全文获取类型
收费全文 | 41688篇 |
免费 | 1100篇 |
国内免费 | 19篇 |
专业分类
林业 | 5026篇 |
农学 | 2268篇 |
基础科学 | 334篇 |
7267篇 | |
综合类 | 5346篇 |
农作物 | 3359篇 |
水产渔业 | 3155篇 |
畜牧兽医 | 11205篇 |
园艺 | 1392篇 |
植物保护 | 3455篇 |
出版年
2021年 | 211篇 |
2020年 | 234篇 |
2019年 | 273篇 |
2018年 | 3442篇 |
2017年 | 3508篇 |
2016年 | 1642篇 |
2015年 | 340篇 |
2014年 | 414篇 |
2013年 | 847篇 |
2012年 | 1660篇 |
2011年 | 3433篇 |
2010年 | 3190篇 |
2009年 | 2354篇 |
2008年 | 2632篇 |
2007年 | 3070篇 |
2006年 | 917篇 |
2005年 | 895篇 |
2004年 | 860篇 |
2003年 | 922篇 |
2002年 | 751篇 |
2001年 | 550篇 |
2000年 | 567篇 |
1999年 | 421篇 |
1998年 | 228篇 |
1997年 | 227篇 |
1996年 | 191篇 |
1995年 | 228篇 |
1994年 | 182篇 |
1993年 | 218篇 |
1992年 | 350篇 |
1991年 | 343篇 |
1990年 | 338篇 |
1989年 | 370篇 |
1988年 | 333篇 |
1987年 | 278篇 |
1986年 | 312篇 |
1985年 | 280篇 |
1984年 | 241篇 |
1983年 | 231篇 |
1979年 | 265篇 |
1978年 | 182篇 |
1977年 | 191篇 |
1975年 | 187篇 |
1974年 | 258篇 |
1973年 | 227篇 |
1972年 | 261篇 |
1971年 | 231篇 |
1970年 | 205篇 |
1969年 | 197篇 |
1968年 | 180篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
31.
32.
33.
34.
35.
1. Eggs from wild and captive populations of Greater Rhea (Rhea americana) were studied to determine their physical and chemical characteristics. 2. Significant differences were found among populations in almost all chemical parameters studied, whereas within physical parameters only shell weight (as a proportion of the entire egg) and density showed differences. 3. Eggs from wild populations had the highest protein and linolenic acid and the lowest total lipid contents, while cholesterol levels of these eggs and of those from the largest captive area were the lowest. 相似文献
36.
37.
38.
Conrado M. Gempesaw J. Richard Bacon Ferdinand F. Wirth 《Journal of the World Aquaculture Society》1992,23(1):38-48
The objective of this study was to evaluate the relationship of pond size and hybrid striped bass growout profitability as an alternative source of farm income in the Mid-Atlantic region. A dynamic, whole farm, Montdarlo capital budgeting simulation model (AQUASIM) and stochastic dominance with respect to a function technique were used to analyze the economics of hybrid striped bass growout from phase II to market production stage for eight farms categorized by pond sizes. Three scenarios are assumed to examine the effects of pond-size dependent changes in feed conversion efficiency and fingerling survival rates on discounted after-tax net present values and probabilities of economic survival and success. Optimal pond sizes were found to be in the 2.5 acre to 10 acre range. 相似文献
39.
Laurence O. Whiteley DVM PhD Samuel K. Maheswaran BVSc PhD Douglas J. Weiss DVM PhD Trevor R. Ames DVM MS Mathur S. Kannan BVSc PhD 《Journal of veterinary internal medicine / American College of Veterinary Internal Medicine》1992,6(1):11-22
The severe fibrinonecrotic pneumonia associated with pneumonic pasteurellosis usually results from colonization of the lower respiratory tract by Pasteurella haemolytica biotype A, serotype 1(A1). Despite recent research efforts, the authors lack a detailed understanding of the interactions and host response to P. haemolytica in the respiratory tract. The authors hypothesize that management and environmental stress factors or viral infection alters the upper respiratory tract (URT) epithelium allowing P. haemolytica to colonize the epithelium. Once the URT is colonized, large numbers of organisms enter the lung where they interact with alveolar macrophages. Endotoxin, released from the bacteria, crosses the alveolar wall where it activates pulmonary intravascular macrophages, endothelium, neutrophils, lymphocytes, platelets, complement, and Hageman factor leading to complex interactions of cells and mediators. It is the progression of this inflammatory response with neutrophil influx that is ultimately responsible for the pulmonary injury. Leukotoxin is a major virulence factor of P. haemolytica that allows it to survive by destroying phagocytic cells. At subcytolytic concentrations it may also enhance the inflammatory response by activating cells to produce mediators and release reactive oxygen metabolites and proteases. 相似文献
40.
A rapid and low cost procedure, the carbon immunoassay (CIA) test, was evaluated for the diagnosis of Toxoplasma gondii infections. Using a closely related parasite (Besnoitia jellisoni) as antigen, and homologous or heterologous immune sera, it was demonstrated by light and electron microscopy that CIA is a very reliable and specific test. As it is neither expensive nor time-consuming, it can be recommended for general and routine laboratory use. 相似文献