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   304765篇
  免费   1778篇
  国内免费   648篇
化学   146362篇
晶体学   4470篇
力学   15082篇
综合类   6篇
数学   46489篇
物理学   94782篇
  2020年   1970篇
  2019年   2265篇
  2018年   10953篇
  2017年   11674篇
  2016年   7997篇
  2015年   3113篇
  2014年   3931篇
  2013年   9372篇
  2012年   10878篇
  2011年   19880篇
  2010年   12516篇
  2009年   12561篇
  2008年   17831篇
  2007年   21219篇
  2006年   7819篇
  2005年   12974篇
  2004年   9270篇
  2003年   8885篇
  2002年   6852篇
  2001年   6097篇
  2000年   4994篇
  1999年   3508篇
  1998年   3054篇
  1997年   3052篇
  1996年   2992篇
  1995年   2426篇
  1994年   2503篇
  1993年   2530篇
  1992年   2666篇
  1991年   2730篇
  1990年   2634篇
  1989年   2617篇
  1988年   2556篇
  1987年   2524篇
  1986年   2436篇
  1985年   3121篇
  1984年   3298篇
  1983年   2652篇
  1982年   2917篇
  1981年   2796篇
  1980年   2592篇
  1979年   2825篇
  1978年   2953篇
  1977年   2889篇
  1976年   2897篇
  1975年   2739篇
  1974年   2714篇
  1973年   2900篇
  1972年   1912篇
  1967年   1868篇
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
991.
A combined-modality treatment program consisting of botulinum toxin injection (Botox) and voice therapy was used to treat 17 subjects diagnosed with adductor spasmodic dysphonia (ADD SD). Ten subjects with ADD SD served as the control and were given Botox only. Voice therapy after Botox injection was directed toward reducing the hyperfunctional vocal behaviors, primarily glottal overpressure at voice onset and anterior-posterior squeezing. The results indicated that subjects who underwent combined-modality treatment maintained significantly higher mean airflow rates for significantly longer periods. Moreover, there was a carryover effect in these patients when they received Botox only. Adductor spasmodic dysphonia is treated most effectively when intrinsic laryngeal muscle spasms are reduced or eliminated by Botox injection and extrinsic hyperfunctional vocal behaviors are treated with voice therapy  相似文献   
992.
993.
994.
Formulas for shifts of gyrotron autooscillation frequency due to change of electron beam parameters are presented. The frequency shifts can be commensurable with the frequency band of the beam-unloaded cavity. The autooscillation frequency is most sensitive to the change of the magnetic field, less to the change of the anode voltage and least to the the change of the beam voltage. Experiments presented are in satisfactory agreement with the theory.The authors wish to thank M.I. Petelin for his interest to the present work.  相似文献   
995.
The methyl 2,6-diphenyl-1-methyl-4-oxopiperidine-3,5-dicarboxylates 1 were synthesized by the Mannich procedure from methyl 3-oxoglutarate, benzaldehyde and methylamine. Keto-enol tautomerism as well as configurational isomerism at C-2 were observed. The stereochemistry of the Ib and Ic enolic forms were determined by 1H and 13C nmr data.  相似文献   
996.
997.
The results of the experimental investigation of the radiation amplification due to the stimulated four-photon parametric process in potassium vapor are reported. Two cells with active medium (an oscillatoramplifier system) are used in the experiments. The dominating role of IR radiation 6S → 5P (3.66 µm) in the amplification of violet radiation 5P → 4S (0.4 µm) generated due to the parametric process at two-photon excitation 4S → 6S is shown. This role is conditioned by optically pumped stimulated emission (OPSE). Optical conditions for the amplification of a seed radiation are determined in accordance with their intensity and the buffer gas (He) pressure. The problem of the image conversion from the IR to a visible one with quantum efficiency above 100% is discussed.  相似文献   
998.
Studies show that branching the side chains of hexakis(acoyloxy)-benzenes (HAB) and -cyclohexanes (HAChx) does not modify the structure of the discotic mesophase formed. Shear fields appear to act on entire columns, not on individual discs, thereby causing alignment of columns in the shear direction. X-ray diffraction patterns of samples at temperatures between 30°C and 40°C above the clearing temperature provide evidence for the presence of mesophase order.  相似文献   
999.
We study numerically the Riemann problem for a 2 x 2 system of conservation laws with a cubic flux function, a particular case of the class of models introduced by Keyfitz and Kranzer. The system is not strictly hyperbolic, and the classical Lax theory for hyperbolic systems is not directly applicable. Correspondingly, some numerical schemes which are accurate for strictly hyperbolic systems are not well behaved for this example. When they do work, different schemes yield markedly different results for certain data. We explain this effect by observing that, near these data, viscous regularization is non-uniform as the viscosity tends to zero. This fact does not contradict the well-posedness of the hyperbolic model; it does imply that precise control of the viscosity introduced into a computational method is crucial for generating the correct numerical solutions. We examine all of these issues and comment on their implications for similar systems which arise in continuum mechanics.  相似文献   
1000.
Differential cross sections of nucleons excited in photonuclear reactions in medium and heavy nuclei are studied by considering all relevant reaction mechanisms leading to the excitation of protons or neutrons. We take advantage of previous microscopic studies for the absorption and scattering of photons and photoproduced pions, and implement a simulation code in order to take into account the propagation of the nucleons as well as their collisions with other nucleons in the nuclear medium, which generate secondary excited nucleons. Comparison with experimental data is done. Cross sections for nucleon emission in coincidence with one pion are also calculated, and some coincidence observables are discussed.  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