全文获取类型
收费全文 | 126040篇 |
免费 | 21279篇 |
国内免费 | 23960篇 |
专业分类
化学 | 57151篇 |
晶体学 | 2331篇 |
力学 | 5001篇 |
综合类 | 2441篇 |
数学 | 11122篇 |
物理学 | 34815篇 |
无线电 | 58418篇 |
出版年
2024年 | 399篇 |
2023年 | 1886篇 |
2022年 | 3616篇 |
2021年 | 4065篇 |
2020年 | 3838篇 |
2019年 | 3775篇 |
2018年 | 3440篇 |
2017年 | 4331篇 |
2016年 | 4242篇 |
2015年 | 5816篇 |
2014年 | 7030篇 |
2013年 | 8790篇 |
2012年 | 9932篇 |
2011年 | 11745篇 |
2010年 | 9805篇 |
2009年 | 10090篇 |
2008年 | 10240篇 |
2007年 | 9560篇 |
2006年 | 9010篇 |
2005年 | 7976篇 |
2004年 | 7547篇 |
2003年 | 5285篇 |
2002年 | 4719篇 |
2001年 | 4377篇 |
2000年 | 3944篇 |
1999年 | 2476篇 |
1998年 | 1544篇 |
1997年 | 1170篇 |
1996年 | 1046篇 |
1995年 | 934篇 |
1994年 | 881篇 |
1993年 | 1444篇 |
1992年 | 1255篇 |
1991年 | 980篇 |
1990年 | 896篇 |
1989年 | 840篇 |
1988年 | 543篇 |
1987年 | 276篇 |
1986年 | 315篇 |
1985年 | 198篇 |
1984年 | 198篇 |
1983年 | 162篇 |
1982年 | 120篇 |
1981年 | 111篇 |
1980年 | 83篇 |
1979年 | 69篇 |
1978年 | 42篇 |
1977年 | 26篇 |
1965年 | 21篇 |
1959年 | 19篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
62.
中国调频频段数字音频广播(CDR)激励器及发射机测试标准已正式发布.CDR采用的是数模同播技术,相关指标测试方法比较复杂,具体测试步骤也较抽象.这里将实际测试积累的一些经验和技巧结合标准内容进行阐述,不但可提高测试效率也能帮助大家比较直观和深入的理解标准内容. 相似文献
63.
In this paper,we investigate the non-autonomous Hamilton-Jacobi equation ■ where H is 1-periodic with respect to t and M is a compact Riemannian manifold without boundary.We obtain the viscosity solution denoted by T_(t_0)~tφ(x) and show T_(t_0)~tφ(x) converges uniformly to a time-periodic viscosity solution u~*(x,t) of ?_tu+H(t,x,?_xu,u)=0. 相似文献
64.
65.
Nonlinear Dynamics - This paper seeks to address the problem of finite-time stabilization for a class of uncertain Hamiltonian systems via sliding mode control approach. A novel sliding function in... 相似文献
66.
对PCB废水总氮的处理,从源头削减、分质收集、分质预处理到末端处理提出了多种方法,着重分析了MAP+管式微滤膜处理氨氮废水、多级组合式RO处理硝态氮废水和A2O+MBR处理综合废水,提出PCB废水总氮达标的组合工艺,项目建成后达到预期效果。 相似文献
67.
Cuixia Cui Yong Gao Dr. Jun Li Chao Yang Meng Liu Prof. Dr. Huile Jin Prof. Dr. Zhenhai Xia Prof. Dr. Liming Dai Prof. Dr. Yong Lei Prof. Dr. Jichang Wang Prof. Dr. Shun Wang 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(20):8002-8007
Although tremendous efforts have been devoted to understanding the origin of boosted charge storage on heteroatom-doped carbons, none of the present studies has shown a whole landscape. Herein, by both experimental evidence and theoretical simulation, it is demonstrated that heteroatom doping not only results in a broadened operating voltage, but also successfully promotes the specific capacitance in aqueous supercapacitors. In particular, the electrolyte cations adsorbed on heteroatom-doped carbon can effectively inhibit hydrogen evolution reaction, a key step of water decomposition during the charging process, which broadens the voltage window of aqueous electrolytes even beyond the thermodynamic limit of water (1.23 V). Furthermore, the reduced adsorption energy of heteroatom-doped carbon consequently leads to more stored cations on the heteroatom-doped carbon surface, thus yielding a boosted charge storage performance. 相似文献
68.
The stable phase equilibria of quaternary systems LiBr-NaBr-MgBr2-H2O and LiBr-KBr-MgBr2-H2O at 298.15 K were studied by both experimental measurement(isothermal solution saturation method) and theoretical prediction(Pitzer model). The solubilities of the saturated solution have been determined experimentally and two stable phase diagrams and relevant water diagrams of the two quaternary systems were obtained. Results show that quaternary system LiBr-NaBr-MgBr2-H2O is hydrate II type as NaBr and NaBr·2H2O coexistence. Its phase diagram consists of only one invariant point, four univariant curves, and five crystallization fields. The quaternary system LiBr-KBr-MgBr2-H2O is a complex type as the double salt KBr·MgBr2·6H2O formed. In addition to this double salt, the three single salts LiBr·2H2O, KBr and MgBr2·6H2O also crystallize. In this paper, the solubilities of phase equilibria in above quaternary systems were also calculated by the Pitzer's electrolyte solution model. All the needed parameters can be obtained from the literature or be fitted by experimental data. On the Basis of the experimental and calculated results, the phase diagram of the quaternary system was plotted for comparison. It shows that the calculation results are consistent with the experimental ones. 相似文献
69.
Four kinds of red phosphorescent organic light-emitting devices were fabricated and compared to investigate the effect of interfacial layers for hole transport and electron injection. 1 nm-thick LiF in the device A and C and 1 nm-thick Cs2CO3 in the device B and D were deposited as an electron injection layer between the anode and the electron transport layer, and 5 nm-thick layer of dipyrazion[2,3-f:2′,2′-h]quinoxaline-2,3,6,7,10,11-hexacarbonitrile[HATCN] was inserted as a hole transport interfacial layer between the hole injection layer and the hole transport layer only in the device C and D. Under a luminance of 1000 cd/m2, the power efficiencies were 7.6 lm/W and 8.5 lm/W in the device A and B, and 8.6 lm/W and 13.4 lm/W in the device C and D. The quantum efficiency of the device D was 15.8% under 1000 cd/m2 which was somewhat lower than those of the device A and C, but a little higher than that of the device B. The luminance of the device D was much higher than those of the other devices at a given votage. The luminance of the device D at 7 V was 23,710 cd/m2, which was 13.0, 3.4, and 4.0 times higher than those of the device A, B, and C at the same voltage, respectively. 相似文献
70.
Sung Hwan Koo Dong Jun Li Taeyeong Yun Dong Sung Choi Kyung Eun Lee Gil Yong Lee Youngtak Oh Joonwon Lim Suchithra Padmajan Sasikala Ho Jin Lee In Ho Kim Hong Ju Jung Rishabh Jain Sang Ouk Kim 《Particle & Particle Systems Characterization》2019,36(7)
Efficient water electrolysis catalyst is highly demanded for the production of hydrogen as a sustainable energy fuel. It is reported that cobalt derived nanoparticle (CoS2, CoP, CoS|P) decorated reduced graphene oxide (rGO) composite aerogel catalysts for highly active and reliable hydrogen evolution reaction electrocatalysts. 7 nm level cobalt derived nanoparticles are synthesized over graphene aerogel surfaces with excellent surface coverage and maximal expose of active sites. CoS|P/rGO hybrid aerogel composites show an excellent catalytic activity with overpotential of ≈169 mV at a current density of ≈10 mA cm?2. Accordingly, efficient charge transfer is attained with Tafel slope of ≈52 mV dec?1 and a charge transfer resistance (Rct) of ≈12 Ω. This work suggests a viable route toward ultrasmall, uniform nanoparticles decorated graphene surfaces with well‐controlled chemical compositions, which can be generally useful for various applications commonly requiring large exposure of active surface area as well as robust interparticle charger transfer. 相似文献