全文获取类型
收费全文 | 36490篇 |
免费 | 352篇 |
国内免费 | 141篇 |
专业分类
化学 | 17987篇 |
晶体学 | 679篇 |
力学 | 1614篇 |
综合类 | 2篇 |
数学 | 3571篇 |
物理学 | 13130篇 |
出版年
2022年 | 291篇 |
2021年 | 339篇 |
2020年 | 310篇 |
2019年 | 312篇 |
2018年 | 512篇 |
2017年 | 444篇 |
2016年 | 700篇 |
2015年 | 400篇 |
2014年 | 705篇 |
2013年 | 1570篇 |
2012年 | 1485篇 |
2011年 | 1837篇 |
2010年 | 1332篇 |
2009年 | 1331篇 |
2008年 | 1524篇 |
2007年 | 1506篇 |
2006年 | 1386篇 |
2005年 | 1197篇 |
2004年 | 1132篇 |
2003年 | 985篇 |
2002年 | 934篇 |
2001年 | 1346篇 |
2000年 | 966篇 |
1999年 | 801篇 |
1998年 | 607篇 |
1997年 | 581篇 |
1996年 | 508篇 |
1995年 | 470篇 |
1994年 | 441篇 |
1993年 | 389篇 |
1992年 | 463篇 |
1991年 | 468篇 |
1990年 | 458篇 |
1989年 | 421篇 |
1988年 | 444篇 |
1987年 | 429篇 |
1986年 | 374篇 |
1985年 | 440篇 |
1984年 | 470篇 |
1983年 | 343篇 |
1982年 | 386篇 |
1981年 | 375篇 |
1980年 | 318篇 |
1979年 | 400篇 |
1978年 | 378篇 |
1977年 | 394篇 |
1976年 | 391篇 |
1975年 | 342篇 |
1974年 | 322篇 |
1973年 | 339篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
901.
Aigars Vītiņš Ģirts Vītiņš Jānis Krastiņš Ints Šteins Ilmārs Zālīte Andrejs Lūsis 《Journal of Solid State Electrochemistry》1998,2(5):299-307
Ceramic specimens have been obtained from the powder of ZrO2-7.5 mol% Y2O3 having a specific surface area of 30 m2/g synthesized in air plasma. The novelty of this research lies in the fact that the plasma process makes it possible to prepare
so-called nanopowders with a particle size less than 100 nm, possessing specific physical, chemical and technological properties.
The sintered density of the specimens was 94–96% of the theoretical value, 6.001 g/cm3. The X-ray diffraction pattern of the specimens corresponded to a face-centered cubic lattice. Impedance in the frequency
range of 100 Hz–15 MHz and d.c. polarization curves in a potential range of −10 to 10 mV were measured in the temperature
range 200–850 °C in heating and cooling cycles. The intragrain, the grain boundary and the total bulk conductivities, the
electrode polarization resistance and their activation energies were determined. The thermal stability of the studied system
was proved in three measurement series up to 600–850 °C in heating and cooling cycles. The results obtained have shown that
the conductivity of ZrO2-7.5 mol% Y2O3 ceramics is not solely a function of temperature, but also depends on the previous thermal state of the ceramics.
Received: 16 October 1997 / Accepted: 19 January 1998 相似文献
902.
903.
V. Z. Vasikov I. A. Serbaev A. M. Gimazetdinov M. S. Miftakhov 《Russian Journal of Organic Chemistry》2007,43(6):915-917
Pantolactone methoxymethyl ether reacted with lithiated 2-trimethylsilyl-1,3-dithiane to give the corresponding ketene dithioacetal and formal monoaddition product of silicon-free 2-lithio-1,3-dithiane at a ratio of 2:1. Possible ways of formation of the latter are discussed. 相似文献
904.
H. Zhang Z. F. Chai H. B. Sun J. L. Zhang H. Ouyang L. Xin Y. D. Chuai 《Journal of Radioanalytical and Nuclear Chemistry》2007,271(1):31-35
The concentrations and distributions of total halogen (TX), extractable organohalogen (EOX) and extractable persistent organohalogen
(EPOX) were determined in 20 kinds of yogurt specimens collected from Chinese supermarkets using neutron activation analysis
(NAA) and gas chromatography equipped with a 63Ni electron capture detector (GC-ECD). The results indicated that the halogens in yogurt mainly existed as non-extractable
organohalogen compounds. About 25–30% of EOX was EPOX. EOCl and EPOCl were the main organohalogen species in yogurt. The average
concentration of the identified organochlorine, such as organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs),
was below 4% of EPOCl. 相似文献
905.
Chiral hydroxyl monophosphane 3 [(2S,3S,4S,5S)-3,4-dihydroxy-2, 5-dimethyl-1-phenylphospholane] and bisphospholanes 5a [1,2-bis[(2S, 3S,4S,5S)-3,4-dihydroxy-2,5-dimethylphospholanyl]benzene] and 5b [1, 2-bis[(2S,3S,4S,5S)-2,5-diethyl-3,4-dihydroxyphospholanyl]benzene] were synthesized from readily available D-mannitol in high yields. Strategies for protection and deprotection of OH-groups in the presence of phosphines have been explored. Rate acceleration in the Baylis-Hillman reaction was observed when a hydroxyl phosphine was used as the catalyst. Rhodium complexes with chiral bisphospholanes are highly enantioselective catalysts for the asymmetric hydrogenation of various kinds of functionalized olefins such as dehydroamino acid derivatives, itaconic acid derivatives, and enamides. An interesting feature of the hydroxyl phospholane system is that hydrogenation of some substrates can be carried out in water with >99% ee and 100% conversion (e.g., itaconic acid). 相似文献
906.
Sarabia Z Hernández D Castell JV van Henegouwen GM 《Journal of photochemistry and photobiology. B, Biology》2000,58(1):32-36
The skin is repeatedly exposed to solar ultraviolet radiation. Photoreaction of drugs in the body may result in phototoxic or photoallergic side effects. Non-steroidal anti-inflammatory drugs, such as tiaprofenic acid (TPA) and the closely related isomer suprofen (SUP) are frequently associated with photosensitive disorders; they may mediate photosensitised damage to lipids, proteins and nucleic acids. Using ex vivo pig skin as a model, we investigated the photodegradation of TPA and SUP, and photobinding of these drugs to protein by means of HPLC analysis and drug-directed antibodies. Both with keratinocytes, which were first isolated from the pig skin and thereafter exposed to UVA and with keratinocytes which were isolated from pig skin after the skin was UVA exposed, time-dependent photodegradation of TPA and SUP was found, beside photoadduct formation to protein. The results of this work show that: (a) TPA and SUP were photodecomposed with similar efficiency; major photoproducts detected were decarboxytiaprofenic acid (DTPA) and decarboxysuprofen (DSUP), respectively. (b) Both drugs form photoadducts, as concluded from recognition by drug-specific antibodies. Pig skin appears to be a good model for studying the skin photosensitising potential of drugs. 相似文献
907.
Sugiyama T Schweinberger E Kazimierczuk Z Ramzaeva N Rosemeyer H Seela F 《Chemistry (Weinheim an der Bergstrasse, Germany)》2000,6(2):369-378
2-Aza-2'-deoxyadenosine (2, z2Ad) is synthesized via its 1,N6-etheno derivative 7 and enzymatically deaminated to 2-aza-2'-deoxyinosine (3). Compound 2 is converted into the phosphoramidite building block 10b. This is employed in solid-phase oligonucleotide synthesis. The 2-azapurine base forms a strong base pair with guanine, but a much weaker one with adenine, thymine, and cytosine. Oligonucleotide duplexes with dangling nucleotide residues, such as 2-aza-2'-deoxyadenosine and 7-deaza-2'-deoxyadenosine (4, c7Ad), either on one or both termini, are synthesized, and the thermal stability of the duplexes is correlated with the hydrophobic properties of the dangling nucleotide residues. 相似文献
908.
Khailova N. A. Shaimardanova A. A. Saakyan G. M. Zyablikova T. A. Azancheev N. M. Krivolapov D. B. Gubaidullin A. T. Litvinov I. A. Musin R. Z. Chmutova G. A. Pudovik M. A. Pudovik A. N. 《Russian Journal of General Chemistry》2003,73(8):1213-1226
Phenyl -aminoalkylphosphonates add to phenyl iso(thio)cyanates to give saturated heterocycles, 1,3,4-diazaphospholidin-2-(thi)ones. The reaction of diphenyl (-methylamino)benzylphosphonate with diethyl isothiocyanatophosphate involves initial formation of 1,3,4-tiazaphospholidine-2-thiones containing exo- and endocyclic phosphorus atoms. These products are readily hydrolyzed in air, yielding diethyl isothio- cyanatophosphate and phenyl hydrogen (-methylamino)benzylphosphonate. The final products of the reaction of chloromethyl isocyanatophosphonates with aminoalkylphosphonates are 1,3,4-oxazaphospholines. Phenyl aminoalkylphosphonates react with chloromethyl isocyanatophosphonates to give saturated heterocycles, 1,3,4-diazaphospholidines, whereas with chloromethyl isothiocyanatophosphonates 1,3,4-thiazaphospholines are formed. 相似文献
909.
S. V. Larionov L. I. Myachina Z. A. Savel’eva L. A. Glinskaya R. F. Klevtsova L. A. Sheludyakova A. V. Tkachev S. N. Bizyaev 《Russian Journal of Coordination Chemistry》2004,30(12):837-845
New optically active levorotatory compounds [Ni(HL1)]NO3 (I) and [Ni(HL2)]NO3H2O (II) containing the anions of chiral diaminodioximes, H2L1 and H2L2, derived from the terpenes ±-pinene and (+)-3-carene, respectively, were synthesized. Complexes I and II were studied by X-ray diffraction. The crystal structures of compounds are ionic, being composed of the [Ni(HL1)]+ or [Ni(HL2)]+ cations and the outer-sphere NO3– anions. The Ni2+ ion coordinates four N atoms of the tetradentate chelating ligand, the NiN4 coordination unit being shaped like a tetrahedrally distorted square. Compounds I and II are diamagnetic, which corresponds to a low-spin d8 configuration. The NMR spectra of compounds were recorded and analyzed.Translated from Koordinatsionnaya Khimiya, Vol. 30, No. 12, 2004, pp. 888–896.Original Russian Text Copyright © 2004 by Larionov, Myachina, Saveleva, Glinskaya, Klevtsova, Sheludyakova, Tkachev, Bizyaev. 相似文献
910.
On the structure formation of hydrophobed particles in the boundary layer of water and octane phases
Two-dimensional aggregation of the surface modified glass beads was carried out in the boundary layer of water and octane phases. The effect of particles' hydrophobicity was investigated on the structure of forming aggregates and the growth process. The structure of the aggregates and their growth were characterized by a density function which demonstrates the change of mean particle density as a function of aggregate size. The growth yielded fractal or nonfractal structures in the investigated systems. The fractal structure of the aggregates was observed to be dependent on restructuring processes controlled by the surface properties of the beads.The experimental results are compared with earlier findings for aggregation of hydrophobic beads in the boundary layer of water and air phases.On leave from Loránd Eötvös University, Budapest, Hungary 相似文献