全文获取类型
收费全文 | 893篇 |
免费 | 24篇 |
国内免费 | 2篇 |
专业分类
化学 | 626篇 |
晶体学 | 14篇 |
力学 | 7篇 |
数学 | 34篇 |
物理学 | 238篇 |
出版年
2021年 | 12篇 |
2020年 | 13篇 |
2019年 | 18篇 |
2018年 | 6篇 |
2017年 | 9篇 |
2016年 | 13篇 |
2015年 | 14篇 |
2014年 | 20篇 |
2013年 | 56篇 |
2012年 | 40篇 |
2011年 | 54篇 |
2010年 | 22篇 |
2009年 | 20篇 |
2008年 | 54篇 |
2007年 | 29篇 |
2006年 | 40篇 |
2005年 | 43篇 |
2004年 | 28篇 |
2003年 | 27篇 |
2002年 | 35篇 |
2001年 | 11篇 |
2000年 | 13篇 |
1999年 | 10篇 |
1998年 | 6篇 |
1997年 | 11篇 |
1996年 | 15篇 |
1995年 | 10篇 |
1994年 | 8篇 |
1993年 | 14篇 |
1992年 | 15篇 |
1991年 | 7篇 |
1990年 | 8篇 |
1988年 | 7篇 |
1987年 | 5篇 |
1986年 | 6篇 |
1985年 | 19篇 |
1984年 | 17篇 |
1983年 | 6篇 |
1982年 | 14篇 |
1981年 | 24篇 |
1980年 | 21篇 |
1979年 | 17篇 |
1978年 | 18篇 |
1977年 | 8篇 |
1976年 | 11篇 |
1975年 | 5篇 |
1974年 | 9篇 |
1973年 | 9篇 |
1968年 | 7篇 |
1966年 | 4篇 |
排序方式: 共有919条查询结果,搜索用时 15 毫秒
11.
Treatment of alkyl allyl carbonates derived from various alcohols with a palladium catalyst in MeCN affords ketones and aldehydes in high yields. This new method of oxidation of alcohols can be applied to various alcohols except simple primary alcohols. 相似文献
12.
A simple and selective route to the Strychnos framework containing 19,20-double bond has been developed employing the thio-Claisen rearrangement. 相似文献
13.
Isotropie Raman spectra of the symmetric C—H stretching bands of several organic molecules are measured in the neat liquid and in solvents including water. The linewidths are interpreted on the basis of the vibrational dephasing model, and intermolecular interactions between the solutes and solvents are discussed. 相似文献
14.
Koichi Tanaka Hideyuki Takano Zofia Urbanczyk-lipkowska 《Journal of inclusion phenomena and macrocyclic chemistry》2006,56(3-4):281-285
The host compounds 1,1’-binaphthyl-2,2′-dihydroxy-5,5′-dicarboxylic acid (1) and 1,1′-binaphthyl-2,2′-dihydroxy-6,6′-dicarboxylic acid (2) have been synthesized, and their inclusion properties have been studied. Inclusion complexes formed by 1 and 2 with volatile guests such as acetone and methanol release the guests only at much higher temperatures than their boiling
points. The crystal structures of the inclusion complexes have been determined from single crystal X-ray diffraction data
and show different host lattices. 相似文献
15.
The conductance of potassium iodide has been measured in the solvents ethylene carbonate, water, methyl ethyl ketone, and pairwise mixtures of these solvents at 40°C; and ethylene carbonate-water, tetramethylene sulfone-water, dimethyl sulfoxide-water, tetrahydrofuran-water, ethylene carbonate-tetramethylene sulfone-water, ethylene carbonate-tetramethylene sulfone, and tetrahydrofuran-dimethyl sulfoxide at 25°C. For dielectric constants greater than about 60, the pairing constants KA are in the range 0.3–2.0; no correlation between KA and solvent properties could be established. For lower dielectric constants, KA increases exponentially with decreasing dielectric constant. Addition of a proton, acceptor to water initially decreases KA regardless of whether the dielectric constant of the mixture is higher or lower than that of water, suggesting that ion pairs in water may be stabilized by cage structures. The Walden product Ao is also decreased by the addition of proton acceptors. 相似文献
16.
Allylation of carbonucleophiles with allylic carbamates under neutral conditions has been studied. The C-allylation of carbonucleophile is competitive with the N-allylation of amines, and the structure of amines is crucial for the selectivity. Bulky secondary amines gave the best results. Also a new method of protection-deprotection of amines as carbamates has been developed. Smooth deprotection is possible by the palladium-catalyzed reaction of allyl carbamates with formic acid. This method is particulary useful for primary amines, including optically active amino acids. 相似文献
17.
M Kaneko T Kobayashi H Takano T Ohnishi T Kaku T Nishi C Kawase K Kaneko 《Radioisotopes》1989,38(8):344-346
Thyroid scintigraphy in rats and mice with 99mTc and 123I was attempted to examine whether this modality might be used in small animals and to describe the possibilities of its application in examining experimentally produced thyroid diseases. A human gamma camera with a pinhole collimator improved for small animals was used for imaging. Thyroid images with 99mTc were obtained 20 minutes after injection and those with 123I were 24 hours after administration. All the scintigrams, although those obtained from mice with 99mTc displayed overlapped salivary gland images, demonstrated sufficiently clear images in size and shape, which showed that thyroid scintigraphy in small animals should be applicable in examining experimentally produced thyroid diseases. 相似文献
18.
[reaction: see text] The enantioselective total synthesis of (+)-allocyathin B(2) has been achieved. Our approach features a convergent enantioselective construction of the 5-6-7 tricyclic core system using the originally developed chiral building blocks via asymmetric catalysis, the intramolecular aldol reaction in high yield, successful samarium diiodide-mediated ring expansion, and a newly developed double-bond installation method. 相似文献
19.
Dehydrroxy-trans-resorcylide () was synthesized by efficient intramolecular alkylation of the protected cyanohydrin. The butadiene telomer obtained by the palladium catalyzed reaction of butadiene with acetic acid was used as a suitable block of the carbocycle. 相似文献
20.
Hiroki Nakamura Jiro Tanaka Nobuaki Nakashima Keitaro Yoshihara 《Chemical physics letters》1981,77(2):419-421
The photoionization of 8-anilino-1-naphthalenesulfonate in polar solvents occurs through a biphotonic process, as proved by nanosecond flash photolysis. A transient absorption of a charge transfer to solvent (CTTS) state is found with ≈10 ns life-time. The state is shown to be an intermediate of the photoionization process. 相似文献