全文获取类型
收费全文 | 39172篇 |
免费 | 3045篇 |
国内免费 | 1757篇 |
专业分类
电工技术 | 2019篇 |
技术理论 | 3篇 |
综合类 | 4726篇 |
化学工业 | 4894篇 |
金属工艺 | 1466篇 |
机械仪表 | 1485篇 |
建筑科学 | 6374篇 |
矿业工程 | 2222篇 |
能源动力 | 1103篇 |
轻工业 | 3177篇 |
水利工程 | 1964篇 |
石油天然气 | 2069篇 |
武器工业 | 176篇 |
无线电 | 2282篇 |
一般工业技术 | 3372篇 |
冶金工业 | 2632篇 |
原子能技术 | 357篇 |
自动化技术 | 3653篇 |
出版年
2024年 | 160篇 |
2023年 | 537篇 |
2022年 | 913篇 |
2021年 | 1098篇 |
2020年 | 981篇 |
2019年 | 895篇 |
2018年 | 792篇 |
2017年 | 915篇 |
2016年 | 1069篇 |
2015年 | 1163篇 |
2014年 | 2034篇 |
2013年 | 1925篇 |
2012年 | 2448篇 |
2011年 | 2661篇 |
2010年 | 2092篇 |
2009年 | 2305篇 |
2008年 | 2091篇 |
2007年 | 2708篇 |
2006年 | 2494篇 |
2005年 | 2256篇 |
2004年 | 1917篇 |
2003年 | 1782篇 |
2002年 | 1510篇 |
2001年 | 1271篇 |
2000年 | 1058篇 |
1999年 | 860篇 |
1998年 | 619篇 |
1997年 | 534篇 |
1996年 | 468篇 |
1995年 | 433篇 |
1994年 | 329篇 |
1993年 | 283篇 |
1992年 | 227篇 |
1991年 | 147篇 |
1990年 | 164篇 |
1989年 | 142篇 |
1988年 | 118篇 |
1987年 | 94篇 |
1986年 | 64篇 |
1985年 | 60篇 |
1984年 | 50篇 |
1983年 | 24篇 |
1982年 | 25篇 |
1981年 | 32篇 |
1980年 | 28篇 |
1979年 | 32篇 |
1978年 | 18篇 |
1976年 | 18篇 |
1975年 | 20篇 |
1974年 | 18篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
21.
22.
考察了双河油田双河联、江河联注入水堵塞地层的因素;膨胀性黏土,悬浮固体颗粒。细菌及悬浮污油。含膨胀性黏土的双河南、双河北及不含膨胀性黏土的双江岩心粉,在注入水中相对于地层水中的体积膨胀度分别为14.5%、11.1%及0.02%;注入100PV不含悬浮颗粒的等体积比地层水、注入水混合水使双河、双江岩心渗透率分别下降7%和4%、9%和7%。注入水中悬浮颗粒引起岩心渗透率下降,粒径越大、颗粒浓度越大、注入量越大,则渗透率越低。在粒径2.1μm或颗粒浓度3mg/L前后下降幅度变化较大。注入水中硫酸盐还原菌引起岩心渗透率下降,含菌量越大则渗透率开始下降时的注水量越小,注入含菌50个/L的水100PV使岩心渗透率下降7%。岩心对注水合油量敏感,注入含油量20mg/L的水50PV使岩心渗透率下降20%。在岩心注水实验中渗透率下降最严重的是双河南岩心,其次是双河北岩心.江河岩心较轻,注入精细过滤水的双河北岩心渗透率下降大大减少.说明悬浮固体是造成注水堵塞的主要因素。为了解除双河油田注水井的堵塞,研制了含黏土稳定剂、缓蚀剂、铁离子稳定剂、互溶剂的土酸液,与南阳油田使用的低伤害酸液一起,用于1口注水井的解堵,效果良好。图7表4参5。 相似文献
23.
24.
针对辽河油区超稠油采油污水的特点,采用Fenton试剂催化氧化,对采油污水处理进行研究。实验研究及现场应用结果表明,此方法对污水的CODCr具有良好的去除效果。处理后污水经过简单生化,进一步降解污染物,能够实现稳定迭标排放,且具有能耗低、运行成本低和操作简单等特点。 相似文献
25.
论文比较详细地阐述了涉密网主机系统所面临的安全隐患,提出了涉密网主机安全防护所要解决的几个技术问题,并就可能实现的技术方法进行了探讨和比较。 相似文献
26.
Fatigue crack propagation of multiple coplanar cracks with the coupled extended finite element/fast marching method 总被引:1,自引:0,他引:1
A numerical technique for modeling fatigue crack propagation of multiple coplanar cracks is presented. The proposed method couples the extended finite element method (X-FEM) [Int. J. Numer. Meth. Engng. 48 (11) (2000) 1549] to the fast marching method (FMM) [Level Set Methods & Fast Marching Methods: Evolving Interfaces in Computational Geometry, Fluid Mechanics, Computer Vision, and Materials Science, Cambridge University Press, Cambridge, UK, 1999]. The entire crack geometry, including one or more cracks, is represented by a single signed distance (level set) function. Merging of distinct cracks is handled naturally by the FMM with no collision detection or mesh reconstruction required. The FMM in conjunction with the Paris crack growth law is used to advance the crack front. In the X-FEM, a discontinuous function and the two-dimensional asymptotic crack-tip displacement fields are added to the finite element approximation to account for the crack using the notion of partition of unity [Comput. Meth. Appl. Mech. Engng. 139 (1996) 289]. This enables the domain to be modeled by a single fixed finite element mesh with no explicit meshing of the crack surfaces. In an earlier study [Engng. Fract. Mech. 70 (1) (2003) 29], the methodology, algorithm, and implementation for three-dimensional crack propagation of single cracks was introduced. In this paper, simulations for multiple planar cracks are presented, with crack merging and fatigue growth carried out without any user-intervention or remeshing. 相似文献
27.
This review article is devoted to the materials containing niobium, which have been discovered or developed in the past few years and exhibit the potential application in heterogeneous catalysis. Niobium oxides and mixed oxides as well as sulfides, nitrides (oxynitrides), carbides (oxycarbides), and phosphates are considered. Among the catalytic processes in which Nb-containing materials were tested, liquid and gas phase oxidation is described in details, and the role of niobium in the prevention of the catalyst from SO2 poisoning is mentioned. 相似文献
28.
The problem of operating freeze drying of pharmaceutical products in vials placed in trays of a freeze dryer to remove free water (in frozen state) at a minimum time was formulated as an optimal control problem. Two different types of freeze dryer designs were considered. In type I freeze dryer design, upper and lower plate temperatures were controlled together, while in type II freeze dryer design, upper and lower plate temperatures were controlled independently. The heat input to the material being dried and the drying chamber pressure were considered as control variables. Constraints were placed on the system state variables by the melting and scorch temperatures during primary drying stage. Necessary conditions of optimality for the primary drying stage of freeze drying process in vials are derived and presented. Furthermore, an approach for constructing the optimal control policies that would minimize the drying time for the primary drying stage was given. In order to analyze optimal control policy for the primary drying stage of the freeze-drying process in vials, a rigorous multi-dimensional unsteady state mathematical model was used. The theoretical approach presented in this work was applied in the freeze drying of skim milk. Significant reductions in the drying times of primary drying stage of freeze drying process in vials were obtained, as compared to the drying times obtained from conventional operational policies. 相似文献
29.
五.牛奶厂的清洗。目前,牛奶厂采用的清洗方式主要是CIP清洗(Cleaning in place),原地清洗或称定置清洗,即在基本不拆卸或挪动机械装置和管线的情况下对生产过程中能与牛奶发生接触的设备表面进行的清洗。其冲刷、清洗、灭菌的整个过程全部实现了自动化因此大大降低了劳动强度。而有一些不 相似文献
30.
套保稠油油田火烧油层可行性分析 总被引:2,自引:1,他引:1
从火烧油层的筛选标准、实际地质条件及室内物理模拟实验入手,对该油田火烧可行性进行了分析。分析结果认为,套保油田进行火烧总体上是可行的,在实际火烧时应避开底水的影响,火烧区域应选在构造高部位或仅烧其主力层。 相似文献