全文获取类型
收费全文 | 2738篇 |
免费 | 93篇 |
国内免费 | 4篇 |
专业分类
化学 | 2110篇 |
晶体学 | 36篇 |
力学 | 62篇 |
数学 | 89篇 |
物理学 | 538篇 |
出版年
2022年 | 16篇 |
2021年 | 26篇 |
2020年 | 48篇 |
2019年 | 45篇 |
2018年 | 36篇 |
2017年 | 16篇 |
2016年 | 50篇 |
2015年 | 43篇 |
2014年 | 38篇 |
2013年 | 117篇 |
2012年 | 136篇 |
2011年 | 132篇 |
2010年 | 49篇 |
2009年 | 91篇 |
2008年 | 146篇 |
2007年 | 134篇 |
2006年 | 155篇 |
2005年 | 111篇 |
2004年 | 112篇 |
2003年 | 103篇 |
2002年 | 98篇 |
2001年 | 66篇 |
2000年 | 62篇 |
1999年 | 35篇 |
1998年 | 24篇 |
1997年 | 26篇 |
1996年 | 40篇 |
1995年 | 38篇 |
1994年 | 36篇 |
1993年 | 31篇 |
1992年 | 49篇 |
1991年 | 33篇 |
1990年 | 42篇 |
1989年 | 49篇 |
1988年 | 42篇 |
1987年 | 36篇 |
1986年 | 30篇 |
1985年 | 65篇 |
1984年 | 65篇 |
1983年 | 19篇 |
1982年 | 39篇 |
1981年 | 30篇 |
1980年 | 34篇 |
1979年 | 43篇 |
1978年 | 33篇 |
1977年 | 27篇 |
1976年 | 29篇 |
1975年 | 24篇 |
1974年 | 20篇 |
1973年 | 15篇 |
排序方式: 共有2835条查询结果,搜索用时 0 毫秒
91.
The α-haloester having an internal double bond was allowed to react with a catalytic amount of Pd(PPh3)4 to afford a cyclized product in a fairly good yield and the same product was obtained by treatment with Pd(OAc)2 to ketene silyl acetal. 相似文献
92.
Kazuo Iguchi Soichiro Kaneta Kenichiro Mori Yasuji Yamada Atsushi Honda Yo Mori 《Tetrahedron letters》1985,26(47):5787-5790
New halogenated marine prostanoids, chlorovulone I, II and III were isolated from the stolonifer Quoy and Gaimard. The structure elucidation and the antitumor activity of chlorovulones were described. 相似文献
93.
Both the enantiomers of 2,3-dihydro-2-isopropyl-2,5-dimethylfuran were synthesized employing the Sharpless asymmetric epoxidation reaction. The (R)-(—)-enantiomer of this cyclic enol ether was also synthesized starting from (R)-(—)-linalool. 相似文献
94.
The reaction of cycloalkanones with silicon tetraisothiocyanate in the presence of (Me3SiO)2SO2?nBu3SnF or Zn(NCS)2 provides 1-cycloalkenyl isothiocyanates in good yields under mild conditions. 相似文献
95.
96.
Both (E)- and (Z)-isomers of (S)-14-methyl-8-hexadecenal (trogodermal) were synthesized from 100% optically pure (R)-(+)-citronellic acid. These antipodes of the khapra beetle pheromone were 1/500 to 1/1000 times as active as the natural (R)-pheromone. Determination of the optical purities of citronellic acid and related compounds was achieved by hplc method. Warning was made not to forget the measurement of density in expressing the optical rotation of a neat liquid as [α]D (neat). 相似文献
97.
Tsuneyuki Sato Osamu Ito Shigeki Mori Takayuki Otsu 《Journal of polymer science. Part A, Polymer chemistry》1984,22(7):1661-1676
Poly(dimethylaminoethyl methacrylate N-oxide) (poly(DMAEMNO)) was prepared by oxidation of poly(dimethylaminoethyl methacrylate) with hydrogen peroxide in methanol. From thermogravimetric and IR spectroscopic investigations Cope elimination of amine oxide group in poly(DMAENO) was found to occur at 120–150°C. The postpolymerization of partially pyrolyzed polymer carrying vinyl ester group as pendant was performed with azobisisobutyronitrile at 60°C in methanol to give cross-linked polymer that was found to form hydrogel. Poly(DMAEMNO) gave metal–polymer complexes with CuCl2, ZnCl2, and CoCl2. Cobalt–polymer complex had a constitution of 1:2 of metal ion to amine oxide group, while copper– and zinc–polymer complexes seemed to have structures of 1:1 and 1:2 of metal ion to amine oxide group. Furthermore, polymer complexes of poly(DMAEMNO) with poly(methacrylic acid) and poly(acrylic acid) were found to be formed by mixing aqueous solutions of both polymers and also by radical polymerization of the acid monomers in the presence of poly(DMAEMNO). From elemental analysis, thermogravimetric investigation, and measurement of turbidity it was concluded that the resulting polymer–polymer complexes contained more than one acid monomer unit per one N-oxide unit. 相似文献
98.
N Kubodera K Miyamoto M Akiyama M Matsumoto T Mori 《Chemical & pharmaceutical bulletin》1991,39(12):3221-3224
Three vitamin D3 analogues, 1 alpha,25-dihydroxy-23-oxavitamin D3 (3), 1 alpha,25-dihydroxy-23-thiavitamin D3 (4) and 1 alpha,25-dihydroxy-23-azavitamin D3 (5) were synthesized. In the differentiation-inducing activity of human myeloid leukemia cells into macrophages in vitro, the 23-aza analogue (5) showed the least activity, while no remarkable differences were observed between the 23-oxa analogue (3) and the 23-thia analogue (4), which were less active than 1 alpha,25-dihydroxyvitamin D3 (1). 相似文献
99.
Xu Q Tanaka K Mori M Helaleh MI Hu W Hasebe K Toada H 《Journal of chromatography. A》2003,997(1-2):183-190
A monolithic ODS-silica gel column modified by saturating it with lithium dodecylsulfate (Li-DS) was used to demonstrate the high-speed separation of H+ from other mono- and divalent cations, such as Na+, NH4+, K+, Mg2+ and Ca2+ using ion chromatography (IC). Using a 5 mM EDTA-2K solution containing 0.10 mM Li-DS (pH 4.80) as eluent, H+ was eluted with a sharp and symmetrical peak within 1.0 min before other cations at a flow-rate of 1.5 ml min(-1). The rapid elution of H+ and its conductimetric detection could be attributed to the presence of EDTA (HY2-), which can convert H+ ions as anions. i.e. H(+) + H2Y(2-) --> H3Y(-). The acidity of rainwater and deionized water samples was determined using this IC system with satisfactory results. 相似文献
100.
Reduction followed by cyclization of (Z)-methyl 3-(6-azido-3-chloro-1-methyl-4-oxo-1,4-dihydropyridazin-5-yl)-2-methylacrylate (I) to pyrido[2,3-c]pyridazines by treatment with triethyl phosphite or hydrazine hydrate as the reducing agents is described. Compound I was also reductively cyclized with sodium borohydride. Treatment of I with concentrated sulfuric acid gave 8-chloro-3,6-dimethyl-2,5-dioxo-5,6-dihydro-2H-pyrano[2,3-d] pyridazine (VII) which also could be synthesized by another independent route. A mechanism for the cyclization is proposed. 相似文献