全文获取类型
收费全文 | 2392篇 |
免费 | 191篇 |
国内免费 | 341篇 |
专业分类
化学 | 1538篇 |
晶体学 | 125篇 |
力学 | 21篇 |
综合类 | 14篇 |
数学 | 6篇 |
物理学 | 219篇 |
综合类 | 1001篇 |
出版年
2024年 | 7篇 |
2023年 | 23篇 |
2022年 | 58篇 |
2021年 | 79篇 |
2020年 | 65篇 |
2019年 | 45篇 |
2018年 | 45篇 |
2017年 | 65篇 |
2016年 | 104篇 |
2015年 | 90篇 |
2014年 | 110篇 |
2013年 | 178篇 |
2012年 | 139篇 |
2011年 | 118篇 |
2010年 | 109篇 |
2009年 | 114篇 |
2008年 | 127篇 |
2007年 | 172篇 |
2006年 | 138篇 |
2005年 | 137篇 |
2004年 | 123篇 |
2003年 | 121篇 |
2002年 | 101篇 |
2001年 | 86篇 |
2000年 | 100篇 |
1999年 | 68篇 |
1998年 | 50篇 |
1997年 | 50篇 |
1996年 | 51篇 |
1995年 | 45篇 |
1994年 | 29篇 |
1993年 | 40篇 |
1992年 | 24篇 |
1991年 | 25篇 |
1990年 | 17篇 |
1989年 | 13篇 |
1988年 | 15篇 |
1987年 | 13篇 |
1986年 | 7篇 |
1985年 | 5篇 |
1983年 | 1篇 |
1981年 | 4篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 2篇 |
1973年 | 2篇 |
1972年 | 2篇 |
排序方式: 共有2924条查询结果,搜索用时 15 毫秒
21.
This paper deals with synthesis and assessment of the hydraulicity of C4A3Cr, analog phase C4A3S to , relevant to the phase chemistry and properties of sulfoaluminate cements. C4A3Cr, synthesized at 1250 °C is well crystallized phase, latently hydraulic, with hydration accelerated in the presence of C4A3S, or CS. Calorimetric curves show reciprocal influence of sulfate and chromate phase in hydration of C4A3S-C4A3Cr system. The total heat expressed at hydration is nearly the same for all specimens, but the rate of heat evolution depends
on the ratio of C4A3S/C4A3Cr phases. X-ray diffraction pattern and DTA curves showed that, increasing content of C4A3Cr in hydrating mixture results in a coexistence of two types of ettringite (chromate and sulfate ettringite) hydrogarnet,
gibbsite and monosulfate.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
22.
Charles S. Oakes John M. Simonson Robert J. Bodnar 《Journal of solution chemistry》1995,24(9):897-916
Relative densities of CaCl
2
(aq) with 0.22ml(mol-kg–1)6.150 were measured with vibrating- tube densimeters between 25 and 250°C and near 70 and 400 bars. Apparent molar volumes V calculated from the measured density differences were represented with the Pitzer ioninteraction treatment, with appropriate expressions chosen for the temperature and pressure dependence of the virial coefficients of the model. It was found that the partial molar volume at infinite dilution V
o
, and the second and third virial coefficients B
V
and C
V
, were necessary to represent V near the estimated experimental uncertainty. The ionic-strength dependent (1)v term in the B
V
coefficient was included in the fit. The representation for V has been integrated with respect to pressure to establish the pressure dependence of excess free energies over the temperature range studied. The volumetric data indicate that the logarithm of the mean ionic activity coefficient, ln ±(CaCl
2
), increases by a maximum of 0.3 at 400 bars, 250°C, and 6 mol-kg–1 as compared with its value at saturation pressure. 相似文献
23.
E. Fleury J. Dubois C. Léonard J. P. Joseleau H. Chanzy 《Cellulose (London, England)》1994,1(2):131-144
Solutions of cellulose diacetate (CDA) from two sources (cotton linters and wood pulp Floranier) were analysed in various solvents by size exclusion chromatography (SEC). Without special precautions, the SEC chromatograms presented three peaks — or prehumps — before the main polymer peak. The first prehump which could be eliminated by ultracentrifugation corresponded to microgels whose sugar composition was determined. These microgels were also investigated by electron microscopy, X-ray and electron diffraction analysis. They corresponded mainly to cellulose triacetate (CTA-II) in the case of CDA from cotton linters and a mixture of CTA-II and xylan diacetate (XDA) in the case of CDA from the wood pulp Floranier. The second and third prehumps could be attributed to ionic effects corresponding to the association of remaining sulfate groups on the CDA molecules with residual calcium. It was found that these ionic effects could be eliminated by the addition of LiBr or LiCl to the elution solvents. This led to chromatograms devoid of prehumps.Presented in part at the Cellulose '91 meeting in New Orleans. 相似文献
24.
25.
The unseeded non-hydrolytic sol-gel synthesis of ZrW2O8 and ZrMo2O8 produces trigonal ZrM2O8 (M = W, Mo) at 740 and 300–400°C, respectively. Cubic ZrW2O8 can be prepared using non-hydrolytic sol-gel methods by seeding with small amounts of preprepared cubic material, and the formation of the trigonal polymorph can be suppressed completely. Seeds with a small particle size are necessary for the preparation of cubic ZrW2O8. In contrast, seeding of ZrMo2O8 gels with either cubic ZrMo2O8 or cubic ZrW2O8 only lowers the temperature at which the trigonal phase crystallizes. 相似文献
26.
对合肥市16671名1-12个月幼儿的发锌,钙含量进行了测定,并对测定值进行了统计分析。结果表明,锌,钙的含量随着月龄的增加呈直线递减。并给出了发锌,钙含量的趋势线方程,丰富了目前文献给出的发锌,钙的标准值,为及时准确判断周岁内幼儿微量元素锌,钙缺乏程度提出依据。 相似文献
27.
28.
CaO和NaCl焙烧混合稀土精矿过程中的分解反应 总被引:5,自引:0,他引:5
用XRD和TG-DTA热分析技术, 研究了含独居石和氟碳铈镧矿的混合稀土精矿在100~1000 ℃焙烧过程中, 添加CaO, NaCl时, REPO4和REFCO3的分解反应. 研究结果表明: 不添加CaO和NaCl时, 仅在377~450 ℃范围内存在REFCO3的分解反应, 其产物是REOF, RE2O3, 以及Ce2O3进一步的氧化产物CeO2, 而REPO4不分解; 添加CaO后在660~750 ℃之间, CaO有3种分解作用: (1) CaO分解REPO4, 其产物是RE2O3和Ca3(PO4)2. (2) CaO分解REOF, 其产物是RE2O3和CaF2. (3) CaO和REOF的分解产物CaF2共同作用分解REPO4, 其分解产物为RE2O3, Ca5F(PO4)3; 添加CaO, NaCl后, 混合精矿的分解率明显提高, NaCl的作用是为反应体系提供了液相, 促进了固相反应物间的传质过程, 加快了反应速度. 与此同时NaCl还可能参加了CaO分解REPO4的反应. 相似文献
29.
Ichikawa K Shimomura N Yamada M Ohkubo N 《Chemistry (Weinheim an der Bergstrasse, Germany)》2003,9(14):3235-3241
In vitro biomimetic mineralization by means of nanotechnology allows the formation of calcium carbonate polymorphs at low temperatures (<25 degrees C) under a CO(2) atmosphere of 500-1500 ppm. A two-dimensional zinc-ion ordered array (zinc array), which acts as an active-site mimic of carbonic anhydrase, has been prepared by immersing the self-organized monolayer of 3-(2-imidazolin-1-y)propyltriethosilane on mica (ImSi substrate) into aqueous zinc solution. The zinc array mounted on the ImSi substrate catalyzed the conversion from CO(2) to HCO(3) (-), and accelerated the formation of calcium carbonate. In situ X-ray diffraction data of the formed calcium carbonate on the poly(L-aspartate)-coated chitin substrate (pAsp substrate), with calcium ion-recognition sites, demonstrated that the interaction between the zinc array and pAsp substrates formed both vaterite and calcite at low temperature (15 degrees C) and mainly vaterite at 25 degrees C; this interaction also controlled the morphology of calcium carbonate formed on pAsp substrate. 相似文献
30.
A novel strategy for the fabrication of microcapsules is elaborated by employing biomacromolecules and a dissolvable template. Calcium carbonate (CaCO(3)) microparticles were used as sacrificial templates for the two-step deposition of polyelectrolyte coatings by surface controlled precipitation (SCP) followed by the layer-by-layer (LbL) adsorption technique to form capsule shells. When sodium alginate was used for inner shell assembly, template decomposition with an acid resulted in simultaneous formation of microgel-like structures due to calcium ion-induced gelation. An extraction of the calcium after further LbL treatment resulted in microcapsules filled with the biopolymer. The hollow as well as the polymer-filled polyelectrolyte capsules were characterized using confocal laser scanning microscopy (CLSM), scanning electron microscopy (SEM), and scanning force microscopy (SFM). The results demonstrated multiple functionalities of the CaCO(3) core - as supporting template, porous core for increased polymer accommodation/immobilization, and as a source of shell-hardening material. The LbL treatment of the core-inner shell assembly resulted in further surface stabilization of the capsule wall and supplementation of a nanostructured diffusion barrier for encapsulated material. The polymer forming the inner shell governs the chemistry of the capsule interior and could be engineered to obtain a matrix for protein/drug encapsulation or immobilization. The outer shell could be used to precisely tune the properties of the capsule wall and exterior. [Diagram: see text] Confocal laser scanning microscopy (CLSM) image of microcapsules (insert is after treating with rhodamine 6G to stain the capsule wall). 相似文献