全文获取类型
收费全文 | 20341篇 |
免费 | 83篇 |
国内免费 | 4篇 |
专业分类
财政金融 | 3068篇 |
工业经济 | 915篇 |
计划管理 | 2815篇 |
经济学 | 4166篇 |
综合类 | 495篇 |
运输经济 | 30篇 |
旅游经济 | 47篇 |
贸易经济 | 4768篇 |
农业经济 | 61篇 |
经济概况 | 1484篇 |
水利工程 | 1961篇 |
信息产业经济 | 45篇 |
邮电经济 | 573篇 |
出版年
2023年 | 16篇 |
2022年 | 15篇 |
2021年 | 25篇 |
2020年 | 25篇 |
2019年 | 56篇 |
2018年 | 2623篇 |
2017年 | 2306篇 |
2016年 | 1480篇 |
2015年 | 129篇 |
2014年 | 144篇 |
2013年 | 283篇 |
2012年 | 649篇 |
2011年 | 2271篇 |
2010年 | 2051篇 |
2009年 | 1596篇 |
2008年 | 1663篇 |
2007年 | 2066篇 |
2006年 | 243篇 |
2005年 | 521篇 |
2004年 | 609篇 |
2003年 | 588篇 |
2002年 | 294篇 |
2001年 | 104篇 |
2000年 | 90篇 |
1999年 | 43篇 |
1998年 | 53篇 |
1997年 | 26篇 |
1996年 | 35篇 |
1995年 | 30篇 |
1994年 | 22篇 |
1993年 | 20篇 |
1992年 | 17篇 |
1991年 | 20篇 |
1990年 | 18篇 |
1989年 | 10篇 |
1988年 | 19篇 |
1987年 | 14篇 |
1986年 | 36篇 |
1985年 | 24篇 |
1984年 | 20篇 |
1983年 | 14篇 |
1982年 | 18篇 |
1981年 | 14篇 |
1980年 | 16篇 |
1979年 | 18篇 |
1978年 | 17篇 |
1977年 | 11篇 |
1976年 | 14篇 |
1973年 | 8篇 |
1971年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
Kim C. Border 《Economic Theory》2007,31(1):167-181
This note uses the Theorem of the Alternative to prove new results on the implementability of general, asymmetric auctions,
and to provide simpler proofs of known results for symmetric auctions. The tradeoff is that type spaces are taken to be finite. 相似文献
62.
Entropy concepts have developed in four general contexts—thermodynamics, communication theory, statistical information theory and social and life sciences. These concepts have five distinct mathematical forms. Ambiguity and complexity in utilization of the concept has been heightened by this multi-faceted heritage. Effective utilization may be strengthened by a sharper articulation of entropy through combinations of literal, mathematical and graphical modes of expression. Geography and planning as user disciplines have important responsibilities in enhancing cross-disciplinary communication of this important adisciplinary concept. Implications of these arguments for the social sciences include the need for caution in drawing social analogies from the ambiguous entropy concepts of statistical mechanics; and an indication of the potential benefits of social science models based on the unambiguous entropic constructs of statistical information theory. 相似文献
63.
We present general results for finding or boundingt
maxB
, the maximum number of arbitrary whole blocks of observations which can be removed from a block design, and still leave all of the elementary treatment contrasts estimable. The block sizes may be larger than the number of treatments. The results are applied to BBDs, reinforced BIBDs and BBDs, BTIBDs, and a series of variance balanced incomplete block designs with two block sizes. Also given for most of these designs, are results fort
max, the maximum number of arbitrary, scattered observations that can become unavailable, and still leave all of the elementary treatment contrasts estimable.The work was undertaken while Dr. Whittinghill was visiting Ohio State University, and supported by a grant from the Natural Sciences Division, Colby College, Waterville, Maine. 相似文献
64.
65.
66.
This work aims to investigate removal efficiency of oxidation and coagulation/flocculation processes, to provide an effective method for the treatment of biologically pre-treated leachate. Leachate containing 985 mg L(-1) COD was treated by using three treatment schemes, i.e. oxidation, coagulation/flocculation and the combined process of coagulation/flocculation followed by oxidation. The application of single oxidation resulted in the effective removal of COD and color up to 80.4 and 83.2%, respectively. However, residual COD values lower than 200 mg L(-1) could only be achieved under intensive experimental conditions (high dosage of Ca(ClO)(2) and prolonged oxidation time). Coagulation/flocculation yielded residual COD values higher than 200 mg L(-1) even at the optimum coagulation conditions. The combined treatment by coagulation/flocculation followed by oxidation yielded final COD lower than 100 mg L(-1) at the following conditions: pre-coagulation with 250 mg L(-1) PFS (poly-ferric sulfate) and over 30-min post-oxidation, or pre-coagulation with 300 mg L(-1) PFS and over 20-min post-oxidation. Hence, pre-coagulation with PFS followed by oxidation with Ca(ClO)(2) was recommended for advanced treatment of biologically treated leachate. 相似文献
67.
Surfactant wastewater is usually difficult to treat due to its toxicity and poor biodegradability. A separate physico-chemical or biochemical treatment method achieves a satisfactory effect with difficulty. In this study, treatment of the wastewater collected from a daily chemical plant by the combination processes of Fe/C internal electrolysis and biological contact oxidation was investigated. For the internal electrolysis process, the optimal conditions were: pH = 4-5, Fe/C = (10-15):1, air-water ratio = (10-20):1 and hydraulic retention time (HRT)= 2 h. For the biological contact oxidation process, the optimal conditions were: HRT = 12 h, DO = 4.0-5.0 mg/L. Treated by the above combined processes, the effluent could meet the I-grade criteria specified in Integrated Wastewater Discharge Standard of China (GB 8978-1996). The results provide valuable information for full-scale linear alkylbenzene sulfonate wastewater treatment. 相似文献
68.
Design of Barrages with Genetic Algorithm Based Embedded Simulation Optimization Approach 总被引:2,自引:2,他引:0
Raj Mohan Singh 《Water Resources Management》2011,25(2):409-429
Barrages are hydraulic structures constructed across rivers to divert flow into irrigation canals or power generation channels.
The most of these structures are founded on permeable foundation. The optimum cost of these structures is nonlinear function
of factors that cause the seepage forces under the structure. There is, however, no procedure to ascertain the basic barrage
parameters such as depth of sheet piles or cutoffs and the length and thickness of floor in a cost–effective manner. In this
paper, a nonlinear optimization formulation (NLOF), which consists of an objective function of minimizing total cost, is solved
using genetic algorithm (GA). The mathematical model that represents the subsurface flow is embedded in the NLOF. The applicability
of the approach has been illustrated with a typical example of barrage profile. The results obtained in this study shows drastic
cost savings when the proposed NLOF is solved using GA than that of using classical optimization technique and conventional
method. A parametric analysis has also been performed to study the effect of varying soil and hydrological conditions on design
parameters and on over all cost. 相似文献
69.
Conventionally drought severity is assessed based on drought indices. Recently the Reconnaissance Drought Index (RDI) was
proposed to assess drought severity based on the precipitation to potential evapotranspiration ratio (P/PET). In this paper
RDI is studied as a bivariate index under a set of assumptions and simplifications. The paper presents a simple computational
procedure for estimating the P/PET ratio for selected reference periods varying from 3 to 12 months, for any return period
of drought. Alternatively, based on this procedure, the severity of any drought episode is rationally assessed. A bivariate
probability analysis is employed based on the assumption that P and PET values are normally distributed and often negatively
correlated. Examples for the application of the proposed procedure are presented using data from several meteorological stations
in Greece. It is shown that the assumption of normality of both P and PET holds for long periods at all examined stations. 相似文献
70.