首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   536篇
  免费   13篇
  国内免费   3篇
化学   271篇
晶体学   4篇
力学   15篇
数学   72篇
物理学   190篇
  2023年   3篇
  2022年   7篇
  2021年   11篇
  2020年   5篇
  2019年   8篇
  2018年   5篇
  2016年   14篇
  2015年   6篇
  2014年   15篇
  2013年   31篇
  2012年   25篇
  2011年   28篇
  2010年   11篇
  2009年   13篇
  2008年   27篇
  2007年   30篇
  2006年   26篇
  2005年   35篇
  2004年   28篇
  2003年   16篇
  2002年   24篇
  2001年   12篇
  2000年   12篇
  1999年   6篇
  1998年   4篇
  1997年   5篇
  1996年   13篇
  1995年   9篇
  1994年   8篇
  1993年   10篇
  1992年   8篇
  1991年   9篇
  1990年   5篇
  1989年   3篇
  1988年   3篇
  1987年   4篇
  1986年   4篇
  1985年   10篇
  1984年   9篇
  1983年   6篇
  1982年   3篇
  1978年   3篇
  1977年   6篇
  1976年   3篇
  1975年   4篇
  1974年   5篇
  1973年   3篇
  1971年   3篇
  1936年   2篇
  1932年   2篇
排序方式: 共有552条查询结果,搜索用时 15 毫秒
1.
Investment projects and businesses can be entered or exited at a cost, and the theory of real option teaches us how to find optimal activity levels that should trigger entry or exit. However, in practice, different managers or owners operate under different constraints and might apply different thresholds to the same business. We are interested in the hedging of the risk related to the cost of sub-optimal entry or exit. We introduce a new class of derivative products that can hedge this risk. The pricing of these derivatives involves the joint law of a Brownian excursion and its supremum, which is calculated thanks to Bessel processes-related distribution laws.  相似文献   
2.
The treatment of nanoscopic silica grafted in the blend during the processing of silica‐filled styrene butadiene rubber was performed with silane, introduced at different concentrations, or at a constant concentration with a given length of alkyl chain. From swelling measurements in water and in solvent, the maximum silane content that can be grafted has been calculated as a function of the length of the silane alkyl chains as well as their efficiency to cover the silica surface. The found values are close to the values found in the literature for grafting in solution. Moreover, a direct correspondence between the length of the silane alkyl chains and their concentration has been deduced. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 143–152, 2006  相似文献   
3.
4.
5.
The kinetics of peptide release during in vitro digestion of 4 protein sources (casein, cod protein, soy protein, and gluten) were investigated. Samples were sequentially hydrolyzed with pepsin (30 min) and pancreatin (2, 4, or 6 h) in a dialysis cell with continuous removal of digestion products. Nondialyzed digests were fractionated by ion-exchange chromatography and ultrafiltration. Animal proteins were digested at a greater rate than plant proteins. Target amino acids of specific enzymes appeared more rapidly in the dialyzed fractions when compared to other amino acids. Throughout the hydrolysis, nondialyzed digests contained a higher proportion of peptide mixtures with basic-neutral properties. Except for gluten, peptide fractions with molecular weights that exceeded 10 kDa (basic-neutral, BN > 10) were rapidly hydrolyzed during the first 2 h of pancreatin digestion. The kinetics of release and the composition of peptide fractions were different when the protein sources were compared. The analysis of amino acids revealed that threonine and proline proportions were relatively high in BN > 10 and in peptide fractions with molecular weight between 10-1 kDa (BN 10-1), while tyrosine, phenylalanine, lysine, and arginine predominated in the low molecular weight (<1 kDa) fractions. More resistant peptides were generally rich in proline and glutamic acid. The role of in vitro digestion assays in dietary protein quality evaluation is discussed.  相似文献   
6.
The conformational preferences for 2,3-O-isopropylidene-α- -sorbopyranose derivatives 3–6 were determined by using 1H NMR data and empirical force field calculations. Proton NMR studies of 3–6 indicate that a twist-boat (or skew) conformation (3S0) prevails over possible chair forms for each compound. Force-field calculations (MM2, MNDO, AM1) on a model 2,3-O-isopropylidene-α- -sorbopyranose system (18) indicate that the 3S0 conformation is among the low-energy structures. X-Ray crystallographic analysis of α- -sorbopyranose sulfamate 3, a compound with potent anticonvulsant activity, demonstrates that the 3S0 skew conformation is manifested in the solid state, as well.  相似文献   
7.
Composite materials were processed by casting a mixture of aqueous suspensions of latex and microfibrils. These microfibrils, or whiskers, are extracted from a sea animal and are monocrystals of cellulose, with an aspect ratio around 100 and an average diameter of 20 nm. It has been found that the mechanical properties (shear modulus) are increased by more than two orders of magnitude in the rubbery state of the polymeric matrix, when the whisker content was 6% (w/w). This very large effect is discussed on the basis of different types of mechanical models and it is concluded that these whiskers form a rigid network, probably linked by hydrogen bonds. The formation of this network is assumed to be governed by a percolation mechanism.  相似文献   
8.
The dissociation of SF5Cl and CF3I sensitized by multiphoton excitation of SF6 by a pulsed CO2 laser has been studied versus pressure, laser fluence, inert gas and optical frequency. Isotopic effects have been observed between 32SF5Cl/33SF5Cl and between 13CF3I/12CF3I and selectivity factors as high as α?13332 = 1.57 or α1312 = 1.23 obtained.  相似文献   
9.
It is shown that the ionization potential I of N,N,N′,N′-tetramethylparaphenylenediamine (TMPD) dissolved in several hydrocarbons is constant in the solid phase from 77 K up to the melting point TM and suffers an abrupt decrease at this temperature ranging from 0.65 eV for tetramethylsilane to 0.42 eV for n-hexane. The meaning of the I jump at TM is discussed. From the invariance of I, it is concluded that the energy of the excess electron, V0, is constant in the solid phase.  相似文献   
10.
The determination of cysteine and homocysteine levels is of great current interest for the monitoring of desease states. A new colorimetric method for the simultaneous detection of l-cysteine and l-homocysteine has been developed. A fluorescein derivative reacts with the above amino acids, producing their respective thiazolidines resulting in color changes. Interference from other amino acids and proteins is minimal.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号