首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   1315篇
  免费   9篇
  国内免费   2篇
电工技术   6篇
综合类   1篇
化学工业   36篇
金属工艺   13篇
机械仪表   17篇
建筑科学   26篇
矿业工程   1篇
能源动力   14篇
轻工业   15篇
水利工程   4篇
石油天然气   1篇
无线电   24篇
一般工业技术   98篇
冶金工业   1037篇
原子能技术   5篇
自动化技术   28篇
  2023年   4篇
  2022年   3篇
  2021年   8篇
  2020年   4篇
  2019年   7篇
  2018年   6篇
  2017年   3篇
  2016年   4篇
  2015年   6篇
  2014年   8篇
  2013年   26篇
  2012年   14篇
  2011年   29篇
  2010年   23篇
  2009年   23篇
  2008年   20篇
  2007年   14篇
  2006年   11篇
  2005年   14篇
  2004年   4篇
  2003年   10篇
  2002年   10篇
  2001年   7篇
  2000年   5篇
  1999年   29篇
  1998年   275篇
  1997年   142篇
  1996年   133篇
  1995年   65篇
  1994年   63篇
  1993年   72篇
  1992年   10篇
  1991年   18篇
  1990年   13篇
  1989年   21篇
  1988年   26篇
  1987年   14篇
  1986年   18篇
  1985年   17篇
  1984年   5篇
  1983年   3篇
  1982年   14篇
  1981年   7篇
  1980年   10篇
  1978年   5篇
  1977年   28篇
  1976年   64篇
  1975年   2篇
  1974年   3篇
  1954年   1篇
排序方式: 共有1326条查询结果,搜索用时 15 毫秒
1.
2.
E-democracy, the design and development of new techniques for improving communication between public administration and citizens, is a major application field for natural language processing and language engineering. Helping citizens access information in a friendly, intuitive way is the primary objective of a global e-democracy framework. The E-democracy European Network project (EDEN) aimed at discovering whether a particular NLP (natural language processing) approach could further e-democracy by increasing citizens' participation in the decision-making process. The goal was twofold: to test whether e-democracy requirements could be meet using advanced linguistic technology and to test whether augmented phrase structure grammars (APSGs) were robust and well-assessed enough to use in a real-world environment. Also, the aim is to develop two toolsets to improve communication between PAs and citizens in the context of urban planning: a set of NLP-based tools to simplify access to information and knowledge and a set of forum and polling devices  相似文献   
3.
Replacement of the pyridinium ring of 6,11-ethanobenzo[b]quinolizinium cations with thiazolium (4a and 4b) and N-methylimidazolium (4c and 4d) resulted in equipotent compounds in the [3H]TCP binding assay. The corresponding N-methyl-1,2,4-triazolium analogs were less potent in this assay. The thiazolium derivative 4b, with a Ki = 2.9 nM, is being evaluated as a possible neuroprotective N-methyl-D-aspartic acid (NMDA) antagonist.  相似文献   
4.
5.
Safety, local and systemic immunomodulation, and tumor response to treatment with aerosolized natural interleukin 2 (nIL-2) applied five times a day were studied in a Phase I trial in 16 patients with pulmonary malignancies refractory to conventional therapy. The toxicity of inhaled nIL-2 was different from that observed after systemic administration. Reversible airway irritation causing a nonproductive cough represented the dose-limiting toxicity. Mild to moderate reduction of the vital capacity and forced expiratory volume (FEV1) with minor effects on relative FEV1, peak expiratory flow, airway resistance, and PaO2 was experienced by individual patients. In 14 patients suffering from pulmonary metastases due to renal cell cancer, one durable complete response, one partial response, and one mixed response were observed. Inhalation of nIL-2 aerosol resulted in a dose-dependent expansion of pulmonary immunocompetent cells in bronchoalveolar lavage fluid. Posttreatment bronchoalveolar lavage showed an activated lymphocyte phenotype with increased HLA-DR expression. The only systemic biological effect detectable in peripheral blood was a marked increase of soluble interleukin 2 receptor serum levels. We conclude that treatment with aerosolized nIL-2 is an effective means for site-specific immunomodulation and deserves further investigation for the treatment of malignant and inflammatory lung disease.  相似文献   
6.
7.
Time-dependent thrombolytic resistance is a critical problem in thrombolytic therapy for acute myocardial infarction. Platelets have been regarded as the main source of plasminogen activator inhibitor-1 (PAI-1) found in occlusive platelet-rich clots. However, endothelial cells are also known to influence the fibrinolytic capacity of blood vessels, but their ability to actively mediate time-dependent thrombolytic resistance has not been fully established. We will show that, in vitro, tumor necrosis factor-alpha-stimulated endothelial cells secrete large amounts of PAI-1 over a period of hours, which then binds to fibrin and protects the clot from tissue plasminogen activator-induced fibrinolysis. In vivo, endothelial cells covering atherosclerotic plaques are influenced by cytokines synthesized by plaque cells. Therefore, we propose that continuous activation of endothelial cells in atherosclerotic blood vessels, followed by elevated PAI-1 secretion and storage of active PAI-1 in the fibrin matrix, leads to clot stabilization. This scenario makes endothelial cells a major factor in time-dependent thrombolytic resistance.  相似文献   
8.
9.
Five cell lines selected for resistance to the cytotoxicity of inhibitors of DNA topoisomerase II have point mutations in the gene that codes for the M(r) 170,000 form of this enzyme. In each case, the mutation results in an amino acid change in or near an ATP binding sequence of the M(r) 170,000 isozyme of topoisomerase II. We used single-strand conformational polymorphism analysis to screen for similar mutations in other drug-resistant cell lines or in leukemic cells from patients previously treated with etoposide or teniposide. We also analyzed the region of the gene that codes for amino acids adjacent to the tyrosine at position 804 of topoisomerase II which binds covalently to DNA. CEM/VM-1, CEM/VM-1-5, and HL-60/AMSA human leukemic cell lines were used as controls; 3 of 3 known mutations were detected by migration differences of polymerase chain reaction products from the RNA extracted from these three lines. A previously unknown mutation was found in the tyrosine 804 region of the M(r) 170,000 topoisomerase II expressed by CEM/VM-1 and CEM/VM-1-5 cells. Sequence analysis showed that substitution of a T for a C at nucleotide 2404 resulted in an amino acid change of a serine for a proline at amino acid 802. No mutations in any of the ATP binding sequences or in the tyrosine 804 region were detected in polymerase chain reaction products from RNA extracted from human leukemia HL-60/MX2 or CEM/MX1 cells (both cell lines selected for resistance to mitoxantrone) or in human myeloma 8226/Dox1V cells (selected for resistance by simultaneous exposure to doxorubicin and verapamil). No mutations were detected in polymerase chain reaction products from RNA extracted from blasts of 15 patients with relapsed acute lymphocytic leukemia, previously treated with etoposide or teniposide. We conclude that: (a) single-strand conformational polymorphism analysis is useful for screening for mutations in topoisomerase II; (b) resistance to the cytotoxicity of inhibitors of DNA topoisomerase II is not always associated with mutations in ATP binding sequences or the active site tyrosine region of M(r) 170,000 topoisomerase II; and (c) mutations similar to those detected in drug resistant cells selected in culture have not been identified in blast cells from patients with relapsed acute lymphocytic leukemia, previously treated with etoposide or teniposide.  相似文献   
10.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号