全文获取类型
收费全文 | 3482篇 |
免费 | 85篇 |
国内免费 | 10篇 |
专业分类
化学 | 2632篇 |
晶体学 | 84篇 |
力学 | 49篇 |
数学 | 130篇 |
物理学 | 682篇 |
出版年
2022年 | 29篇 |
2021年 | 43篇 |
2020年 | 34篇 |
2019年 | 46篇 |
2018年 | 33篇 |
2017年 | 20篇 |
2016年 | 48篇 |
2015年 | 66篇 |
2014年 | 77篇 |
2013年 | 164篇 |
2012年 | 172篇 |
2011年 | 188篇 |
2010年 | 106篇 |
2009年 | 106篇 |
2008年 | 173篇 |
2007年 | 208篇 |
2006年 | 199篇 |
2005年 | 188篇 |
2004年 | 194篇 |
2003年 | 167篇 |
2002年 | 151篇 |
2001年 | 93篇 |
2000年 | 79篇 |
1999年 | 48篇 |
1998年 | 33篇 |
1997年 | 36篇 |
1996年 | 44篇 |
1995年 | 42篇 |
1994年 | 39篇 |
1993年 | 37篇 |
1992年 | 73篇 |
1991年 | 35篇 |
1990年 | 33篇 |
1989年 | 36篇 |
1988年 | 30篇 |
1987年 | 33篇 |
1986年 | 34篇 |
1985年 | 45篇 |
1984年 | 48篇 |
1983年 | 26篇 |
1982年 | 25篇 |
1981年 | 25篇 |
1980年 | 30篇 |
1979年 | 38篇 |
1978年 | 31篇 |
1977年 | 20篇 |
1976年 | 20篇 |
1975年 | 15篇 |
1974年 | 25篇 |
1973年 | 17篇 |
排序方式: 共有3577条查询结果,搜索用时 171 毫秒
241.
Jrg Kressler Bernd Rudolf Ken Shimomai Toshiaki Ougizawa Takashi Inoue 《Macromolecular rapid communications》1995,16(8):631-636
Pressure, volume, temperature (PVT) measurements reveal that during the intramolecular cyclization reaction of poly(acrylonitrile) (PAN) and poly(styrene-co-acrylonitrile) (SAN) the volume decreases. This volume contraction becomes smaller with increasing styrene content in the random copolymers and should be related to the simultaneous decrease of longer acrylonitrile homo-sequences. The onset temperature of the cyclization reaction is raised with higher styrene contents in the random copolymers. Thus, it can be excluded that the cyclization reaction has a major influence on the discoloration process of SAN samples having relatively small acrylonitrile contents (less than 50 mol-%) during thermal annealing below 300°C. 相似文献
242.
243.
N-m-Tolyl-n-phenylhydroxylamine is proposed for the spectrophotometric determination of titanium. The reagent forms a yellow chloroform-soluble complex with titanium in media with a hydrochloric acid concentration of at least 9M. The apparent molar absorptivity at 380 nm is 7.4 x 10(3) 1.mole(-1).cm(-1). The optimum final concentration range is 0-54 mug of titanium in 10 ml of chloroform. The complex contains the metal and reagent in 1:2 ratio. The proposed method has been successfully applied to the determination of titanium in coal, coal fly-ash, pond sediment and asphalt. 相似文献
244.
A. Yamazaki Y. Inoue M. Koike T. Sakamoto R. Otsuka 《Journal of Thermal Analysis and Calorimetry》1993,40(1):85-97
Thomsonite with ideal chemical composition and with an ordered framework structure was synthesised hydrothermally from zeolite Na?A, which was ground to X-ray amorphous, with 0.05 mol dm?3 CaCl2 solution at 200°C. The dehydration behaviour of the prepared thomsonite was examined by TG-DTA. It was revealed that thomsonite lost most of zeolitic water below 450°C in three steps at about 180°, 340° and 390°C. The peak profiles of, the two higher-temperature endotherms were sharp and similar, and the weight loss at each step was approximately equal. 相似文献
245.
Yoshitake T Ichinose F Yoshida H Todoroki K Kehr J Inoue O Nohta H Yamaguchi M 《Biomedical chromatography : BMC》2003,17(8):509-516
A highly sensitive, selective and simple method is described for the determination of histamine by high-performance liquid chromatography (HPLC) with fluorescence detection. The method is based on an intramolecular excimer-forming fluorescence derivatization of histamine with 4-(1-pyrene)butyric acid N-hydroxysuccinimide ester (PSE), followed by reversed-phase HPLC. Histamine, having two amino moieties in a molecule, was converted to the dipyrene-labeled derivative by reaction with PSE. The derivative afforded intramolecular excimer fluorescence (450-540 nm), which can clearly be discriminated from the monomer fluorescence (370-420 nm) emitted from PSE. Typically, a 10 micro L sample solution was mixed with 100 micro L of derivatization reagent solution, which was a mixture of 0.5 mm PSE in acetonitrile and 0.5 mm potassium carbonate in water (8:2, v/v). The derivatization was carried out at 100 degrees C for 90 min. The PSE derivative of histamine could be separated by reversed-phase ODS column with isocratic elution using acetonitrile:water (82:18, v/v) containing 0.03% triethylamine. The detection limit (singnal-to-noise ratio = 3) of histamine was 0.5 fmol for a 30 micro L injection. The method was successfully applied to the determination of histamine in human urine, and had enough selectivity and sensitivity for urinary histamine quantification. 相似文献
246.
Inside Back Cover: Plasmon‐Assisted Water Splitting Using Two Sides of the Same SrTiO3 Single‐Crystal Substrate: Conversion of Visible Light to Chemical Energy (Angew. Chem. Int. Ed. 39/2014)
下载免费PDF全文
![点击此处可从《Angewandte Chemie (International ed. in English)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
247.
The dependence of dislocation density on the crystal diameter of the Czochralski grown KCl crystals (both pure and Sr doped) was investigated by the method of the etch pit and X-ray topograph. (1) The dislocation density drastically decreased with the decrease in diameter (D) for small D (D < 2 mm, Fig. 2). (2) The dislocation density in the Sr doped crystal was lower than that of pure component in the diameter examined. (3) Many helical dislocations and dislocation loops were observed in the thin crystals (D ∼ 0.5 mm) of the pure KCl and Sr doped one, respectively, by X-ray projection topography. These results were discussed in connection with the dislocation generation mechanisms due to thermal stresses or supersaturated point defects. 相似文献
248.
The photo-enhanced reaction between metallic silver and vitreous chalcogenides is known as “photodoping”. Based on a series of experimental results, a model for photodoping was proposed. It was assumed in this model, that a junction barrier at the silver-chalcogenide interface worked for separating photocarriers. Holes are captured by metallic silver, and electrons are trapped by active or loosely bound chalcogen atoms after travel toward the interior of a glass layer. The Coulomb attraction field between ions thus formed is large enough to overcome the kinetic barrier in the process of silver diffusion. The square root dependence for the growth of the photodoped depth with exposure time has been explained in the light of this proposed model. 相似文献
249.
The coadsorption of carbon monoxide (CO) and water molecules on a Ru(0 0 1) surface has been studied by infrared spectroscopy, LEED and STM. At high CO coverage phases, a 2×2-(2CO+D2O) structure was observed on both UHV and electrode surfaces. Electrode potential dependent structures from CO and water adlayers on an electrode surface were reproduced on a UHV surface by controlling molecular orientations of the first layer and second over-layer water molecules. At lower CO coverages, a CO band center showed coverage dependent shift down to 1444 cm−1 due to an electron transfer from a lone pair of a water molecule to CO 2π*. 相似文献
250.
The transition temperatures between high- and low-spin states of the assembled spin-crossover complexes, Fe(NCX)2(bpa)2(guest) (X = S, Se, BH3; bpa = 1,2-bis(4-pyridyl)ethane; guest = biphenyl, 2-nitrobiphenyl, diphenylmethane, or 1,4-dichlorobenzene), were compared with the Mössbauer parameters. The transition temperature increases when the QS value of FeII high-spin state becomes small. The transition temperature also increases by changing the anion from NCS to NCSe and then to NCBH3. 相似文献