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901.
Reduction of tetranuclear heterometallic complex Mo2Mg2 was simulated using the B3LYP and PBE density functional methods. The results of geometry calculations of the initial complex
[MoVIO2Mg(MeOH)2(OMe)4]2 and a partially reduced MoV complex are in good agreement with experimental data. The reduced MoIII complex is characterized by a decrease in the binding energy of aqua ligands. Structural rearrangement of the complex with
release of a coordination position at the Mo atoms requires small energy expenditure. One can assume that the reduction of
the polynuclear complex causes overcrowding of its coordination sphere, which favors formation of dinitrogen complexes.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 441–457, March, 2008. 相似文献
902.
李凡 《贵州师范大学学报(社会科学版)》2007,(4):90-94
当前,美国深陷伊拉克战争泥潭,有人提出美实力地位正发生由盛转衰的变化.通过分析可知美国硬实力仍举世无双,软实力在世界各地仍具有重要影响,而美国创新机制和自我修复能力为美提供巨大的力量来源.在未来较长时间内美国仍将保持一超独霸地位.另一方面,世界各国对美国更加缺乏信任,伊拉克战争大大销蚀美实力等,都构成了美国实力的局限.鉴此,美国不得不加强国际合作,承担相应国际责任,外交政策最终向现实主义回归. 相似文献
903.
生姜增产技术及病害的防治 总被引:1,自引:0,他引:1
杨春文 《甘肃联合大学学报(自然科学版)》2007,21(6):53-56
研究了催芽大小,遮荫程度,常用肥料-氮、磷、钾肥、微肥-锌、硼、植物激素-乙烯利和绿植灵对生姜的增产作用及生姜常见病害--姜瘟病、班点病和炭疽病的症状,病原、传播途径、发病条件及防治方法. 相似文献
904.
This paper studies the problem of uniformly dissipative solutions of somefifth order non-linear differential equations by the use of frequency domaintechnique. We use the generalized theorem of Yacubovich on dissipativity toobtain some new sufficient conditions of the existence of solutions that aredissipative for (1.1) and (1.2). 相似文献
905.
Titanium tetrachloride promoted reaction of silyl ketene acetals with epoxides, followed by acidic work-up, affords butanolides in moderate/good yields. With epihalohydrins the reaction is regioselective and occurs at the less substituted end of the epoxide; the γ-haloalkyl-γ-butanolides thus obtained can be further transformed into various products. 相似文献
906.
Three new tetracyclic diterpenes were isolated from the chloroform-soluble extract of Euphorbia villosa, together with one new and one known lathyrane diterpene. The structures were elucidated by means of various spectroscopic methods, including HREI-MS, HRFAB-MS, UV, and 1D and 2D NMR techniques. Spectral analyses revealed that two of the tetracyclic compounds contain the rare 5-6-6-4 fused ring system, while the third has a 5-6-7-3 fused diterpene core. Such diterpene skeletons have previously been found only in euphoractines A-E isolated from Euphorbia micractina. As a new structural feature, the diterpene framework described here has a C-2 epimer configuration. The new lathyrane diterpene is a diester of a hitherto unknown polyfunctional parent alcohol. 相似文献
907.
A new numerical method called linearized and rational approximation method is presented to solve non‐linear evolution equations. The utility of the method is demonstrated for the case of differentiation of functions involving steep gradients. The solution of Burgers' equation is presented to illustrate the effectiveness of the technique for the solution of non‐linear evolution equations exhibiting nearly discontinuous solutions. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
908.
This paper presents the applications of digital image correlation technique to the mesoscopic damage and fracture study of
some granular based composite materials including steelfiber reinforced concrete, sandstone and crystal-polymer composite.
The deformation fields of the composite materials resulted from stress localization were obtained by the correlation computation
of the surface images with loading steps and thus the related damage prediction and fracture parameters were evaluated. The
correlation searching could be performed either directly based on the gray levels of the digital images or from the wavelet
transform (WT) coefficients of the transform spectrum. The latter was developed by the authors and showed higher resolution
and sensitivity to the singularity detection. Because the displacement components came from the rough surfaces of the composite
materials without any coats of gratings or fringes of optical interferometry, both surface profiles and the deformation fields
of the composites were visualized which was helpful to compare each other to analyze the damage of those heterogeneous materials.
The project supported by the National Natural Science Foundation of China (10125211 and 10072002), the Scientific Committee
of Yunnan Province for the Program of Steel Fiber Reinforced Concrete, and the Institute of Chemical Materials, CAEP at Mianyang 相似文献
909.
S. Han H. Kühn F. W. Hsing K. Münnemann B. Blümich S. Appelt 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2004,167(2):187
We have visualized the melting and dissolution processes of xenon (Xe) ice into different solvents using the methods of nuclear magnetic resonance (NMR) spectroscopy, imaging, and time resolved spectroscopic imaging by means of hyperpolarized 129Xe. Starting from the initial condition of a hyperpolarized solid Xe layer frozen on top of an ethanol (ethanol/water) ice block we measured the Xe phase transitions as a function of time and temperature. In the pure ethanol sample, pieces of Xe ice first fall through the viscous ethanol to the bottom of the sample tube and then form a thin layer of liquid Xe/ethanol. The xenon atoms are trapped in this liquid layer up to room temperature and keep their magnetization over a time period of 11 min. In the ethanol/water mixture (80 vol%/20%), most of the polarized Xe liquid first stays on top of the ethanol/water ice block and then starts to penetrate into the pores and cracks of the ethanol/water ice block. In the final stage, nearly all the Xe polarization is in the gas phase above the liquid and trapped inside the pores. NMR spectra of homogeneous samples of pure ethanol containing thermally polarized Xe and the spectroscopic images of the melting process show that very high concentrations of hyperpolarized Xe (about half of the density of liquid Xe) can be stored or delivered in pure ethanol. 相似文献
910.
V. F. Radantsev V. V. Kruzhaev G. I. Kulaev 《Physica E: Low-dimensional Systems and Nanostructures》2004,20(3-4):396
The Rashba effect in metal–insulator–semiconductor (MIS) structures based on zero-gap HgCdTe is investigated experimentally and theoretically over a wide doping range NA–ND=3×1015–3×1018 cm−3. Increase of doping enlarges the magnitude of the effect at the same 2D concentration and strengthens a gate-voltage dependence of the Rashba splitting. The results demonstrate values of Rashba polarization as high as PR0.5 and a capability to control the Rashba effect strength at constant electron concentration. 相似文献