全文获取类型
收费全文 | 145047篇 |
免费 | 35666篇 |
国内免费 | 41234篇 |
专业分类
化学 | 93536篇 |
晶体学 | 4399篇 |
力学 | 10278篇 |
综合类 | 3294篇 |
数学 | 22091篇 |
物理学 | 88349篇 |
出版年
2024年 | 614篇 |
2023年 | 1297篇 |
2022年 | 3355篇 |
2021年 | 3179篇 |
2020年 | 3259篇 |
2019年 | 3606篇 |
2018年 | 3432篇 |
2017年 | 5385篇 |
2016年 | 4218篇 |
2015年 | 5679篇 |
2014年 | 6371篇 |
2013年 | 8836篇 |
2012年 | 9632篇 |
2011年 | 11738篇 |
2010年 | 15497篇 |
2009年 | 16066篇 |
2008年 | 10899篇 |
2007年 | 9424篇 |
2006年 | 9075篇 |
2005年 | 8481篇 |
2004年 | 7931篇 |
2003年 | 5910篇 |
2002年 | 5861篇 |
2001年 | 6192篇 |
2000年 | 5815篇 |
1999年 | 4320篇 |
1998年 | 3004篇 |
1997年 | 2586篇 |
1996年 | 2841篇 |
1995年 | 3278篇 |
1994年 | 3300篇 |
1993年 | 3364篇 |
1992年 | 2898篇 |
1991年 | 2454篇 |
1990年 | 2102篇 |
1989年 | 2201篇 |
1988年 | 2155篇 |
1987年 | 1398篇 |
1986年 | 1392篇 |
1985年 | 970篇 |
1984年 | 1126篇 |
1983年 | 510篇 |
1982年 | 999篇 |
1981年 | 832篇 |
1980年 | 842篇 |
1979年 | 620篇 |
1978年 | 561篇 |
1977年 | 645篇 |
1976年 | 1053篇 |
1972年 | 532篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
941.
R. Murugesan P. Sami T. Jeyabalan A. Shunmugasundaram 《Journal of Chemical Sciences》1995,107(1):1-10
Bonding and redox properties of mono- and dititanium substituted 12-heteropolytungsto-phosphates and their complexes with
bivalent Mn, Co, Ni and Cu are studied by UV-Vis, ESR and cyclicvoltammetric techniques. The heteropoly blue analogue [TiIIITiIVW10PO40]8− is unstable and its presence in solution is proved by optical and ESR spectroscopy. ESR results reveal that the odd electron
is trapped on the titanium atom at 77 K. The optical electronegativity of Ti(III) in this heteropoly blue is estimated to
be 2.4 from the intervalence charge transfer (IVCT) bands. X-ray powder diffraction results show that the complexes K5MII[Ti2W10PO40].xH2O(MII = Cu or Mn) are isomorphous with K7[Ti2W10PO40].6H2O. Electronic spectroscopy indicates very high symmetry around the bivalent metal ion M in the K5MII[Ti2W10PO40].xH2O complexes. This high symmetry is confirmed in K5Cu[Ti2W10PO40] by the observation of dynamic Jahn-Teller (JT) distortion at 300 K and static JT distortion at 77 K. 相似文献
942.
Timur Seidel Alfred Golloch Hans Beerwald Günther Böhm 《Fresenius' Journal of Analytical Chemistry》1993,347(3-4):92-102
Summary A new analytical radiation source combined with fiber optics linked to a diode array detection device with modified software is described. The direct-reading spectrometer simultaneously covers the wavelength range 185–510 nm with a spectral resolution of <1.5 nm. Intense optical emission is observed when positionally stable high-current surface sparks supplied by a pulse-generator with definite discharge parameters (max. 800 Ampere/pulse) are sliding over compact non-conductive materials such as plastics, glasses, quartz filters or powder pellets. Substrate vaporization, ionization and excitation processes in the surface discharge plasma channel generate emission corresponding to neutral and ionic states. The spectra are essentially composed of lines emitted by the electrode material (e.g. copper, silver), from the substrate under investigation, radiation continuum as well as structured background from the surrounding air atmosphere. Due to the occurrence of emission lines of reactive fillers, inorganic pigments and stabilizers, a rapid multi-element screening method is demonstrated. A rapid identification system (mix-up test) of PVC or fire-retardant thermoplastics within one second has been realized from the atomic emission line intensity originating from the sputtered copper electrode material according to its increased volatility in the presence of chlorine (modified Beilstein test).Puls-Plasma-Technik GmbH, Dortmund 相似文献
943.
Jadwiga Frelek Günther Snatzke Wojciech J. Szczepek 《Fresenius' Journal of Analytical Chemistry》1993,345(11):683-687
Summary Bidentate complexes of dimolybdenum tetraacetate with 1,3-diaxial diols show Cotton effects around 490–540 nm (CD band I), 400–440 nm (II), 350–380 nm (III), 320 nm (IV) and 280 nm (V). The sign of the Cotton effect II can be predicted by a proposed sector rule. It seems that from the Cotton effects for cyclic 1,3-diols the absolute configurations or conformations can be obtained.A part of this material was presented at III-rd International Conference on CD Spectroscopy [1] 相似文献
944.
The complete proofs of Krein’s theorem on the spectral shift function and the trace formula are given for a pair of self-adjoint
operators such that either (i) their difference is trace-class or (ii) the difference of their resolvents is trace-class.
The proofs, essentially due to Krein, is based on Herglotz’s theorem on the boundary value of the analytic functions whose
imaginary part is non-negative on the upper half plane, and an almost optimal class of functions are obtained for which the
trace formula is valid. Also an alternative method based on Weyl-von Neumann’s theorem for self-adjoint operators, avoiding
the complex function theory and inspired by Voiculescu’s work, is given for the first case. Furthermore, some applications
of the spectral shift function have been discussed. 相似文献
945.
Detection and tracking of cooperative airborne targets are very important for military and also for civilian purposes. Previous research has shown that detection and tracking LASER offer high precision but their operation range is limited to less than 40 km even in good visibility propagation conditions. For long operation ranges, high power and bulky RADAR are required which can be significantly reduced by using active transponders on the cooperative target. A trimode LADAR/RADAR/Transponder system is investigated providing optimum performances. A L band Radar with active transponder is operated for all weather long ranges up to Low Earth Orbit satellites. The L mode is switched to a Mm wave mode RADAR for operation distances lower than 350 km and to an accurate LASER mode for the final tracking steps. 相似文献
946.
947.
关于结合方案和PBIB设计的定义及所用的有关符号见文献[1].设F_q为特征为2的有限域,q=2~r.熟知F_q上的对称矩阵合同于以下三种形式的矩阵(见[1]p.24). 相似文献
948.
Electrochemical oxidation of thio/carbohydrazide and their hydrazone derivatives Benzaldehyde thiocarbohydrazone [BTCH] diacetylene
thiocarbohydrazone [DATCH] have been studied in Brit-ton Robinson buffer in aqueous and nonaqueous media at a glassy carbon
electrode. The effects of pH, sweep rate, concentration, temperature and surfactants have been studied. The complex bis (carbo/thiocabohydrazide) Zn(II) chloride was also subjected to voltammetric analysis in order to understand the reactivity
both in free and metal bound states. The reaction conditions were optimized for the determination of above compounds in micrograms
quantities by differential pulse voltammetry, analytical utility of this investigation is also highlighted. 相似文献
949.
950.
O. Yilmaz F. Y. Lambrecht N. Gokmen S. Erbayraktar K. Durkan 《Journal of Radioanalytical and Nuclear Chemistry》2007,273(2):311-313
The aim of the present study was to demonstrate the possible transplacental transmission of 131I labeled recombinant human erythropoietin (131I-rh-EPO) in pregnant rats and its distribution through maternal and fetal organs. Six Wistar Albino Rats in their pregnancy
of 18 days were used 131I labeled recombinant human erythropoietin (specific activity = 2.4 μCi/IU) was injected into the tail vein of rats. After
30 minutes labeled erythropoietin infusion maternal stomach, kidney, lung, liver, brain and heart as well as fetus were removed.
Then, the same organs were removed from each fetus. Measuring weight of maternal and fetal organs as well as placenta were
followed by radioactivity count via Cd(Te) detector. 131I labeled recombinant human erythropoietin was found to be able to pass rat placenta and its distribution order in fetal organs
was similar to those of maternal organs. Besides, as measurements were performed closer to cornu uteri, uptakes were decreasing
in every fetus and its corresponding placenta. 相似文献