全文获取类型
收费全文 | 4653篇 |
免费 | 266篇 |
国内免费 | 3篇 |
出版年
2023年 | 15篇 |
2022年 | 15篇 |
2021年 | 47篇 |
2020年 | 36篇 |
2019年 | 47篇 |
2018年 | 79篇 |
2017年 | 77篇 |
2016年 | 93篇 |
2015年 | 172篇 |
2014年 | 201篇 |
2013年 | 320篇 |
2012年 | 284篇 |
2011年 | 340篇 |
2010年 | 200篇 |
2009年 | 157篇 |
2008年 | 282篇 |
2007年 | 313篇 |
2006年 | 282篇 |
2005年 | 306篇 |
2004年 | 254篇 |
2003年 | 267篇 |
2002年 | 246篇 |
2001年 | 49篇 |
2000年 | 35篇 |
1999年 | 67篇 |
1998年 | 71篇 |
1997年 | 48篇 |
1996年 | 60篇 |
1995年 | 48篇 |
1994年 | 32篇 |
1993年 | 41篇 |
1992年 | 41篇 |
1991年 | 21篇 |
1990年 | 31篇 |
1989年 | 44篇 |
1988年 | 21篇 |
1987年 | 24篇 |
1986年 | 22篇 |
1985年 | 25篇 |
1984年 | 31篇 |
1983年 | 21篇 |
1982年 | 27篇 |
1981年 | 12篇 |
1980年 | 20篇 |
1979年 | 14篇 |
1978年 | 10篇 |
1975年 | 9篇 |
1974年 | 12篇 |
1973年 | 9篇 |
1971年 | 9篇 |
排序方式: 共有4922条查询结果,搜索用时 15 毫秒
81.
82.
We report here about an antigen that is expressed in the central nervous system (CNS) of Drosophila only during the embryonic and metamorphic stages. In Drosophila, axonogenesis and synaptogenesis occur twice during the development: first in the embryonic and second in the metamorphic stages. We generated monoclonal antibodies (MAbs) in order to obtain molecular probes for analyzing axonogenesis or synaptogenesis in the CNS on the assumption that good candidates for molecules responsible for such phenomena must be present in the neuropil during those stages exclusively. As a result, we found MAb 66B2 whose intense immunoreactivity in the neuropil of the CNS was observed exclusively in the embryo and pupa, and not in the larva and adult. Immunoblot analyses showed that MAb 66B2 binds specifically to a protein with an apparent molecular weight of 350 K and neutral pl in the prepupal CNS. A significant amount of the antigen was isolated in forms that were soluble without detergent. Results of immunohistochemistry with MAb 66B2 in a primary culture of embryos showed that some live cells in the ganglion-like cluster were stained, and that neuronal cell bodies and neurites emanating from there were negative. These results strongly suggest that the 66B2 antigen observed in the CNS is an extracellular matrix component secreted from nonneuronal cells. These developmental changes in the 66B2 immuno-reactivity in the CNS presumably reflect dynamic changes of an extracellular matrix in the CNS that are accompanied by axonogenesis or synaptogenesis. © 1992 John Wiley & Sons, Inc. 相似文献
83.
gamma-Crystallin isolated from the shark of cartilaginous fishes was compared with the cognate gamma-crystallin from the carp of bony fishes. Distinct differences in amino acid compositions, primary, secondary and tertiary structures were found. The most salient features of shark gamma-crystallin lie in the fact that this crystallin possessed a significant alpha-helical structure in the peptide backbone as revealed by circular dichroism study, in contrast to those orthologous gamma-crystallins from other vertebrate species including bony fishes which all show a predominant beta-sheet secondary structure. The tertiary structure as reflected in the intrinsic microenvironments of various aromatic amino acids in the native crystallins also shows unambiguous differences between these two classes of gamma-crystallins. N-Terminal sequence analysis corroborates the structural differences between shark and carp gamma-crystallins. gamma-Crystallin from the more primitive shark seems to be more in line with the main evolutionary phylogeny leading to the modern mammalian gamma-crystallin. 相似文献
84.
A wasp venom, mastoparan, rapidly increased the cytosolic free Ca2+ concentration ([Ca2+]i) and activated phosphorylase in rat hepatocytes in a concentration-dependent manner. Mastoparan could increase [Ca2+]i even in the absence of extracellular Ca2+, but a larger increase was observed in the presence of extracellular Ca2+. Thus, mastoparan mobilized Ca2+ from intracellular and extracellular Ca2+ stores. It also activated inositol triphosphate (IP3) accumulation, but did not stimulate cAMP production. From these results, we conclude that mastoparan activates rat hepatic glycogenolysis mediated by the accumulation of IP3, which causes an increase of [Ca2+]i but not that mediated by cAMP. 相似文献
85.
Yoshiya Sato Hiromu Toma Masahiro Takara Yoshiyuki Shiroma 《International journal for parasitology》1990,20(8):1025-1029
The enzyme-linked immunosorbent assay was tested to evaluate whether it could be applicable in screening for mass examination of strongyloidiasis. A total of 2906 inhabitants in three areas (858 in Gushikawa Village, 849 in Nakazato Village and 1199 in Sashiki Town) were screened by the enzymatic assay and approximately 11–30% (11.8% in Gushikawa, 17.0% in Nakazato and 27.7% in Sashiki) were considered to be antibody positive. In the parasitological follow-up examinations of those who were antibody positive, actual infection was found in more than half (51%) the subjects. The overall infection rates estimated from the results reached 5.8% in Gushikawa, 9.1% in Nakazato and 14.0% in Sashiki (mean = 10.4%). The infection rates were significantly higher than those in previous surveys conducted in the same areas. The ELISA technique was found to be useful for strongyloidiasis screening and for seroepidemiological purposes in Okinawa. 相似文献
86.
Nonshivering thermogenesis and cold resistance during seasonal acclimatization in the Djungarian hamster 总被引:6,自引:0,他引:6
Masahiro Hori Lynn M. Riddiford 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1982,147(1):1-9
Summary The absence of juvenile hormone (JH) at the time of head capsule slippage during the molt to the fifth (final) instar of the tobacco hornworm was found to cause ommochrome (primarily dihydroxanthommatin) synthesis in the epidermis during the first two days after ecdysis. Then synthesis decreased until its transient reappearance during the wandering stage. Either JH-I (ED50=8x10–4 g) or methoprene (ED50=1.4x10–2 g) applied at this critical time during the molt prevented the first synthesis. A comparison of developmental profiles of tryptophan and its metabolites, kynurenine and 3-hydroxykynurenine, in normal and allatectomized wild type larvae showed that JH at this critical time prevented both the conversion of kynurenine to 3-hydroxykynurenine and 3-hydroxykynurenine to ommochromes. A similar study in normal and methoprene-treatedblack mutant larvae showed that only the latter conversion was inhibited by JH. The accumulation of 3-hydroxykynurenine in the epidermis of the JH-treatedblack mutant is thought to be due to the altered tryptophan metabolism in these mutants in previous instars due to lower JH levels. Neither starvation of theblack mutant nor injection of 3-hydroxykynurenine significantly affected ommochrome synthesis by the epidermis. Preliminary studies of the enzymes involved showed that JH at the critical period suppressed the later activity and/or production of kynurenine 3-hydroxylase in the wild type larva, but had little effect on the particulate ommochrome synthetase activity of the epidermis.Abbreviations
CA
corpora allata
-
JH
juvenile hormone
-
PTTH
prothoracicotropic hormone 相似文献
87.
The complete nucleotide sequence of a 16S ribosomal RNA gene from tobacco chloroplasts has been determined. This nucleotide sequence has 96% homology with that of maize chloroplast 16S rRNA gene and 74% homology with that of Escherichia coli16S gene.The 3′ terminal region of this gene contains the sequence ACCTCC which is complementary to sequences found at the 5′ termini of prokaryotic mRNAs.The large stem and loop structure can be constructed from the sequences surrounding the 5′ and 3′ ends of the 16S gene. These observations demonstrate the prokaryotic nature of chloroplast 16S rRNA. 相似文献
88.
Seiji Suzuki Hiroshi Oka Hiroko Yasuda Masahiro Ikeda Po Yuan Cheng Toshitsugu Oda 《Biochemical and biophysical research communications》1981,99(3):987-993
Isolated rat pancreatic islets, incubated in the presence of extracellular 32Pi to steady state 32P incorporation into cellular phosphopeptides, were exposed to glucose for 10 min. Glucose (16.7 mM) significantly stimulated the phosphorylation of six phosphoproteins with molecular weights of 15,000, 35,000, 49,000, 64,000, 93,000 and 138,000. Mannoheptulose (16.7 mM) markedly inhibited glucose-stimulated phosphorylation of these six phosphoproteins. This protein phosphorylation might be important in mediating glucose-stimulated insulin release. 相似文献
89.
Native bovine liver catalase [EC 1.11.1.6] and catalase acetylated with N-acetylimidazole (AI) both combined with sodium dodecyl sulfate (SDS) to form catalase-SDS complexes. The differences between native and acetylated catalase bound to SDS were investigated as regards enzymatic activity, absorption spectra, ORD and CD, sedimentation velocity and fluorescence spectra. It was found that the binding of SDS with both catalases depended on incubation time and SDS concentration, and that the acetylation of catalase had some protective effect on the denaturation of the molecule by SDS, which may be ascribed to a reduction of ionic interaction between SDS and the protein on acetylation. The native catalase was found to split into three smaller components on incubation with 1% SDS for 96 hr, whereas the acetylated catalase split into two smaller components. These smaller components were isolated by gel filtration through Sephadex G-100. The isolated components has estimated molecular weights of 60,000, 30,000, aide. It seemed likely that the modification occurred stepwise. Approximately 26% of the carboxyl groups of fibrinogen was modified finally. The modified fibrinogen had no interaction with cationic detergent, and did not form any complex with the detergent. In dilute acid, fibrinogen was observed to show only a slight interaction with cationic detergent. It is probable that the exposed and ionized carboxyl groups are essential for the formation of a complex between fibrinogen and cationic detergent. 相似文献
90.
Katsuyuki Watanabe Kazuo Kimura Hirofuto Marumo Hirotoshi Samejima 《Bioscience, biotechnology, and biochemistry》2013,77(3):547-552
Alkali protease partially purified from a strain of Bacillus subtilis and yeast alcohol dehydrogenase were immobilized to weakly basic anion exchange resins using a bifunctional reagent, 2-carboxymethyIamino-4,6-dichloro-s-triazine.Properties of these immobilized enzymes were studied both in batchwise operation and in packed bed reactor systems. 相似文献