全文获取类型
收费全文 | 2981篇 |
免费 | 104篇 |
国内免费 | 14篇 |
专业分类
化学 | 2290篇 |
晶体学 | 47篇 |
力学 | 24篇 |
数学 | 116篇 |
物理学 | 622篇 |
出版年
2023年 | 13篇 |
2022年 | 23篇 |
2021年 | 23篇 |
2020年 | 32篇 |
2019年 | 33篇 |
2018年 | 31篇 |
2017年 | 24篇 |
2016年 | 55篇 |
2015年 | 63篇 |
2014年 | 67篇 |
2013年 | 148篇 |
2012年 | 177篇 |
2011年 | 192篇 |
2010年 | 120篇 |
2009年 | 124篇 |
2008年 | 177篇 |
2007年 | 199篇 |
2006年 | 194篇 |
2005年 | 193篇 |
2004年 | 146篇 |
2003年 | 164篇 |
2002年 | 137篇 |
2001年 | 37篇 |
2000年 | 38篇 |
1999年 | 46篇 |
1998年 | 23篇 |
1997年 | 35篇 |
1996年 | 48篇 |
1995年 | 15篇 |
1994年 | 22篇 |
1993年 | 20篇 |
1992年 | 35篇 |
1991年 | 23篇 |
1990年 | 15篇 |
1989年 | 15篇 |
1988年 | 14篇 |
1987年 | 13篇 |
1986年 | 14篇 |
1985年 | 48篇 |
1984年 | 50篇 |
1983年 | 13篇 |
1982年 | 38篇 |
1981年 | 40篇 |
1980年 | 36篇 |
1979年 | 29篇 |
1978年 | 23篇 |
1977年 | 14篇 |
1976年 | 16篇 |
1975年 | 10篇 |
1973年 | 10篇 |
排序方式: 共有3099条查询结果,搜索用时 0 毫秒
991.
992.
Takeuchi Y Azuma K Abe H Sasaki K Harayama T 《Chemical & pharmaceutical bulletin》2002,50(7):1011-1012
The stereo structure of piperidine lactone (3), an intermediate of the antimalarial agent febrifugine ((+)-1) prepared by a synthetic method, was re-revised to the cis-form from the trans-form. 相似文献
993.
The effect of various substances on the suppression of the bitterness of quinine-human gustatory sensation,binding, and taste sensor studies 总被引:2,自引:0,他引:2
Nakamura T Tanigake A Miyanaga Y Ogawa T Akiyoshi T Matsuyama K Uchida T 《Chemical & pharmaceutical bulletin》2002,50(12):1589-1593
The purpose of this study was to quantify the degree of suppression of the perceived bitterness of quinine by various substances and to examine the mechanism of bitterness suppression. The following compounds were tested for their ability to suppress bitterness: sucrose, a natural sweetener; aspartame, a noncaloric sweetener; sodium chloride (NaCl) as the electrolyte; phosphatidic acid, a commercial bitterness suppression agent; and tannic acid, a component of green tea. These substances were examined in a gustatory sensation test in human volunteers, a binding study, and using an artificial taste sensor. Sucrose, aspartame, and NaCl were effective in suppressing bitterness, although at comparatively high concentrations. An almost 80% inhibition of bitterness (calculated as concentration %) of a 0.1 mM quinine hydrochloride solution required 800 mM of sucrose, 8 mM of aspartame, and 300 mM NaCl. Similar levels of bitterness inhibition by phosphatidic acid and tannic acid (81.7, 61.0%, respectively) were obtained at much lower concentrations (1.0 (w/v)% for phosphatidic acid and 0.05 (w/v)% for tannic acid). The mechanism of the bitterness-depressing effect of phosphatidic acid and tannic acid was investigated in terms of adsorption and masking at the receptor site. With phosphatidic acid, 36.1% of the bitterness-depressing effect was found to be due to adsorption, while 45.6% was due to suppression at the receptor site. In the case of 0.05 (w/v)% tannic acid, the total bitterness-masking effect was 61.0%. The contribution of the adsorption effect was about 27.5% while the residual masking effect at the receptor site was almost 33%. Further addition of tannic acid (0.15 (w/v)%), however, increased the bitterness score of quinine, which probably represents an effect of the astringency of tannic acid itself. Finally, an artificial taste sensor was used to evaluate or predict the bitterness-depressing effect. The sensor output profile was shown to reflect the depressant effect at the receptor site rather well. Therefore, the taste sensor is potentially useful for predicting the effectiveness of bitterness-depressant substances. 相似文献
994.
Kenji Miyatake Allan S. Hay 《Journal of polymer science. Part A, Polymer chemistry》2001,39(11):1854-1859
Three arylene difluoride monomers containing phosphine oxide ( 1 ), phosphinic acid ( 2 ), or phosphinate ester ( 3 ) groups were prepared and polymerized with bisphenol A to give novel poly-(arylene ether)s ( 4 , 5 , and 6 ). The polymers obtained had moderate molecular weights (ηinh: 0.14–0.30 dL g−1 in N-methylpyrrolidinone) and glass-transition temperatures (Tg: 102–200 °C), depending on the phosphine group in the main chain. Using bis(4-fluorophenyl)sulfone as a comonomer improved the polymerization to give copolymers with higher solution viscosities. The stoichiometric investigation revealed that 7 mol % excess of fluoride monomer gave the highest molecular weight copolymer 8 with ηinh of 0.78 dL g−1, which had a Tg of 176 °C, a T of 432 °C, and formed a hard film by casting from solution. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1854–1859, 2001 相似文献
995.
The derivatives of the strain energy function u with respect to the invariants of the strain tensor (I1 and I2) are estimated for uncross-linked butadiene rubber by using the BKZ constitutive equation. The derivatives at small deformations
show anomalous behavior; namely, an upturn for ∂u/∂I1 and a downturn for ∂u/∂I2 take place, as is the case of cross-linked rubbers. At large deformations, u is well described by u = A1(I1 −3) + A2(I2 −3) with numerical constants A1 and A2. This behavior is also quite similar to that for cross-linked rubbers. The non-zero positive constant A2 for the melt suggests that the non-zero value is due to neither the inhomogeneity in network structure nor high extension
of constituent polymer chains. 相似文献
996.
Seto Kenji Hollenshead Jeromy T. Watson A. Ted Chang C. T. Philip Slattery John C. 《Transport in Porous Media》2001,42(3):351-387
This study develops a methodology for determining the absolute permeability distribution in a porous media sample using velocity data obtained from NMR imaging experiments. An objective function describing the discrepancy between observed and simulated data is reduced by iteratively updating the permeability. This parameter estimation scheme is based on an iterative method which uses optimal control theory to refine the estimates. Although this theory is developed for both isotropic and anisotropic porous media, the permeability reconstructions examined in this paper are restricted to the isotropic case. Synthetic data are used to investigate the impact of varying the noise in the experimental data, the degree of parameterization, the relative weighting of the regularization term in the objective function, and the amount and type of data required to obtain a satisfactory permeability reconstruction. These synthetic data are extracted from the solution of numerical experiments that have utilized an assumed permeability distribution. The methodology is also applied to data gathered in laboratory experiments for water flow in a sandstone sample. 相似文献
997.
Kenji Sasaki Ying‐Xue Zhang Kensuke Okuda Takashi Hirota 《Journal of heterocyclic chemistry》2001,38(2):425-429
The reactions of N‐(5,6‐dihydro[1]benzoxepino[5,4‐ d]pyrimidin‐4‐yl)amidines or its amide oxime derivatives with hydroxylamine hydrochloride gave abnormal cyclization products via a ring cleavage of pyrimidine component accompanied with a ring closure of [1,2,4]oxadiazole. 相似文献
998.
We prove a smoothing property for one dimensional time dependent Schr?dinger equations with potentials which satisfy at infinity, k≥ 2. As an application, we show that the initial value problem for certain nonlinear Schr?dinger equations with such potentials
is L
2 well-posed. We also prove a sharp asymptotic estimate of the L
p
-norm of the normalized eigenfunctions of H=−Δ+V for large energy.
Dedicated to Jean-Michel Combes on the occasion of his Sixtieth Birthday
Received: 10 October 2000 / Accepted: 29 March 2001 相似文献
999.
A solid state ionic device to titrate electrolytes in water was produced, and the performance of the device was examined. The device named the coulometric titration apparatus is a three-component electrochemical cell like an electrodialyzer. The central component, the analyzing room, is a container of the sample solution. The sample solution, 10−1 M H2SO4, NaOH, Na2SO4, or 10−7–10−2 M Na2SO4, is separated from the cathode and the anode room solutions, 10−2 M H2SO4, NaOH, or Na2SO4, by Nafion-117 and Tosflex IE-SF34 membranes working as the anion and the cation blocking electrodes, respectively. The quantity of electricity to extract whole electrolytes in the sample solution is evaluated from the peak area of the titration curve. The sample concentration is successfully determined by the calibration curve method, with the quantity of electricity and the sample volume (6 ml) in the range from 10−1 to 10−5 M. 相似文献
1000.
Kenji Nishihara 《数学进展》2001,(4)
本文讨论单个粘性守恒律方程与具有粘性的p方程组的Cauchy问题.根据初始资料的不同情形,其相应的Riemann问题以疏散波,激波或它们的迭加为弱解.本文的目的是指出Cauchy问题的解将分别趋于疏散波,激波或它们的迭加.本文基本方法是能量积分法.文中综述了现有的成果,也提出了一些未解决的问题. 相似文献