全文获取类型
收费全文 | 1457篇 |
免费 | 37篇 |
专业分类
电工技术 | 13篇 |
化学工业 | 230篇 |
金属工艺 | 22篇 |
机械仪表 | 24篇 |
建筑科学 | 21篇 |
矿业工程 | 1篇 |
能源动力 | 24篇 |
轻工业 | 127篇 |
水利工程 | 7篇 |
石油天然气 | 2篇 |
无线电 | 80篇 |
一般工业技术 | 119篇 |
冶金工业 | 715篇 |
原子能技术 | 6篇 |
自动化技术 | 103篇 |
出版年
2024年 | 3篇 |
2023年 | 5篇 |
2022年 | 19篇 |
2021年 | 38篇 |
2020年 | 17篇 |
2019年 | 32篇 |
2018年 | 29篇 |
2017年 | 20篇 |
2016年 | 29篇 |
2015年 | 23篇 |
2014年 | 41篇 |
2013年 | 61篇 |
2012年 | 48篇 |
2011年 | 39篇 |
2010年 | 47篇 |
2009年 | 49篇 |
2008年 | 43篇 |
2007年 | 41篇 |
2006年 | 29篇 |
2005年 | 19篇 |
2004年 | 29篇 |
2003年 | 31篇 |
2002年 | 22篇 |
2001年 | 13篇 |
2000年 | 13篇 |
1999年 | 21篇 |
1998年 | 196篇 |
1997年 | 131篇 |
1996年 | 76篇 |
1995年 | 60篇 |
1994年 | 32篇 |
1993年 | 44篇 |
1992年 | 4篇 |
1991年 | 12篇 |
1990年 | 12篇 |
1989年 | 11篇 |
1988年 | 5篇 |
1987年 | 5篇 |
1986年 | 10篇 |
1985年 | 8篇 |
1984年 | 6篇 |
1983年 | 3篇 |
1982年 | 7篇 |
1981年 | 9篇 |
1980年 | 10篇 |
1977年 | 22篇 |
1976年 | 63篇 |
1975年 | 3篇 |
1973年 | 1篇 |
1971年 | 2篇 |
排序方式: 共有1494条查询结果,搜索用时 234 毫秒
1.
2.
Cypriano G da Trindade Neto Ana LP Fernandes Ana IB Santos Waldenice A Morais Marcos VM Navarro Tereza NC Dantas Mrcia R Pereira Jos LC Fonseca 《Polymer International》2005,54(4):659-666
Complexation of chitosan in aqueous solutions by low molecular weight electrolytes is one of the simplest methods for the preparation of aqueous chitosan dispersions. In this work, the influence of storage time, sulfate concentration, method of preparation and surfactant content on some properties of the resultant chitosan dispersions (turbidity, viscosity and zeta potential) was analyzed. Turbidimetry was adequate to monitor the formation of particles, while viscometry was suitable to monitor changes in the dispersing phase. An analysis of the properties of these systems, mainly in terms of particle–particle and macromolecule–macromolecule interactions was carried out. Copyright © 2004 Society of Chemical Industry 相似文献
3.
LA Pérula de Torres J Martínez de la Iglesia J Espejo Espejo MV Rubio Cuadrado I Enciso Berge FJ Fonseca del Pozo JM Aranda Lara 《Canadian Metallurgical Quarterly》1997,20(8):425-434
OBJECTIVE: To describe the health status of a population over 60 years and to study their relationship with several socio-demographic variables. DESIGN: A cross-sectional study, population based. SETTINGS: A community. PARTICIPANTS: A randomized sample of 1,103 non institutionalized people over 60 years living in the city of Cordoba (Spain). MEASUREMENTS AND MAIN RESULTS: By mean of a personal interview at home we used the OARS-MFAQ-VE questionnaire. Low self-rated health was associated with the age, to be female sex, a low cultural background, and a low income. Only 5.2% of the study people do not suffered any illness and 56% state that their health problems are major problems for doing their current activities. 4.9% declared to have some degree of physical incapacity. 3.7% of elderly population has an important cognitive deficit. CONCLUSIONS: The majority of elderly people has good health. Age is related with a poor health. Women have more health problems than men. 相似文献
4.
Gag rules-clauses in managed care contracts that prevent physicians from disclosing information that the plan may find disparaging, but that could relate directly to the patient's health-have recently been the subject of ethical condemnation and legislative prohibition. Another serious problem in managed care contracts, trade secrets, or guidelines and quality assurance mechanisms that are imposed on physicians while their origins are shrouded in proprietary secrecy, have by contrast received little attention. Responses to these ethical challenges to the physician's integrity must involve individual physicians, managed care organizations, professional organizations, and public policymakers. 相似文献
5.
The structural gene for V antigen (lcrV) is known to be encoded within the lcrGVH-yopBD operon of the approximately 70-kb low-calcium-response or Lcr plasmid of Yersinia pestis. This 37-kDa monomeric peptide was reported to provide active immunity in mice, suppress inflammatory cytokines, and regulate expression of the low calcium response (Lcr+). Here we describe pVHB62, encoding a polyhistidine-V antigen fusion peptide (Vh) and linked LcrH. Vh underwent degradation from both the C terminus and N terminus during classical chromatographic fractionation but remained intact within two compartments during Ni2+ affinity chromatography. The first was homogeneous, capable of active immunization (mouse intravenous 50% lethal dose, > 10(7) bacteria), and stable at 4 degrees C. The second remained bound to the affinity column but could be eluted as a mixture of Vh, LcrH, and low-molecular-weight material by application of 6 M guanidine HCl. This mixture was dialyzed, denatured in 8 M urea, and again applied to the affinity column, which then hound Vh but not LcrH. The latter was recovered and renatured, and low-molecular-weight material was removed by biochemical fractionation. The resulting homogeneous LcrH bound protein AN antigen fusion peptide but not protein A in a sandwich enzyme-linked immunosorbent assay, and this reaction was inhibited by Vh. These observations indicate that LcrH normally binds V antigen in bacterial cytoplasm and suggest that only free LcrH down-regulates expression of the low calcium response. 相似文献
6.
What ethical concerns regarding the application of new antidementia compounds are pertinent to the best interests of patients with Alzheimer's disease and their caregivers? Based on collected preliminary anecdotal accounts, these concerns are important and should be considered carefully by clinicians, researchers, and families. 相似文献
7.
Y Yonemura H Kimura S Fushida K Tugawa Y Nakai M Kaji L Fonseca A Yamaguchi I Miyazaki 《Canadian Metallurgical Quarterly》1993,71(8):2448-2453
BACKGROUND: Proliferative activities of tumors are thought to be prognostic features of malignant tumors, but their value as measured by proliferating cell nuclear antigen (PCNA) labeling remains unclear in gastric cancer. METHODS: PCNA labeling rates (LR) were quantified in 121 paraffin-embedded biopsy specimens from primary tumors by immunocytochemistry. RESULTS: Immunohistochemical analyses have demonstrated that PCNA presents an intense staining in the nuclei of tumor cells and mucous neck cells of gastric glands. The PCNA LR ranged from 12% to 79% (mean +/- standard deviation), and a significant correlation was found between bromodeoxyuridine labeling indices and PCNA LR: PCNA LR were closely associated with tumor size, serosal invasion, and nodal involvement. The patients with tumors with high PCNA LR (greater than 40%) were dead significantly earlier than were those with tumors with low PCNA LR: When the PCNA LR and all the clinicopathologic parameters were entered into a Cox regression model, PCNA LR emerged as an independent prognostic factor. CONCLUSION: These results indicate that PCNA LR may be a potentially useful prognostic factor for gastric cancer. 相似文献
8.
1. Microelectrode recording techniques were used to study the effects of several potassium channel blockers which are considered to be Class III antiarrhythmic compounds. The effects of (+)-sotalol, UK-66,914, UK-68,798 and E-4031 on action potential duration (APD) were determined in guinea-pig isolated papillary muscles. The compounds were evaluated under normoxic or hypoxic/ischaemic conditions at 36.5 degrees C and compared to glibenclamide, which is considered to be a blocker of ATP-dependent potassium channels. Prolongation of action potential duration at 90% repolarization (APD90) was taken as an indirect measure of potassium channel blockade. 2. Under normoxic conditions, the Class III compounds prolonged APD in a concentration-dependent manner. According to EC15 values, the order of potency of the Class III compounds was found to be UK-68,798 > E-4031 > UK-66,914 > (+)-sotalol. Glibenclamide did not significantly prolong APD90 under normoxic conditions. 3. Perfusion with an experimental hypoxic or ischaemic bathing solution produced qualitatively similar effects on action potentials. Over a period of 20-25 min in either of the experimental solutions, there was a small decrease in action potential amplitude (APA) and a prominent shortening of APD. The ischaemic solution also depolarized the resting membrane potential by about 15 mV. 4. (+)-Sotalol and UK-66,914 did not reverse the shortening of APD induced by perfusion with hypoxic Krebs solution. High concentrations of glibenclamide (10 microM) and UK-68,798 (30 and 60 microM) partially reversed the hypoxia-shortened APD. Glibenclamide was more potent and exhibited a greater time-dependent action than UK-68,798. 5. During experimental ischaemia, the Class III compound E-4031 (10 microM, n = 7) produced small, but significant, increases in the APD90 (11 +/-3 ms after 20 min) which were not clearly time-dependent(14 +/- 4 ms after 30 min). UK-68,798 (10 microM) also produced a small, but insignificant, increase in APD90(12 =/-6 ms at 20 min, n = 4). Higher concentrations of UK-68,798 (30 and 60 microM, n = 4) did not produce a consistently significant increase in APD90 during ischaemia: significance was only attained after 20 min in the presence of 60 microM UK-68,798 (24 +/- 12 ms). However, in marked contrast to the effects of the Class III compounds, glibenclamide (10 microM) produced large time-dependent increases in ischaemic APD90 (34 +/- 11 ms at 7 min, n = 9) which were significant 15 min or more after drug addition(52 +/- 12 ms at 20 min, n = 7; 74 +/- 5 ms at 30 min, n = 6).6. The present microelectrode data suggest that blockers of ATP-dependent potassium channels, such as glibenclamide, might prove to be more effective than Class III compounds against ischaemia-induced shortening of cardiac action potentials. 相似文献
9.
10.
Two forms of glutathione synthetase deficiency have been described. While one form is mild, causing hemolytic anemia, the other more severe form causes 5-oxo-prolinuria with secondary neurological involvement. Despite the existence of two deficiency phenotypes, Southern blots hybridized with a glutathione synthetase cDNA suggest that there is a single glutathione synthetase gene in the human genome. Analysis of somatic cell hybrids showed the human glutathione synthetase gene (GSS) to be located on chromosome 20, and this assignment has been refined to subband 20q11.2 using in situ hybridization. 相似文献