全文获取类型
收费全文 | 626篇 |
免费 | 36篇 |
国内免费 | 17篇 |
专业分类
电工技术 | 23篇 |
综合类 | 28篇 |
化学工业 | 37篇 |
金属工艺 | 28篇 |
机械仪表 | 11篇 |
建筑科学 | 28篇 |
矿业工程 | 7篇 |
能源动力 | 6篇 |
轻工业 | 20篇 |
水利工程 | 14篇 |
石油天然气 | 12篇 |
武器工业 | 4篇 |
无线电 | 41篇 |
一般工业技术 | 14篇 |
冶金工业 | 338篇 |
原子能技术 | 1篇 |
自动化技术 | 67篇 |
出版年
2024年 | 4篇 |
2023年 | 5篇 |
2022年 | 10篇 |
2021年 | 9篇 |
2020年 | 14篇 |
2019年 | 8篇 |
2018年 | 6篇 |
2017年 | 8篇 |
2016年 | 11篇 |
2015年 | 11篇 |
2014年 | 19篇 |
2013年 | 22篇 |
2012年 | 27篇 |
2011年 | 27篇 |
2010年 | 19篇 |
2009年 | 21篇 |
2008年 | 24篇 |
2007年 | 20篇 |
2006年 | 17篇 |
2005年 | 17篇 |
2004年 | 21篇 |
2003年 | 7篇 |
2002年 | 9篇 |
2001年 | 6篇 |
2000年 | 3篇 |
1999年 | 7篇 |
1998年 | 108篇 |
1997年 | 62篇 |
1996年 | 41篇 |
1995年 | 19篇 |
1994年 | 18篇 |
1993年 | 15篇 |
1992年 | 3篇 |
1991年 | 3篇 |
1990年 | 3篇 |
1989年 | 7篇 |
1988年 | 3篇 |
1987年 | 2篇 |
1986年 | 6篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1980年 | 5篇 |
1978年 | 4篇 |
1977年 | 6篇 |
1976年 | 14篇 |
1971年 | 1篇 |
1970年 | 1篇 |
1955年 | 1篇 |
排序方式: 共有679条查询结果,搜索用时 0 毫秒
201.
202.
The physiology of the pelvic territory after the ligation of the hypogastric arteries may be resumed in the following phenomena: the absence of bleeding, absence of ischemia and changes in pelvic vascular pattern. The hemostatic effect is noticed immediately after ligation, when the bleeding is considerably diminished, permitting to finish the surgical act. The blood pressure has been measured before ligation, immediately and it increases after five minutes due to the changes in local characteristic impedance. The impedance profile is in concordance with geometrical modification of the microvascular network made to prevent the ischemia. The increase in blood pressure five minutes after ligation is the result of the anastomosis between the ischiatic artery and other branches of the hypogastric artery, remaking the capillary bed in the pelvic territory. 相似文献
203.
KJ Greenlund K Liu AR Dyer CI Kiefe GL Burke C Yunis 《Canadian Metallurgical Quarterly》1996,86(4):480-485
OBJECTIVES: Associations of parental education, parental body size, and offspring's education with body mass index and 7-year change in body mass index were examined among participants in the Coronary Artery Risk Development in Young Adults (CARDIA) study. METHODS: CARDIA is a study of coronary artery disease risk factors in 5115 Black and White persons aged 18 to 30 at baseline. Analyses of covariance were carried out with body mass index and change in body mass index as the dependent variables, and with parental education, parental body size, and participant education as the major independent variables. RESULTS: Father's body size was positively associated with participant's baseline body mass index among Black men, White men, and White women. Mother's body size was positively associated with baseline body mass index among all race-sex groups, and with change in body mass index among White women. Father's education was inversely associated with baseline body mass index among Black men and White women, and with change among White women. CONCLUSIONS: Parental education may influence body mass index and changes in young adulthood, especially among White women. Such associations may be both genetic and environmental and may be important for obesity prevention efforts. 相似文献
204.
K Jandeleit-Dahm B Jackson D Paxton R Perich CI Johnston 《Canadian Metallurgical Quarterly》1995,4(3):170-176
To gain further insight into the operation of 5-HT autoreceptor-mediated feedback control of 5-HT biosynthesis in serotonergic nerve terminal areas, the effect of the 5-HT1B and the 5-HT1A receptor agonists, TFMPP and 8-OH-DPAT, respectively, were investigated in the rat central nervous system (CNS) using in vivo and in vitro neurochemical approaches. TFMPP suppressed 5-HT synthesis (5-HTP accumulation after decarboxylase inhibition) both in vivo and in vitro. In vivo, the 5-HT synthesis-suppressing effect of the drug (3.0 mg/kg, s.c.) proved resistant to either acute hemitransection or reserpine (5 mg/kg, i.p.; 90 min before) pretreatment. In vitro, in cortical, hippocampal and striatal slice preparations, TFMPP (0.1-10 microM) decreased 5-HT synthesis under basal and stimulated (30 mM K+) conditions, an effect which was unaltered by prior in vivo reserpine-induced 5-HT depletion but was attenuated in the presence of 5-HT1B receptor antagonists such as methiothepin, cyanopindolol or propranolol. The 8-OH-DPAT (0.1 mg/kg, s.c.)-induced decrease of 5-HT synthesis in vivo was abolished by hemitransection but resistant to acute reserpine pretreatment; 8-OH-DPAT (10 microM) did not decrease 5-HT synthesis in vitro. In conclusion, the present study confirms the importance of 5-HT autoreceptors in the feedback control of nerve terminal 5-HT biosynthesis. Specifically, our data indicate: (1) that the reduction of rat brain 5-HT synthesis after TFMPP is mediated by 5-HT1B autoreceptors located on the serotonergic axon terminals, and (2) that the effect is directly mediated and occurs independently of 5-HT neuronal firing and intact monoamine stores. 相似文献
205.
The Substance Abuse Monitor is a comprehensive community-based addictions information system that forms the basis for an innovative approach to community needs assessment. This paper describes: (1) the conditions that created the need and support for the monitoring system; (2) the community development strategy that was employed to secure the commitment of agencies to the project; (3) the specifics of the needs assessment procedures; (4) some of the theoretical, clinical and methodological issues on which the procedures are based; (5) the practical applications of the system; and (6) the limitations of the system. The establishment of the database was based upon the idea that there would be benefits at several levels: the community, the participating agencies, the individual counsellors and the clients. The realization of these benefits requires that the information collected and the results generated must be capable of addressing specific service delivery problems with practical and tangible solutions. It is argued that the project has been successful in generating such solutions, and has considerable potential as an ongoing needs assessment tool. 相似文献
206.
Wound repair is characterized by the presence of a fibrin-rich matrix, but the effect of fibrin on re-epithelialization remains unclear. In this study, we determined the effects of different fibrin matrices on cultured human neonatal keratinocytes. Using purified fibrinogen and fibrin gels generated by the enzymatic action of thrombin, batroxobin (it leads to retention of fibrinopeptide B), or Agkistrodon contortrix thrombin-like enzyme (ACTE; it leads to retention of fibrinopeptide A), we determined the effect of each of these matrices on keratinocyte morphology, attachment, spreading, and replication as compared to tissue culture plastic. Morphologically, keratinocytes seeded on fibrin surfaces were more rounded and formed three-dimensional structures. Specific cell attachment, as measured at either 37 degrees C or 4 degrees C, was not altered on the different fibrin substrates (P > .05) but was increased on fibrinogen and factor XIII cross-linked fibrin (P < .01). However, keratinocytes seeded on fibrin, regardless of the presence or absence of fibrinopeptides A or B, showed a marked decrease (up to 71%) in cell numbers by days 5 (P = .0357) and 10 (P = .0114). Keratinocyte spreading was decreased by 78.8% (P = .0006), 80.3% (P = .0001), and 89.2% (P = .0001) on thrombin-, batroxobin-, and ACTE-generated fibrin, respectively, but not on fibrinogen-coated dishes. However, either the addition of fibronectin or cross-linking of fibrin with factor XIII allowed full keratinocyte spreading to occur (P = .0002 and P = .0013, respectively). We conclude that fibrin inhibits keratinocyte spreading in the absence of other matrix or plasma proteins or cross-linking by factor XIII. 相似文献
207.
Resistance to the action of endotoxin varies among inbred strains of mice, indicating that a component of this resistance has a genetic basis. Different responses to endotoxin that are characteristic of individual inbred strains represent phenotypes that can be used to genetically map the response modifier genes. This study compares the acute histologic lesions in 8-week-old male A/J and C57BL/6J (B6) mice injected intraperitoneally with endotoxin of E. coli O265:B6 (15 mg/kg). Animals of both strains exhibited splenitis, splenic lymphoid hyperplasia, splenic lymphoid necrosis, and sequestration of neutrophils in the pulmonary alveoli. The B6 mice showed increased margination of white blood cells to the pulmonary vascular endothelium relative to A/J mice. A large number of degenerating neutrophils was observed in the liver sinusoids of most B6 animals, while this lesion was much less severe in A/J mice. This difference was quantified, demonstrating a highly significant difference in neutrophil infiltration in B6 mice relative to A/J mice. Analysis of this phenotype in F1 mice demonstrates that major genes encoding the trait are not X-linked, imprinted, or maternally inherited and do not show the codominant inheritance expected if Lps(d) were primarily responsible. The distinctive, quantitative nature of these differences provides a useful assay for mapping genes that modify endotoxin responsiveness using the AXB and BXA recombinant inbred (RI) strains derived from A/J and B6 mice. 相似文献
208.
209.
本文从研究正常降雨对土壤性状的影响出发,进行了模拟雨水对酸性紫色土和石灰性紫色土的连续淋洗试验。试验结果表明在模拟雨水连续淋洗150天的过程中,土壤中钙、镁、钾、钠等盐基离子几乎都显示出一定程度的净淋溶特征,土壤中各盐基离子的动力学变化特征几乎都与抛物线扩散方程吻合。淋洗结束后土壤酸度未发生显著变化,但两种土壤CEC值均有所降低。 相似文献
210.
Text entry on handheld computers by older users 总被引:1,自引:0,他引:1
Small pocket computers offer great potential in workplaces where mobility is needed to collect data or access reference information while carrying out tasks such as maintenance or customer support. This paper reports on three studies examining the hypothesis that data entry by older workers is easier when the pocket computer has a physical keyboard, albeit a small one, rather than a touch-screen keyboard. Using a counter-balanced, within-subjects design the accuracy and speed with which adults over 55 years of age could make or modify short text entries was measured for both kinds of pocket computer. The keyboard computer was the Hewlett Packard 360LX (HP), but the touch-screen computers varied across studies (experiment 1: Apple Newton and PalmPilot; experiment 2: Philips Nino; experiment 3: Casio E10). All studies showed significant decrements in accuracy and speed when entering text via the touch-screen. Across studies, most participants preferred using the HP's small physical keyboard. Even after additional practice with the touch screen (experiments 2 and 3) many entries still contained errors. Experiment 3 showed that younger people were faster but not more accurate than older people at using the touch-screen keyboard. It is concluded that satisfactory text entry on palm-size computers awaits improvements to the touch-screen keyboard or alternative input methods such as handwriting or voice. Interface developments that assist older people typically benefit younger users too. 相似文献