全文获取类型
收费全文 | 487篇 |
免费 | 82篇 |
出版年
2021年 | 11篇 |
2019年 | 7篇 |
2017年 | 6篇 |
2016年 | 7篇 |
2015年 | 12篇 |
2014年 | 5篇 |
2013年 | 12篇 |
2012年 | 20篇 |
2011年 | 14篇 |
2010年 | 9篇 |
2009年 | 6篇 |
2008年 | 11篇 |
2007年 | 16篇 |
2006年 | 16篇 |
2005年 | 10篇 |
2004年 | 17篇 |
2003年 | 13篇 |
2002年 | 10篇 |
2001年 | 10篇 |
2000年 | 14篇 |
1999年 | 14篇 |
1998年 | 14篇 |
1997年 | 8篇 |
1993年 | 12篇 |
1992年 | 17篇 |
1991年 | 16篇 |
1990年 | 10篇 |
1989年 | 12篇 |
1988年 | 14篇 |
1987年 | 10篇 |
1986年 | 10篇 |
1985年 | 20篇 |
1984年 | 16篇 |
1983年 | 11篇 |
1982年 | 5篇 |
1978年 | 6篇 |
1977年 | 7篇 |
1976年 | 6篇 |
1975年 | 5篇 |
1974年 | 7篇 |
1973年 | 10篇 |
1972年 | 8篇 |
1971年 | 4篇 |
1970年 | 4篇 |
1969年 | 6篇 |
1968年 | 17篇 |
1967年 | 6篇 |
1966年 | 11篇 |
1965年 | 11篇 |
1963年 | 4篇 |
排序方式: 共有569条查询结果,搜索用时 13 毫秒
61.
Juhwan Lee Gabriel Pedroso Bruce A. Linquist Daniel Putnam Chris van Kessel Johan Six 《Global Change Biology Bioenergy》2012,4(5):521-533
The production potential of switchgrass (Panicum virgatum L.) has not been estimated in a Mediterranean climate on a regional basis and its economic and environmental contribution as a biofuel crop remains unknown. The objectives of the study were to calibrate and validate a biogeochemical model, DAYCENT, and to predict the biomass yield potential of switchgrass across the Central Valley of California. Six common cultivars were calibrated using published data across the US and validated with data generated from four field trials in California (2007–2009). After calibration, the modeled range of yields across the cultivars and various management practices in the US (excluding California) was 2.4–41.2 Mg ha?1 yr?1, generally compatible with the observed yield range of 1.3–33.7 Mg ha?1 yr?1. Overall, the model was successfully validated in California; the model explained 66–90% of observed yield variation in 2007–2009. The range of modeled yields was 2.0–41.4 Mg ha?1 yr?1, which corresponded to the observed range of 1.3–41.1 Mg ha?1 yr?1. The response to N fertilizer and harvest frequency on yields were also reasonably validated. The model estimated that Alamo (21–23 Mg ha?1 yr?1) and Kanlow (22–24 Mg ha?1 yr?1) had greatest yield potential during the years after establishment. The effects of soil texture on modeled yields tended to be consistent for all cultivars, but there were distinct climatic (e.g., annual mean maximum temperature) controls among the cultivars. Our modeled results suggest that early stand maintenance of irrigated switchgrass is strongly dependent on available soil N; estimated yields increased by 1.6–5.5 Mg ha?1 yr?1 when residual soil mineral N was sufficient for optimal re‐growth. Therefore, management options of switchgrass for regional biomass production should be ecotype‐specific and ensure available soil N maintenance. 相似文献
62.
Zahava Vadasz Tharwat Haj Katalin Halasz Itzhak Rosner Gleb Slobodin Dina Attias Aharon Kessel Ofra Kessler Gera Neufeld Elias Toubi 《Arthritis research & therapy》2012,14(3):R146
Introduction
Semaphorin 3A (sema3A) and neuropilin-1 (NP-1) play a regulatory role in immune responses and have a demonstrated effect on the course of collagen induced arthritis. This study was undertaken to evaluate the role of sema3A and NP-1 in the pathogenesis of systemic lupus erythematosus (SLE) and the specific effect of sema3A on the auto-reactive properties of B cells in SLE patients.Methods
Thirty two SLE and 24 rheumatoid arthritis (RA) patients were assessed and compared with 40 normal individuals. Sema3A serum levels were measured and correlated with SLE disease activity. The in vitro effect of sema3A in reducing Toll-like receptor 9 (TLR-9) expression in B cells of SLE patients was evaluated.Results
Sema3A serum levels in SLE patients were found to be significantly lower than in RA patients (55.04 ± 16.30 ng/ml versus 65.54 ± 14.82 ng/ml, P = 0.018) and lower yet than in normal individuals (55.04 ± 16.30 ng/ml versus 74.41 ± 17.60 ng/ml, P < 0.0001). Altered serum sema3A levels were found to be in inverse correlation with SLE disease activity, mainly with renal damage. The expression of both sema3A and NP-1 on B cells from SLE patients was significantly different in comparison with normal healthy individuals. Finally, when sema3A was co-cultured with cytosine-phosphodiester-guanine oligodeoxynucleotides (CpG-ODN)-stimulated B cells of SLE patients, their TLR-9 expression was significantly reduced, by almost 50% (P = 0.001).Conclusions
This is the first study in which a reduced serum level of sema3A was found in association with SLE disease activity. It also raises the possibility that sema3A may have a regulatory function in SLE. 相似文献63.
64.
65.
Laura J. Marinelli Mariana Piuri Zuzana Swigoňová Amrita Balachandran Lauren M. Oldfield Julia C. van Kessel Graham F. Hatfull 《PloS one》2008,3(12)
Advances in DNA sequencing technology have facilitated the determination of hundreds of complete genome sequences both for bacteria and their bacteriophages. Some of these bacteria have well-developed and facile genetic systems for constructing mutants to determine gene function, and recombineering is a particularly effective tool. However, generally applicable methods for constructing defined mutants of bacteriophages are poorly developed, in part because of the inability to use selectable markers such as drug resistance genes during viral lytic growth. Here we describe a method for simple and effective directed mutagenesis of bacteriophage genomes using Bacteriophage Recombineering of Electroporated DNA (BRED), in which a highly efficient recombineering system is utilized directly on electroporated phage DNA; no selection is required and mutants can be readily detected by PCR. We describe the use of BRED to construct unmarked gene deletions, in-frame internal deletions, base substitutions, precise gene replacements, and the addition of gene tags. 相似文献
66.
67.
68.
David Kessel 《Autophagy》2015,11(10):1941-1943
The high degree of selectivity for photodamage to subcellular organelles can provide a means for evaluation of autophagic death pathways. While many current reports rely on ambiguous criteria, there are glimmers of unequivocal evidence. 相似文献
69.
Gas exchange following lactate and pyruvate injections 总被引:1,自引:0,他引:1
70.
Summary Nodule biomass and yearly C2H2 reduction rates are reported forInga jinicuil, a leguminous tree used for shade in Mexican coffee plantations. Annual fixation by this species approximates 35 kg ha–1; which, when compared to nitrogen additions from fertilizers, represents an important nitrogen input to the coffee ecosystem. 相似文献