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   1355篇
  免费   56篇
  国内免费   5篇
林业   101篇
农学   34篇
基础科学   6篇
  222篇
综合类   115篇
农作物   52篇
水产渔业   87篇
畜牧兽医   583篇
园艺   69篇
植物保护   147篇
  2023年   18篇
  2022年   24篇
  2021年   45篇
  2020年   31篇
  2019年   46篇
  2018年   37篇
  2017年   38篇
  2016年   47篇
  2015年   25篇
  2014年   40篇
  2013年   49篇
  2012年   102篇
  2011年   123篇
  2010年   53篇
  2009年   39篇
  2008年   85篇
  2007年   90篇
  2006年   93篇
  2005年   90篇
  2004年   72篇
  2003年   76篇
  2002年   58篇
  2001年   16篇
  2000年   27篇
  1999年   11篇
  1998年   7篇
  1997年   6篇
  1996年   4篇
  1995年   4篇
  1994年   4篇
  1992年   4篇
  1991年   2篇
  1990年   4篇
  1989年   2篇
  1988年   5篇
  1987年   4篇
  1985年   3篇
  1984年   3篇
  1983年   3篇
  1980年   3篇
  1979年   2篇
  1978年   6篇
  1976年   2篇
  1975年   2篇
  1974年   1篇
  1968年   1篇
  1966年   1篇
  1960年   1篇
  1950年   1篇
  1924年   1篇
排序方式: 共有1416条查询结果,搜索用时 15 毫秒
921.
This paper, the first of a two-part series, aims to find the effect of stitch length, check spring tension, fabric feed timing and needle thread in-take length on tension peaks occurring on a spun polyester needle thread during a sewing cycle of a SNLS sewing machine. The pre-tensions on the bobbin and needle threads and sewing speed were kept constant. A PC interfaced measuring instrument was fabricated to measure dynamic sewing tension on needle thread above the needle bar. Four prominent tension peaks were detected. Longer stitch length causes higher tension peaks; and shorter length stitch requires higher pre-tension to obtain a balanced stitch. The check spring tension has no effect on tightening tension. Incorrect timing of feed dog can cause very high tightening tension. The change in the position of thread length guide alters the friction of needle thread at critical guides which determines the length of thread to be released through tensioner; release of longer length of thread results in lower tension peaks (1, 2 and 4) and vice versa.  相似文献   
922.
Fucoidan compounds may increase immune activity and are known to have cancer inhibitory effects in vitro and in vivo. In this study, we aimed to investigate the effect of fucoidan compounds on ex vivo human peripheral blood mononuclear cells (PBMCs), and to determine their cancer cell killing activity both solely, and in combination with an immune-checkpoint inhibitor drug, Nivolumab. Proliferation of PBMCs and interferon gamma (IFNγ) release were assessed in the presence of fucoidan compounds extracted from Fucus vesiculosus, Undaria pinnatifida and Macrocystis pyrifera. Total cell numbers and cell killing activity were assessed using a hormone resistant prostate cancer cell line, PC3. All fucoidan compounds activated PBMCs, and increased the effects of Nivolumab. All fucoidan compounds had significant direct cytostatic effects on PC3 cells, reducing cancer cell numbers, and PBMCs exhibited cell killing activity as measured by apoptosis. However, there was no fucoidan mediated increase in the cell killing activity. In conclusion, fucoidan compounds promoted proliferation and activity of PBMCs and added to the effects of Nivolumab. Fucoidan compounds all had a direct cytostatic effect on PC3 cells, as shown through their proliferation reduction, while their killing was not increased.  相似文献   
923.
924.
Landscape Ecology - The role of protected areas as biodiversity repositories has become increasingly important in face of increased deforestation. By adding free-living exotic mammals, removing...  相似文献   
925.
926.
Twenty-eight strains of Salmonella enterica serovar Typhimurium were characterized by three PCR-based methods. Ten strains harbored type I integrons and two different integron profiles were detected. Typing by amplified fragment length polymorphism (AFLP) resulted in observation of 10 profiles that differed by one to six bands. Salmonella strains were screened for presence of phage genes using a PCR-phage typing; five genes from P22 phage and genes encoding putative virulence factors from phages Gifsy-1, Gifsy-2 and Fels-1 were selected for testing. This set of genes was sufficient for dividing the strains into eight different PCR-phage profiles. Similar grouping of strains was observed in case of all the employed DNA techniques and they corresponded well with the phage type and antimicrobial resistance of the strains. The highest discriminating power was achieved with use of the AFLP, yet the detection of integrons and PCR-phage typing also proved to be valuable in typing the S. Typhimurium strains.  相似文献   
927.
928.
Three oligonucleotide primers for semi-nested polymerase chain reaction (PCR) were designed according to already published sequences of porcine circovirus types 1 (PCV-1) and 2 (PCV-2) isolates. These primers were used to detect PCV-2 DNA. A positive amplification reaction was visualized from a DNA suspension containing as few as 10 copies of virus DNA. In total. 77 samples of inguinal lymph nodes and nasal swabs from pigs in the Czech Republic were used to detect the virus. Thirty-seven of them were positive for PCV-2 DNA. In order to confirm specificity of the PCR reaction, seven DNA fragments were sequenced. Czech PCV sequences were found to have a 92-97% homology with other known PCV-2 strains and only 80-83% homology with PCV-1 strains.  相似文献   
929.
In this paper we examine how internal migration redistributes earned income across U.S. states between 1995 and 2010. We examine interregional income flows by first describing the movement of earned income between U.S. states. Second, we examine the effect of income migration on spatial patterns of income inequality. The question we ask is, “does migration increase or decrease convergence income across U.S. States?” A primary contribution of this paper is that instead of using only 1 year of income migration data to explore these issues, we use yearly data from the first year the Internal Revenue Service (IRS) data started including income (1995/1996) up to the most current data available (2009/2010). Results indicate that income convergence/divergence across states varies by whether or not there is general economic expansion or contraction. Nevertheless, some high‐amenity states continually attract high‐income households.  相似文献   
930.
The ratio of monounsaturated oleic fatty acid to polyunsaturated linoleic fatty acid (O/L) and the associated agronomic traits were profiled for local peanut (Arachis hypogaea L.) cultivars and accessions in Botswana. The research was tested on 16 entries planted in four localities across the country. The average total oil yield of the genotypes studied was about 42.1% and there was no significant difference in total oil yield (P < 0.05) across the four research sites and among all entries (accessions). The average mean O/L ratio for all entries was about 1.47. The highest was that of the locally improved variety, Peolwane (2.58), which was significantly different (P < 0.05) from all other accessions, and the lowest is that of the local accession GO 63 (1.23). This study also profiled the agronomic yield traits to identify genotypes that have both high oil quality and high yielding potential. No correlation was detected between pod yield and O/L ratio among the tested genotypes. The station with little rainfall but adequate repartition showed a very high O/L ratio for some genotypes, and future work is recommended to test this interesting observation on the correlation between moisture stress and oil quality.  相似文献   
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