全文获取类型
收费全文 | 96370篇 |
免费 | 10399篇 |
国内免费 | 5870篇 |
专业分类
电工技术 | 7561篇 |
技术理论 | 4篇 |
综合类 | 7025篇 |
化学工业 | 14653篇 |
金属工艺 | 5595篇 |
机械仪表 | 6650篇 |
建筑科学 | 7308篇 |
矿业工程 | 3137篇 |
能源动力 | 2892篇 |
轻工业 | 6964篇 |
水利工程 | 2106篇 |
石油天然气 | 4980篇 |
武器工业 | 1102篇 |
无线电 | 12196篇 |
一般工业技术 | 10897篇 |
冶金工业 | 4249篇 |
原子能技术 | 1311篇 |
自动化技术 | 14009篇 |
出版年
2024年 | 430篇 |
2023年 | 1696篇 |
2022年 | 3267篇 |
2021年 | 4901篇 |
2020年 | 3454篇 |
2019年 | 2923篇 |
2018年 | 3131篇 |
2017年 | 3362篇 |
2016年 | 3166篇 |
2015年 | 4497篇 |
2014年 | 5510篇 |
2013年 | 6498篇 |
2012年 | 7390篇 |
2011年 | 7798篇 |
2010年 | 6738篇 |
2009年 | 6472篇 |
2008年 | 6278篇 |
2007年 | 5816篇 |
2006年 | 5558篇 |
2005年 | 4397篇 |
2004年 | 3140篇 |
2003年 | 2487篇 |
2002年 | 2379篇 |
2001年 | 1950篇 |
2000年 | 1678篇 |
1999年 | 1490篇 |
1998年 | 1135篇 |
1997年 | 950篇 |
1996年 | 847篇 |
1995年 | 721篇 |
1994年 | 535篇 |
1993年 | 348篇 |
1992年 | 306篇 |
1991年 | 250篇 |
1990年 | 212篇 |
1989年 | 185篇 |
1988年 | 119篇 |
1987年 | 96篇 |
1986年 | 70篇 |
1985年 | 59篇 |
1984年 | 47篇 |
1983年 | 43篇 |
1982年 | 38篇 |
1981年 | 32篇 |
1980年 | 42篇 |
1979年 | 29篇 |
1978年 | 22篇 |
1977年 | 17篇 |
1976年 | 36篇 |
1973年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
论文提出了一种混沌通信系统的噪音衰减算法,该算法利用混沌同步现象在接收端获得正确的噪音估计值,从而从接收信号中滤除噪音恢复出正确的信号。通过数值仿真试验表明该方法是可行的。 相似文献
102.
论文将Fermat素性检验的思想运用于不可约多项式的判断,给出了一个对于不可约判断问题的Monte Carlo 算法,分析了该算法的计算复杂度问题,并且给出了次数在200以内的检验结果。 相似文献
103.
With the creation of a pattern recognition system for metal transfer mode, this article has collected five kinds of spectrum signals in gas metal arc welding (MIG, MAG and CO2) and take them as training samples. These samples have been pretreated by computer, several key characteristic parameters of the spectrum signal have been creatively extracted, and a corresponding recognition function and a minimum-distance-classifier have been constructed. The results show that the pattern recognition of several kinds of metal transfer modes for the metal gas arc welding can be done successfully, and relative important parameters in welding process, such as the frequency of droplet transfer and the approximate diameter of each droplet, can also be obtained. 相似文献
104.
Flow-mode static and dynamic laser light scattering (SLS/DLS) studies of polymers, including polystyrene, polyethylene, polypropylene and poly(dimethylsiloxane) (PDMS), in 1,2,4-trichlorobenzene (TCB) at 150 °C were performed on a high temperature gel permeation chromatography (GPC) coupled with a SLS/DLS detector. Both absolute molecular weight (M) and molecular sizes (radius of gyration, Rg and hydrodynamic radius, Rh) of polymers eluting from the GPC columns were obtained simultaneously. The conformation of different polymers in TCB at 150 °C were discussed according to the scaling relationships between Rg, Rh and M and the ρ-ratio (ρ=Rg/Rh). Flow-mode DLS results of PDMS were verified by batch-mode DLS study of the same sample. The presented technique was proved to be a convenient and quick method to study the shape and conformation of polymers in solution at high temperature. However, the flow-mode DLS was only applicable for high molecular weight polymers with a higher refractive index increment such as PDMS. 相似文献
105.
106.
Mining constrained gradients in large databases 总被引:1,自引:0,他引:1
Dong G. Han J. Lam J.W.M. Pei J. Wangm K Zou W. 《Knowledge and Data Engineering, IEEE Transactions on》2004,16(8):922-938
Many data analysis tasks can be viewed as search or mining in a multidimensional space (MDS). In such MDSs, dimensions capture potentially important factors for given applications, and cells represent combinations of values for the factors. To systematically analyze data in MDS, an interesting notion, called "cubegrade" was recently introduced by Imielinski et al. [2002], which focuses on the notable changes in measures in MDS by comparing a cell (which we refer to as probe cell) with its gradient cells, namely, its ancestors, descendants, and siblings. We call such queries gradient analysis queries (GQs). Since an MDS can contain billions of cells, it is important to answer GQs efficiently. We focus on developing efficient methods for mining GQs constrained by certain (weakly) antimonotone constraints. Instead of conducting an independent gradient-cell search once per probe cell, which is inefficient due to much repeated work, we propose an efficient algorithm, LiveSet-Driven. This algorithm finds all good gradient-probe cell pairs in one search pass. It utilizes measure-value analysis and dimension-match analysis in a set-oriented manner, to achieve bidirectional pruning between the sets of hopeful probe cells and of hopeful gradient cells. Moreover, it adopts a hypertree structure and an H-cubing method to compress data and to maximize sharing of computation. Our performance study shows that this algorithm is efficient and scalable. In addition to data cubes, we extend our study to another important scenario: mining constrained gradients in transactional databases where each item is associated with some measures such as price. Such transactional databases can be viewed as sparse MDSs where items represent dimensions, although they have significantly different characteristics than data cubes. We outline efficient mining methods for this problem. 相似文献
107.
PKI/CA技术综述 总被引:6,自引:0,他引:6
公开密钥基础设施(PKI)是解决网络安全的技术.典型PKI应用系统包括安全Web、注册机构(RA)、认证机构(CA)、目录(LDAP)和数据库等服务器.RA验证客户证书申请后提交CA.CA检查信息完整和数字签名正确后把证书存放到证书库和目录服务器,并将签发证书序列号通知客户和RA.客户即可使用该号通过目录服务器下载证书.1993年以来,美、加、欧洲、韩、日等国已相继展开PKI研究.我国2001年将PKI列入十五863计划,并着手解决PKI标准化、CA互联互通等关键技术问题。 相似文献
108.
109.
Nanocrystalline Gd2O3:A (A=Eu3+, Dy3+, Sm3+, Er3+) phosphor films and their patterning were fabricated by a Pechini sol–gel process combined with a soft lithography. X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM) and optical microscopy, UV/vis transmission and photoluminescence (PL) spectra as well as lifetimes were used to characterize the resulting films. The results of XRD indicated that the films began to crystallize at 500 °C and that the crystallinity increased with the elevation of annealing temperatures. Uniform and crack free non-patterned phosphor films were obtained by optimizing the composition of the coating sol, which mainly consisted of grains with an average size of 70 nm and a thickness of 550 nm. Using micro-molding in capillaries technique, we obtained homogeneous and defects-free patterned gel and crystalline phosphor films with different stripe widths (5, 10, 20 and 50 μm). Significant shrinkage (50%) was observed in the patterned films during the heat treatment process. The doped rare earth ions (A) showed their characteristic emission in crystalline Gd2O3 phosphor films due to an efficient energy transfer from Gd2O3 host to them. Both the lifetimes and PL intensity of the rare earth ions increased with increasing the annealing temperature from 500 to 900 °C, and the optimum concentrations for Eu3+, Dy3+, Sm3+, Er3+ were determined to be 5, 0.25, 1 and 1.5 mol% of Gd3+ in Gd2O3 films, respectively. 相似文献
110.
空间数据立方体的物化视图选择方法研究 总被引:1,自引:0,他引:1
针对决策支持系统(DSS)中集成空间分析能力的应用趋势,研究基于空间数据仓库的一种决策分析工具——空间在线分析处理(Spatial OLAP),拟解决影响空间OLAP在线响应的瓶颈难点——空间数据立方体的物化问题。首先系统地提出空间OLAP的模型,然后对现有空间度量物化视图选择方法进行改进,提出了双向空间Greedy算法。实验证明.该算法在降低选择时间和求解质量两方面具有更好的表现。 相似文献