全文获取类型
收费全文 | 2716篇 |
免费 | 67篇 |
国内免费 | 13篇 |
专业分类
化学 | 2163篇 |
晶体学 | 38篇 |
力学 | 30篇 |
数学 | 165篇 |
物理学 | 400篇 |
出版年
2022年 | 21篇 |
2021年 | 25篇 |
2020年 | 18篇 |
2019年 | 28篇 |
2018年 | 30篇 |
2016年 | 35篇 |
2015年 | 31篇 |
2014年 | 45篇 |
2013年 | 116篇 |
2012年 | 116篇 |
2011年 | 133篇 |
2010年 | 74篇 |
2009年 | 63篇 |
2008年 | 133篇 |
2007年 | 152篇 |
2006年 | 156篇 |
2005年 | 180篇 |
2004年 | 127篇 |
2003年 | 104篇 |
2002年 | 128篇 |
2001年 | 28篇 |
2000年 | 31篇 |
1999年 | 33篇 |
1998年 | 36篇 |
1997年 | 26篇 |
1996年 | 38篇 |
1995年 | 33篇 |
1994年 | 29篇 |
1993年 | 34篇 |
1992年 | 32篇 |
1991年 | 24篇 |
1990年 | 24篇 |
1989年 | 25篇 |
1988年 | 33篇 |
1987年 | 37篇 |
1986年 | 26篇 |
1985年 | 47篇 |
1984年 | 59篇 |
1983年 | 36篇 |
1982年 | 47篇 |
1981年 | 32篇 |
1980年 | 35篇 |
1979年 | 38篇 |
1978年 | 36篇 |
1977年 | 36篇 |
1976年 | 42篇 |
1975年 | 35篇 |
1974年 | 30篇 |
1973年 | 29篇 |
1971年 | 16篇 |
排序方式: 共有2796条查询结果,搜索用时 15 毫秒
11.
The environmental radioactivity caused by the reactor accident at Chernobyl' was investigated from May 7 to May 31 of 1986 in Toyama. Measurement of radioactivities in airborne particles, rain water, drinking water, milk, and mugwort are carried out by gamma-ray spectrometry (pure Ge detector; ORTEC GMX-23195). Ten different nuclides (103Ru, 106Ru, 131I, 132Te-I, 134Cs, 136Cs, 137Cs, 140Ba-La) are identified from samples of airborne particles. In the air samples, a maximum radioactivity concentration of each nuclide is observed on 13th May 1986. The time of the reactor shut-down and the flux of thermal neutron at the reactor were calculated from 131I/132I and 137Cs/134Cs ratio. The exposure dose in Toyama by this accident is given as follows: internal exposure; [thyroid] adult-59 microSv, child-140 microSv, baby-130 microSv, [total body] adult-0.2 microSv, child, baby-0.4 microSv, external exposure; 7 microSv, effective dose equivalent; adult-9 microSv, child-12 Sv, baby-11 microSv. 相似文献
12.
13.
An automated on-line sample-preparation method using a computer-controlled pretreatment system (Auto-Pret AES system) coupled with ICP-AES was developed. In this work, an iminodiacetate chelating resin, packed in a mini-column and installed in the system was employed for the collection/concentration of 13 trace metals, including such toxic metals as Be, Cd, Cr, Cu and Pb. The limits of detection of the proposed method for trace metals were in the range of 0.001 (Be) -0.18 (Pb) ng mL-1. The enrichment factors for metal ions were about 19 times, when 5 mL of samples were used. The sample throughput was 11 h-1. The accuracy and the precision of the method were evaluated using river-water reference materials, SLRS-4 from NRCC, JSAC 0301-1 and JSAC 0302 from the Japan Society for Analytical Chemistry. The proposed method can be favorably applied to the collection/concentration of trace metals in natural water samples. 相似文献
14.
15.
Copper(II) is determined by non-extractive spectrophotometry as a complex of butylene dithiocarbamate formed in situ by reaction between carbon disulfide and pyrrolidine in aqueous Triton X-100 medium. This method is similar to that with butylene dithiocarbamate as starting material in the sense of simplicity, sensitivity, precision and accuracy. Pyrrolidine is the best of seven secondary amines tested in this way for copper determinations. 相似文献
16.
1,3-Di-tert-butylazulene reacted with highly electrophilic trifluoromethanesulfonate of N-containing heterocycles to give 5-(dihydroheteroaryl)azulene derivatives in good yield and treatment of the 5-(dihydroheteroaryl)azulene derivatives with KOH afforded 5-(heteroaryl)azulenes in excellent yield. 相似文献
17.
18.
A highly sensitive fluorescence quenching method for the determination of silicate based on the formation of an ion associate between molybdosilicate and Rhodamine B (RB) in nitric acid medium was developed. A flow injection system coupled with a fluorescence detector was used for the measurement of fluorescence intensity at 560 and 580 nm as excitation and emission wavelengths, respectively. The calibration graph for Si showed a linear range of 0.1–5 ng cm−3 with correlation coefficient of 0.9999, and the detection limit of 0.06 ng cm−3. The proposed method was successfully applied to the determination of silicate in ultrapurified water with satisfactory results. 相似文献
19.
Arakawa R Shimomae Y Morikawa H Ohara K Okuno S 《Journal of mass spectrometry : JMS》2004,39(8):961-965
A low molecular mass polyester was analyzed by desorption/ionization on porous silicon (DIOS) mass spectrometry. The results were compared with those of matrix-assisted laser desorption ionization (MALDI) mass spectrometry using matrixes of alpha-cyano-4-hydroxycinnamic acid (CHCA) and 10,15,20-tetrakis(pentafluorophenyl)porphyrin (F20TPP). The CHCA matrix was not suitable for characterization of low molecular mass components of the polyester because the matrix-related ions interfered with the component ions. On the other hand, the F20TPP matrix showed no interference because no matrix-related ions appeared below m/z 822. However, the solvent selection for determining optimal conditions of sample preparation was limited, because F20TPP does not dissolve readily in any of the available organic solvents. In the DIOS spectra, the polymer ions were observed at high sensitivity without a contaminating ion. No matrix is needed for DIOS spectra of low molecular mass polyesters, facilitating sample preparation and selectivity of a precursor ion in post-source decay measurements. 相似文献
20.