全文获取类型
收费全文 | 2507篇 |
免费 | 266篇 |
出版年
2023年 | 13篇 |
2022年 | 34篇 |
2021年 | 48篇 |
2020年 | 25篇 |
2019年 | 29篇 |
2018年 | 35篇 |
2017年 | 42篇 |
2016年 | 60篇 |
2015年 | 94篇 |
2014年 | 110篇 |
2013年 | 144篇 |
2012年 | 179篇 |
2011年 | 174篇 |
2010年 | 105篇 |
2009年 | 101篇 |
2008年 | 133篇 |
2007年 | 124篇 |
2006年 | 128篇 |
2005年 | 134篇 |
2004年 | 134篇 |
2003年 | 110篇 |
2002年 | 99篇 |
2001年 | 39篇 |
2000年 | 40篇 |
1999年 | 41篇 |
1998年 | 33篇 |
1997年 | 22篇 |
1996年 | 31篇 |
1995年 | 31篇 |
1994年 | 23篇 |
1993年 | 15篇 |
1992年 | 25篇 |
1991年 | 22篇 |
1990年 | 22篇 |
1989年 | 17篇 |
1988年 | 24篇 |
1987年 | 22篇 |
1986年 | 25篇 |
1985年 | 29篇 |
1984年 | 24篇 |
1983年 | 15篇 |
1982年 | 16篇 |
1981年 | 22篇 |
1980年 | 11篇 |
1979年 | 12篇 |
1976年 | 11篇 |
1975年 | 14篇 |
1974年 | 15篇 |
1972年 | 10篇 |
1967年 | 9篇 |
排序方式: 共有2773条查询结果,搜索用时 31 毫秒
31.
32.
Alston-Mills Brenda Li Qi Chang Ottinger Mary Ann 《In vitro cellular & developmental biology. Plant》1989,25(10):934-938
Summary Production of antibodies against peptides or poorly antigenic proteins by conventional methods often requires either large
quantities of the native immunogen or some chemical modification to increase their antigenicity. In this study an in vivo
and in vitro immunization protocol has been used to generate monoclonal antibodies against the decapeptide luteinizing hormone-releasing
hormone (LHRH). Two injections of 100 μg of avian LHRH-I into BALB/c mice were given 7 d apart. Dissociated splenocytes were
collected under sterile conditions. They were incubated with 100 μg of the immunogen in 75-cm2 tissue culture flasks in thymocyte-conditioned media. After 5 to 8 d exposure to the antigen, splenocytes were fused with
SP2/O myeloma cells by polyethylene glycol. The cells were plated into 24 wells and then incubated in hypoxanthine aminopterin
and thymidine selective media. After 14 d an initial screening was done by enzyme immunoassay. The positive wells (6/24) were
expanded into 96-well plates and rescreened. Selected lines were cloned out 3 times by limiting dilution and the most positive
expanded for ascites production. The antibody was affinity purified in a protein A column. The antibody cross-reacted with
LHRH-I and II but preferentially to LHRH-I, as shown by competitive assay. A hypothalamic extract from a mature chick showed
a higher response than preparations from whole brain explants of 1- to 3-d posthatched chicks, mature quail, and mature mouse.
This work was funded by the Maryland Agricultural Experiment Station artical no. A4975, contribution no. 8019. 相似文献
33.
Norepinephrine stimulates the growth in size of non-dividing, neonatal cardiac muscle cells, and it can stimulate the growth in numbers of dividing hepatocytes and endothelial cells in culture. The objective of this study was to test the hypothesis that in dividing fetal cardiocytes, norepinephrine would stimulate growth in cell number rather than in cell size. Fourteen-day fetal heart cells were placed in serum-free or serum-supplemented cultures in the presence or absence of norepinephrine (NE), NE plus propranolol, or isoproterenol for 4 days. Almost 90% of the cardiocytes in serum-supplemented medium were in the cell cycle as determined by proliferating cell nuclear antigen (PCNA) antibody staining during this period. In addition, between days 2 and 4 of culture, 35% and 40% of these cardiocytes were labeled with 3H-thymidine. After 4 days the cardiocytes increased in cell number in the serum-supplemented NE cultures as compared to serum-free cultures. In contrast, there was no significant change in cardiocyte volume between any of the groups examined. It was concluded that in dividing muscle cell populations the effect of norepinephrine was to enhance cell proliferation rather than to stimulate cell growth in size. 相似文献
34.
35.
36.
James K. Friel Claude Mercer Wayne L. Andrews Brian R. Simmons Simon E. Jackson 《Biological trace element research》1996,54(2):135-142
Contamination in a trace element laboratory can come from a variety of sources, including laboratory gloves. Therefore, vinyl
and latex gloves were obtained from as many manufacturers as would supply gloves. These gloves were either prepared for acid-washing
and subsequent soaking in an acid solution, or immersed in an acid solution for a duration of either 1 min or 1 h. Incubation
washes were analyzed for a variety of trace elements by flame atomic abosrption spectroscopy (AAS) or inductively coupled
mass spectrometry (ICP-MS). Results indicated that only three brands of vinyl gloves were acceptable for use in a trace element
laboratory, whereas others had contamination of different elements. Latex gloves contained such high levels of biologically
important elements that they were not considered suitable for routine trace element work. Vinyl gloves of choice should be
routinely acid-washed before use in a trace element laboratory. 相似文献
37.
Ligand-regulated transport of the Menkes copper P-type ATPase efflux pump from the Golgi apparatus to the plasma membrane: a novel mechanism of regulated trafficking. 总被引:31,自引:1,他引:30 下载免费PDF全文
M J Petris J F Mercer J G Culvenor P Lockhart P A Gleeson J Camakaris 《The EMBO journal》1996,15(22):6084-6095
The Menkes P-type ATPase (MNK), encoded by the Menkes gene (MNK; ATP7A), is a transmembrane copper-translocating pump which is defective in the human disorder of copper metabolism, Menkes disease. Recent evidence that the MNK P-type ATPase has a role in copper efflux has come from studies using copper-resistant variants of cultured Chinese hamster ovary (CHO) cells. These variants have MNK gene amplification and consequently overexpress MNK, the extents of which correlate with the degree of elevated copper efflux. Here, we report on the localization of MNK in these copper-resistant CHO cells when cultured in different levels of copper. Immunofluorescence studies demonstrated that MNK is predominantly localized to the Golgi apparatus of cells in basal medium. In elevated copper conditions there was a rapid trafficking of MNK from the Golgi to the plasma membrane. This shift in steady-state distribution of MNK was reversible and not dependent on new protein synthesis. In media containing basal copper, MNK accumulated in cytoplasmic vesicles after treatment of cells with a variety of agents that inhibit endosomal recycling. We suggest that MNK continuously recycles between the Golgi and the plasma membrane and elevated copper shifts the steady-state distribution from the Golgi to the plasma membrane. These data reveal a novel system of regulated protein trafficking which ultimately leads to the efflux of an essential yet potentially toxic ligand, where the ligand itself appears directly and specifically to stimulate the trafficking of its own transporter. 相似文献
38.
A diverse collection of actinomycete strains were screened for production of extracellular peroxidase activity by adapting a chemiluminescence analysis system developed for horseradish peroxidase-based enzyme-linked immunosorbent assay. Extracellular peroxidase activity was found to be common but quantitatively variable, and this rapid and sensitive screening system permitted identification of a small group of high-producing strains. A range of spectrophotometric assays were compared for the measurement of peroxidase activity in concentrated culture supernatants of two selected thermophilic streptomycetes. Of these, the peroxide-dependent oxidation of 2,4-dichlorophenol was identified as the most robust and reproducible assay for quantitative studies. 相似文献
39.
E. R. Chin H. J. Green F. Grange J. D. Mercer P. J. O'Brien 《Molecular and cellular biochemistry》1994,139(1):41-52
A multiple measurement system for assessing sarcoplasmic reticulum (SR) Ca++-ATPase activity and Ca++-uptake was used to examine the effects of SR fractionation and quick freezing on rat white (WG) and red (RG) gastrocnemius muscle.In vitro measurements were performed on whole muscle homogenates (HOM) and crude microsomal fractions (CM) enriched in SR vesicles before and after quick freezing in liquid nitrogen. Isolation of the CM fraction resulted in protein yields of 0.96±0.1 and 0.99±0.1 mg/g in WG and RG, respectively. The percent Ca++-ATPase recovery for CM compared to HOM was 14.5% (WG) and 10.1% (RG). SR Ca++-activated Ca++-ATPase activity was not affected by quick freezing of HOM or CM, but basal ATPase was reduced (P<0.05) in frozen HOM (5.12±0.18–3.98±0.20 mole/g tissue/min in WG and from 5.39±0.20–4.48±0.24 mole/g tissue/min in RG). Ca++-uptake was measured at a range of physiological free [Ca++] using the Ca++ fluorescent dye Indo-1. Maximum Ca++-uptake rates when corrected for initial [Ca++]f were not altered in HOM or CM by quick freezing but uptake between 300 and 400nM free Ca++ was reduced (P<0.05) in quick frozen HOM (1.30±0.1–0.66±0.1 mole/g tissue/min in WG and 1.04±0.2–0.60±0.1 mole/g tissue/min in RG). Linear correlations between Ca++-uptake and Ca++-ATPase activity measured in the presence of the Ca++ ionophore A23187 were r=+0.25, (P<0.05) and r=+0.74 (P<0.05) in HOM and CM preparations, respectively, and were not altered by freezing. The linear relationships between HOM and CM maximum Ca++-uptake (r=+0.44, P<0.05) and between HOM and CM Ca++-ATPase activity (r=+0.34, P<0.05) were also not altered by tissue freezing. These data suggest that alterations in maximal SR Ca++-uptake function and maximal Ca++-ATPase activity may be measured in both HOM and CM fractions following freezing and short term storage. (Mol Cell Biochem139, 41–52, 1994) 相似文献
40.
Oligochaeta in Spartina stems: the microdistribution of Enchytraeidae and Tubificidae in a salt marsh,Sapelo Island,USA 总被引:1,自引:1,他引:0
The distribution and abundance of Enchytraeidae and Tubificidae in and around Spartina alterniflora plants in a tidal salt marsh on Sapelo Island, Georgia, USA were studied using two different sampling techniques: wet funnel extraction and stem dissection. At least 80% of all worms inhabited leaf sheaths at the bases of S. alterniflora plants, and densities were low in sediment, root and surface debris samples. Oligochaete densities were dependent on the position within the marsh, the height on stems and the stage of sheath decay. Six predominant species were identified and included Marionina appendiculata, Marionina spartinae, Marionina waltersi, Marionina paludis, and Monopylephorus parvus. Individual species were distributed differently on stems and enchytraeids were more common than tubificids on standing-dead and further up S. alterniflora stems. Estimates of oligochaete densities in salt marsh habitats are increased dramatically when the numbers of worms on stems are considered. Possible advantages of the stem microhabitat are discussed in relation to the biology and ecology of oligochaetes. 相似文献