全文获取类型
收费全文 | 1434篇 |
免费 | 46篇 |
国内免费 | 8篇 |
专业分类
化学 | 1092篇 |
晶体学 | 14篇 |
力学 | 37篇 |
数学 | 68篇 |
物理学 | 277篇 |
出版年
2023年 | 16篇 |
2022年 | 11篇 |
2021年 | 12篇 |
2020年 | 16篇 |
2019年 | 20篇 |
2018年 | 17篇 |
2017年 | 11篇 |
2016年 | 31篇 |
2015年 | 33篇 |
2014年 | 21篇 |
2013年 | 58篇 |
2012年 | 72篇 |
2011年 | 69篇 |
2010年 | 59篇 |
2009年 | 54篇 |
2008年 | 81篇 |
2007年 | 100篇 |
2006年 | 89篇 |
2005年 | 60篇 |
2004年 | 79篇 |
2003年 | 56篇 |
2002年 | 48篇 |
2001年 | 36篇 |
2000年 | 27篇 |
1999年 | 20篇 |
1998年 | 19篇 |
1997年 | 17篇 |
1996年 | 16篇 |
1995年 | 11篇 |
1994年 | 18篇 |
1993年 | 14篇 |
1992年 | 20篇 |
1991年 | 14篇 |
1990年 | 15篇 |
1989年 | 14篇 |
1988年 | 9篇 |
1987年 | 12篇 |
1986年 | 15篇 |
1985年 | 25篇 |
1984年 | 28篇 |
1983年 | 11篇 |
1982年 | 16篇 |
1981年 | 8篇 |
1980年 | 11篇 |
1979年 | 14篇 |
1978年 | 10篇 |
1976年 | 12篇 |
1974年 | 9篇 |
1973年 | 8篇 |
1965年 | 7篇 |
排序方式: 共有1488条查询结果,搜索用时 0 毫秒
91.
Hirofumi Kuroda Ikuyoshi Tomita Takeshi Endo 《Journal of polymer science. Part A, Polymer chemistry》1996,34(8):1597-1604
Tri-n-butylphosphine-catalyzed polyadditions of activated internal diynes (bifunctional β-substituted propiolate, 1B and 1C ) with diols are described. Although a terminal bispropiolate ( 1A ) could not produce soluble polymers, with secondary diols, the polyaddition of 1B or 1C with primary as well as secondary diols gave corresponding polymers ( 3 , only composed of E isomeric units) in high yield. The rate of the present polyaddition was estimated by a model reaction of benzyl alcohol with methyl 2-heptynoate ( 4 ), from which the introduction of alkyl groups at the β-position of propiolate moieties was found to decrease the rate of the reaction by 80 times. Furthermore, the rate-determining step on this polymerization system was speculated to be a protonation step of zwitterionic intermediates with protons from diols. © 1996 John Wiley & Sons, Inc. 相似文献
92.
Kazuhisa Maeda Yasushi Tomita Masako Naganuma Hachiro Tagaml 《Photochemistry and photobiology》1996,64(1):220-223
Guinea pig skin becomes more pigmented following exposure to UV rays. This melanization was accompanied by enhanced intensity of tyrosinase-staining and increased number of tyrosinase-positive melanocytes (MELty+), with resultant enhancement of melanin synthesis. To clarify the regulatory mechanism for melanization following UV irradiation, organ-cultured guinea pig skins have been used to examine their melanogenic responses to exogenous stimulation. This organ culture system responded well to UV irradiation, by increasing melanogenic activity. Also, in this system, phospholipases (PL), arachidonic acid, interleukin-1α and melanocytestimulating hormone, but not endothelin-1 or phosphatidylinositol-specific PLC (PI-PLC), stimulated melanogenesis to various extents as indicated by the number of MELty+ and morphological changes. Among them, the PLA2 and PLD were found to have a potent stimulatory property for melanocytes. They might affect melanocytes directly or indirectly through an effect on keratinocytes. These results suggest that PLA2 and PLD play a key role in epidermal hyperpigmentation after UV irradiation or inflammation. 相似文献
93.
The iodine/DMAP-mediated intramolecular tandem C–C/C–O bond forming reaction of malonate bearing alkene moiety proceeded to give bicyclic lactones with good diastereoselectivity in good yield. The mechanistic investigation was also discussed on the basis of various control experimental results. 相似文献
94.
Dr. Tatsuki Kurokawa Dr. Shigeki Kiyonaka Dr. Eiji Nakata Dr. Masayuki Endo Shohei Koyama Emiko Mori Nam Ha Tran Huyen Dinh Dr. Yuki Suzuki Kumi Hidaka Dr. Masaaki Kawata Dr. Chikara Sato Prof. Hiroshi Sugiyama Prof. Takashi Morii Prof. Yasuo Mori 《Angewandte Chemie (International ed. in English)》2018,57(10):2586-2591
In native systems, scaffolding proteins play important roles in assembling proteins into complexes to transduce signals. This concept is yet to be applied to the assembly of functional transmembrane protein complexes in artificial systems. To address this issue, DNA origami has the potential to serve as scaffolds that arrange proteins at specific positions in complexes. Herein, we report that Kir3 K+ channel proteins are assembled through zinc‐finger protein (ZFP)‐adaptors at specific locations on DNA origami scaffolds. Specific binding of the ZFP‐fused Kir3 channels and ZFP‐based adaptors on DNA origami were confirmed by atomic force microscopy and gel electrophoresis. Furthermore, the DNA origami with ZFP binding sites nearly tripled the K+ channel current activity elicited by heterotetrameric Kir3 channels in HEK293T cells. Thus, our method provides a useful template to control the oligomerization states of membrane protein complexes in vitro and in living cells. 相似文献
95.
Tokuyama R Takahashi Y Tomita Y Suzuki T Yoshida T Iwasaki N Kado N Okezaki E Nagata O 《Chemical & pharmaceutical bulletin》2001,49(4):347-352
A structure-activity relationship (SAR) study on 5-substituted oxazolidinones as an antibacterial agent is described. The oxazolidinones, of which 5-acetylaminomethyl moiety was converted into other functions, were prepared and evaluated for antibacterial activity. Elongation of the methylene chain (8) and conversion of the acetamido moiety into guanidino moiety (12) decreased the antibacterial activity. The replacement of carbonyl oxygen (=O) by thiocarbonyl sulfur (=S) enhanced in vitro antibacterial activity. Especially, compound 16, which had the 5-thiourea group, showed 4-8 stronger in vitro activity than linezolid. Our SAR study revealed that the antibacterial activity was greatly affected by the conversion of 5-substituent. 相似文献
96.
Tokuyama R Takahashi Y Tomita Y Tsubouchi M Yoshida T Iwasaki N Kado N Okezaki E Nagata O 《Chemical & pharmaceutical bulletin》2001,49(4):353-360
5-Thiourea and 5-dithiocarbamate oxazolidinones were synthesized as a continuation of research on 5-thiocarbonyl oxazolidinone antibacterial agents considering the hydrophobic parameters of the molecule. The structure-activity relationship (SAR) study revealed that the antibacterial activity on 5-thiocarbonyl oxazolidinones was significantly affected by the lipophilicity, especially the calculated log P value and the balance between 5-hydrophilic (or hydrophobic) substituent and hydrophobic (or hydrophilic) substituents on the benzene ring. Some of 5-thiocarbonyl oxazolidinones were found to have good in vitro antibacterial activity against gram-positive bacteria including methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant enterococci (VRE). 相似文献
97.
Wang CR Kai T Tomiyama T Yoshida T Kobayashi Y Nishibori E Takata M Sakata M Shinohara H 《Angewandte Chemie (International ed. in English)》2001,40(2):265
The cover picture shows a section of the electron charge density of the first metal carbide endohedral metallofullerene (Sc(2)C(2))@C(84) obtained from a synchrotron X-ray powder diffraction study by the maximum entropy method (MEM). The several density maxima, which correspond to scandium and carbon atoms, are clearly seen inside the C(84) carbon cage. The MEM charge density distribution also reveals that the C(84) cage has D(2d) symmetry (no. 23) and that the C(2) axis is parallel to the <100> face-centered cubic (fcc) direction of the unit cell. As a consequence of the site symmetry being 4mm, the C(2) axis of (Sc(2)C(2))@C(84) is oriented to six equivalent <100> directions and shows a merohedral disorder. The resultant Sc small middle dot small middle dot small middle dotSc distances and C-C bond lengths of the Sc(2)C(2) cluster are 0.429(2) and 0.142(6) nm, respectively. The observed C-C bond length is between that of a typical single and a double bond, and is very close to that of the C-C bond (0.143 nm) combining two pentagons in a C(60) molecule. More about this fascinating structure can be found in the contribution by Shinohara and co-workers on p. 397 ff. 相似文献
98.
99.
100.
The electrochemical fluorination of cycloalkyl-substituted acetic and propionic acids were conducted to obtain several kinds of perfluorobicyclic ethers [reaction conditions: Anodic current density: 3.5 A/dm2, Volt: 5~8V, Temp: 5~6 °C] . For example, from cyclopentyl-substituted acetic acids, perfluoro(4-alkyl-2-oxabicyclo[3.3.0]octane)s (I) were formed as the cyclization products in yields of 10~19% together with the corresponding perflouroalkanoyl flourides (II) (Y=3~13%). While, perfluorospiro-ethers were obtained from the fluorination of 3-cycloalkyl-substituted propionic acids. The characterization of these perfluorobicyclic ethers which consists of the reaction with anhydrous aluminum chloride will be reported also. 相似文献