全文获取类型
收费全文 | 2761篇 |
免费 | 152篇 |
国内免费 | 3篇 |
专业分类
2916篇 |
出版年
2023年 | 21篇 |
2022年 | 39篇 |
2021年 | 79篇 |
2020年 | 51篇 |
2019年 | 55篇 |
2018年 | 73篇 |
2017年 | 77篇 |
2016年 | 88篇 |
2015年 | 141篇 |
2014年 | 116篇 |
2013年 | 207篇 |
2012年 | 197篇 |
2011年 | 200篇 |
2010年 | 134篇 |
2009年 | 104篇 |
2008年 | 138篇 |
2007年 | 139篇 |
2006年 | 129篇 |
2005年 | 108篇 |
2004年 | 88篇 |
2003年 | 80篇 |
2002年 | 78篇 |
2001年 | 40篇 |
2000年 | 30篇 |
1999年 | 31篇 |
1998年 | 16篇 |
1997年 | 21篇 |
1995年 | 18篇 |
1994年 | 14篇 |
1992年 | 15篇 |
1991年 | 18篇 |
1990年 | 19篇 |
1989年 | 16篇 |
1988年 | 16篇 |
1987年 | 14篇 |
1986年 | 15篇 |
1985年 | 16篇 |
1984年 | 21篇 |
1983年 | 16篇 |
1982年 | 21篇 |
1981年 | 12篇 |
1979年 | 14篇 |
1977年 | 15篇 |
1976年 | 13篇 |
1975年 | 15篇 |
1974年 | 12篇 |
1972年 | 14篇 |
1971年 | 11篇 |
1968年 | 11篇 |
1967年 | 11篇 |
排序方式: 共有2916条查询结果,搜索用时 15 毫秒
61.
62.
Electronmicroscopic observations indicate that bacteriophage CVX-5 has an angular head with long spiral tail which is noncontractile, possibly having 2--3 tail fibres attached at the distal part of the tail. This phage is antigenically unrelated to any of the T-phages. Inhibition of phage CVX-5 multiplication by mitomycin C and incorporation of 3H-thymidine into this phage indicate that phage CVX-5 is a DNA phage. 相似文献
63.
64.
65.
Subcellular fractionation of oviduct tissue from estrogen-treated chicks indicated that the bulk of the protein kinase activity of this tissue is located in the cytoplasmic and nuclear fractions, DEAE-cellulose chromatography of cytosol revealed a major peak of cAMP stimulatable activity eluting at 0.2 M KCl. This peak was further characterized and found to exhibit properties consistent with cytoplasmic cAMP dependent protein kinases isolated from other tissues; it had a Km for ATP of 2 X 10(-5) M, preferred basic proteins such as histones, as substrate, and had a M of 165 000. Addition of 10(-6) M cAMP caused the holoenzyme to dissociate into cAMP binding regulatory subunit and a protein kinase catalytic subunit. Extraction of purified oviduct nuclei with 0.3 M KCl released greater than 80% of the kinase activity in this fraction. Upon elution from phospho-cellulose, the nuclear extract was resolved into two equal peaks of kinase activity (designated I and II). Peak I had a sedimentation coefficient of 3S and a Km for ATP of 13 muM. while peak II had a sedimentation coefficient of 6S and a Km for ATP of 9 muM. Both enzymes preferred alpha-casein as a substrate over phosvitin or whole histone, although they exhibited different salt-activity profiles. The cytoplasmic and nuclear enzymes were well separated on phospho-cellulose and this resin was used to quantitate the amount of cAMP dependent histone kinase activity in the nucleus and the amount of casein kinase activity in the cytosol. Protein kinase activity in nuclei from estrogen-stimulated chicks was found to be 40% greater than hormone-withdrawn animals. This increase in activity was not due to translocation of the cytoplasmic protein kinase in response to hormone, but to an increase in nuclear (casein) kinase activity. During the course of this work, we observed small but significant amounts of cAMP binding activity very tightly bound to the nuclear fraction. Solubilization of the binding activity by sonication in high salt allowed comparison studies to be performed which indicated that the nuclear binding protein is identical with the cytoplasmic cAMP binding regulatory subunit. The possible role of the nuclear binding activity is discussed. 相似文献
66.
Pollination induced dissolution of nucellar cells at the micropylar end forming a passage for pollen tube entry even when the pollen tubes are in the stylar region. 相似文献
67.
68.
69.
Saravanan Munisankar Anuradha Rajamanickam Suganthi Balasubramanian Satishwaran Muthusamy Chandra Kumar Dolla Pradeep Aravindan Menon Ponnuraja Chinnayan Christopher Whalen Paschaline Gumne Inderdeep Kaur Varma Nadimpalli Akshay Deverakonda Zhenhao Chen John David Otto Tesfalidet Habitegiyorgis Harish Kandaswamy Thomas B. Nutman Subash Babu 《PLoS neglected tropical diseases》2022,16(7)
BackgroundThe prevalence of Strongyloides stercoralis infection is estimated to be 30–100 million worldwide, although this an underestimate. Most cases remain undiagnosed due to the asymptomatic nature of the infection. We wanted to estimate the seroprevalence of S. stercoralis infection in a South Indian adult population.MethodsTo this end, we performed community-based screening of 2351 individuals (aged 18–65) in Kanchipuram District of Tamil Nadu between 2013 and 2020. Serological testing for S. stercoralis was performed using the NIE ELISA.ResultsOur data shows a seroprevalence of 33% (768/2351) for S. stercoralis infection which had a higher prevalence among males 36% (386/1069) than among females 29.8% (382/1282). Adults aged ≥55 (aOR = 1.65, 95% CI: 1.25–2.18) showed higher adjusted odds of association compared with other age groups. Eosinophil levels (39%) (aOR = 1.43, 95% CI: 1.19–1.74) and hemoglobin levels (24%) (aOR = 1.25, 95% CI: 1.11–1.53) were significantly associated with S. stercoralis infection. In contrast, low BMI (aOR = 1.15, 95% CI: 0.82–1.61) or the presence of diabetes mellitus (OR = 1.18, 95% CI: 0.83–1.69) was not associated with S. stercoralis seropositivity.ConclusionsOur study provides evidence for a very high baseline prevalence of S. stercoralis infection in South Indian communities and this information could provide realistic and concrete planning of control measures. 相似文献