全文获取类型
收费全文 | 13385篇 |
免费 | 2543篇 |
国内免费 | 3074篇 |
专业分类
化学 | 10179篇 |
晶体学 | 265篇 |
力学 | 755篇 |
综合类 | 345篇 |
数学 | 1659篇 |
物理学 | 5799篇 |
出版年
2024年 | 49篇 |
2023年 | 187篇 |
2022年 | 490篇 |
2021年 | 462篇 |
2020年 | 496篇 |
2019年 | 562篇 |
2018年 | 421篇 |
2017年 | 510篇 |
2016年 | 547篇 |
2015年 | 714篇 |
2014年 | 834篇 |
2013年 | 1006篇 |
2012年 | 1166篇 |
2011年 | 1159篇 |
2010年 | 1001篇 |
2009年 | 1023篇 |
2008年 | 1144篇 |
2007年 | 1046篇 |
2006年 | 939篇 |
2005年 | 741篇 |
2004年 | 644篇 |
2003年 | 492篇 |
2002年 | 534篇 |
2001年 | 450篇 |
2000年 | 459篇 |
1999年 | 335篇 |
1998年 | 184篇 |
1997年 | 148篇 |
1996年 | 164篇 |
1995年 | 148篇 |
1994年 | 139篇 |
1993年 | 133篇 |
1992年 | 118篇 |
1991年 | 85篇 |
1990年 | 78篇 |
1989年 | 64篇 |
1988年 | 64篇 |
1987年 | 66篇 |
1986年 | 46篇 |
1985年 | 43篇 |
1984年 | 26篇 |
1983年 | 22篇 |
1982年 | 17篇 |
1981年 | 10篇 |
1980年 | 13篇 |
1979年 | 8篇 |
1975年 | 2篇 |
1971年 | 2篇 |
1959年 | 2篇 |
1936年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
131.
132.
The long chain branching of polybutadienes (PB) was measured with gel permeation chroma-tography coupled to an automatically recording capillary viscometer. In this method the experimentalrelation [η] (V) was translated into the calibration curve [η] (V_R) for the monodisperse species. The curve is combined with the universal calibration so that the molecular weight distributionand an additional parameter, e.g. the average branching factor of this samples may be obtained. Longchain branching molecular weight changes with polyemerization conditions. 相似文献
133.
马来酸二丁基锡的合成及其共聚合 总被引:1,自引:0,他引:1
马来酸二丁基锡的合成及其共聚合刘云桥金根河李福绵(北京大学化学与分子工程学院北京100871)关键词马来酸二丁基锡,醋酸乙烯酯,交替共聚物,光聚合关于马来酸酐[1],马来酰亚胺 N 取代物[2,3]与富电子烯类单体如苯乙烯,醋酸乙烯酯,乙烯基烷基醚... 相似文献
134.
超低温快速冷冻固定以极高的冷冻速率(10000K/s)对生物组织进行物理固定,可使生物组织结构、组织内可溶性离子及游离性物质得到保存,使被固定后的生物组织保持最接近于原自然状态,这种样品制备方法大大优于化学制备法,因而在X-射线微分析及免疫细胞化学中得到广泛应用。生物样品超低温快速冷冻后,利用冷冻置换法,在低温下将生物组织内的结晶水缓慢置换出来,而后常规包埋切片,可获得理想的组织结构及组织内待分析成分。本文应用超低温快速冷冻固定技术及冷冻置换法对大鼠肾皮质部的快速冷冻固定及损伤进行探讨。 相似文献
135.
136.
A binuclear complex [Cu2(DTB)(DMF)4(H2O)]·2DMF (DTB = 1,4-dinitro-2,3,5,6-tetracarboxylatobenzenic anion; DMF = N,N-dimethylformamide) has been synthesized and its crystal structure determined by X-ray crystallography. In the complex Cu ion is located in a distorted square pyramidal environment with two oxygen atoms O(1) and O(3) from two carboxylate groups, another two oxygen atoms O(7) and O(8) from terminal ligands of two DMF molecules, and a fifth coordinated oxygen atom O(9) from the terminal ligand of one H2O molecule, in which the O(8) atom is situated in the apex of the pyramid. DTB as bridging ligand coordinates two Cu ions through its four carboxylate groups. The variable-temperature magnetic susceptibility of the complex was measured in the 5–300 K range. The magnetic coupling parameter is consistent with a ferromagnetic exchange between the two copper(II) centers and the data fit a binuclear magnetic exchange model based on the Hamiltonian operator ( = -2J12, 1 = 2= 1/2), giving the ferromagnetic coupling parameter of 2J = 1.80 cm- 1. This is the first example of a tetracarboxylatobenzenic bridging complex exhibiting ferromagnetic interaction. 相似文献
137.
A novel method for preparing silver nanoelectrode ensembles(SNEEs) and gold nanoelectrode ensembles (GNEEs) has been developed. Silver colloid particles were first absorbed to the gold electrode surface to form a monolayer silver colloid. N-hexadecyl nercaptan was then assembled on the electrode to form a thoil monolayer on which hydrophilic ions cannot be transfered. The SNEEs was prepared by removing thiol from silver colloid surface through applying and AC voltage with increasing frequency at 0.20V(vs.SCE). Finally,GNEEs was obtained by immersing a SNEEs into 6 mol/L HNO3 to remove the silver colloid particles. By comparison with other methods such as template method ect., this method enjoys some advantages of lower resistance, same diameter,easy preparation,controllable size and density. 相似文献
138.
139.
The solid diffusion coefficient of lithium-ion in LiCoO2 cathode material has been investigated by the capacity intermittent titration technique (CITT) at different voltages and at different charge/discharge cycles. By SEM, XRD and FTIR techniques, the structure of LiCoO2 was studied before and after charge-discharge cycles, and the relationship between solid diffusion coefficient and crystal structure was further discussed. CITT results show that the value of Li+ solid diffusion coefficient of LiCoO2 is about 10-12 cm2·s-1. During the whole charge-discharge cycles, the Li+ solid diffusion coefficient decreased within the voltage of 4.0~4.3 V, which is attributed to the change of the structure of LiCoO2. 相似文献
140.