全文获取类型
收费全文 | 33989篇 |
免费 | 376篇 |
国内免费 | 273篇 |
专业分类
化学 | 13265篇 |
晶体学 | 282篇 |
力学 | 1409篇 |
综合类 | 12篇 |
数学 | 9374篇 |
物理学 | 8354篇 |
无线电 | 1942篇 |
出版年
2023年 | 56篇 |
2021年 | 89篇 |
2020年 | 89篇 |
2019年 | 90篇 |
2018年 | 1311篇 |
2017年 | 1572篇 |
2016年 | 925篇 |
2015年 | 792篇 |
2014年 | 663篇 |
2013年 | 952篇 |
2012年 | 3557篇 |
2011年 | 2750篇 |
2010年 | 2006篇 |
2009年 | 1712篇 |
2008年 | 875篇 |
2007年 | 906篇 |
2006年 | 871篇 |
2005年 | 4976篇 |
2004年 | 4099篇 |
2003年 | 2460篇 |
2002年 | 620篇 |
2001年 | 358篇 |
2000年 | 133篇 |
1999年 | 196篇 |
1998年 | 131篇 |
1997年 | 97篇 |
1996年 | 86篇 |
1995年 | 56篇 |
1994年 | 56篇 |
1992年 | 187篇 |
1991年 | 168篇 |
1990年 | 167篇 |
1989年 | 131篇 |
1988年 | 125篇 |
1987年 | 98篇 |
1986年 | 84篇 |
1985年 | 80篇 |
1984年 | 65篇 |
1983年 | 55篇 |
1982年 | 42篇 |
1979年 | 42篇 |
1976年 | 96篇 |
1975年 | 48篇 |
1974年 | 56篇 |
1973年 | 68篇 |
1972年 | 48篇 |
1970年 | 48篇 |
1969年 | 39篇 |
1968年 | 46篇 |
1966年 | 41篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
921.
?zdemir ümmühan Karacan Nurcan ?entürk Ozan Sanlι Sert Sema U?ur Fadime 《Transition Metal Chemistry》2003,28(4):443-446
Five new complexes, [M(CO)5(apmsh)] [M = Cr; (1), Mo; (2), W; (3)], [Re(CO)4Br(apmsh)] (4) and [Mn(CO)3(apmsh)] (5) have been synthesized by the photochemical reaction of metal carbonyls [M(CO)6] (M = Cr, Mo and W), [Re(CO)5Br], and [Mn(CO)3Cp] with 2-hydroxyacetophenone methanesulfonylhydrazone (apmsh). The complexes have been characterized by elemental analysis, mass spectrometry, f.t.-i.r. and 1H spectroscopy. Spectroscopic studies show that apmsh behaves as a monodentate ligand coordinating via the imine N donor atom in [M(CO)5(apmsh)] (1–4) and as a tridentate ligand in (5). 相似文献
922.
The effects of addition of alkanols (ethanol, n-hexanol, and 3-ethyl-3-pentanol) on the micropolarity and microviscosity of the head group region in reverse micelles of AOT-heptane-water have been investigated by fluorescence probing methods (ANS fluorescence yield and TMADPH fluorescence anisotropy), complemented by the use of the solvatochromic probe E(T)(30) in absorption spectroscopy. For all the alkanols considered, ANS fluorescence in AOT reverse micelles (at W=3) is quenched by additive incorporation, being the effect elicited almost independent of the alkanol chain length and topology. As sensed by the E(T)(30) parameter, the micropolarity of the micelle surface increases, remains unmodified, and decreases upon addition of ethanol, 3-ethyl-3-pentanol, and hexanol, respectively. While ethanol barely modifies the fluorescence anisotropy of TMADPH, 3-ethyl-3-pentanol and n-hexanol addition strongly decrease it. The similarity of the tendencies of ANS data to TMADPH anisotropies and the differences between ANS data and E(T)(30) values would indicate that, at least for 3-ethyl-3-pentanol and n-hexanol, microviscosity, rather than micropolarity, must be considered to interpret the effect of the alkanols upon the fluorescent behavior of ANS. 相似文献
923.
Liu JM Hu SR He XM Li XL Zhan FP Zeng LQ Li LD Zhu GH Huang XM 《Analytical and bioanalytical chemistry》2005,382(7):1507-1512
Silicon dioxide nano-particles, diameter 50 nm, containing morin (morin–SiO2) have been synthesized by the sol–gel method. They emit strong and stable room-temperature phosphorescence (SS-RTP) on filter paper as substrate, and bismuth can quench the intensity of the SS-RTP. On this basis a new morin–SiO2 solid-substrate room-temperature phosphorescence-quenching method has been established for determination of traces of bismuth. Reduction of phosphorescence intensity (Ip) is directly proportional to the concentration of bismuth in the working range 0.16–14.4 ag spot–1 (sample volume 0.40 L spot–1, corresponding to the concentration range 0.40–36.0 fg mL–1). The regression equation of the working curve is Ip=14.86+5.279×[Bi3+] (ag spot–1) (n=6, r=0.9982). The detection limit of this method is 0.026 ag spot–1 (corresponding to a concentration of 6.5×10–17 g mL–1).This sensitive, reproducible and accurate method has been used for successful analysis of real samples. 相似文献
924.
We present a detailed study of the photophysical properties of a tetraphenoxy-substituted perylene bisimide derivative. The probe molecules were immobilized in a Shpol'skii matrix of hexadecane and investigated by single-molecule spectroscopy at cryogenic temperatures. By using single-molecule spectroscopic techniques we reveal the triplet substate kinetics and the fluorescence quantum yield, and we provide an estimate for the S1-S0 transition dipole moment. 相似文献
925.
Capillary electrophoresis of inorganic anions 总被引:1,自引:0,他引:1
This review deals with the separation mechanisms applied to the separation of inorganic anions by capillary electrophoresis (CE) techniques. It covers various CE techniques that are suitable for the separation and/or determination of inorganic anions in various matrices, including capillary zone electrophoresis, micellar electrokinetic chromatography, electrochromatography and capillary isotachophoresis. Detection and sample preparation techniques used in CE separations are also reviewed. An extensive part of this review deals with applications of CE techniques in various fields (environmental, food and plant materials, biological and biomedical, technical materials and industrial processes). Attention is paid to speciations of anions of arsenic, selenium, chromium, phosphorus, sulfur and halogen elements by CE. 相似文献
926.
A flow injection–capillary electrophoresis system with contactless conductivity detection and hydrostatic-pressure-generated flow was used for the fast and sensitive speciation of Se(IV) and Se(VI). The sample throughput was 25 samples per hour using a background electrolyte solution containing 8.75 mM l-histidine (His) adjusted to pH 4.00 with acetic acid. The repeatability of peak areas (n=8) was better than 1.41% and the limits of detection were 190 g L–1 and 7.5 g L–1 for Se(IV) and Se(VI), respectively. The interference from carbonate, typically present in water samples, was eliminated by using a low-pH electrolyte in which carbonate is uncharged and migrates at the EOF front. The method was applied to the analysis of Se(IV) and Se(VI) in soil samples that were spiked with both selenium species and the results for recovery of both selenium species were in good agreement with their introduced concentrations. 相似文献
927.
Size-related vaporisation and ionisation of laser-induced glass particles in the inductively coupled plasma 总被引:1,自引:0,他引:1
Ongoing discussions about the origin of elemental fractionation occurring during LA-ICP-MS analysis show that this problem is still far from being well understood. It is becoming accepted that all three possible sources (ablation, transport, excitation) contribute to elemental fractionation. However, experimental data about the vaporisation size limit of different particles in the ICP, as produced in laser ablation, have not been available until now. This information should allow one to determine the signal contributing mass within the ICP and would further clarify demands on suitable laser ablation systems and gas atmospheres in terms of their particle size distribution.The results presented here show a vaporisation size limit of laser induced particles, which was found at particle sizes between 90 nm and 150 nm using an Elan 6000 ICP-MS. Due to the fact that the ICP-MS response was used as evaluation parameter, vaporisation and ionisation limits are not distinguishable.The upper limit was determined by successively removing the larger particles from the aerosol, which was created by ablation of a NIST 610 glass standard at a wavelength of 266 nm, using a recently developed particle separation device. Various particle fractions were separated from the aerosol entering the ICP. The decrease in signal intensity is not proportional to the decrease in volume, indicating that particles above 150 nm in diameter are not completely ionised in the ICP. Due to the limited removal range of the particle separation device, which cannot remove particles smaller than 150 nm, single hole ablations were used to determine the lower vaporisation limit. This is based on measurements showing that larger particles occur dominantly during the first 100 laser pulses only. After this period, the ratio of ICP-MS counts and total particle volume was found to be constant while most of the particles are smaller than 90 nm, indicating complete vaporisation and ionisation of these particles.To describe the influence of different plasma forward powers on the vaporisation limit, the range 1000–1600 W was studied. Results indicate that optimum vaporisation and ionisation occurs at 1300 W. However, an increase of the particle ionisation limit towards larger particles was not observed within the accuracy of this study using the full range of parameters available for optimisation on commonly used ICP-MS instruments. 相似文献
928.
Roberto?S.?Fernandes Gaspar?González Elizabete?F.?LucasEmail author 《Colloid and polymer science》2004,283(2):219-224
During oil production and treatment, oil-in-water (O/W) emulsions are formed. These dispersions require treatment prior to disposal. In order to improve oil/water separation processes through any physical process (decanting, flotation, centrifuging etc), the particle size of the dispersed phase should be increased. This may be obtained by a flocculation process, which consists in the agglomeration of several particles or drops using as flocculating agent hydrophilic high molecular weight macromolecules. Poly (ethylene-b-propylene oxide) and poly (vinyl alcohol) polymers have been evaluated as flocculating agents for oily water systems. Their performance is related to the particle size increase of the dispersed phase. In this work, a photometric dispersion analyzer (PDA) has been used to accomplish the oil drop agglomeration. Synthetic as well as produced water was used. Data are in good agreement with previous tests. Qualitative information related to aggregates or particle size distribution of the oily water systems can be obtained using PDA. 相似文献
929.
Hiroyuki?OhshimaEmail author Hiroko?Sato Hiroki?Matsubara Atsushi?Hyono Masayoshi?Okubo 《Colloid and polymer science》2004,282(10):1174-1178
A theory of adsorption kinetics with time delay [Ohshima et al. (1992) Colloid Polym. Sci. 270:707] is developed and applied to the surface tension of a polymer solution. It is found that the general appearance of the overshoot and oscillation in the time course of the surface tension of aqueous gelatin solution observed by Sato and Ueberreiter [(1979) Makromol. Chem. 180:829, 1107; (1979) Polym. Prepr. Am. Chem. Soc. Div. Polym. Chem. 20:907) can be explained by the present theory. 相似文献
930.
The effect of ß-cyclodextrin (ß-CD) on cetyltrimethylammonium bromide (CTAB) micellar properties was studied by the determination of the diffusion coefficient, D. When the CTAB micelles have a spherical structure, D firstly increased and then remained unchanged, while the micellar aggregation number, N, decreased with the addition of ß-CD. When the CTAB concentration was less than the first critical micellar concentration, CTAB molecules could be included into ß-CD cavities with the molar ratio of CTAB to ß-CD being about 1:1. However, when the CTAB concentration was higher than the first critical micellar concentration, mixed spherical micelles were formed with the molar ratio of CTAB to ß-CD being 9:1. 相似文献