全文获取类型
收费全文 | 1787篇 |
免费 | 81篇 |
国内免费 | 3篇 |
专业分类
1871篇 |
出版年
2023年 | 15篇 |
2022年 | 43篇 |
2021年 | 59篇 |
2020年 | 49篇 |
2019年 | 50篇 |
2018年 | 50篇 |
2017年 | 45篇 |
2016年 | 68篇 |
2015年 | 85篇 |
2014年 | 95篇 |
2013年 | 119篇 |
2012年 | 158篇 |
2011年 | 156篇 |
2010年 | 79篇 |
2009年 | 70篇 |
2008年 | 78篇 |
2007年 | 82篇 |
2006年 | 79篇 |
2005年 | 73篇 |
2004年 | 60篇 |
2003年 | 51篇 |
2002年 | 48篇 |
2001年 | 23篇 |
2000年 | 20篇 |
1999年 | 17篇 |
1998年 | 7篇 |
1997年 | 9篇 |
1996年 | 7篇 |
1995年 | 5篇 |
1994年 | 10篇 |
1993年 | 7篇 |
1992年 | 14篇 |
1991年 | 9篇 |
1990年 | 14篇 |
1989年 | 8篇 |
1988年 | 9篇 |
1987年 | 3篇 |
1986年 | 7篇 |
1985年 | 8篇 |
1984年 | 5篇 |
1982年 | 10篇 |
1981年 | 6篇 |
1980年 | 5篇 |
1979年 | 8篇 |
1978年 | 12篇 |
1977年 | 10篇 |
1976年 | 7篇 |
1974年 | 3篇 |
1972年 | 3篇 |
1967年 | 2篇 |
排序方式: 共有1871条查询结果,搜索用时 0 毫秒
21.
Ass. Prof. Dr. A. Römmler W. Seinsch A. S. Hasan F. Haase 《Cell and tissue research》1978,190(1):135-149
The effects of single and repeated LH-RH injections at 120 min intervals on female rat LH gonadotrophs and on pituitary and serum LH levels were investigated using electronmicroscopy and radioimmunoassay. A temporary stimulation of granule release, of protein and new granule synthesis and of the accumulation of lysosomal structures was found in LH cells after the first LH-RH injection. The temporary stimulations were massively enhanced after the second injection. These consecutive yet in their time-sequence overlapping processes account for the initial depletion of secretory granule content (3--15 min after LH-RH injection), for the subsequent regranulation and accumulation of granules above control levels (60--120 min after injection) and also for the reduction in the number of granules to control levels (150 min after LH-RH injection and thereafter). Increased polymorphic lysosomal structures are believed to be responsible for this reduction of excess granules. The amount of assayable pituitary and serum LH generally corresponds with the morphological changes observed in LH-gonadotrophs, thus further substantiating the above observations. A schema which summarizes the observed morphological and hormonal changes in their time-sequence in response to LH-RH stimulation depicts the short-term regulation of secretory processes in female gonadotrophs. 相似文献
22.
S. Hasan 《BioControl》1978,23(1):19-23
Investigations carried out in Iran, to discover biological control agents for skeleton weed (Chondrilla juncea L.), showed that the buprestid,Sphenoptera clarescens Kerr, was one of the insects highly damaging to the weed. The larvae of this beetle were active throughout theChondrilla season and fed mainly on the rootstocks, causing a progressive decline in naturalChondrilla populations. The host range of the beetle was examined in the field and in the glasshouse, and it was demonstrated thatS. clarescens occurs on and attacks severalCompositae related toC. juncea. As lettuce,Lactuca sativa L., and endive,Cichorium endivia L. could have been at risk in Australia, studies were discontinued. 相似文献
23.
Ashwini Kumar M. M. Husain Hasan Mukhtar C. R. Krishna Murti 《Journal of biosciences》1980,2(3):181-189
Glutathione-S-transferase (EC 2.5.1.18) activity was assayed in hepatic and extra-hepatic tissues of pigeons using l-chloro-2,4-dinitrobenzene
and 1,2-dichloro-4-nitrobenzene as substrates. Gluthathione-S-transferase activity towards 1-chloro-2,4-dinitrobenzene in
pigeon was in the order: kidney > liver > testes > brain > lung> heart. The enzyme activity with 1-chloro-2,4-dinitrobenzene
as substrate was 40–44 times higher in pigeon liver and kidney than that observed with 1,2-dichloro-4-dinitrobenzene as substrate.K
m values of hepatic and renal glutathione transferase with l-chloro-2,4-dinitrobenzene as substrate were 2.5 and 3 mM respectively.
Double reciprocal plots with varying reduced gluthathione concentrations resulted in biphasic curves with twoK
m values (liver 0.31 mM and 4mM; kidney 0.36 mM and 1.3 mM). The enzyme activity was inhibited by oxidized gluthathione in
a dose-dependent pattern. 3-Methylcholanthrene elicited about 50% induction of hepatic glutathione transferase activity whereas
phénobarbital was ineffective. 相似文献
24.
Lawrence W. Adler Tomio Ichikawa Syed M. Hasan Tomofusa Tsuchiya Barry P. Rosen 《Journal of cellular biochemistry》1977,7(1):15-27
Membrane vesicles of Escherichia coli can be produced by 2 different methods: lysis of intact cells by passage through a French pressure cell or by osmotic rupturing of spheroplasts. The membrane of vesicles produced by the former method is everted relative to the orientation of the inner membrane in vivo. Using NADH, D-lactate, reduced phenazine methosulfate, or ATP these vesicles produce protonmotive forces, acid and positive inside, as determined using flow dialysis to measured the distribution of the weak base methylamine and the lipophilic anion thiocyanate. The vesicles accumulate calcium using the same energy sources, most likely by a calcium/proton antiport. Calcium accumulation, therefore, is presumably indicative of a proton gradient, acid inside. The latter type of vesicle, on the other hand, exhibits D-lactate-dependent proline transport but does not accumulate calcium with D-lactate as an energy source. NADH oxidation or ATP hydrolysis, however, will drive the transport of calcium but not proline in these vesicles. Oxidation of NADH or hydrolysis of ATP simultaneous with oxidation of D-lactate does not result in either calcium or proline transport. These results suggest that the vesicles are a patchwork or mosiac, in which certain enzyme complexes have an orientation opposite to that found in vivo, resulting in the formation of electrochemical proton gradients with an orientation opposite to that found in the intact cell. Other complexes retain their original orientation, making it possible to set up simultaneous proton fluxes in both directions, causing an apparent uncoupling of energy-linked processes. That the vesicles are capable of generating protonmotive forces of the opposite polarity was demonstrated by measurements of the distribution of acetate and methylamine (to measure the ΔpH) and thiocyanate (to measure the Δψ). 相似文献
25.
Dehydroquinate synthase, the enzyme which catalyzes the conversion of 3-deoxy-D-arabino-heptulosonic acid 7-phosphate (DAHP) to 5-dehydroquinate, has been purified from Bacillus subtilis in association with chorismate synthase and NADPH-dependent flavin reductase. The enzyme was only active when associated with chorismate synthase, whereas the flavin reductase could be separated from the complex with retention of dehydroquinate synthase activity. The enzyme requires NAD and either Co2+ or Mn2+ for maximal activity. The activity was completely inhibited by EDTA. The Km of the enzyme for DAHP, NAD, and Co2+ were estimated to be 1.3 X 10(-4), 5.5 X 10(-5), and 5.5 X 10(-5) M, respectively. Enzyme activity was completely inhibited by NADH and the inhibition was not reversed by the addition of NAD, NADPH and NADP were not inhibitory. The enzyme was unstable to heat and lost all activity at 55 degrees C. A protein fraction which did not adsorb to phosphocellulose was found to inhibit the enzyme. 相似文献
26.
The comparative effects of propofol, thiopental, and diazepam, administered intravenously, on pentylenetetrazol seizure threshold in the rabbit. 总被引:4,自引:0,他引:4
The anticonvulsant effects of propofol, thiopental, and diazepam, administered intravenously, on pentylenetetrazol (PTZ) seizure threshold were studied and compared in the rabbit. The PTZ seizure threshold determined in various rabbit groups during the control phase of conducted experiments, was found to be in the range of 10.1 +/- 2.0 to 13.5 +/- 3.7 mg/kg. Intravenous administration of comparable doses of propofol, thiopental, and diazepam resulted in marked and significant increases in PTZ seizure threshold. At all administered doses (1.25-10.0 mg/kg), propofol was found to be more effective than thiopental in increasing the PTZ threshold dose. However, the anticonvulsant effects of diazepam were more marked than those of propofol, except at a dose of 10 mg/kg where both agents exhibited equipotent activities. These data demonstrate that propofol enjoys a considerable degree of anticonvulsant activity in the rabbit. This anticonvulsant action is greater than that of thiopental at doses ranging from 2.5 to 10 mg/kg and equipotent with diazepam at the 10 mg/kg dose. 相似文献
27.
A new single gene-recessive internode length mutant inPisum, lkc, is characterized. The internodes oflkc plants are 30–40% shorter than those of comparableLkc plants, and this is attributable to reductions in both cell length and the number of cells per internode. Dwarfism in the mutant is not due to modified gibberellin (GA) levels, as determined by gas chromatography-selected ion monitoring (GC-SIM) for GA1 and GA20, and bioassay (rice cv. Tan-ginbozu). Furthermore,lkc plants are not as responsive as the wild-type to applied GA1. The diminished stature oflkc plants appears to result from a direct or indirect interference with the transduction of the GA1 signal. 相似文献
28.
29.
30.
Properties and function of the proton-translocating adenosine triphosphatase of Clostridium perfringens.
下载免费PDF全文
![点击此处可从《Journal of bacteriology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Growth of Clostridium perfringens was inhibited by compounds which dissipate or prevent the formation of electrochemical proton gradients. Membrane vesicles prepared from this organism exhibited Mg2+-dependent adenosine triphosphatase (ATPase) activity sensitive to N,N'-dicyclohexylcarbodiimide. Mg2+-ATPase activity was optimal of 50 degrees C, but no discrete pH optimum was observed. Adenosine triphosphate-dependent quenching of the fluorescence of the weak base quinacrine by everted membrane vesicles suggested that the Mg2+-ATPase is a proton pump capable of generating an electrochemical proton gradient. Adenosine triphosphate-dependent transport of Ca2+ by everted vesicles was sensitive to uncouplers and inhibitors of the Mg2+-ATPase. 相似文献