全文获取类型
收费全文 | 2604篇 |
免费 | 120篇 |
国内免费 | 6篇 |
专业分类
化学 | 2165篇 |
晶体学 | 16篇 |
力学 | 19篇 |
数学 | 136篇 |
物理学 | 394篇 |
出版年
2023年 | 18篇 |
2022年 | 17篇 |
2021年 | 33篇 |
2020年 | 58篇 |
2019年 | 46篇 |
2018年 | 38篇 |
2017年 | 25篇 |
2016年 | 61篇 |
2015年 | 71篇 |
2014年 | 81篇 |
2013年 | 126篇 |
2012年 | 189篇 |
2011年 | 191篇 |
2010年 | 102篇 |
2009年 | 118篇 |
2008年 | 207篇 |
2007年 | 200篇 |
2006年 | 195篇 |
2005年 | 182篇 |
2004年 | 154篇 |
2003年 | 96篇 |
2002年 | 76篇 |
2001年 | 42篇 |
2000年 | 28篇 |
1999年 | 16篇 |
1998年 | 21篇 |
1997年 | 13篇 |
1996年 | 17篇 |
1995年 | 11篇 |
1994年 | 14篇 |
1993年 | 10篇 |
1992年 | 16篇 |
1991年 | 12篇 |
1990年 | 19篇 |
1989年 | 18篇 |
1988年 | 13篇 |
1987年 | 13篇 |
1985年 | 19篇 |
1984年 | 22篇 |
1983年 | 10篇 |
1982年 | 14篇 |
1981年 | 15篇 |
1980年 | 8篇 |
1979年 | 11篇 |
1978年 | 16篇 |
1977年 | 10篇 |
1976年 | 7篇 |
1975年 | 11篇 |
1974年 | 8篇 |
1973年 | 6篇 |
排序方式: 共有2730条查询结果,搜索用时 531 毫秒
121.
The new tripeptide reported here is composed of (R)-2-(3-aminophenoxy)propionic acid and is a bowl-shaped receptor that simultaneously binds both cations and anions of acetylcholine chloride and benzyltrimethylammonium compounds. An intriguing conformational change of the host was observed in the complexation of the ionic pair, where anion-induced flipping of the amide group on the macrocycle occurred. 相似文献
122.
123.
Yasuhiro Igarashi Daisuke Asano Kazuo Furihata Naoya Oku Satoshi Miyanaga Hiroaki Sakurai Ikuo Saiki 《Tetrahedron letters》2012,53(6):654-656
During the course of screening natural products for the inhibitors of tumor cell invasion, pterocidin, a linear polyketide with a δ-lactone terminus, was rediscovered from a Streptomyces strain of a marine sediment-origin. A series of J-based configuration analyses and NOESY analysis, coupled with chemical derivatization and chiral anisotropy analysis, established the absolute stereochemistry of five asymmetric centers in this compound. 相似文献
124.
Total Synthesis of the 7,10‐Epimer of the Proposed Structure of Amphidinolide N,Part II: Synthesis of C17–C29 Subunit and Completion of the Synthesis
下载免费PDF全文
![点击此处可从《Chemistry (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Dr. Koji Ochiai Dr. Sankar Kuppusamy Yusuke Yasui Kenji Harada Dr. Nishant R. Gupta Dr. Yohei Takahashi Prof. Dr. Takaaki Kubota Prof. Dr. Jun'ichi Kobayashi Prof. Dr. Yujiro Hayashi 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(10):3287-3291
The total synthesis of 7,10‐epimer of the proposed structure of amphidinolide N was accomplished. The requisite chiral C17–C29 subunit was assembled stereoselectively via Keck allylation, Shi epoxidation, diastereoselective 1,3‐reduction, and a later oxidative synthesis of the THF framework. The C1–C13 and C17–C29 subunits were successfully coupled using a Enders RAMP “linchpin” as the C14–C16 three carbon unit, thereby controlling the chirality at C14 and C16. The labile allyl epoxy moiety was successfully constructed by Grieco–Nishizawa olefination at a final stage of the synthesis. 相似文献
125.
126.
Stereodivergent Synthesis and Stereochemical Reassignment of the C79–C104 Fragment of Symbiodinolide
下载免费PDF全文
![点击此处可从《Chemistry (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Prof. Dr. Hiroyoshi Takamura Takayuki Fujiwara Yohei Kawakubo Prof. Dr. Isao Kadota Prof. Dr. Daisuke Uemura 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(6):1984-1996
We have synthesized eight possible diastereoisomers 3 a – h of the C79–C97 fragment of symbiodinolide ( 1 ) in a stereodivergent manner by utilizing a dithiane addition to the aldehyde as a key step. Comparison of the 13C NMR chemical shifts of the natural product 1 and the synthetic products 3 a – h indicated that the relative stereostructure of this fragment in symbiodinolide ( 1 ) is that represented in 3 a or f . We have stereodivergently synthesized eight possible diastereoisomers of the C94–C104 fragment 4 a – h , and we have compared their 13C NMR chemical shifts with those of the natural product, which established the relative stereochemistry of this fragment to be that described in diastereoisomers 4 a or e . By combining the stereostructural outcomes of the C79–C97 and C94–C104 fragments, we have proposed four candidate compounds of the C79–C104 fragment 2 a – d . We also synthesized diastereoisomers 2 a and b ( 2 a in the preceding article; Chem. Eur. J. 2015 , DOI: 10.1002/chem.201503880) by a Julia–Kocienski olefination and diastereoisomers 2 c and d by a Wittig reaction. By comparing the 13C NMR chemical shifts of natural symbiodinolide ( 1 ) with those of the synthetic products 2 a – d , we have reassigned the stereostructure of the C79–C104 fragment of natural product 1 to be that depicted in diastereoisomer 2 b . 相似文献
127.
128.
Shinji Nakaya Daisuke Segawa Toshikazu Kadota Yoshiaki Nagashima Tomoya Furuta 《Proceedings of the Combustion Institute》2011,33(2):2031-2038
The burning and sooting behaviors of isolated fuel droplets for ethanol and n-decane are examined in high concentration of the ambient carbon dioxide under microgravity. A quartz fiber with the diameter of 50 μm maintains the droplet in the center of the combustion chamber and the range in the initial droplet diameter is from 0.30 to 0.80 mm. The ambience consists of oxygen, nitrogen and carbon dioxide. The concentration of oxygen is 21% in volume, and that of carbon dioxide is varied from 0% to 60% in volume. Detail measurements of the projected image of the droplet are conducted by using a high speed video camera and the effective droplet diameter squared are calculated from the surface area of the rotating body of the projected object. From evolutions of the droplet diameter squared, the instantaneous burning rates are calculated. Time history of the instantaneous burning rate clearly represents the droplet combustion events, such as the initial thermal expansion, ignition and following combustion. The instantaneous burning rate for n-decane shows an increasing trend during combustion, while that for non-sooting ethanol remains almost constant or shows a decreasing trend. A slight stepwise increase in the instantaneous burning rate is observed for larger n-decane droplets in air, which may be attributed to soot accumulation. However, this behavior of the burning rate disappears in higher concentration of carbon dioxide. Direct observation of the droplet flame indicates suppression of soot production in higher concentration of carbon dioxide and the suppression is enhanced for smaller droplet. 相似文献
129.
Naoyuki Toriumi Atsuya Muranaka Daisuke Hashizume Masanobu Uchiyama 《Tetrahedron letters》2017,58(23):2267-2271
Methylene-bridged benziphthalocyanine dimer 2 was unexpectedly generated by the reaction of dihydroxybenziphthalocyanine 1 and formaldehyde in the presence of a catalytic amount of a base at room temperature. Single-crystal X-ray diffraction analysis of 2 revealed a V-shaped structure. Dimer 2 exhibited longer-wavelength absorption and fluorescence bands than monomer 1 in the near-IR region. 相似文献
130.
In this paper, we give a polytopal estimate of Mirkovi?–Vilonen polytopes lying in a Demazure crystal in terms of Minkowski sums of extremal Mirkovi?–Vilonen polytopes. As an immediate consequence of this result, we provide a necessary (but not sufficient) polytopal condition for a Mirkovi?–Vilonen polytope to lie in a Demazure crystal. 相似文献