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   2093篇
  免费   29篇
  国内免费   160篇
化学   1061篇
晶体学   41篇
力学   19篇
综合类   31篇
数学   1055篇
物理学   75篇
  2024年   2篇
  2023年   14篇
  2022年   11篇
  2021年   3篇
  2020年   20篇
  2019年   28篇
  2018年   31篇
  2017年   45篇
  2016年   15篇
  2015年   17篇
  2014年   62篇
  2013年   229篇
  2012年   55篇
  2011年   113篇
  2010年   133篇
  2009年   127篇
  2008年   133篇
  2007年   151篇
  2006年   131篇
  2005年   145篇
  2004年   137篇
  2003年   106篇
  2002年   76篇
  2001年   36篇
  2000年   63篇
  1999年   41篇
  1998年   40篇
  1997年   28篇
  1996年   51篇
  1995年   32篇
  1994年   44篇
  1993年   28篇
  1992年   26篇
  1991年   11篇
  1990年   6篇
  1989年   11篇
  1988年   16篇
  1987年   11篇
  1986年   8篇
  1985年   5篇
  1984年   6篇
  1982年   6篇
  1981年   4篇
  1980年   7篇
  1979年   7篇
  1978年   4篇
  1977年   2篇
  1976年   2篇
  1973年   1篇
  1972年   1篇
排序方式: 共有2282条查询结果,搜索用时 0 毫秒
31.
Ideal Topology on Effect Algebras   总被引:2,自引:0,他引:2  
The ideals of effect algebras induce a topology on effect algebras. The operations and of effect algebras are continuous with respect to this topology.  相似文献   
32.
The fragmentation of the Isoscalar Giant Quadrupole Resonance (ISGQR) in 40Ca has been investigated in high energy-resolution experiments using proton inelastic scattering at Ep=200 MeVEp=200 MeV. Fine structure is observed in the region of the ISGQR and its characteristic energy scales are extracted from the experimental data by means of a wavelet analysis. The experimental scales are well described by Random Phase Approximation (RPA) and second-RPA calculations with an effective interaction derived from a realistic nucleon–nucleon interaction by the Unitary Correlation Operator Method (UCOM). In these results characteristic scales are already present at the mean-field level pointing to their origination in Landau damping, in contrast to the findings in heavier nuclei and also to SRPA calculations for 40Ca based on phenomenological effective interactions, where fine structure is explained by the coupling to two-particle–two-hole (2p–2h) states.  相似文献   
33.
Young′s moduli of various epoxy coated polyethylene terephthalate (PET) micro-cantilevers were determined from the deflection results obtained using the phase-shift shadow moiré (PSSM) method. The filler materials for epoxy coatings were aluminum and graphite powders that were mixed with epoxy at various percentages. Young′s moduli were calculated from theory based on the deflection results. The PET micro-cantilever coated with aluminum-epoxy coating showed increasing value of Young′s modulus when the ratios of the aluminum-epoxy were increased. The graphite-epoxy coating on the PET micro-cantilever also showed the same trend. The experimental results also show that Young′s modulus of the graphite-epoxy coating is higher than aluminum-epoxy coating in comparison at the same mixing ratio.  相似文献   
34.
Antimicrobial property of chalcone coated high density polyethylene (HDPE), low density polyethylene (LDPE), polypropylene (PP) and polyurethane (PU) against Staphylococcus aureus, Escherichia coli and Pseudomonas aeruginosa is reported here. The presence of chalcone on the surface was confirmed from fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Bacterial adhesion decreased considerably on all the coated surfaces. Bacterial adhesion was highest on PU surface (most hydrophobic) and lowest on HDPE (most hydrophilic) surface. Chalcone seems to damage the membrane of the bacteria as well as exhibit slimicidal activity. Reasonably good correlation was observed between the CFU (Colony Forming Units) ratio (it is defined as the ratio of CFU on coated surface to the chalcone uncoated surface) at the 24th hour against both hydrophobicity of the microorganism and roughness of the coated polymeric surfaces. Increasing roughness of the polymer and hydrophobicity of the microorganisms were positively and negatively correlated respectively with CFU ratio. Hence, the chalcone coated polymers can be used in the development of newer biomaterials.  相似文献   
35.
We report the formation of β′-Gd2(MoO4)3 (GMO) crystal on the surface of the 21.25Gd2O3-63.75MoO3-15B2O3 glass, induced by 250 kHz, 800 nm femtosecond laser irradiation. The morphology of the modified region in the glass was clearly examined by scanning electron microscopy (SEM). By micro-Raman spectra, the laser-induced crystals were confirmed to be GMO phases and it is found that these crystals have a strong dependence on the number and power of the femtosecond laser pulses. When the irradiation laser power was 900 mW, not only the Raman peaks of GMO crystals but also some new peaks at 214 cm−1, 240 cm−1, 466 cm−1, 664 cm−1 and 994 cm−1which belong to the MoO3 crystals were observed. The possible mechanisms are proposed to explain these phenomena.  相似文献   
36.
在[1]中A.Hopenwasser讨论了Nest代数的一类超凝聚理想,称为Hopenwasser理想,本文将给出这类理想的距离公式,这个结果一般化为[2]中的距离公式.特别地,我们得到了Nest代数的Jacobson根和Larson强根的距离公式.  相似文献   
37.
粗糙子群和粗糙子环   总被引:3,自引:0,他引:3  
文[1]研究了半群中的理想,首次提出了粗半群和粗理想的概念.本文继续研究了群中的粗糙子群和粗正规子群.同时,在环中引入了粗子环的概念.最后,研究了粗糙集的同态问题.  相似文献   
38.
39.
This paper first found the co-luminescence effect of guanosine-5′-monophosphate (GMP) system. Experiment showed that La3+, Gd3+, Sc3+ and Y3+ all could enhance the luminescence of Tb-GMP system, among which Gd3+ has the greatest enhancement. Under the optimum conditions, the enhanced intensity of the system is in proportion to the concentration of GMP in the range from 3×10−8 to 3×10−5 mol/l. The detection limit is 3.9×10−9 mol/l. In the study of mechanism, we propose that both Tb and Gd complexes can form bigger netlike compound by the link of the oxygen bridge, through which the energy absorbed by Gd complex may transfer to Tb3+ in Tb complex.  相似文献   
40.
For a ring R, endomorphism α of R and positive integer n we define a skew triangular matrix ring T n (R, α). By using an ideal theory of a skew triangular matrix ring T n (R, α) we can determine prime, primitive, maximal ideals and radicals of the ring R[x; α]/ ? x n  ?, for each positive integer n, where R[x; α] is the skew polynomial ring, and ? x n  ? is the ideal generated by x n .  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