全文获取类型
收费全文 | 2090篇 |
免费 | 105篇 |
国内免费 | 3篇 |
专业分类
化学 | 1764篇 |
晶体学 | 24篇 |
力学 | 24篇 |
数学 | 75篇 |
物理学 | 311篇 |
出版年
2023年 | 16篇 |
2022年 | 13篇 |
2021年 | 28篇 |
2020年 | 48篇 |
2019年 | 42篇 |
2018年 | 29篇 |
2017年 | 17篇 |
2016年 | 45篇 |
2015年 | 64篇 |
2014年 | 84篇 |
2013年 | 114篇 |
2012年 | 172篇 |
2011年 | 170篇 |
2010年 | 90篇 |
2009年 | 98篇 |
2008年 | 175篇 |
2007年 | 163篇 |
2006年 | 157篇 |
2005年 | 158篇 |
2004年 | 120篇 |
2003年 | 72篇 |
2002年 | 58篇 |
2001年 | 26篇 |
2000年 | 18篇 |
1999年 | 13篇 |
1998年 | 15篇 |
1997年 | 11篇 |
1996年 | 4篇 |
1995年 | 4篇 |
1994年 | 8篇 |
1993年 | 8篇 |
1992年 | 4篇 |
1991年 | 10篇 |
1990年 | 18篇 |
1989年 | 6篇 |
1988年 | 7篇 |
1987年 | 7篇 |
1986年 | 10篇 |
1985年 | 12篇 |
1984年 | 10篇 |
1983年 | 6篇 |
1982年 | 5篇 |
1981年 | 10篇 |
1980年 | 9篇 |
1979年 | 5篇 |
1978年 | 10篇 |
1977年 | 5篇 |
1976年 | 3篇 |
1975年 | 4篇 |
1974年 | 5篇 |
排序方式: 共有2198条查询结果,搜索用时 31 毫秒
21.
Masafumi Kobayashi Tetsuya Inoguchi Takashi Iida Takashi Tanioka Hiroshi Kumase Yasushi Fukai 《Journal of fluorine chemistry》2003,120(2):2838-110
Direct fluorination of 1,3-dioxolan-2-one with elemental fluorine was successfully carried out to provide 4-fluoro-1,3-dioxolan-2-one, which was expected as an additive for lithium ion secondary battery. 4-Fluoro-1,3-dioxolan-2-one was also further fluorinated with elemental fluorine to give three isomers of difluoro derivatives by the same methodology. Another topic is the preparation of trifluoromethanesulfonyl fluoride, an intermediate of lithium battery electrolyte, by the reaction of methanesulfonyl fluoride with elemental fluorine. The use of perfluoro-2-methylpentane as a solvent gave satisfactory selectivity of trifluoromethanesulfonyl fluoride. 相似文献
22.
A simple high-performance liquid chromatographic method was developed for the simultaneous determination of the therapeutic levels of acyclovir and ganciclovir in human plasma. After precipitation of plasma proteins with 6% perchloric acid, acyclovir and ganciclovir were simultaneously determined by reversed-phase chromatography with spectophotometric detection at 254 nm. The peak heights for acyclovir and ganciclovir were linearly related to their concentrations ranging from 0.063 to 2.080 micro g/mL. The recovery was 100.48-102.84% for acyclovir and 99.26-103.07% for ganciclovir. The intra- and inter-day relative standard deviation values were in the range 0.186-8.703% for acyclovir and 0.137-6.424% for ganciclovir. The detection limits for both compounds were 0.01 micro g/mL determined as the signal-to-noise ratio of 3. The present method is applicable to therapeutic monitoring during antiviral medication. 相似文献
23.
Masayoshi Watanabe Tadashi Iida Kohei Sanui Naoya Ogata Tadahiko Kobayashi Zentaro Ohtaki 《Journal of polymer science. Part A, Polymer chemistry》1984,22(6):1299-1307
Novel polyamides that contain tetrathiafulvalene (TTF) moieties were synthesized by direct polycondensation of Δ2,2′ -bi-1,3-dithiole-4,4′(5′)-dicarboxylic acid with aromatic diamines in the presence of triphenylphosphine, hexachloroethane, and pyridine. Complexes of these polyamides with bromine were TTF cation radical () salts which resulted from the charge transfer of TTF moieties to bromine. The electrical conductivity of undoped polyamides increased with a decrease in diamine length. By doping the bromine the conductivity of the polyamides was enhanced by 3–5 orders of magnitude and reached 10?5–;10?9S cm?1. Maximum conductivity was observed at the doping ratio of [Br]/[repeat unit] < 1. The electrical conduction in the bromine complexes may be attributed to the hopping of odd electrons of between TTF moieties. 相似文献
24.
Akinori Ohshita Masaaki Okuhara Chiharu Matsuya Koichi Hata Kazuo Iida 《Mikrochimica acta》2006,155(1-2):225-228
A new electron holographic method is presented to directly visualize pure phase objects such as electromagnetic microfields,
which is achieved by superposition of two kinds of electron holograms. The method is very simple and is twice as sensitive
as the conventional double-exposure electron holography and the four-electron-wave interference. Using this technique, an
electric field around a charged latex sphere and a magnetic field around a barium ferrite particle have been directly observed. 相似文献
25.
Samples (0.5 g) are decomposed with mixed acids in a sealed teflon vessel. After suitable treatment, barium, cobalt, chromium, copper, lithium, nickel, scandium. strontium, vanadium and zirconium are determined sequentially. The method is satisfactory for a variety of standard silicate materials. 相似文献
26.
Takao K Yasui H Yamamoto S Sasaki D Kawasaki S Watanabe G Tadano K 《The Journal of organic chemistry》2004,69(25):8789-8795
The total syntheses of (+)-mycoepoxydiene and (-)-1893A have been completed. The present synthetic strategy features the use of one-pot ring-opening/cross metathesis (ROM/CM) followed by a ring-closing metathesis (RCM) reaction, allowing for the concise construction of the 9-oxabicyclo[4.2.1]nona-2,4-diene framework from a 7-oxabicyclo[2.2.1]hept-2-ene derivative and 1,3-butadiene. The sequential metathesis product was converted into (+)-mycoepoxydiene through the oxidative rearrangement of a furfuryl alcohol to a pyranone, thereby establishing its absolute stereochemistry. From the common intermediate, a structurally related natural product (-)-1893A was also synthesized via the vinylogous aldol reaction. 相似文献
27.
Yasuo Saegusa Sakayu Iida Shigeo Nakamura Nguyen Chau Yoshio Iwakura 《Journal of polymer science. Part A, Polymer chemistry》1984,22(5):1017-1023
Aromatic polythioamide-oxothioxoquinazolines were synthesized by the polycondensation of 2,2′-(m-phenylene)bis-1,3,4-thiadiazoline-5-thione with aromatic bis-o-amino esters. The polymerizations were carried out at 160°C in acidic media such as m-cresol, sulfolane, and polyphosphoric acid to produce polymers with reduced viscosities up to 0.5 dL/g. These polymers were soluble in polar aprotic solvents like N-methyl-2-pyrrolidone and some acidic media including m-cresol. The polythioamide-oxothioxoquinazolines showed relatively good thermal stability with 10% weight loss at 344–394°C in air. 相似文献
28.
The mass resolution of a time-of-flight (TOF) mass spectrometer is directly proportional to its total flight pathlength. Multi-turn or multi-passage ion optical geometries are necessary to obtain fight distances of sufficient length within reasonable size limitations. We have investigated ion optics for a multi-turn TOF mass spectrometer with electrostatic sectors. The concept of 'perfect' focusing conditions is introduced. Furthermore, a new type of multi-turn TOF mass spectrometer, the MULTUM Linear plus, was developed. It consists of four cylindrical electric sectors and 28 electric quadrupole lenses. It has a vacuum chamber 60 x 70 x 20 cm in size. Mass resolution is demonstrated to increase according to the number of ion cycles. A mass resolution of 350 000 (m/z = 28, FWHM) was achieved after 501.5 cycles. The MULTUM Linear plus analyzer is not simple, however; 28 electric quadrupole lenses are used. In order to reduce the number of ion optical parts, an improved multi-turn TOF mass spectrometer, the MULTUM II, consisting of only four toroidal electric sectors, was also developed. The possibility of tandem mass spectrometric applications using multi-turn TOF mass spectrometers is also discussed. 相似文献
29.
Iida K Hayakawa Y Okamoto H Danjo K Luenbergerb H 《Chemical & pharmaceutical bulletin》2003,51(12):1455-1457
The effect of the surface covering of lactose carrier particles on the dry powder inhalation properties of salbutamol sulfate was investigated. Lactose carrier surfaces were covered with sucrose tristearate (J-1803F) by a high-speed elliptical-rotor-type powder mixer (Theta-Composer). In the present study, drug/carrier powder mixtures were prepared consisting of micronized salbutamol sulfate and lactose carriers with various particle surface conditions prepared by surface covering. These powder mixtures were aerosolized by a Jethaler), and the in vitro inhalation properties of salbutamol sulfate were evaluated by a twin impinger. Compared with the powder mixed with uncovered lactose carrier, the in vitro inhalation properties of the powder mixture prepared using the surface covering lactose carrier were significantly different, showing that the in vitro inhalation properties of salbutamol sulfate were improved. In vitro inhalation properties increased with the percentage of J-1803F added. Using this surface covering system would thus be valuable for increasing the inhalation properties of dry powder inhalation with lactose carrier particles. 相似文献
30.
Influence of storage humidity on the in vitro inhalation properties of salbutamol sulfate dry powder with surface covered lactose carrier 总被引:1,自引:0,他引:1
Iida K Hayakawa Y Okamoto H Danjo K Luenberger H 《Chemical & pharmaceutical bulletin》2004,52(4):444-446
The influence of storage humidity on the in vitro inhalation properties of salbutamol sulfate dry powder with surface covered lactose carrier was investigated. In the present study, drug/carrier powder mixtures were prepared consisting of micronized salbutamol sulfate and lactose carriers with different particle surface conditions prepared by surface covering. Lactose carrier surfaces were covered with vegetable magnesium stearate (Mg-St-V) by a high-speed elliptical-rotor-type powder mixer (Theta-Composer). These powder mixtures were aerosolized by a Jethaler), and the in vitro inhalation properties of salbutamol sulfate were evaluated by a twin impinger. Compared with the powder mixed with uncovered lactose carrier, the in vitro inhalation properties of the powder mixture prepared using the surface covered lactose carrier were little decreased with increased in relative humidity (RH), showing that the in vitro inhalation properties of salbutamol sulfate were improved at high RH. Using this surface covering technique would thus be valuable for storage humidity of dry powder inhalation (DPI) with lactose carrier particles. 相似文献