全文获取类型
收费全文 | 2746篇 |
免费 | 37篇 |
国内免费 | 5篇 |
专业分类
电工技术 | 10篇 |
化学工业 | 310篇 |
金属工艺 | 14篇 |
机械仪表 | 25篇 |
建筑科学 | 15篇 |
能源动力 | 39篇 |
轻工业 | 120篇 |
水利工程 | 10篇 |
石油天然气 | 4篇 |
无线电 | 118篇 |
一般工业技术 | 343篇 |
冶金工业 | 1679篇 |
原子能技术 | 16篇 |
自动化技术 | 85篇 |
出版年
2023年 | 7篇 |
2022年 | 14篇 |
2021年 | 25篇 |
2020年 | 16篇 |
2019年 | 9篇 |
2018年 | 27篇 |
2017年 | 29篇 |
2016年 | 24篇 |
2015年 | 20篇 |
2014年 | 33篇 |
2013年 | 73篇 |
2012年 | 54篇 |
2011年 | 50篇 |
2010年 | 62篇 |
2009年 | 52篇 |
2008年 | 75篇 |
2007年 | 63篇 |
2006年 | 51篇 |
2005年 | 41篇 |
2004年 | 37篇 |
2003年 | 42篇 |
2002年 | 19篇 |
2001年 | 23篇 |
2000年 | 15篇 |
1999年 | 76篇 |
1998年 | 588篇 |
1997年 | 311篇 |
1996年 | 210篇 |
1995年 | 113篇 |
1994年 | 98篇 |
1993年 | 124篇 |
1992年 | 32篇 |
1991年 | 30篇 |
1990年 | 23篇 |
1989年 | 21篇 |
1988年 | 26篇 |
1987年 | 23篇 |
1986年 | 17篇 |
1985年 | 22篇 |
1984年 | 7篇 |
1983年 | 9篇 |
1982年 | 16篇 |
1981年 | 14篇 |
1980年 | 11篇 |
1978年 | 10篇 |
1977年 | 46篇 |
1976年 | 71篇 |
1975年 | 4篇 |
1973年 | 5篇 |
1971年 | 3篇 |
排序方式: 共有2788条查询结果,搜索用时 0 毫秒
71.
Balaji T Acharya RN Nair AG Reddy AV Rao KS Naidu GR Manohar SB 《The Science of the total environment》2000,253(1-3):75-79
The concentrations of some elements in a few varieties of cereals and pulses are determined by Instrumental Neutron Activation Analysis using a single comparator method (k0-standardised NAA method). A total of 15 elements are measured. The method was validated by analysing the Standard Reference Material (SRM-1571) of NIST; the results are within +/-10% of the reported values for the majority of the elements. The measured concentrations of major and minor elements are analysed in terms of the average intake of mineral content and the role of these elements in terms of the nutritional value. 相似文献
72.
BACKGROUND: Synthetic homopyrimidine peptide nucleic acids (PNAs) can bind complementary targets in double-stranded DNA, generating strand-displacement complexes, and so offering an opportunity to modulate specific gene expression. Several issues remain to be addressed before these attributes can be exploited in vivo, however. RESULTS: The kinetics of the interaction between a homopyrimidine PNA and a complementary homopurine target on double-stranded DNA were analyzed in the presence or absence of a preformed strand-displacement complex proximal to the target. The complex was established under low salt conditions by the binding of a different homopyrimidine PNA to a target situated adjacent to the first PNA target. These two targets were placed next to each other on opposite strands at distances of 0, 2, 4 and 8 base pairs apart. The presence of a preformed strand-displacement complex near the target accelerates the binding of PNA to double-stranded DNA in a salt-dependent manner. The influence of salt on the binding rates was also examined. The binding rate is increased by a factor of 1 x exp(70[NaCl]), that is, 16-fold at 40 mM NaCl and more than 10(4)-fold if extrapolated to 140 mM NaCl. This effect is significantly reduced if the two targets are 2 base pairs apart and completely absent if the distance is 4 base pairs or more. CONCLUSIONS: The perturbation of the DNA helix imposed by a PNA strand-displacement complex only propagates a few base pairs. It is therefore possible to target sites in the immediate vicinity of strand invasion complexes specifically. The results presented have implications for the mechanism of strand displacement and for the application of PNA in a genomic context. 相似文献
73.
1. The mean incidence of deaths from ascites in the UK in 1993 was 1.4% (0.7% in 1991 and 0.9% in 1992) and 0.8% from sudden death syndrome (SDS). In total, the economic loss to the UK Broiler Industry in 1993 as a result of these 2 conditions was 24 Pounds M. 2. Clear geographical differences emerged in the occurrence of ascites, with, not only the lowest incidences being observed in Northern Ireland, but also the peak of the mortality from ascites occurring much later in the rearing cycle than in other regions on the mainland. 3. In all regions the incidence of SDS was lower than that of ascites but the reason for this disparity remains to be established. 4. Some of the variables associated with the road transportation of day-old chicks from the hatchery to the farm appeared to influence the incidence of ascites. These included distance or time travelled, stocking density, internal lorry temperature and the length of time the lorry was heated before transport as well as the time the shed was heated before chick arrival. Temperature was also an important factor during growth (brooding and finishing). 5. Negative pressure-powered ventilation was preferred in most organisations but more ascites was seen with positive pressure ventilation. However, the lowest incidence of ascites occurred with natural ventilation. There was more ascites relative to shed orientation when the wind direction was from the west compared to the east. 6. This survey identifies the extent of the problem of broiler ascites in the UK and also highlights the importance of good management control of day-old chicks, not only following placement, but even before their arrival on the farm. 相似文献
74.
75.
ML van Oppenraay CM van der Beek JE de Boer M Danz MK Schutte JP Verduijn 《Canadian Metallurgical Quarterly》1998,142(12):633-636
The Central Medical Pharmaceutical Committee of the Health Insurance Council informs the medical profession annually about the effects of drugs through the Pharmacotherapeutical Compass. The 1998 edition now contains a chapter on pharmacokinetics as well. Compared with previous editions the main alterations of the contents concern an introduction and advice on the antidepressants, two protocols with respect to the medical treatment of patients suffering from epilepsy, advice with respect to oral drugs for the treatment of inflammatory bowel disease, an introduction and advice regarding the treatment of allergic rhinitis, the treatment of patients suffering from AIDS with antiretroviral drugs, the treatment of genital herpes, the taking of insulin lispro by patients with diabetes and the taking of bisphosphonates to prevent or to treat osteoporosis. Two corrections to the 1998 edition are given. 相似文献
76.
77.
The Pi typing methods acid starch-gel electrophoresis (ASGE) and isoelectric focusing (IEF) have been compared by three reference laboratories: 564 samples of phenotypes Pi M, MS and MZ were tested in each of the three laboratories with a 96% agreement on initial typing. The discrepancies are recorded and reasons for disagreement discussed. IEF is a reliable method for Pi typing and gives results comparable to those obtained by ASGE. 相似文献
78.
79.
A complex perovskite oxide Ba2HoNbO6 has been developed as a non-reacting substrate for YBa2Cu3O7– superconducting film with lattice constant a = 8.3905 Å. The dielectric constant (30) and loss factor value (5 × 10–3) of the material are in the range suitable for its use as substrate for microwave applications. A YBa2Cu3O7–delta; superconducting thick film dip coated on Ba2HoNbO6 substrate gave a T
c(0) of 92 K and current density of 1.2 × 104 A cm–2. 相似文献
80.
Bibin John C. P. Reghunadhan Nair K. Ambika Devi K. N. Ninan 《Journal of Materials Science》2007,42(14):5398-5405
Syntactic foam composites of cyanate ester with varying volume fractions of resin and glass microballoon were processed and
evaluated for tensile, flexural and compressive properties. The effect of nature and volume fraction of microballoon on the
mechanical properties was studied. The mechanical properties showed a gradual decrease in strength with increase in volume
fraction of microballoon. The specific strength values also manifested a similar order. A similar behaviour was observed for
syntactic foams with microballoons of varying true density. The properties increased proportional to the strength of the microballoon
in resin-rich systems implying a strong microballoon-resin interface, corroborated by Scanning Electron Microscopy studies.
The compressive modulus showed a decreasing trend with enhanced microballoon loading. 相似文献