全文获取类型
收费全文 | 11782篇 |
免费 | 2110篇 |
国内免费 | 1366篇 |
学科分类
数理化 | 15258篇 |
出版年
2024年 | 39篇 |
2023年 | 279篇 |
2022年 | 466篇 |
2021年 | 534篇 |
2020年 | 498篇 |
2019年 | 506篇 |
2018年 | 430篇 |
2017年 | 384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 | 138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
101.
SynthesisandMagneticPropertiesofBinuclearMn(Ⅱ)ComplexeswithAlkoxideBridgeYanShi-ping;FanBo;LiaoDai-zheng;JiangZong-huiandWang... 相似文献
102.
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
103.
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
104.
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
105.
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
106.
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
107.
108.
109.
Ga3(HPO3)4F4(H3DETA) is a new open-framework fluorinated gallium phosphite obtained by mild hydrothermal synthesis using diethylenetriamine as templated agent and characterized by single crystal X-ray diffraction, the powder X-ray diffraction, IR spectroscopy, TGA, ICP and elemental analyses. It crystallizes in the monoclinic space group C2/c, a=12.741(6) Å, b=12.068(6) Å, c=11.988(5) Å, β=94.902(8)o, V=1836.6(15) Å3, Z=4. The construction of 3D open-framework structure in the title compound may be viewed as the assembly of pentameric building units and HPO3 groups. The pentameric building unit is the first to be found, which lead to form the three types of channels along a-, b- and c-axes, respectively, in gallium phosphite. The triprotonated DETA cations are inserted within the 10-membered ring channels and interact with anions of the framework via hydrogen bonds. 相似文献
110.
[Chemical reaction: see text] Polysubstituted furans and highly functionalized 2H-pyrans were prepared in good yields by DABCO-catalyzed reactions of alpha-halo carbonyl compounds with dimethyl acetylenedicarboxylate (DMAD) at room temperature. 相似文献