全文获取类型
收费全文 | 4029篇 |
免费 | 157篇 |
国内免费 | 12篇 |
专业分类
化学 | 2675篇 |
晶体学 | 41篇 |
力学 | 64篇 |
数学 | 432篇 |
物理学 | 986篇 |
出版年
2023年 | 41篇 |
2022年 | 90篇 |
2021年 | 123篇 |
2020年 | 103篇 |
2019年 | 120篇 |
2018年 | 94篇 |
2017年 | 101篇 |
2016年 | 173篇 |
2015年 | 129篇 |
2014年 | 127篇 |
2013年 | 244篇 |
2012年 | 268篇 |
2011年 | 331篇 |
2010年 | 200篇 |
2009年 | 204篇 |
2008年 | 288篇 |
2007年 | 258篇 |
2006年 | 207篇 |
2005年 | 185篇 |
2004年 | 168篇 |
2003年 | 119篇 |
2002年 | 95篇 |
2001年 | 69篇 |
2000年 | 70篇 |
1999年 | 43篇 |
1998年 | 26篇 |
1997年 | 28篇 |
1996年 | 33篇 |
1995年 | 28篇 |
1994年 | 24篇 |
1993年 | 25篇 |
1992年 | 32篇 |
1991年 | 14篇 |
1990年 | 12篇 |
1989年 | 13篇 |
1988年 | 6篇 |
1987年 | 7篇 |
1986年 | 8篇 |
1985年 | 8篇 |
1984年 | 11篇 |
1983年 | 4篇 |
1982年 | 8篇 |
1981年 | 9篇 |
1980年 | 7篇 |
1978年 | 4篇 |
1977年 | 7篇 |
1976年 | 4篇 |
1975年 | 4篇 |
1974年 | 5篇 |
1972年 | 4篇 |
排序方式: 共有4198条查询结果,搜索用时 250 毫秒
981.
982.
A column liquid chromatographic method for simultaneous determination of carbadox and olaquindox in swine feeds is described. The drugs were extracted from feeds with carbon tetrachloride-dimethylformamide (80:20) at 60 degrees C for 30 min. The extract was mixed with water (25:45). After centrifugation the aqueous layer was chromatographed on a reversed-phase column using gradient elution and ultraviolet detection at wavelengths of 305 and 262 nm. Recoveries from samples fortified at levels of 20-50 ppm were 92 +/- 9% for carbadox and 93 +/- 6% for olaquindox (means +/- standard deviations, n = 71). 相似文献
983.
Schilardi PL Dip P dos Santos Claro PC Benítez GA Fonticelli MH Azzaroni O Salvarezza RC 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,12(1):38-49
Pattern transfer with high resolution is a frontier topic in the emerging field of nanotechnologies. Electrochemical molding is a possible route for nanopatterning metal, alloys and oxide surfaces with high resolution in a simple and inexpensive way. This method involves electrodeposition onto a conducting master covered by a self-assembled alkanethiolate monolayer (SAMs). This molecular film enables direct surface-relief pattern transfer from the conducting master to the inner face of the electrodeposit, and also allows an easy release of the electrodeposited film due their excellent anti-adherent properties. Replicas of the original conductive master can be also obtained by a simple two-step procedure. SAM quality and stability under electrodeposition conditions combined with the formation of smooth electrodeposits are crucial to obtain high-quality pattern transfer with sub-50 nm resolution. 相似文献
984.
A. M. G. F. Azeredo L. M. Q. C. Julião M. S. Santos D. R. Melo J. L. Lipsztein 《Journal of Radioanalytical and Nuclear Chemistry》1994,182(1):127-132
Internal contamination with radioactive materials of mining workers is a common problem in Brazil. This is caused by the presence of uranium, thorium, and their natural decay series associated with the mined ore. The clear examples are the workers at the niobium mine located in the state of Goiás. The niobium is associated with considerable quantities of uranium and thorium, but the mine is not legally subject to radiation protection requirements.Twenty mine workers were evaluated using in vitro bioassay techniques (urine and feces). The fecal samples were analyzed by alpha spectrometry using the method developed in the Bioassay Laboratory of the Instituto de Radioproteção e Dosimetria/CNEN which evaluates thorium and uranium isotopes simultaneously. Minor modifications were introduced to measure a higher level of activity, around 1 Bq of uranium per sample. The urine samples were analyzed by alpha spectrometry for thorium and by fluorimetry for uranium. The results obtained show that a control of the occupationally-exposed workers is necessary. 相似文献
985.
M. Dos Santos Afonso Cecilia Di Risio M. Zysmilich Roberto O. Marqués M.A. Blesa 《Radiation Physics and Chemistry》1996,48(6):715-718
The influence of gamma and reactor (n + γ) preirradiation on the dissolution of magnetite microcrystals synthetized by a low-temperature wet method was studied. Two opposite effects affect the dissolution rate: the annealing due to the gamma radiation and the generation of new imperfect coordination polyhedra. A model for the kinetic processes was proposed and the kinetic parameters were calculated. 相似文献
986.
Beta2-agonist extraction procedures for chromatographic analysis 总被引:1,自引:0,他引:1
dos Ramos FJ 《Journal of chromatography. A》2000,880(1-2):69-83
Normally, different procedures were necessary to prepare sample matrices for chromatographic determination of β2-agonists. The present review includes sampling, pre-treatment and extraction/purification for urine, plasma, liver, meat, feeds, hair and milk powder, as previous steps for chromatographic analysis of β2-agonists. Six methodologies were especially revised for extraction/purification namely, liquid–liquid extraction, solid-phase extraction (SPE), matrix solid-phase dispersion, immunoaffinity chromatography, dialysis and supercritical fluid extraction. SPE was discussed in detail and five mechanisms were described: adsorption, apolar, polar, ion-exchange and mixed phase. A brief conclusion in this field was also outlined. 相似文献
987.
A new flexible approach to hexahydropyrrolo[2,3-b]indole system via the [3,3]-sigmatropic rearrangement of 1-(2′-methoxycarbonyl-N-methylvinylamino)skatole, culminating in the synthesis of (±)-desoxyeseroline, is described. 相似文献
988.
Santos JP Corpart P Wong K Galembeck F 《Langmuir : the ACS journal of surfaces and colloids》2004,20(24):10576-10582
Low-Tg styrene-butadiene (SB) latex films were investigated by noncontact atomic force microscopy and scanning electric potential microscopy, revealing a number of different morphologies and electric potential patterns across films cast from the same SB latex dispersions under the same conditions. Surface leveling and charge dispersion throughout the films are, thus, restrained even at temperatures above Tg and the minimum film-formation temperature. An unprecedented electric pattern is observed, in which the particle cores are more positive than the contacting particle outer layers. Different packing patterns, including cubic and hexagonal arrays, coexist in neighboring areas. Zonal centrifugation of the SB latex in sucrose density gradient shows that particles cover a broad range of densities. Thus, film surface heterogeneity is at least partly due to particle heterogeneity. Fractal dimensions of topographic profiles are lower than those of the electric potential profiles, showing that charge mobility is much more restrained than polymer chain motion at the film surface and that it imposes a limit to the charged chain-ends motion. 相似文献
989.
990.
Arribas C Carreño MC García-Ruano JL Rodríguez JF Santos M Sanz-Tejedor MA 《Organic letters》2000,2(20):3165-3168
Hetero Diels-Alder (HDA) cycloaddition of chiral 1-p-tolylsulfinyl-1,3-pentadiene with benzyl nitrosoformate, under mild conditions, yields 2H-1,2-oxazine 3 with complete regioselectivity and pi-facial diastereoselectivity. Sequential osmylation and protection of the resulting glycol gives the oxazine 5 which is directly transformed into enantiomerically pure 1,4,5-trideoxy-1,4-imino-L-ribitol 8 by reduction under Pd/C. 相似文献