全文获取类型
收费全文 | 8993篇 |
免费 | 546篇 |
国内免费 | 1333篇 |
专业分类
化学 | 6624篇 |
晶体学 | 216篇 |
力学 | 653篇 |
综合类 | 60篇 |
数学 | 936篇 |
物理学 | 2383篇 |
出版年
2024年 | 25篇 |
2023年 | 262篇 |
2022年 | 110篇 |
2021年 | 125篇 |
2020年 | 155篇 |
2019年 | 166篇 |
2018年 | 160篇 |
2017年 | 196篇 |
2016年 | 203篇 |
2015年 | 162篇 |
2014年 | 334篇 |
2013年 | 596篇 |
2012年 | 567篇 |
2011年 | 494篇 |
2010年 | 461篇 |
2009年 | 579篇 |
2008年 | 583篇 |
2007年 | 740篇 |
2006年 | 554篇 |
2005年 | 535篇 |
2004年 | 528篇 |
2003年 | 355篇 |
2002年 | 316篇 |
2001年 | 283篇 |
2000年 | 307篇 |
1999年 | 273篇 |
1998年 | 239篇 |
1997年 | 231篇 |
1996年 | 198篇 |
1995年 | 197篇 |
1994年 | 166篇 |
1993年 | 141篇 |
1992年 | 138篇 |
1991年 | 101篇 |
1990年 | 63篇 |
1989年 | 76篇 |
1988年 | 67篇 |
1987年 | 40篇 |
1986年 | 26篇 |
1985年 | 11篇 |
1984年 | 17篇 |
1983年 | 6篇 |
1982年 | 13篇 |
1981年 | 14篇 |
1980年 | 5篇 |
1979年 | 20篇 |
1978年 | 12篇 |
1977年 | 6篇 |
1976年 | 8篇 |
1973年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 10 毫秒
121.
1-Aryl-6,7-dimethoxy-1,2,3,4-tetrahydroisoquinolines were prepared according to a one-pot procedure involving the reaction of 2-(3,4-dimethoxyphenyl)-ethylamine with aromatic aldehydes in TFA at reflux. The tetrahydroisoquinolines were treated with H2O2-WO42− in methanol at room temperature to give the corresponding 3,4-dihydroisoquinoline-2-oxides. Treatment of these cyclic nitrones with DMAD in toluene at room temperature gave the corresponding isoxazolo[3,2-a]isoquinolines. These compounds were heated in toluene at reflux to give the corresponding ylides in high yields (Method A). The effect of the substituents on the rate of the rearrangement of such compounds prompted us to discuss a new mechanism involving consecutive C-C bond heterolysis and 1,3-sigmatropic shift. A one-pot reaction involving the treatment of the nitrones with equimolar amounts of DMAD in refluxing toluene also gave the ylides (Method B). The structures of the prepared compounds were elucidated by spectral means and elemental analyses. 相似文献
122.
Vukadin M. Leovac Vladimir Divjaković Ana F. Petrović Nikolai V. Gerbeleu 《Monatshefte für Chemie / Chemical Monthly》1989,120(3):181-186
Summary The reaction of warmDMF solutions of Cu(II) perchlorate, 5-nitrosalicylaldehyde S-methylisothiosemicarbazone (H2
L) and piperidine (Pip) yielded the paramagnetic (eff=2.19 B.M.) Cu(L)Pip complex, whereL is the dianionic form of H2
L, formed as a result of deprotonation of the phenolic hydroxyl and NH2 group. Crystal data of the complex are: monoclinic P21,a=11.902(4),b=6.765(3),c=11.343(4)Å; =112.92°,V=841.20(8)Å3,M=400.9,Z=2,d
0=1.60 gcm–3,d
c
=1.58 gcm–3,F(000)=424. The structure was refined to a residualR=0.047. The copper(II) ion is coordinated in a square-planar arrangement by the piperidine nitrogen and the NNO set of donor atoms ofL.
Komplexe der Übergangsmetalle mit Thiosemicarbazid-Liganden, IV. Synthese und molekulare Struktur von 5-Nitrosalicylaldehyd-S-methylisothiosemicarbazonato-piperidin-kupfer(II)
Zusammenfassung Durch die Reaktion in warmenDMF-Lösungen von Cu(II) Perchlorat, 5-Nitrosalicylaldehyd-S-methylisothiosemicarbazon (H2 L) und Piperidin (Pip) wurde ein paramagnetischer Komplex (eff=2.19 B.M.) Cu(L)Pip erhalten, wobeiL nach doppelter Deprotonierung (NH2- und Phenolhydroxyl-Gruppe) als dianionische Form von H2 L vorliegt. Die kristallographischen Daten des Komplexes sind: monokline Raumgruppe P21,a=11.902(4),b=6.765(3),c=11.343(4)Å, =112.92°;V=841.20Å3,M=400.9,Z=2,d 0=1.60 gcm–3,d c =1.58 gcm–3,F(000)=424. Die struktur wurde bis zu einemR-Wert von 0.047 verfeinert. Die Koordination des Kupfers wird quadratisch-planar über den Piperidin-Stickstoff und die NNO-Donorhülle der Chelatliganden gebildet.相似文献
123.
A series of 1-(2,4-dichlorophenoxyacetoxy)alkylphosphonic acid dimethyl esters 5 and its corresponding phosphonate monosalts 6 were synthesized as potential herbicide. The phosphonate monosalts can be prepared from 1-(2,4-dichlorophenoxyacetoxy)alkylphosphonic acid dimethyl esters 5, which were synthesized by the condensation of O,O-dimethyl-1-hydroxyalkylphosphonates with dichlorophenoxyacetic chloride. This method provides a simple and efficient procedure for the synthesis of phosphonate derivatives containing sensitive groups to acid, base or water such as carboxylate ester bond; and the herbicidal activity of title compounds was evaluated in a set of experiments in greenhouse. Most of the compounds exhibited notable herbicidal activity. 相似文献
124.
Synthesis of New Chiral C2-Symmetrical Bis(oxazoline )Compounds 总被引:2,自引:0,他引:2
New chiral C2-symmetrical bis(oxazoline)compounds bearing one isobutyl-,secbutyl-benzyl- or isopropyl-substituent at the 4-position have been prepared and characterized. 相似文献
125.
126.
The novel applications of molybdenum disulfide in recent research were reviewed, such as in lubricant, catalyst and photoelectrochemical solar cells. Recently, we found that LiMoS2 is a good candidate for new anode materials for lithium ion batteries with high lithium storage capacity.Here, the anode material LiMoS2 was synthesized by a hydrothermal method at 150℃ and the electrochemical characterization as an anode material for lithium ion batteries was examined.put in Teflon-lined stainless steel autoclaves of capacity 40 mL. Distilled water was used to fill the autoclaves to 70 % of the total volume. The autoclaves were maintained at 150℃ for 24 h and then cooled naturally. The resulting dark-gray powders were filled and washed with distilled water,diluted hydrochloric acid and ethanol, successively. The final products were dried at 80℃ for 24 h.The powder X-ray diffraction pattern showed the prepared LiMoS2 was amorphous structure. A test cell using LiMoS2 as the active material was discharged and charged between 3 and 0.01 V with respect to Li metal at a constant current density of C/5 (that is, one lithium per formula unit in 5 hours). During the first discharge, the potential rapidly drops to reach a large plateau at 2.2 V, then slowly drops to the other plateau at 0.8 V, and then continuously decreases down to 0.01V. There is only a plateau at 1.35 V in the subsequent discharge curves. The plateaus of charge potential appear at about 1.9 V.The irreversible loss was 41% in the first cycle. The ratio of discharge and charge is more than 99%in the subsequent cycles. Moreover, the ratio of discharge and charge almost reaches 100% after thedemonstrated that LiMoS2 has a very high capacity and a good cycle-ability as an anode material forlithium ion batteries. 相似文献
127.
128.
E. Lancry E. Levi A. Mitelman S. Malovany D. Aurbach 《Journal of solid state chemistry》2006,179(6):1879-1882
The Chevrel phase (CP), Mo6S8, was found to be an excellent cathode material for rechargeable magnesium batteries. Mo6S8 is obtained by a leaching process of Cu2Mo6S8, which removes the copper. A new method of Cu2Mo6S8 production was developed. In contrast to the well-known solid-state synthesis of CP, the method is based on the reaction in a molten salt media (KCl). A fast kinetics of this reaction allows using less active, but more convenient precursors (sulfides instead of sulfur), decreasing temperature and synthesis duration, as well as operation in the inert atmosphere instead of dynamic evacuated systems. It was shown that the composition and the electrochemical behavior of the products obtained by MSS and by the solid-state synthesis are identical. Thus, the molten salt method is extremely attractive for the large-scale production of the active materials for Mg batteries. 相似文献
129.
Yunsong Yang 《European Polymer Journal》2004,40(3):531-541
A series of α,ω-dihydroxy polyarylene sulfones (PAES) were synthesized comprising bisphenol A (PAES1, Mn=1800, 4900, and 9500 daltons), 4,4′-biphenol (PAES2, Mn=4100 daltons), and hexafluorobisphenol A (PAES3, Mn=3300 daltons). These were reacted with α,ω-dibromo poly(vinylidene fluoride) (PVDF, Mn=1200 daltons) prepared by telomerization, to yield block copolymers possessing rigid and flexible segments. Block copolymers were characterized by FTIR, NMR, GPC, DSC, TGA and TEM. In several cases the block copolymers exhibited distinct thermal transitions, i.e. Tm and Tg for PVDF and PAES segments, respectively. Where observable, Tg of PAES domains in the block copolymers occurred at a temperature lower than the corresponding PAES homopolymer due to the flexible nature of the surrounding PVDF domains. Block copolymers exhibited a similar thermal stability to the corresponding PAES homopolymers but higher stability than the PVDF homopolymer, and much higher still than α,ω-dibromo PVDF. TEM analyses indicate that phase separation of PAES and PVDF domains occurs on the nanometer scale. 相似文献
130.
IntroductionMicellarelectrokineticchromatography (MEKC)wasinventedtoextendtheutilityofcapillaryelectrophoresis(CE)andpermittedtheseparationandanalysisofneutralcompounds .ButjustlikeothermodesofCE ,MEKCarehamperedbythelowconcentrationsensitivityoftheultra … 相似文献