全文获取类型
收费全文 | 146315篇 |
免费 | 12180篇 |
国内免费 | 14913篇 |
专业分类
系统科学 | 8583篇 |
丛书文集 | 3726篇 |
教育与普及 | 753篇 |
理论与方法论 | 559篇 |
现状及发展 | 967篇 |
研究方法 | 29篇 |
综合类 | 158790篇 |
自然研究 | 1篇 |
出版年
2024年 | 409篇 |
2023年 | 911篇 |
2022年 | 2065篇 |
2021年 | 2574篇 |
2020年 | 2919篇 |
2019年 | 4530篇 |
2018年 | 4699篇 |
2017年 | 5326篇 |
2016年 | 5623篇 |
2015年 | 7048篇 |
2014年 | 8827篇 |
2013年 | 9197篇 |
2012年 | 9466篇 |
2011年 | 10667篇 |
2010年 | 10375篇 |
2009年 | 10729篇 |
2008年 | 10897篇 |
2007年 | 10769篇 |
2006年 | 9703篇 |
2005年 | 8054篇 |
2004年 | 7922篇 |
2003年 | 5522篇 |
2002年 | 5480篇 |
2001年 | 4585篇 |
2000年 | 3798篇 |
1999年 | 2034篇 |
1998年 | 1043篇 |
1997年 | 1105篇 |
1996年 | 546篇 |
1995年 | 437篇 |
1994年 | 706篇 |
1993年 | 1050篇 |
1992年 | 871篇 |
1991年 | 879篇 |
1990年 | 680篇 |
1989年 | 458篇 |
1988年 | 426篇 |
1987年 | 297篇 |
1986年 | 285篇 |
1985年 | 129篇 |
1984年 | 49篇 |
1983年 | 24篇 |
1982年 | 16篇 |
1981年 | 28篇 |
1980年 | 32篇 |
1977年 | 23篇 |
1972年 | 66篇 |
1969年 | 11篇 |
1968年 | 11篇 |
1955年 | 29篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
941.
The key to mass customizing effectively is postponingthe deco upling point of customer order in the supplynetwork. This paper focused on quantitative analysison postponement strategies of multiple decouplingpoints in mass customization to improve operating 相似文献
942.
吴嘉麟 《东华大学学报(英文版)》2003,20(2)
In this paper, the model of inverse cascade fractal super-blocks along one direction (in the positive or negative) in the 3-dimensional space is developed to describe the self-similar motion in macromolecular system. Microscopically the cohesive and dispersed states of the motion blocks are co- existent states with vastly different probability of occurrence. Experimental results and theoretical analysis show that the microscopic cohesive state energy and dispersed state energy of each motion block are respectively equal to the macroscopic glassy state energy kTg and molten state energy kTm of the system. This singularity unveils topologically the non-integrability, mathematically the anholonomy, and macroscopically the emergent property. This singularity also reveals that the glass, viscoelastic and melt states are three distinct emergent properties of macromolecular motion from a macroscopic viewpoint. The fractal concept of excluded volume is introduced to depict the random motion at various scales in 相似文献
943.
Multi-objective Scheduling Using an Artificial Immune System 总被引:1,自引:0,他引:1
944.
The influences of carboxymethyl starch used as stabilizer upon the stability of native cornstarch-polyvinyl alcohol blend pastes for warp sizing have been investigated. The effect of the modified starch on the paste stability was evaluated in terms of the initial demixing time and the volume percentage of separated starch. The carboxymethyl starch with a series of different degrees of substitution was prepared in ethanol dispersion by varying the amount of monochloroacetic acid reacted with refined native cornstarch. The paste stability strongly depends on the modification extent and amount of carboxymethyl starch used, and on native starch content in the paste. Increase in the modification extent and/or the amount of the modified starch effectively retards the phase separation and reduces the separation extent of native cornstarch-polyvinyl alcohol blend pastes. Moreover, the mechanism and favorable modification extent of carboxymethyl starch for enhancing paste stability are also investigated and disc 相似文献
945.
A group of grafted PET fibers with different graft yield are formed by grafting acrylamide onto the PET main chains. The structure of grafted fibers are studied by scanning electronic microscope ( SEM ), infra-red spectrophotometer ( IR ), and differential scanning calorimetry(DSC). At the same time, the moisture regain, dyeability, strength, and elongation at break of the samples are measured and their relations with structural changes are discussed. Compared with ungrafted fiber, shape of the fiber cross-section, IR characteristic absorption peaks, and melting behavior of the grafted fibers have been changed, causing the fiber dyeability and moisture regain to be increased, and mechanical properties to be changed. 相似文献
946.
This paper deals with the use of optimal control techniques in large-scale water distribution networks. According to the network characteristics and actual state of the water supply system in China, the implicit model, which may be solved by utilizing the hierarchical optimization method,is established. In special, based on the analyses of the water supply system containing variable-speed pumps, a software tool has been developed successfully. The application of this model to the city of Shenyang (China) is compared to experiential strategy. The results of this study show that the developed model is a very promising optimization method to control the large-scale water sup-ply systems. 相似文献
947.
用锐钛型纳米TiO2制备了纳米级SO4^2-/TiO2固体超强酸,分析了硫酸浓度不同时其比表面积、失重率、红外光谱及催化活性的不同。当硫酸浓度为1.0mol/L时,它在450~900℃的失重率为3.3%,比表面积为105.2m^2/g,对乙酸和丁醇酯化反应的酯化率达到98.4%。玻璃球负载纳米级SO4^2-/TiO2固体超强酸的重复使用性能好,在乙酸和丁醇的酯化反应中重复使用9次后的酯化率才由初次的99.3%变为84.9%。 相似文献
948.
Dynamical framework with blocking topography coordinates for atmospheric GCM and its validation 总被引:1,自引:0,他引:1
Lin Zhaohui ZHANG Ming LIANG Danqing WANG Aihui ZHANG Dongling ZENG Qingcun 《科学通报(英文版)》2003,48(Z2):9-17
The dynamical framework with Blocking Topography Coordinates (hereafter, BTC), which is suited to handle the steep topography for the atmospheric general circulation models, is presented in this paper, together with its validation results. The integral properties of both the differential and finite-difference equations for the BTC dynamical core are: gross mass conservation, quadratic conservation for advection terms, Coriolis force does not change the kinetic energy, conservation of total available energy. The improved nonlinear iteration scheme is utilized for the time-integration. The energy conservation for BTC dynamical core is validated by using the integration results from 9-layer and 21-layer version respectively. Comparison results show that, the changes of the kinetic energy and total available potential energy during the integration are quite close for both the BTC dynamical framework and the dynamical framework of IAP 9-level and IAP 21-level AGCM, and this may suggest that the BTC dynamical core can be used for long-term integration with good computational stability. Furthermore, the BTC dynamical core has the advantage over the terrain following (sigma) coordinates in its better representation of the influence of the large-scale topography on the atmospheric general circulation. Finally, the correctness and reasonableness of the BTC dynamical core has been further proved by the numerical simulation of the topography influence on the quasi-stationary planetary wave with 21-layer version of BTC dynamical framework. 相似文献
949.
Using a global OGCM and its relevant coupled ocean-atmosphere GCM with the contemporary, 6 MaBP and 14 MaBP oceanic topography, respectively, a series of numerical experiments are implemented in order to investigate the effect of the north shift of Australian continent on the tropical oceanic circulation, especially the formation of the western Pacific warm pool. The numerical experiments of the individual OGCM forced by the modern atmospheric circulation indicate that the closure of Indonesian passage results in warming in the tropical Pacific Ocean and cooling in the tropical Indian Ocean; furthermore, it also results in change in source of the Indonesian Through Flow (ITF) water, e.g. ITF mainly originates from the south Pacific at 14 MaBP, but it mainly originates from the north Pacific now. The coupled model shows similar results as the individual OGCM qualitatively. 相似文献
950.