全文获取类型
收费全文 | 15639篇 |
免费 | 859篇 |
国内免费 | 887篇 |
专业分类
17385篇 |
出版年
2023年 | 152篇 |
2022年 | 248篇 |
2021年 | 286篇 |
2020年 | 311篇 |
2019年 | 390篇 |
2018年 | 414篇 |
2017年 | 341篇 |
2016年 | 355篇 |
2015年 | 398篇 |
2014年 | 872篇 |
2013年 | 1055篇 |
2012年 | 772篇 |
2011年 | 917篇 |
2010年 | 678篇 |
2009年 | 749篇 |
2008年 | 857篇 |
2007年 | 870篇 |
2006年 | 713篇 |
2005年 | 672篇 |
2004年 | 590篇 |
2003年 | 600篇 |
2002年 | 499篇 |
2001年 | 337篇 |
2000年 | 331篇 |
1999年 | 353篇 |
1998年 | 358篇 |
1997年 | 294篇 |
1996年 | 259篇 |
1995年 | 262篇 |
1994年 | 248篇 |
1993年 | 221篇 |
1992年 | 193篇 |
1991年 | 167篇 |
1990年 | 134篇 |
1989年 | 149篇 |
1988年 | 96篇 |
1987年 | 109篇 |
1986年 | 81篇 |
1985年 | 115篇 |
1984年 | 161篇 |
1983年 | 108篇 |
1982年 | 107篇 |
1981年 | 114篇 |
1980年 | 80篇 |
1979年 | 78篇 |
1978年 | 65篇 |
1977年 | 36篇 |
1976年 | 46篇 |
1975年 | 31篇 |
1974年 | 39篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
81.
82.
Bernhard Knig Patricia A. DiNitto Peter M. Blumberg 《Journal of cellular biochemistry》1985,29(1):37-44
The major phorbol ester receptor is the Ca++-activated, phospholipid-dependent protein kinase C. Diacylglycerol stimulates protein kinase C in a fashion similar to the phorbol esters. Likewise, it inhibits phorbol ester binding competitively. Both results suggest that diacylglycerol is the/an endogenous phorbol ester analogue. Alternatively, the diacylglycerol might simply be acting to modify the phospholipid environment of the protein. If diacylglycerol were indeed functioning as an analogue, it should interact with the receptor stoichiometrically. This interaction can be quantitated by measuring the perturbation in apparent diacylglycerol binding affinity as a function of the ratio of diacylglycerol to receptor. We report here that 1,2-dioleoylglycerol interacts with the receptor with the predicted stoichiometry. 相似文献
83.
84.
Phosphorylation of zymogen granule membrane proteins in intact rat pancreatic acinar cells 总被引:2,自引:0,他引:2
A Peiffer C Gagnon S Heisler 《Biochemical and biophysical research communications》1984,122(1):413-419
The comparative effects of insulin and ethanolamine on 14CO2 production and lipid synthesis from [U-14C]-D-glucose in isolated rat adipocytes were studied. Ethanolamine (10 mM) increased 14CO2 production (glucose oxidation) about 5-fold and lipogenesis about 3-fold as compared to the control. Ethanolamine was more efficient than 25 microU/ml insulin regarding both parameters, but it was less efficient than 200 microU/ml insulin in glucose oxidation, and equally potent in lipogenesis. The combination of ethanolamine and insulin was more active than insulin alone. The mechanisms of ethanolamine action include facilitation of glucose transport and increase of pyruvate dehydrogenase activity. 相似文献
85.
Kinetics of micronucleus formation in relation to chromosomal aberrations in mouse bone marrow 总被引:1,自引:0,他引:1
A simulation analysis of the kinetics of micronucleus formation in polychromatic erythrocytes in mouse bone marrow was performed after a single administration of 3 chemicals--mitomycin C (MMC), 6-mercaptopurine (6-MP) and 1-beta-D-arabinofuranosylcytosine (Ara-C)--with different modes of action. The time-response patterns in the incidence of chromosomal aberrations and micronuclei after treatment with each chemical were compared and subjected to the simulation study with 3 parameters. Two of them, the time between the final mitotic metaphase of the erythroid series and nucleus expulsion (T1), and the duration of the polychromatic erythrocyte (PCE) stage in the bone marrow (T2), were almost identical for the 3 chemicals. However, the coefficients of formation rate of micronucleated cells resulting from cells with chromosomal aberration(s) (k) differed: Ara-C differed from the other two. These results indicate that chromosomal aberrations, especially chromatid breaks and probably gaps, induced by this chemical, effectively contribute to micronucleus formation. The DNA content of micronuclei was also compared to the length of acentric fragments induced by Ara-C and it was found that their distributions were comparable. These findings strongly suggest that chromosomal aberrations induced by chemicals are essential events for the induction of micronuclei in the PCE of bone marrow. 相似文献
86.
Operation of the glycolate pathway in isolated bundle sheath (BS) strands of two C4 species was demonstrated from 14C incorporation into two intermediates, glycine and serine, under conditions favourable for photorespiratory activity. Isolated BS strands fixing 14CO2 under light at physiological rates incorporate respectively 3% (Zea mays L., cv. INRA 258) and 7% (Panicum maximum Jacq.) of total 14C fixed into glycine + serine, at low bicarbonate levels (less than the Km for CO2 fixation, 0.8 mM). Higher bicarbonate concentrations depressed the percentage of incorporation into the two amino acids. No labelling was observed in the absence of added glutamate. Oxygen was required for glycine + serine labelling, since 14C incorporation into glycine was largely depressed by argon flushing, and labelling of the two amino acids was nearly suppressed by the addition of the strong reductant, dithionite, especially in maize. Two inhibitors of the glycolate pathway were tested. With α-hydroxypyridine-methanesulfonic acid, an inhibitor of glycolate oxidase, labelling of glycine and serine remained minimal whereas glycolate was accumulated. Isoniazid, an inhibitor of the transformation of glycine to serine induced a 50% increased labelling of glycine in maize BS, and a large decrease in serine labelling. In Panicum, the increase in [14C]-glycine was 90%. These results suggest that the pathway glycolate → glycine → serine operates in these plants. However, leakage of metabolites occurs in BS cells, especially in maize and a large part of newly formed glycolate, glycine and serine is exported out of the cells. Operation of ribulose-1,5-bisphosphate oxygenase activity in competition with ribulose-1,5-bisphosphate carboxylase is demonstrated by the lowering of total 14CO2 fixation when O2 is increased at low bicarbonate concentration. An interesting feature observed in maize BS, at low bicarbonate concentration, was an increase in ribulose-1,5-bisphosphate labelling when the O2 level was decreased. This was accompanied by an increase in CO2 fixation. This could indicate an increased rate in synthesis of ribulose-1,5-bisphosphate (which accumulated) due to a stimulation of ATP synthesis by cyclic photophosphorylation under anaerobic conditions. 相似文献
87.
R E Gibson W J Rzeszotarski E M Jagoda B E Francis R C Reba W C Eckelman 《Life sciences》1984,34(23):2287-2296
We have prepared a radioiodinated ligand which binds with high affinity to the muscarinic acetylcholine receptor (m-AChR). A derivative of 3-quinuclidinyl benzilate, [125I] labeled (R) 1-aza-bicyclo(2.2.2)oct-3-yl (R,S)-alpha-hydroxy-alpha-(4-[125I]iodophenyl)phenyl acetate (4- IQNB ) exhibits an affinity for the m-AChR from corpus striatum higher than that of (R) [3H] QNB. Additionally, [125I] 4- IQNB exhibits receptor selectivity for the M1 receptor since the affinity for the receptor from dog and rat heart is lower than that using dog or rat corpus striatum. 相似文献
88.
Soichi Kojima Wakako Soga Hiromi Hagiwara Motoyuki Shimonaka Yuji Saito Yuji Inada 《Bioscience reports》1986,6(12):1029-1033
We have succeeded in corroborating the enhancing effect of vitamin A, vitamin C, sitosterol and fucosterol on the fibrinolytic activity of endothelial cells. The assay system consisted of anin situ dissolution of a fibrin layer coated onto a culture dish, over which endothelial cells were grown in a culture medium containing 10 % serum. The dissolution was enhanced by the addition of these vitamins and phytosterols to the culture medium.To whom correspondence should be addressed. 相似文献
89.
Sadaaki Iwanaga Takashi Morita Toshiyuki Miyata Takanori Nakamura Jun Aketagawa 《Journal of Protein Chemistry》1986,5(4):255-268
A hemocyte lysate from horseshoe crab produced a gel, when exposed to Gram-negative bacterial endotoxins. This gelation reaction of the lysate, so-called Limulus test, has been widely employed as a simple and very sensitive assay method for endotoxins. Recent biochemical studies on the principle of Limulus test indicate that the hemocytes contain several serine protease zymogens, which constitute a coagulation cascade triggered by endotoxins, and that there is a (1 3)--d-glucan-mediated coagulation pathway which also results in the formation of gel. Up to now, six protein components, designated coagulogen, proclotting enzyme, factor B, factor C, factor G and anti-LPS factor, all of which are closely associated with the endotoxin-mediated coagulation pathway, have been purified and biochemically characterized. Among these components, the complete amino acid sequences of coagulogens isolated from one American and three Asian species of horseshoe crabs have been established. Moreover, the reconstitution experiment using the isolated clotting factors, C, B, proclotting enzyme and coagulogen in the presence of endotoxin, leads to the formation of coagulin get. Based on these results, we propose here a mechanism for the Limulus coagulation cascade. 相似文献
90.
Growth form parameters ofCapsella bursa-pastoris populations, including a wide range of different environments, have been analyzed from random block field and growth chamber experiments. Changes in one character are often correlated with changes in another. Of special interest are correlations detected with the onset of first flowering. Variation in each of the characters is clearly influenced by both phenotypic and genotypic components. However, genotype — environment interactions are also subject to variation. Therefore, the adaptive significance of a given parameter is not found to be constant over the entire geographical range of the genus. Alpine populations tend to shift from annual to biannual life cycles.Part of a series Adaptation in life history traits of colonizing plant species. Part of a doctoral thesis by the first author. Dedicated to Prof. Dr.Karl Mägdefrau on the occasion of his 80th birthday. 相似文献