全文获取类型
收费全文 | 1267篇 |
免费 | 73篇 |
国内免费 | 39篇 |
专业分类
化学 | 899篇 |
力学 | 93篇 |
综合类 | 21篇 |
数学 | 78篇 |
物理学 | 288篇 |
出版年
2024年 | 4篇 |
2023年 | 17篇 |
2022年 | 69篇 |
2021年 | 57篇 |
2020年 | 46篇 |
2019年 | 27篇 |
2018年 | 36篇 |
2017年 | 34篇 |
2016年 | 43篇 |
2015年 | 57篇 |
2014年 | 57篇 |
2013年 | 90篇 |
2012年 | 94篇 |
2011年 | 47篇 |
2010年 | 62篇 |
2009年 | 69篇 |
2008年 | 43篇 |
2007年 | 62篇 |
2006年 | 56篇 |
2005年 | 57篇 |
2004年 | 36篇 |
2003年 | 47篇 |
2002年 | 24篇 |
2001年 | 31篇 |
2000年 | 33篇 |
1999年 | 18篇 |
1998年 | 13篇 |
1997年 | 24篇 |
1996年 | 24篇 |
1995年 | 14篇 |
1994年 | 10篇 |
1993年 | 13篇 |
1992年 | 8篇 |
1991年 | 5篇 |
1990年 | 5篇 |
1989年 | 6篇 |
1988年 | 6篇 |
1987年 | 4篇 |
1986年 | 3篇 |
1985年 | 6篇 |
1984年 | 7篇 |
1983年 | 2篇 |
1982年 | 6篇 |
1981年 | 3篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1976年 | 2篇 |
排序方式: 共有1379条查询结果,搜索用时 15 毫秒
991.
利用N,N-二甲基甲酰胺同时萃取血样中痕量的锌原卟啉和原卟啉,以三维荧光-交替三线性分解算法和导数恒基体同步荧光法同时分析血样中的锌原卟啉和原卟啉.前者中锌原卟啉和原卟啉分别在0.6~35 μg/L和0.4~27 μg/L范围内呈良好的线性,检出限分别为0.18和 0.12 μg/L;后者中锌原卟啉和原卟啉在0.14~45 μg/L和0.056~28.5 μg/L范围内呈良好的线性,检出限分别为0.12和 0.045 μg/L.实际血样中两种方法的平均回收率分别为(82±9)%和(85±10)%,且两种方法测定20份血样时获得的相关性良好. 相似文献
992.
Ilaria Marchetti Luca Menichetti Claudia Kusmic Laura Aldave de las Heras Piero Salvadori Roger Fuoco Fabio Belloni Antonio L'Abbate Maria Betti 《Spectrochimica Acta Part B: Atomic Spectroscopy》2009
The development of a complete, standard analytical procedure for a quantitative use of secondary ion mass spectrometry to map the distribution in animal tissues of exogenous isotopes presents difficulties inherently related to sample preparation and preservation, as well as to the specific application being considered. We have tested in two very different cases a procedure based on the cryo-preparation of samples and calibration standards. The applications under investigation were the mapping of 10B in mouse brain tissue, with relevance to the boron neutron capture therapy, and of the perfusion tracer 99Tc in mouse heart tissue, with relevance to the study of microcirculation and cardiovascular pathologies. Scanning electron microscopy and inductively coupled mass spectrometry analysis were used as reference techniques for secondary ion mass spectrometry images and analyte measurements, respectively. Cryo-preparation of tissue sections for ion microscopy proved to be simple and efficient (in terms of structural and chemical integrity) for both brain and heart samples derived from fresh organs. This technique, however, turned out to be reliable only on the brain tissue when applied to the preparation of standards, which required chemical fixation of portions of organs. Brain and heart tissues showed a totally different response to chemical fixation, from both a structural and an analytical point of view. On the one hand, we were able to estimate a relative sensitivity factor for 10B in the cryo-sectioned brain matrix; on the other hand, even without the possibility of an absolute quantification of the 99Tc signal and notwithstanding the presence of an isobaric interference, secondary ion mass spectrometry mapping however proved to be capable to resolve the specific response of the cardiac tissue to the perfusion mechanism. 相似文献
993.
Maruizumi Takuya Wegmann Dorothée Suter Gabriela Ammann Daniel Simon Wilhelm 《Mikrochimica acta》1986,88(5-6):331-336
The ionophore N,N,N,N-tetracyclohexyl-1,2-phenylenedioxydiacetamide (4) shows higher lipophilicity and superior Na+/K+ selectivity than the previously described N,N-dibenzyl-N,N-diphenyl-1,2-phenylenedioxydiacetamide (2). It is a suitable component of Na+-selective liquid membrane electrodes for the assay of Na+ in clinical analysers.On leave from Hitachi Ltd., Central Research Laboratory, Kokubunji, Tokyo 185, Japan. 相似文献
994.
An attempt has been made to graft a hydrophylic monomer of N,N.dimethyl acrylamide (DMAA) onto natural rubber (NR) tube by simultaneous, per-oxidation and preirradiation grafting techniques. It was found that the grafting by simultaneous grafting technique results a maximum 29 wt% degree of grafting and by peroxidation and preirradiation techniques, results the maximum 42 wt% and 13 wt% degree of grafting, respectively. It was concluded that the peroxidation technique is the most appropriate to obtain a high degree of grafting in radiation copolymerization of DMAA onto NR. 相似文献
995.
本文研究了人血、唾液及尿中锂的测定.对人血灰化条件作了探讨,采用灰化辅助剂硫酸以提高锂的回收率,并对直接测定法与标准加入法作了比较,本文C.V。小于3.2%,标准加入回收率在98.2~105%之间,适用于精神病治疗中锂的临床分析。 相似文献
996.
With the aid of spectral-luminescent analysis, our hypothesis on the determining role of free-radical oxidation in damage
of blood serum components (low-density lipoproteins) in ischemia has been confirmed. An increase in the luminescence intensity
of the blood serum of animals that suffered from brain ischemia as against that of healthy animals is registered. Lipoperoxide
free-radical damage of phospholipids of the amphipathic layer of low-density lipoproteins after an ischemic procedure has
also been confirmed by fluorescent probes (rhodamine 6G and Nile Blue).
__________
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 6, pp. 827–831, November–December, 2005. 相似文献
997.
Taisuke?HironoEmail author Katsumi?Yabusaki Yukio?Yamada 《Optical and Quantum Electronics》2005,37(8):735-753
Image cytometry centrifugation (ICC) method has been developed and applied to count residual leukocytes in transfusion blood products for quality assurance testing. The standard leukocyte fluorescence image profile was established by averaging the actual fluorescence images of leukocytes. It was used for development of an optimum image analysis algorithm to avoid misinterpretation of the dust contaminated from the environment. The centrifugal concentration process of the ICC method was investigated by a computer simulation, and it was found that it caused leukocyte overlapping and limited the enumeration range. By introducing a double thresholding algorithm to the fluorescence images analysis and correcting the number of the overlapped leukocytes, we succeeded in improving the accuracy and the measurement range up to 25 [WBC/μl] of the ICC method. 相似文献
998.
Two antidiabetic compounds named 4-methoxybenzo[b]azet-2(1H)-one (1) and 3β-hydroxy-35-(cyclohexyl-5′-propan-7′-one)-33-ethyl-34-methyl-bacteriohop-16-ene (2) together with stigmasterol and β-sitosterol were isolated from the aerial part of Roylea cinerea (D.Don) Baill. The structures of these compounds were elucidated by advanced spectroscopic methods, including two-dimensional NMR and MS techniques. These compounds were evaluated for their antidiabetic efficacy using in vitro and in vivo methods. Both compounds (1 and 2) showed a significant decline in blood glucose level of alloxan-induced diabetic rats at 10 mg/kg, p.o. when compared with glibenclamide at a similar dose. The in vitro studies revealed that compound 1 reduced α-amylase and α-glucosidase by 83.0 and 78.5%, respectively, whereas compound 2 reduced the same by 58.2 and 58.4%, respectively, at 100 μM. The present study supports the role of R. cinerea in Ayurvedic medicine for diabetes. 相似文献
999.
采用新极谱法对吉林省白山市健康居民的全血样品进行了硒含量的测定 ,并对数据进行了微机处理。总样本数为 1 1 5例 ,血硒含量为 1 5 1 3± 3 9 7μg/L ,男性 70例 ,血硒含量为 1 45 5±3 9 0 μg/L ,女性 45例 ,血硒含量为 1 60 2± 3 9 4μg/L ,两者之间有显著性差异 ( 0 0 5 >P≥ 0 0 1 ) ,但均处于营养状态 相似文献
1000.
Martin Müller Marizel Rouilly Bruno Rusterholz Magdalena Maj-Żurawska Zhongmin Hu Wilhelm Simon 《Mikrochimica acta》1988,96(1-6):283-290
Magnesium selective ionophores are described which induce a rejection of Na+ and K+ in solvent polymeric membranes by factors of up to 6300 and 5000, respectively. Depending on the membrane composition, ion selective electrodes may be obtained with equal selectivity for Mg2+ and Ca2+ as well as sensors with a discrimination of Ca2+ by a factor up to 8. Sensors of the type described are candidates for water hardness determination as well as for an Mg2+ assay in blood by chemometric procedures.On leave from the Chemistry Department, University of Warsaw, ul. L. Pasteura 1, PL-02-093 Warsaw, PolandOn leave from the Shanghai University of Technology, 149 Yanchang Road, Shanghai, People's Republic of China 相似文献