全文获取类型
收费全文 | 4946篇 |
免费 | 125篇 |
国内免费 | 6篇 |
专业分类
化学 | 3901篇 |
晶体学 | 6篇 |
力学 | 42篇 |
数学 | 645篇 |
物理学 | 483篇 |
出版年
2019年 | 40篇 |
2018年 | 36篇 |
2017年 | 26篇 |
2016年 | 101篇 |
2015年 | 64篇 |
2014年 | 99篇 |
2013年 | 142篇 |
2012年 | 145篇 |
2011年 | 155篇 |
2010年 | 130篇 |
2009年 | 119篇 |
2008年 | 163篇 |
2007年 | 159篇 |
2006年 | 181篇 |
2005年 | 199篇 |
2004年 | 169篇 |
2003年 | 139篇 |
2002年 | 180篇 |
2001年 | 109篇 |
2000年 | 108篇 |
1999年 | 105篇 |
1998年 | 86篇 |
1997年 | 96篇 |
1996年 | 96篇 |
1995年 | 76篇 |
1994年 | 88篇 |
1993年 | 92篇 |
1992年 | 93篇 |
1991年 | 86篇 |
1990年 | 67篇 |
1989年 | 90篇 |
1988年 | 87篇 |
1987年 | 84篇 |
1986年 | 71篇 |
1985年 | 97篇 |
1984年 | 111篇 |
1983年 | 62篇 |
1982年 | 86篇 |
1981年 | 112篇 |
1980年 | 84篇 |
1979年 | 102篇 |
1978年 | 68篇 |
1977年 | 69篇 |
1976年 | 59篇 |
1975年 | 77篇 |
1974年 | 50篇 |
1973年 | 70篇 |
1972年 | 51篇 |
1971年 | 44篇 |
1970年 | 52篇 |
排序方式: 共有5077条查询结果,搜索用时 203 毫秒
101.
K. Torkar G. W. Herzog W. Schintlmeister Dieter Fischer 《Monatshefte für Chemie / Chemical Monthly》1967,98(2):245-253
It is shown that in the case of thermal decomposition of sodium azide the overall kinetics can be predicted by defined particle size of the decomposed sodium azide crystals. This is always the case if the rate constant is a function of the particle size. Hence this special example can be generalized for similar decomposition reactions. It is necessary that the particles decompose independently which could be proved experimentally with sodium azide. If for this reason we state for true that the pressure/time-function of each particle size add together it is possible to set up a formula for the pressure/time-function of any particle size distribution. With the pressure/time function holding for sodium azide of uniform particle size, the total function for a Gauß distribution can be calculated exactly. Moreover, the trivial case of one single particle size and the case of two different particle sizes are discussed. Furthermore an approximation method for any arbitrary pressure/time-functions and distribution by means of “Schwerpunktdeutung” are discussed which can be carried out graphically as well as numerically. The numerical approximation is illustrated by an example. Pressure/time-functions then loose their characteristic form because of their dependence on the particle size distributions under consideration. In this case, reaction mechanism cannot be derived from pressure/time functions. 相似文献
102.
Luzgin MV Stepanov AG Arzumanov SS Rogov VA Parmon VN Wang W Hunger M Freude D 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,12(2):457-465
By using 13C MAS NMR spectroscopy (MAS = magic angle spinning), the conversion of selectively 13C-labeled n-butane on zeolite H-ZSM-5 at 430-470 K has been demonstrated to proceed through two pathways: 1) scrambling of the selective 13C-label in the n-butane molecule, and 2) oligomerization-cracking and conjunct polymerization. The latter processes (2) produce isobutane and propane simultaneously with alkyl-substituted cyclopentenyl cations and condensed aromatic compounds. In situ 13C MAS NMR and complementary ex situ GC-MS data provided evidence for a monomolecular mechanism of the 13C-label scrambling, whereas both isobutane and propane are formed through intermolecular pathways. According to 13C MAS NMR kinetic measurements, both pathways proceed with nearly the same activation energies (E(a) = 75 kJ mol(-1) for the scrambling and 71 kJ mol(-1) for isobutane and propane formation). This can be rationalized by considering the intermolecular hydride transfer between a primarily initiated carbenium ion and n-butane as being the rate-determining stage of the n-butane conversion on zeolite H-ZSM-5. 相似文献
103.
104.
A restricted access material (RAM), alkyl-diol-silica (ADS), was used to prepare a highly bio-compatible solid-phase microextraction (SPME) capillary for the automated and direct in-tube extraction of several benzodiazepines from human serum. The bifunctionality of the ADS extraction phase prevented fouling of the capillary by protein adsorption while simultaneously trapping the analytes in the hydrophobic porous interior. This the first report of a restricted access material utilized as an extraction phase for in-tube SPME. The approach simplified the required apparatus in comparison to existing RAM column switching procedures, and more importantly eliminated the excessive use of extraction solvents. The biocompatibility of the ADS material also overcame the existing problems with in-tube SPME that requires an ultrafiltration or other deproteinization step prior to handling biological samples, therefore further minimizing the sample preparation requirements. The calculated oxazepam, temazepam, nordazepam and diazepam detection limits were 26, 29, 22 and 24 ng/ml in serum, respectively. The method was linear over the range of 50-50 000 ng/ml with an average linear coefficient (R2) value of 0.9998. The injection repeatability and intra-assay precision of the method were evaluated with five injections of a 10-microg/ml serum sample (spiked with all compounds), resulting in an average RSD<7%. The ADS extraction column was robust, providing many direct injections of biological fluids for the extraction and subsequent determination of benzodiazepines. 相似文献
105.
Dieter H. Mayer 《Journal of statistical physics》1985,38(3-4):785-803
We derive universal scaling properties for k–1 actions on the circle whose generators have rotation numbers algebraic of degreek. As fork=2 these properties can be explained for arbitraryk in terms of a renormalization group transformation. It has at least one trivial fixed point corresponding to an action whose generators are pure rotations. The spectrum of the linearized transformation in this fixed point is analyzed completely. The fixed point is hyperbolic with a (k–1)-dimensional unstable manifold. In the casek=2 the known results are therefore recovered. 相似文献
106.
107.
108.
109.
110.
Prakash R Czaja AU Heinemann FW Sellmann D 《Journal of the American Chemical Society》2005,127(40):13758-13759
The new ruthenium compound [Ru(NO)(pysiS4)]Br (3) (pysiS4 = 2,6-bis(3-triphenylsilyl-2-sulfanylphenylthiomethyl)pyridine), containing sterically bulky SiPh3 groups ortho to the thiolate donors, has been synthesized. In solution, 3 releases NO efficiently on exposure to visible light (lambda >/= 455 nm) at room temperature to afford [Ru(Br)(pysiS4)] (4). Treatment of 4 with NO yielded exclusively 3 without any metal-bound side reaction. 相似文献