全文获取类型
收费全文 | 10721篇 |
免费 | 1512篇 |
国内免费 | 1249篇 |
专业分类
化学 | 7571篇 |
晶体学 | 118篇 |
力学 | 682篇 |
综合类 | 67篇 |
数学 | 1284篇 |
物理学 | 3760篇 |
出版年
2024年 | 56篇 |
2023年 | 262篇 |
2022年 | 398篇 |
2021年 | 410篇 |
2020年 | 429篇 |
2019年 | 446篇 |
2018年 | 387篇 |
2017年 | 375篇 |
2016年 | 517篇 |
2015年 | 512篇 |
2014年 | 584篇 |
2013年 | 800篇 |
2012年 | 887篇 |
2011年 | 938篇 |
2010年 | 652篇 |
2009年 | 588篇 |
2008年 | 724篇 |
2007年 | 603篇 |
2006年 | 549篇 |
2005年 | 412篇 |
2004年 | 369篇 |
2003年 | 278篇 |
2002年 | 310篇 |
2001年 | 212篇 |
2000年 | 204篇 |
1999年 | 257篇 |
1998年 | 183篇 |
1997年 | 131篇 |
1996年 | 142篇 |
1995年 | 134篇 |
1994年 | 100篇 |
1993年 | 110篇 |
1992年 | 91篇 |
1991年 | 86篇 |
1990年 | 77篇 |
1989年 | 58篇 |
1988年 | 42篇 |
1987年 | 36篇 |
1986年 | 22篇 |
1985年 | 31篇 |
1984年 | 20篇 |
1983年 | 14篇 |
1982年 | 12篇 |
1981年 | 6篇 |
1980年 | 4篇 |
1979年 | 3篇 |
1978年 | 5篇 |
1976年 | 4篇 |
1975年 | 3篇 |
1957年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 11 毫秒
951.
A colorimetric strategy based on conjugated polyelectrolyte aggregates has been applied to determine and distinguish anionic, cationic and non-ionic surfactants. 相似文献
952.
953.
Seydou Yao Giancarlo DellaVentura Cyril Petibois 《Analytical and bioanalytical chemistry》2010,397(6):2079-2089
Asbestos is a fiber causing lung diseases such as asbestosis and mesothelioma. Although the process involving these diseases
remains to be elucidated for developing drugs and treatments, direct consequences of fiber exposure in humans have been clearly
demonstrated. These diseases are first characterized by histological heterogeneity and combine chronic inflammation with fibrosis
and cellular alterations. As a consequence, asbestosis is usually diagnosed at advanced stages of the disease and treatments
are usually inefficient to cure the patients. Here, we review the links established between asbestos fiber chemistry and morphology
with the occurrence of associated lung diseases. Cytological and histological aspects of diseases are described with respect
to current analytical capabilities, notably for microscopy techniques. 相似文献
954.
Wenlong Yin Dajiang Mei Jiyong Yao Peizhen Fu Yicheng Wu 《Journal of solid state chemistry》2010,183(11):2544-2551
Two new ternary bismuth chalcogenides, Bi3In4S10 and Bi14.7In11.3S38, were synthesized from the reactions of binary sulfides via a two-step flux technique. Single-crystal X-ray diffraction analyses indicate that Bi3In4S10 crystallizes in the non-centrosymmetric space group Pm and Bi14.7In11.3S38 crystallizes in the centrosymmetric space group P21/m. Both compounds adopt three-dimensional frameworks. A distinct structural feature in the two structures is the presence of chains of Bi atoms with alternating short Bi-Bi bonds of around 3.1 Å and longer distances of around 4.6 Å. The optical band gaps of 1.42(2) eV for Bi3In4S10 and 1.45(2) eV for Bi14.7In11.3S38 were deduced from the diffuse reflectance spectra. 相似文献
955.
This paper presents a new sample preparation procedure for determination of selected acidic pharmaceuticals (ibuprofen, naproxen, ketoprofen, and diclofenac) in sewage sludge using microwave assisted solvent extraction, dispersive matrix extraction (DME) followed by the conventionally applied solid phase extraction (SPE), derivatization, and gas chromatography-mass spectrometry. The recoveries calculated from analytical data of spiked sludge samples changed in the range of 80-105% ± 15% for the four pharmaceuticals in mixed and activated sludge depending on the efficiency of the clean-up procedure. The measured concentration values of ibuprofen and naproxen were identical in the mixed and the activated sludge samples. However, ketoprofen and diclofenac showed about twice as high concentration in activated sludge than in the mixed one independently of the applied extraction method. The typical concentration ranges of ibuprofen, naproxen, ketoprofen and diclofenac in sewage sludge were 10-30 ng/g, 30-50 ng/g, 50-130 ng/g, and 50-140 ng/g respectively. 相似文献
956.
This work exploited a sequential injection lab-on-valve (LOV) system for the determination of cadmium by anodic stripping voltammetry (ASV). A miniaturized electrochemical flow cell (EFC) was fabricated in LOV, in which a nafion coated bismuth film electrode was used as working electrode. The cadmium was electrodeposited on the electrode surface in bismuth solution, and measured with the subsequential stripping scan. Under optimal conditions, the proposed system responded linearly to cadmium concentrations in a range 2.0-100.0 μg L−1. The detection limit of this method was found to be 0.88 μg L−1. By loading a sample volume of 800 μL, a sampling frequency of 22 determinations h−1 was achieved. The repeatability expressed as relative standard derivation (R.S.D.) was 3.65% for 20 μg L−1 cadmium (n = 11). The established method was applied to analysis of trace cadmium in environmental water samples and the spiked recoveries were satisfactory. 相似文献
957.
Pengjun Shi Ning Li Peilong Yang Yaru Wang Huiying Luo Yingguo Bai Bin Yao 《Applied biochemistry and biotechnology》2010,162(3):707-718
An α-l-arabinofuranosidase gene, abf51S9, was cloned from Streptomyces sp. S9 and successfully expressed in Escherichia coli BL21 (DE3). The full-length gene consisted of 1,506 bp and encoded 501 amino acids with a calculated mass of 55.2 kDa. The
deduced amino acid sequence was highly homologous with the α-l-arabinofuranosidases belonging to family 51 of the glycoside hydrolases. The recombinant protein was purified to electrophoretic
homogeneity by Ni-NTA affinity chromatography and subsequently characterized. The optimal pH and temperature for the recombinant
enzyme were 6.0 and 60∼65 °C, respectively. The enzyme showed a broad pH range of stability, retaining over 75% of the maximum
activity at pH 5.0 to 11.0. The specific activity, K
m, and V
max with p-nitrophenyl-α-l-arabinofuranoside as substrate were 60.0 U mg−1, 1.45 mM, and 221 μmol min−1 mg−1, respectively. Abf51S9 showed a mild but significant synergistic effect in combination with xylanase on the degradation of
oat-spelt xylan and soluble wheat arabinoxylan substrates with a 1.19- and 1.21-fold increase in the amount of reducing sugar
released, respectively. These favorable properties make Abf51S9 a good candidate in various industrial applications. 相似文献
958.
Composite CoFe2O4-BaTiO3 films were prepared by combining method of sol-gel and electrophoretic deposition. CoFe2O4 thick films were prepared by electrophoretic deposition method and then BaTiO3 precursor solution was spin-coated on these thick films to obtain dense structure. X-ray diffraction indicated that the films consisted of both spinel CoFe2O4 and perovskite BaTiO3 phase. Dielectric properties and leakage current conduction of the films were studied. Leakage current characterization of the films exhibits an Ohmic conduction behavior at lower electric field and space charge limited conduction behavior at higher electric field, respectively. 相似文献
959.
This paper reports the synthesis of a perylene-bridged bis(crown ether) through the condensation reaction between primary amine-armed dibenzo-24-crown-8 and 3,4,9,10-perylenetetracarboxylic dianhydride. Pseudorotaxane with a perylene moiety at the wheel and a fullerene unit in the middle of the axle was prepared, which was evidenced by 1H NMR and fluorescence experiments. Subsequent investigations show that the formation and disassociation of the pseudorotaxane can be controlled by the alternating addition of KPF6 and 18-crown-6, following the change of the florescence intensity of perylene.
相似文献960.
Bo Ding Wei‐Wei Ma Yi Dai Hao Gao Yang Yu Ye Tao Yi Zhong Xin‐Sheng Yao 《Helvetica chimica acta》2010,93(12):2488-2494
Two new iridoids, 10‐O‐benzoyl‐6′‐O‐α‐L ‐arabino(1→6)‐β‐D ‐glucopyranosylgeniposidic acid ( 1 ), deacetyl‐6‐ethoxyasperulosidic acid methyl ester ( 2 ), along with 14 other known iridoids, were isolated from the whole plant of Hedyotis diffusa Willd. Their structures were determined on the basis of spectroscopic analysis. The short‐term‐memory‐enhancement activities of compounds 1, 7 – 9, 11 , and 13 were evaluated on an Aβ transgenic drosophila model. 相似文献