全文获取类型
收费全文 | 118681篇 |
免费 | 9368篇 |
国内免费 | 10568篇 |
专业分类
138617篇 |
出版年
2024年 | 274篇 |
2023年 | 1600篇 |
2022年 | 3613篇 |
2021年 | 6035篇 |
2020年 | 4197篇 |
2019年 | 5166篇 |
2018年 | 4897篇 |
2017年 | 3593篇 |
2016年 | 5073篇 |
2015年 | 7350篇 |
2014年 | 8662篇 |
2013年 | 9142篇 |
2012年 | 11039篇 |
2011年 | 9982篇 |
2010年 | 6201篇 |
2009年 | 5499篇 |
2008年 | 6319篇 |
2007年 | 5698篇 |
2006年 | 4928篇 |
2005年 | 3923篇 |
2004年 | 3268篇 |
2003年 | 2964篇 |
2002年 | 2512篇 |
2001年 | 2036篇 |
2000年 | 1851篇 |
1999年 | 1822篇 |
1998年 | 1142篇 |
1997年 | 1093篇 |
1996年 | 1039篇 |
1995年 | 905篇 |
1994年 | 862篇 |
1993年 | 675篇 |
1992年 | 899篇 |
1991年 | 668篇 |
1990年 | 520篇 |
1989年 | 492篇 |
1988年 | 389篇 |
1987年 | 369篇 |
1986年 | 293篇 |
1985年 | 313篇 |
1984年 | 170篇 |
1983年 | 173篇 |
1982年 | 111篇 |
1981年 | 90篇 |
1980年 | 64篇 |
1979年 | 87篇 |
1977年 | 62篇 |
1975年 | 64篇 |
1974年 | 55篇 |
1973年 | 57篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
31.
32.
Hailong Jin Congran Li Ding Li Ming Cai Zhouli Li Shuang Wang Xin Hong Bingyi Shi 《Cell biochemistry and biophysics》2013,67(3):1067-1074
Immunotoxins with selective cytotoxicity are frequently used as therapeutic immunosuppressive agents in solid-organ transplantation because of their efficiency and high specificity. In this study, we present a new recombinant immunotoxin termed anti-CTLA-4-scFv–melittin prepared from Escherichia coli aimed at clearing activated T cells at the same time avoiding all-round decline in systematic immunity. This fusion protein is composed of anti-CTLA-4-scFv unit and melittin analog unit with properties of low immunogenicity and selective cytotoxicity to CTLA-4-positive T cells. In preliminary biological activity assays, our results confirmed the feasibility of activated T cell clearance strategy and there were significant differences in cell survival rates between CTLA-4-positive group and control group at all experimental concentrations of the immunotoxin. The selective cytotoxicity, low immunogenicity, and low production cost make it an attractive alternate to traditional immunosuppressants. 相似文献
33.
Background: Little is known about geographic variations in liver cancer at high incident regions. We aimed to identify spatial variation of hepatocellular carcinoma (HCC) at a high-risk area in China and determine its association with socioeconomic status (SES). Methods: Based on 2299 liver cancer cases diagnosed in Haimen from 2003 to 2006, we calculated age–sex standardized incidence ratios (SIRs) and used two spatial scan statistics to determine the geographic variations in HCC. Bayesian hierarchical model was used to explore the association between HCC incidence and SES. Results: Age and sex SIRs for HCC varied from 0.54 to 1.97 for 24 townships. The eastern region of Haimen was identified to have a significantly increased risk of HCC. Fitting of a Bayesian hierarchical model linking per-capita fiscal revenue with SIRs of HCC indicated that the area with a lower revenue had a significantly higher incidence of HCC [βlog(revenue) = ?0.179, posterior 95% Bayesian credible interval (CI) = (?0.326, ?0.04)]. Conclusions: This study demonstrated substantial geographic variation in the incidence of HCC within a high-risk region, which was associated with SES. HCC control and intervention should focus on disadvantaged areas to reduce the HCC disparities. 相似文献
34.
Endogenous CD8+ T cell expansion during regression of monoclonal EBV-associated posttransplant lymphoproliferative disorder. 总被引:5,自引:0,他引:5
V P Khatri R A Baiocchi R Peng A R Oberkircher J M Dolce P M Ward G P Herzig M A Caligiuri 《Journal of immunology (Baltimore, Md. : 1950)》1999,163(1):500-506
There are experimental data which suggest that the primary immune effector cell responsible for maintaining immune surveillance against the outgrowth of EBV-transformed B cells in humans is the CTL, but in vivo proof of this is lacking. In this study we perform a series of cellular and molecular assays to characterize an autologous, endogenous immune response against a transplantation-associated, monoclonal, EBV+ posttransplant lymphoproliferative disorder (PTLD). Following allogeneic bone marrow transplantation, a patient developed a monoclonal PTLD of donor B cell origin. With a decrease in immune suppression, we document the emergence of endogenous, donor-derived CD3+CD8+ CTLs, followed by regression of the PTLD. The TCR Vbeta repertoire went from a polyclonal pattern prior to the development of PTLD to a restricted TCR Vbeta pattern during the outgrowth and regression of PTLD. Donor-derived CD3+CD8+ T lymphocytes displayed MHC class I-restricted cytolytic activity against the autologous EBV+ B cells ex vivo without additional in vitro sensitization. The striking temporal relationship between the endogenous expansion of a TCR Vbeta-restricted, CD3+CD8+ population of MHC class I-restricted CTL, and the regression of an autologous monoclonal PTLD, provides direct evidence in humans that endogenous CD3+CD8+ CTLs can be responsible for effective immune surveillance against malignant transformation of EBV+ B cells. 相似文献
35.
36.
Qiliang Li 《Genome biology》2006,7(10):238-3
A Melanesian variant of the genetic disease α-thalassemia has recently been shown to be due to a single-nucleotide polymorphism
located between the adult α-globin genes and their enhancers. The finding that this mutation creates a novel promoter provides
support for a mechanism of gene regulation by facilitated chromatin looping. 相似文献
37.
A food-producing role for cephalic exocrine glands has arisen independently in both taxa of highly eusocial bees, Apis and Meliponini. With several exceptions, there is little evidence that food is produced by glands of solitary bees or by most bees at lower levels of sociality. We suggest that this association with sociality is due to four adaptive features of these glands: (1) food from the glands allows feces from queens and larvae to have a small volume, (2) the queen's fecundity can be increased, (3) nutrient recovery via cannibalism can be facilitated, and (4) rearing of emergency replacement queens is accelerated. Acceleration of the rearing of other castes and of queens in the normal process of colony fission is not clearly an advantage ascribed to these glands. Trophic eggs produced by meliponine colony workers are analogous to the secretions from food-producing glands in Meliponini and Apis workers. 相似文献
38.
39.
40.