全文获取类型
收费全文 | 26403篇 |
免费 | 1736篇 |
国内免费 | 3549篇 |
专业分类
化学 | 26706篇 |
晶体学 | 421篇 |
力学 | 910篇 |
综合类 | 124篇 |
数学 | 287篇 |
物理学 | 3240篇 |
出版年
2024年 | 47篇 |
2023年 | 264篇 |
2022年 | 637篇 |
2021年 | 579篇 |
2020年 | 837篇 |
2019年 | 813篇 |
2018年 | 827篇 |
2017年 | 1097篇 |
2016年 | 1294篇 |
2015年 | 1022篇 |
2014年 | 1040篇 |
2013年 | 2499篇 |
2012年 | 1719篇 |
2011年 | 1432篇 |
2010年 | 1331篇 |
2009年 | 1640篇 |
2008年 | 1605篇 |
2007年 | 1519篇 |
2006年 | 1403篇 |
2005年 | 1218篇 |
2004年 | 1063篇 |
2003年 | 941篇 |
2002年 | 758篇 |
2001年 | 683篇 |
2000年 | 681篇 |
1999年 | 589篇 |
1998年 | 522篇 |
1997年 | 468篇 |
1996年 | 454篇 |
1995年 | 454篇 |
1994年 | 361篇 |
1993年 | 323篇 |
1992年 | 240篇 |
1991年 | 192篇 |
1990年 | 168篇 |
1989年 | 159篇 |
1988年 | 170篇 |
1987年 | 180篇 |
1986年 | 107篇 |
1985年 | 80篇 |
1984年 | 94篇 |
1983年 | 23篇 |
1982年 | 58篇 |
1981年 | 27篇 |
1980年 | 20篇 |
1979年 | 19篇 |
1978年 | 6篇 |
1977年 | 5篇 |
1976年 | 3篇 |
1973年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
A new, high performance liquid chromatography method has been developed for the separation of monovinyl- and divinyl-protochlorophyllides, using commercially available, C30 reverse phase column and isocratic elution. This method can be used both for analytical applications and preparative scale purification of monovinyl- and divinyl-protochlorophyllides using the same column where submilimolar concentrations of the crude protochlorophyllide extract can be separated in one run. The purity of the obtained protochlorophyllides was demonstrated by spectroscopic methods, as well by the formation of aggregates in toluene. 相似文献
92.
We investigated the features of the glass transition relaxation of two room temperature ionic liquids using DSC. An important
observation was that the heat capacity jump, that is the signature of the glass transition relaxation, shows a particularly
strong value in this type of new and promising materials, candidates for a range of applications. This suggests a high degree
of molecular mobility in the supercooled liquid state. The study of the influence of the heating rate on the temperature location
of the glass transition signal, allowed the determination of the activation energy at the glass transition temperature, and
the calculation of the fragility index of these two ionic glass-formers. It was concluded that this kind of materials belong
to the class of relatively strong glass-forming systems.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
93.
Kaname SasakiHideyuki Nagai Shuichi MatsumuraKazunobu Toshima 《Tetrahedron letters》2003,44(30):5605-5608
The glycosidations of glucopyranosyl diethyl phosphite and alcohols using an ionic liquid, 1-n-hexyl-3-methylimidazolium trifluoromethanesulfonimidide (C6mim[NTf2]) containing a protic acid, trifluoromethanesulfonimide (HNTf2), as a novel solvent-catalyst system, effectively proceeded under mild conditions to give the corresponding glycosides in good to high yields. Furthermore, this acid-ionic liquid combination could be reused many times for the glycosidations without any loss in efficiency. 相似文献
94.
《Electroanalysis》2003,15(4):294-302
Macrocyclic lipophilic polyamines were applied as the sensory elements of polymeric liquid membrane electrodes. These hosts gain the anion receptor functionality upon protons uptake from the aqueous solutions. The electrodes studied were able to distinguish potentiometricaly isomers of monocharged and doublecharged forms of ethylene and benzene dicarboxylic acids. The selectivity of interaction between protonated hosts and anionic guests relays not only on the electrostatic interactions, but on hydrogen bounds formations as well. The influence of lipophilicity of protonated hosts on the potential response generation was discussed. 相似文献
95.
Roxana S. Timofte 《Tetrahedron letters》2004,45(1):39-42
High surface area silica pellets are excellent supports for the preparation of silica supported reagents and solid-phase basal linkers through reaction with (RO)3Si(CH2)3FG (FG=NH2, NHMe, Cl, NHC(O)NH2, OC(O)CMe(CH2), NCO, NEt2). High loadings (0.66-2.15 mmol g−1) of grafted silane materials are realised at synthetically useful loadings per pellet (ca. 0.06 mmol). Preliminary trials show that trial linker chemistry and ligand synthesis can be carried out on these materials and that these reactions can be monitored by solid state 13C NMR studies on individual pellets. 相似文献
96.
Kuan‐Wei Lee Hong‐Cheu Lin 《Journal of polymer science. Part A, Polymer chemistry》2007,45(20):4564-4572
A series of new liquid crystalline homopolymers, copolymers, and block copolymers were polymerized from styrene‐macroinitiator ( SMi ) and methacrylates with pendent 4,4′‐bis(biphenyl)fluorene ( M1 ) and biphenyl‐4‐ylfluorene ( M2 ) groups through atom transfer radical polymerization (ATRP). The number‐average molecular weights (Mn) of polymers P1 ‐ P4 were 10,007, 14,852, 6,275, and 10,463 g mol?1 with polydispersity indices values of 1.21, 1.15, 1.31, and 1.22, respectively. All polymers exhibit the nematic phase. The thermal, mesogenic, and photoluminescent properties of all polymers were investigated. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4564–4572, 2007 相似文献
97.
A liquid chromatography-mass spectrometry method for the determination of the coccidiostats metronidazole, ronidazole, dimetridazole,
secnidazole, tinidazole and ipronidazole in feedstuff was developed. The 5-nitroimidazoles were extracted from animal feed
with a pH 2 phosphate buffer solution followed by a solid phase extraction procedure based on HLB cartridges. The liquid chromatographic
separation of the extracts was performed on a C18 bonded silica column applying a gradient of elution with pH 4.3 ammonium acetate buffer solution and acetonitrile. Quantification
for each 5-nitroimidazole was carried out monitoring its molecular ion [M + H]+ obtained by positive electrospray ionisation mode. A pool of feedstuffs was used to optimise and validate the method. Linearity,
quantification limit, intra-day and inter-day reproducibility and accuracy were estimated using this pool of feedstuffs spiked
with the drugs. For the confirmatory assay, several fragment ions from each 5-nitroimidazole were obtained and monitored.
The method was applied successfully to determine 5-nitroimidazoles in feedstuff at level of 0.05 mg kg−1. 相似文献
98.
Thi Thi Nge Naruhito Hori Akio Takemura Hirokuni Ono Tsunehisa Kimura 《Journal of Polymer Science.Polymer Physics》2003,41(7):711-714
A high magnetic field of 5 T was used to fabricate a magnetically aligned, optically anisotropic, liquid‐crystalline chitin/poly(acrylic acid) composite. The aligned mesophase was fixed by photoinitiated free‐radical polymerization. From an examination of polarized optical micrographs and an X‐ray diffraction study, a high degree of orientation of 0.70 was observed for the composite with a higher liquid‐crystalline chitin concentration (10.70 wt %); the orientation was reduced with a decreased chitin concentration at a given acrylic acid concentration. The X‐ray data for the developed composite showed a uniplanar orientation for the chitin crystallites, with its molecular long axes perpendicular to the direction of the magnetic field. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 711–714, 2003 相似文献
99.
Perdigón-Melón J. A. Auroux A. Bonnetot B. 《Journal of Thermal Analysis and Calorimetry》2003,72(2):443-451
As supported palladium oxide catalysts present the best performances in methane combustion in lean conditions, microcalorimetric
studies of the interaction between methane and palladium oxide or metallic palladium supported on Al2O3, ZrO2 and BN have been performed at 673 K. At this temperature methane reduced the palladium oxide, and the heat of reduction of
palladium oxide was shown to depend on the dispersion and on the support. The lowest heats of reduction corresponded to the
highest rates of methane combustion. Moreover methane reforming occurred on metallic palladium, producing hydrogen, and again
methane decomposition was shown to depend on the support.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
100.
Isabel Cristina S. F. Jardim Kenneth E. Collins Carol H. Collins 《Microchemical Journal》2004,77(2):191-198
Polysiloxanes immobilized onto the surfaces of porous silica particles have proven to be good stationary phases for the separation of multiresidues of pesticides and their metabolic/degradation products by reversed-phase high-performance liquid chromatography (RP-HPLC). Similar materials have proven effective for pre-concentration and clean-up procedures using solid phase extraction. The present paper describes the preparation and some applications of several of these packing materials. 相似文献