全文获取类型
收费全文 | 4319篇 |
免费 | 327篇 |
国内免费 | 4篇 |
出版年
2021年 | 45篇 |
2020年 | 48篇 |
2019年 | 56篇 |
2018年 | 83篇 |
2017年 | 71篇 |
2016年 | 72篇 |
2015年 | 112篇 |
2014年 | 172篇 |
2013年 | 252篇 |
2012年 | 261篇 |
2011年 | 301篇 |
2010年 | 187篇 |
2009年 | 144篇 |
2008年 | 172篇 |
2007年 | 214篇 |
2006年 | 198篇 |
2005年 | 163篇 |
2004年 | 151篇 |
2003年 | 136篇 |
2002年 | 114篇 |
2001年 | 126篇 |
2000年 | 131篇 |
1999年 | 101篇 |
1998年 | 51篇 |
1997年 | 42篇 |
1996年 | 40篇 |
1995年 | 41篇 |
1994年 | 37篇 |
1993年 | 35篇 |
1992年 | 74篇 |
1991年 | 91篇 |
1990年 | 88篇 |
1989年 | 84篇 |
1988年 | 44篇 |
1987年 | 65篇 |
1986年 | 70篇 |
1985年 | 73篇 |
1984年 | 66篇 |
1983年 | 43篇 |
1982年 | 47篇 |
1981年 | 34篇 |
1980年 | 25篇 |
1979年 | 32篇 |
1978年 | 30篇 |
1977年 | 33篇 |
1976年 | 24篇 |
1975年 | 22篇 |
1974年 | 23篇 |
1973年 | 14篇 |
1972年 | 25篇 |
排序方式: 共有4650条查询结果,搜索用时 296 毫秒
101.
102.
Kumar B. Reddy Barbara A. Hocevar Philip H. Howe 《Journal of cellular biochemistry》1994,56(3):418-425
Transforming growth factor β1 (TGFβ1) inhibits epithelial cell proliferation late in the G1 phase of the cell cycle. We examined the effect of TGFβ1 on known late G1 cell cycle regulators in an attempt to determine the molecular mechanism of growth inhibition by this physiological inhibitor. The results demonstrate the TGFβ1 inhibits the late G1 and S phase specific histone H1 kinase activity of p33cdk2. This inhibitiion is not dur to TGFβ1's effect on p33cdk2 synthesis, but rather due to its negative effect on the late G1 phosphorylation of p33cdk2. It is also shown that TGFβ1 inhibits both late G1 cyclin A and cyclin E associated histon H1 kinase activities. The inhibitor has no effects on the synthesis of cyclin E but to inhibit the synthesis of cyclin A protein in a cell cycle dependent manner. If TGFβ1 is added to cells which have progressed futher than 8 hours into G1, then it is without inhibitory effect on cyclin A synthesis. These effect on TGFβ1 on late G1 cell cycle regulators correlate well with its inhibitory effects on cellular growth and suggest that these G1 cyclin dependent kinases might serve as targets for TGFβ1-mediated growth arrest. 相似文献
103.
Anthony P. Fordham-Skelton F. Safadi M. Golovkin A. S. N. Reddy 《Plant Molecular Biology Reporter》1994,12(4):358-366
Calmodulin labeled with125I or34S has been used to screen expression libraries to isolate cDNAs encoding calmodulin-binding proteins (CBPs) from several eukaryotic
systems. The use of radiolabeled calmodulin has, however, several disadvantages. We have developed a nonradiactive method
to isolate cDNAs for CBPs using biotinylated calmodulin. Screening of a cDNA library in an expression vector with biotinylated
calmodulin resulted in the isolation of cDNAs encoding CBPs. Avidin and biotin blocking steps, prior to incubation of the
filters with biotinylated calmodulin, are found to be essential to eliminate the cDNAs that code for biotin-containing polypeptides.
The cDNA clones isolated using this nonradioactive method bound calmodulin in a calcium-dependent manner. The binding of biotinylated
calmodulin to these clones was completely abolished by ethylene glycolbis(\-aminoethylether)-N,N′-tetraacetic acid (EGTA),
a calcium chelator. Furthermore, the isolated cDNAs were confirmed by probing the clones with35S-labeled calmodulin. All the isolated clones bound to radiolabeled calmodulin in the presence of calcium but not in the presence
of EGTA. The method described here is simple, fast, and does not involve preparation and handing of radiolabeled calmodulin.
All the materials used in this method are commercially available; hence, this procedure should be widely applicable to isolate
cDNAs encoding CBPs from any eukaryotic organism. 相似文献
104.
Sachin Pannuri G. Ramakrishna Reddy Dianne McNeill Wayne R. Curtis 《Applied microbiology and biotechnology》1993,38(4):550-555
The effect of thiamine limitation in combination with fungal elicitation on sesquiterpene (solavetivone) production was studied in Agrobacterium-transformed hairy-root cultures of Hyoscyamus muticus as a potential means of manipulating the growth rate independent of phosphorus availability. Limiting the initial supply of thiamine did not affect the growth of these cultures compared to growth at the control level of thiamine (0.01 g/l). There was also no enhancement in sesquiterpene production when thiamine supply was limited. Serial culturing in thiamine-free media suggests that these root cultures are not strictly auxotrophic for thiamine, in contrast to previously published results for untransformed root culture. The effect of phosphate limitation combined with elicitation on the production of solavetivone was examined at constant media volume to provide a constant elicitor concentration and to eliminate feedback-inhibition effects. Limiting the initial supply of phosphate to elicited cultures resulted in a twofold increase in solavetivone production as compared to the elicitation at control media phosphate levels (1.1mm). Because growth was attenuated, production per unit cell mass increased 11-fold compared to the control. The effect of phosphate limitation on solavetivone production at constant cell mass and elicitor per root mass was studied. Limiting the initial supply of phosphate to elicited cultures under these conditions did not result in enhanced production of solavetivone. The initially observed enhanced production of solavetivone at limiting initial phosphate concentrations is therefore due to factors other than the growth rate or phosphate involvement in secondary metabolism.
Correspondence to: W. R. Curtis 相似文献
105.
B. H. Junker J. Reddy K. Gbewonyo R. Greasham 《Bioprocess and biosystems engineering》1994,10(5-6):195-207
Commercially available on-line and in-situ devices for monitoring cell density are reviewed in this article. Principles of operation are described as well as capabilities of these probes in specific measurement applications based on literature reports. Pilot-scale experimental observations from three optical density probes, the Cerex, Monitek and Wedgewood designs, have been included for Escherichia coli fermentations. Requirements for future on-line and in-situ instruments are discussed as well as the impact of current limitations on widespread application. 相似文献
106.
D. P. Chora L. Reddy S. K. Gupta L. Wan P. A. Mathieu R. L. Shoemaker J. S. Rhim 《In vitro cellular & developmental biology. Animal》1994,30(8):539-546
Summary Cystic fibrosis (CF) involves abnormalities in mucus production and secretion of the airway. Studies of the regulation of
airway mucin production and secretion has been difficult due to the lack of in vitro models of the airway epithelial cells
which express functional differentiation. Because the majority of the mucin in the airway is apparently produced by the submucosal
glands, we have focused our attention on the development of cell culture models of human airway submucosal glands. This report
describes the propagation of CF airway submucosal gland epithelial cells which continue to express mucin production. The CF
bronchus was obtained from a 31-yr-old patient who received a double lung transplant. The glands were dissected out and primary
cultures prepared by the explant/outgrowth procedure. The cells were immortalized by infection with Adl2-SV40 hybrid virus.
The cultures are maintained in serum-free keratinocyte basal medium supplemented with insulin (5μg/ml), hydrocortisone (0.5μg/ml), epidermal growth factor (10 ng/ml), bovine pituitary extract (25μg/ml), and antibiotics. Cultures were passaged using 0.125% trypsin in Ca+2 and Mg+2-free Hanks’, balanced salt solution. Polymerase chain reaction (PCR) analysis demonstrated that the cells were homozygous
for the ΔF508 mutation. Morphologic observations showed that the cells were epithelial and were interconnected by sparsely
distributed desmosomes. Their cytoplasm contained secretory-type structures including abundant Golgi, rough endoplasmic reticulum,
and secretory vesicles. Immunofluorescent studies determined that all cells were positive for cytokeratins, mucin glycoconjugates,
and cystic fibrosis transmembrane conductance regulator. The cultures secreted substantial amounts of mucin glycoproteins
and expressed the MUC-2 mucin gene. Patch clamp experiments revealed that the cells expressed defective Cl− channels which were not activated by Forskolin. 相似文献
107.
Sarvesh Adda T. P. Reddy P. B. Kavi Kishor 《In vitro cellular & developmental biology. Plant》1994,30(2):104-107
Summary Induction of somatic embryogenesis, shoot organogenesis, and subsequent plant regeneration in niger seem to be dependent on
genotype, choice of explant, and composition of media growth regulators. Two distinct regeneration protocols have been developed
for somatic embryogenesis and shoot organogenesis. Somatic embryogenesis was induced from epicotyls and cotyledonary explants
(9 to 35%) (but not from hypocotyls and roots) in presence of 2,4-dichlorophenoxyacetic acid, 2,4,5-trichlorophenoxyacetic
acid, and 2,4,5-trichlorophenoxypropionic acid. These embryos matured in MS medium containing Kinetin plus naphthalene acetic
acid (NAA), Kinetin plus Zeatin, and Kinetin plus abscisic acid (ABA). Matured embryos could be germinated on LS and MS basal
media without hormones. Non-embryogenic callus initiated on Linsmaier and Skoog’s (LS) medium from cotyledons of six
different genotypes produced shoots (9 to 32%) on Murashige and Skoog’s (MS) medium fortified with 6-benzylaminopurine
(BAP, 0.5 mg · liter−1), and BAP (1 mg · liter−1) plus NAA (0.1 mg · liter−1). These shoots were rooted with 100% frequency by using indole-3-acetic acid or NAA and transferred successfully to the soil. 相似文献
108.
Analysis of a genomic DNA segment carrying the wheat high-molecular-weight (HMW) glutenin Bx17 subunit and its use as an RFLP marker 总被引:12,自引:2,他引:10
P. Reddy R. Appels 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1993,85(5):616-624
Summary A genomic fragment containing the Bx17 high-molecular-weight (HMW) glutenin gene was isolated from a wheat genomic library. The fragment contains a coding region of 2.82kb with 1.98-kb downstream and 12.8-kb upstream flanking regions. The fragment was sequenced and compared with previously published glutenin genes from chromosomes 1A, 1B and 1D using a computer alignment package. The Bx17 gene shows marked similarity to the Bx7 gene sequence. A phenetic tree derived from the alignments is presented. Also shown are restriction fragment length polymorphisms (RFLPs) at the glutenin loci in a set of Australian and international wheat varieties using different regions of the glutenin clone as probes. The RFLPs correlated well with the protein composition in all cultivars analysed. 相似文献
109.
110.
v-myb blocks granulocyte colony-stimulating factor-induced myeloid cell differentiation but not proliferation. 总被引:7,自引:2,他引:5 下载免费PDF全文
To understand the effects of v-myb expression on mammalian hematopoietic cell differentiation, we have constructed a retroviral vector which can efficiently express v-myb gene product in mammalian cells. Infection of interleukin-3-dependent murine progenitor cell line 32D Cl3, which undergoes terminal differentiation to mature granulocytes in the presence of granulocyte colony-stimulating factor (GCSF), with this recombinant retrovirus does not abrogate its requirement of interleukin-3 for growth. However, expression of v-myb in these cells blocks their ability to differentiate in response to GCSF. Instead, the v-myb-infected cells proliferate indefinitely in the presence of GCSF. 32D Cl3 cells infected with empty vector carrying only the neomycin resistance gene responded to the addition of GCSF in a manner identical to that of the uninfected cells and underwent terminal differentiation into granulocytes. These results suggest that oncogenic forms of myb gene bring about transformation by blocking the differentiation signal derived by cytokines while promoting the proliferative signal transduction pathways. 相似文献