全文获取类型
收费全文 | 2476篇 |
免费 | 239篇 |
国内免费 | 301篇 |
专业分类
化学 | 1246篇 |
晶体学 | 38篇 |
力学 | 175篇 |
综合类 | 14篇 |
数学 | 275篇 |
物理学 | 454篇 |
综合类 | 814篇 |
出版年
2024年 | 2篇 |
2023年 | 17篇 |
2022年 | 41篇 |
2021年 | 56篇 |
2020年 | 77篇 |
2019年 | 45篇 |
2018年 | 46篇 |
2017年 | 62篇 |
2016年 | 89篇 |
2015年 | 84篇 |
2014年 | 113篇 |
2013年 | 179篇 |
2012年 | 123篇 |
2011年 | 141篇 |
2010年 | 112篇 |
2009年 | 118篇 |
2008年 | 150篇 |
2007年 | 163篇 |
2006年 | 131篇 |
2005年 | 134篇 |
2004年 | 128篇 |
2003年 | 116篇 |
2002年 | 113篇 |
2001年 | 82篇 |
2000年 | 97篇 |
1999年 | 71篇 |
1998年 | 70篇 |
1997年 | 67篇 |
1996年 | 68篇 |
1995年 | 54篇 |
1994年 | 25篇 |
1993年 | 33篇 |
1992年 | 37篇 |
1991年 | 34篇 |
1990年 | 29篇 |
1989年 | 26篇 |
1988年 | 23篇 |
1987年 | 18篇 |
1986年 | 7篇 |
1985年 | 9篇 |
1984年 | 7篇 |
1983年 | 7篇 |
1982年 | 5篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1974年 | 2篇 |
1972年 | 1篇 |
排序方式: 共有3016条查询结果,搜索用时 15 毫秒
41.
A(n,4)与A(n,5)的精确公式与简单公式 总被引:12,自引:2,他引:10
蔺大正 《四川大学学报(自然科学版)》1998,35(5):660-663
设A(n,k)表示不定方程k∑i=1ixi=n非负整数解的个数,给出了A(n,4)与A(n,5)的精确公式及求得应简单公式的方法。 相似文献
42.
通过现代测试技术研究了化学沉积Ni-W-P合金镀层的结构、热稳定性、硬度、耐蚀性和抗冲刷腐蚀性能的影响.结果表明:Ni-W-P合金镀层的结晶状态主要由磷含量决定,但钨却使镀层形成非晶态结构所需的磷含量降低,同时钨的存在大大提高了合金镀层的热稳定性、硬度、耐蚀性和抗冲刷腐蚀性能. 相似文献
43.
Cui X Yu SH Li L Biao L Li H Mo M Liu XM 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,10(1):218-223
Selective synthesis of uniform single crystalline silver molybdate/tungstate nanorods/nanowires in large scale can be easily realized by a facile hydrothermal recrystallization technique. The synthesis is strongly dependent on the pH conditions, temperature, and reaction time. The phase transformation was examined in details. Pure Ag(2)MoO(4) and Ag(6)Mo(10)O(33) can be easily obtained under neutral condition and pH 2, respectively, whereas other mixed phases of Mo(17)O(47), Ag(2)Mo(2)O(7,) Ag(6)Mo(10)O(33) were observed under different pH conditions. Ag(6)Mo(10)O(33) nanowires with uniform diameter 50-60 nm and length up to several hundred micrometers were synthesized in large scale for the first time at 140 degrees C. The melting point of Ag(6)Mo(10)O(33) nanowires were found to be about 238 degrees C. Similarly, Ag(2)WO(4), and Ag(2)W(2)O(7) nanorods/nanowires can be selectively synthesized by controlling pH value. The results demonstrated that this route could be a potential mild way to selectively synthesize various molybdate nanowires with various phases in large scale. 相似文献
44.
《Mendeleev Communications》2020,30(1):126-128
- Download : Download high-res image (65KB)
- Download : Download full-size image
45.
Investigations carried out in order to determine traces of 25 elements in tungsten in the lower g/g range are reported on. Atomic absorption spectrometry and plasma atomic emission spectrometry as well as solution photometry and activation analysis were the main techniques used. 相似文献
46.
本文在两次标准加入法[1]的基础上,提出了三组份同时测定的三次标准加入法,并应用于钼、钨和钛的流动注射同时测定。测定条件:[水杨基荧光酮(SAF)]=1.25 ×10-4mol/L,[溴化+六烷基三甲基铵(CTMAB)」=2.5×10-3mol/L,pH1.35,25℃,采样、进样时间分别为10s和18s,进样频率128次/h。为消除组份间协同作用引起的吸光度加合性的偏离,定义了三组份协同系数。将其引入三组份同时测定方法,补偿了吸光度对线性的偏离。补偿后钼、钨和钛的测定范围分别为0.05~0.35,0.25~1.00,0.025~0.30mg/L。测定了钢样及模拟样品中钼、钨和钛含量,结果较好。 相似文献
47.
Baeten V von Holst C Garrido A Vancutsem J Michotte Renier A Dardenne P 《Analytical and bioanalytical chemistry》2005,382(1):149-157
In this paper we present an alternative method for detection of meat and bone meal (MBM) in feedstuffs by near-infrared microscopic (NIRM) analysis of the particles in the sediment fraction (dense fraction (d >1.62) from dichloroethylene) of compound feeds. To apply this method the particles of the sediment fraction are spread on a sample holder and presented to the NIR microscope. By using the pointer of the microscope the infrared beam is focussed on each particle and the NIR spectrum (1112–2500 nm) is collected. This method can be used to detect the presence of MBM at concentrations as low as 0.05% mass fraction. When results from the NIRM method were compared with the classical microscopic method, a coefficient of determination (R2) of 0.87 was obtained. The results of this study demonstrated that this method could be proposed as a complementary tool for the detection of banned MBM in feedstuffs by reinforcement of the monitoring of feeds. 相似文献
48.
碳五馏分中微量阻聚剂二乙基羟胺的气相色谱测定法 总被引:2,自引:0,他引:2
提出采用HP-l毛细管色谱柱测定碳五馏分中微量阻聚剂二乙基羟胺组分的气相色谱方法。在本文提出的条件下,二乙基羟胺与其他组分分离良好,检出限低于20mg/kg,相对标准偏差为3.86%,结果准确可靠,方法满足控制分析的要求。 相似文献
49.
The analytical performance of a glow discharge quadrupole mass spectrometer is demonstrated using sintered tungsten as an example. The inherent problem of molecular interferences in glow discharge mass Spectrometry has been considerably reduced using neon as a complementing discharge gas. Particular attention has been paid to time dependences. Analytical figures of merit are presented. 相似文献
50.
A. Z. Voskoboinikov E. B. Chuklanova A. I. Gusev A. V. Kisin I. P. Beletskaya 《Russian Chemical Bulletin》1993,42(3):547-551
The cluster [Na(DME)3]2[W3(CO)14] (1) was prepared by treating CpLuCl2 with an equimolar mixture of Na2W(CO)5 and Na2W2(CO)10 in DME and characterized by X-ray analysis (MoK
radiation, 653 reflections,R = 0.125). The crystals are rhombic,a=18.749(4) Å,b=15.074(3) Å,c=9.505(3) Å,Z = 2, space groupC
mmm. The W-W distance in the W-W-W chain is 2.79 Å. The carbonyl ligands at the tungsten atoms are eclipsed. Compound 1 is the first example of a homometallic carbonyl cluster of an early transition metal. It is suggested that CpLuCl2 interacts with Na2W(CO)5 to afford the highly reactive species CpLu
(CO)5 which further reacts with Na2W2(CO)10 to form1.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 582–585, March, 1993. 相似文献