全文获取类型
收费全文 | 2276篇 |
免费 | 137篇 |
出版年
2022年 | 17篇 |
2021年 | 64篇 |
2020年 | 19篇 |
2019年 | 32篇 |
2018年 | 34篇 |
2017年 | 37篇 |
2016年 | 61篇 |
2015年 | 75篇 |
2014年 | 120篇 |
2013年 | 129篇 |
2012年 | 130篇 |
2011年 | 140篇 |
2010年 | 110篇 |
2009年 | 76篇 |
2008年 | 101篇 |
2007年 | 104篇 |
2006年 | 88篇 |
2005年 | 84篇 |
2004年 | 59篇 |
2003年 | 58篇 |
2002年 | 58篇 |
2001年 | 55篇 |
2000年 | 49篇 |
1999年 | 32篇 |
1998年 | 20篇 |
1996年 | 15篇 |
1993年 | 15篇 |
1992年 | 16篇 |
1991年 | 31篇 |
1990年 | 28篇 |
1989年 | 21篇 |
1988年 | 23篇 |
1987年 | 36篇 |
1986年 | 35篇 |
1985年 | 27篇 |
1984年 | 27篇 |
1983年 | 24篇 |
1982年 | 19篇 |
1981年 | 23篇 |
1980年 | 15篇 |
1979年 | 29篇 |
1977年 | 21篇 |
1976年 | 19篇 |
1975年 | 21篇 |
1974年 | 16篇 |
1973年 | 24篇 |
1972年 | 27篇 |
1971年 | 22篇 |
1969年 | 15篇 |
1967年 | 16篇 |
排序方式: 共有2413条查询结果,搜索用时 578 毫秒
861.
Tatini Rakshit Subhadip Senapati Satyabrata Sinha A. M. Whited Paul S.-H. Park 《PloS one》2015,10(10)
Rhodopsin forms nanoscale domains (i.e., nanodomains) in rod outer segment disc membranes from mammalian species. It is unclear whether rhodopsin arranges in a similar manner in amphibian species, which are often used as a model system to investigate the function of rhodopsin and the structure of photoreceptor cells. Moreover, since samples are routinely prepared at low temperatures, it is unclear whether lipid phase separation effects in the membrane promote the observed nanodomain organization of rhodopsin from mammalian species. Rod outer segment disc membranes prepared from the cold-blooded frog Xenopus laevis were investigated by atomic force microscopy to visualize the organization of rhodopsin in the absence of lipid phase separation effects. Atomic force microscopy revealed that rhodopsin nanodomains form similarly as that observed previously in mammalian membranes. Formation of nanodomains in ROS disc membranes is independent of lipid phase separation and conserved among vertebrates. 相似文献
862.
Sankha Pattanayak Sibasish Paul Bappaditya Nandi Surajit Sinha 《Nucleosides, nucleotides & nucleic acids》2013,32(11):763-782
An inexpensive and much improved protocol has been developed for the synthesis of protected morpholino monomers from unprotected ribonucleosides in high overall yield, using oxidative glycol cleavage and reductive amination strategy. Unlike the previous methods, the present strategy allows installing the exocyclic amine protections at a later stage, and thus avoids the use of expensive, or commercially unavailable, exocyclic amine-protected ribonucleosides as starting materials. To demonstrate the flexibility of the present method in choosing protecting groups, the monomers have been protected with several such groups of different deblocking properties at the exocyclic amine position. 相似文献
863.
Eukaryotic microalgae serve as indicators of environmental change when exposed to severe seasonal fluctuations. Several environmental stress conditions are known to produce reactive oxygen species in cellular compartments, resulting in oxidative damage and apoptosis. The study of cell death in higher plants and animals has revealed the existence of an active ‘programmed cell death’ (PCD) process and similarities between such processes suggest an evolutionary origin. A study was undertaken to examine the morphological, biochemical and molecular responses of the unicellular green alga Chlamydomonas reinhardtii after exposure to oxidative (10 mM H2O2) and osmotic (200 mM NaCl and 360 mM sorbitol) stress. Concentrations of H2O2 (2–50 mM), NaCl and sorbitol (100–800 mM) were negatively correlated with growth. Biochemical analyses showed an increase in intracellular H2O2 production (2.2-fold with H2O2 and ~1.2–1.4-fold with NaCl and sorbitol) and activities of some antioxidant enzymes [super oxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX)]. Alteration of mitochondrial membrane potential (MMP) was observed upon treatment with H2O2 and NaCl, but not with sorbitol, indicating that the ionic stress component of NaCl altered the MMP. In addition, H2O2 led to the activation of a caspase-3-like protein, increase in the cleavage of a poly(ADP) ribose polymerase-1 (PARP-1)-like enzyme and formation of DNA nicks and laddering. With NaCl and sorbitol, no caspase activation, nor oligonucleosomal DNA laddering was observed, indicating non-apoptotic death. However, genomic DNA of NaCl (800 mM)-stressed cells, but not those of sorbitol-treated cells showed complete shearing. We conclude that the ionic rather than the osmotic component of NaCl leads to necrosis. These results unequivocally suggest that the vegetative cells of C. reinhardtii respond differentially to various stress agents, leading to different death types in the same organism. Moreover, unlike most other organisms, when exposed to NaCl this alga does not undergo PCD. 相似文献
864.
Songlei Liu Sukanya Punthambaker Eswar P R Iyer Thomas Ferrante Daniel Goodwin Daniel Fürth Andrew C Pawlowski Kunal Jindal Jenny M Tam Lauren Mifflin Shahar Alon Anubhav Sinha Asmamaw T Wassie Fei Chen Anne Cheng Valerie Willocq Katharina Meyer King-Hwa Ling Conor
K Camplisson Richie E Kohman John Aach Je Hyuk Lee Bruce
A Yankner Edward S Boyden George M Church 《Nucleic acids research》2021,49(10):e58
865.
The viability of freeze-dried cells of Streptococcus lactis C-2 was studied by suspending washed cells in reconstituted skim milk and in solutions of ascorbic acid, thiourea and ammonium chloride used alone or in various combinations. Low cell survival was observed with the use of reconstituted skim milk. Fortification of this menstruum with ascorbic acid and thiourea gave maximum survival of freeze-dried cells. 相似文献
866.
867.
Sarika Sinha Richa Srivastava Bhupesh Prusty B. C. Das Ramendra K. Singh 《Nucleosides, nucleotides & nucleic acids》2013,32(6-7):773-777
Two novel adenosine analogs, viz. 9-(1′-β-D-arabinofuranosyl)-6-nitro-1,3-dideazapurine or Ara-NDDP (1) and 9-(5′-deoxy-5′-S-(propionic acid) (1′-β-D-ribofuranosyl) adenine or SAH analog (2), indigenously synthesized, have been found to be potential anticancer agents against cervical cancer caused by human papilloma virus. 相似文献
868.
869.
Immunomodulatory effect of laser on whole body exposure. 总被引:2,自引:0,他引:2
L Ganju A Salhan D Karan S Chanda K K Srivastava 《Indian journal of experimental biology》1999,37(5):444-449
All biomedical laser applications are based on the interaction of laser light with biological system. During the past decade considerable evidence has accumulated demonstrating that non-thermal exposure to laser can elicit cellular changes in the immune system. In the present study, we have analyzed the effect of laser on immune response in rats. A group of rats were exposed to 0.225 mu j/cm2 for 90 min for 3 days in specially designed fiberglass chambers. The whole body exposure of rats of He-Ne laser modulated both the humoral and cellular responses to tetanus toxoid stimulation. Plain red light used as a control for red laser light showed an appreciable degree of response as compared to the control groups, but not to the extent of the response to laser. Non-responders turned responders after exposure to laser. There was no response in unimmunized groups when exposed to laser and red light alone. The early and heightened immune response and proliferation of lymphocytes after exposure to laser is suggestive of a complex interaction at the cellular immune response level. 相似文献
870.
J. Chaudhuri T. K. Chakraborti S. Chanda C. N. Pope 《Journal of biochemical and molecular toxicology》1993,8(4):207-216
We previously reported similar levels of brain cholinesterase inhibition but marked differences in toxicity following acute maximum tolerated doses of the organophosphate pesticides parathion and chlorpyrifos. Because extensive acetylcholinesterase inhibition often induces compensatory changes in cholinergic receptor populations, we compared the effects of parathion and chlorpyrifos on brain muscarinic receptors. Adult male rats were treated with vehicle or the maximum tolerated dose of parathion (18 mg/kg, sc) or chlorpyrifos (279 mg/kg, sc) and observed for signs of acute toxicity. Similarly treated animals were sacrificed at 2, 7, or 14 days after treatment for measurement of cholinesterase activity and binding to the nonselective muscarinic antagonist [3H]quinuclidinyl benzilate, the M2-preferential antagonist [3H]AFDX-384, and the high-affinity agonist [3H]cis-methyldioxolane. More acute toxicity was noted after parathion treatment. Both insecticides caused similar levels (> 85%) of maximal cholinesterase inhibition and reductions (up to 55%) in atropine-sensitive quinuclidinyl benzilate binding (i.e., total muscarinic receptors) and [3H]AFDX-384 binding in cortex and striatum. Parathion also reduced, whereas chlorpyrifos increased, total muscarinic receptor binding and [3H]AFDX-384 binding in the cerebellum. When tissues were preincubated with paraoxon (10 μM), radiolabeling of a subset of quinuclidinyl benzilate binding sites was blocked and the apparent densities of these organophosphate-sensitive receptors in all three tissues were decreased (16% maximal) by parathion but increased (up to 37%) by chlorpyrifos. Similarly, parathion decreased whereas chlorpyrifos increased [3H]cis-methyldioxolane binding sites in all three brain regions. We propose that differential modulation of these organophosphate-sensitive muscarinic receptors contributes to differences in acute toxicity following exposure to these pesticides. 相似文献