全文获取类型
收费全文 | 1634篇 |
免费 | 68篇 |
国内免费 | 2篇 |
专业分类
化学 | 1330篇 |
晶体学 | 16篇 |
力学 | 19篇 |
数学 | 45篇 |
物理学 | 294篇 |
出版年
2023年 | 13篇 |
2022年 | 14篇 |
2021年 | 25篇 |
2020年 | 30篇 |
2019年 | 41篇 |
2018年 | 30篇 |
2017年 | 15篇 |
2016年 | 41篇 |
2015年 | 36篇 |
2014年 | 40篇 |
2013年 | 70篇 |
2012年 | 120篇 |
2011年 | 115篇 |
2010年 | 61篇 |
2009年 | 65篇 |
2008年 | 83篇 |
2007年 | 77篇 |
2006年 | 109篇 |
2005年 | 82篇 |
2004年 | 75篇 |
2003年 | 51篇 |
2002年 | 53篇 |
2001年 | 30篇 |
2000年 | 34篇 |
1999年 | 24篇 |
1998年 | 11篇 |
1997年 | 9篇 |
1996年 | 20篇 |
1995年 | 12篇 |
1994年 | 15篇 |
1993年 | 8篇 |
1992年 | 18篇 |
1991年 | 17篇 |
1990年 | 20篇 |
1989年 | 8篇 |
1988年 | 13篇 |
1987年 | 9篇 |
1986年 | 9篇 |
1985年 | 11篇 |
1984年 | 17篇 |
1982年 | 11篇 |
1981年 | 10篇 |
1980年 | 10篇 |
1979年 | 15篇 |
1978年 | 14篇 |
1977年 | 10篇 |
1975年 | 9篇 |
1974年 | 17篇 |
1973年 | 20篇 |
1970年 | 8篇 |
排序方式: 共有1704条查询结果,搜索用时 15 毫秒
1.
Kento Nishikibe Keisuke Nishikawa Momochika Kumagai Matsumi Doe Yoshiki Morimoto 《化学:亚洲杂志》2022,17(1):e202101137
There are marine cytotoxic bromotriterpenoids, named the thyrsiferol family that are structurally characterized by some tetrahydropyran (THP) and tetrahydrofuran (THF) rings. The thyrsiferol family belongs to natural products that are often difficult to determine their stereostructures even by the current, highly advanced spectroscopic methods, especially in acyclic systems including stereogenic tetrasubstituted carbon centers. In such cases, it is effective to predict and synthesize the possible stereostructures. Herein, to elucidate ambiguous stereostructures and unassigned absolute configurations of aplysiol B, laurenmariannol, and saiyacenol A, members of the thyrsiferol family, we carried out their asymmetric chemical syntheses featuring 6-exo and 5-exo oxacyclizations of epoxy alcohol precursors and 6-endo bromoetherification of a bishomoallylic alcohol. In this paper, we report total assignments of their stereostructures through their asymmetric chemical syntheses and also their preliminary cytotoxic activities against some tumor cells. These results could not have been achieved without depending on asymmetric total synthesis. 相似文献
2.
3.
Toshiro Watanabe Tapan Kumar Mazumder Shiro Nagai Keisuke Tsuji Shigeru Terabe 《Analytical sciences》2003,19(1):159-161
A micellar electrokinetic chromatography (MEKC) method was developed for estimating the angiotensin-I converting enzyme (ACE) inhibitory activity by separating the hippuric acid liberated in the ACE reaction mixture in the presence of an inhibitor, captopril. The hippuric acid was successfully separated and detected by MEKC with a 25 mM sodium dodecyl sulfate solution in a 25 mM phosphate-50 mM borate buffer at pH 7.0; the total analysis took about 5 min. A good linear relationship was observed between the inhibitor and the peak area of hippuric acid release. No significant difference in the ACE inhibitory activity (IC50) of captopril (an antihypertensive medicine) or autolyzed-mushrooms (functional foods) was observed between the conventional method and the MEKC method. The MEKC method was found to be a useful technique for a rapid assay of the ACE inhibitory activity. 相似文献
4.
Kosuke Morita Kouji Morimoto Daiya Kaji Yu Liang Zhao Atsushi Yoshida Toshimi Suda Akira Yoneda Tetsuya Ohnishi Hiromitsu Haba Eiji Ideguchi Hu Shan Xu Tao Zheng Hisaaki Kudo Keisuke Sueki Kenji Katori Isao Tanihata 《Acta Physica Hungarica A》2004,19(1-2):53-60
A gas-filled type of recoil separator for heavy element research was installed at an experimental hall of RIKEN Linear Accelerator facility to realize getting higher intensity of primary beam and long beam time. Performance of the separator was studied using target recoils and various nuclear reactions. The results show the high performance of the separator for heave element research. As an application of the GARIS, production and identification of an isotope of the 110th element 271[110] have been performed using the 208Pb(64Ni,1n)271[110] reaction. Three decay chains coincide well both in decay times and energies with the ones reported by the group of SHIP experiment at GSI, Germany. Our results provide a confirmation of the synthesis of an isotope 271[110] of element 110. 相似文献
5.
6.
A new 20-membered macrolide designated exiguolide has been isolated from the marine sponge Geodia exigua, and its structure determined by interpretation of spectroscopic data. Exiguolide specifically inhibited fertilization of sea urchin (Hemicentrotus pulcherrimus) gametes but not embryogenesis of the fertilized egg. 相似文献
7.
8.
Arsenic speciation analysis in marine samples was performed using ion chromatography (IC) with inductively coupled plasma mass spectrometry (ICP‐MS) detection. The separation of eight arsenic species, viz. arsenite, monomethyl arsonic acid, dimethylarsinic acid, arsenate, arsenobetaine, tetramethylarsine oxide, arsenocholine and tetramethylarsonium ion was achieved on a Dionex AS4A (weaker anion exchange column) by using a nitric acid pH gradient eluent (pH 3.3 to 1.3). The entire separation was accomplished in 12 min. The detection limits for the eight arsenic species by IC–ICP‐MS were in the range 0.03–1.6 µ g l?1, based on 3σ of the blank response (n = 6). The repeatability and day‐to‐day reproducibility were calculated to be less than 10% (residual standard deviation) for all eight species. The method was validated by analyzing a certified reference material (DORM‐2, dogfish muscle) and then successfully applied to several marine samples, e.g. oyster, fish muscle, shrimp and marine algae. The low power microwave digestion was employed for the extraction of arsenic from seafood products. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
9.
Copper(II) is determined by non-extractive spectrophotometry as a complex of butylene dithiocarbamate formed in situ by reaction between carbon disulfide and pyrrolidine in aqueous Triton X-100 medium. This method is similar to that with butylene dithiocarbamate as starting material in the sense of simplicity, sensitivity, precision and accuracy. Pyrrolidine is the best of seven secondary amines tested in this way for copper determinations. 相似文献
10.