全文获取类型
收费全文 | 2655篇 |
免费 | 130篇 |
国内免费 | 13篇 |
专业分类
化学 | 1958篇 |
晶体学 | 36篇 |
力学 | 19篇 |
数学 | 129篇 |
物理学 | 444篇 |
无线电 | 212篇 |
出版年
2023年 | 14篇 |
2022年 | 28篇 |
2021年 | 39篇 |
2020年 | 43篇 |
2019年 | 49篇 |
2018年 | 39篇 |
2017年 | 30篇 |
2016年 | 85篇 |
2015年 | 71篇 |
2014年 | 121篇 |
2013年 | 130篇 |
2012年 | 188篇 |
2011年 | 194篇 |
2010年 | 91篇 |
2009年 | 92篇 |
2008年 | 191篇 |
2007年 | 178篇 |
2006年 | 168篇 |
2005年 | 139篇 |
2004年 | 125篇 |
2003年 | 109篇 |
2002年 | 99篇 |
2001年 | 37篇 |
2000年 | 32篇 |
1999年 | 29篇 |
1998年 | 27篇 |
1997年 | 32篇 |
1996年 | 23篇 |
1995年 | 26篇 |
1994年 | 23篇 |
1993年 | 14篇 |
1992年 | 25篇 |
1991年 | 13篇 |
1990年 | 25篇 |
1989年 | 28篇 |
1988年 | 11篇 |
1987年 | 17篇 |
1986年 | 23篇 |
1985年 | 21篇 |
1984年 | 14篇 |
1983年 | 11篇 |
1982年 | 18篇 |
1981年 | 8篇 |
1980年 | 12篇 |
1979年 | 16篇 |
1978年 | 14篇 |
1977年 | 10篇 |
1976年 | 11篇 |
1975年 | 15篇 |
1974年 | 10篇 |
排序方式: 共有2798条查询结果,搜索用时 15 毫秒
991.
Hayashi Y Regnier T Nishiguchi S Sydnes MO Hashimoto D Hasegawa J Katoh T Kajimoto T Shiozuka M Matsuda R Node M Kiso Y 《Chemical communications (Cambridge, England)》2008,(20):2379-2381
Herein, we describe an efficient strategy for the total synthesis of (+)-negamycin using commercially available achiral N-Boc-2-aminoacetaldehyde as starting material with 42% overall yield for a limited number of steps. 相似文献
992.
Yamada M Wakahara T Tsuchiya T Maeda Y Kako M Akasaka T Yoza K Horn E Mizorogi N Nagase S 《Chemical communications (Cambridge, England)》2008,(5):558-560
Dimetallofullerene Ce(2)@C(78) and its bis-silylated derivative (1) were successfully prepared and fully characterized. 相似文献
993.
994.
Takahiro Kazami Kô hei Uchiyama 《Transactions of the American Mathematical Society》2008,360(11):6065-6087
This paper concerns random walks on periodic graphs embedded in the -dimensional Euclidian space and obtains asymptotic expansions of the Green functions of them up to the second order term, which, expressed fairly explicitly, are easily computable for many examples. The result is used to derive an asymptotic form of the hitting distribution of a hyperplane of co-dimension one, which involves not only the first but also second order terms of the expansion of the Green function. We also give similar expansions of the transition probabilities of the walks.
995.
996.
997.
Nicolas Delsuc Dr. Takahiro Kawanami Julien Lefeuvre Atsuomi Shundo Dr. Hirotaka Ihara Prof. Makoto Takafuji Prof. Ivan Huc Dr. 《Chemphyschem》2008,9(13):1882-1890
A series of helically folded oligoamides of 8‐amino‐2‐quinoline carboxylic acid possessing 6, 7, 8, 9, 10 or 16 units are prepared following convergent synthetic schemes. The right‐handed (P) and the left‐handed (M) helical conformers of these oligomers undergo an exchange slow enough to allow their chromatographic separation on a chiral stationary phase. Thus, the M conformer is isolated for each of these oligomers and its slow racemization in hexane/CHCl3 solutions is monitored at various temperatures using chiral HPLC. The kinetics of racemization at different temperatures in hexane/CHCl3 (75:25 vol/vol) are fitted to a first order kinetic model to yield the kinetic constant and the Gibbs energy of activation for oligomers having 6, 7, 8, 9, 10 or 16 quinoline units. This energy gives the first quantitative measure of the exceptional stability of the helical conformers of an aromatic amide foldamer with respect to its partly unfolded conformations that occur between an M helix and a P helix. The trend of the Gibbs energy as a function of oligomer length suggests that helix‐handedness inversion does not require a complete unfolding of a helical strand and may instead occur through the propagation of a local unfolding separating two segments of opposite handedness. 相似文献
998.
Ferrocene, a double-decker organometallic compound that generates angular motion, can be used as a unique rotary module for molecular machines. By interlocking a ferrocene-based rotary module with a photochromic unit, we have developed novel molecular machines that operate via power-conversion mechanisms. This design strategy, which mimics real machines in our daily life, allows for remote control of molecular events. 相似文献
999.
The excess partial molar enthalpies of urea (UR), H U R (E ), were experimentally determined in UR-H 2O at 25 degrees C. The H U R (E ) data were determined accurately and in small increments in the mole fraction of UR, x U R , up to x U R approximately 0.22. Hence it was possible to evaluate one more x U R -derivative graphically without resorting to any fitting function, and the model-free UR-UR enthalpic interaction, H U R- U R (E ), was calculated. Using previous data for the excess chemical potential, mu U R (E ), the entropy analogue, S U R- U R (E ), was also calculated. The x U R -dependences of both H U R- U R (E ) and S U R- U R (E ) indicate that there is a boundary at x U R approximately 0.09 at which the aggregation nature of urea changes. From the results of our earlier works, we suggest that a few UR molecules aggregate at x U R approximately 0.09, while the integrity of H 2O is retained at least up to x U R approximately 0.20. Together with the findings from our previous studies, we suggest that in the concentration range x U R < 0.22, UR or its aggregate form hydrogen bonds to the H 2O network, reducing the degree of fluctuation characteristic to liquid H 2O. However, up to at least x U R = 0.20 the hydrogen bond network remains intact. Above x U R approximately 0.22, the integrity of H 2O is likely be lost. Thus, in discussing the effect of urea on H 2O and in relating it to the structure and function of biopolymers in aqueous solutions, the concentration region in question must be specified. 相似文献
1000.
Kuramoto M Sakata Y Terai K Kawasaki I Kunitomo J Ohishi T Yokomizo T Takeda S Tanaka S Ohishi Y 《Organic & biomolecular chemistry》2008,6(15):2772-2781
A series of 2-(2-aminothiazol-4-yl)benzo[b]furan and 3-(2-aminothiazol-4-yl)benzo[b]furan derivatives were prepared, and their leukotriene B(4) inhibitory activity and growth inhibitory activity in cancer cell lines were evaluated. Several compounds showed strong inhibition of calcium mobilization in CHO cells overexpressing human BLT(1) and BLT(2) receptors and growth inhibition to human pancreatic cancer cells MIA PaCa-2. 3-(4-Chlorophenyl)-2-[5-formyl-2-[(dimethylamino)methyleneamino]thiazol-4-yl]-5-methoxybenzo[b]furan 8b showed the most potent and selective inhibition for the human BLT(2) receptor, and its IC(50) value was smaller than that of the selected positive control compound, ZK-158252. 3-(4-Chlorophenyl)-2-[2-[(dimethylamino)methyleneamino]-5-(2-hydroxyethyliminomethyl)thiazol-4-yl]-5-methoxybenzo[b]furan 9a displayed growth inhibitory activity towards MIA PaCa-2. 相似文献