全文获取类型
收费全文 | 5100篇 |
免费 | 108篇 |
国内免费 | 34篇 |
专业分类
化学 | 3506篇 |
晶体学 | 59篇 |
力学 | 73篇 |
数学 | 339篇 |
物理学 | 1265篇 |
出版年
2022年 | 35篇 |
2021年 | 39篇 |
2020年 | 45篇 |
2019年 | 73篇 |
2018年 | 52篇 |
2017年 | 36篇 |
2016年 | 70篇 |
2015年 | 104篇 |
2014年 | 93篇 |
2013年 | 303篇 |
2012年 | 255篇 |
2011年 | 284篇 |
2010年 | 166篇 |
2009年 | 187篇 |
2008年 | 283篇 |
2007年 | 314篇 |
2006年 | 307篇 |
2005年 | 263篇 |
2004年 | 206篇 |
2003年 | 185篇 |
2002年 | 209篇 |
2001年 | 111篇 |
2000年 | 129篇 |
1999年 | 81篇 |
1998年 | 50篇 |
1997年 | 52篇 |
1996年 | 84篇 |
1995年 | 49篇 |
1994年 | 38篇 |
1993年 | 56篇 |
1992年 | 74篇 |
1991年 | 51篇 |
1990年 | 54篇 |
1989年 | 49篇 |
1988年 | 66篇 |
1987年 | 48篇 |
1986年 | 55篇 |
1985年 | 79篇 |
1984年 | 71篇 |
1983年 | 34篇 |
1982年 | 53篇 |
1981年 | 46篇 |
1980年 | 48篇 |
1979年 | 44篇 |
1978年 | 42篇 |
1977年 | 52篇 |
1976年 | 27篇 |
1975年 | 36篇 |
1974年 | 32篇 |
1973年 | 33篇 |
排序方式: 共有5242条查询结果,搜索用时 15 毫秒
991.
Hiroshi Takahashi 《Hyperfine Interactions》2001,138(1-4):365-371
A high-intensity neutron source that is highly correlated spatially and with time and will be used for neutron scattering
experiments can be obtained by dt m catalyzed fusion by enhancing the formation rate of dtμ molecules using a high-intensity
pulsed laser to dtμ gas. This paper considers the use of dtμ fusion for fast ignition of inertial confinement fusion, and
the possibility of ensuring energy balance in energy production. dt fusion can be quickly ignited by depositing dtμ fusion
energy into a smaller space than is done in other methods, such as Z-pinch or heavy-ion fusion. Space propulsion can be obtained
with a light fuel mass rather than by a fission repulsion system using the muons produced by annihilation of the anti-protons
stored in liquid superfluid of condensed He. Using an extremely highly compressed target can create a source of high luminosity
muons for muon–muon collider- and neutrino-oscillation experiments. This approach can eliminate the need for a super-conducting
solenoidal for capturing the beam of pions and muons generated in a large target, and then these pions and muons can be manipulated
by a laser beam instead of by employing RF manipulation.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
992.
Naoki Taka Hiroshi Koga Haruhiko Sato Takenori Ishizawa Tadakatsu Takahashi 《合成通讯》2013,43(23):4263-4269
The novel potassium channel openers benzopyran-4-amides have been synthesized via palladium-catalyzed amidation of 4-bromobenzopyrans under an atmoshere in the presence of an equivalent of potassium iodide. 相似文献
993.
994.
Synthesis of medium-sized carbocyclic ketones via the intramolecular B-alkyl Liebeskind-Srogl coupling reaction is described. The sequence of hydroboration of ω-alkenyl thiol ester with 9-BBN and the Liebeskind-Srogl reaction results in the formation of medium-sized carbocyclic ketones with good yield. 相似文献
995.
Sulphoximides (Ia–Ie) were found to react with dimethyl diazomalonate (DDM) in the presence of a catalytic amount of Cu-salts affording the corresponding oxosulphonium ylides in moderate yields. The reaction did not proceed at all under irradiation of UV light. (?)-Methylphenyloxosulphonium bis(methoxycarbonyl)-methylide ((?)-IIb) was obtained from (+)-(S)-methylphenylsulphoximide ((+)-(S)-Ib) together with (?)-(S)-methyl phenyl sulphoxide ((?)-(S)-IIIb) by this reaction. Hydrolysis of (?)-IIb gave (+)-methylphenyloxosulphonium methoxycarbonylmethylide ((+)-IIf) which was converted to (?)-(S)-IIIb upon treatment with dibenzoylethylene. Stereochemical cycle starting from (+)-(S)-Ib to (?)-(S)-IIIb was established and the absolute configurations of both ylides, (?)-IIb and (+)-IIf were assigned as (R)-configuration. The stereochemical courses, namely from (+)-(S)-Ib or (?)-(S)-IIIb to (?)-(R)-IIb or (+)-(R)-IIf to (?)-(S)-IIIb were determined as retention processes. The optical purities of the oxosulphonium ylides obtained from both reactions, (+)-(S)-Ib→(?)-(R)-IIb and (?)-(S)-IIIb→(?)-(R)-IIb, were almost equal. These results indicate that the mechanism of the reaction of sulphoximides with carbenes (or carbenoids) involves the initial formation of the sulphoxides which react subsequently with carbenes to afford the final products. 相似文献
996.
Eiichi Kitazawa Akira Ogiso Shuji Takahashi Masaaki Kurabayashi Harumitsu Kuwano Tadashi Hata Chihiro Tamura 《Tetrahedron letters》1979,20(13):1117-1120
Two new diterpenelactones named plaunol A () and B () exhibiting anti-Shay ulcer activity were isolated from Thai medicinal plant, . Structure of was determined by X-ray analysis of its -bromobenzoate and structure of was deduced from the results of chemical correlation and the spectral data. 相似文献
997.
Aldol reactions, conjugate additions, and alkylation reactions of O-silylated ketene acetals take place under neutral conditions by using a high pressure technique. 相似文献
998.
Tetsuo Suami Hiroaki Sasai Kazuhiro Matsuno Nobuo Suzuki Yoshimasa Fukuda Osamu Sakanaka 《Tetrahedron letters》1984,25(40):4533-4536
Tunicamycins and their eight analogs have been synthesized by condensation of a N-acetyl-D-glucosamine derivative and an anomeric chloride of tunicaminyl uracil, followed by deprotections and N-acylation. 相似文献
999.
SERS from phthalazine adsorbed on an Ag electrode was investigated under several conditions of applied voltage and solution concentration. Spectral assignments of the Raman bands were successfully performed and two differently oriented adsorbates, i.e. flat and end-on species, were identified. The contribution of the image field to the SERS intensity was considerable. 相似文献
1000.
Takayuki DoiNobuaki Fujimoto Jun WatanabeTakashi Takahashi 《Tetrahedron letters》2003,44(10):2161-2165
We have developed a practical route for the synthesis of peptides containing unnatural amino acids. Mizoroki-Heck reaction of polymer-supported dehydroalanine, followed by asymmetric hydrogenation was accomplished using Pd(0) and Rh(I)-DuPHOS catalysts, respectively, leading to 36 dipeptides containing phenylalanine derivatives with high stereocontrol. 相似文献