全文获取类型
收费全文 | 21803篇 |
免费 | 2363篇 |
国内免费 | 1238篇 |
专业分类
电工技术 | 1610篇 |
技术理论 | 1篇 |
综合类 | 1564篇 |
化学工业 | 3072篇 |
金属工艺 | 1114篇 |
机械仪表 | 1366篇 |
建筑科学 | 1610篇 |
矿业工程 | 639篇 |
能源动力 | 658篇 |
轻工业 | 1326篇 |
水利工程 | 598篇 |
石油天然气 | 905篇 |
武器工业 | 166篇 |
无线电 | 2630篇 |
一般工业技术 | 2345篇 |
冶金工业 | 2024篇 |
原子能技术 | 410篇 |
自动化技术 | 3366篇 |
出版年
2024年 | 103篇 |
2023年 | 319篇 |
2022年 | 600篇 |
2021年 | 915篇 |
2020年 | 667篇 |
2019年 | 642篇 |
2018年 | 580篇 |
2017年 | 679篇 |
2016年 | 671篇 |
2015年 | 817篇 |
2014年 | 1108篇 |
2013年 | 1226篇 |
2012年 | 1353篇 |
2011年 | 1548篇 |
2010年 | 1424篇 |
2009年 | 1344篇 |
2008年 | 1242篇 |
2007年 | 1190篇 |
2006年 | 1215篇 |
2005年 | 900篇 |
2004年 | 771篇 |
2003年 | 795篇 |
2002年 | 936篇 |
2001年 | 737篇 |
2000年 | 495篇 |
1999年 | 485篇 |
1998年 | 600篇 |
1997年 | 401篇 |
1996年 | 329篇 |
1995年 | 234篇 |
1994年 | 189篇 |
1993年 | 173篇 |
1992年 | 94篇 |
1991年 | 94篇 |
1990年 | 90篇 |
1989年 | 69篇 |
1988年 | 69篇 |
1987年 | 32篇 |
1986年 | 27篇 |
1985年 | 18篇 |
1984年 | 9篇 |
1983年 | 8篇 |
1982年 | 12篇 |
1981年 | 9篇 |
1980年 | 17篇 |
1979年 | 8篇 |
1978年 | 14篇 |
1977年 | 43篇 |
1976年 | 83篇 |
1951年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
The paper investigates the performance of various time stepping schemes for coupled displacement and pore pressure analysis.
A number of alternative forms of the automatic time stepping method proposed by Sloan and Abbo (1999a) are also presented.
These alternative schemes use different updates for the displacements and pore pressures and also adopt different starting
conditions for the iterations. The automatic schemes are compared with an implicit θ-method, as well as an explicit method,
through analysis of a variety of problems involving undrained loading, drained loading, and consolidation for Mohr-Coulomb
and critical state models. As expected, the numerical results confirm that the explicit scheme is neither accurate nor robust.
Although the implicit θ-method is accurate and fast, it fails to give a solution in a number of cases where the time step
is large. The automatic schemes are shown to be accurate, fast and generally robust. Two of the automatic schemes proposed
never fail to furnish a solution for the cases considered. In addition, all the automatic schemes are able to constrain the
time-stepping (temporal integration) error in the displacements and pore pressures to lie near a prescribed tolerance, provided
the iteration error tolerance is properly chosen. For complex soil models, it is important that the latter is set sufficiently
small in order for the schemes to be able to constrain the time-stepping error to lie within a prescribed tolerance.
Dedicated to the memory of Prof. Mike Crisfield, for his cheerfulness and cooperation as a colleague and friend over many
years. 相似文献
62.
63.
Composite element model for discontinuous rock masses 总被引:2,自引:0,他引:2
64.
通过对碎煤齿环的失效分析 ,找出了影响齿环寿命的因素及薄弱环节 ,并研制成功了最优成分的耐磨材料和堆焊工艺 ,显著提高了生产率和企业的经济效益 相似文献
65.
66.
The molecular mechanisms underlying the clustering and localization of K+ channels in specific microdomains on the neuronal surface are largely unknown. The Shaker subclass of voltage-gated K+ channel alpha-subunits interact through their cytoplasmic C-terminus with a family of membrane-associated putative guanylate kinases, including PSD-95 and SAP97. We show here that heterologous coexpression of either sap97 or PSD-95 with various Shaker-type subunits results in the coclustering of these proteins with the K+ channels. Mutation of the C-terminal sequence (-ETDV) of the Shaker subunit Kv1.4 abolishes its binding to, and prevents its clustering with, SAP97 and PSD-95. Whereas PSD-95 induces plaque-like clusters of K+ channels at the cell surface; however, SAP97 coexpression results in the formation of large round intracellular aggregates into which both SAP97 and the K+ channel proteins are colocalized. The efficiency of surface clustering by PSD-95 varies with different Shaker subunits: striking Kv1.4 clustering occurs in > 60% of cotransfected cells, whereas Kv1.1 and Kv1.2 form convincing clusters with PSD-95 only in approximately 10% of cells. 相似文献
67.
68.
BACKGROUND: Tissue plasminogen activator (tPA) is elevated in cancer patients and is thought to promote tumor angiogenesis by facilitating endothelial cell migration through plasmin-mediated degradation of extracellular matrix. Due to the presence of an epidermal growth factor (EGF)-finger domain in the tPA A-chain and the existence of an endothelial cell (EC) receptor that binds this domain, it was hypothesized that tPA has a direct receptor-mediated effect on EC proliferation, independent of plasmin. METHODS AND RESULTS: Using cultured canine ECs, tPA (7.25 microg/ml, approximately 107 nM) increased proliferation as much as 50 and 170% in the absence and presence of growth factors, respectively. tPA-induced increases in EC proliferation occurred independent of plasmin generation, as the plasmin inhibitor, aprotinin (10 microg/ml) did not inhibit tPA-induced proliferation. However, tPA-induced proliferation was inhibited dose-dependently to a maximum of 78% using a monoclonal antibody against the tPA EGF-finger domain. This antibody, known to inhibit tPA binding to its receptor, did not inhibit tPA-induced plasmin generation. To investigate the role of potential signal transduction pathways, ECs were exposed to lavendustin A, a tyrosine kinase inhibitor, at 33.5 microM (IC50 for basic fibroblast growth factor). Lavendustin A did not inhibit tPA-induced EC proliferation. However, Rp-cAMP, an inhibitor of cAMP-dependent kinases, specifically inhibited tPA-induced EC proliferation in a dose-dependent manner (IC50 = 50.5 microM). Pertussis toxin at maximal concentrations for this system (0.5 ng/ml) did not inhibit tPA-induced EC proliferation. CONCLUSION: These results lend support to the hypothesis that tPA may have a direct receptor-mediated effect on EC proliferation and that this effect occurs independent of plasmin and may be dependent upon protein kinase A activity. 相似文献
69.
对《基于GIS技术的安徽省重大农业气象灾害测评系统》的总体设计方法作了概要介绍。该系统的建立主要是采用GIS技术,综合气候分析、遥感监测、地理环境影响评判等方法,提高对安徽省干旱、洪涝、低温冻害等重大农业气象灾害实时监测、趋势预测,以及对农业生产影响的分析评价结果的准确性。 相似文献
70.