全文获取类型
收费全文 | 59268篇 |
免费 | 7425篇 |
国内免费 | 4750篇 |
专业分类
电工技术 | 5364篇 |
综合类 | 5871篇 |
化学工业 | 8151篇 |
金属工艺 | 4098篇 |
机械仪表 | 4184篇 |
建筑科学 | 4706篇 |
矿业工程 | 2218篇 |
能源动力 | 1654篇 |
轻工业 | 6205篇 |
水利工程 | 1722篇 |
石油天然气 | 2061篇 |
武器工业 | 902篇 |
无线电 | 6590篇 |
一般工业技术 | 5607篇 |
冶金工业 | 2092篇 |
原子能技术 | 1143篇 |
自动化技术 | 8875篇 |
出版年
2024年 | 312篇 |
2023年 | 1175篇 |
2022年 | 2657篇 |
2021年 | 3563篇 |
2020年 | 2420篇 |
2019年 | 1866篇 |
2018年 | 1920篇 |
2017年 | 2046篇 |
2016年 | 1779篇 |
2015年 | 2865篇 |
2014年 | 3445篇 |
2013年 | 4030篇 |
2012年 | 4845篇 |
2011年 | 5099篇 |
2010年 | 4684篇 |
2009年 | 4466篇 |
2008年 | 4574篇 |
2007年 | 4165篇 |
2006年 | 3718篇 |
2005年 | 2955篇 |
2004年 | 2122篇 |
2003年 | 1504篇 |
2002年 | 1510篇 |
2001年 | 1344篇 |
2000年 | 979篇 |
1999年 | 454篇 |
1998年 | 181篇 |
1997年 | 146篇 |
1996年 | 117篇 |
1995年 | 96篇 |
1994年 | 72篇 |
1993年 | 61篇 |
1992年 | 34篇 |
1991年 | 36篇 |
1990年 | 23篇 |
1989年 | 30篇 |
1988年 | 24篇 |
1987年 | 16篇 |
1986年 | 16篇 |
1985年 | 9篇 |
1984年 | 4篇 |
1983年 | 10篇 |
1982年 | 6篇 |
1981年 | 7篇 |
1980年 | 17篇 |
1979年 | 12篇 |
1965年 | 1篇 |
1960年 | 1篇 |
1959年 | 9篇 |
1951年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
气动贯通式潜孔锤反循环连续取心取样钻进新技术在河南钼矿中应用 总被引:4,自引:0,他引:4
三道庄钼矿勘探生产中钻遇的地层非常复杂,采用其他方法均无法实现钻进,经过分析比较,决定采用贯通式潜孔锤反循环连续取心(样)钻进新技术来解决该地层钻进难、成孔难、取样难等三大问题。文章从钻进技术特点、工作原理等方面对该技术进行详细分析,得出其具有钻进效率高、岩心(样)采取率高、成孔质量好等突出优点。并介绍了钻进主要设备机具的配套、施工工序、操作要点、遇到问题的解决方法等。在河南钼矿露天采石场应用该项技术,有效避免了塌孔和卡钻事故,工程进展顺利、质量好、岩心(样)采取率在98%以上,取得了良好的效果。针对在生产试验中遇到的某些问题,作者提出了一些改进建议。 相似文献
52.
深水海底泥浆举升钻井技术及其应用前景 总被引:2,自引:1,他引:1
为了解决深水钻井中遇到的问题,由Conoco公司领导的工业联合项目组研发了海底泥浆举升钻井(以下简称SMD)技术。采用该技术进行深水钻井时,隔水管内充满海水,泥浆用小直径管线从海底返回,在返回环空中形成两个压力梯度,实现双梯度控压钻井。文中着重介绍了SMD的理论依据、系统工作原理、系统关键设备以及SMD井控程序的HAZOP分析等。从技术适用性、经济性、装备以及可能存在的风险等方面对该技术在南中国海钻井中使用的可行性进行研究,并展望其应用前景。 相似文献
53.
表面贴装工艺流程的关键工序之一就是焊膏印刷,其工艺控制的好坏直接影响着装配的线路板的质量。通过对印刷工艺参数的分析,利用试验设计的方法来找出关键工艺参数,并加以优化设定,从而为控制工序参数奠定基础。 相似文献
54.
文章提出了一种面向XML文档的基于XMLschema并结合RDF的访问控制模型,它实现了对XML文档的细粒度的安全访问控制,同时提供了对XML文档中associationsecurityobject的安全访问控制。 相似文献
55.
1 Introduction High power laser diode arrays (LDA) have many advan- tages such as small volume, long working life, high slope efficiency and high optical density, so they have many applications in medical treatment, material pro- cessing, and for the pumping source of solid laser and etc. But unfortunately, the LDA can not be easy to use directly in these fields because of their poor beam quality and extremely asymmetric divergent beams (!x≈ 5°~10°and !y≈20°~35°, for example), so it … 相似文献
56.
Nd3+:Y0.5Gd0.5VO4晶体生长和基本特性 总被引:5,自引:0,他引:5
Nd^3 :Y0.5Gd0.5VO4晶体作为一种新的激光材料,可以用中频感应加热提拉法生长。X射线粉末衍射分析表明它的结构与Nd^3 :YVO4晶体结构相同,它的晶格常数介于YVO4和NdVO4晶格常数之间。用ICP光谱法测定晶体中Nd^3 含量为0.8at%,分凝系数为0.8,与Nd^3 :GdVO4晶体中Nd^3 的分凝系数0.78相当;用称重法测定其密度为5.00g/cm^3;用稳态纵向热流法测出其室温热导率为12.5W/mK。实验表明Nd^3 :Y0.5Gd0.5VO4晶体有希望作为高功率ID泵浦激光晶体材料。 相似文献
57.
Three-dimensional models, or pharmacophores, describing Euclidean constraints on the location on small molecules of functional
groups (like hydrophobic groups, hydrogen acceptors and donors, etc.), are often used in drug design to describe the medicinal
activity of potential drugs (or ‘ligands’). This medicinal activity is produced by interaction of the functional groups on
the ligand with a binding site on a target protein. In identifying structure-activity relations of this kind there are three
principal issues: (1) It is often difficult to “align” the ligands in order to identify common structural properties that
may be responsible for activity; (2) Ligands in solution can adopt different shapes (or `conformations’) arising from torsional
rotations about bonds. The 3-D molecular substructure is typically sought on one or more low-energy conformers; and (3) Pharmacophore
models must, ideally, predict medicinal activity on some quantitative scale. It has been shown that the logical representation
adopted by Inductive Logic Programming (ILP) naturally resolves many of the difficulties associated with the alignment and
multi-conformation issues. However, the predictions of models constructed by ILP have hitherto only been nominal, predicting
medicinal activity to be present or absent. In this paper, we investigate the construction of two kinds of quantitative pharmacophoric
models with ILP: (a) Models that predict the probability that a ligand is “active”; and (b) Models that predict the actual
medicinal activity of a ligand. Quantitative predictions are obtained by the utilising the following statistical procedures
as background knowledge: logistic regression and naive Bayes, for probability prediction; linear and kernel regression, for
activity prediction. The multi-conformation issue and, more generally, the relational representation used by ILP results in
some special difficulties in the use of any statistical procedure. We present the principal issues and some solutions. Specifically,
using data on the inhibition of the protease Thermolysin, we demonstrate that it is possible for an ILP program to construct
good quantitative structure-activity models. We also comment on the relationship of this work to other recent developments
in statistical relational learning.
Editors: Tamás Horváth and Akihiro Yamamoto 相似文献
58.
59.
The estimation of the link capacity and its available bandwidth in an end-to-end path is crucial for network management, admission
control and flow control for adaptive applications. This paper introduces an estimation mechanism able to accurately estimate
the available bandwidth of all links in an end-to-end path, through its capacity and cross-traffic estimation. The estimation
procedures resort to the dispersions of packet pairs and trains using the concepts of ICMP Timestamp and Traceroute that,
efficiently used together, enable the measurement of the dispersions in all links in the path. These mechanisms were evaluated
through simulation experiments, where we analyzed the influence of the several network parameters on each estimation mechanism.
The results show that these estimation methods are able to accurately estimate both the capacity and the cross-traffic of
all links in a path with moderate length and with low overhead. 相似文献
60.