全文获取类型
收费全文 | 1323篇 |
免费 | 81篇 |
国内免费 | 3篇 |
出版年
2023年 | 8篇 |
2022年 | 14篇 |
2021年 | 9篇 |
2018年 | 18篇 |
2017年 | 8篇 |
2016年 | 25篇 |
2015年 | 28篇 |
2014年 | 30篇 |
2013年 | 47篇 |
2012年 | 59篇 |
2011年 | 56篇 |
2010年 | 41篇 |
2009年 | 41篇 |
2008年 | 63篇 |
2007年 | 67篇 |
2006年 | 65篇 |
2005年 | 58篇 |
2004年 | 47篇 |
2003年 | 51篇 |
2002年 | 41篇 |
2001年 | 46篇 |
2000年 | 38篇 |
1999年 | 33篇 |
1998年 | 20篇 |
1997年 | 7篇 |
1996年 | 13篇 |
1995年 | 11篇 |
1994年 | 19篇 |
1993年 | 10篇 |
1992年 | 23篇 |
1991年 | 20篇 |
1990年 | 15篇 |
1989年 | 28篇 |
1988年 | 29篇 |
1987年 | 17篇 |
1986年 | 37篇 |
1985年 | 25篇 |
1984年 | 24篇 |
1983年 | 20篇 |
1982年 | 11篇 |
1981年 | 8篇 |
1980年 | 10篇 |
1979年 | 26篇 |
1978年 | 19篇 |
1977年 | 10篇 |
1976年 | 12篇 |
1975年 | 22篇 |
1974年 | 15篇 |
1973年 | 12篇 |
1972年 | 7篇 |
排序方式: 共有1407条查询结果,搜索用时 15 毫秒
91.
92.
Culture and regeneration of mesophyll-derived protoplasts of sorghum [Sorghum bicolor (L.) Moench] 总被引:1,自引:0,他引:1
R. V. Sairam N. Seetharama P. S. Devi A. Verma U. R. Murthy I. Potrykus 《Plant cell reports》1999,18(12):972-977
A protocol for plant regeneration from mesophyll/protoplasts of sorghum [Sorghum bicolor (L.) Moench] was developed. The yield of intact protoplasts, their subsequent divisions and regeneration were genotype-dependent.
The genotype 296B was always more responsive than IS 32266. For 296B, the sixth leaf from 18-day-old plants kept in dark for
2 days before harvesting was found to be the most suitable source of viable protoplasts. The first division was observed 10–12
days after plating, and the second division after 12–14 days. The maximum plating efficiency was 4.8% in 296 B, followed by
2.48% in IS 32266. Microcolonies were visible after 25–30 days, and microcalli after 60–75 days. Whole plants were obtained
after 6–8 weeks of culture of microcalli on MS medium containing 0.2 mg l–1 kinetin and 2 mg l–1 BAP. The frequency of regeneration in 296B and IS 32266 was 12.80% and 10.58%, respectively. Ten plants transferred to pots
in the glasshouse established well. The seeds collected from glasshouse-grown plants were sown in the field where plants were
grown to maturity.
Received: 7 October 1998 / Revision received: 13 January 1999 / Accepted: 20 January 1999 相似文献
93.
J.M.R. Victor B.N.S. Murthy S.J. Murch S. KrishnaRaj P.K. Saxena 《Plant Growth Regulation》1999,28(1):41-47
Somatic embryogenesis was induced at the hypocotyledonary notch region of intact peanut (Arachis hypogaea L.) seedings cultured on a medium containing 10 mol·L–1 thidiazuron (TDZ). Inclusion of the purine analogs 2,6-diaminopurine (DAP), azaadenine or azaguanine to the thidiazuron amended medium inhibited the embryogenic response of the seedlings. DAP-mediated inhibition was not overcome by the addition of adenine sulphate. Inhibition of the embryogenic response by DAP provides evidence that the TDZ-induced accumulation of purine cytokinins is an essential component of TDZ-induced somatic embryogenesis process. Analyses of the endogenous level of purine metabolites indicated that supplementation of the media with TDZ resulted in an overall increase in the endogenous cytokinins while DAP inhibited the purine recycling resulting in decreased levels of endogenous adenine and zeatin. 相似文献
94.
Effect of UV-B (1.9 W m-2) alone or in combination with supplemental "white light". WL (20 W m-2) exposure was studied on the energy transfer process of intact phycobilisomes isolated from Spirulina platensis. Exposure of UV-B or supplemental irradiation induced a decrease in room temperature fluorescence intensity and caused a
shift towards shorter wavelengths. The low temperature fluorescence measurements showed that UV-B impairs energy transfer
from phycocyanin to allophycocyanin B and the extent of damage may be reduced by the exposure to supplemental WL.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
95.
The entorhinal cortex (EC) provides the predominant excitatory drive to the hippocampal CA1 and subicular neurons in chronic epilepsy. Discerning the mechanisms underlying signal integration within EC neurons is essential for understanding network excitability alterations involving the hippocampus during epilepsy. Twenty-four hours following a single seizure episode when there were no behavioral or electrographic seizures, we found enhanced spontaneous activity still present in the rat EC in vivo and in vitro. The increased excitability was accompanied by a profound reduction in I(h) in EC layer III neurons and a significant decline in HCN1 and HCN2 subunits that encode for h channels. Consequently, dendritic excitability was enhanced, resulting in increased neuronal firing despite hyperpolarized membrane potentials. The loss of I(h) and the increased neuronal excitability persisted for 1 week following seizures. Our results suggest that dendritic I(h) plays an important role in determining the excitability of EC layer III neurons and their associated neural networks. 相似文献
96.
Distinctive G protein-dependent signaling in smooth muscle by sphingosine 1-phosphate receptors S1P1 and S1P2 总被引:3,自引:0,他引:3
We examined expression of sphingosine 1-phosphate (S1P) receptors and sphingosine kinase (SPK) in gastric smooth muscle cells and characterized signaling pathways mediating S1P-induced 20-kDa myosin light chain (MLC20) phosphorylation and contraction. RT-PCR demonstrated expression of SPK1 and SPK2 and S1P1 and S1P2 receptors. S1P activated Gq, G13, and all Gi isoforms and stimulated PLC-1, PLC-3, and Rho kinase activities. PLC- activity was partially inhibited by pertussis toxin (PTX), G or Gq antibody, PLC-1 or PLC-3 antibody, and by expression of Gq or Gi minigene, and was abolished by a combination of antibodies or minigenes. S1P-stimulated Rho kinase activity was partially inhibited by expression of G13 or Gq minigene and abolished by expression of both. S1P stimulated Ca2+ release that was inhibited by U-73122 and heparin and induced concentration-dependent contraction of smooth muscle cells (EC50 1 nM). Initial contraction and MLC20 phosphorylation were abolished by U-73122 and MLC kinase (MLCK) inhibitor ML-9. Initial contraction was also partially inhibited by PTX and Gq or G antibody and abolished by a combination of both antibodies. In contrast, sustained contraction and MLC20 phosphorylation were partially inhibited by a PKC or Rho kinase inhibitor (bisindolylmaleimide and Y-27632) and abolished by a combination of both inhibitors but not affected by U-73122 or ML-9. These results indicate that S1P induces 1) initial contraction mediated by S1P2 and S1P1 involving concurrent activation of PLC-1 and PLC-3 via Gq and Gi, respectively, resulting in inositol 1,4,5-trisphosphate-dependent Ca2+ release and MLCK-mediated MLC20 phosphorylation, and 2) sustained contraction exclusively mediated by S1P2 involving activation of RhoA via Gq and G13, resulting in Rho kinase- and PKC-dependent MLC20 phosphorylation. muscle contraction; signal transduction 相似文献
97.
98.
The objective of the study was to optimize the formulation parameters of cytarabine liposomes by using artificial neural networks (ANN) and multiple regression analysis using 3(3) factorial design (FD). As model formulations, 27 formulations were prepared. The formulation variables, drug (cytarabine)/lipid (phosphatidyl choline [PC] and cholesterol [Chol]) molar ratio (X1), PC/Chol in percentage ratio of total lipids (X2), and the volume of hydration medium (X3) were selected as the independent variables; and the percentage drug entrapment (PDE) was selected as the dependent variable. A set of causal factors was used as tutorial data for ANN and fed into a computer. The optimization was performed by minimizing the generalized distance between the predicted values of each response and the optimized one that was obtained individually. In case of 3(3) factorial design, a second-order full-model polynomial equation and a reduced model were established by subjecting the transformed values of independent variables to multiple regression analysis, and contour plots were drawn using the equation. The optimization methods developed by both ANN and FD were validated by preparing another 5 liposomal formulations. The predetermined PDE and the experimental data were compared with predicted data by paired t test, no statistically significant difference was observed. ANN showed less error compared with multiple regression analysis. These findings demonstrate that ANN provides more accurate prediction and is quite useful in the optimization of pharmaceutical formulations when compared with the multiple regression analysis method. 相似文献
99.
100.
Identification of the G protein-activating sequence of the single-transmembrane natriuretic peptide receptor C (NPR-C) 总被引:4,自引:0,他引:4
Rat natriuretic peptideclearance receptor (NPR-C) contains four sequences capable ofinhibiting adenylyl cyclase. We have undertaken mutational and deletionstudies on the intracellular domain of rat NPR-C to determine which ofthese sequences is functionally relevant. Nine mutant receptors wereconstructed by deletion of 11 or 28 COOH-terminal residues or bysite-directed mutagenesis of basic residues in a 17-amino acidsequence, R469RNHQEESNIGKHRELR485,corresponding to the main active peptide. Substitution of arginine residues (R469R470) flanking theNH2 terminus abolished Gi1 and Gi2and PLC- activities and inhibition of adenylyl cyclase. Substitutionof one or two basic residues (H481 and/or R482or R485) in the COOH-terminal motif(H481RELR485) greatly decreased or abolished Gprotein and PLC- activities and inhibition of adenylyl cyclase. Thisimplies that sequences NH2-terminal to the motif orCOOH-terminal to R470 could not sustain receptor activityin situ, although they exhibited activity when used as syntheticpeptides. Deletion of the 11 COOH-terminal residues (E486to A496) suggested an autoinhibitory function for thissequence. We conclude that the 17-amino acid sequence (R469to R485) in the middle region of the intracellular domainof NPR-C is both necessary and sufficient for activation of G proteinsand effector enzymes. 相似文献