全文获取类型
收费全文 | 373篇 |
免费 | 17篇 |
出版年
2022年 | 3篇 |
2021年 | 5篇 |
2020年 | 3篇 |
2019年 | 7篇 |
2018年 | 7篇 |
2016年 | 7篇 |
2015年 | 16篇 |
2014年 | 19篇 |
2013年 | 16篇 |
2012年 | 36篇 |
2011年 | 28篇 |
2010年 | 14篇 |
2009年 | 15篇 |
2008年 | 13篇 |
2007年 | 17篇 |
2006年 | 18篇 |
2005年 | 10篇 |
2004年 | 18篇 |
2003年 | 8篇 |
2002年 | 10篇 |
2001年 | 7篇 |
2000年 | 3篇 |
1998年 | 5篇 |
1997年 | 8篇 |
1996年 | 5篇 |
1995年 | 4篇 |
1994年 | 2篇 |
1992年 | 3篇 |
1990年 | 3篇 |
1987年 | 2篇 |
1985年 | 3篇 |
1984年 | 3篇 |
1981年 | 5篇 |
1980年 | 3篇 |
1979年 | 4篇 |
1977年 | 2篇 |
1976年 | 3篇 |
1975年 | 7篇 |
1973年 | 2篇 |
1966年 | 2篇 |
1958年 | 2篇 |
1942年 | 2篇 |
1938年 | 2篇 |
1936年 | 2篇 |
1935年 | 2篇 |
1934年 | 3篇 |
1933年 | 3篇 |
1910年 | 1篇 |
1907年 | 2篇 |
1906年 | 2篇 |
排序方式: 共有390条查询结果,搜索用时 15 毫秒
1.
Exogenous long-chain fatty acids are readily taken up by unstimulated lymphocytes derived from the thymus of calves or rabbits and esterified to complex lipids, primarily phospholipids and triacylglycerols. Compared to saturated fatty acids, unsaturated fatty acids are incorporated preferentially. Furthermore, unsaturated fatty acids are transferred from triacylglycerols to phospholipids. The transfer cannot be observed with palmitic acid. With regard to individual phospholipid species, oleic acid and linoleic acid are found primarily in phosphatidylcholine. Arachidonic acid, however, is transferred to phosphatidylethanolamine and phosphatidylinositol as well. This suggests an arachidonic-specific transfer between individual phospholipids. Stimulation of the cells with the mitogen concanavalin A results in an enhanced incorporation of the fatty acids and an enhanced transfer from triacylglycerols to phospholipids. Triacylglycerols may thus be regarded as a labile intracellular storage pool that may be activated upon mitogenic stimulation. 相似文献
2.
Zusammenfassung Werden Keimlinge vonHelianthus annuus undVicia faba mittels einer Wasserstrahlpumpe mit Wasser infiltriert, so führt dies sofort in allen Organen der Pflanze zu einer sehr starken und mitunter völligen Hemmung des Wachstums. Wirkt der Unterdruck in Luft ein, so daß es hernach zu keiner Wasserfüllung der Interzellularen kommt, so unterbleibt jede Wachstumshemmung.Die Frage nach der Kausalbeziehung zwischen Infiltration und Wachstumshemmung konnte nicht geklärt werden, da die nächstiliegende Annahme, Infiltration führe zu einer Atmungshemmung, durch das Experiment nicht bestätigt werden konnte.Es wird darauf hingewiesen, daß die Zufuhr von Wirk- oder Nährstoffen durch Infiltration eine Methode ist, die in wachsenden Organen nur mit großem Vorbehalt angewendet werden darf, da eine im Wachstum weitgehend gehemmte Pflanze sich in einem anomalen Zustand befindet.Mit 8 Textabbildungen. 相似文献
3.
Margarete Traiser Bernd Diener Dietmar Utesch Franz Oesch 《In vitro cellular & developmental biology. Animal》1995,31(4):266-273
Summary In primary monocultures of adult rat liver parenchymal cells (PC), the activities of the xenobiotic metabolizing enzymes microsomal
epoxide hydrolase (mEHb), soluble epoxide hydrolase (sEH), glutathione S-transferases (GST), and phenolsulfotransferase (ST) were reduced after 7
d to values below 33% of the initial activities. Furthermore, the gap junctional intercellular communication (GJIC), measured
after microinjection by dye transfer, decreased from 90% on Day 1 to undetectable values after 5 d in monoculture. Co-culture
of PC with nonparenchymal rat liver epithelial cells (NEC) increased (98% on Day 1) and stabilized (82% on Day 7) the homotypic
GJIC of PC. Additionally, most of the measured xenobiotic metabolizing enzyme activities were well stabilized over 1 wk in
co-culture. Because GJIC is one of several mechanisms playing an important role in cell differentiation, the importance of
GJIC for the stabilization of xenobiotic metabolizing enzymes in PC was investigated. PC in monoculture were, therefore, treated
with 2% dimethyl sulfoxide (DMSO), a differentiation promoting factor, and 1,1,1-trichloro-2,2,-bis (p-chlorophenyl) ethane
(DDT) (10 μg/ml), a liver tumor promotor and inhibitor of GJIC, was given to co-cultures of PC with NEC. DMSO significantly
stabilized (68% on Day 7), while DDT significantly inhibited (8% on Day 7) homotypic GJIC of PC in the respective culture
systems. In contrast, the activities of mEHb, sEH, GST, and ST were not affected in the presence of DMSO or DDT. These results lead to the assumption that the differentiation
parameters measured in this study (i.e., homotypic GJIC and the activities of xenobiotic metabolizing enzymes) are independently
regulated in adult rat liver PC. 相似文献
4.
Fritz Thümmler Margarete Kirchner Raphael Teuber Peter Dittrich 《Plant molecular biology》1995,29(3):551-565
22 novel members of the Arabidopsis thaliana protein kinase family (AKs) were identified by using degenerate oligonucleotide primers directed to highly conserved amino acid sequences of the protein kinase (PK) catalytic domain. Of these 22 genes, 16 turned out to carry intron sequences. Homologies of AK sequences were detected to S-locus receptor protein kinases (SRKs) from Brassica spp., to SRK-like PKs from maize and A. thaliana and to several other receptor PKs from A. thaliana. Sequence similarity was also detected to Ca2+-dependent PKs (CDPKs) from rape and soybean, to SNF1 and to CDC2 homologues. The genomic organization and the accumulation of the mRNAs from these 22 AK genes were investigated. 相似文献
5.
ADENOSINE REGULATES VIA TWO DIFFERENT TYPES OF RECEPTORS, THE ACCUMULATION OF CYCLIC AMP IN CULTURED BRAIN CELLS 总被引:24,自引:2,他引:22
Abstract— In cell cultures of glial character derived from perinatal mouse brain adenosine elicits two effects. (a) At submicromolar concentrations It inhibits the increase in the intracellular level of cyclic AMP caused by β-adrenoceptor agonists. (b) At concentrations above micromolar it increases the level of cyclic AMP in the cultures. These two effects are mediated by two different adenosine receptors present on the outer surface of the cells. This is concluded from the following evidence. (a) Both effects are antagonized by methylxanthines but not by blockage of adenosine uptake or inhibition of phosphodiesterase activity. (b) In both cases activity depends on the integrity of the ribose moiety of the nucleotide. Substituents of the purine system are tolerated comparatively well. (c) The order of potency of adenosine analogues is different for the two effects. We suggest the name A1 receptors for those that mediate the inhibition and A2 for those that mediate the stimulation of cyclic AMP accumulation. 相似文献
6.
Gray R. Kunkel Margarete Mehrabian Harold G. Martinson 《Molecular and cellular biochemistry》1981,34(1):3-13
Summary Contact-site cross-linking agents comprise a heterogeneous grouping of cross-linkers which share the common property of being
able to cross-link only very closely juxtaposed residues in macromolecular complexes. We have defined contact-site cross-linking
arbitrarily as the covalent joining of residues such that they are constrained to a distance which is equivalent to or less
than their closest possible steric approach prior to becoming linked (1). We recognize two classes of contact-site cross-linkers,
bridge type and zero-length type. The former, such as formaldehyde, become incorporated during cross-linking as one-atom bridges.
The latter, such as the carbodiimides, operate as condensing agents with the result that the cross-linked residues become
interjoined directly.
Contact-site cross-linkers have been used in several ways as specific probes of both the static and dynamic aspects of macromolecular
structure. They can yield precise structural information about macromolecular contacts when actual sites of cross-linking
are determined by peptide or nucleotide mapping techniques. In this way exact contacs between histones in the nucleosome,
between protein and RNA in the ribosome, and between RNA polymerase and DNA have been determined. Contact-site cross-linkers
have also been used to probe the perturbation of contacts following macromolecular conformational changes. Certain histonehistone
‘cross-linkable’ sites are rendered unreactive after induction of chromatin conformational changes thus serving to localize
sites of perturbation. 相似文献
7.
8.
9.
Daniela Machado Teresa Baptista Catarina Anjos Susana Mendes Ana Margarete Matias 《Invertebrate reproduction & development.》2013,57(4):179-190
ABSTRACTIn Portugal, the European clam (Ruditapes decussatus) is an important commercial resource. Óbidos Lagoon is a strong candidate as a cultivation area to increase European clam exploitation. However, the reproductive biology of this population has not been described. In this work, the reproductive cycle of R. decussatus was characterized by determining gonadal development stages, gonad index, condition index, and biochemical composition. The relationship between reproduction and environmental parameters (sea surface temperature, chlorophyll a, and particulate organic matter) was assessed. Ruditapes decussatus had an annual reproductive cycle. The gametogenic cycle started in late winter, and the ripe stage in spring was followed by spawning that began at the end of spring/early summer and extended until early autumn. The subsequent period of sexual rest occurred during the winter. Condition index showed seasonal variations related to food availability (chlorophyll a). The European clams in Óbidos Lagoon recovered rapidly after their reproductive period, most likely owing to the availability of food. This study will help to improve sustainable management of this wild stock and is important for future aquaculture development of this species. 相似文献
10.
Various treatments have been proposed to attenuate and eventually inhibit the generation of acid mine drainage (AMD) or acid-rock drainage (ARD). The addition of Natural Phosphate Rocks (NPR) to mining wastes has been shown to reduce acid generation. The biogeochemical reactions underlying the phosphate precipitation reactions are however poorly understood, even though the chemical reactions are well defined. The present study was designed to study the role of solution chemistry and bacterial activity on phosphate precipitation on waste rock surfaces. Waste rock samples (rich in sulphides) previously weathered for 989 days in the presence of NPR were submersed in 2 different phosphate-rich growth media in order to enhance the growth of acidophilic and neutrophilic bacteria. DAPI and FISH analyses revealed that most cells belonged to the bacteria domain, and that alpha- and beta-proteobacteria were the dominant neutrophiles. ESEM, SEM and TEM observations of the samples revealed the presence of a biofilm on the surface of the rocks at both pH conditions. Bacteria and fine-grained precipitates were trapped in an exopolymer matrix. At low pH, the formation of fine precipitates rich in Fe and P within the biofilm corresponded to a decline of phosphate concentrations in the growth medium. This was in agreement with the solubility calculations which indicated that the medium became over-saturated with respect to some Fe-phosphate minerals. In the pH neutral system, solubility calculations indicated that Ca- and Mg-phosphate minerals were stable, but they were not detected in the biofilm. Solubility calculations also indicated that vivianite became unstable over time, which could explain the release of soluble phosphate over time in the pH neutral system. Our results showed that precipitation reactions played an important role in the solubility of phosphate in both systems, but a series of complex nucleation reactions involving bacterial exopolymers and the presence of microenvironments within the biofilms were likely important factors as well. Our findings also imply that the reduction of acid generation in NPR-treated waste rocks could be due in part to the formation of biofilms on the rock surfaces because the biofilms would act as a physical and chemcial barrier to limit the extent of pyrite oxidation. 相似文献