全文获取类型
收费全文 | 11787篇 |
免费 | 2115篇 |
国内免费 | 1366篇 |
专业分类
化学 | 8017篇 |
晶体学 | 162篇 |
力学 | 822篇 |
综合类 | 105篇 |
数学 | 1251篇 |
物理学 | 4911篇 |
出版年
2024年 | 39篇 |
2023年 | 279篇 |
2022年 | 466篇 |
2021年 | 542篇 |
2020年 | 498篇 |
2019年 | 506篇 |
2018年 | 430篇 |
2017年 | 385篇 |
2016年 | 622篇 |
2015年 | 589篇 |
2014年 | 701篇 |
2013年 | 836篇 |
2012年 | 1067篇 |
2011年 | 1024篇 |
2010年 | 799篇 |
2009年 | 730篇 |
2008年 | 714篇 |
2007年 | 631篇 |
2006年 | 647篇 |
2005年 | 564篇 |
2004年 | 368篇 |
2003年 | 309篇 |
2002年 | 311篇 |
2001年 | 231篇 |
2000年 | 211篇 |
1999年 | 211篇 |
1998年 | 177篇 |
1997年 | 204篇 |
1996年 | 180篇 |
1995年 | 162篇 |
1994年 | 139篇 |
1993年 | 97篇 |
1992年 | 88篇 |
1991年 | 79篇 |
1990年 | 78篇 |
1989年 | 69篇 |
1988年 | 53篇 |
1987年 | 29篇 |
1986年 | 44篇 |
1985年 | 32篇 |
1984年 | 18篇 |
1983年 | 15篇 |
1982年 | 15篇 |
1981年 | 7篇 |
1980年 | 9篇 |
1975年 | 7篇 |
1973年 | 4篇 |
1972年 | 7篇 |
1965年 | 6篇 |
1964年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
91.
A new highly sensitive and selective chromogenic reagent, 2-(2,5-disulfonic-4-methoxyphenylazo)-7-(2-hydroxyl-5-carboxylphenylazo)-1,8-dihydroxynaphthalene-3,6-disulfonic
acid (1), was synthesized and applied to the spectrophotometric determination of trace thorium. In 5 mL of a 6 M perchloric acid
medium, which greatly increases the selectivity, thorium reacts with 1 to form a 1: 2 green complex, having a sensitive absorption peak at 670 nm. Under optimal conditions, Beer’s law is obeyed
over the range from 0 to 0.8 μg/mL Th(IV) and the apparent molar absorptivity is 2.09 × 105 L/mol cm. It is found that, uranium(VI), Ti(IV), heavy rare earths, and most of other common metal ions do not interfere.
The method has been tested on the determination of thorium in food samples with satisfactory results.
The text was submitted by the authors in English. 相似文献
92.
我国的生活饮用水行业中,目前常使用的管材分为金属类管材和非金属类管材两种。由于金属类管材本身的化学特性,行业内必须在此类管材的内壁上进行防腐处理,通常采用一些高分子防腐涂料。可用于给水行业的涂料品种繁多,涂料质量好坏直接影响到水质。我们针对一些常用产品作了浸泡试验,用吹扫捕集-GC-MS方法对水中溶出的可挥发性有机物进行了检测,发现一些产品在水中溶出了大量的甲苯、乙苯、二甲苯、甲乙苯等苯系物,且浸泡30d后仍有溶出物。这些物质长期存在会导致人体中枢神经系统紊乱,严重危害人体健康。行业内关于水源水中此类有机物污染的监测比较充分,而对于防护涂料可能污染水质的状况并未引起足够重视。 相似文献
93.
Solution-cast films of the major isomer of Dy@C(82) (Dy@C(82)(I)) have been studied by cyclic voltammetry (CV) in acetonitrile. The films are found to display pronounced and stable redox responses in solution. The reduction/reoxidation processes exhibit large splittings between the first two reduction and reoxidation waves. However, a pair of reversible oxidation and rereduction waves is observed after the reoxidation of a reduced film. The characteristics and the inter-relationship of these waves are uncovered by the CV technique, scanning electron microscopy (SEM), and UV/Vis-NIR spectra. A possible mechanism is proposed for the film electrode processes, which emphasizes the redox-induced structural reorganization of the metallofullerene film by the incorporation and expulsion of electrolyte ions into and out of the film. The influence of the counter ion diffusivity and the ion-pair stability on the electrochemical activity of the metallofullerene film has also been indicated. 相似文献
94.
SynthesisandMagneticPropertiesofBinuclearMn(Ⅱ)ComplexeswithAlkoxideBridgeYanShi-ping;FanBo;LiaoDai-zheng;JiangZong-huiandWang... 相似文献
95.
Yong Zhu Jin-lian Hu Kwok-wing Yeung Hao-jun Fan Ye-qiu 《高分子科学》2006,(2):173-186
SMPU (shape memory polyurethane) non-ionomers and ionomers, synthesized with poly(c-caprolactone) (PCL), 4, 4'-diphenylmethane diisocyanate (MDI), 1,4-butanediol (BDO), dimethylolpropionic acid (DMPA) were measured with cyclic tensile test and strain recovery test. The relations between the structure and shape memory effect of these two series were studied with respect to the ionic group content and the effect of neutralization. The resulting data indicate that, with the introduction of asymmetrical extender, the stress at 100% elongation is decreased for PU non-ionomer and ionomer series, especially lowered sharply for non-ionomer series; the fixation ratio of ionomer series is not affected obviously by the ionic group content; the total recovery ratio of ionomer series is decreased greatly. After sufficient relaxation time for samples stretched beforehand, the switching temperature is raised slightly, whereas the recovery ratio measured with strain recovery test method is lowered with increased DMPA content. The characterization with FT-IR, DSC, DMA elucidated that, the ordered hard domain of the two series is disrupted with the introduction of DMPA which causes more hard segments to dissolve in soft phase; ionic groups on hard segment enhance the cohesion between hard segments especially at high ionic group content and significantly facilitate the phase separation compared with the corresponding non-ionomer at moderate ionic group content. 相似文献
96.
LiCl—HOAc和LiCl—HOAc—H2O体系(25℃)相图 总被引:2,自引:0,他引:2
测定了LiCl-HOAc和LiCl-HOAc-H_2O体系25℃时的溶度,绘制了溶度图.在LiCl-HOAc体系的相图中有LiCl及LiCl·1/2HOAc2种固相,后者是固液异成分化合物,体系中未发现LiCl·5HOAc或LiCL·HOAc的生成.LiCl-HOAc-H_2O体系25℃时的相图中有3种固相,即LiCl·H_2O、LiCl和LiCl·(1/2)HOAc.相变LiCl·H_2O→LiCl→LiCl·(1/2)HOAc表明HOAc在该三元体系中具有盐溶、脱水和溶剂合3种作用.此结果提供了一种制备无水LiCl的新方法. 相似文献
97.
W. Y. Choy S. C. F. Au-Yeung S. Y. Fan W. L. A. K. Chiu C. S. Cockram 《Analytical and bioanalytical chemistry》1998,361(5):500-503
Glucose in 5% D2O/95% H2O solution was successfully determined quantitatively by measurements of the 1H NMR peak height (intensity) of the single peaks at δ(1H) = 5.22 and 4.64 ppm corresponding to the α-D and the β-D-glucose spectrum, respectively. The single peaks were obtained from decoupling of the high field part of the AX spectrum of the α-D- or the β-D-glucose by incorporation of time shared homonuclear decoupling in the WATR-CPMG method (WATR-HDCPMG) without re-attenuation of the water peak. The method was applied to the determination of total glucose in blood plasma from human subjects undergoing oral glucose tolerance test (OGTT) in the teaching hospital. The results compared favorably with those obtained from the standard glucose oxidase method obtained in a hospital pathology laboratory. The accuracy of the results obtained using the WATR-HDCPMG method was within 3.5% of the glucose oxidation method. 相似文献
98.
Xiong Wen Ye Yu Ping Zhang Ling Bo Qu Li Qun Fan Bo Li 《中国化学快报》2007,18(11):1399-1402
Microwave irradiation was firstly attempted for the preparation of organic-based monoliths of poly(styrene-divinylbenzene- methacrylic acid), which single step in situ polymerization was carried out during 15 min. The colunm permeability, electrophoretic and chromatographac behaviors were comparatively evaluated using pressure-assisted CEC, GEC and low pressure-driven separation modes. The largest theoretical plates for the preparing column could be close to 18,0000 plates/m for thiourea in the mode of p-CEC. It provided a viable alternative to traditional initiation means for the perparation of monolithic capillary columns. 相似文献
99.
The performance of 17 exchange-correlation functionals for molecules containing heavy elements are numerically examined through four-component relativistic density DFT calculations. The examined functionals show the similar accuracy as they do for the molecules containing light elements only except for bond lengths. LDA and OP86 produce good results for bond lengths and frequencies but bad bond energies. Different functionals do not show much different performance for bond energies except LDA. BP86 and GP86 produce results with average accuracy while LYP does not perform well. Although encouraging results are obtained with functional B97GGA-1, other heavily parameterized and meta-GGA functionals do not produce impressive results. 相似文献
100.