全文获取类型
收费全文 | 48785篇 |
免费 | 5373篇 |
国内免费 | 3039篇 |
专业分类
电工技术 | 3881篇 |
技术理论 | 3篇 |
综合类 | 3772篇 |
化学工业 | 6956篇 |
金属工艺 | 2987篇 |
机械仪表 | 3178篇 |
建筑科学 | 4053篇 |
矿业工程 | 1536篇 |
能源动力 | 1561篇 |
轻工业 | 3638篇 |
水利工程 | 999篇 |
石油天然气 | 2358篇 |
武器工业 | 527篇 |
无线电 | 5887篇 |
一般工业技术 | 5777篇 |
冶金工业 | 2029篇 |
原子能技术 | 593篇 |
自动化技术 | 7462篇 |
出版年
2024年 | 292篇 |
2023年 | 1103篇 |
2022年 | 1955篇 |
2021年 | 2830篇 |
2020年 | 2111篇 |
2019年 | 1684篇 |
2018年 | 1775篇 |
2017年 | 1935篇 |
2016年 | 1739篇 |
2015年 | 2420篇 |
2014年 | 2825篇 |
2013年 | 3376篇 |
2012年 | 3604篇 |
2011年 | 3617篇 |
2010年 | 3160篇 |
2009年 | 2957篇 |
2008年 | 2896篇 |
2007年 | 2741篇 |
2006年 | 2516篇 |
2005年 | 2076篇 |
2004年 | 1514篇 |
2003年 | 1219篇 |
2002年 | 1295篇 |
2001年 | 1096篇 |
2000年 | 865篇 |
1999年 | 765篇 |
1998年 | 507篇 |
1997年 | 460篇 |
1996年 | 402篇 |
1995年 | 336篇 |
1994年 | 274篇 |
1993年 | 176篇 |
1992年 | 149篇 |
1991年 | 112篇 |
1990年 | 98篇 |
1989年 | 66篇 |
1988年 | 49篇 |
1987年 | 40篇 |
1986年 | 44篇 |
1985年 | 10篇 |
1984年 | 13篇 |
1983年 | 10篇 |
1982年 | 16篇 |
1981年 | 13篇 |
1980年 | 11篇 |
1979年 | 6篇 |
1976年 | 10篇 |
1973年 | 5篇 |
1959年 | 4篇 |
1951年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
51.
Wei Li Zhang Wei Pan Bin Luo Xi Hua Zou Meng Yao Wang 《Photonics Technology Letters, IEEE》2008,20(9):712-714
A theoretical construction of one-to-many (OTM) and many-to-one (MTO) chaos synchronization communications using semiconductor lasers is presented. One center laser provides strong injections (strong link) to other side lasers, and the side lasers also provide weak injections (weak link) to the center one. Simulation results show that the side lasers synchronize with the center laser through injection-locking. In addition, messages transmitted via the strong links or the weak links experience strong chaos pass filtering, enabling us to realize OTM and MTO communications. 相似文献
52.
Stretching dominated Kagome lattices reinforced by carbon fibers were designed and manufactured. The sandwich panels were assembled with bonded laminate skins. The mechanical behaviors of the sandwich panels were tested by out-of-plane compression, in-plane compression and three-point bending. Different failure modes of the sandwich structures were revealed. The experimental results showed that the carbon fiber reinforced lattice grids are much stiffer and stronger than foams and honeycombs. It was found that buckling and debonding dominate the mechanical behavior of the sandwich structures, and that more complaint skin sheets might further improve the overall mechanical performance of the sandwich panels. 相似文献
53.
This paper discusses the fundamental convergence and frequency tracking properties of the recursive-least-squares (RLS) lattice filter in the presence of narrowband interference (NBI) whose frequency varies in discrete steps. It is shown for filters of this type, that the residual forward energy (RFE) after a frequency transition is a function of the input signal-to-noise ratio (SNR), separation of the sequential frequencies and the filter time constant and is exponentially decaying in nature. Reducing the RFE is important in removing unwanted transient artefacts from the desired signal. The convergence behaviour of the RLS algorithm based on a posteriori estimation errors is analysed under a number of conditions by varying the SNR and frequency step size. In order to limit the impact of the RFE while maintaining a minimum frequency tracking error in steady conditions, a fast-converging minimum frequency error (FCMFE) RLS lattice filter is suggested. For comparison, a least-mean-square (LMS) based gradient-adaptive lattice (GAL) filter is also analysed for this class of narrowband interference. 相似文献
54.
B. Meng 《Materials and Structures》1996,29(4):195-205
A knowledge of fractal properties of the pore system is extremely useful with regard to the interrelationships between moisture transport and pore structure. The fractal dimension characterises the egree of resolutiondependence of a property. Given a completely interlaced pore system such as that of sandstone, the fractal dimension of the pore volume, or the porosity, quantifies the cross-sectional variability of the pore channels and is thus of great relevance with regard to transport processes. The fractal dimension of the pore surface describes the surface roughness. A newly-developed measuing technique is presented for the simultaneous determination of fractal dimensions of porosity and pore surface and for establishing fraction radii distributions in order to derive relevant parameters for moisture transport. 相似文献
55.
The width of the transition layer between the crystalline and amorphous zones in nylon 1010 was determined by SAXS with point collimation and long-slit collimation, respectively. The width of the transition layer, E, was found to be 1.7 nm. The results show that the width of the transition layer is independent of crystallinity. 相似文献
56.
The normal prostate is, structurally and functionally, a highly complex glandular tissue in which populations of epithelial and stromal cells interact, one with the other, and are under a constant state of proliferation, differentiation, elimination and selective secondary replenishment so that functional integrity of the tissue is maintained. The ability of normal prostatic tissue to maintain its structure and function is dependent upon retention of cells, generally regarded as 'stem cells', which are able to respond by proliferation and selective differentiation within a wide range of phenotypic alternatives. With respect to cells in the epithelial compartment, replenishment is possible at several levels from within distinct pathways of normal cellular differentiation. It is now appreciated that fully differentiated prostatic epithelial cells retain a far greater degree of phenotypic 'plasticity' than was earlier apparent from morphological examination of the intact tissue. This inherent plasticity, coupled with the ability of the intact tissue to respond to diverse environmental (particularly humoral) stimuli by regenerating a wide and divergent spectrum of functional prostatic epithelial phenotypes is its strength--but also its weakness. Disturbance and distortion of the homeostatic regulatory mechanisms, whether physical or humoral, which control the normal sequence of epithelial proliferation, differentiation and elimination exposes these cells, particularly multipotent 'stem cells', to an increased probability of genetic change, thus resulting in either transient, or permanent, neoplastic transformation. 相似文献
57.
在对Sirius叠前深度偏移软件应用开发的基础上,分析讨论了Sirius 2D叠前深度偏移速度模型建立、层析成像及演、叠前深度偏移以及深度聚焦等技术环节的基本原理,并以莺歌海盆地某测线的处理为例,具体分析了Sirius 2D叠前深度偏移处理的流程、主要参数及时效.文中还分析讨论了莺歌海盆地中央“泥拱带”叠前深度偏移处理的地质效果.实践表明,莺歌海盆地广泛发育的与“泥拱模糊带”有关的构造各有其特殊性,只有通过3D叠前深度偏移处理才能从根本上解决“泥拱模糊带”的成像问题. 相似文献
58.
59.
60.
Jifu Huang Ke Wu 《Microwave Theory and Techniques》1996,44(8):1508-1511
A generalized transmission line matrix (TLM) algorithm is developed in the frequency domain to tackle arbitrary both reciprocal and nonreciprocal anisotropic waveguiding problems. In particular, the modeling issue for arbitrary planar structures is stressed in this work. A new three-dimensional (3-D) condensed node is used to consider the effect of both electric and magnetic constitutive tensors. Various results indicate how the modal dispersive behavior can be manipulated by changing not only the anisotropic characteristics of the substrate, but also the strip/slot geometry as well as the magnitude and orientation of the applied static magnetic field. The present algorithm is useful for CAD and simulation of a large class of gyrotropic waveguide-based microwave and millimeter-wave circuits 相似文献