全文获取类型
收费全文 | 3802篇 |
免费 | 139篇 |
国内免费 | 45篇 |
专业分类
化学 | 2504篇 |
晶体学 | 28篇 |
力学 | 135篇 |
综合类 | 2篇 |
数学 | 563篇 |
物理学 | 754篇 |
出版年
2023年 | 24篇 |
2022年 | 38篇 |
2021年 | 49篇 |
2020年 | 48篇 |
2019年 | 43篇 |
2018年 | 43篇 |
2016年 | 74篇 |
2015年 | 69篇 |
2014年 | 96篇 |
2013年 | 194篇 |
2012年 | 249篇 |
2011年 | 266篇 |
2010年 | 137篇 |
2009年 | 141篇 |
2008年 | 231篇 |
2007年 | 219篇 |
2006年 | 220篇 |
2005年 | 192篇 |
2004年 | 173篇 |
2003年 | 149篇 |
2002年 | 112篇 |
2001年 | 94篇 |
2000年 | 97篇 |
1999年 | 58篇 |
1998年 | 56篇 |
1997年 | 34篇 |
1996年 | 74篇 |
1995年 | 52篇 |
1994年 | 50篇 |
1993年 | 46篇 |
1992年 | 43篇 |
1991年 | 37篇 |
1990年 | 28篇 |
1989年 | 22篇 |
1988年 | 27篇 |
1987年 | 24篇 |
1986年 | 20篇 |
1985年 | 47篇 |
1984年 | 29篇 |
1983年 | 29篇 |
1982年 | 24篇 |
1981年 | 38篇 |
1980年 | 29篇 |
1979年 | 25篇 |
1978年 | 30篇 |
1977年 | 27篇 |
1976年 | 20篇 |
1975年 | 25篇 |
1974年 | 37篇 |
1973年 | 19篇 |
排序方式: 共有3986条查询结果,搜索用时 0 毫秒
31.
Prefractionation of protein samples prior to two-dimensional electrophoresis (2-DE) has the potential to increase the dynamic detection range for proteomic analysis. We evaluated a membrane-based electrophoretic separation technique (Gradiflow) for its ability to fractionate an exoproteome sample from the filamentous fungus Trichoderma reesei. The sample was separated on the basis of size and charge. Buffer optimization was found to be necessary for successful size fractionation. Fractionation by charge was used to resolve the sample into four fractions that were subjected to analysis by two-dimensional electrophoresis (2-DE). Enhanced detection of low-abundance proteins with selective removal of high-abundance species was achieved. Fractionated and unfractionated samples were examined for differences in the ability to identify proteins following 2-DE using trypsin in-gel digestion followed by peptide mass fingerprinting using matrix assisted laser desorption/ionization-time of flight-mass spectrometry (MALDI-TOF-MS). Fractionated samples showed marked improvement in protein identification ability and sequence coverage. This study demonstrates the utility of the Gradiflow for fractionation, resulting in an enhancement of resolution and characterization of a moderately complex proteome. 相似文献
32.
The molecular structure of TTF dissolved in nematic liquid crystalline solvents has been determined from the proton magnetic resonance including couplings due to 13C in natural abundance. The molecule is puckered in a boat conformation with the SCHCHS planes making a dihedral angle of 13 ± 2° with the S2C CS2 plane. The other structural parameters obtained are rCH = 1.085 ± 0.014 Å and the angel CCH = 123.7 ± 1.5°. 相似文献
33.
A simple, rapid and sensitive high-performance liquid chromatographic method with fluorescence detection for the simultaneous determination of oxytetracycline, doxycycline, tetracycline and chlortetracycline was developed, and successfully applied to the analysis of commercial tetracycline antibiotics. The separation was performed on a reverse-phase C18 column with a gradient elution composed of methanol and sodium acetate buffer (containing disodium ethylenediaminetetraacetate and calcium chloride, pH 8.10) as the mobile phase, and fluorescence detection at 532 nm (excitation at 380 nm). The detection limits for oxytetracycline, doxycycline, tetracycline and chlortetracycline were 0.1, 0.5, 0.3 and 0.4 g L–1, respectively. Data with respect to precision and accuracy were reported and discussed. 相似文献
34.
J. F. Ying B. J. Flinn M. Y. Zhou P. C. Wong K. A. R. Mitchell T. Fostert 《Progress in Surface Science》1995,50(1-4):259-267
A zinc phosphate coating process on 7075-T6 aluminum alloy has been significantly improved through a combined approach of titanium colloid pretreatment, pH level adjustment, fluoride additive and ZnO/H3PO4 ratio adjustment. In particular, optimum phosphate coatings were formed in coating baths with a ZnO/H3PO4 ratio of 0.205 and 0.256. Coating morphology studied by SEM reveals that the adjustment in the coating procedure produces an improved crystalline coating layer with high coverage and small grain size. For coatings formed in a bath with a ratio of 0.205, the coverage of the crystalline patches on top of the amorphous coating base is almost complete. The chemical composition of the coating layers has been characterized by XPS and SIMS. The crystalline and amorphous coating phases formed in the bath with a ratio of 0.205 were found to have compositions given schematically as Znx(PO4) and ZnxAly(PO4), respectively. In contrast, neither coating phase formed in the bath with a ratio of 0.256 shows the presence of Al. 相似文献
35.
A series of acyclic vinyl ethers have been prepared and treated with Grubbs' ruthenium catalyst ((Cy3P)2RuCl2=CHPh). Contrary to previous findings, it has been shown that certain vinyl ethers are excellent substrates for the ring closing metathesis with ruthenium based catalysts. 相似文献
36.
Wang X Yu JC Yip HY Wu L Wong PK Lai SY 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(10):2997-3004
A novel metal/semiconductor nanocomposite with catalytic and photocatalytic functions has been prepared. The new material consists of highly dispersed platinum (Pt) nanoparticles embedded in a cubic mesoporous nanocrystalline anatase (meso-nc-TiO2) thin film. The porous thin film possesses a narrow pore-size distribution and a large surface area. The diameter of the Pt cluster can be controlled to below 5 nm, and the high dispersion of these clusters gives rise to catalytic activity for the oxidation of carbon monoxide, an important reaction for automobile exhaust treatment. This novel ordered mesoporous Pt/TiO2 nanoarchitecture is also a promising photochemical material, as demonstrated by the photo-driven killing of Micrococcus lylae cells on the film. 相似文献
37.
A practical speciation method for a solid mixture of nickel species applicable to atmospheric monitoring of Ni0, Ni2+ and NiOx is reported. This involves magnetic extraction of Ni0 to separate it from the water-soluble nickel salts and the insoluble oxides, followed by adsorptive stripping voltammetry to quantify the nickel in each fraction. The separation scheme was validated by using calibration standards and by simulating air-filter samples prepared with authentic nickel products. The recoveries of nickel were Ni0 94–105% and total nickel 95–102%. 相似文献
38.
Most tropical fruits for export must be treated with an approved quarantine treatment. Three and a half decades of research have demonstrated the efficacy of irradiation as a quarantine treatment in terms of efficiency, effectiveness, and product quality retention. The USFDA and the USDA-APHIS approved irradiation to disinfest fresh foods/fresh papayas in 1986 and 1989, respectively. In early 1995, the Hawaii Department of Agriculture was granted a special permit from USDA-APHIS allowing untreated Hawaiian fruits to be irradiated on the US mainland. The objectives were to gain experience in commercial irradiation as a quarantine treatment and to gather data on shipping and handling procedures, and on product quality. In April 1995, the first shipment of Hawaiian fruit was irradiated at a minimum quarantine dose of 0.25 kGy in an Isomedix plant near Chicago, and then distributed to supermarkets in Illinois and Ohio. Continuous shipments, irradiation, and marketing of various tropical fruits in the US have shown commercial efficacy, quality retention, and excellent consumer acceptance. A commercial e-beam/converted X-ray facility was installed by Titan Corp. on the Island of Hawaii and was operational by late July 2000. Hawaii has become the first place in the world to use irradiation as a quarantine treatment of fruits. 相似文献
39.
The importance of palladium complexes in catalytic processes is well-demonstrated by its applications in hydrogenation processes in industry. Mixed metal clusters of palladium are of interest as the palladium ion can attain either a 16- or 18-electron configuration which is an important feature for catalytic processes. Recent developments in the preparation, characterization, chemical and physical properties of these clusters are discussed in this review. 相似文献
40.
This paper describes the synthesis of 1,1-linked galactosyl mannosides as sialyl Lewis X mimetics that contain a spiro-ring to position the carboxylate group in a well-defined orientation. It was found that compound 4 is more active as a P-selectin inhibitor (IC50 = 19 microM) than the parent disaccharide 2, which contains a flexible carboxyl group (IC50 = 193 microM). This result is consistent with that observed in the previous NMR study of sialyl Lewis X bound to P-selectin. The chemistry described here should be useful for the development of selective inhibitors of E-, P-, and L-selectins. 相似文献