全文获取类型
收费全文 | 1549篇 |
免费 | 43篇 |
国内免费 | 10篇 |
专业分类
电工技术 | 136篇 |
综合类 | 5篇 |
化学工业 | 408篇 |
金属工艺 | 70篇 |
机械仪表 | 37篇 |
建筑科学 | 29篇 |
矿业工程 | 5篇 |
能源动力 | 32篇 |
轻工业 | 75篇 |
水利工程 | 2篇 |
石油天然气 | 7篇 |
无线电 | 121篇 |
一般工业技术 | 333篇 |
冶金工业 | 148篇 |
原子能技术 | 53篇 |
自动化技术 | 141篇 |
出版年
2022年 | 8篇 |
2021年 | 11篇 |
2020年 | 13篇 |
2019年 | 18篇 |
2018年 | 18篇 |
2017年 | 21篇 |
2016年 | 16篇 |
2015年 | 29篇 |
2014年 | 33篇 |
2013年 | 97篇 |
2012年 | 50篇 |
2011年 | 57篇 |
2010年 | 65篇 |
2009年 | 66篇 |
2008年 | 94篇 |
2007年 | 58篇 |
2006年 | 58篇 |
2005年 | 52篇 |
2004年 | 46篇 |
2003年 | 47篇 |
2002年 | 34篇 |
2001年 | 42篇 |
2000年 | 28篇 |
1999年 | 29篇 |
1998年 | 57篇 |
1997年 | 52篇 |
1996年 | 48篇 |
1995年 | 37篇 |
1994年 | 34篇 |
1993年 | 41篇 |
1992年 | 20篇 |
1991年 | 14篇 |
1990年 | 16篇 |
1989年 | 14篇 |
1988年 | 16篇 |
1987年 | 23篇 |
1986年 | 27篇 |
1985年 | 24篇 |
1984年 | 21篇 |
1983年 | 22篇 |
1982年 | 23篇 |
1981年 | 21篇 |
1980年 | 23篇 |
1979年 | 23篇 |
1978年 | 16篇 |
1977年 | 7篇 |
1976年 | 12篇 |
1975年 | 3篇 |
1974年 | 5篇 |
1969年 | 4篇 |
排序方式: 共有1602条查询结果,搜索用时 15 毫秒
141.
This paper is concerned with rolling piston type rotary compressors for air conditioners. Friction losses at the vane tip and sides and at the rolling piston bearing are analysed taking account of the kinematics of the compressor. Characteristics of the losses and the influences of design parameters on them are investigated. It is indicated that the short length/diameter configuration of the cylinder is favourable to decrease total loss but the reverse is desirable to achieve maximum reliability of the compressor. 相似文献
142.
In real-time systems, the scheduling plays an important role to carry out all tasks within predefined time frames. The scheduling problem, however, is known to be intractable, that is, NP-hard or NP-complete for most cases (Garey and Johnson 1979). In this paper, one of the neural computation techniques is introduced to solve it within a limited time under the hard real-time environment, instead of improving algorithms on conventional computers. Although the neural computation can be realized on a multiprocessor, a special hardware using neural networks is designed to obtain the schedule results without overhead. 相似文献
143.
Mechanism‐Based Trapping of the Quinonoid Intermediate by Using the K276R Mutant of PLP‐Dependent 3‐Aminobenzoate Synthase PctV in the Biosynthesis of Pactamycin 下载免费PDF全文
Akane Hirayama Dr. Akimasa Miyanaga Prof. Dr. Fumitaka Kudo Prof. Dr. Tadashi Eguchi 《Chembiochem : a European journal of chemical biology》2015,16(17):2484-2490
Mutational analysis of the pyridoxal 5′‐phosphate (PLP)‐dependent enzyme PctV was carried out to elucidate the multi‐step reaction mechanism for the formation of 3‐aminobenzoate (3‐ABA) from 3‐dehydroshikimate (3‐DSA). Introduction of mutation K276R led to the accumulation of a quinonoid intermediate with an absorption maximum at 580 nm after the reaction of pyridoxamine 5′‐phosphate (PMP) with 3‐DSA. The chemical structure of this intermediate was supported by X‐ray crystallographic analysis of the complex formed between the K276R mutant and the quinonoid intermediate. These results clearly show that a quinonoid intermediate is involved in the formation of 3‐ABA. They also indicate that Lys276 (in the active site of PctV) plays multiple roles, including acid/base catalysis during the dehydration reaction of the quinonoid intermediate. 相似文献
144.
Fumitaka Kudo Dr. Atsushi Motegi Kazutoshi Mizoue Dr. Tadashi Eguchi Prof. Dr. 《Chembiochem : a European journal of chemical biology》2010,11(11):1574-1582
FD‐891 is a 16‐membered cytotoxic antibiotic macrolide that is especially active against human leukemia such as HL‐60 and Jurkat cells. We identified the FD‐891 biosynthetic (gfs) gene cluster from the producer Streptomyces graminofaciens A‐8890 by using typical modular type I polyketide synthase (PKS) genes as probes. The gfs gene cluster contained five typical modular type I PKS genes (gfsA, B, C, D, and E), a cytochrome P450 gene (gfsF), a methyltransferase gene (gfsG), and a regulator gene (gfsR). The gene organization of PKSs agreed well with the basic polyketide skeleton of FD‐891 including the oxidation states and α‐alkyl substituent determined by the substrate specificities of the acyltransferase (AT) domains. To clarify the involvement of the gfs genes in the FD‐891 biosynthesis, the P450 gfsF gene was inactivated; this resulted in the loss of FD‐891 production. Instead, the gfsF gene‐disrupted mutant accumulated a novel FD‐891 analogue 25‐O‐methyl‐FD‐892, which lacked the epoxide and the hydroxyl group of FD‐891. Furthermore, the recombinant GfsF enzyme coexpressed with putidaredoxin and putidaredoxin reductase converted 25‐O‐methyl‐FD‐892 into FD‐891. In the course of the GfsF reaction, 10‐deoxy‐FD‐891 was isolated as an enzymatic reaction intermediate, which was also converted into FD‐891 by GfsF. Therefore, it was clearly found that the cytochrome P450 GfsF catalyzes epoxidation and hydroxylation in a stepwise manner in the FD‐891 biosynthesis. These results clearly confirmed that the identified gfs genes are responsible for the biosynthesis of FD‐891 in S. graminofaciens. 相似文献
145.
146.
Tomoharu Suzuki Shigeru Oshio Mari Iwata Hisayo Saburi Takashi Odagiri Tadashi Udagawa Isamu Sugawara Masakazu Umezawa Ken Takeda 《Particle and fibre toxicology》2010,7(1):1-8
Background
Epidemiological studies suggest that inhalation of carbonaceous particulate matter from biomass combustion increases susceptibility to bacterial pneumonia. In vitro studies report that phagocytosis of carbon black by alveolar macrophages (AM) impairs killing of Streptococcus pneumoniae. We have previously reported high levels of black carbon in AM from biomass smoke-exposed children and adults. We therefore aimed to use a mouse model to test the hypothesis that high levels of carbon loading of AM in vivo increases susceptibility to pneumococcal pneumonia.Methods
Female outbred mice were treated with either intranasal phosphate buffered saline (PBS) or ultrafine carbon black (UF-CB in PBS; 500 μg on day 1 and day 4), and then infected with S. pneumoniae strain D39 on day 5. Survival was assessed over 72 h. The effect of UF-CB on AM carbon loading, airway inflammation, and a urinary marker of pulmonary oxidative stress was assessed in uninfected animals.Results
Instillation of UF-CB in mice resulted a pattern of AM carbon loading similar to that of biomass-smoke exposed humans. In uninfected animals, UF-CB treated animals had increased urinary 8-oxodG (P = 0.055), and an increased airway neutrophil differential count (P < 0.01). All PBS-treated mice died within 72 h after infection with S. pneumoniae, whereas morbidity and mortality after infection was reduced in UF-CB treated animals (median survival 48 h vs. 30 h, P < 0.001). At 24 hr post-infection, UF-CB treated mice had lower lung and the blood S. pneumoniae colony forming unit counts, and lower airway levels of keratinocyte-derived chemokine/growth-related oncogene (KC/GRO), and interferon gamma.Conclusion
Acute high level loading of AM with ultrafine carbon black particles per se does not increase the susceptibility of mice to pneumococcal infection in vivo. 相似文献147.
The developing acrosome in spermatids contains pituitary adenylate cyclase-activating polypeptide (PACAP). However, the role of the acrosomal PACAP remains unclear because it has not been detected in mature spermatids and sperm. We reinvestigated whether the sperm acrosome contains PACAP. An antiserum produced against PACAP reacted to the anterior acrosome in epididymal sperm fixed under mild conditions, suggesting that PACAP acts on oocytes and/or cumulus cells at the site of fertilization. Immunolabeling and RT-PCR demonstrated the presence of PACAP type I receptor, a PACAP-specific receptor, in postovulatory cumulus cells. To investigate the role of PACAP in fertilization, we pretreated cumulus-oocyte complexes with the polypeptide. At a low concentration of sperm, the fertilization rate was significantly enhanced by PACAP in a dose-dependent manner. Sperm penetration through the oocyte investment, cumulus layer, and zona pellucida was also enhanced by PACAP. The enhancement was probably due to an enhancement in sperm motility and the zona-induced acrosome reaction, which were stimulated by a cumulus cell-releasing factor. Indeed, PACAP treatment increased the secretion of progesterone from the cumulus-oocyte complexes. These results strongly suggest that in response to PACAP, cumulus cells release a soluble factor that probably stimulates sperm motility and the acrosome reaction, thereby promoting fertilization. 相似文献
148.
Eiji Akiyama Songjie Li Tadashi Shinohara Zuogui Zhang Kaneaki Tsuzaki 《Electrochimica acta》2011,(4):1799
Electrochemical hydrogen permeation tests of Fe sheets under two cyclic corrosion test (CCT) conditions were performed to understand hydrogen entry behavior under atmospheric corrosions. Hydrogen entry into 1300 MPa-class high strength steels under two CCT conditions was also investigated using thermal desorption analysis. One CCT consisted of salt spray, dry and wet stages (Salt Spray CCT; SSCCT), and the other consisted of dry and wet stages after NaCl deposition (Dry–Wet CCT; DWCCT). The corrosion rates of Fe and the steels were almost constant under SSCCT and they decreased under DWCCT with time. Nevertheless, both CCTs resulted in increases in hydrogen permeation current and diffusible hydrogen content with time indicating enhancement of hydrogen entry. Corrosion current monitored by means of an atmospheric corrosion monitoring sensor consisting of Fe anode and Ag cathode decreased obviously under dry stage of the CCTs, whereas hydrogen permeation was high at the beginning of the dry stage. The discrepancy between hydrogen entry and corrosion rate indicates that the hydrogen entry is not directly controlled by corrosion rate. Increase in acidity of underlying rust layer with growth of rust layer monitored using a W/WO3 electrode is considered to be one of the factors affecting the hydrogen entry efficiency. 相似文献
149.
150.
Raimundo Almeida-Filho Fernando P. Miranda Tadashi Yamakawa 《International journal of remote sensing》2013,34(13):2683-2688
Mapping of a tonal anomaly in an area of hydrocarbon microseepage was possible using a Landsat-Thematic Mapper false-colour composite consisting of TM2/3, TM4/3 and of the difference TM2/3-TM4/3, displayed as red, green and blue, respectively. In this false-colour composite, green and yellow express variations in the vegetation cover, whereas hues of magenta are related to terrain conditions representing bleached materials, which occur close to the centre of a soil gas anomaly. Simultaneous occurrence of anomalous soil gas values with magnetic and radioactive minerals suggests that a reducing environment associated with the microseepage phenomenon created the bleached materials, identified as a tonal anomaly in the enhanced TM image. 相似文献