首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   975篇
  免费   117篇
  国内免费   57篇
  2023年   22篇
  2022年   28篇
  2021年   41篇
  2020年   51篇
  2019年   60篇
  2018年   47篇
  2017年   45篇
  2016年   57篇
  2015年   72篇
  2014年   50篇
  2013年   61篇
  2012年   39篇
  2011年   50篇
  2010年   45篇
  2009年   51篇
  2008年   68篇
  2007年   45篇
  2006年   34篇
  2005年   29篇
  2004年   24篇
  2003年   14篇
  2002年   20篇
  2001年   25篇
  2000年   26篇
  1999年   25篇
  1998年   17篇
  1997年   11篇
  1996年   12篇
  1995年   8篇
  1994年   4篇
  1993年   10篇
  1992年   8篇
  1991年   2篇
  1990年   4篇
  1989年   2篇
  1988年   4篇
  1987年   4篇
  1986年   2篇
  1985年   5篇
  1984年   2篇
  1982年   2篇
  1980年   1篇
  1979年   1篇
  1978年   4篇
  1977年   3篇
  1976年   1篇
  1974年   1篇
  1973年   4篇
  1972年   2篇
  1971年   4篇
排序方式: 共有1149条查询结果,搜索用时 15 毫秒
61.
62.
Background and Objectives  Multiple Criteria Decision Aid (MCDA) methods may be employed in a great number of fields. Life Cycle Assessment (LCA) is a specific method among the MCDA Methods. A stage of MCDA methods to be respected in LCA is the comparative evaluation of the environmental impacts. This stage is the most difficult to implement because it is a question of estimating the global environmental impact of the life cycles studied. To achieve this purpose, it is necessary to model the environmental impacts and to apply a Multicriteria Analysis (MCA) method. The problem is to choose the most suitable among the available MCA methods. The objective of this paper is to help the LCA practitioner to make this choice. Methodology  The MCA methods are compared according to their non-compensatory degree, their sensitivity to thresholds, their practicability and their workability. Results and Conclusion  The protocol presented in this paper allows to choose the most appropriate MCA method for a given LCA according to the four previous criteria. This choice will depend on the priorities of the decision maker with concern to the comparison criteria.  相似文献   
63.
(1) Spatially explicit simulation of clonal plant growth is used to determine how ramet-level traits affect ramet density, spatial pattern of ramets and competitive ability of a clonal plant. The simulation model used combines elements of (i) an individual-based model of plant interactions, (ii) an architectural model of clonal plant growth, and (iii) a model of resource translocation within a set of physiologically integrated plant individuals. (2) The effects of two groups of parameters were studied: growth and resource acquisition parameters (resource accumulation, density-dependence of resource accumulation, resource translocation between ramets) and architectural rules (branching angle and probability of branching, internode length). The model was parameterised by values approximating those of clonally growing grasses as closely as possible. The basic parameter values were chosen from a short-turf grassland. Sensitivity analysis was carried out on relevant parameters around three basic points in the parameter space. Both single-species and two-species systems were studied. (3) It is shown that increasing resource acquisition and growth parameters increase ramet density, genet number and competitive ability. Translocation parameters and architectural parameters modify the effects of resource acquisition and growth, but their effect in single-species stands was smaller. (4) The simulations of species with fixed ramet sizes showed that ramet density in single-species stands cannot be used for predicting competitive ability. Increase in resource acquisition and growth parameters was correlated with an increase in equilibrium ramet density and competitive ability. Increasing branching angle, branching probability or internode length lead to an increased competitive ability, but did not affect equilibrium ramet density. Change of architectural parameters could therefore affect competitive ability independently of their effect on the final ramet density. (5) Spatial pattern both in single-species and two-species stands was also highly parameter-dependent. Changes in architectural parameters and in translocation usually lead to pronounced change in the spatial pattern; change in growth and resource acquisition parameters generally had little effect on spatial pattern.  相似文献   
64.
An Escherichia coli mutant, ER437, which was originally isolated for colicin tolerance, was found to carry two amino acid changes in the C-terminal portion of FtsH (HflB). These mutations were demonstrated to reduce the ability of FtsH to degrade the phage lambda CII protein in vivo and in vitro, providing a rationalization for the mutant Hfl phenotype.  相似文献   
65.
66.
区域农业综合生产力的AHP-Fuzzy综合评判   总被引:9,自引:0,他引:9  
根据系统分析原理,在确定区域农业综合生产力系统的层次结构基础上,用层次分析法确定各因素的权重,用模糊多级综合评判法对各区域综合生产力进行综合的评价.具有一定的科学性和实用价格.  相似文献   
67.
Heterogeneous cell populations form an interconnected network that determine their collective output. One example of such a heterogeneous immune population is tumor‐infiltrating lymphocytes (TILs), whose output can be measured in terms of its reactivity against tumors. While the degree of reactivity varies considerably between different TILs, ranging from null to a potent response, the underlying network that governs the reactivity is poorly understood. Here, we asked whether one can predict and even control this reactivity. To address this we measured the subpopulation compositions of 91 TILs surgically removed from 27 metastatic melanoma patients. Despite the large number of subpopulations compositions, we were able to computationally extract a simple set of subpopulation‐based rules that accurately predict the degree of reactivity. This raised the conjecture of whether one could control reactivity of TILs by manipulating their subpopulation composition. Remarkably, by rationally enriching and depleting selected subsets of subpopulations, we were able to restore anti‐tumor reactivity to nonreactive TILs. Altogether, this work describes a general framework for predicting and controlling the output of a cell mixture.  相似文献   
68.
Meta-analysis in applied ecology   总被引:1,自引:0,他引:1  
This overview examines research synthesis in applied ecology and conservation. Vote counting and pooling unweighted averages are widespread despite the superiority of syntheses based on weighted combination of effects. Such analyses allow exploration of methodological uncertainty in addition to consistency of effects across species, space and time, but exploring heterogeneity remains controversial. Meta-analyses are required to generalize in ecology, and to inform evidence-based decision-making, but the more sophisticated statistical techniques and registers of research used in other disciplines must be employed in ecology to fully realize their benefits.  相似文献   
69.
Integrated product policy, according to the European Union, requires reliable data on the impact of consumer products along their life cycles. We argue that this necessarily requires the development of an information tool for hybrid analysis, combining aspects of life-cycle assessment and input-output analysis. A number of requirements in the development of such a hybrid information tool are identified, mainly concerning data and computational structure. For the former, some important points of attention are discussed, whereas for the latter, operational formulas are developed.  相似文献   
70.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号