全文获取类型
收费全文 | 92791篇 |
免费 | 5067篇 |
国内免费 | 11911篇 |
专业分类
化学 | 71066篇 |
晶体学 | 1158篇 |
力学 | 2598篇 |
综合类 | 849篇 |
数学 | 13852篇 |
物理学 | 20246篇 |
出版年
2024年 | 119篇 |
2023年 | 693篇 |
2022年 | 1903篇 |
2021年 | 1826篇 |
2020年 | 2248篇 |
2019年 | 2200篇 |
2018年 | 1898篇 |
2017年 | 2760篇 |
2016年 | 2886篇 |
2015年 | 2435篇 |
2014年 | 3393篇 |
2013年 | 6832篇 |
2012年 | 6340篇 |
2011年 | 5114篇 |
2010年 | 4364篇 |
2009年 | 5955篇 |
2008年 | 6133篇 |
2007年 | 6345篇 |
2006年 | 5737篇 |
2005年 | 4838篇 |
2004年 | 4503篇 |
2003年 | 3694篇 |
2002年 | 4963篇 |
2001年 | 2868篇 |
2000年 | 2645篇 |
1999年 | 2485篇 |
1998年 | 2158篇 |
1997年 | 1714篇 |
1996年 | 1433篇 |
1995年 | 1373篇 |
1994年 | 1211篇 |
1993年 | 1013篇 |
1992年 | 965篇 |
1991年 | 644篇 |
1990年 | 543篇 |
1989年 | 524篇 |
1988年 | 384篇 |
1987年 | 302篇 |
1986年 | 284篇 |
1985年 | 233篇 |
1984年 | 244篇 |
1983年 | 143篇 |
1982年 | 220篇 |
1981年 | 175篇 |
1980年 | 198篇 |
1979年 | 185篇 |
1978年 | 173篇 |
1977年 | 124篇 |
1976年 | 108篇 |
1973年 | 68篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
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
992.
Shkumbatiuk R Bazel YR Andruch V Török M 《Analytical and bioanalytical chemistry》2005,382(6):1431-1437
A new, simple, rapid, and sensitive spectrophotometric method has been developed for the determination of nitrophenols [picric acid (PA); dinitrophenols (DNP)] in wastewater samples. The method is based on the reaction of nitrophenols with 2-[(E)-2-(4-diethylaminophenyl)-1-ethenyl]-1,3,3-trimethyl-3 H-indolium chloride reagent to form the colored ion associates, which are extracted by organic solvents. The molar absorptivity of the ion associates of PA with the investigated reagent ranges from 8.3×104 to 11.3×104 L mol–1 cm–1, depending on the extractant. Because only PA is extracted in an acidic medium with the investigated reagent, but both PA and DNP are extracted in an alkaline medium, it is possible to determine both substances in a mixture. Appropriate reaction conditions have been established. The absorbance of the colored extracts obeys Beers law in the range of 0.04–4.58 mg L–1 PA, 1.0–18.4 mg L–1 2,4-DNP and 1.2–14.7 mg L–1 2,6-DNP, respectively. The limit of detections, calculated from a blank test (n=10; P=0.95), are 0.05 mg L–1 PA, 0.9 mg L–1 (2,4-DNP), and 1.1 mg L–1 (2,6-DNP), respectively. 相似文献
993.
Luciani G. Costantini A. Branda F. Scardi P. Lanotte L. 《Journal of Thermal Analysis and Calorimetry》2003,72(1):105-111
A traditional TG apparatus was modified by placing two permanent magnets producing a controlled magnetic field (TG(M): Magneto
Thermogravimetry). This technique proved to be useful to study both structural relaxation and crystallisation of ferromagnetic
metallic glasses. Results obtained for the amorphous alloys Fe40Ni40P14B6 and Fe62.5Co6Ni7.5Zr6Nb2Cu1B15, are reported in this paper. Structural relaxation can be evaluated by measuring changes in Curie temperature induced by
thermal treatments. Crystallisation in TG(M) is detected through a change in the measured apparent mass (difference between
the sample mass and magnetic force driving it upward). These results were confirmed by DSC analysis. Whether the obtained
crystalline phase is ferromagnetic, it can be identified through its Curie temperature, measured by TG(M). In fact the value
of 770°C measured as Curie temperature of crystallised Fe62.5Co6Ni7.5Zr6Nb2Cu1B15led to conclude that the only ferromagnetic crystalline phase is a-Fe. These hypothesis was confirmed by XRD analysis, showing
that the first crystallisation yields to a-Fe nanocrystals.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
994.
995.
996.
997.
制取了4-二氰基亚甲基-2-甲基-6-对二甲胺基苯乙烯基-4H-吡喃(DCM)和1,2-双(5-甲基苯并恶唑)基乙烯(DT)两种荧光分子的LB膜以及两者的混合膜,以吸收光谱和荧光光谱探讨了膜中分子的构型,微环境,发光性能等特征,发现在LB膜的缀密排布环境中DCM顺式构型的含量较之在溶液中大为增加。 相似文献
998.
999.
Xin Ying ZHANG Xue Sen FAN Hong Ying NIU Jian Ji WANGSchool of Chemical Environmental Sciences Henan Normal University Key Laboratory ofEnvironmental Science Engineering of Henan Education Department Xinxiang 《中国化学快报》2003,(10)
a, a'-Bis(substituted benzylidene)cycloalkanones were efficiently prepared from cycloalkanones and benzaldehydes in [bmim][BF4] by using iron(III) chloride hexahydrate as a catalyst. It is shown that [bmim][BF4] and iron(III) chloride hexahydrate can be quantitatively recovered and be reused effectively for many times. Compared with the known methods, this novel process has the advantage of being an envkonmentally benign process together with good yields and mild reaction conditions. 相似文献
1000.
合成了MnPPCl,RhPPCl,RhPPN3,RhPP(CO)Cl四种配合物 (PP =ProtophyrinIXDimethy1Ester) ,用元素分析、红外吸收光谱及紫外吸收光谱确定了配合物的组成 ,测定了它们的共振拉曼光谱 ,对特征谱带进行了归属。分析了拉曼谱带和电子吸收谱带变化的原因 ,提出了谱带频率的变化受金属离子外层d电子和轴配体的影响。 相似文献