全文获取类型
收费全文 | 4404篇 |
免费 | 270篇 |
国内免费 | 1篇 |
出版年
2024年 | 3篇 |
2023年 | 41篇 |
2022年 | 75篇 |
2021年 | 161篇 |
2020年 | 111篇 |
2019年 | 116篇 |
2018年 | 170篇 |
2017年 | 148篇 |
2016年 | 185篇 |
2015年 | 242篇 |
2014年 | 300篇 |
2013年 | 336篇 |
2012年 | 355篇 |
2011年 | 349篇 |
2010年 | 199篇 |
2009年 | 166篇 |
2008年 | 213篇 |
2007年 | 192篇 |
2006年 | 205篇 |
2005年 | 160篇 |
2004年 | 146篇 |
2003年 | 119篇 |
2002年 | 118篇 |
2001年 | 98篇 |
2000年 | 66篇 |
1999年 | 63篇 |
1998年 | 23篇 |
1997年 | 16篇 |
1996年 | 18篇 |
1995年 | 12篇 |
1994年 | 17篇 |
1993年 | 10篇 |
1992年 | 27篇 |
1991年 | 20篇 |
1990年 | 16篇 |
1989年 | 19篇 |
1988年 | 21篇 |
1987年 | 20篇 |
1986年 | 15篇 |
1985年 | 19篇 |
1984年 | 15篇 |
1983年 | 10篇 |
1981年 | 8篇 |
1980年 | 4篇 |
1979年 | 9篇 |
1976年 | 4篇 |
1975年 | 6篇 |
1974年 | 5篇 |
1973年 | 3篇 |
1966年 | 3篇 |
排序方式: 共有4675条查询结果,搜索用时 890 毫秒
21.
R Borojevic S A Vinhas A N Monteiro G B Domont F R Zyngier J A Grimaud 《Biology of the cell / under the auspices of the European Cell Biology Organization》1985,53(3):231-238
Hepatic connective tissue cells associated with schistosomal fibrosis and alcoholic cirrhosis were studied in vitro. Primary cell lines were isolated from all biopsies: they were identified as specific homogeneous cell populations, named liver connective tissue cells (LCTC). They were recognized as analogous to smooth muscle cells, different from true fibroblasts by morphological and physiological criteria. The proliferative capacity of LCTC is directly proportional to the degree of fibrosis in hepatic tissues. LCTC are able to secrete type I, III and IV collagen, fibronectin, laminin and amyloid P component. Their relationship with specific pathology of intrahepatic vascular tree in schistosomiasis is hypothesized. 相似文献
22.
Antonio Campos-Neto Fernanda W. M. Lima Arnaldo F. B. Andrade 《The Journal of eukaryotic microbiology》1985,32(1):84-88
A rapid and simple method for the purification of amastigotes of Trypanosoma cruzi from spleens of infected mice is described. A protein A-Scpharose 4B immunoadsorbent column bound with antisera to epimastigotes of T. cruzi was used to purify the tissue forms of this parasite. Host cells and debris are not retained, and parasites can be eluted in high yields and purity. Studies of surface glycoproteins and glycolipids of the purified amastigotes with 18 lectins of various specificities revealed the presence on the parasites of receptors for N-acetylglucosamine, N-acetylgalactosamine, D-galactose, and D-mannose binding lectins. 相似文献
23.
To determine the influence of feeding, lighting and time of day on the copulating behavior of Panstrongylus megistus, 480 insect pairs were divided into four groups of 120 each and tested in the following respective situations: without food deprivation (F.D.), with five days of F.D., with ten days of F.D., and with 20 days of F.D. The tests were performed between 9:00 a.m. to 12:00 a.m. and 7:00 p.m. to 10:00 p.m., with light (700-1400 lux) and in the dark (1.4-2.8 lux) and behavior was recorded by the time sampling technique. Mating speed (MS) and duration of copulation (DC) were also calculated for each situation. The maximum frequency of copulation was observed after five days of F.D., at night, in the dark (n = 16), and the minimum was observed for recently-fed pairs, at night, with light (n = 4). Males approached females more often than females approached males. MS was lowest in pairs with twenty days of F.D., at night, with light (mean = 23.0 +/- 16.0 minutes), and highest in recently-fed pairs, during the day, with light (mean = 2.9 +/- 2.5 minutes). DC was shortest in recently-fed insects, during the day, in the dark (mean = 23.5 +/- 6.7 minutes), and longest in recently-fed animals, at night, in the dark (mean = 38.3 +/- 6.9 minutes). 相似文献
24.
25.
W T Garvey T P Huecksteadt F B Lima M J Birnbaum 《Molecular endocrinology (Baltimore, Md.)》1989,3(7):1132-1141
26.
Alkaline extracts of adult opossum red cells were used to determine triphosphates of adenosine, deoxyadenosine and guanosine by anion exchange HPLC. Mean (nm/g Hg) ATP content of erythrocytes was 3713 and that of dATP 1913 (n = 12). Sonicates of red cells deaminated adenosine (ADO) at a rate of 1.55 nm/mg Hg/h and deoxyadenosine (dADO) at 1.82 nm/mg Hg/h. dATP synthesis from provided dADO was one order of magnitude greater in opossum than in human erythrocytes at both low and high dADO and Pi concentrations. 相似文献
27.
Shlomo Nir Nejat Düzgünes Maria C. Pedroso De Lima Dick Hoekstra 《Cell biochemistry and biophysics》1990,17(2):181-201
The fusion of viruses with cells and liposomes is reviewed with focus on the analysis of the final extents and kinetics of
fusion.Influenza virus andSendai virus exhibit 100% of fusion capacity with cells at pH 5 and pH 7.5, respectively. On the other hand, there may be in certain
cases, a limit on the number of virions that can fuse with a single cell, that is significantly below the limit on binding.
It still remains to be resolved whether this limit reflects a limited number of possible fusion sites, or a saturation limit
on the amount of viral glycoproteins that can be incorporated in the cellular membrane, like the case of virus fusion with
pure phospholipid vesicles, in which the fusion products were shown to consist of a single virus and several liposomes. Both
viruses demonstrate incomplete fusion activity towards liposomes of a variety of compositions. In the case ofSendai virus, fusion inactive virions bind essentially irreversibly to liposomes. Yet, preliminary results revealed that such bound,
unfused virions can be released by sucrose gradient centrifugation. The separated unfused virions subsequently fuse when incubated
with a “fresh” batch of liposomes. We conclude, therefore, that the fraction of initially bound unfused virions does not consist
of dective particles, but rather of particles bound to liposomes via “inactive” sites.
Details of the low pH inactivation of fusion capacity ofinfluenza virus towards cells and liposomes are presented. This inactivation is caused by protonation and exposure of the hydrophobic
segment of HA2, and affects primarily the fusion rate constants. Some degree of inactivation also occurs when virions are bound to cellular
membranes. 相似文献
28.
Maria Claudia Gonzalez Deniselle Susana L. Gonzalez Gerardo G. Piroli Analia E. Lima Alejandro F. De Nicola 《Cellular and molecular neurobiology》1996,16(1):61-72
Summary 1. Wobbler mice suffer an autosomal recessive mutation producing severe motoneuron degeneration and dense astrogliosis, with
increased levels of glial fibrillary acidic protein (GFAP) in the spinal cord and brain stem. They have been considered animal
models of amyotrophic lateral sclerosis and infantile spinal muscular atrophy.
2. Using Wobbler mice and normal littermates, we investigated the effects of the membrane-active steroid Lazaroid U-74389F
on the number of GFAP-expressing astrocytes and glucocorticoid receptors (GR). Lazaroids are inhibitors of oxygen radical-induced
lipid peroxidation, and proved beneficial in cases of CNS injury and ischemia.
3. Four days after pellet implantation of U-74389F into Wobbler mice, hyperplasia and hypertophy of GFAP-expressing astrocytes
were apparent in the spinal cord ventral and dorsal horn, areas showing already intense astrogliosis in untreated Wobbler
mice. In control mice, U-74389F also produced astrocyte hyperplasia and hypertophy in the dorsal horn and hyperplasia in the
ventral-lateral funiculi of the cord.
4. Givenin vivo U-74389F did not change GR in spinal cord of Wobbler or control mice, in line with the concept that it is active in membranes
but does not bind to GR. Besides, U-74390F did not compete for [3H]dexamethasone binding when addedin vitro.
5. The results suggest that stimulation of proliferation and size of GFAP-expressing astrocytes by U-74389F may be a novel
mechanism of action of this compound. The Wobbler mouse may be a valuable animal model for further pharmacological testing
of glucocorticoid and nonglucocorticoid steroids in neurodegenerative diseases. 相似文献
29.
In a study of purine alkaloid catabolism pathways in coffee,14C-labelled theobromine, caffeine, theophylline and xanthine were incubated with leaves ofCoffea arabica. Incorporation of label into14CO2 was determined and methanol-soluble metabolites were analysed by high-performance liquid chromatography-radiocounting. The data obtained demonstrate catabolism of caffeine theophylline 3-methylxanthine xanthine. Xanthine is degraded further by the conventional purine catabolism pathway to CO2 and NH3 via uric acid, allantoin and allantoic acid. The conversion of caffeine to theophylline is the rate-limiting step in purine alkaloid catabolism and provides a ready explanation for the high concentration of endogenous caffeine found inC. arabica leaves. Although theobromine is converted primarily to caffeine, a small portion of the theobromine pool appears to be degraded to xanthine by a caffeine-independent pathway. In addition to being broken down to CO2, via the purine catabolism pathway, xanthine is metabolised to 7-methylxanthine. Metabolism of [2-14C]xanthine byC. arabica leaves in the presence of 5 mM allopurinol results in very large increases in incorporation of radioactivity into 7-methylxanthine as degradation of the substrate via the purine catabolism pathway is blocked. The identity of 7-methylxanthine in these studies was confirmed by gas chromatography-mass spectrometry analysis.Abbreviations HPLC-RC
high-performance liquid chromatography-radiocounting
This work was supported by the British Council which provided H.A. with Japan-UK travel grants. F.M.G. was supported by a Biotechnology and Biological Sciences Research Council grant to A.C. 相似文献
30.
Alvaro N. A. Monteiro Radovan Borojevic 《In vitro cellular & developmental biology. Animal》1995,31(2):149-155
Summary Liver connective tissue cells (LCTC) isolated from patients with fibrotic livers have morphological and biochemical characteristics
of myofibroblasts. We have examined the proliferation of LCTC derived from normal livers and from livers with fibrosis of
different etiologies, as well as proliferation of skin fibroblasts. We have compared proliferation rates in the presence of
fresh human serum and heat-inactivated serum. While skin fibroblast and LCTC from normal liver showed no difference, proliferation
of LCTC from fibrotic livers was markedly decreased in the presence of heat-inactivated serum. We demonstrate that the native
complement component C1 is a factor involved in the induction of DNA synthesis and proliferation of LCTC isolated from fibrotic
livers. We propose that native C1, acting probably in cooperation with other growth factors, is involved in the expansion
of connective tissue cells during the development of liver fibrosis. 相似文献