全文获取类型
收费全文 | 1778篇 |
免费 | 62篇 |
国内免费 | 10篇 |
专业分类
化学 | 1405篇 |
晶体学 | 24篇 |
力学 | 15篇 |
数学 | 116篇 |
物理学 | 290篇 |
出版年
2023年 | 17篇 |
2022年 | 13篇 |
2021年 | 23篇 |
2020年 | 22篇 |
2019年 | 36篇 |
2018年 | 29篇 |
2017年 | 14篇 |
2016年 | 43篇 |
2015年 | 27篇 |
2014年 | 54篇 |
2013年 | 91篇 |
2012年 | 92篇 |
2011年 | 114篇 |
2010年 | 79篇 |
2009年 | 79篇 |
2008年 | 94篇 |
2007年 | 104篇 |
2006年 | 104篇 |
2005年 | 98篇 |
2004年 | 76篇 |
2003年 | 91篇 |
2002年 | 100篇 |
2001年 | 51篇 |
2000年 | 31篇 |
1999年 | 19篇 |
1998年 | 25篇 |
1997年 | 14篇 |
1996年 | 17篇 |
1995年 | 11篇 |
1994年 | 11篇 |
1993年 | 12篇 |
1992年 | 21篇 |
1991年 | 16篇 |
1990年 | 13篇 |
1989年 | 12篇 |
1987年 | 16篇 |
1986年 | 9篇 |
1985年 | 21篇 |
1984年 | 10篇 |
1983年 | 12篇 |
1982年 | 13篇 |
1981年 | 8篇 |
1980年 | 8篇 |
1979年 | 9篇 |
1978年 | 16篇 |
1977年 | 12篇 |
1976年 | 9篇 |
1975年 | 9篇 |
1974年 | 9篇 |
1973年 | 8篇 |
排序方式: 共有1850条查询结果,搜索用时 15 毫秒
101.
Dr. Yuki Ohishi Kentaro Masuda Kazuki Kudo Prof. Dr. Hajime Abe Prof. Dr. Masahiko Inouye 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(2):785-793
Generally, cage-shaped hosts for saccharides can bind strongly to guest molecules because of the three-dimensional preorganized hydrogen-bonding sites. However, the preparation of cage molecules is often difficult because of the low yield of the macrocyclization step. Here, we report a three-arm-shaped molecule possessing pyridine-acetylene-phenol units as a new kind of host having a preorganized three-dimensional hydrogen-bonding site. This three-arm-shaped host was readily prepared compared to a cage-shaped analogue. This host associated with lipophilic glycosides to form chiral complexes, and the association constants were sufficiently high as to be comparable to those of the cage-shaped analogue. Furthermore, this host extracted native monosaccharides into a lipophilic solvent. 相似文献
102.
Kentaro Okuma Kazuki Kojima Kosei Shioji 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1):583-586
Reactions of selenobenzophenones with methyl propiolate afforded two types of cycloadducts regioselectively. The reaction with tetracyanoethylene gave selenophene derivatives. Mechanisms of these reactions were discussed. 相似文献
103.
Yoshiki Horikawa Naoya Konakahara Tomoya Imai Abe Kentaro Yoshinori Kobayashi Junji Sugiyama 《Polymer Degradation and Stability》2013
The enzymatic hydrolysis of cellulose I achieves almost complete digestion when sufficient enzyme loading as much as 20 mg/g-substrate is applied. However, the yield of digestion reaches the limit when the enzyme dosage is decreased to 2 mg/g-substrate. Therefore, we have performed three pretreatments such as mercerization, dissolution into phosphoric acid and EDA treatment. Transformation into cellulose II hydrate by mercerization and dissolution into phosphoric acid were not sufficient because substrate changed to highly crystalline structure during saccharification. On the other hand, in the case of crystalline conversion of cellulose I to IIII by EDA, almost perfect digestion was achieved even in enzyme loading as small as 0.5 mg/g-substrate, furthermore, hydrolyzed residue was typical cellulose I. The structural analysis of substrate after saccharification provides an insight into relationships between cellulose crystalline property and cellulase toward better enzymatic digestion. 相似文献
104.
105.
Prof. Joe Otsuki Takumi Okumura Dr. Kosuke Sugawa Dr. Shin-ichiro Kawano Prof. Kentaro Tanaka Dr. Takehiro Hirao Prof. Takeharu Haino Yu Jin Lee Seongsoo Kang Prof. Dongho Kim 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(12):4053-4063
Self-assembly of porphyrins is a fascinating topic, not only for mimicking chlorophyll assemblies in photosynthetic organisms, but also for the potential of creating molecular-level devices. Herein, zinc porphyrin derivatives bearing a meta-pyridyl group at the meso position were prepared and their assemblies studied in chloroform. Among the porphyrins studied, one with a carbamoylpyridyl moiety gave a distinct 1H NMR spectrum in CDCl3, which allowed the supramolecular structure in solution to be probed in detail. Ring-current-induced chemical-shift changes in the 1H NMR spectrum, together with vapor-pressure osmometry and diffusion-ordered NMR spectroscopy, among other evidence, suggested that the porphyrin molecules form a trimer with a triangular cone structure. Incorporation of a directly linked porphyrin–ferrocene dyad with the same assembling properties in the assemblies led to a rare example of a light-harvesting/charge-separation system in which an energy gradient is incorporated and reductive quenching occurs. 相似文献
106.
107.
Tatsuro Ouchi Toshio Banba Hiroshi Masuda Tatsuji Matsumoto Shigeo Suzuki Masuko Suzuki 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(10):959-975
In order to provide a macromolecular prodrug of 5-fluorouracil (5FU) reducing the side effects, having an affinity for tumor cells, and exhibiting strong antitumor activity, the covalent attachments of 5FUs to chitosan and chitosamino-oligosaccharide (COS) through hexamethylene spacer groups via urea, urea bonds were carried out. The effect of prolongation of life was tested in vivo against p388 lyrnphocytic leukemia in female CDF, mice by intra-peritoneal (i.p.) transplantation/i.p. injection and the growth-inhibitory effect on Meth-A fibrosarcoma or MH-134Y heputoma was evaluated in vivo in SPF-C3H/He scl male or Balb/c male mice by subcutaneous (s.c.) implantation/intravenous (i.v.) injection. The effects of the degree of polymerization of chitosan and 相似文献
108.
This article reviews recent topics on the polymerization of substituted acetylenes, focusing on the synthesis of poly(diphenylacetylenes) and the living polymerization of phenylacetylenes. Diphenylacetylene (DPA) polymerizes with TaCls-n-Bu4Sn to give a polymer which is thermally very stable but insoluble in any solvents. DPAs with various groups (e.g.,p-Me3Si,m-Me3Ge, p-t-Bu,and_p-PhO) polymerize similarly. These polymers are soluble and their M¯w's reach 1 × 106 to 3 × 106. Some of them are more gas-permeable than poly(dimethylsiloxane). Several acetylenes (e.g., ClC -n-C6H13 and HCUC-t-Bu) have been found to undergo living polymerization with MoOCl4-n-Bu4Sn-EtOH. Whereas phenylacetylene (PA) does not polymerize in a living fashion, ortho-substituents in PA more or less suppress termination and chain transfer. PAs with bulky ortho groups (e.g., CF3 and Me3Ge) especially undergo virtually ideal living polymerization. 相似文献
109.
The labeling of oligo- and polynucleotides with fluorescent probes is an important technique for the analysis of DNAs and RNAs. The effect of duplex formation with complementary oligo-DNA on the quenching behavior of two fluorescent chromophores (eosin, Eo and tetramethylrhodamine, TMR) attached to the 5′-terminal of various 10mer oligo-DNAs was investigated and the dependence of the quenching on DNA base sequence is discussed. We found that guanine residues played a major role in the quenching of the fluorescence of the chromophores. Guanine residues on the complementary DNA near the chromophores, in particular, had a significant influence on the quenching. 相似文献
110.
O. Takahashi Y. Masuda A. Muroya T. Furuya 《SAR and QSAR in environmental research》2013,24(5-6):547-558
In general, the docking scoring tends to have a size dependence related to the ranking of compounds. In this paper, we describe a novel method of parameter optimization for docking scores which reduce the size dependence and can efficiently discriminate active compounds from chemical databases. This method is based on a simplified theoretical model of docking scores which enables us to utilize large amounts of data of known active and inactive compounds for a particular target without requiring large computational resources or a complicated procedure. This method is useful for making scoring functions for the identification of novel scaffolds using the knowledge of active compounds for a particular target or a customized scoring function for an interesting family of drug targets. 相似文献