全文获取类型
收费全文 | 4682篇 |
免费 | 119篇 |
国内免费 | 15篇 |
专业分类
化学 | 3534篇 |
晶体学 | 33篇 |
力学 | 74篇 |
数学 | 223篇 |
物理学 | 952篇 |
出版年
2022年 | 36篇 |
2021年 | 43篇 |
2020年 | 51篇 |
2019年 | 60篇 |
2018年 | 37篇 |
2017年 | 43篇 |
2016年 | 83篇 |
2015年 | 97篇 |
2014年 | 84篇 |
2013年 | 226篇 |
2012年 | 204篇 |
2011年 | 226篇 |
2010年 | 127篇 |
2009年 | 117篇 |
2008年 | 216篇 |
2007年 | 222篇 |
2006年 | 257篇 |
2005年 | 252篇 |
2004年 | 235篇 |
2003年 | 205篇 |
2002年 | 227篇 |
2001年 | 151篇 |
2000年 | 111篇 |
1999年 | 75篇 |
1998年 | 59篇 |
1997年 | 51篇 |
1996年 | 71篇 |
1995年 | 59篇 |
1994年 | 64篇 |
1993年 | 58篇 |
1992年 | 79篇 |
1991年 | 67篇 |
1990年 | 56篇 |
1989年 | 54篇 |
1988年 | 47篇 |
1987年 | 43篇 |
1986年 | 52篇 |
1985年 | 79篇 |
1984年 | 68篇 |
1983年 | 28篇 |
1982年 | 54篇 |
1981年 | 32篇 |
1980年 | 32篇 |
1979年 | 48篇 |
1978年 | 41篇 |
1977年 | 45篇 |
1976年 | 33篇 |
1975年 | 30篇 |
1974年 | 31篇 |
1973年 | 35篇 |
排序方式: 共有4816条查询结果,搜索用时 15 毫秒
971.
Atsushi Yamamoto Mio Kawai Mitsunori Sakamoto Shuji Kodama Kazuichi Hayakawa 《Analytical sciences》2008,24(3):361-364
A sensitive and variable-wavelength optical rotatory (OR) detector for high-performance liquid chromatography is presented. This design is entirely different from that of conventional OR detectors consisting of a crossed polarizer pair. By placing a polarizing prism and a retardation plate into a commercial circular dichroism (CD) detector, the OR signal was obtained. The Mueller matrix approach was used to prove the principle of the OR signal appearance. Sugars and 4-androstene-3,17-dione were chosen as test compounds. The limit of detection was below 0.5 microg of injected sucrose at 260 nm, which was superior to that obtained with a conventional OR detector. For 4-androstene-3,17-dione, which is CD active, and shows a large anomalous OR dispersion curve, our detector gave a large OR signal with approximately half the intensity of the CD signal at 340 nm. 相似文献
972.
Combination of the dianion of dialky 3-hexenedioate and β-bromopropionate leads directly to a 2,3-disubstituted cyclopentanone, which can be transformed to a variety of primary prostaglandins and sarkomycin. 相似文献
973.
974.
975.
976.
Akira Mori Kanji Kubo Manabu Takemoto Hayato Kitaura Seiji Ujiie 《Liquid crystals》2006,33(5):521-530
Two types of symmetric dimers with 5-(4-alkoxybenzoyloxy)tropone cores or with 4-(4-alkoxybenzoyloxy)phenyl cores were synthesized to evaluate the effect of the core structure and the length of the spacer on the mesomorphic properties. The former had smectic C phases whereas the latter had smectic C and F phases. Both types of dimer showed a remarkable odd-even effect on varying the spacer on the mesomorphic properties. Comparison of the thermal stability between them demonstrated that benzenoid twins are more stable than troponoid ones. The layer spacings of the smectic C phases were measured to determine the tilt angles of the core part, the spacer, and the side chains on changing the length of the spacer and the side chains. Troponoid dimers had a larger tilt angle of the core part of the smectic C phase than benzenoid twins, which lowered the thermal stability of the troponoid. Entropy changes of the smectic C phase to the isotropic liquid showed a contrast between troponoids and benzenoids. The former had smaller values and odd-even effects than the latter, which indicated that the former troponoids had a limited number of conformers in mesophases. 相似文献
977.
Manabu Oura 《Discrete Mathematics》2008,308(16):3722-3725
It is known that the weight enumerator of a self-dual doubly even code in genus g=1 can be uniquely written as an isobaric polynomial in certain homogeneous polynomials with integral coefficients. We settle the case where g=2 and prove the non-existence of such polynomials under some conditions. 相似文献
978.
Mayumi Takasu Hiroaki Wakabayashi Kyoji Furuta Hisashi Yamamoto 《Tetrahedron letters》1988,29(52):6943-6946
Achiral and chiral crowns complexed with potassium bases catalyze the Michael additions of enolates to cycloalkenones. 相似文献
979.