全文获取类型
收费全文 | 1802篇 |
免费 | 109篇 |
国内免费 | 2篇 |
专业分类
1913篇 |
出版年
2024年 | 4篇 |
2023年 | 20篇 |
2022年 | 31篇 |
2021年 | 61篇 |
2020年 | 33篇 |
2019年 | 47篇 |
2018年 | 35篇 |
2017年 | 30篇 |
2016年 | 67篇 |
2015年 | 96篇 |
2014年 | 115篇 |
2013年 | 108篇 |
2012年 | 162篇 |
2011年 | 121篇 |
2010年 | 80篇 |
2009年 | 73篇 |
2008年 | 109篇 |
2007年 | 113篇 |
2006年 | 76篇 |
2005年 | 82篇 |
2004年 | 87篇 |
2003年 | 63篇 |
2002年 | 74篇 |
2001年 | 9篇 |
2000年 | 7篇 |
1999年 | 16篇 |
1998年 | 18篇 |
1997年 | 13篇 |
1996年 | 13篇 |
1995年 | 7篇 |
1994年 | 11篇 |
1993年 | 8篇 |
1992年 | 9篇 |
1991年 | 6篇 |
1990年 | 6篇 |
1989年 | 5篇 |
1988年 | 4篇 |
1987年 | 6篇 |
1986年 | 12篇 |
1985年 | 8篇 |
1984年 | 13篇 |
1983年 | 5篇 |
1982年 | 12篇 |
1981年 | 3篇 |
1980年 | 6篇 |
1979年 | 3篇 |
1977年 | 4篇 |
1969年 | 3篇 |
1968年 | 2篇 |
1957年 | 2篇 |
排序方式: 共有1913条查询结果,搜索用时 0 毫秒
961.
Kosinska AD Johrden L Zhang E Fiedler M Mayer A Wildner O Lu M Roggendorf M 《Journal of virology》2012,86(17):9297-9310
Induction of hepatitis B virus (HBV)-specific cytotoxic T cells by therapeutic immunization may be a strategy to treat chronic hepatitis B. In the HBV animal model, woodchucks, the application of DNA vaccine expressing woodchuck hepatitis virus (WHV) core antigen (WHcAg) in combination with antivirals led to the prolonged control of viral replication. However, it became clear that the use of more potent vaccines is required to overcome WHV persistence. Therefore, we asked whether stronger and more functional T-cell responses could be achieved using the modified vaccines and an optimized prime-boost vaccination regimen. We developed a new DNA plasmid (pCGWHc) and recombinant adenoviruses (AdVs) showing high expression levels of WHcAg. Mice vaccinated with the improved plasmid pCGWHc elicited a stronger WHcAg-specific CD8+ T-cell response than with the previously used vaccines. Using multicolor flow cytometry and an in vivo cytotoxicity assay, we showed that immunization in a DNA prime-AdV boost regimen resulted in an even more vigorous and functional T-cell response than immunization with the new plasmid alone. Immunization of naïve woodchucks with pCGWHc plasmid or AdVs induced a significant WHcAg-specific degranulation response prior to the challenge, this response had not been previously detected. Consistently, this response led to a rapid control of infection after the challenge. Our results demonstrate that high antigen expression levels and the DNA prime-AdV boost immunization improved the T-cell response in mice and induced significant T-cell responses in woodchucks. Therefore, this new vaccination strategy may be a candidate for a therapeutic vaccine against chronic HBV infection. 相似文献
962.
Lietz R Bayer W Ontikatze T Johrden L Tenbusch M Bonsmann MS Uberla K Dittmer U Wildner O 《Journal of virology》2012,86(3):1706-1716
Processing and presentation of vaccine antigens by professional antigen-presenting cells (APCs) is of great importance for the efficient induction of protective immunity. We analyzed whether the efficacy of an adenovirus-based retroviral vaccine can be enhanced by coadministration of adenovirus-encoded chemokines that attract and stimulate APCs. In the Friend retrovirus (FV) mouse model we coexpressed CCL3, CCL20, CCL21, or CXCL14 from adenoviral vectors, together with FV Gag and Env antigens, and then analyzed immune responses and protection from pathogenic FV infection. Although most tested chemokines did not improve protection against FV challenge, mice that received adenoviral vectors encoding CCL3 together with FV antigens showed significantly better control over viral loads and FV-induced disease than mice immunized with the viral antigens only. Improved protection correlated with enhanced virus-specific CD4+ T cell responses and higher neutralizing antibody titers. To apply these results to an HIV vaccine, mice were immunized with adenoviral vectors encoding the HIV antigens Env and Gag-Pol and coadministered vectors encoding CCL3. Again, this combination vaccine induced higher virus-specific antibody titers and CD4+ T cell responses than did the HIV antigens alone. These results indicate that coexpression of the chemokine CCL3 by adenovirus-based vectors may be a promising tool to improve antiretroviral vaccination strategies. 相似文献
963.
964.
Patterns of shoot architecture in locally adapted populations are linked to intraspecific differences in gene regulation 总被引:1,自引:0,他引:1
? Shoot architecture, including the number and location of branches, is a crucial aspect of plant function, morphological diversification, life history evolution and crop domestication. ? Genes controlling shoot architecture are well characterized in, and largely conserved across, model flowering plant species. The role of these genes in the evolution of morphological diversity in natural populations, however, has not been explored. ? We identify axillary meristem outgrowth as a primary driver of divergent branch number and life histories in two locally adapted populations of the monkeyflower, Mimulus guttatus. ? Furthermore, we show that MORE AXILLARY GROWTH (MAX) gene expression strongly correlates with natural variation in branch outgrowth in this species, linking modification of the MAX-dependent pathway to the evolutionary diversification of shoot architecture. 相似文献
965.
Christoffer Tamm Lena Kjellén Jin-Ping Li 《The journal of histochemistry and cytochemistry》2012,60(12):943-949
Embryonic stem (ES) cells are derived from the inner cell mass of the blastocyst and can
give rise to all cell types in the body. The fate of ES cells depends on the signals they
receive from their surrounding environment, which either promote self-renewal or initiate
differentiation. Heparan sulfate proteoglycans are macromolecules found on the cell
surface and in the extracellular matrix. Acting as low-affinity receptors on the cell
surface, heparan sulfate (HS) side chains modulate the functions of numerous growth
factors and morphogens, having wide impact on the extracellular information received by
cells. ES cells lacking HS fail to differentiate but can be induced to do so by adding
heparin. ES cells defective in various components of the HS biosynthesis machinery, thus
expressing differently flawed HS, exhibit lineage-specific effects. Here we discuss recent
studies on the biological functions of HS in ES cell developmental processes. Since ES
cells have significant potential applications in tissue/cell engineering for cell
replacement therapies, understanding the functional mechanisms of HS in manipulating ES
cell growth in vitro is of utmost importance, if the stem cell regenerative medicine from
scientific fiction ever will be made real. 相似文献
966.
967.
Chellakkan?S?BlessonEmail author Edgar?Büttner Britt?Masironi Lena?Sahlin 《Reproductive biology and endocrinology : RB&E》2012,10(1):3
Background
Prostaglandins are important for female reproduction. Prostaglandin-E2 acts via four different receptor subtypes, EP1, EP2, EP3 and EP4 whereas prostaglandin-F2alpha acts through FP. The functions of prostaglandins depend on the expression of their receptors in different uterine cell types. Our aim was to investigate the expression of EPs and FP in rat uterus and to identify the regulation by estradiol, progesterone and estrogen receptor (ER) selective agonists. 相似文献968.
969.
Brindley DA Davie NL Sahlman WA Bonfiglio GA Culme-Seymour EJ Reeve BC Mason C 《Cell Stem Cell》2012,10(5):492-496
In the first quarter of 2012, publicly traded companies in the cell-based therapy industry continued to show promising overall growth. Highlights included $85 million in new capital investment and steady clinical trial progress. 相似文献
970.
Effect of grazing on carbon stocks and assimilate partitioning in a Tibetan montane pasture revealed by 13CO2 pulse labeling 总被引:2,自引:0,他引:2
Silke Hafner Sebastian Unteregelsbacher Elke Seeber Becker Lena Xingliang Xu Xiaogang Li Georg Guggenberger Georg Miehe Yakov Kuzyakov 《Global Change Biology》2012,18(2):528-538
Since the late 1950s, governmental rangeland policies have changed the grazing management on the Tibetan Plateau (TP). Increasing grazing pressure and, since the 1980s, the privatization and fencing of pastures near villages has led to land degradation, whereas remote pastures have recovered from stronger overgrazing. To clarify the effect of moderate grazing on the carbon (C) cycle of the TP, we investigated differences in below‐ground C stocks and C allocation using in situ 13CO2 pulse labeling of (i) a montane Kobresia winter pasture of yaks, with moderate grazing regime and (ii) a 7‐year‐old grazing exclosure plot, both in 3440 m asl. Twenty‐seven days after the labeling, 13C incorporated into shoots did not differ between the grazed (43% of recovered 13C) and ungrazed (38%) plots. In the grazed plots, however, less C was lost by shoot respiration (17% vs. 42%), and more was translocated below‐ground (40% vs. 20%). Within the below‐ground pools, <2% of 13C was incorporated into living root tissue of both land use types. In the grazed plots about twice the amount of 13C remained in soil (18%) and was mineralized to CO2 (20%) as compared to the ungrazed plots (soil 10%; CO2 9%). Despite the higher contribution of root‐derived C to CO2 efflux, total CO2 efflux did not differ between the two land use types. C stocks in the soil layers 0–5 and 5–15 cm under grazed grassland were significantly larger than in the ungrazed grassland. However, C stocks below 15 cm were not affected after 7 years without grazing. We conclude that the larger below‐ground C allocation of plants, the larger amount of recently assimilated C remaining in the soil, and less soil organic matter‐derived CO2 efflux create a positive effect of moderate grazing on soil C input and C sequestration. 相似文献