全文获取类型
收费全文 | 9026篇 |
免费 | 35篇 |
国内免费 | 37篇 |
专业分类
9098篇 |
出版年
2023年 | 13篇 |
2022年 | 97篇 |
2021年 | 221篇 |
2020年 | 118篇 |
2019年 | 194篇 |
2018年 | 336篇 |
2017年 | 327篇 |
2016年 | 583篇 |
2015年 | 761篇 |
2014年 | 619篇 |
2013年 | 1104篇 |
2012年 | 631篇 |
2011年 | 461篇 |
2010年 | 692篇 |
2009年 | 571篇 |
2008年 | 485篇 |
2007年 | 437篇 |
2006年 | 416篇 |
2005年 | 284篇 |
2004年 | 101篇 |
2003年 | 40篇 |
2002年 | 34篇 |
2001年 | 39篇 |
2000年 | 154篇 |
1999年 | 64篇 |
1998年 | 56篇 |
1997年 | 51篇 |
1996年 | 29篇 |
1995年 | 13篇 |
1994年 | 6篇 |
1993年 | 4篇 |
1992年 | 21篇 |
1991年 | 10篇 |
1990年 | 4篇 |
1989年 | 10篇 |
1987年 | 9篇 |
1986年 | 5篇 |
1985年 | 6篇 |
1984年 | 6篇 |
1983年 | 7篇 |
1982年 | 7篇 |
1981年 | 7篇 |
1980年 | 10篇 |
1979年 | 5篇 |
1978年 | 5篇 |
1976年 | 4篇 |
1975年 | 4篇 |
1973年 | 4篇 |
1964年 | 3篇 |
1935年 | 6篇 |
排序方式: 共有9098条查询结果,搜索用时 0 毫秒
41.
42.
Shu’a Yagev Michael Heller Arié Pinson 《In vitro cellular & developmental biology. Plant》1984,20(12):893-898
Summary Postnatal rat heart cells in culture enriched with respect to muscle cells were obtained by either high density seeding or
by the replating technique. [3H]Thymidine incorporation to DNA and the enzymatic pattern of cytoplasmic and lysosomal enzymes have been studied as a function
of the culture’s age, of seeding density, and replating. It was shown that (a) replating maintains predominance of myocyte
population for at least 2 wk in culture; (b) heavy seeding density allows homogeneous myocyte population for the 1st wk in
culture; and (c) the enzyme profile of the culture may serve as an indicator for the type of cell population in culture and
its state of differentiation.
This study was done as partial fulfilment of the M.Sc. thesis in Biochemistry (SY). Supported by grants from The Chief Scientist,
Ministry of Health, State of Israel; The Ministry of Education and Sciences, State of Niedersachssen (FRG); and The Foundation
for Heart Research from Mr. and Mrs. D. Vidal-Madjar, Paris, France. 相似文献
43.
3H-thymidine incorporation and DNA-polymerase activity during early hours of wheat embryo germination at two viability levels
have been studied. The patterns of two biosynthetic activities, as well as the dependence of DNA synthesis on protein synthesis,
indicated the presence of a delay in the early phase of imbibition of the aged embryos with respect to viable germs. 相似文献
44.
Brigitte Tréton Marie -Thérèse Le Dall H. Heslot 《Applied microbiology and biotechnology》1978,6(1):67-77
Summary We investigated the excretion of citric and isocitric acids in a strain of Saccharomycopsis lipolytica grown on either n-paraffins, glucose, or glycerol. These acids were excreted in the ratio of 67:33 on n-paraffins and roughly 92:8 on either glucose or glycerol. However, with all the carbon sources used, the relative amount of isocitric acid in the intracellular pool remained below 10%. The assimilation of citric and isocitric acids was prevented when glucose or glycerol were the carbon sources, but not when n-paraffins were used. Citric acid stopped isocitric acid assimilation. These phenomena of selective assimilation and/or uptake might explain the variations observed in the ratio of citric to isocitric acids excreted on different carbon sources. 相似文献
45.
46.
47.
Keith Paige Melanie Palomares Patricia A. D’Amore Susan J. Braunhut 《In vitro cellular & developmental biology. Animal》1991,27(2):151-157
Summary The growth of the endothelial cell (EC) is tightly regulated throughout the body. Many factors have been implicated in modulating
EC growth including diffusible compounds, cell-to-cell interactions, and the extracellular matrix (ECM). Retinol, or vitamin
A alcohol, has recently been shown to inhibit the growth of bovine capillary ECs, in vitro. Retinoids are known to modify
ECM in other cell systems, and pure ECM components have been shown to effect EC growth rates. We, therefore, examined the
role of the matrix in the retinol-induced inhibition of ECs. Cell-free matrices from control and vitamin A-treated ECs were
prepared by removing cells with EGTA treatment after 7 d of culture. Matrix proteins were analyzed by solubilizing the matrices
in 5M quanidine-HCl and performing Western blot analysis using specific antibodies to matrix proteins. In isolating the ECM, we
observed that retinol-treated cultures of ECs were resistant to EGTA removal; retinol-treated ECs required twice the exposure
time to EGTA to detach from their matrix than did controls cells. Western blot analysis of matrix proteins derived from control
and retinol-treated EC cultures demonstrated a 1.6-fold increase in lamininβ chains and a 2.5-fold increase in fibronectin in the ECM of retinol-treated EC compared to control cell matrix. Functional
properties of these matrices were assessed by plating control and Day 6 retinol-treated ECs onto the matrices and measuring
attachment and growth by determining cell numbers at 24, 72, and 144 h. These studies revealed that control cells attached
in greatest numbers to a control matrix whereas retinol-treated ECs preferentially attached to a matrix derived from retinol-treated
cells. Furthermore, control ECs which grew rapidly on a control matrix were growth inhibited on a retinol-derived matrix.
These data indicate that vitamin A treatment of ECs effects both their phenotype and influences the composition and the functional
properties of their underlying ECM. These studies also demonstrate that alterations of the matrix are at least in part responsible
for the growth inhibition of EC by retinol. 相似文献
48.
Kim B. Saunders Patricia A. D’Amore 《In vitro cellular & developmental biology. Animal》1992,28(7-8):521-528
Summary Heterotypic cell-cell interactions appear to be involved in the control of development and function in a wide variety of tissues.
In the vasculature, endothelial cells and mural cells (smooth muscle cells or pericytes) make frequent contacts, suggesting
a role for intercellular interactions in the regulation of vascular growth and function. We have previously grown endothelial
cells and mural cells together in mixed cultures and found that heterocellular contact led to endothelial growth inhibition.
However, this mixed culture system does not lend itself to the examination of the effects of contact on the phenotype of the
individual cell types. We have therefore developed a co-culture system in which cells can be co-cultured across a porous membrane,
permitting intercellular contact while maintaining pure cell populations. Co-culture of endothelial cells and smooth muscle
cells across membranes with pore sizes of 0.02, 0.4, 0.6, and 0.8μm maintained the two cell types as homogeneous populations, whereas smooth muscle cells migrated across the membrane through
pores of 2.0μm. Vascular cell co-culture across membranes with 0.8-μm pores resulted the inhibition of endothelial cell proliferation and the generation of conditioned media which inhibited
endothelial cell growth. The arrangement of the cells in this co-culture system mimics thein vivo orientation of vascular cells in which mural cells are separated from the abluminal surface of the endothelium by a fenestrated
internal elastic lamina or basement membrane. Because this co-culture system maintains separable populations of cells in contact
or close proximity allowing for biochemical and molecular analyses of pure populations, it should prove useful for the study
of cell-cell interactions in a variety of systems. 相似文献
49.
W. Dall 《Journal of experimental marine biology and ecology》1975,19(1):43-58
Free leucine, valine, proline, tyrosine, alanine, taurine, glutamic acid, and glycine are present in both blood and muscle of Panulirus longipes (Milne Edw.). Arginine is present in muscle only. Five unidentified ninhydrin-positive spots appeared in thin-layer chromatograms of blood, and four in chromatograms of muscle.Non-protein, ninhydrin-positive substances (NPS) in muscle do not appear to function in the moulting process. Concentrations averaged 278 mM/kg wet weight of muscle and NPS were the most abundant of organic osmotically active substances (total ions were 325 mM/kg). Trimethylamine oxide and glycine betaine together amounted to a further 121 mM.With lowered salinity, NPS concentrations in muscle were sharply reduced within 24 h, but with increased salinity, concentrations rose slowly over 7 days suggesting that NPS are produced by intracellular processes. When rock lobsters were fully adapted to salinities ranging from 25 to 45‰ concentrations of muscle NPS were linearly related to external salinity. When the salinity was lowered the blood was initially flooded with NPS, concentrations reaching a maximum at 12 h, and returning to normal after 72 h. Gastric fluid concentrations also rose, and evidence indicates that a large part of the NPS lost from muscle is excreted into the external water via the gastric fluid. At a salinity of 30‰, 56 % of the NPS lost from muscle appears in the external water, the remainder being excreted as ammonia; at 27‰, 82 % of NPS was excreted into the water, the remainder as ammonia.It is concluded that a changing external salinity would cause a continual loss of NPS from the body of a decapod crustacean. Although wasteful of nitrogenous compounds, such a process is of high survival value in permitting osmotic adjustment in the absence of more efficient mechanisms, such as those present in teleost fishes. 相似文献
50.
The biochemical mechanisms underlying thidiazuron (TDZ)-induced regeneration in plant cells have not been clearly elucidated.
Exposure of leaf explants of Echinacea purpurea to a medium containing TDZ results in undifferentiated cell proliferation and differentiated growth as mixed shoot organogenesis
and somatic embryogenesis. The current studies were undertaken to determine the potential roles of auxin, indoleamines, and
ion signaling in the dedifferentiation and redifferentiation of plant cells. E. purpurea leaf explants were found to contain auxin and the related indoleamine neurotransmitters, melatonin, and serotonin. The levels
of these endogenous indoleamines were increased by exposure to TDZ associated with the induction of regeneration. The auxin-transport
inhibitor 2,3,5-triiodobenzoic acid and auxin action inhibitor, p-chlorophenoxyisobutyric acid decreased the TDZ-induced regeneration but increased concentrations of endogenous serotonin
and melatonin. As well, inhibitors of calcium and sodium transport significantly reduced TDZ-induced morphogenesis while increasing
endogenous indoleamine content. These data indicate that TDZ-induced regeneration is the manifestation of a metabolic cascade
that includes an initial signaling event, accumulation, and transport of endogenous plant signals such as auxin and melatonin,
a system of secondary messengers, and a concurrent stress response. 相似文献