全文获取类型
收费全文 | 27938篇 |
免费 | 2376篇 |
国内免费 | 1024篇 |
专业分类
电工技术 | 1430篇 |
技术理论 | 1篇 |
综合类 | 1533篇 |
化学工业 | 4522篇 |
金属工艺 | 1532篇 |
机械仪表 | 1532篇 |
建筑科学 | 2109篇 |
矿业工程 | 779篇 |
能源动力 | 772篇 |
轻工业 | 1895篇 |
水利工程 | 470篇 |
石油天然气 | 1278篇 |
武器工业 | 207篇 |
无线电 | 2933篇 |
一般工业技术 | 3399篇 |
冶金工业 | 2957篇 |
原子能技术 | 353篇 |
自动化技术 | 3636篇 |
出版年
2024年 | 138篇 |
2023年 | 527篇 |
2022年 | 875篇 |
2021年 | 1212篇 |
2020年 | 967篇 |
2019年 | 759篇 |
2018年 | 797篇 |
2017年 | 995篇 |
2016年 | 853篇 |
2015年 | 1087篇 |
2014年 | 1287篇 |
2013年 | 1585篇 |
2012年 | 1619篇 |
2011年 | 1780篇 |
2010年 | 1486篇 |
2009年 | 1405篇 |
2008年 | 1340篇 |
2007年 | 1245篇 |
2006年 | 1229篇 |
2005年 | 1201篇 |
2004年 | 755篇 |
2003年 | 665篇 |
2002年 | 583篇 |
2001年 | 495篇 |
2000年 | 527篇 |
1999年 | 700篇 |
1998年 | 1182篇 |
1997年 | 759篇 |
1996年 | 708篇 |
1995年 | 533篇 |
1994年 | 451篇 |
1993年 | 368篇 |
1992年 | 209篇 |
1991年 | 190篇 |
1990年 | 150篇 |
1989年 | 112篇 |
1988年 | 119篇 |
1987年 | 74篇 |
1986年 | 58篇 |
1985年 | 40篇 |
1984年 | 31篇 |
1983年 | 17篇 |
1982年 | 21篇 |
1981年 | 22篇 |
1980年 | 18篇 |
1979年 | 10篇 |
1978年 | 9篇 |
1977年 | 42篇 |
1976年 | 85篇 |
1959年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 29 毫秒
61.
CM Wheeler CA Parmenter WC Hunt TM Becker CE Greer A Hildesheim MM Manos 《Canadian Metallurgical Quarterly》1993,20(5):286-289
OBJECTIVES: To confirm the risk factors for genital human papillomavirus (HPV) infection. GOAL OF THIS STUDY: To investigate risk factors for HPV detection apart from the correlated risk factors for cervical neoplasia. STUDY DESIGN: Cervical human papillomavirus (HPV) DNA was assessed in 357 cytologically normal women attending the University of New Mexico student health center. Cervical swab samples were obtained for HPV DNA detection and typing using a PCR-based DNA amplification system. Possible determinants of cervical HPV were examined including age, ethnicity, history of sexually transmitted disease, oral contraceptive use, smoking, age at first intercourse, lifetime number of sex partners, marital status, and history of pregnancy. RESULTS: A 44.3% overall prevalence of cervical HPV was observed. On univariate analysis, factors associated with increasing HPV prevalence included higher lifetime number of sex partners and single marital status. After adjustment for potential confounding variables, we found that HPV prevalence increased with higher lifetime number of sexual partners. CONCLUSION: These findings, along with those from the companion reports in this issue of the journal, support the sexual route of transmission of the virus. 相似文献
62.
An aromatic diamine, CMOMDA, was synthesized and used as a chain extender for reaction injection molding (RIM) polyurethane–urea. The morphology and properties of CMOMDA-, DETDA-, and MDA-extended poly(ether–urethane–urea)s (PEUUs) were measured by IR, DSC, DMS, SEM, and tensile testing apparatus. Well-matched values of Ch and Xut,b/Ch were necessary for aromatic diamine-extended PEUU. DSC and SEM showed that the aggregation state of hard segments might undergo some changes with increasing hard-segment content. © 1994 John Wiley & Sons, Inc. 相似文献
63.
M Pan J Suárez de Lezo A Medina M Romero E Hernández J Segura F Melian F Wangüemert M Landin F Benítez M Amat F Velasco A Torres 《Canadian Metallurgical Quarterly》1997,80(10):1336-1338
Two hundred twenty-eight patients with successful coronary stent implantation were randomized either to protamine administration and femoral sheath removal (group I, n = 117) or no heparin neutralization and delayed sheath removal (group II, n = 111). The hospital stay after treatment was shorter in patients receiving protamine; therefore, protamine use for neutralizing circulating heparin may be safely administered immediately after stent implantation. 相似文献
64.
K Hashimoto M Noshiro S Ohno T Kawamoto H Satakeda Y Akagawa K Nakashima A Okimura H Ishida T Okamoto H Pan M Shen W Yan Y Kato 《Canadian Metallurgical Quarterly》1997,1355(3):303-314
Malignant human gliomas are the most common forms of primary tumors in the central nerve system. Due to their location and invasive nature, treatment so far has been mainly palliative. Thus, understanding the molecular detail of tumor transformation and progression is crucial for developing effective therapeutic strategy for this fetal tumor. Among the genetic alternations found in these tumors, p53 inactivation and PDGF/PDGFR activation represent the early events, and the loss of chromosome 10 and gene amplification and rearrangement of EGFR represent the late events. Studies with both glioma cell lines and primary tumor tissues have strongly suggested that TGF-alpha and EGFR function as an important autocrine loop in supporting proliferation of human glioma, especially in high grade glioma, since elevated TGF-alpha expression is also found in these high grade tumors. Furthermore, down regulation of the expression of TGF-alpha by antisense constructs has been shown to inhibit several types of human tumor cell growth including glioma. Other means of therapeutic approaches using this autocrine loop as a target also include the use of monoclonal antibodies and their cytotoxic conjugated. Considerable understanding of the EGFR-mediated signal transduction pathways has become available recently, which including GRB2/mSOS1 mediated MAP kinase activation; JAK/STATs pathway; PLC-gamma pathway. However, much work still needs to be done before a specific component of these pathways can be applied for effective control of tumor growth in the clinic. 相似文献
65.
The stress and velocity fields ahead of a grain-boundary crack in a material which deforms by Coble creep are investigated for a series of grain sizes using the numerical analysis technique established by Cocks [1–3]. The numerical results are compared with the linear viscous fields obtained by the boundary element method and the finite element method. It is demonstrated that a detailed knowledge of the micromechanical processes of material transport and deformation are required to determine the stress and displacement fields for the grains which immediately surround the crack tip. But the response of the surrounding material can be adequately described from a conventional linear viscous analysis of the problem. 相似文献
66.
67.
从理论上研究了纸张背衬不同衬底的光反射率,得出下列表达式:Rb=Ro+(R∞-Ro)×(1/R∞-Ro)/(1/B-Ro)(B为衬底的光反射率),该式简单实用且物理意义明确。利用上述公式,可将Tappi标准列出的Tappi不透明度C0.89的换算公式简化,并可从理论上定性地讨论纸张不透明度与印刷透印性的关系。 相似文献
68.
The effects of chronic injection of U50,488H (trans-3,4-dichloro-N-[2-(1-pyrrolidinyl)cyclohexyl]benzeacetamidel++ +), a selective kappa opioid agonist, on the properties of the binding sites of tritiated U69593 [(5 alpha,7 alpha,8 beta)-(-)-N-methyl-N-(7-(1-pyrrolidinyl)-1-oxaspiro (4,5)dec-8-yl)benzeneacetamide], another selective kappa opioid agonist, and mechanical responses to U50,488H of the heart were studied. Rats received injection twice a day with U50,488H for 4 days. Binding studies on the crude membrane homogenates revealed that there was no change in maximum binding, but a significant increase in Kd after the treatment, indicating that the number of kappa binding sites remained unchanged whereas the affinity of the binding sites to kappa-agonist decreased. The study on the mechanical responses to U50,488H in the isolated perfused heart preparation showed that although the agonist at 10(-6) M caused MR2266 reversible reductions in heart rate and force of contraction as well as ventricular ectopic beat in the heart of rats in the control group, its effects were absent in the U50,488H-treated group, indicating the development of tolerance to the mechanical effects of U50,488H on the heart. The results indicate that the development of tolerance to the mechanical effects of a kappa-agonist after chronic treatment with the agonist was not accompanied by down-regulation, but only a slight and significant reduction in affinity of kappa binding sites in the rat heart. 相似文献
69.
70.