全文获取类型
收费全文 | 29174篇 |
免费 | 1106篇 |
国内免费 | 2篇 |
专业分类
林业 | 4666篇 |
农学 | 1709篇 |
基础科学 | 185篇 |
5575篇 | |
综合类 | 1509篇 |
农作物 | 2663篇 |
水产渔业 | 2850篇 |
畜牧兽医 | 6693篇 |
园艺 | 1368篇 |
植物保护 | 3064篇 |
出版年
2023年 | 127篇 |
2022年 | 194篇 |
2021年 | 374篇 |
2020年 | 396篇 |
2019年 | 350篇 |
2018年 | 3174篇 |
2017年 | 3124篇 |
2016年 | 1713篇 |
2015年 | 537篇 |
2014年 | 575篇 |
2013年 | 856篇 |
2012年 | 1788篇 |
2011年 | 3007篇 |
2010年 | 2505篇 |
2009年 | 1645篇 |
2008年 | 2076篇 |
2007年 | 2264篇 |
2006年 | 662篇 |
2005年 | 729篇 |
2004年 | 669篇 |
2003年 | 678篇 |
2002年 | 502篇 |
2001年 | 323篇 |
2000年 | 320篇 |
1999年 | 240篇 |
1998年 | 85篇 |
1997年 | 64篇 |
1996年 | 56篇 |
1995年 | 69篇 |
1994年 | 46篇 |
1993年 | 48篇 |
1992年 | 91篇 |
1991年 | 73篇 |
1990年 | 68篇 |
1989年 | 68篇 |
1988年 | 70篇 |
1987年 | 49篇 |
1986年 | 48篇 |
1985年 | 49篇 |
1984年 | 49篇 |
1983年 | 40篇 |
1981年 | 23篇 |
1979年 | 39篇 |
1974年 | 26篇 |
1973年 | 24篇 |
1972年 | 24篇 |
1971年 | 26篇 |
1970年 | 29篇 |
1969年 | 29篇 |
1968年 | 30篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
981.
982.
Lima Pedro Paulo Arcanjo Narciso Luis Gustavo Alcindo Jefferson Filgueira Deschk Maurício Ciarlini Paulo Cesar dos Santos Paulo Sérgio Patto de Almeida Breno Fernando Martins 《Veterinary research communications》2022,46(1):27-35
Veterinary Research Communications - Propofol is a widely used drug in veterinary medicine to induce anesthesia; as well as the chosen compound for protocols of intravenous anesthesia. The present... 相似文献
983.
Pérez-Brígido Carlos D. Romero-Salas Dora Pardío-Sedas Violeta T. Cruz-Romero Anabel González-Hernández Milagros Delprá-Cachulo Joyce Mara Ascencio Mariano Florin-Christensen Mónica Schnittger Leonhard Rodríguez Anabel E. 《Veterinary research communications》2022,46(1):295-302
Veterinary Research Communications - The black-handed spider monkey (Ateles geoffroyi) is a platyrrhine primate distributed in southern Mexico, Central America, and part of South America. Two... 相似文献
984.
E. Dieterman H. Hermans I. J. M. Slenter N. W. Kuijpers G. C. M. Grinwis M. H. Boevé 《Equine Veterinary Education》2022,34(8):e323-e330
This case report describes four horses with unilateral superficial or mid-stromal immune-mediated keratitis (IMMK) treated with a superficial keratectomy (SK) without a conjunctival graft. In two horses, the surgery was performed under general anaesthesia, and in two horses standing with sedation and local blocks. Results of this report show that SK is a viable treatment option in horses with chronic superficial and/or mid-stromal IMMK that can even be performed in the standing, sedated horse. When sufficient corneal tissue is removed, no recurrence is to be expected in the long-term follow-up (up to 31 months). In two horses, healing occurred without complications. Two horses developed a secondary bacterial infection post-operatively (Enterococcus faecalis and Staphylococcus aureus). In one case, this resulted in a pre-perforating melting corneal ulcer necessitating conjunctival pedicle graft surgery 13 days post keratectomy. In three horses, there was no recurrence of the IMMK with a long-term follow-up of 6–31 months. One case showed recurrence of IMMK in the cornea region surrounding the keratectomy 9 months after surgery. 相似文献
985.
Abecia José-Alfonso Barrio Antonio Ruiz José-Antonio 《Veterinary research communications》2022,46(2):609-612
Veterinary Research Communications - Twenty-five ewe-lambs born in November were used to measure the effect of the presence of cyclic or non-cyclic adult ewes on the age at first fertile estrus.... 相似文献
986.
Sousa Larissa Nascimento Batista Samira Pereira Silva Samara Santos da Silva Rômulo Fylipe Sarmento Wlysse Ferreira Mota Rinaldo Aparecido Brasil Arthur Willian Lima Amaku Marcos Feitosa Thais Ferreira Vilela Vinícius Longo Ribeiro 《Veterinary research communications》2022,46(2):507-515
Veterinary Research Communications - This study aimed to describe the transmission of T. gondii in naturally infected goats in the semiarid region of northeastern Brazil, through evaluating the... 相似文献
987.
Sun Hong-gang Zhang Jian-guo Duan Ai-guo He Cai-yun 《中国林学(英文版)》2007,9(1):85-94
Growth and yield modeling has a long history in forestry. The methods of measuring the growth of stand basal area have evolved from those developed in the U.S.A. and Germany during the last century. Stand basal area modeling has progressed rapidly since the first widely used model was published by the U.S. Forest Service. Over the years, a variety of models have been developed for predicting the growth and yield of uneven/even-aged stands using stand-level approaches. The modeling methodology has not only moved from an empirical approach to a more ecological process-based approach but also accommodated a variety of techniques such as: 1) simultaneous equation methods, 2) difference models, 3) artificial neural network techniques, 4) linear/nonlinear regres-sion models, and 5) matrix models. Empirical models using statistical methods were developed to reproduce accurately and precisely field observations. In contrast, process models have a shorter history, developed originally as research and education tools with the aim of increasing the understanding of cause and effect relationships. Empirical and process models can be married into hybrid mod-els in which the shortcomings of both component approaches can, to some extent, be overcome. Algebraic difference forms of stand basal area models which consist of stand age, stand density and site quality can fully describe stand growth dynamics. This paper reviews the current literature regarding stand basal area models, discusses the basic types of models and their merits and outlines recent progress in modeling growth and dynamics of stand basal area. Future trends involving algebraic difference forms, good fitting variables and model types into stand basal area modeling strategies are discussed. 相似文献
988.
Wang Wei Zhao Lin-sen 《中国林学(英文版)》2007,9(3):213-216
The importance of ecological benefit analyses about green space systems has been widely discussed on the basis of a per-ceived bias towards the landscaping effect of green spaces to be built in urban areas as opposed to the perception of comprehensive ecological benefits of designed plant communities. Given the basic principle of ecological benefit analyses and evaluation methods widely applied today, the methodology to calculate ecological benefits and to model the expansion of urban green spaces by CITY-green 5.0 and its conditions for application were explored. We propose that aerial images can be substituted by AutoCAD graphics of a green space containing detailed information of plant dispositions by digitizing the key features during the working process in order to evaluate the ecological benefits quickly and to offer proper guidance to the establishment of small scale green spaces in urban areas. The theoretical foundation, potential application range and prospects for extension of the method are introduced by using the analysis of ecological benefits of the green spaces on the campus of Southwest Forestry College, Kunming, as an example. 相似文献
989.
990.
Reproductive phenology was observed over three years in a Eucalyptus grandis seed orchard in Madagascar to determine the impact of geographic differences of parental selections on the expected genetic composition of seed crops. Pollen flow (observed pollen cloud) was deduced from a paternity assignment based on sampling from one year’s seed production. The two approaches were used to verify whether knowledge of phenology is sufficient to predict the genetic quality of the seeds collected. Despite the high flowering level, with a constant cycle over three years, the results demonstrated wide reproductive phenological differences associated with the parents’ origin, suggesting putative pollination disequilibrium. From both observed and expected pollen clouds, the results showed preferential mating among different provenances, which has consequences for seed crop composition. Phenological observations, which can be made inexpensively, can be used to promote methods of effective seed orchard management in order to improve the genetic quality of seeds. 相似文献