全文获取类型
收费全文 | 10158篇 |
免费 | 299篇 |
国内免费 | 36篇 |
专业分类
化学 | 7684篇 |
晶体学 | 106篇 |
力学 | 111篇 |
综合类 | 2篇 |
数学 | 444篇 |
物理学 | 1975篇 |
综合类 | 171篇 |
出版年
2022年 | 69篇 |
2021年 | 91篇 |
2020年 | 126篇 |
2019年 | 157篇 |
2018年 | 93篇 |
2017年 | 87篇 |
2016年 | 168篇 |
2015年 | 160篇 |
2014年 | 177篇 |
2013年 | 438篇 |
2012年 | 471篇 |
2011年 | 539篇 |
2010年 | 268篇 |
2009年 | 284篇 |
2008年 | 553篇 |
2007年 | 555篇 |
2006年 | 561篇 |
2005年 | 573篇 |
2004年 | 521篇 |
2003年 | 373篇 |
2002年 | 389篇 |
2001年 | 273篇 |
2000年 | 239篇 |
1999年 | 154篇 |
1998年 | 93篇 |
1997年 | 113篇 |
1996年 | 124篇 |
1995年 | 100篇 |
1994年 | 103篇 |
1993年 | 138篇 |
1992年 | 144篇 |
1991年 | 135篇 |
1990年 | 126篇 |
1989年 | 124篇 |
1988年 | 123篇 |
1987年 | 92篇 |
1986年 | 102篇 |
1985年 | 145篇 |
1984年 | 157篇 |
1983年 | 96篇 |
1982年 | 111篇 |
1981年 | 106篇 |
1980年 | 103篇 |
1979年 | 109篇 |
1978年 | 108篇 |
1977年 | 116篇 |
1976年 | 82篇 |
1975年 | 68篇 |
1974年 | 75篇 |
1973年 | 78篇 |
排序方式: 共有10000条查询结果,搜索用时 10 毫秒
81.
Masahiko Kurihara Fumitoshi Hirayama Kaneto Uekama Masaki Yamasaki 《Journal of inclusion phenomena and macrocyclic chemistry》1990,8(4):363-373
Inclusion complexation of nocloprost, a potent antiulcer prostaglandin derivative, with -, -, and -cyclodextrins (CyDs) in aqueous solutions has been studied by the solubility method and13C-NMR spectroscopy. The steric requirement of host-guest interaction was reflected in the magnitude of the stability constants and the thermodynamic parameters of the inclusion complexes. Solid complexes of nocloprost with - and -CyDs in a molar ratio of 1 : 2 were obtained on the basis of aBs-type phase solubility diagram. The X-ray diffraction data suggested that nocloprost is included in the cylindrical channel formed by coaxial alignment of -CyD molecules to give a channel type structure. Release and thermal behavior of the solid complexes was examined and compared with nocloprost itself. The results indicated that the -CyD complex may have great utility among the three CyDs, being a rapid dissolving form of nocloprost with improved thermal stability. 相似文献
82.
M. Takeuchi S. Tanaka M. Yamawaki S. Tachimori 《Journal of Radioanalytical and Nuclear Chemistry》1995,191(1):189-199
The coextraction equilibrium of technetium(VII) and uranium(VI) from nictric acid solution was studied in a system involvingn-octyl(phenyl)-N,N-diisobutylcarbamoylmethyl phosphine oxide (CMPO) in decalin. Stoichiometry of technetium, uranium and CMPO in the Tc-U-CMPO complex was obtained from the distribution data by slope analysis. The results indicated that the enhanced extraction of technetium was caused by the formation of UO2NO3TcO4·nCMPO (wheren=2 and/or 3). It was found that this coextraction of technetium with uranium was well explained by using ion exchange reaction between UO2(NO3)2·2CMPO complex and TcO
4
–
. 相似文献
83.
K. Komura K. Komura Y. Kuwahara Y. Kuwahara T. Abe T. Abe K. Tanaka K. Tanaka Y. Murata Y. Murata M. Inoue M. Inoue 《Journal of Radioanalytical and Nuclear Chemistry》2006,269(2):511-516
Summary Extremely low activity levels of cosmic ray induced nuclides have been measured in freshly precipitated rainwater by quick
chemical separation coupled with ultra low background gamma-spectrometry. The nuclides detected were 38S (T1/2 = 2.83 h)-38Cl (37.2 m), 39Cl (55.6 m), 24Na (14.96 h), 28Mg (20.9 h), 7Be (53.3 d) and 22Na (2.602 y). The number of atoms in rain water were evaluated to be ranging from 400-1900 l-1 for 39Cl (n = 6, mean: 1200), 30-1500 l-1 for 24Na (n = 16, mean: 520), 80-600 l-1 for 28Mg (n = 13, mean: 260), 1 . 106-4 . 107 l-1 for 7Be (n = 16, mean: 7 . 106) and 2 . 103-1 . 105 l-1 for 22Na (n = 9, mean: 2 . 104). Measurements of activity levels and activity ratios of short-lived cosmic-ray induced short-lived nuclides will open new
method to understand atmospheric processes occurred at the altitude of rain cloud. 相似文献
84.
(+)-Biotin (1) was synthesized in 25% overall yield over 11 steps from L-cysteine. The contiguous asymmetric centers at C-3a and C-6a were formed through a novel and highly stereoselective Lewis base-catalyzed cyanosilylation of alpha-amino aldehyde 3 to provide anti-O-TMS-cyanohydrin 4 with high stereoselectivity and in high yield (anti/syn = 92:8, 96%). Treatment of 4 with a di-Grignard reagent, 1,4-bis(bromomagnesio)butane, followed by carbon dioxide, efficiently installed the 4-carboxybutyl chain at C-4 to give keto acid 5. The final cyclization to bicyclic compound 7b, a precursor to 1, was realized by a palladium-catalyzed intramolecular allylic amination of cis-allylic carbonate 6b that was elaborated from 5. 相似文献
85.
Matsuhisa A Taniguchi N Koshio H Yatsu T Tanaka A 《Chemical & pharmaceutical bulletin》2000,48(1):21-31
Arginine vasopressin (AVP) has a dual action mainly in the periphery, i.e., vasoconstriction and water reabsorption via V1A and V2 receptors; it may play a role in a number of diseases, including congestive heart failure (CHF), hypertension, renal disease, edema, and hyponatremia. We have attempted to develop a new series of orally active AVP antagonists for both V1A and V2 receptors based on the hypothesis that the blockade of both V1A and V2 receptors might be beneficial to CHF patients. In this report, a series of compounds structurally related to 4'-(1,4,5,6-tetrahydroimidazo[4,5-d][1]benzoazepine-6- carbonyl)benzanilide and 4'-(5,6-dihydro-4H- thiazolo[5,4-d][1]benzoazepine-6-carbonyl)benzanilide were synthesized and examined for AVP antagonist activity for both V1A and V2 receptors. As a result, it was found that the 4'-(1,4,5,6-tetrahydroimidazo[4,5-d][1]benzoazepine-6-carbon yl)-2- phenylbenzanilide derivatives showed potent binding affinity for both V1A and V2 receptors. Especially, 4'-(2-methyl-1,4,5,6- tetrahydroimidazo[4,5-d][1]benzoazepine-6-carbonyl)-2-phe nylbenzanilide monohydrochloride (18, YM087 = conivaptan hydrochloride) exhibited potent binding affinity and AVP antagonist activity, after intravenous administration, for both V1A and V2 receptors. Furthermore, YM087 exhibited the most potent oral activity for the V2 receptor. Details of the synthesis and pharmacological properties of this series are presented. 相似文献
86.
Hiromu Hayashi 《Catalysis Surveys from Japan》1999,3(1):43-52
Additive telluromolybdates, MoO3·2TeO2 and MIIO·TeO2·MoO3 (MIITeMoO6; MII = Co, Mn, Zn), converted ethyl lactate selectively to pyruvate in a vaporphase fixedbed flow system at 250–300 °C. A synergy in activity was observed for binary TeO2–MoO3, and crystalline Te2MoO7 was suggested as the active species. The Rietveld analysis of powder XRD patterns of ternary CoTeMoO6 revealed the layer structure quite different from that of the reference Te2MoO7, but tellurium was again located adjacent to molybdenum linked through lattice oxygen. 相似文献
87.
Practical asymmetric synthesis of (S)-MA20565, a wide-spectrum agricultural fungicide 总被引:1,自引:0,他引:1
Tanaka K Katsurada M Ohno F Shiga Y Oda M Miyagi M Takehara J Okano K 《The Journal of organic chemistry》2000,65(2):432-437
A practical asymmetric synthesis of a wide-spectrum agricultural fungicide, (S)-MA20565 (1), is described. The convergent synthesis was achieved starting from commercially available 3-(trifluoromethyl)aniline (7) in 44% overall yield through five steps and 2-bromobenzaldehyde (9) in 48% overall yield through four steps, respectively. (S)-O-[1-(3-Trifluoromethylphenyl)ethyl]hydroxylamine (2), a key intermediate of 1, was prepared via ruthenium(II)-catalyzed asymmetric transfer hydrogenation of 1-(3-trifluoromethylphenyl)ethanone (6) followed by chlorination using methanesulfonyl chloride and oxyamination using potassium acetohydroxamate with high level of stereocontrol. 相似文献
88.
Hidetake Sakuraba Toshimori Nakai Yoshio Tanaka 《Journal of inclusion phenomena and macrocyclic chemistry》1984,2(3-4):829-839
Asymmetric halogenation and hydrohalogenation oftrans-cinnamic acid have been achieved in the microcrystals of cyclodextrin complexes. The bromination of the organic acid in the cavity of -cyclodextrin gave theerythro-dibromide in 40 % optical yield which was much larger than that from the resolution treatment of the racemic dibromide with -cyclodextrin and the absolute configuration was opposite in sign. The asymmetric induction in the gas-solid reaction was not due to optical resolution but to the reaction itself which was influenced by the chiral frame of cyclodextrin. The reaction shows the molecular size effect that the acid in the cavity of -cyclodextrin reacted with smaller hydrogen bromide but did not with larger bromine and chlorine. In contrast, the guest molecule in the wider cavity of -cyclodextrin reacted with bromine and chlorine as well as hydrogen bromide. The stereospecificities of the gas-solid halogenations of the acid in -cyclodextrin were similar to those of the both reactions in the solid state and in carbon tetrachloride solution without -cyclodextrin: bromination of the acid yieldederythro-2, 3-dibromo-3-phenylpropionic acid stereospecifically in 100 % in three different conditions, but chlorination gave an excess ofthreo-2, 3-dichloro-3-phenylpropionic acid to theerythro-isomer in 7287 % yields. 相似文献
89.
Hideki Namba Okihiro Tokunaga Tadashi Tanaka Yoshimi Ogura Shinji Aoki Ryoji Suzuki 《Radiation Physics and Chemistry》1993,42(4-6):669-672
The fundamental research work with simulated coal-fired flue gas was performed in JAERI to get basic data for electron beam treatment of flue gas from thermal power plants in Japan. The standard condition of the experiments was set to be the same as that of next large scale pilot test in Nagoya. The concentrations of NOx and SOx were 225 ppm and 800 ppm, respectively. The temperature of the system was 65°C. The effect of multiple irradiation was observed for NOx removal. The target SOx and NOx removals (94% and 80%, respectively) with low NH3 leakage (less than 10 ppm) were achieved at 9 kGy irradiation with 0.9 NH3 stoichiometry during 7 hours continuous operation. The facility for the pilot plant (12,000 Nm3/hr) has just built at the site of Shin-Nagoya power plant of Chubu Electric Power Company and will be started in full operation in November 1992. 相似文献
90.
Chiral β-dimethylaminoalkylphosphines were prepared starting with amino acids, (S)-alanine, (S)-phenylalanine, (R)-phenylglycine, (S)-valine, and (R)-tert-leucine. The chiral phosphines were found to be highly efficient ligands for a nickel catalyzed asymmetric Grignard cross-coupling reaction (38~94% optical yield). 相似文献