全文获取类型
收费全文 | 37288篇 |
免费 | 776篇 |
国内免费 | 167篇 |
专业分类
化学 | 20810篇 |
晶体学 | 232篇 |
力学 | 1198篇 |
综合类 | 9篇 |
数学 | 5306篇 |
物理学 | 10676篇 |
出版年
2022年 | 208篇 |
2021年 | 483篇 |
2020年 | 503篇 |
2019年 | 414篇 |
2018年 | 510篇 |
2017年 | 441篇 |
2016年 | 791篇 |
2015年 | 696篇 |
2014年 | 821篇 |
2013年 | 1435篇 |
2012年 | 1755篇 |
2011年 | 2049篇 |
2010年 | 1150篇 |
2009年 | 1070篇 |
2008年 | 1738篇 |
2007年 | 1764篇 |
2006年 | 1665篇 |
2005年 | 2104篇 |
2004年 | 2015篇 |
2003年 | 1466篇 |
2002年 | 1068篇 |
2001年 | 952篇 |
2000年 | 888篇 |
1999年 | 527篇 |
1998年 | 458篇 |
1997年 | 459篇 |
1996年 | 572篇 |
1995年 | 510篇 |
1994年 | 486篇 |
1993年 | 551篇 |
1992年 | 514篇 |
1991年 | 447篇 |
1990年 | 365篇 |
1989年 | 358篇 |
1988年 | 348篇 |
1987年 | 345篇 |
1986年 | 291篇 |
1985年 | 390篇 |
1984年 | 367篇 |
1983年 | 303篇 |
1982年 | 332篇 |
1981年 | 315篇 |
1980年 | 295篇 |
1979年 | 281篇 |
1978年 | 306篇 |
1977年 | 235篇 |
1976年 | 251篇 |
1975年 | 201篇 |
1974年 | 231篇 |
1973年 | 208篇 |
排序方式: 共有10000条查询结果,搜索用时 24 毫秒
981.
Two vibrational spectrometry-based methodologies were developed for Metamitron determination in pesticide formulations. Fourier transform-middle infrared (FT-MIR) procedure was based on the extraction of Metamitron by CHCl3 and latter determination by peak area measurement between 1556 and 1533 cm−1, corrected with a two points baseline established from 1572 to 1514 cm−1. Fourier transform-near infrared (FT-NIR) determination was made after the extraction of Metamitron in acetonitrile and measuring the peak area between 6434 and 6394 cm−1 corrected using a two points baseline defined between 6555 and 6228 cm−1. Repeatability, as relative standard deviation, of 5 independent measurements at mg g−1 concentration level, of 0.16% and 0.07% for MIR and NIR and a limit of detection of 0.03 and 0.004 mg g−1 were obtained for MIR and NIR, respectively.NIR determination provides a sample frequency of 120 h−1, higher than that found by MIR and liquid chromatographic methods (60 and 15 h−1, respectively). On the other hand, the NIR method reduces the solvent consumption and waste generation, to only 1 ml acetonitrile per sample as compared with 3.4 ml chloroform required for the MIR determination and 60 ml acetonitrile used in the chromatographic reference procedure. So, vibrational procedures can be considered serious alternatives to long and time consuming chromatographic methods usually recommended for quality control of commercially available pesticide formulations. 相似文献
982.
Karen?Glenn Andrew?van?Bommel Subhash?C.?Bhattacharya Rama?M.?PalepuEmail author 《Colloid and polymer science》2005,283(8):845-853
The mixed micelles of sodium dodecyl sulphate (SDS) with Brij35 and Brij 97 were studied separately by fluorescence measurement using pyrene as fluorescent probe. In the range of 0–1.0 mole fraction (X) of added SDS to Brij solutions, the cmc value of the mixed micelles varies from 0.085 to 8 mmol with Brij 35 and 0.04 to 8 mmol with Brij 97. The aggregation number also changes. A measure of the stability of mixed micelles is also presented. The interaction parameter 12 and the chain–chain contribution parameter (B1) are extracted from the analysis of the results. This parameter B1 is related to the standard free energy change associated with the introduction of one ionic species into a nonionic micelle coupled with the release of one nonionic species from the micelle. The clouding behaviour of Brij 97 in the presence of SDS was investigated and the associated thermodynamic parameters of clouding were generated and discussed. 相似文献
983.
984.
de Oliveira Neto Marçal Pires José M. Giambiagi Mario de Giambiagi Myriam Segre Alvarez Fernando A. 《Structural chemistry》1998,9(5):339-348
Electronic properties of lamotrigine (LTG) and two analogues (A1 and A2) are compared through MOPAC-AM1 calculations. Two stable conformers of LTG are calculated to exist in agreement with X-ray crystallography. In the three compounds and the two conformers for each of them, the more favorable protonation sites are N2 and N4; these should then be the sites appropriate for interaction with a receptor, and group valence reinforces the supposition. The molecular electrostatic potentials show that a region between the two chlorine atoms in LTG could be the site for an electrostatic interaction with a corresponding site in the receptor. The fluorine atom in A1 would play an equivalent role. A simple model for LTG-receptor interaction is proposed. 相似文献
985.
986.
Square-wave voltammetry with the hanging drop mercury electrode as the working electrode was used for the determination of
ultratraces of explosives in aqueous solution. It was shown that the strong pressure dependence of the pneumatically controlled
multimode electrode system of a conventional Metrohm apparatus could be compensated by an additional pressure regulation,
through which the pressure variations could be decreased when switching from deaeration to the static measurements. By using
square-wave voltammetry with this electrode system after this modification the limits of detection for 2,4,6-trinitrotoluene
(TNT) and other TNT-metabolites could be decreased down to 0.2 μg L−1 when using a measurement time of 6 min. Also a simultaneous determination of TNT and hexahydro-1,3,5-trinitro-1,3,5-triazine
(RDX) was shown to be possible over a wide linear range and the detection limits then were 2.2 μg L−1 for TNT and 25 μg L−1 for RDX. By applying the highly stable and adjustable pressure as mentioned before, the calibrations could be kept stable
over a period of up to 1 week. 相似文献
987.
988.
989.
U R Tjaden J P Langenberg K Ensing W P van Bennekom E A de Bruijn A T van Oosterom 《Journal of chromatography. A》1982,232(2):355-367
The performance of a number of normal phase and reversed-phase systems, with ultraviolet detection at 360 nm, has been investigated with respect to their applicability to pharmacokinetic studies of mitomycin C (MMC). The reversed-phase system developed was also combined with a polarographic detector in order to compare the sensitivity and selectivity of ultraviolet and electrochemical detection. A simple isolation procedure, based on the adsorption of MMC on a non-ionogenic resin, has been developed. The developed assay is applied to a pharmacokinetic study from which some examples are given. 相似文献
990.
Joachim Angelkort Sander van Smaalen Prof. Dr. Sven Oliver Hauber Mark Niemeyer 《无机化学与普通化学杂志》2007,633(7):1031-1035
Single crystal X‐ray diffraction of Eu(SC36H49)2 has revealed a first order phase transition at a temperature of 119 K, that involves a reduction of the specific volume by 1 %. The transition corresponds to a doubling of the unit cell, as it is the result from reorientations of isopropyl groups that appear at peripheral sites of the organic ligands. It is argued that a denser packing is achieved at the expense of a less favourable conformation of one of the two crystallographically‐independent complexes in the low‐temperature phase. The Bond‐Valence method is used to show that interactions of equal strengths are present between europium and both sulphur atoms and both coordinating phenyl rings. 相似文献