全文获取类型
收费全文 | 27855篇 |
免费 | 4442篇 |
国内免费 | 3794篇 |
专业分类
化学 | 13825篇 |
晶体学 | 399篇 |
力学 | 1092篇 |
综合类 | 341篇 |
数学 | 2054篇 |
物理学 | 7412篇 |
无线电 | 10968篇 |
出版年
2024年 | 144篇 |
2023年 | 655篇 |
2022年 | 954篇 |
2021年 | 1022篇 |
2020年 | 986篇 |
2019年 | 990篇 |
2018年 | 826篇 |
2017年 | 964篇 |
2016年 | 1073篇 |
2015年 | 1331篇 |
2014年 | 1611篇 |
2013年 | 2129篇 |
2012年 | 2342篇 |
2011年 | 2457篇 |
2010年 | 1926篇 |
2009年 | 1972篇 |
2008年 | 2017篇 |
2007年 | 1997篇 |
2006年 | 1732篇 |
2005年 | 1400篇 |
2004年 | 1130篇 |
2003年 | 849篇 |
2002年 | 868篇 |
2001年 | 767篇 |
2000年 | 730篇 |
1999年 | 490篇 |
1998年 | 347篇 |
1997年 | 308篇 |
1996年 | 306篇 |
1995年 | 260篇 |
1994年 | 273篇 |
1993年 | 224篇 |
1992年 | 201篇 |
1991年 | 151篇 |
1990年 | 124篇 |
1989年 | 106篇 |
1988年 | 72篇 |
1987年 | 60篇 |
1986年 | 54篇 |
1985年 | 50篇 |
1984年 | 38篇 |
1983年 | 35篇 |
1982年 | 15篇 |
1981年 | 16篇 |
1980年 | 8篇 |
1979年 | 15篇 |
1978年 | 6篇 |
1977年 | 8篇 |
1976年 | 8篇 |
1975年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
11.
Non-dispersive atomic fluorescence spectrometry (NDAFS) coupled with vapor generation (VG) sample introduction was applied to the determination of the concentrations of hazardous heavy metals, such as arsenic, cadmium, lead and mercury, in seawater, soils and total airborne particulate matter (PM) collected around the Xiamen area in China. Almost 100% sample introduction efficiency was achieved by using thiourea and ascorbic acid for the pre-reduction of As(V) to As(III), K3Fe(CN)6 and tartaric acid for pre-oxidation of Pb(II) to Pb(IV), and masking the interferences arising from the co-existing transition metals to As, Cd, Hg and Pb during their vapor generation process. Moreover, a novel sample pretreatment device was developed to avoid the loss of mercury, lead, cadmium and arsenic during sample pretreatment. With such methods, the detection limit (DL) of arsenic, cadmium, lead and mercury was down to 0.08, 0.03, 0.05, 0.01 ng mL(-1) (3sigma), respectively. The relative standard deviations (RSD, n = 11) for arsenic, cadmium, lead and mercury at 10 ng mL(-1) were 0.9%, 1.6%, 1.3% and 2.0%, respectively. The concentrations of hazardous heavy metals in the environmental samples collected in Xiamen, China are in the range from 0.02 +/- 0.001 ng mL(-1) in seawater to 15.3 +/- 0.2 microg g(-1) in soils. Besides flame/GF-AAS and ICP-AES/MS, VG-NDAFS should be another choice for the determination of hazardous heavy metals in environmental samples. 相似文献
12.
本文介绍了广播发射台利用计算机技术、网络技术、遥控遥测技术、现代测试手段,对设备进行自动化控制与管理;实现设备技术指标自动测试,发射台无人值班、有人留守,建立机器的计算机档案制度,确保安全优质播出的方法和经验。 相似文献
13.
Jie Xue Liang Chen Li Zhou Zhifeng Jia Yanping Wang Xinyuan Zhu Deyue Yan 《Journal of Polymer Science.Polymer Physics》2006,44(15):2050-2057
α‐Cyclodextrin (α‐CD) has been complexed with various poly(ethylene glycol) (PEG) derivatives in aqueous solution. It has been found that the end groups of PEG derivatives affect the complexation kinetics greatly, but have only a little influence on the thermodynamic behavior. By increasing the hydrophobicity of end groups, the complexation speeds up rapidly. On the other hand, the bulky end groups slow down the threading of polymeric guests into the cavity of CD. By changing the hydrophobicity and the size of end groups, the complexation rate can be adjusted in the range of several orders of magnitudes, which should be quite useful in the design of new supramolecular systems. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2050–2057, 2006 相似文献
14.
We present integral-type Darboux transformation for the mKdV hierarchy and for the mKdV hierarchy withself-consistent sources. In contrast with the normal Darboux transformation, the integral-type Darboux transformationscan offer non-auto-Backlund transformation between two (2n 1)-th mKdV equations with self-consistent sources withdifferent degrees. This kind of Darboux transformation enables us to construct the N-soliton solution for the mKdVhierarchy with self-consistent sources. We also propose the formulas for the m times repeated integral-type Darbouxtransformations for both mKdV hierarchy and mKdV hierarchy with self-consistent sources. 相似文献
15.
脉冲电镀最佳参数之探索和优化 总被引:3,自引:0,他引:3
本文利用正交实验法对脉冲电镀各控制参数进行试验,对影响分散能力、镀层可靠性及外观质量的各种因素进行探讨,寻找影响外观质量的显著因子并加以控制,同时进一步优化脉冲电镀的工艺参数。 相似文献
16.
A new integrated magnetic full wave DC/DC power converter that provides flexible transformer design by incorporating an independent output inductor winding is introduced. The transformer is implemented on a traditional three-leg magnetic core. The inductor winding can be separately designed to control the output current ripple. The cross-sectional area of the inductor core leg can be reduced dramatically. The operation and performance of the proposed circuit are verified on a 100 W prototype converter. 相似文献
17.
Zhen‐Feng Chen Hong‐Li Zhou Hong Liang Yan Li Ren‐Gen Xiong Xiao‐Zeng You 《应用有机金属化学》2003,17(11):883-884
The centrosymmetric binuclear structure of [Pb2(H‐Norf)2(ONO2)4]shows the geometry around each lead(II) atom to be distorted trigonal bipyramidal with Pb–O distances ranging from 2.357(3) to 2.769(4) Å. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
18.
Chung S.S. Shui-Ming Cheng Lee R.G.-H. Song-Nian Kuo Mong-Song Liang 《Electron Devices, IEEE Transactions on》1997,44(12):2220-2226
This paper reports a simple I-V method for the first time to determine the lateral lightly-doped source/drain (S/D) profiles (n- region) of LDD n-MOSFETs. One interesting result is the direct observation of the reverse-short-channel effect (RSCE). It is observed that S/D n- doping profile is channel length dependent if reverse short-channel effect exists as a result of the interstitial imperfections caused by Oxide Enhanced Diffusion (OED) or S/D implant. Not only the lateral profiles for long-channel devices but also for short-channel devices can be determined. One other practical application of the present method for device drain engineering has been demonstrated with a LATID MOS device drain engineering work. It is convincible that the proposed method is well suited for the characterization and optimization of submicron and deep-submicron MOSFETs in the current ULSI technology 相似文献
19.
20.