全文获取类型
收费全文 | 39142篇 |
免费 | 6138篇 |
国内免费 | 4675篇 |
专业分类
化学 | 20316篇 |
晶体学 | 378篇 |
力学 | 2052篇 |
综合类 | 298篇 |
数学 | 3080篇 |
物理学 | 11474篇 |
无线电 | 12357篇 |
出版年
2024年 | 163篇 |
2023年 | 884篇 |
2022年 | 1173篇 |
2021年 | 1567篇 |
2020年 | 1541篇 |
2019年 | 1397篇 |
2018年 | 1241篇 |
2017年 | 1191篇 |
2016年 | 1687篇 |
2015年 | 1896篇 |
2014年 | 2289篇 |
2013年 | 2862篇 |
2012年 | 3188篇 |
2011年 | 3437篇 |
2010年 | 2451篇 |
2009年 | 2423篇 |
2008年 | 2539篇 |
2007年 | 2390篇 |
2006年 | 2354篇 |
2005年 | 1936篇 |
2004年 | 1545篇 |
2003年 | 1195篇 |
2002年 | 1091篇 |
2001年 | 984篇 |
2000年 | 885篇 |
1999年 | 782篇 |
1998年 | 682篇 |
1997年 | 583篇 |
1996年 | 564篇 |
1995年 | 503篇 |
1994年 | 448篇 |
1993年 | 353篇 |
1992年 | 342篇 |
1991年 | 277篇 |
1990年 | 238篇 |
1989年 | 196篇 |
1988年 | 121篇 |
1987年 | 115篇 |
1986年 | 95篇 |
1985年 | 96篇 |
1984年 | 52篇 |
1983年 | 49篇 |
1982年 | 42篇 |
1981年 | 24篇 |
1980年 | 15篇 |
1979年 | 10篇 |
1977年 | 7篇 |
1975年 | 7篇 |
1969年 | 4篇 |
1957年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
81.
Enantioselective catalytic trimethylsilylcyanations of aldehydes with 48% to 92% e.e. have been studied using the novel Ti-chiral Schiff base complexes. We have found that the catalyst led to high enantoselectivity when the molar ratio of the Schiff base 1 to Ti(O-i-Pr)4 was 2:1. 相似文献
82.
Linear mode conversion of waves near the maxima or minima of the density in a warm magnetized plasma
Behaviour of the h. f. electrostatic waves near the plasma or upper hybrid resonances was studied in the case that these resonances are situated at the maxima or minima of the plasma density. Supposing the parabolic density profile in these regions we obtained the connection formulae for the WKB solutions. In a weakly inhomogeneous magnetoplasma the effect of the parabolic profile manifests itself only in narrow frequency band centred at the resonance frequency corresponding to the extreme value of the density. The whole process can be then described by only two coefficients, viz. the power conversion and power transmission coefficients. 相似文献
83.
氦氖激光穴位照射治疗牙痛的疗效观察 总被引:1,自引:0,他引:1
牙科疾病引起的牙痛比较常见,每当牙痛发作时,往往使人坐卧不安,难以忍受,影响学习和工作。我们使用氦氖激光照射穴位,对牙病出现的疼痛有较好的止痛效果,现介绍如下。 相似文献
84.
85.
86.
87.
[reaction in text] An acyclic bolaamphiphile forms ion channels in vesicles and planar bilayer membranes that are closely similar to the channels formed by related bismacrocyclic compounds. Thus the function of these ion channels does not depend on synthetically difficult macrocyclic subunits. 相似文献
88.
[formula: see text] A new chiral azetidinone-carboxylate ligand for dirhodium(II) catalysis enhances reactivity toward diazo decomposition and selectivity toward cyclopropanation enabling diazomalonates, vinyldiazoacetates, and aryldiazoacetates to be effectively used with a dirhodium(II) carboxamidate catalyst. 相似文献
89.
90.
A new method based on hollow fiber-protected liquid-phase microextraction (LPME) was developed for the simultaneous determination
of atrazine, desethyl atrazine and desisopropyl atrazine in environmental water samples. In LPME, analytes were extracted
into 1-octanol immobilized in the micropores of a poly(vinylidene fluoride) porous hollow fiber membrane, and back extracted
into the acceptor (4 M HCl) filled in the lumen of the hollow fiber. After LPME, the analytes trapped in the acceptor were
analyzed with high-performance liquid chromatography after neutralization. The effect of extraction factors such as sample
pH, acceptor pH, salinity, extraction time, stirring rate, and humic acid were studied. Under the optimized conditions, the
limits of detection and relative standard deviations were respectively in the range of 0.5–1.0 μg L−1 and 3.9–4.7% (n = 5). The proposed method was applied to determine atrazine, desethyl atrazine and desisopropyl atrazine in wastewater and
groundwater samples. The three analytes were below the limits of detection, but good relative spiked recoveries over 90.1
± 5.9% at 5 μg L−1 spiked level were obtained. 相似文献