全文获取类型
收费全文 | 1530篇 |
免费 | 68篇 |
国内免费 | 5篇 |
专业分类
化学 | 1237篇 |
晶体学 | 20篇 |
力学 | 9篇 |
数学 | 64篇 |
物理学 | 273篇 |
出版年
2023年 | 8篇 |
2022年 | 9篇 |
2021年 | 19篇 |
2020年 | 30篇 |
2019年 | 33篇 |
2018年 | 23篇 |
2017年 | 17篇 |
2016年 | 33篇 |
2015年 | 34篇 |
2014年 | 41篇 |
2013年 | 89篇 |
2012年 | 104篇 |
2011年 | 104篇 |
2010年 | 58篇 |
2009年 | 60篇 |
2008年 | 78篇 |
2007年 | 77篇 |
2006年 | 73篇 |
2005年 | 67篇 |
2004年 | 64篇 |
2003年 | 41篇 |
2002年 | 48篇 |
2001年 | 27篇 |
2000年 | 40篇 |
1999年 | 27篇 |
1998年 | 18篇 |
1996年 | 23篇 |
1995年 | 17篇 |
1994年 | 20篇 |
1993年 | 16篇 |
1992年 | 15篇 |
1991年 | 10篇 |
1990年 | 12篇 |
1989年 | 14篇 |
1988年 | 13篇 |
1987年 | 10篇 |
1986年 | 12篇 |
1985年 | 14篇 |
1984年 | 17篇 |
1982年 | 10篇 |
1981年 | 18篇 |
1980年 | 10篇 |
1979年 | 8篇 |
1978年 | 10篇 |
1977年 | 17篇 |
1976年 | 17篇 |
1975年 | 14篇 |
1974年 | 11篇 |
1973年 | 15篇 |
1972年 | 11篇 |
排序方式: 共有1603条查询结果,搜索用时 46 毫秒
71.
72.
73.
74.
[formula: see text] The conformation of the retinal chromophore in rhodopsin is central for understanding the visual transduction process. The absolute twist around the 12-s bond of the chromophore in rhodopsin has been determined by studies with 11-cis-locked 11,12-cyclopropylretinal analogues (11S,12R)-2 and (11R,12S)-3, enantioselectively synthesized with the aid of an enzyme. The finding that enantiomer 2 binds to opsin while the other 3 does not defines the absolute sense of twist around the 12-s bond. 相似文献
75.
K. Norisuye K. Okamura Y. Sohrin H. Hasegawa T. Nakanishi 《Journal of Radioanalytical and Nuclear Chemistry》2005,267(1):183-193
Summary The present paper describes a new analytical method for determining the 240Pu/239Pu isotopic ratio and 238Pu/239+240Pu α -activity ratio in seawater, both of which are important parameters for determining Pu sources in the ocean. Plutonium
isotopes were preconcentrated from a large volume of seawater (4700-10800 liter) by solid phase extraction using MnO2-impregnated fibers and eluted into 3M HCl. After the elution, the Pu species of all oxidation states were converted to Pu(IV)
using NaNO2, purified by solvent extraction using thenoyltrifluoroacetone (TTA)-benzene, and concentrated in 5 ml of 0.2M HNO2. The 240Pu/239Pu and 238Pu/239+240Pu ratios in the 5-ml final solution were determined by inductively coupled plasma-mass spectrometry (ICP-MS) and α-spectrometry,
respectively. A pg level of Pu, which was a sufficiently large amount for the determination, was obtained by the solid phase
extraction. Through the redox conversion and solvent extraction, the Pu species, such as Pu(III), Pu(IV) and Pu(VI), were
collected at a high recovery of 96±2% (n=3) despite the presence of large amounts of Mn, and interfering 238U (3.3 μg. l-1in seawater) was effectively removed with a decontamination factor of 1.7·107. The accuracy of the method for the 240Pu/239Pu ratio was verified using reference materials of seawater and a terrestrial soil sample. The present technique was applied
to the determination of the 240Pu/239Pu and 238Pu/239+240Pu ratios in coastal and oceanic water. 相似文献
76.
Nakanishi M Eguchi A Akuta T Nagoshi E Fujita S Okabe J Senda T Hasegawa M 《Current protein & peptide science》2003,4(2):141-150
Improving the performance of non-viral gene-delivery vehicles that consist of synthetic compounds and nucleic acids is a key to successful gene therapy. Supplementing synthetic vehicles with various biological functions by using natural or artificial peptides is a promising approach with which to achieve this goal. One of the obstacles hindering this effort is that some of the potentially useful peptides, especially those with many basic amino acid residues, interfere with the formation of the complex owing to strong electrostatic interactions with the nucleic acid. In this review, we describe our recent work in examining the potential of these peptides in gene delivery, using a recombinant lambda phage particle as the model for the gene-delivery complex. Lambda phage encapsulates large duplex DNA in a rigid polyplex-like shell with a diameter of 55 nm, and can display various peptides on this capsid, independently of particle formation. By examining the expression of marker genes encapsulated in the phage capsid, we have demonstrated that the protein transduction domain of HIV Tat protein and the nuclear localization signal derived from SV40 T antigen can remarkably facilitate the delivery of these marker genes across the two major barriers, the cell membrane and the nuclear membrane, respectively. Our results indicate that these basic peptides can constitute effective components of synthetic gene-transfer complexes, as long as sufficient copies are displayed on the outer surface of the complex. 相似文献
77.
Isao Takahashi Fumika Morita Shunsuke Kusagaya Haruhiko Fukaya Osamu Kitagawa 《Tetrahedron: Asymmetry》2012,23(24):1657-1662
In the presence of an (R)-MOP-Pd2(dba)3 catalyst, the reaction of ortho-tert-butylaniline with 2-bromophenyl arylethynyl ketone proceeded via a tandem amination (1,4-addition of aniline to an ynone and subsequent intramolecular Buchwald–Hartwig amination) to afford axially chiral N-(2-tert-butylphenyl)-2-aryl-4-quinolinone derivatives with moderate enantioselectivity (up to 72% ee). 相似文献
78.
Assembly of submicron-sized microspheres has received much attention due to its high potential for wide variety of applications. We have developed a preparation method of polymer particles by simple mixing of a poor solvent into the polymer solution followed by evaporation of a good solvent. By using this technique, silica nanoparticles and polymer composite particles were prepared. Preparation of three-dimensional assemblies of silica particles in polymer particles and composite Janus particles are shown. 相似文献
79.
General acid‐catalyzed reaction can be enhanced by the addition of base. Self‐catalyzed esterification of benzoic acid and octan‐1‐ol was enhanced by the addition of certain base such as imidazole. The rate of the esterification was accelerated as the concentration of imidazole increased. Trans‐esterification of 4‐nitrophenyl acetate was promoted in chloroform by the mixture of benzoic acid and imidazole, but not by benzoic acid or imidazole alone. 相似文献
80.