全文获取类型
收费全文 | 2556篇 |
免费 | 92篇 |
国内免费 | 16篇 |
专业分类
化学 | 1632篇 |
晶体学 | 48篇 |
力学 | 48篇 |
数学 | 270篇 |
物理学 | 666篇 |
出版年
2023年 | 13篇 |
2022年 | 27篇 |
2021年 | 37篇 |
2020年 | 43篇 |
2019年 | 41篇 |
2018年 | 54篇 |
2017年 | 41篇 |
2016年 | 86篇 |
2015年 | 64篇 |
2014年 | 74篇 |
2013年 | 168篇 |
2012年 | 165篇 |
2011年 | 205篇 |
2010年 | 102篇 |
2009年 | 116篇 |
2008年 | 148篇 |
2007年 | 155篇 |
2006年 | 125篇 |
2005年 | 97篇 |
2004年 | 102篇 |
2003年 | 83篇 |
2002年 | 84篇 |
2001年 | 52篇 |
2000年 | 46篇 |
1999年 | 29篇 |
1998年 | 17篇 |
1997年 | 22篇 |
1996年 | 22篇 |
1995年 | 21篇 |
1994年 | 22篇 |
1993年 | 20篇 |
1992年 | 18篇 |
1991年 | 13篇 |
1990年 | 24篇 |
1989年 | 29篇 |
1988年 | 17篇 |
1987年 | 12篇 |
1986年 | 18篇 |
1985年 | 16篇 |
1984年 | 22篇 |
1983年 | 17篇 |
1982年 | 14篇 |
1981年 | 26篇 |
1980年 | 17篇 |
1979年 | 16篇 |
1978年 | 21篇 |
1977年 | 17篇 |
1976年 | 19篇 |
1975年 | 18篇 |
1974年 | 11篇 |
排序方式: 共有2664条查询结果,搜索用时 264 毫秒
241.
242.
243.
Dragana Mutavdžić Pavlović Sandra Babić Davor Dolar Danijela Ašperger Krešimir Košutić Alka J. M. Horvat Marija Kaštelan‐Macan 《Journal of separation science》2010,33(2):258-267
This paper focuses on the investigation of different types of SPE sorbents for the preconcentration of eight veterinary pharmaceuticals from water samples. The pharmaceuticals studied were sulfamethazine, sulfadiazine, sulfaguanidine, trimethoprim, oxytetracycline, enrofloxacin, norfloxacin and penicillin G/procaine. Five different SPE materials (Strata‐X, Strata‐X‐C, Strata SDB‐L, Strata C8 and Strata C18) from Phenomenex were compared with Oasis HLB with a view to obtaining the best cartridges for all pharmaceuticals investigated. Extraction efficiency was determined by HPLC with diode array detection (DAD). HPLC‐DAD separation and quantification of the selected pharmaceuticals were carried out under gradient elution by a binary mixture of 0.01 M oxalic acid and ACN based on cyano modified column (LiChrosphere 100 CN) from Merck. Strata‐X provided the best results in the preconcentration of 100 mL water samples, yielding average pharmaceutical recoveries of higher than 90%, except for sulfaguanidine (76.1%). The developed Strata‐X‐HLPC‐DAD method was validated and applied, for the efficient investigation of reverse osmosis/nanofiltration membranes and for the removal of these eight pharmaceuticals from the production wastewater samples. NF90 and XLE membranes were shown to be the best for the rejection of all investigated pharmaceuticals. 相似文献
244.
Jae Chul Cheong Sung Ill Suh Beom Jun Ko Jin Young Kim Moon Kyo In Won Jo Cheong 《Journal of separation science》2010,33(12):1767-1778
A simple and rapid GC‐MS method has been developed for the screening and quantification of many illicit drugs and their metabolites in human urine by using automatic SPE and trimethylsilylation. Sixty illicit drugs, including parent drugs and their metabolites that are possibly abused in Korea, can be monitored by this method. Among them, 24 popularly abused illicit drugs were selected for quantification. Very delicate optimizations were carried out in SPE, trimethylsilylation derivatization, and GC/MS to enable such remarkable achievements. Trimethylsilylated analytes were well separated within 21 min by GC‐MS. In the validation results, the LOD of all the analytes were in the range of 2–75 ng/mL. The LOQ of the quantified analytes were in the range of 5–98 ng/mL. The linearity (r2) of the quantified analytes ranged 0.990–1.000 in each concentration range between 10 and 1000 ng/mL. The mean recoveries ranged from 62 to 126% at three different concentrations of each analyte. The inter‐day and inter‐person accuracies were within ?13.3~14.9%, and ?10.1~13.0%, respectively, and the inter‐day and inter‐person precisions were less than 12.9%. The method was reliable and efficient for the screening and quantification of abused illicit drugs in routine urine analysis. 相似文献
245.
Haladhara Naik Guinyun Kim Ashok Goswami Sarbjit Singh Vijay Kumar Manchanda Devesh Raj Srinivasan Ganesan Young Do Oh Hee-Seock Lee Kyung Sook Kim Man-Woo Lee Moo-Hyun Cho In Soo Ko Won Namkung 《Journal of Radioanalytical and Nuclear Chemistry》2010,283(2):439-445
The mass–yield distributions of various fission products have been determined in the 50-, 60- and 70-MeV end point bremsstrahlung induced fission of natPb using off-line γ-ray spectrometric technique in the electron linac at Pohang Accelerator Laboratory, Korea. The mass–yield distributions are symmetric with average mass of 102.34, 102.25 and 102.03 and FWHM of 21, 22 and 23 mass unit, respectively. From the present data and literature data in the 50–85 MeV bremsstrahlung induced fission of 209Bi the following observations were obtained: (i) The average masses of the yield distributions in the 50–85 MeV bremsstrahlung induced fission of natPb and 209Bi are around 102.25 ± 0.25 and 103 ± 0.5, respectively. (ii) The FWHM of the mass–yield distributions increases from about 21 mass units at 50 MeV to 23 mass units at 70–85 MeV, which is explained from the point of increase in multi-chance fission probability with increasing excitation energy. (iii) Within the bremsstrahlung energy range of 50–85 MeV, the role of nuclear structure effect in the mass–yield distribution was observed in the photo-fission of 209Bi, whereas it was not seen in case of natPb. This may be due to the presence of so many isotopes in natPb unlike mono-isotopic 209Bi. 相似文献
246.
Despite its long history, detailed studies on the dynamics of mechanical watch movement are still lacking. In this paper, extending our previous mechanics model, the dynamical wave motion of the hairspring—balance wheel assembly, the core of the timekeeping mechanism called the escapement, is analyzed by partial differential equations. It is found that the corresponding eigenfunctions may be formulated into a Fourier series, through which the relative amplitudes of high order harmonics can be obtained. The relative error incurred owing to the high order harmonics is estimated to be around 10−3, or 102 s/day, much higher than the needed accuracy. This is why manual adjustment is needed in practice. Moreover, addition of the pricy Tourbillon mechanism, which is designed to counteract the gravity effect, is found to trigger complexity in the motion and hence, may not be worth much. 相似文献
247.
Vossen A Seidl R Adachi I Aihara H Aushev T Balagura V Bartel W Bischofberger M Bondar A Bračko M Browder TE Chang MC Chen A Chen P Cheon BG Cho K Choi Y Eidelman S Feindt M Gaur V Gabyshev N Garmash A Golob B Perdekamp MG Haba J Hayasaka K Horii Y Hoshi Y Hou WS Hyun HJ Inami K Ishikawa A Iwabuchi M Iwasaki Y Iwashita T Joshi NJ Kichimi H Kim HO Kim MJ Ko BR Kumita T Lange JS Lee MJ Lee SH Leitgab M Li Y Liu C Liventsev D Louvot R McOnie S Miyata H Miyazaki Y Mizuk R Mohanty GB Nakano E 《Physical review letters》2011,107(7):072004
The interference fragmentation function translates the fragmentation of a quark with a transverse projection of the spin into an azimuthal asymmetry of two final-state hadrons. In e(+)e(-) annihilation the product of two interference fragmentation functions is measured. We report nonzero asymmetries for pairs of charge-ordered π(+)π(-) pairs, which indicate a significant interference fragmentation function in this channel. The results are obtained from a 672 fb(-1) data sample that contains 711 × 10(6) π(+)π(-) pairs and was collected at and near the Υ(4S) resonance, with the Belle detector at the KEKB asymmetric-energy e(+)e(-) collider. 相似文献
248.
Ko KT Kim K Kim SB Kim HD Kim JY Min BI Park JH Chang FH Lin HJ Tanaka A Cheong SW 《Physical review letters》2011,107(24):247201
We investigated the magnetic nature of Fe(1/4)TaS2 using x-ray absorption spectroscopy, photoemission spectroscopy, and first principles band calculations. The results show a large unquenched orbital magnetic moment (~1.0 μ(B)/Fe) at intercalated Fe sites, resulting in a gigantic magnetic anisotropy (H(A)?60 T). The magnetic coupling is well understood in terms of the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction, suggesting a novel RKKY ferromagnet with Ising-type spin states. We also found that this indirect exchange coupling between the neighboring Fe spins is ferromagnetic and maximized at the Fe-Fe distance of 2×2 superstructure. 相似文献
249.
A. Sobczyk M. Sypek Ag. Siemion M. Makowski A. Siemion J. Suszek A. Kołodziejczyk 《Opto-Electronics Review》2011,19(2):189-192
This article presents a new optical set-up for illumination of a common area with a few independent light sources. The main
aim is to create a uniform light distribution of a constant shape even if one of the light sources will stop working. In such
a case, the shape of the light distribution should remain unchanged, however, the total light intensity will be lower. The
novelty of the proposed solution is based on the usage of a small number of the independent light sources in opposite to a
well known LED arrays approach. The beam shaping is made using Dammann gratings and specially designed blazed phase diffractive
gratings. The article contains the theoretical analysis and the computer simulation verified by the experiment. 相似文献
250.
Tomasz ?ojewski Jacek Bagniuk Andrzej Ko?odziej Joanna ?ojewska 《Applied Physics A: Materials Science & Processing》2011,105(3):753-761
This study proposes a method to estimate the lipid content in binding media in paintings that can be used at any laboratory
equipped with an infrared spectrometer. The lipid content estimator, termed greasiness index (GI), is defined as a ratio of
lipid ν(C=O) and protein amide I bands at 1743 and 1635 cm−1, respectively. Three Fourier transform infrared (FTIR) sampling techniques were evaluated for GI determination: reflective
attenuated total reflection—ATR, specular reflection microscopy—μSR and photoacoustic—PAS. A set of model painting samples containing three tempera binding media (casein, egg, egg + oil),
seven pigments and one varnish type were used in the study. Multivariate analysis was used to evaluate the resulting data.
A good reproducibility of GI was obtained by ATR and PAS but not with μSR. The discriminative power of the technique is higher for unvarnished samples, but, generally, the GI estimator can be used
for the categorisation of binding media in large populations of painting samples analysed with the same FTIR technique (sampling
technique, detection, etc.). 相似文献