全文获取类型
收费全文 | 9818篇 |
免费 | 885篇 |
国内免费 | 758篇 |
专业分类
11461篇 |
出版年
2024年 | 35篇 |
2023年 | 119篇 |
2022年 | 311篇 |
2021年 | 510篇 |
2020年 | 303篇 |
2019年 | 423篇 |
2018年 | 422篇 |
2017年 | 305篇 |
2016年 | 425篇 |
2015年 | 611篇 |
2014年 | 774篇 |
2013年 | 749篇 |
2012年 | 891篇 |
2011年 | 777篇 |
2010年 | 475篇 |
2009年 | 434篇 |
2008年 | 414篇 |
2007年 | 416篇 |
2006年 | 352篇 |
2005年 | 299篇 |
2004年 | 240篇 |
2003年 | 259篇 |
2002年 | 234篇 |
2001年 | 199篇 |
2000年 | 186篇 |
1999年 | 194篇 |
1998年 | 114篇 |
1997年 | 104篇 |
1996年 | 112篇 |
1995年 | 80篇 |
1994年 | 91篇 |
1993年 | 57篇 |
1992年 | 83篇 |
1991年 | 73篇 |
1990年 | 60篇 |
1989年 | 62篇 |
1988年 | 47篇 |
1987年 | 41篇 |
1986年 | 18篇 |
1985年 | 29篇 |
1984年 | 12篇 |
1983年 | 23篇 |
1982年 | 14篇 |
1981年 | 12篇 |
1980年 | 7篇 |
1979年 | 16篇 |
1978年 | 7篇 |
1976年 | 6篇 |
1975年 | 5篇 |
1973年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
Phosphatidylcholine‐specific phospholipase C (PC‐PLC) is the major enzyme in the Phosphatidylcholine (PC) cycle and is involved in many long‐term cellular responses such as activation, proliferation, and differentiation events. Cell division cycle 20 homolog (Cdc20) is an essential cell‐cycle regulator required for the completion of mitosis. Our previous studies identified the interaction between PC‐PLC and Cdc20. Through the interaction, Cdc20 could mediate the degradation of PC‐PLC by Cdc20‐mediated ubiquitin proteasome pathway (UPP). In this study, we found that PC‐PLC might not be involved in cancer metastasis. Inhibition of PC‐PLC by D609 could cause cell proliferation inhibition and apoptosis inhibition in CBRH‐7919 cells. Inhibition of PC‐PLC could also influence the cell cycle by arresting the cells in G1 phase, and Cdc20 might be involved in these processes. Taken together, in this report, we provided new evidence for the functional roles of PC‐PLC and Cdc20 in the cell cycle, proliferation, and apoptosis in CBRH‐7919 cells. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
992.
A dual-marker combination, manA-gfp, comprising 2 independent expression cassettes of genes encoding an Escherichia coli phosphomannose isomerase (PMI) and a synthetic green fluorescent protein (GFP), was incorporated into the binary vector pPZP201. Agrobacterium tumefaciens-mediated transfer was used to introduce the manA-gfp into the mature-seed derived calli of Agrostis stoloifera L. 'Crenshaw'. The putative transgenic bentgrass calli were screened in Murashige and Skoog medium containing 15 g mannose/L, in conjunction with a visual examination of the GFP expression with a fluorescence stereomicroscope. Calli with GFP fluorescence grew well on the mannose selection media. A total of 24 transgenic plants derived from a single piece of callus lobe were studied for the genomic integration, expression, and function of the transgene. Genomic integration of the dual markers manA and gfp was confirmed by Southern blotting analysis, and the expression of manA also was validated by using PMI-specific antiserum. The inheritance and expression of the dual marker, manA-gfp, was demonstrated in the T1 generation. This study on the environmentally friendly markers further documented the feasibility of using alternative selection methods without using herbicide- or antibiotic-resistance markers. 相似文献
993.
The polymerase chain reaction (PCR) is an efficient method for sexing embryos. The objective of this study was to develop an accurate and reliable method for sexing swamp buffalo (Bubalus bubalis) embryos. The SRY gene from swamp buffalo genomic DNA was amplified by PCR, using primers based on the sequence of the Holstein SRY gene. This fragment was sequenced based on a BLAST search; the SRY gene was highly conserved. Using a Southern blot, there was a strong signal in genomic DNA only from male swamp buffalo. Two pairs of nested primers, targeted to amplify the swamp buffalo SRY conserved region, were designed for sex identification. Simultaneously, the G3PDH gene was co-amplified to serve as an internal control. A multiplex-nested PCR system was optimized by varying the following individually: concentrations of Mg(2+) and dNTPs, ratio of concentrations of primers and numbers of cycles. Biopsies of 27 IVF-derived embryos and 24 embryos fertilized with Y-chromosome-bearing sperm were examined. Using optimized procedures, clear signals following PCR amplification were obtained from all embryo samples; PCR amplification accuracy was further verified by comparing PCR and dot blots. We concluded that this PCR technique was highly reliable for sexing swamp buffalo embryos. 相似文献
994.
Xi-yan Yang Xian-long Zhang Shuang-xia Jin Li-li Fu Ling-gang Wang 《Plant Cell, Tissue and Organ Culture》2007,89(2-3):225-235
Asymmetric somatic hybrids were obtained between Gossypium hirsutum Coker 201 and wild cotton G. klozschianum Anderss. An investigation on the effect of ultraviolet (UV) irradiation on donor protoplasts was carried out, and the lethal
dose was determined to be 38.7 J cm−2. We firstly screened the putative hybrids by the color of the calli produced, followed by morphological, cytological, and
molecular analysis of putative hybrid plants. Most regenerated plants derived from fused protoplasts displayed a recipient-like
morphology, while some showed an intermediate phenotype between Coker 201 and G. klozschianum. Chromosome numbers in these somatic hybrids ranged from 54 to 74. The hybrids were verified by random amplified polymorphic
DNA (RAPD) and simple sequence repeat (SSR). Absence or co-existence of parents’ genome DNA fragments was identified through
molecular analysis. The heredity of cytoplasm was investigated by cleaved amplified polymorphic sequence (CAPS) analysis using
mitochondrial and chloroplast universal primer pairs. The results indicated that recombination and rearrangements might have
occurred in some regions of mitochondria (mt) and chloroplast (cp) DNA. To our knowledge, this is the first report about asymmetric
protoplast fusion in cotton, and the hybrids obtained would be useful for breeding programs. 相似文献
995.
We have investigated the effects of low molecular weight organic acid ligands on the adsorption of the insecticidal toxin
from Bacillus thuringiensis (Bt) by the colloidal (<2 μm particle-size) fraction of some soils. The desorption of the bound toxin by NaCl and phosphate
buffer has also been measured. The soils used were a red soil (Ultisol), a latosol (Oxisol), a yellow brown soil (Alfisol)
and a yellow cinnamon soil (Alfisol) from central and southern China. The adsorption isotherms were all of the L-type, and
the data fitted the Langmuir equation (R2 > 0.97). When present at low concentrations, organic acids (acetate, oxalate, citrate) had an inhibitory effect on toxin
adsorption. Uptake, however, was promoted when the organic acid concentration exceeded 10 mM. The toxin was very strongly
bound by the soils but the soil-toxin interaction weakened in the presence of organic acids. A small portion of the toxin
was adsorbed by electrostatic and ligand exchange interactions. The addition of organic acids appeared to enhance these interactions.
Responsible Editor: Thomas B. Kinraide 相似文献
996.
A biochemical investigation of arabinogalactan proteins (AGPs) in Physcomitrella
patens was undertaken with particular emphasis on the glycan chains. Following homogenization and differential centrifugation of
moss gametophytes, AGPs were obtained by Yariv phenylglycoside-induced precipitation from the soluble, microsomal membrane,
and cell wall fractions. Crossed-electrophoresis indicated that each of these three AGP fractions was a mixture of several
AGPs. The soluble AGP fraction was selected for further separation by anion-exchange and gel-permeation chromatography. The
latter indicated molecular masses of ∼100 and 224 kDa for the two major soluble AGP subfractions. The AGPs in both of these
subfractions contained the abundant (1,3,6)-linked galactopyranosyl residues, terminal arabinofuranosyl residues, and (1,4)-linked
glucuronopyranosyl residues that are typical of many angiosperm AGPs. Unexpectedly, however, the moss AGP glycan chains contained
about 15 mol% terminal 3-O-methyl-l-rhamnosyl residues, which have not been found in angiosperm AGPs. This unusual and relatively nonpolar sugar, also called
l-acofriose, is likely to have considerable effects on the overall polarity of Physcomitrella AGPs. A review of the literature indicates that the capacity to synthesize polymers containing 3-O-methyl-l-rhamnosyl residues is present in a variety of bacteria, algae and lower land plants but became less common through evolution
to the extent that this sugar has been found in only a few species of angiosperms where it occurs as a single residue on steroidal
glycosides. 相似文献
997.
998.
999.
Yuan X Ren F Zeng G Zhong H Fu H Liu J Xu X 《Applied microbiology and biotechnology》2007,76(5):1189-1198
The adsorption behavior of five surfactants, cetyltrimethylammonium bromide (CTAB), Triton X-100, Tween 80, sodium dodecyl
sulfate (SDS), and rhamnolipid, on a Pseudomonas aeruginosa strain and the effect of temperature and ionic strength (IS) on the adsorption were studied. The change of cell surface lypohydrophilic
property caused by surfactant adsorption was also investigated. The results showed that the adsorption kinetics of the surfactants
on the cell followed the second-order law. CTAB adsorption was the fastest one under the experimental conditions, and it took
longest for SDS adsorption to equilibrate because of electric repulsion. The adsorption of Triton X-100 and Tween 80 was characterized
by short equilibration time, and rhamnolipid adsorption reached equilibrium in about 90 min. The adsorption isotherms of all
the surfactants on the bacterium fitted Freundlich equation well, but the adsorption capacity and mode were variations for
the surfactants as indicated by k and n parameters in the equations. The adsorption mode for all the surfactants except SDS is probably hydrophilic interaction because
the adsorption totally turned the cell surface to be more hydrophobic. Neither the temperature nor the IS had significant
effect on CTAB adsorption, but higher IS significantly enhanced SDS adsorption and modestly strengthened adsorption of Triton
X-100, Tween 80, and rhamnolipid. Higher temperature strengthened adsorption of SDS but weakened the adsorption of Triton
X-100, Tween 80, and rhamnolipid. 相似文献
1000.
Differential roles of Rap1 and Rap2 small GTPases in neurite retraction and synapse elimination in hippocampal spiny neurons 总被引:1,自引:0,他引:1
The Rap family of small GTPases is implicated in the mechanisms of synaptic plasticity, particularly synaptic depression. Here we studied the role of Rap in neuronal morphogenesis and synaptic transmission in cultured neurons. Constitutively active Rap2 expressed in hippocampal pyramidal neurons caused decreased length and complexity of both axonal and dendritic branches. In addition, Rap2 caused loss of dendritic spines and spiny synapses, and an increase in filopodia-like protrusions and shaft synapses. These Rap2 morphological effects were absent in aspiny interneurons. In contrast, constitutively active Rap1 had no significant effect on axon or dendrite morphology. Dominant-negative Rap mutants increased dendrite length, indicating that endogenous Rap restrains dendritic outgrowth. The amplitude and frequency of alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA)-mediated miniature excitatory postsynaptic currents (mEPSCs) decreased in hippocampal neurons transfected with active Rap1 or Rap2, associated with reduced surface and total levels of AMPA receptor subunit GluR2. Finally, increasing synaptic activity with GABA(A) receptor antagonists counteracted Rap2's inhibitory effect on dendrite growth, and masked the effects of Rap1 and Rap2 on AMPA-mediated mEPSCs. Rap1 and Rap2 thus have overlapping but distinct actions that potentially link the inhibition of synaptic transmission with the retraction of axons and dendrites. 相似文献