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   298162篇
  免费   2255篇
  国内免费   517篇
化学   142491篇
晶体学   5008篇
力学   14787篇
综合类   11篇
数学   43274篇
物理学   95363篇
  2020年   1720篇
  2019年   1918篇
  2018年   10842篇
  2017年   11726篇
  2016年   7479篇
  2015年   3042篇
  2014年   3673篇
  2013年   9200篇
  2012年   10767篇
  2011年   20318篇
  2010年   12679篇
  2009年   12768篇
  2008年   17528篇
  2007年   21026篇
  2006年   6886篇
  2005年   12779篇
  2004年   8901篇
  2003年   8439篇
  2002年   6266篇
  2001年   6298篇
  2000年   4933篇
  1999年   3559篇
  1998年   2791篇
  1997年   2720篇
  1996年   2755篇
  1995年   2533篇
  1994年   2415篇
  1993年   2239篇
  1992年   2894篇
  1991年   2798篇
  1990年   2743篇
  1989年   2769篇
  1988年   2798篇
  1987年   2802篇
  1986年   2665篇
  1985年   3387篇
  1984年   3413篇
  1983年   2693篇
  1982年   2794篇
  1981年   2851篇
  1980年   2620篇
  1979年   2976篇
  1978年   2976篇
  1977年   3009篇
  1976年   2878篇
  1975年   2605篇
  1974年   2559篇
  1973年   2552篇
  1972年   1740篇
  1968年   1799篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
911.
A method of synthesis of acetylacetonated humin-like compounds was developed. The effect of modification on the sorption capacity of humin-like compounds with respect to heavy metals was studied.  相似文献   
912.
High-frequency characteristics of CoFeVAlONb thin films were studied. A thin film of Co43.47Fe35.30V1.54Al5.55O9.93Nb4.21 is observed to exhibit excellent magnetic properties; magnetic coercivity of 1.24 Oe, uniaxial in-plane anisotropy field of 66.99 Oe, and saturation magnetization of 19.8 kG. The effective permeability of the film is as high as 1089 and is stable up to 1.8 GHz, and with ferromagnetic resonance over 3 GHz. This film also has very high electrical resistivity of about 628 μΩ cm. These superior properties make it ideal for high-frequency magnetic applications.  相似文献   
913.
To explain line broadening in emission Mössbauer spectra as compared to the corresponding absorber measurements, the model of trapped electrons has been proposed. Auger electrons (emitted, e.g. after electron capture by 57Co or after the converted isomeric transition of 119mSn), as well as secondary electrons, may be trapped in the proximity to the nucleogenic ion. Electrons captured by lattice traps at different distances from the daughter ion induce an asymmetric distribution of quadrupole splitting in the resulting emission spectra, as shown in a few examples. This model is supported by estimates of quadrupole splitting values which may be caused by such trapped electrons located at specified distances from the nucleogenic atom.  相似文献   
914.
C Dufour  K Dumesnil  P H Mangin 《Pramana》2006,67(1):173-190
Rare earths exhibit complex magnetic phase diagrams resulting from the competition between various contributions to the magnetic energy: exchange, anisotropy and magnetostriction. The epitaxy of a rare-earth film on a substrate induces (i) a clamping to the substrate and (ii) pseudomorphic strains. Both these effects are shown to lead to modifications of the magnetic properties in (0 0 1)Dy, (0 0 1)Tb and (1 1 0)Eu films. In Dy and Tb films, spectacular variations of the Curie temperature have been evidenced. Additionally, Tb films exhibit a new large wavelength magnetic modulation. In Eu films, one of the helical magnetic domains disappears at low temperature whereas the propagation vectors of the other helices are tilted. The link between structural and magnetic properties is underlined via magnetoelastic models. Moreover, molecular beam epitaxy permits the growth of Sm in a metastable dhcp phase. The magnetic structure of dhcp Sm has been elucidated for the first time. In this review, neutron scattering is shown to be a powerful technique to reveal the magnetic structures of rare-earth films.  相似文献   
915.
This is summary of the activities of the working group on collider physics in the IXth Workshop on High Energy Physics Phenomenology (WHEPP-9) held at the Institute of Physics, Bhubaneswar, India in January 2006. Some of the work subsequently done on these problems by the subgroups formed during the workshop is included in this report.  相似文献   
916.
P. K. Sahu  N. Otuka  M. Isse  Y. Nara  A. Ohnishi 《Pramana》2006,66(5):809-816
We analyze the spectra of pions and protons in heavy-ion collisions at relativistic energies from 2 A GeV to 65+65 A GeV by using a jet-implemented hadron-string cascade model. In this energy region, hadron transverse mass spectra first show softening until SPS energies, and re-hardening may emerge at RHIC energies. Since hadronic matter is expected to show only softening at higher energy densities, this re-hardening of spectra can be interpreted as a good signature of the quark-gluon plasma formation  相似文献   
917.
918.
919.
The stannous chloride dihydrate-mediated deprotection-bicyclisation of a range of amides possessing a pendant acetal group is reported. These mild reaction conditions have been used to prepare a number of ring-fused heterocyclic compounds, some in enantiomerically pure form, which should be of interest both in their own right and as building blocks for the production of more complex target molecules.  相似文献   
920.
This paper provides a quantitative and comparative economic and risk approach to strategic quality control in a supply chain, consisting of one supplier and one producer, using a random payoff game. Such a game is first solved in a risk-neutral framework by assuming that both parties are competing with each other. We show in this case that there may be an interior solution to the inspection game. A similar analysis under a collaborative framework is shown to be trivial and not practical, with a solution to the inspection game being an ‘all or nothing’ solution to one or both the parties involved. For these reasons, the sampling random payoff game is transformed into a Neyman–Pearson risk constraints game, where the parties minimize the expected costs subject to a set of Neyman–Pearson risk (type I and type II) constraints. In this case, the number of potential equilibria can be large. A number of such solutions are developed and a practical (convex) approach is suggested by providing an interior (partial sampling) solution for the collaborative case. Numerical examples are developed to demonstrate the procedure used. Thus, unlike theoretical approaches to the solution of strategic quality control random payoff games, the approach we construct is both practical and consistent with the statistical risk Neyman–Pearson approach.  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