全文获取类型
收费全文 | 1811篇 |
免费 | 101篇 |
国内免费 | 11篇 |
专业分类
电工技术 | 55篇 |
综合类 | 1篇 |
化学工业 | 261篇 |
金属工艺 | 32篇 |
机械仪表 | 19篇 |
建筑科学 | 122篇 |
矿业工程 | 8篇 |
能源动力 | 26篇 |
轻工业 | 169篇 |
水利工程 | 15篇 |
石油天然气 | 1篇 |
无线电 | 73篇 |
一般工业技术 | 286篇 |
冶金工业 | 556篇 |
原子能技术 | 2篇 |
自动化技术 | 297篇 |
出版年
2023年 | 19篇 |
2022年 | 13篇 |
2021年 | 25篇 |
2020年 | 25篇 |
2019年 | 37篇 |
2018年 | 51篇 |
2017年 | 57篇 |
2016年 | 55篇 |
2015年 | 60篇 |
2014年 | 62篇 |
2013年 | 129篇 |
2012年 | 102篇 |
2011年 | 119篇 |
2010年 | 73篇 |
2009年 | 60篇 |
2008年 | 78篇 |
2007年 | 71篇 |
2006年 | 64篇 |
2005年 | 46篇 |
2004年 | 33篇 |
2003年 | 32篇 |
2002年 | 30篇 |
2001年 | 27篇 |
2000年 | 15篇 |
1999年 | 36篇 |
1998年 | 158篇 |
1997年 | 91篇 |
1996年 | 72篇 |
1995年 | 34篇 |
1994年 | 24篇 |
1993年 | 32篇 |
1992年 | 11篇 |
1991年 | 14篇 |
1990年 | 6篇 |
1989年 | 10篇 |
1988年 | 6篇 |
1987年 | 5篇 |
1986年 | 8篇 |
1985年 | 12篇 |
1984年 | 12篇 |
1983年 | 5篇 |
1982年 | 4篇 |
1981年 | 14篇 |
1980年 | 8篇 |
1979年 | 7篇 |
1978年 | 3篇 |
1977年 | 17篇 |
1976年 | 34篇 |
1975年 | 5篇 |
1973年 | 3篇 |
排序方式: 共有1923条查询结果,搜索用时 8 毫秒
121.
OBJECTIVES: Little information is available about the intake of very-long-chain n-3 fatty acids in random samples of populations. We examined if the intake of these fatty acids was associated with gender, social status and lifestyle in a similar way as other indicators for a healthy diet in a nationwide survey. DESIGN AND SUBJECTS: Data were obtained from self-administered quantitative food frequency questionnaires filled in by a representative sample of Norwegian men and women, aged 16-79 y. 3144 (63%) of the invited subjects responded with acceptable questionnaires. RESULTS: Daily intake of very-long-chain n-3 fatty acids was on average 0.9 g/d and 0.4% of total energy was derived from these fatty acids. Energy derived from very-long-chain n-3 fatty acids was slightly higher among men than women, and two-fold higher among subjects aged 60-79 vs 16-29 y. White collar workers had higher intake of very-long-chain n-3 fatty acids than blue collar workers. Men and women in the highest quartile of intake of very-long-chain n-3 fatty acids had 2-3 E% higher fat intake (mostly mono- and polyunsaturated fatty acids), as compared to individuals in the lowest quartile. They also had 3-4 fold higher daily intake of retinol and vitamin D, as well as 20-50% higher intake of fruits and vegetables, dietary fibre and vitamin C. CONCLUSIONS: Intake of very-long-chain n-3 fatty acids was correlated to indicators for healthy dietary habits. However, contrary to many other indicators of a healthy diet, energy derived from very-long-chain n-3 fatty acids was not significantly associated with female gender or non-smoking. 相似文献
122.
123.
BJ Pogson KK Niyogi O Bj?rkman D DellaPenna 《Canadian Metallurgical Quarterly》1998,95(22):13324-13329
Collectively, the xanthophyll class of carotenoids perform a variety of critical roles in light harvesting antenna assembly and function. The xanthophyll composition of higher plant photosystems (lutein, violaxanthin, and neoxanthin) is remarkably conserved, suggesting important functional roles for each. We have taken a molecular genetic approach in Arabidopsis toward defining the respective roles of individual xanthophylls in vivo by using a series of mutant lines that selectively eliminate and substitute a range of xanthophylls. The mutations, lut1 and lut2 (lut = lutein deficient), disrupt lutein biosynthesis. In lut2, lutein is replaced mainly by a stoichiometric increase in violaxanthin and antheraxanthin. A third mutant, aba1, accumulates normal levels of lutein and substitutes zeaxanthin for violaxanthin and neoxanthin. The lut2aba1 double mutant completely lacks lutein, violaxanthin, and neoxanthin and instead accumulates zeaxanthin. All mutants were viable in soil and had chlorophyll a/b ratios ranging from 2.9 to 3.5 and near wild-type rates of photosynthesis. However, mutants accumulating zeaxanthin exhibited a delayed greening virescent phenotype, which was most severe and often lethal when zeaxanthin was the only xanthophyll present. Chlorophyll fluorescence quenching kinetics indicated that both zeaxanthin and lutein contribute to nonphotochemical quenching; specifically, lutein contributes, directly or indirectly, to the rapid rise of nonphotochemical quenching. The results suggest that the normal complement of xanthophylls, while not essential, is required for optimal assembly and function of the light harvesting antenna in higher plants. 相似文献
124.
125.
P Bj?rses J Aaltonen A Vikman J Perheentupa G Ben-Zion G Chiumello N Dahl P Heideman JJ Hoorweg-Nijman L Mathivon PE Mullis M Pohl M Ritzen G Romeo MS Shapiro CS Smith J Solyom J Zlotogora L Peltonen 《Canadian Metallurgical Quarterly》1996,59(4):879-886
Autoimmune polyglandular disease type I (APECED) is an autosomal recessive autoimmune disease (MIM 240300) characterized by hypoparathyroidism, primary adrenocortical failure, and chronic mucocutaneous candidiasis. The disease is highly prevalent in two isolated populations, the Finnish population and the Iranian Jewish one. Sporadic cases have been identified in many other countries, including almost all European countries. The APECED locus has previously been assigned to chromosome 21q22.3 by linkage analyses in 14 Finnish families. Locus heterogeneity is a highly relevant question in this disease affecting multiple tissues and with great phenotypic diversity. To solve this matter, we performed linkage and haplotype analyses on APECED families rising from different populations. Six microsatellite markers on the critical chromosomal region of 2.6 cM on 21q22.3 were analyzed. Pairwise linkage analyses revealed significant LOD scores for all these markers, maximum LOD score being 10.23. The obtained haplotype data and the geographic distribution of the great-grandparents of the Finnish APECED patients suggest the presence of one major, relatively old mutation responsible for approximately 90% of the Finnish cases. Similar evidence for one founder mutation was also found in analyses of Iranian Jewish APECED haplotypes. These haplotypes, however, differed totally from the Finnish ones. The linkage analyses in 21 non-Finnish APECED families originating from several European countries provided independent evidence for linkage to the same chromosomal region on 21q22.3 and revealed no evidence for locus heterogeneity. The haplotype analyses of APECED chromosomes suggest that in different populations APECED is due to a spectrum of mutations in a still unknown gene on chromosome 21. 相似文献
126.
M Olsson C Lidman S Latouche A Bj?rkman P Roux E Linder M Wahlgren 《Canadian Metallurgical Quarterly》1998,36(6):1737-1740
To evaluate the risk of a nosocomial spread of Pneumocystis carinii f. sp. hominis (P. carinii hominis), air filter samples from rooms of P. carinii pneumonia (PCP) patients, adjacent corridors, and other hospital environments have been investigated for the presence of P. carinii hominis. Amplified DNA from air filters and sputum or bronchoalveolar lavage samples from the PCP patients have been genotyped with the P. carinii hominis genes of the mitochondrial large-subunit (mtLSU) rRNA and the internal transcribed spacers (ITS1 and ITS2) of the rRNA. Genotypes of the two loci were identified by direct sequencing, and for site 85 of the mtLSU locus, three allele-specific PCR assays were used. P. carinii hominis DNA was identified in the air of five of seven PCP patient rooms and in the air of two of four air filtrations from the ward corridors. The P. carinii hominis genotypes were the same in four of the five room air samples as those in the corresponding patients, suggesting a risk of person-to-person transmission of P. carinii hominis from PCP patients. Three of 16 air samples collected in infectious disease wards without the presence of PCP patients and one sample from a cardiology unit in a separate hospital building were also positive, which further strengthens the possibility of acquisition of P. carinii hominis from the environment. 相似文献
127.
J Bj?rheim S Lystad A Lindblom U Kressner S Westring S Wahlberg G Lindmark G Gaudernack P Ekstr?m J R?e WG Thilly AL B?rresen-Dale 《Canadian Metallurgical Quarterly》1998,403(1-2):103-112
Pefloxacin plus metronidazole versus netilmicin plus metronidazole in the prevention of nosocomial infections during contaminated surgery. Surgical prophylaxis is widely used in contaminated surgery, especially colorectal surgery. In this clinical trial the efficacy of pefloxacin 800 mg i.v. slow infusion associated to metronidazole 500 mg i.v. 1-2 hours before surgery and then metronidazole alone after 6 and 12 hours versus netilmicin 200 mg i.m. associated to metronidazole 500 mg i.v. 1-2 hours before surgery and then both after 6 and 12 hours were evaluated in 97 patients suffering by colorectal surgery. Efficacy of prophylaxis in patients was evaluated in terms of appearance of post-surgical infections (abdominal, urinary, respiratory and wound infections). In pefloxacin + metronidazole group (53 patients), two cases of wound infections (3.8%) and three cases of respiratory infections (5.8%) were observed. In netilmicin + metronidazole group (44 patients), two cases of wound infections (4.9%), three cases of urinary infections (7%), three cases of respiratory infections (7.5%) and one case of intra-abdominal infection were observed. Our data confirmed that in colorectal surgery, the association pefloxacin, drug with microbiological and pharmacokinetics characteristics suitable for prophylaxis + metronidazole, active against anaerobes pathogens, prevents post-surgical infections as well as a reference association (netilmicin + metronidazole), with the advantage of a single administration. 相似文献
128.
A graphical tool to facilitate rapid primary annotation of genomic sequence has been developed. Within a single interface the user can import sequences or database entries, run feature prediction programs and similarity searches, filter results, add additional manually found features and notes, and finally export annotations for database submission. Integrated rule-based feature corroboration and a novel decision support heuristic using ORF orientation, length and base-composition further enhances the efficiency of the annotation process without compromising flexibility. The program has been explicitly tailored to use in protozoan parasite genome projects, but can constitute a useful tool for prokaryote annotation as well. It is successfully being used by our lab in the Trypanosoma cruzi genome project, and can be obtained from the authors upon request. 相似文献
129.
Many modern compact soft-x-ray and extreme-ultraviolet (EUV) imaging systems operate with small fields of view and therefore benefit from the use of small high-brightness sources. Such systems include water-window microscopes and EUV lithography tools. We show that the photon losses in such systems can be minimized while uniformity of object-plane illumination is maintained by controlled scanning of the source. The improved collection efficiency is demonstrated both theoretically and experimentally for a scanned laser-plasma source compared with static sources. A prospective aerial image microscope and a liquid-xenon-jet laser-plasma source are offered as examples of modern imaging tools that may benefit from such scanning of the source. 相似文献
130.