全文获取类型
收费全文 | 833篇 |
免费 | 109篇 |
国内免费 | 2篇 |
专业分类
944篇 |
出版年
2022年 | 10篇 |
2021年 | 12篇 |
2020年 | 7篇 |
2019年 | 10篇 |
2018年 | 12篇 |
2017年 | 10篇 |
2016年 | 12篇 |
2015年 | 31篇 |
2014年 | 35篇 |
2013年 | 47篇 |
2012年 | 36篇 |
2011年 | 37篇 |
2010年 | 28篇 |
2009年 | 22篇 |
2008年 | 38篇 |
2007年 | 40篇 |
2006年 | 35篇 |
2005年 | 30篇 |
2004年 | 30篇 |
2003年 | 21篇 |
2002年 | 23篇 |
2001年 | 16篇 |
2000年 | 24篇 |
1999年 | 20篇 |
1998年 | 19篇 |
1997年 | 9篇 |
1996年 | 9篇 |
1995年 | 13篇 |
1994年 | 8篇 |
1993年 | 11篇 |
1992年 | 20篇 |
1991年 | 11篇 |
1990年 | 8篇 |
1989年 | 14篇 |
1988年 | 14篇 |
1987年 | 20篇 |
1986年 | 10篇 |
1985年 | 11篇 |
1984年 | 11篇 |
1982年 | 8篇 |
1981年 | 7篇 |
1980年 | 8篇 |
1979年 | 8篇 |
1977年 | 10篇 |
1976年 | 7篇 |
1975年 | 9篇 |
1974年 | 9篇 |
1969年 | 7篇 |
1968年 | 7篇 |
1960年 | 7篇 |
排序方式: 共有944条查询结果,搜索用时 0 毫秒
31.
Ascorbate and ascorbate peroxidase are important antioxidants that are abundant in N2-fixing legume root nodules. Antioxidants are especially critical in root nodules because leghemoglobin, which is present at high concentrations in nodules, is prone to autoxidation and production of activated oxygen species such as O2.- and H2O2. The merits of ascorbate and ascorbate peroxidase for maintaining conditions favorable for N2 fixation were examined in two model systems containing oxygen-binding proteins (purified myoglobin or leghemoglobin) and N2-fixing microorganisms (free-living Azorhizobium or bacteroids of Bradyrhizobium japonicum) in sealed vials. The inclusion of ascorbate alone to these systems led to enhanced oxygenation of hemeproteins, as well as to increases in nitrogenase (acetylene reduction) activity. The inclusion of both ascorbate and ascorbate peroxidase resulted in even greater positive responses, including increases of up to 4.5-fold in nitrogenase activity. In contrast, superoxide dismutase did not provide beneficial antioxidant action and catalase alone provided only very marginal benefit. Optimal concentrations were 2 mM for ascorbate and 200 micrograms/ml for ascorbate peroxidase. These concentrations are similar to those found in intact soybean nodules. These results support the conclusion that ascorbate and ascorbate peroxidase are beneficial for maintaining conditions favorable for N2 fixation in nodules. 相似文献
32.
Anna Wasiuk Dyana K. Dalton William L. Schpero Radu V. Stan Jose R. Conejo-Garcia Randolph J. Noelle 《Cancer immunology, immunotherapy : CII》2012,61(12):2273-2282
Mast cells have emerged as critical intermediaries in the regulation of peripheral tolerance. Their presence in many precancerous lesions and tumors is associated with a poor prognosis, suggesting mast cells may promote an immunosuppressive tumor microenvironment and impede the development of protective anti-tumor immunity. The studies presented herein investigate how mast cells influence tumor-specific T cell responses. Male MB49 tumor cells, expressing HY antigens, induce anti-tumor IFN-??+ T cell responses in female mice. However, normal female mice cannot control progressive MB49 tumor growth. In contrast, mast cell-deficient c-KitWsh (Wsh) female mice controlled tumor growth and exhibited enhanced survival. The role of mast cells in curtailing the development of protective immunity was shown by increased mortality in mast cell-reconstituted Wsh mice with tumors. Confirmation of enhanced immunity in female Wsh mice was provided by (1) higher frequency of tumor-specific IFN-??+ CD8+ T cells in tumor-draining lymph nodes compared with WT females and (2) significantly increased ratios of intratumoral CD4+ and CD8+ T effector cells relative to tumor cells in Wsh mice compared to WT. These studies are the first to reveal that mast cells impair both regional adaptive immune responses and responses within the tumor microenvironment to diminish protective anti-tumor immunity. 相似文献
33.
34.
T Dalton 《Biochimica et biophysica acta》1979,555(2):362-365
The responses of isolated frog skin to 5-hydroxytryptamine (increased active sodium transport and decreased passive chloride permeability) are diminished by incubation with the enzymes neuraminidase and N-acetylneuraminic acid aldolase but only in the absence of Ca2+ and presence of EDTA. The responses induced by oxytocin, adrenalin and aldosterone are unaffected by enzyme treatment. 相似文献
35.
36.
Aya Ibrahim Danielle Kirkpatrick Laura J. Nixon Dalton C. Ludwick Gianfranco Anfora Tracy C. Leskey 《Journal of Applied Entomology》2020,144(7):589-597
The brown marmorated stink bug, Halyomorpha halys Stål (Hemiptera: Pentatomidae), is an invasive pest that attacks specialty and row crops in North America and Europe. There has been a concerted effort to reduce frequent broad-spectrum insecticide applications made on vulnerable crops. One tool that has emerged recently is the use of long-lasting insecticide-treated nets (LLINs) as a killing agent. Here, we conducted bioassays to evaluate the effect of direct contact on deltamethrin-impregnated LLINs on the behaviour and survivorship of H. halys nymphs and adults in the laboratory. Following exposure at three different durations (1.25, 4.25 or 7.25 min), vertical and horizontal mobility of adults and nymphs and the flight capacity of adults were recorded and compared with individuals that were not exposed (control). Exposure to LLINs reduced the horizontal distance and velocity and increased the angular velocity of adults only but reduced vertical mobility of adults and nymphs. Adult flights were not significantly affected by LLIN exposure. Mortality of adults and nymphs at 7-day post-exposure ranged from 73% to 77% regardless of exposure time. We discuss our findings within the context of the potential for and limitations of deploying LLINs in vulnerable crops to manage H. halys populations. 相似文献
37.
Phukuntsi Metlholo A. Du Plessis Morne Dalton Desiré L. Jansen Raymond Sauther Michelle L. Cuozzo Frank P. Kotze Antoinette 《Primates; journal of primatology》2021,62(4):667-675
Primates - The habitats of Galago moholi are suspected to be largely fragmented, while the species is thought to be expanding further into the southernmost fringe of its range, as well as into... 相似文献
38.
Bobby G. Ng Paulina Sosicka François Fenaille Annie Harroche Sandrine Vuillaumier-Barrot Mindy Porterfield Zhi-Jie Xia Shannon Wagner Michael J. Bamshad Marie-Christine Vergnes-Boiteux Sophie Cholet Stephen Dalton Anne Dell Thierry Dupré Mathieu Fiore Stuart M. Haslam Yohann Huguenin Tadahiro Kumagai Hudson H. Freeze 《American journal of human genetics》2021,108(6):1040-1052
39.
Christopher C.R. Allen Claire E. Walker Narain D. Sharma Nuala A. Kerley Derek R. Boyd Howard Dalton 《Biocatalysis and Biotransformation》2013,31(4):257-264
The enantiopure (1 S, 2 S )- cis -dihydrodiol metabolites 2B - 5B have been obtained in low yield from the corresponding monosubstituted halobenzene substrates 2A - 5A, using a wild-type strain of Pseudomonas putida (ML2) containing benzene dioxygenase (BDO). Benzene cis -dihydrodiol dehydrogenase (BCD) from P. putida ML2 and naphthalene cis -dihydrodiol dehydrogenase (NCD) from P. putida 8859 were purified and used in a comparative study of the stereoselective biotransformation of cis -dihydrodiol enantiomers 2B - 5B. The BCD and NCD enzymes were found to accept cis -dihydrodiol enantiomers of monosubstituted benzene cis -dihydrodiol substrates 2B - 5B of opposite absolute configuration. The acyclic alkene 1,2-diols 10 - 17 were also found to be acceptable substrates for BCD. 相似文献
40.
Michael Eriksen Benros Thomas Munk Laursen Susanne Oksbjerg Dalton Merete Nordentoft Preben Bo Mortensen 《PloS one》2013,8(11)