全文获取类型
收费全文 | 13211篇 |
免费 | 721篇 |
国内免费 | 1337篇 |
专业分类
林业 | 1761篇 |
农学 | 930篇 |
基础科学 | 854篇 |
2615篇 | |
综合类 | 5341篇 |
农作物 | 583篇 |
水产渔业 | 992篇 |
畜牧兽医 | 819篇 |
园艺 | 218篇 |
植物保护 | 1156篇 |
出版年
2024年 | 106篇 |
2023年 | 268篇 |
2022年 | 450篇 |
2021年 | 474篇 |
2020年 | 492篇 |
2019年 | 593篇 |
2018年 | 400篇 |
2017年 | 564篇 |
2016年 | 701篇 |
2015年 | 574篇 |
2014年 | 708篇 |
2013年 | 814篇 |
2012年 | 935篇 |
2011年 | 956篇 |
2010年 | 759篇 |
2009年 | 778篇 |
2008年 | 690篇 |
2007年 | 735篇 |
2006年 | 637篇 |
2005年 | 425篇 |
2004年 | 440篇 |
2003年 | 330篇 |
2002年 | 306篇 |
2001年 | 237篇 |
2000年 | 221篇 |
1999年 | 210篇 |
1998年 | 184篇 |
1997年 | 158篇 |
1996年 | 149篇 |
1995年 | 179篇 |
1994年 | 121篇 |
1993年 | 125篇 |
1992年 | 121篇 |
1991年 | 100篇 |
1990年 | 96篇 |
1989年 | 98篇 |
1988年 | 63篇 |
1987年 | 38篇 |
1986年 | 12篇 |
1985年 | 5篇 |
1984年 | 3篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 3篇 |
1980年 | 1篇 |
1976年 | 1篇 |
1963年 | 2篇 |
1962年 | 2篇 |
1956年 | 1篇 |
1955年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
Fernanda S. ORREGO Mathias HÜNE Hugo A. BENÍTEZ Mauricio F. LANDAETA 《Integrative zoology》2023,18(2):372-384
Phenotypic variation in organisms depends on the genotype and the environmental constraints of the habitat that they exploit. Therefore, for marine species inhabiting contrasting aquatic conditions, it is expected to find covariation between the shape and its spatial distribution. We studied the morphology of the head and cephalic sensory canals of the eelpout Austrolycus depressiceps (4.5–22.5 cm TL) across its latitudinal distribution in South Pacific (45°S–55°S). Geometric morphometric analyses show that the shape varied from individuals with larger snout and an extended suborbital canal to individuals with shorter snouts and frontally compressed suborbital canal. There was size variation across the sampled populations, but that size does not have a clear latitudinal gradient. Only 8% of the shape variation relates to this size variation (allometry), represented by a decrease in the relative size of the eye, and a depression of the posterior margin of the head. There were spatial differences in the shape of the head, but these differences were probably caused by allometric effects. Additionally, 2 of the canals of the cephalic lateralis pores and the head shape showed modularity in its development. This study shows that the morphology of marine fish with a shallow distribution varies across distances of hundreds of kilometers (i.e., phenotypic modulation). 相似文献
62.
63.
The test of functional groups of microorganisms in Spiral Up-flow Reactor System and the correlation between microorganisms in the water and the main environmental factors are studied.The results show that the diversity of microorganisms population in the SUFR system is complex and the bio-community formed in the SUFR system is stable.The close relations between abundance of bacteria and nutrients are found.The correlation between heterotrophic bacteria and COD is 0.949.The correlation between organic phosphate bacteria and TP is 0.815. The correlation between nitrosobacteria and NH_3-N is 0.909. The correlation between disnitrifier bacteria and TN is 0.653. 相似文献
64.
A theoretical model is developed for the dropwise condensation heat transfer on the horizontal circular surface with radial gradient surface energy based on the heat transfer model of individual condensate drop and the size distribution model of condensate drop on homogeneous condensation surface.The effect of variation of contact angle on the gradient surface on condensation heat transfer and condensate drop size distribution is taken account of in this model.The theoretical calculation method was obtained to predict the dropwise condensation heat transfer coefficient on the horizontal circular surface with radial gradient surface energy under various wall subcooled temperature,contact angle profile on wall surface,and working fluid.The effects of surface energy gradient,wall subcooled temperature,and thermophysical properties of condensate on the condensation heat transfer are discussed respectively.The calculation results show that the condensation heat transfer coefficient increases slightly with the increase of wall subcooled temperature.As latent heat and surface tension increasing,the condensation heat transfer coefficient increases.A larger surface energy gradient induces a larger condensation heat transfer coefficient. 相似文献
65.
The traditional scheduling for vehicle is option in the fixed network. But it can't satisfy the real time environment. The demand of order is changeable and uncertain in real environment. It is convenient for scheduling transforming it into static data, but can't get the advantage on time. This paper proposes a real time vehicle scheduling on the study of traditional scheduling and discusses the model structure and the key technology for the real time system that establishes the base for develop teal time system. 相似文献
66.
Distribution Network Structure planning is a complex combinatorial optimization problem,which is difficult to solve properly by using traditional optimization methods.In order to solve this problem,Improved Immune Genetic Algorithm is introduced to the distribution network optimal planning. Improved Immune Genetic Algorithm draws into the immune diversity and antibody's density mechanism to maintain the individual's diversity and remains evolution algorithm's global stochastic searching ability,so it can promote diversity and the whole optimal-searching ability of genetic algorithm.The optimal module takes the minimum annual cost as its object,and the capacity and voltage drop of feeder and the radiation of distribution network as its restrictions.According to the require of radiation of distribution network,the spanning tree of the alternative network is taken as the initial solution to speed up the calculation.And the branch-exchange method is used in designing crossover operator and mutation operator to avoid the radiation checking and enhance the optimizing ability.This algorithm has been illustrated effectively by examples,at the same time,the calculation example demonstrates that,the algorithm has higher calculation speed than the traditional immune genetic algorithm. 相似文献
67.
68.
69.
The author introduces a method and experimental procedures that determine dn/dc,molecular weight and its distribution of the hyroxyethyl starch(HES) by means of Gel Permeation Chromatography-Refractive index-Multi-angle laser light scattering detection(GPC-RI-MALLS)techniques.The key experimental technique and results are discussed.The method takes CH3COOH/CH3COONa as mobile phase and solvent.The experiment gets satisfactory results.It can be used as a routine method to determine the hyroxyethyl starch(HES) molecular weight and its distribution. 相似文献
70.
煤水浆(CWM)是一种新型的正在开发的可工业化的石油代用燃料。而将煤水浆用于柴油机则处于试验阶段。流变特性是煤水浆性质判定的主要依据之一。本文将就下列三方面对超细煤木浆与柴油组成的混合液(用作柴油机燃料)的流变特性进行分析:(1)流变模型和流变参量;(2)超细煤水浆与柴油的最佳混合比;(3)触变性。 相似文献