全文获取类型
收费全文 | 460篇 |
免费 | 27篇 |
专业分类
487篇 |
出版年
2022年 | 4篇 |
2021年 | 9篇 |
2020年 | 5篇 |
2019年 | 9篇 |
2018年 | 13篇 |
2017年 | 7篇 |
2016年 | 16篇 |
2015年 | 15篇 |
2014年 | 16篇 |
2013年 | 32篇 |
2012年 | 22篇 |
2011年 | 44篇 |
2010年 | 31篇 |
2009年 | 22篇 |
2008年 | 28篇 |
2007年 | 29篇 |
2006年 | 21篇 |
2005年 | 16篇 |
2004年 | 16篇 |
2003年 | 16篇 |
2002年 | 13篇 |
2001年 | 6篇 |
2000年 | 4篇 |
1999年 | 4篇 |
1998年 | 4篇 |
1996年 | 2篇 |
1995年 | 4篇 |
1994年 | 5篇 |
1993年 | 5篇 |
1992年 | 3篇 |
1991年 | 2篇 |
1990年 | 4篇 |
1989年 | 4篇 |
1988年 | 2篇 |
1987年 | 4篇 |
1986年 | 4篇 |
1985年 | 2篇 |
1984年 | 8篇 |
1983年 | 3篇 |
1982年 | 2篇 |
1980年 | 3篇 |
1978年 | 2篇 |
1974年 | 4篇 |
1973年 | 4篇 |
1970年 | 3篇 |
1969年 | 2篇 |
1968年 | 4篇 |
1964年 | 2篇 |
1934年 | 1篇 |
1932年 | 1篇 |
排序方式: 共有487条查询结果,搜索用时 15 毫秒
1.
A mutant strain of Penicillium citrinum grown in a chemically-defined production medium, yielded 145 mg compactin l–1. The medium also facilitated spectrophotometric analysis of compactin. Addition of KH2PO4in the production medium did not increase the compactin production, while addition of a surfactant, Tween 80, increased compactin to 175 mg l–1. Inoculation with 107 spores ml–1 and initial pH of 6.5–7 were the most suitable for compactin production. 相似文献
2.
Ramesh Chand Manoj Kumar Chanda Kushwaha Kavita Shah Arun K. Joshi 《Current microbiology》2014,69(2):202-211
Eighteen barley isolates of Bipolaris sorokiniana belonging to wild and clonal type of black, mixed and white subpopulations were quantitatively assayed for their melanin content and aggressiveness with respect to production of some of the extracellular enzymes such as cellulase, pectinase, amylase and protease. Cellulase and pectinase constituted major portion of the enzymes recovered from the black, mixed and white isolates. Enzyme production and aggressiveness were relatively higher in melanin devoid or low melanin isolates. The melanin deficient isolates were also differentiated from black and mixed isolates on the basis of variation in internal transcribed spacer region of the ribosomal DNA. Higher enzyme productions positively correlated with area under disease progress curve (AUDPC) and lesion development. Melanin content was negatively correlated with extracellular enzymes and aggressiveness of the isolates. Based on melanin content, lesion size, AUDPC and extracellular enzymes, the isolates were grouped in two major clusters (I and II) with further division of cluster II into two sub-clusters (II-A and II-B). The results appears to indicate a possible role of melanin in release of extracellular enzymes and hence in evolution and selection of aggressive isolates of B. sorokiniana in barley. 相似文献
3.
4.
Environmental parameters influencing phenolics production by batch cultures of Nicotiana tabacum 总被引:2,自引:0,他引:2
The influence of temperature, illumination, hormonal levels (2,4-D and kinetin), carbon to nitrogen ratios, antibiotics, and precursor feeding on phenolics production by Nicotiana tabacum (tobacco) was studied. This plant cell system was chosen as a model system to learn more about secondary product formation in plant cell tissue cultures. This is the first study to manipulate all of these environmental parameters with a single plant cell system. The most striking results were with 2,4-D manipulation. The removal of 2,4-D resulted in significant phenolics production during the stationary phase, while normal levels strongly suppressed phenolics production during the stationary phase. The addition of phenylalanine stimulated phenolics production per gram of cells but strongly inhibited growth. 相似文献
5.
The feasibility of operating a multistage continuous culture of plant cells was demonstrated for Nicotiana tabacum. Cells in the second stage of a two-stage chemostat were morphologically distinct from cells in the first stage or cells in a single-stage unit with a holding time equal to the combined holding times in the two-stage system. Cells in the second stage produced much higher levels of phenolics per unit weight of cells than cells in either the first-stage or single-stage unit. The steady-state was reproduced. When a glucose side stream was fed to the second stage, an increase in apparent cell division was observed with a simultaneous decrease in phenolics productivity. When the toxic precursor phenylalanine was pulsed into the reactor, the quantity of biomass decreased temporarily while phenolic productivity increased. These experiments demonstrate that multistage continuous culture may be useful in increasing secondary metabolite formation in cells and in exploring mechanisms controlling secondary metabolite formation. 相似文献
6.
K B Smith I Losonczy A Sahai M Pannerselvam P Fehnel D S Salomon 《Journal of cellular physiology》1983,117(1):91-100
Epidermal growth factor (EGF) inhibited the growth of A431 human epidermoid carcinoma cells. The tumor promoting, phorbol ester, 12-O-tetradecanoylphorbol-13-acetate (TPA) also retarded A431 cell growth. Addition of both TPA and EGF inhibited cell growth in an additive or synergistic manner depending upon the initial plating density of the cultures. EGF increased the production of diacylglycerol (60-70%) and stimulated the synthesis of phosphatidylinositol (PI) from 3H-inositol (three- to fourfold increase). Both of these responses were attenuated in the presence of TPA. TPA alone stimulated the production of diacylglycerol (DG) but had little effect on PI synthesis. The biological effect of TPA appeared to be mediated by the presence of a high-affinity receptor for phorbol esters on A431 cells. Moreover, the binding of 125I-EGF to A431 cells was unaffected by TPA, suggesting that the antagonistic effects of TPA were occurring distal to the EGF receptor. These findings also indicated that although TPA and EGF both inhibited A431 cell growth, this effect could be dissociated from changes in PI synthesis but may be dependent upon transient changes in DG production. 相似文献
7.
8.
Cellulase enzyme production was enhanced using the mutant strain Trichoderma reesei, E-12, which was shown to be partially resistant to catabolite repression. An optimal profile for pH, which was found to be the critical environmental parameter, was determined using a rigorous mathematical optimization procedure. Semi-empirical models were used to minimize complications in the computation. A 30% increase in enzyme activity and productivity was obtained using the optimal pH strategy as compared to the pH cycling strategy.List of Symbols
a
1
, a
2
, a
3
d–1, d–2, d–3
coefficients of the polynomial in the generalized logistic growth model
-
a
4, a
5, a
6 d–1, d–2, d–3
coefficients of the polynomial in the generalized logistic product model
-
b
1 d–1
enzyme synthesis rate constant
-
b
2
d
–1
enzyme decay rate constant
-
b
3
power coefficient in the polynomial model for enzyme synthesis
-
H
Hamiltonian function
-
J
Objective function of the maximization procedure
-
K
1 kg/m3
limiting cell mass concentration in biomass logistic model
-
K
s
kg/m3
saturation constant
-
K
s
kg/m3
saturation death rate constant
-
q
power coefficient in polynomial model
-
s kg/m3
substrate concentration
-
t d
fermentation time
-
T d
total fermentation time (=7 d)
-
x
10 kg/m3
initial biomass concentration
-
x
1 kg/m3
biomass concentration at time t
-
x
2 F.P.A
enzyme activity at time t
-
x
3 d
state variable replacing time term on the right hand side of biomass equation
-
x
f kg/m3
final biomass concentration
-
z
1, z
2, z
3
adjoint variable corresponding to state variable x
1, x
2, x
3
-
d–1
specific death rate
-
d–1
specific growth rate 相似文献
9.
The production of cellulases in batch culture was studied using a mutant strain of Trichoderma reesei C-5 growing on lactose. Growth kinetic parameters on 2% lactose were studied and the comparative results for growth and enzyme productivities at two different lactose levels are discussed. The cellulase synthesis rate depended on the lactose concentration in the medium. Although growth was favoured at a higher lactose level, the volumetric enzyme productivity did not increase in proportion and the specific enzyme productivity decreased to a certain extent, indicating that partial catabolic inhibition at higher lactose concentrations may be possible. However, it was noted that the mutant strain was highly depressed and capable of synthesising active cellulases on lactose. 相似文献
10.
A Sahai K B Smith M Panneerselvam D S Salomon 《Biochemical and biophysical research communications》1982,109(4):1206-1214
A calcium and phospholipid-dependent protein kinase (protein kinase C) was detected in the crude soluble extracts of A431 human epidermoid carcinoma cells. The enzyme required calcium, phosphatidylserine or phosphatidylinositol, and diacylglycerol (DG) for maximal activation. Protein kinase C phosphorylated both endogenous cytosolic proteins and various histones. Addition of epidermal growth factor (EGF) to A431 cultures resulted in a 2 to 3-fold stimulation of protein kinase activity. 12-0-tetradecanoylphorbol-13-acetate (TPA) in concert with EGF attenuated the EGF-induced enhanced phosphorylation of endogenous proteins. It is conceivable that DG, derived from phosphatidylinositol turnover, acts as a natural activator of protein kinase C activity. 相似文献