全文获取类型
收费全文 | 12907篇 |
免费 | 254篇 |
国内免费 | 1355篇 |
专业分类
化学 | 11132篇 |
晶体学 | 646篇 |
力学 | 297篇 |
综合类 | 4篇 |
数学 | 229篇 |
物理学 | 2208篇 |
出版年
2024年 | 6篇 |
2023年 | 210篇 |
2022年 | 93篇 |
2021年 | 70篇 |
2020年 | 169篇 |
2019年 | 144篇 |
2018年 | 144篇 |
2017年 | 187篇 |
2016年 | 248篇 |
2015年 | 219篇 |
2014年 | 332篇 |
2013年 | 545篇 |
2012年 | 1648篇 |
2011年 | 721篇 |
2010年 | 618篇 |
2009年 | 784篇 |
2008年 | 995篇 |
2007年 | 1141篇 |
2006年 | 772篇 |
2005年 | 680篇 |
2004年 | 685篇 |
2003年 | 508篇 |
2002年 | 541篇 |
2001年 | 480篇 |
2000年 | 445篇 |
1999年 | 377篇 |
1998年 | 329篇 |
1997年 | 181篇 |
1996年 | 193篇 |
1995年 | 161篇 |
1994年 | 174篇 |
1993年 | 132篇 |
1992年 | 116篇 |
1991年 | 104篇 |
1990年 | 67篇 |
1989年 | 59篇 |
1988年 | 53篇 |
1987年 | 41篇 |
1986年 | 19篇 |
1985年 | 22篇 |
1984年 | 9篇 |
1983年 | 11篇 |
1982年 | 11篇 |
1981年 | 18篇 |
1980年 | 15篇 |
1979年 | 13篇 |
1975年 | 3篇 |
1973年 | 4篇 |
1969年 | 4篇 |
1966年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 281 毫秒
71.
The crystal structure of a novel ferrocene derivative with potential flame-retardant/smoke-suppressant activity, 1,4,5,6,7,7-hexachloro-2-endo-ferrocenyl-hydroxymethyl-3-endo-hydroxymethyl-5-norbornene, has been determined. Some of the carbon–carbon bonds within the chlorendic residue are unusually long, and there is no interaction between the hydroxyl groups and the iron atom. There is evidence of intramolecular hydrogen bonding between the two hydroxyl groups. 相似文献
72.
P. Guenoun M. Delsanti D. Gazeau J.W. Mays D.C. Cook M. Tirrell M. Tirrell L. Auvray 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,1(1):77-86
Aqueous micellar solutions of ionic/neutral block copolymers have been studied by light scattering, small angle neutron scattering
and small angle X-ray scattering. We made use of a polymer comprised of a short hydrophobic block (polyethylene-propylene)
PEP and of a long polyelectrolytic block (polystyrene-sulfonate) PSSNa which has been shown previously to micellize in water.
The apparent polydispersity of these micelles is studied in detail, showing the existence of a few large aggregates coexisting
with the population of micelles. Solutions of micelles are found to order above some threshold in polymer concentration. The
order is liquid-like, as demonstrated by the evolution with concentration of the peak observed in the structure factor (), and the degree of order is found to be identical over a large range of concentrations (up to 20 wt%). Consistent values
of the aggregation number of the micelles are found by independent methods. The effect of salt addition on the order is found
to be weak.
Received: 19 June 1997 / Received in final form: 4 September 1997 / Accepted: 9 October 1997 相似文献
73.
用结晶紫选择性电极(自制)以催化电位法对测定微量锰进行了研究。该方法测定标的线性范围为7~74μg/L,对标准钢样中的锰含量测定结果满意,且操作方便。 相似文献
74.
75.
WU Xiu-Lan WANG Fen REN Qiang 《结构化学》2007,26(6):732-736
Homogeneous cordierite has been synthesized at low cost by talc-magnesite and coal gangue as the main raw materials. The mechanism of synthesizing cordierite under such a com- posing system of raw materials, and the effect of temperature on the crystal cell parameters and microstructure and thermal expansion coefficient of cordierite crystal have been studied via testing methods of XRD, SEM, etc. The result shows that the homogeneous cordierite can be synthesized by the systematic composing materials of “talc-magnesite—coal gangue—talc” with heat pre- servation at 1350 ℃ for 1 h; as the keeping time is prolonged, Al3+ and Mg2+ in cordierite crystal are replaced by a few impurity ions such as Fe3+, Fe2+, etc., and the crystal cell parameters of cordierite present an increase trend; as the high-temperature heat preservation is prolonged, the content of glassy phase in the sample is increased, its density is improved, and its thermal expansion coeffi- cient presents an increase trend. 相似文献
76.
Three novel hetero-polyoxovanadates, [Cd(2,2′-bpy)3]{[Cd(dien)]As8V14O42(H2O)} (1, 2,2′-bpy=2,2′-bipyridine, and dien=diethylenetriamine), [Zn(2,2′-bpy)2]2[As8V14O42(H2O)]·H2O (2) and [Ni(en)2]3[As8V14O42(HPO3)]·4H2O (3, en=ethlenediamine), were hydrothermally synthesized and characterized by single-crystal X-ray diffraction. Crystal data: 1 monoclinic, P2(1)/n, a=15.1728(5), b=19.2863(5), , β=96.005(2)°, Z=4. 2, orthorhombic, P2(1)2(1)2(1), a=12.1270(3), b=15.8678(8), , Z=4. 3, triclinic, , a=12.9340(3), b=13.4130(3), , α=87.170(3)°, β=77.517(3)°, γ=68.480(3)°, Z=2. Compounds 1-3 are all made of the {As8V14O42} shells linked by corresponding transition metal complexes into extended structures. Compound 1 and 2 present 1-D wave-like and tubular structures, respectively, while compound 3 exhibits a novel 2-D structure containing interwinding puckery layers. Variable temperature susceptibility measurements demonstrate the presence of antiferromagnetic interaction between VIV cations in 1 and 2. 相似文献
77.
双邻苯二酚锑二甲基羟乙铵的晶体结构 总被引:3,自引:1,他引:3
含锑配合物是治疗血吸虫病、肿瘤等的常用药物,我们曾对双邻苯二酚锑二乙基羟乙胺进行了晶体结构测定,本文简要报导双邻苯二酚锑二甲基羟乙胺的结构.锑化合物的制法与其二乙基羟乙铵衍生物类似.产物为淡黄色晶体,它在水溶液中长时间放置会变成紫黑色,因此,制得的晶体须立即用丙酮溶解进行重结晶.晶体的密度为1.667g/cm~3.按C_(16)H_(20)O_5NSb的元素分析结果(%)如下:Sb 28.3(28.5),C 43.9(44.9),N 3.3(3.3),H 4.7(4.7).括号内为理论值. 相似文献
78.
NBR/ORGANOMODIFIED BENTONITE INTERCALATED HYBRIDS AND THEIR EFFECTS ON THE TOUGHNESS OF PVC 总被引:4,自引:0,他引:4
Hybrids of intercalative nitrile-butadiene rubber/organomodified bentonite (NBR/OMB) were prepared by thelatex intercalation technique. Investigation of their mechanical properties and the microstructore of NBR/OMB showed thatthe organomodified bentonite is an effective toughener for NBR. Transmission electronic microscopy (TEM) and X-rnydiffraction (XRD) tests showed that the NBR macromolecule could be intercalated into the galleries of bentonite.Incorporation of NBR/OMB hybrids as tougheners into poly(vinyl chloride) (PVC) results in a substantial increase in theimpact strength of PVC, but little decrease in its tensile strength and flexural strength, compared to the unmodified PVC. 相似文献
79.
Hubert HuppertzRolf-Dieter Hoffmann Rainer Pöttgen 《Journal of solid state chemistry》2002,169(2):155-159
EuPd0.72In1.28 and EuPt0.56In1.44 were prepared under multianvil high-pressure (10.5 GPa) high-temperature (1500 and 1400 K) conditions from the precursor compounds EuPdIn and EuPtIn. They were investigated by X-ray diffraction on both powders and single crystals: MgZn2-type, space group P63/mmc, a=578.7(1) pm, c=944.9(3) pm, wR2=0.0734, 263 F2 values for EuPd0.72In1.28 and a=591.1(2) pm, c=933.8(2) pm, wR2=0.0853, 151 F2 values for EuPt0.56In1.44 with 13 variable parameters per refinement. Both structures are built up from face- and corner-sharing tetrahedra of palladium (platinum) and indium atoms. The europium cations are located in cavities within the three-dimensional [Pd0.72In1.28] and [Pt0.56In1.44] networks. The 2a and 6 h positions of the tetrahedral networks show mixed Pd/In and Pt/In occupancy in EuPd0.72In1.28 and EuPt0.56In1.44, respectively. The crystal chemistry of these indides is briefly discussed. 相似文献
80.
ZnO对Ag/SiO2催化剂银的分散作用及对吲哚合成稳定性的影响 总被引:2,自引:0,他引:2
将ZnO助剂加到由苯胺和乙二醇一步合成吲哚的Ag/SiO2催化剂中,发现ZnO助剂能大大提高催化剂的稳定性.XRD和TEM表征首次得到:ZnO是结构型助剂,它能使银很好地分散在SiO2表面上,并可有效地抑制反应过程中银粒子的烧结. 相似文献