全文获取类型
收费全文 | 720篇 |
免费 | 74篇 |
国内免费 | 165篇 |
专业分类
化学 | 860篇 |
晶体学 | 18篇 |
力学 | 9篇 |
物理学 | 72篇 |
出版年
2023年 | 7篇 |
2022年 | 19篇 |
2021年 | 16篇 |
2020年 | 23篇 |
2019年 | 32篇 |
2018年 | 17篇 |
2017年 | 16篇 |
2016年 | 34篇 |
2015年 | 19篇 |
2014年 | 34篇 |
2013年 | 76篇 |
2012年 | 39篇 |
2011年 | 49篇 |
2010年 | 19篇 |
2009年 | 37篇 |
2008年 | 45篇 |
2007年 | 44篇 |
2006年 | 47篇 |
2005年 | 40篇 |
2004年 | 53篇 |
2003年 | 45篇 |
2002年 | 37篇 |
2001年 | 18篇 |
2000年 | 17篇 |
1999年 | 27篇 |
1998年 | 12篇 |
1997年 | 24篇 |
1996年 | 28篇 |
1995年 | 31篇 |
1994年 | 11篇 |
1993年 | 7篇 |
1992年 | 8篇 |
1991年 | 6篇 |
1990年 | 4篇 |
1989年 | 5篇 |
1988年 | 5篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1975年 | 1篇 |
1973年 | 1篇 |
排序方式: 共有959条查询结果,搜索用时 15 毫秒
121.
《Composite Interfaces》2013,20(2):151-165
This study compared bony fusion in autologous bone grafting with HA/ZrO2 graded composite in terms of mineral depositions, histological characteristics, and biomechanical properties of bonding interface. Twenty-four beagle dogs were established four places of bone defect in two adjacent lumbar vertebral bodies (L4 and L5) and were successively implanted with HA/ZrO2 graded composite (group A), HA/ZrO2 unilayer composite (group B), pure ZrO2 (group C), and pure HA (group D). After operation, lumbar vertebral specimens were respectively harvested per time at week 6, 12, and 16. Then, the bony fusion interface was evaluated by fluorescence microscope and computer image analysis system to measure mineral apposition rates (MAR). Histological analysis of specimen was used to determine bone bonding rates (BBR) and possible foreign body reactions associated with each groups. And interface bonding force between implant and autogenous bone was quantified with biomechanical push-out test. Compared with other groups, group A led to significantly higher MAR from week 6 to 12 (p < 0.05). Histologically, new bony tissue and hyaline cartilage were seen around the HA/ZrO2 graded composite, accompanied by mild chronic inflammation. And the BBR of HA/ZrO2 graded composite were the highest (p < 0.05), while reaching (90.3 ± 3.8) % at week 16. Moreover, the biomechanical push-out tests revealed that the maximum interface shear strength of group A was respectively (2.64 ± 0.16) MPa, (2.95 ± 0.19) MPa, and (3.45 ± 0.23) MPa at week 6, 12, and 16, which all possessed significantly statistical differences with other three groups (p < 0.05). 相似文献
122.
Mannepalli L. Kantam Sutapa Ghosh Khathija Aziz B. Sreedhar Boyapati M. Choudary 《Journal of molecular catalysis. A, Chemical》2005,240(1-2):103-108
Heterogeneous nanoparticle NA-MgO-MAO/NA-TiO2 (anatase)-MAO supported bis (cyclopentadienyl) zirconium dichloride (Cp2ZrCl2) are synthesized and used for the polymerization of styrene monomer. The supporting process is confirmed via X-ray photoelectron spectroscopy (XPS) and FTIR. Characterization of the obtained polymer is done by gel permeation chromatography (GPC), 13C NMR spectroscopy and differential scanning calorimetry (DSC). 相似文献
123.
A. I. Sizov T. M. Zvukova A. V. Khvostov A. A. Gorkovskii Z. A. Starikova B. M. Bulychev 《Russian Chemical Bulletin》2005,54(11):2496-2501
A procedure was developed for the synthesis of trinuclear cyclic (ZrIII)2—Al hydrides [(Cp2Zr)2(μ-H)](μ-H)2AlX2 (X = Cl (1a) or Br (1b)). These complexes were prepared in 60–65% yields by the reaction of Cp2ZrX2 with LiAlH4 in the presence of CoBr2 and tolane. The structures of complexes 1a and 1b and iodide 1c (X = I) were studied by NMR spectroscopy in solvents of different basicities (toluene, THF, and pyridine). Complex 1a is unsolvated and monomeric in all solvents; complex 1b, in toluene and THF; complex 1c, in toluene only. At room temperature, complex 1a does not catalyze hydrogenation of hex-1-ene and does not react with tolane, but reacts with the latter at high temperature
to give bis(η5-cyclopentadienyl)-2,3,4,5-tetraphenylzirconacyclopentadiene. The reaction of equivalent amounts of complex 1a and HCl produces the [(Cp2Zr)2(μ-Cl)](μ-H)2AlCl2 complex. The structure of the latter was established by X-ray diffraction.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2418–2423, November, 2005. 相似文献
124.
L. I. Strunkina M. Kh. Minacheva P. V. Petrovskii Z. S. Klemenkova B. V. Lokshin V. V. Burlakov V. B. Shur 《Russian Chemical Bulletin》1997,46(4):820-823
The first acetylene complex of hafnium, Cp2Hf[Me3SiC=CHf(H)Cp2], was synthesized by the reaction of hafnocene dihydride Cp2HfH2 with bis(trimethylsilyl)acetylene in benzene. The reaction is accompanied by elimination of the Me3Si group from the molecule of the initial acetylene, as a result of which the acetylenide derivative of hafnium Cp2Hf(C=CSiMe3)(H) acts as an acetylene ligand in the complex. Under analogous conditions, the reaction of zirconocene dihydride Cp2ZrH2 with bis(trimethylsilyl)acetylene affords an analogous acetylene complex of zirconium Cp2Zr(M3SiC=CZr(H)Cp2]. Reactions of Cp2HfH2 with tolane and 3-hexyne proceed differently than the reaction with bis(trimethylsilyl)acetylene. Here the corresponding
hafnacyclopentadiene metallacycles are the final products.
For preliminary communication, see Ref. 3.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 853–856, April, 1997. 相似文献
125.
Thomas R. Cundari Aaron W. Pierpont Hassan Raba 《International journal of quantum chemistry》2006,106(7):1611-1619
A density functional theory (DFT) study of carbon? hydrogen versus carbon? heteroatom bond activation is presented. Heteroatom groups (X) investigated include X = F, Cl, OH, SH, NH2, PH2. The activating model complex is a prototypical d0 zirconium‐imide. While C? X activation has a thermodynamic advantage over C? H activation, the former has been found to have a kinetic advantage. Implications for catalytic hydrocarbon functionalization and phosphine–ligand degradation are discussed. The present results for a high‐valent metal complex are compared/contrasted with low‐valent bond activating complexes. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006 相似文献
126.
127.
128.
Koichiro Fukuda Akira Moriyama Tomoyuki Iwata 《Journal of solid state chemistry》2005,178(6):2144-2151
The crystal structure of BaZr(PO4)2 at 298 K was determined from conventional X-ray powder diffraction data using direct methods, and it was further refined by the Rietveld method. The structure was monoclinic (space group C2/m, Z=2) with , , , β=93.086(1)° and . Final reliability indices were Rwp=8.21%, Rp=5.64% and RB=2.92%. The atom arrangement is similar to that of yavapaiite (KFe(SO4)2), however, these crystal structures differ distinctly in the coordination numbers of barium and potassium atoms; the former is tenfold coordinated, whereas the latter is sixfold coordinated. The powder specimens were also examined by high-temperature XRD and DTA to reveal the occurrence of a phase transition from monoclinic to orthorhombic at 732 K during heating. Upon cooling the reverse transition occurred at 710 K. The monoclinic crystal expanded almost one-dimensionally along [503] during the heating process. The orthorhombic phase also showed a tendency to expand one-dimensionally along the c-axis above 732 K. 相似文献
129.
130.
Durch Aktivierungsanalyse mit Reaktorneutronen (zerstörungsfrei und mit chemischer Aufarbeitung) sowie mittels zerstörungsfreier Untersuchungen an einem Neutronengenerator wurden O, Al, Si, P, Mn, Cu, Nb, Mo, Cd, Ti, Cr und Hf in Zirkoniumlegierungen bestimmt. 相似文献