U-turn and assemble the large-sized cyclophane transition state for the remote C−H activation, a synthetically useful phenyl nitrile functional group could also direct remote meta-C−H activation. This reaction provides a useful method for the modification of biaryl compounds because the nitrile group can be readily converted to amines, acids, amides, or other heterocycles. Notably, the remote meta-selectivity of biphenylnitriles could not be expected from previous results with a macrocyclophane nitrile template. DFT computational studies show that a ligand-containing Pd–Ag heterodimeric transition state (TS) favors the desired remote meta-selectivity. Control experiments demonstrate the directing effect of the nitrile group and exclude the possibility of non-directed meta-C−H activation. Substituted 2-pyridone ligands were found to be key in assisting the cleavage of the meta-C−H bond in the concerted metalation–deprotonation (CMD) process.  相似文献   
106.
Russian Chemical Bulletin - The study is concerned with structural rearrangements in the crystals of heterospin complexes Cu(hfac)2 with nitroxide radicals LR (hfac is hexafluoroacetylacetonate, LR...  相似文献   
107.
In this work, we have used the MuMax3 software to simulate devices consisting of a ferromagnetic thin film placed over a heavy metal thin film. The devices are two interconnected partial-disks where a Néel domain wall is formed in the disks junction. In our simulations we investigate devices with disk radius r=50 nm and different distance d between the disks centers (from d=12 nm to d=2R=100 nm). By applying strong sinusoidal external magnetic fields, we find a mechanism able to create, annihilate and even manipulate a skyrmion in each side of the device. This mechanism is discussed in terms of interactions between skyrmion and domain wall. The Néel domain wall formed in the center of the device interacts with the Néel skyrmion, leading to a process of transporting a skyrmion from one disk to the other periodically. Our results have relevance for potential applications in spintronics such as logical devices.  相似文献   
108.
Gurbatov  S. N.  Pelinovsky  E. N. 《Doklady Physics》2020,65(8):269-272
Doklady Physics - In this paper, we study the statistical characteristics of the Riemann wave and the integral of it. Such problems arise in the physics of fronts’ propagation, in particular,...  相似文献   
109.
110.

The behavior of group-4 homologs Zr and Hf on extraction-chromatographic sorbents LN resin and TRU resin in mixtures of HF and HNO3 is considered. Distribution coefficients of the elements in the mixtures of 5·10−4 M–1 M HF and 0.01 M–5 M HNO3 are determined. Strong retention of both elements was found on LN resin in the range of concentrations c(HF) ≤ 0.01 M for all concentrations of HNO3. Retention tends to gradually disappear while increasing c(HF) to 0.5 M. On TRU resin retention is observed only in solutions with c(HNO3) ≥ 2 M and c(HF) ≤ 0.01 M. The possibility of separating Zr(IV) and Hf(IV) on LN resin is illustrated in two different acid mixtures, whereas their separation on TRU resin under the conditions studied in this work is difficult. The results obtained can be used to isolate analytes from multicomponent mixtures during analytical tasks, as well as to separate them from each other.

  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