全文获取类型
收费全文 | 147468篇 |
免费 | 3163篇 |
国内免费 | 2053篇 |
专业分类
化学 | 76563篇 |
晶体学 | 2170篇 |
力学 | 5809篇 |
综合类 | 100篇 |
数学 | 13510篇 |
物理学 | 43509篇 |
综合类 | 11023篇 |
出版年
2016年 | 1772篇 |
2015年 | 1496篇 |
2014年 | 2034篇 |
2013年 | 5700篇 |
2012年 | 4491篇 |
2011年 | 5627篇 |
2010年 | 3522篇 |
2009年 | 3346篇 |
2008年 | 4942篇 |
2007年 | 4994篇 |
2006年 | 4999篇 |
2005年 | 4890篇 |
2004年 | 4271篇 |
2003年 | 3803篇 |
2002年 | 3684篇 |
2001年 | 4243篇 |
2000年 | 3308篇 |
1999年 | 2893篇 |
1998年 | 2447篇 |
1997年 | 2402篇 |
1996年 | 2310篇 |
1995年 | 2217篇 |
1994年 | 2002篇 |
1993年 | 1865篇 |
1992年 | 2165篇 |
1991年 | 2104篇 |
1990年 | 2071篇 |
1989年 | 2004篇 |
1988年 | 1980篇 |
1987年 | 1959篇 |
1986年 | 1814篇 |
1985年 | 2348篇 |
1984年 | 2398篇 |
1983年 | 1996篇 |
1982年 | 2287篇 |
1981年 | 2095篇 |
1980年 | 2148篇 |
1979年 | 2195篇 |
1978年 | 2301篇 |
1977年 | 2201篇 |
1976年 | 2207篇 |
1975年 | 2156篇 |
1974年 | 2056篇 |
1973年 | 2211篇 |
1972年 | 1363篇 |
1971年 | 1150篇 |
1970年 | 1204篇 |
1969年 | 1085篇 |
1968年 | 1217篇 |
1967年 | 1287篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
To assess the historical and sociological significance of the cold fusion saga, researchers need accurate information about the dates of various events associated with the saga. Based on materials in the Cornell Cold Fusion Archive, this article provides both a chronology and citations to documentary evidence for cold fusion events from 1926 to the end of 1990. 相似文献
102.
周期摄动保守系统的存在性定理 总被引:5,自引:0,他引:5
本文利用全局反函数定理讨论了一类非线性边值问题解的存在性与唯一性. 相似文献
103.
L Jirovetz G Buchbauer W J?ger A Woidich A Nikiforov 《Biomedical chromatography : BMC》1992,6(3):133-134
After inhalation experiments with sandalwood oil and the pure fragrance compounds coumarin and alpha-terpineol, substances were detected and measured in the blood samples of test animals (mice) using gas chromatography/mass spectrometry (GC/MS) (MID) in connection with GC/FTIR (SWC), GC/AES (carbon and oxygen trace) and flame ionization detection/gas chromatography. Using tiglinic acid benzyl ester as the internal standard the following concentrations in serum could be found: alpha-santalol 6.1 ng/mL, beta-santalol 5.3 ng/mL and alpha-santalene 0.5 ng/mL. In separate inhalation experiments with coumarin and with alpha-terpineol the corresponding concentrations were 7.7 ng/mL and 6.9 ng/mL, respectively. 相似文献
104.
以机体硒水平,GSH-Px,SOD的活性,相关的抗癌致癌元素的综合效应比值,食管癌死亡率与硒等元素的多元回归分析及MDA的含量等合指标,评价食管癌患者的硒营养状况,结果表明,食管癌患者的营养状况差,表现为:硒水平低、含硒酶GSG-Px以及抗氧自由基的SOD活性差,脂质过氧化加剧;MDA含量高将使核酸,蛋白质含等含氨基活性物质产生交联反应而使细胞失活,食管癌患者硒营养状况差,与癌肿的一定相关关系,是 相似文献
105.
106.
Structure of the detoxification catalyst mercuric ion reductase from Bacillus sp. strain RC607 总被引:10,自引:0,他引:10
Several hundred million tons of toxic mercurials are dispersed in the biosphere. Microbes can detoxify organo-mercurials and mercury salts through sequential action of two enzymes, organomercury lyase and mercuric ion reductase (MerA). The latter, a homodimer with homology to the FAD-dependent disulphide oxidoreductases, catalyses the reaction NADPH + Hg(II)----NADP+ + H+ + Hg(0), one of the very rare enzymic reactions with metal substrates. Human glutathione reductase serves as a reference molecule for FAD-dependent disulphide reductases and between its primary structure and that of MerA from Tn501 (Pseudomonas), Tn21 (Shigella), p1258 (Staphylococcus) and Bacillus, 25-30% of the residues have been conserved. All MerAs have a C-terminal extension about 15 residues long but have very varied N termini. Although the enzyme from Streptomyces lividans has no addition, from Pseudomonas aeruginosa Tn501 and Bacillus sp. strain RC607 it has one and two copies respectively of a domain of 80-85 residues, highly homologous to MerP, the periplasmic component of proteins encoded by the mer operon. These domains can be proteolytically cleaved off without changing the catalytic efficiency. We report here the crystal structure of MerA from the Gram-positive bacterium Bacillus sp. strain RC607. Analysis of its complexes with nicotinamide dinucleotide substrates and the inhibitor Cd(II) reveals how limited structural changes enable an enzyme to accept as substrate what used to be a dangerous inhibitor. Knowledge of the mode of mercury ligation is a prerequisite for understanding this unique detoxification mechanism. 相似文献
107.
Methotrexate (MTX) has been convalently attached to an IgG-type monoclonal antibody (791T/36) directed to tumour-associated antigen gp72. Conjugates were synthesized by the active ester method using MTX N-succinimidyl ester at various pH values (7.5-10.5). Following purification by gel filtration, high performance liquid chromatography was used to assess the free drug or its derivatives in samples of MTX-791T/36 conjugates previously treated (or not) with hydroxylamine. Quantitative analysis, performed on a reversed phase column (pore size 300 A) with isocratic acetonitrile-sodium acetate buffer (pH 4.8) as mobile phase, indicated no detectable amount of free methotrexate in hydroxylamine-treated conjugates even six months after their preparation. Similar observations were made with conjugates, whose synthesis were performed at pH greater than or equal to 10. In contrast, the presence of increasing amounts of drug/metabolite could be demonstrated in samples produced at lower pH values. Based on these findings, the pH-dependent kinetics of MTX release has been determined and used to design conditions under which stable MTX-791T/36 conjugates could be prepared without hydroxylamine reaction. 相似文献
108.
W. H. Langbeck 《Fresenius' Journal of Analytical Chemistry》1885,24(1):467-468
Ohne Zusammenfassung 相似文献
109.
Saint-Venant’s Problem, Almansi–Michell Problems, Meshfree Methods, Piezoelectricity. We present a semi-analytical method for analyzing prismatic nonhomogeneous piezoelectric cylinders with arbitrary cross-sectional geometry. The prescribed loads considered in this study include axial forces, torques, moments, and voltage resultants prescribed at the cylinder’s ends, as well as body forces, lateral surface shears, voltages, and pressures as long as they can be represented by a power series in the axial coordinate. This problem can be considered as an extension of Saint-Venant and Almansi–Michell problems for elastic bodies to piezoelectric bodies. In this computationally efficient method, the cross-sectional plane is discretized with a meshfree approach, and the solution is obtained analytically with respect to the axial coordinate. A number of examples are provided to demonstrate the veracity and utility of the proposed method. 相似文献
110.
W. v. Moraczewski 《Analytical and bioanalytical chemistry》1909,48(12):788-789