全文获取类型
收费全文 | 16102篇 |
免费 | 871篇 |
国内免费 | 23篇 |
专业分类
电工技术 | 186篇 |
综合类 | 13篇 |
化学工业 | 4134篇 |
金属工艺 | 312篇 |
机械仪表 | 347篇 |
建筑科学 | 540篇 |
矿业工程 | 22篇 |
能源动力 | 605篇 |
轻工业 | 2587篇 |
水利工程 | 125篇 |
石油天然气 | 48篇 |
无线电 | 977篇 |
一般工业技术 | 2618篇 |
冶金工业 | 1827篇 |
原子能技术 | 123篇 |
自动化技术 | 2532篇 |
出版年
2024年 | 31篇 |
2023年 | 136篇 |
2022年 | 491篇 |
2021年 | 607篇 |
2020年 | 356篇 |
2019年 | 426篇 |
2018年 | 635篇 |
2017年 | 607篇 |
2016年 | 665篇 |
2015年 | 471篇 |
2014年 | 681篇 |
2013年 | 1023篇 |
2012年 | 986篇 |
2011年 | 1161篇 |
2010年 | 828篇 |
2009年 | 833篇 |
2008年 | 761篇 |
2007年 | 638篇 |
2006年 | 541篇 |
2005年 | 461篇 |
2004年 | 383篇 |
2003年 | 372篇 |
2002年 | 323篇 |
2001年 | 234篇 |
2000年 | 224篇 |
1999年 | 206篇 |
1998年 | 722篇 |
1997年 | 433篇 |
1996年 | 324篇 |
1995年 | 201篇 |
1994年 | 161篇 |
1993年 | 159篇 |
1992年 | 72篇 |
1991年 | 70篇 |
1990年 | 62篇 |
1989年 | 62篇 |
1988年 | 46篇 |
1987年 | 41篇 |
1986年 | 48篇 |
1985年 | 46篇 |
1984年 | 42篇 |
1983年 | 39篇 |
1982年 | 40篇 |
1981年 | 48篇 |
1980年 | 39篇 |
1979年 | 20篇 |
1978年 | 20篇 |
1977年 | 42篇 |
1976年 | 67篇 |
1973年 | 22篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
L. Serra-Majem L. Bassas R. Garcí a-Glosas L. Ribas C. Ingl s I. Casals P. Saavedra A. G. Renwick 《Food Additives & Contaminants》2003,20(12):1097-1104
Cyclamate and its metabolite cyclohexylamine affect male fertility in high dose animal studies, but this affect has not been investigated in epidemiological studies. This paper reports the first epidemiological study designed to investigate the possibility of a relationship between cyclamate and cyclohexylamine and male fertility in humans, in which 405 cases of clinically defined infertility in men and 379 controls were surveyed. Semen evaluation, urine analysis for cyclamate and cyclohexylamine and dietary questionnaires were compared between cases and controls. No evidence was found of a significant association between cyclamate intake and male infertility; neither high cyclamate nor high cyclohexylamine excretion were associated with elevated risk. The lack of association remained after adjusting by age, area of residence, education, total energy intake and other variables. No significant correlations were observed between cyclamate intake, metabolism or excretion, and sperm count and motility. The results demonstrate no effect of cyclamate or cyclohexylamine on male fertility at the present levels of cyclamate consumption. 相似文献
22.
Peter Eaton Andrea Ragusa Caroline Clavel Cristina T Rojas Paul Graham Raúl V Durán Soledad Penadés 《IEEE transactions on nanobioscience》2007,6(4):309-318
Glyconanoparticles which present carbohydrate and amino groups motifs at their surface were produced. These particles were highly stable and soluble in aqueous solutions. The presence of the carbohydrate groups also allowed the inclusion of more strongly binding groups, without affecting solubility. The binding of a model DNA, plasmid by these nanoparticles was studied by atomic force microscopy, transmission electron microscopy, and gel electrophoresis. Significant differences between the nanoparticles based on their affinities for the DNA were found, with implications for their potential use as nonviral gene delivery agents. 相似文献
23.
Alexei Manso Corrêa Machado 《Journal of Mathematical Imaging and Vision》2007,29(2-3):107-117
We present a novel method for correcting the significance level of hypothesis testing that requires multiple comparisons. It is based on the spectral graph theory, in which the variables are seen as the vertices of a complete undirected graph and the correlation matrix as the adjacency matrix that weights its edges. The method increases the statistical power of the analysis by refuting the assumption of independence among variables, while keeping the probability of false positives low. By computing the eigenvalues of the correlation matrix, it is possible to obtain valuable information about the dependence levels among the variables of the problem, so that the effective number of independent variables can be estimated. The method is compared to other available models and its effectiveness illustrated in case studies involving high-dimensional sets of variables. 相似文献
24.
András Ványolos Balázs Dóra Attila Virosztek 《Journal of Superconductivity and Novel Magnetism》2007,20(7-8):643-645
We report of a theoretical study on quasi-one dimensional unconventional charge density wave (UCDW) driven by electron–phonon
interaction. Within mean field theory, we find that the wavevector dependence of the coupling leads to a momentum dependent
single particle gap on the Fermi surface. The presence of small energy single particle excitations around the gap nodes significantly
changes the optical conductivity compared to the conventional CDW result. In addition to that, the collective phase excitation
arising from fluctuation of the order parameter leads to further qualitative changes of the conductivity and results in an
effective mass that is nonmonotonic in temperature.
相似文献
25.
26.
Antnio Ravara Ana G. Matos Vasco T. Vasconcelos Luís. Lopes 《Electronic Notes in Theoretical Computer Science》2003,85(1):61-79
We define a lexically scoped, asynchronous and distributed π-calculus, with local communication and process migration. This calculus adopts the network-awareness principle for distributed programming and follows a simple model of distribution for mobile calculi: a lexical scope discipline combines static scoping with dynamic linking, associating channels to a fixed site throughout computation. This discipline provides for both remote invocation and process migration. A simple type system is a straightforward extension of that of the π-calculus, adapted to take into account the lexical scope of channels. An equivalence law captures the essence of this model: a process behavior depends on the channels it uses, not on where it runs. 相似文献
27.
INTRODUCTION AND DEVELOPMENT: Multiple sclerosis (ME) is an inflammatory disease of the myelin of the central nervous system, the origin of which is still unknown. Genetic, infectious, immunological and environmental factors have all been blamed, but none of these factors on their own can explain the whole spectrum of this disease. Of the environmental factors, fat in the diet has given rise to most discussion. At the present time, it is known that polyunsaturated essential fatty acids form a part of biological membranes. A relationship has been found between the dietary fat consumed and the plasma levels and cell membrane content. CONCLUSIONS: The possible immuno-modulation function of these fatty acids justify rigorous evaluation of this hypothesis. 相似文献
28.
Studied the social reputations of elementary school children. Ss were 76 2nd-grade (mean age 7.5 yrs), 71 3rd-grade (mean age 8.5 yrs), and 83 4th-grade students (mean age 9.7 yrs). Using the peer nomination technique, Ss were assessed collectively on 8 dimensions requiring both social and academic judgments. A cluster analysis was performed to identify groups with different sociometric profiles. Correlations between peer evaluations and teacher evaluations of Ss' social reputations were determined. (English abstract) (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
29.
Synthesis of ultrafine LiCoO2 powders by the sol-gel method 总被引:8,自引:0,他引:8
Ultrafine high-temperature (HT) LiCoO2 powders were synthesized by the sol-gel method using polyacrylic acid (PAA) as a chelating agent. The decomposition process of the gel precursor was examined to determine the crystallization temperature and the dependence of the physicochemical properties of HT-LiCoO2 powders on the PAA quantity was extensively investigated. Polycrystalline HT-LiCoO2 powders, composed of very uniformly sized ultrafine particulates with an average particle size of 30–50 nm and a specific surface area of 2.3–17 m2g–1, could be obtained at the lower calcination temperature of 550 °C and the shorter calcination time of 1 h compared to the solid-state reaction. 相似文献
30.
G Pons-Lladó F Carreras X Borrás J Palmer J Llauger A Bayés de Luna 《Canadian Metallurgical Quarterly》1997,79(12):1651-1656
To compare the value of echocardiography and magnetic resonance imaging (MRI) in the assessment of the amount and extent of hypertrophy in hypertrophic cardiomyopathy (HC) and, second, to correlate the degree of hypertrophy, as assessed by MRI, with clinical and electrocardiographic parameters, 30 consecutive patients (16 men and 14 women, aged 20 to 74 years) with HC were studied. Measurements of left ventricular wall thickness were performed at 11 predetermined segments (5 basal, 5 midventricular, and 1 apical) by 2-dimensional echocardiography and MRI. Two parameters derived from MRI studies were considered as indicators of the degree and extent of hypertrophy: (1) mean of the measured wall thickness at the 11 segments, and (2) the number of segments with thickness > 15 mm. Results showed that, from a total of 330 myocardial segments, thickness could be measured by echocardiography in 221 (67%), whereas MRI allowed measurement of 320 segments (97%). When compared with clinical and electrocardiographic data, no correlation was found regarding mean wall thickness and number of hypertrophied segments by MRI except for the presence of an abnormal electrocardiographic repolarization pattern. It is concluded that MRI allows a better assessment of the degree and extension of left ventricular hypertrophy than echocardiography in HC. Despite the precise information on hypertrophy provided by MRI, the amount and degree of hypertrophy bears no correlation with most of the clinical data in these patients. 相似文献