全文获取类型
收费全文 | 77199篇 |
免费 | 6552篇 |
国内免费 | 5894篇 |
出版年
2023年 | 841篇 |
2022年 | 1149篇 |
2021年 | 3259篇 |
2020年 | 2450篇 |
2019年 | 3198篇 |
2018年 | 3329篇 |
2017年 | 2598篇 |
2016年 | 3524篇 |
2015年 | 4366篇 |
2014年 | 5454篇 |
2013年 | 5826篇 |
2012年 | 6770篇 |
2011年 | 6353篇 |
2010年 | 4297篇 |
2009年 | 3888篇 |
2008年 | 4512篇 |
2007年 | 4097篇 |
2006年 | 3485篇 |
2005年 | 2935篇 |
2004年 | 2604篇 |
2003年 | 2442篇 |
2002年 | 2077篇 |
2001年 | 1538篇 |
2000年 | 1309篇 |
1999年 | 1047篇 |
1998年 | 640篇 |
1997年 | 553篇 |
1996年 | 496篇 |
1995年 | 478篇 |
1994年 | 424篇 |
1993年 | 324篇 |
1992年 | 437篇 |
1991年 | 370篇 |
1990年 | 307篇 |
1989年 | 263篇 |
1988年 | 187篇 |
1987年 | 230篇 |
1986年 | 195篇 |
1985年 | 188篇 |
1984年 | 117篇 |
1983年 | 118篇 |
1982年 | 95篇 |
1981年 | 92篇 |
1980年 | 61篇 |
1979年 | 73篇 |
1978年 | 74篇 |
1977年 | 56篇 |
1975年 | 56篇 |
1973年 | 66篇 |
1972年 | 55篇 |
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
1.
Bong Jin Kim Kyung Seob Song Hyun-Hee Kong Hee-Jae Cha Meesun Ock 《The Korean journal of parasitology》2014,52(1):85-87
We encountered a patient with heavy Hymenolepis nana infection. The patient was a 44-year-old Korean man who had suffered from chronic hepatitis (type B) for 15 years. A large number of H. nana adult worms were found during colonoscopy that was performed as a part of routine health screening. The parasites were scattered throughout the colon, as well as in the terminal ileum, although the patient was immunocompetent. Based on this study, colonoscopy may be helpful for diagnosis of asymptomatic H. nana infections. 相似文献
2.
András Szilágyi István Scheuring David P. Edwards Jerome Orivel Douglas W. Yu 《Ecology letters》2009,12(12):1306-1316
Theory suggests that spatial structuring should select for intermediate levels of virulence in parasites, but empirical tests are rare and have never been conducted with castration (sterilizing) parasites. To test this theory in a natural landscape, we construct a spatially explicit model of the symbiosis between the ant-plant Cordia nodosa and its two, protecting ant symbionts, Allomerus and Azteca . Allomerus is also a castration parasite, preventing fruiting to increase colony fecundity. Limiting the dispersal of Allomerus and host plant selects for intermediate castration virulence. Increasing the frequency of the mutualist, Azteca , selects for higher castration virulence in Allomerus , because seeds from Azteca -inhabited plants are a public good that Allomerus exploits. These results are consistent with field observations and, to our knowledge, provide the first empirical evidence supporting the hypothesis that spatial structure can reduce castration virulence and the first such evidence in a natural landscape for either mortality or castration virulence. 相似文献
3.
4.
5.
6.
A partial swine cDNA which encodes the functional domain of PIT-1 was isolated by the polymerse chain reaction (PCR). The swine PIT-1 cDNA clone is 95% identical at the protein level to the rat Pit-1 gene. Thus, Pit-l's known function in control of rat growth hormone and prolactin expression is likely to be conserved in swine. This swine cDNA clone was used to investigate genetic variability at PIT-1 in several American and Chinese breeds. Polymorphic BamIII fragments were found in pure-bred Meishan animals (n= 13), but only monomorphic fragments in five American breeds (n= 36). 相似文献
7.
8.
A.N. Reshetilov A.B. Medvinsky T.P. Eliseeva V.Yu. Shakhbazian M.A. Tsyganov A.M. Boronin G.R. Ivanitsky 《FEMS microbiology letters》1992,94(1-2):59-62
A method of pH distribution measurements in agar nutrient media containing expanding bacterial populations is described. It is based on measuring pH microsamples taken at different points of the media. The sample volume was 10 microliters. A pH sensitive field effect transistor was used as a measuring electrode. Acidification was found to occur in glucose media, while alkalization occurred in the media containing peptone. 相似文献
9.
10.