全文获取类型
收费全文 | 2031篇 |
免费 | 119篇 |
出版年
2022年 | 6篇 |
2021年 | 14篇 |
2019年 | 12篇 |
2018年 | 26篇 |
2017年 | 25篇 |
2016年 | 32篇 |
2015年 | 55篇 |
2014年 | 57篇 |
2013年 | 175篇 |
2012年 | 114篇 |
2011年 | 125篇 |
2010年 | 66篇 |
2009年 | 67篇 |
2008年 | 102篇 |
2007年 | 132篇 |
2006年 | 107篇 |
2005年 | 98篇 |
2004年 | 106篇 |
2003年 | 112篇 |
2002年 | 120篇 |
2001年 | 23篇 |
2000年 | 30篇 |
1999年 | 36篇 |
1998年 | 31篇 |
1997年 | 29篇 |
1996年 | 20篇 |
1995年 | 21篇 |
1994年 | 18篇 |
1993年 | 27篇 |
1992年 | 31篇 |
1991年 | 13篇 |
1990年 | 13篇 |
1989年 | 28篇 |
1988年 | 19篇 |
1987年 | 17篇 |
1986年 | 25篇 |
1985年 | 19篇 |
1984年 | 21篇 |
1983年 | 12篇 |
1982年 | 7篇 |
1981年 | 17篇 |
1980年 | 19篇 |
1979年 | 16篇 |
1978年 | 10篇 |
1977年 | 16篇 |
1976年 | 15篇 |
1975年 | 12篇 |
1974年 | 9篇 |
1973年 | 12篇 |
1969年 | 5篇 |
排序方式: 共有2150条查询结果,搜索用时 46 毫秒
1.
2.
Some RNAs, including both single- and double-stranded RNAs, when incubated with chick embryo cell culture induce cellular resistance against viruses. Evidence was now obtained indicating that the induction of cellular resistance by RNA depends on the cellular metabolic activity, especially on the synthesis of cellular RNA and protein. Thus, inhibitors of RNA and protein synthesis, actinomycin D and cycloheximide, were found to inhibit the development of an antiviral state when added before, or during the relatively early period of, incubation of the cells with RNA. In the course of induction of cellular resistance, three stages may be distinguished, the priming stage, the developing stage, and the established resistant stage. 相似文献
3.
Organic Acid Metabolism in Aluminum-Phosphate Utilizing Cells of Carrot (Daucus carota L.) 总被引:3,自引:0,他引:3
Carbohydrate metabolism in Al-phosphate utilizing cells of carrot[designated as IPG, Koyama et al. (1992) Plant Cell Physiol.33: 171], which grow normally in Al-phosphate medium accompaniedby citrate excretion, was investigated. The excretion of citratewas strongly related to the availability of sucrose in medium,indicating that citrate excretion was severely limited by sucrosein medium. The ratio of the amount of carbon in the excretedcitrate to the consumed sucrose, was significantly higher inIPG cells than in wild-type cells. When 50% of the sucrose inthe medium was consumed, the ratio was 0.6% for the IPG cellsand 0.2% the wild-type cells. Under these conditions, IPG cellsshowed altered citrate synthesis metabolism, which resultedin increased citrate production. Specific activity of mitochondrialcitrate synthase was higher in IPG cells than in wild-type cells,whereas the activity of cytosolic NADP-specific isocitrate dehydrogenasewas lower in IPG cells than in wild-type cells. (Received August 27, 1998; Accepted February 21, 1999) 相似文献
4.
5.
In order to elucidate the evolution of C4 syndrome, the taxonomic relationships, leaf anatomy, and ecological and global distribution of C3 and C4 species in the genusRhynchospora were investigated. The anatomical observation for 181 species revealed that 26 C4 species occurred within theCapitatae group of the subgenusHaplostyleae, a natural group showing highly advanced morphological characteristics, together with several C3 species. In spite of there being rather few C4 species, they possessed two kinds of Kranz anatomical structure differing from each other in the location of Kranz cells. Some C3 species ofCapitatae showed radial arrangement in mesophyll cells surrounding vascular bundles, which is distinguished from typical non-Kranz anatomy. The C4 species extended their ecological ranges from wet habitats to dry savanna grasslands, while the C3 species showed the best development in wet habitats. The C3 species were widespread from tropical to temperate regions with partial range extension into subarctic regions of both hemispheres, showing conspicuously high concentration of species in the New World, but being absent from arid climatic regions. The C4 species were distributed mostly in tropics and subtropics, showing two separate distributional centers in South and Central America and in Tropical Asia and Australia. The range of C4 species was nearly completely included in the C3 range. In conclusion, it seems that inRhynchospora the C4 syndrome evolved relatively recently, and arose in at least two separate phylogenetic trends in the tropics and the subtropics, more probably in the Neotropics. 相似文献
6.
Aminergic and peptidergic amplification of intracellular cyclic AMP levels in a molluscan neural network 总被引:1,自引:0,他引:1
1. Serotonin (5-hydroxytryptamine; 5-HT), dopamine (DA), and small cardioactive peptide B (SCPB) can activate adenylate cyclase and increase the intracellular cyclic AMP (cAMP) levels in the Limax procerebrum (PC), with differing time courses and to differing extents. 5-HT and SCPB are potent stimulators of adenylate cyclase, and when both were applied simultaneously, an additive effect was observed. 2. In contrast, DA shows a great variability in the time course of cAMP synthesis and is a weak stimulator. Ergonovine, a DA antagonist, failed to inhibit cyclase activation, indicating that ergonovine-sensitive receptors are absent or ergonovine-sensitive DA receptors are not coupled to adenylate cyclase. 3. 5-HT and SCPB cause a rapid synthesis of cAMP, reaching the maximum 20- to 30-fold increase within a minute. DA's effect is slow in onset and very prolonged, reaching a maximum of only a two- to three-fold increase in the cAMP level. Reasons for variability in DA action are discussed. 相似文献
7.
Heinz W. Kunz Andrea L. Cortese Hassett Tetsuo Inomata D. N. Misra Thomas J. Gill III 《Immunogenetics》1989,30(3):181-187
A new antigenic system in the rat homologous to theQa/TL antigen system in the mouse has been characterized. It was detected by antibodies raised in donor-recipient combinations
that were matched for theRT1. A, B, D, E loci in the major histocompatibility complex (MHC): (R11×BN)F1 anti-BN.1L(LEW), (R18×BN)F1 anti-BN.1L, and BN.1LV1(F344) anti-BN.1L. Absorption analyses using these antisera and a variety of inbred, congenic and
recombinant strains identified three alleles,RT1.G
a
,G
b
,G
c
, of whichG
c
is a null allele. The strain distribution of these alleles was determined, using 37 strains of rats representative of all
of the prototypic haplotypes and a number of congenic and recombinant strains. The use of the congenic and recombinant strains
showed that theRT1.G locus was linked to the MHC and that the most probable gene order wasA-E-G. Testcross analysis showed that the map distance betweenA andG was 1.4 cM(4/285 recombinants). The RT1.G antigen has a heavy chain ofM
r 46 000 and is present on both T and B cells. 相似文献
8.
ATL-derived factor (ADF), an IL-2 receptor/Tac inducer homologous to thioredoxin; possible involvement of dithiol-reduction in the IL-2 receptor induction. 总被引:27,自引:4,他引:23 下载免费PDF全文
Y Tagaya Y Maeda A Mitsui N Kondo H Matsui J Hamuro N Brown K Arai T Yokota H Wakasugi et al. 《The EMBO journal》1989,8(3):757-764
HTLV-I transformed T cells not only express a large number of interleukin-2 receptors [IL-2R/p55(Tac)], but also produce a factor named ATL-derived factor (ADF) that augments the expression of IL-2R/p55(Tac). Based on a partial N-terminal amino acid sequence, complementary DNA (cDNA) clones for human and mouse ADF were isolated and sequenced. Recombinant ADF produced by COS-7 monkey kidney cells showed IL-2R/Tac inducing activity on YT cells, which are sensitive for ADF. ADF mRNA was strongly expressed in HTLV-I(+) T cells lines, but not in inactivated cells (THP-1, unstimulated PBMC). Furthermore, in normal human peripheral blood mononuclear cells, the expression of ADF mRNA was enhanced by mitogens or phorbol myristate acetate, suggesting a possible involvement of ADF in the lymphocyte activation. Homology analysis revealed an unexpected relationship between ADF and dithiol-reducing enzyme, thioredoxin, involved in many important biological reactions such as the conversion of ribonucleotides into deoxyribonucleotides, or the stabilization of glucocorticoid receptors. The biological significance of the generation of a redox potential in lymphocyte activation, and the possible involvement of dithiol reduction in the induction of IL-2R/Tac are discussed. 相似文献
9.
Characterization of an ATPase Associated with the Inner Envelope Membrane of Amyloplasts from Suspension-Cultured Cells of Sycamore (Acer pseudoplatanus L.) 总被引:2,自引:2,他引:0 下载免费PDF全文
Amyloplast envelope membranes isolated from cultured, white-wild cells of sycamore (Acer pseudoplatanus L.) have been found to contain a Mg2+-ATPase, ranging in specific activity from 5 to 30 nanomoles per minute per milligram protein. This ATPase hydrolyzes a broad range of nucleoside triphosphates, whereas it hydrolyzes nucleoside mono- and diphosphates poorly, if at all. The ATPase activity was stimulated by several divalent cations, including Mg2+, Mn2+ and Ca2+, whereas it was not affected by Sr2+, K+, or Na+. The Km for total ATP was 0.6 millimolar, and the activity showed a broad pH optimum between 7.5 and 8.0. The ATPase was insensitive to N,N′-dicyclohexylcarbodiimide and oligomycin, but it was inhibited by vanadate. All these characteristics are basically similar to those reported previously for the Mg2+-ATPase of the chloroplast inner-envelope membrane. Likewise, the amyloplast envelope enzyme was shown to be located specifically on the inner envelope membrane. The amyloplast envelope membranes were chemically modified with a series of unique affinity labeling reagents, the adenosine polyphosphopyridoxals (M Tagaya, T Fukui 1986 Biochemistry 25: 2958-2964). About 90% of the ATPase activity was lost when the envelope membranes were preincubated with 0.1 millimolar adenosine triphosphopyridoxal. Notably, the enzyme was protected completely from inactivation in the presence of its substrate, ATP. In contrast, both adenosine diphosphopyridoxal and pyridoxal phosphate caused much less of an inhibitory effect. This greater relative reactivity of the triphosphopyridoxal analog is similar to that reported previously with Escherichia coli F1 ATPase (T Noumi et al. 1987 J Biol Chem 262: 7686-7692). 相似文献
10.
Organic anion transport study in mutant rats with autosomal recessive conjugated hyperbilirubinemia 总被引:2,自引:0,他引:2
H Kurisu K Kamisaka T Koyo S Yamasuge H Igarashi H Maezawa T Uesugi O Tagaya 《Life sciences》1991,49(14):1003-1011
The EHBR is a mutant rat strain with congenital conjugated hyperbilirubinemia bred from a Sprague-Dawley rat. Transport of conjugated bilirubin, indocyanine green, and tetrabromosulfophtalein from liver to bile is severely impaired in these rats. Serum bilirubin amounts to 6.0 +/- 0.05 mg/dl (n = 4) in adult rats, with 97% conjugates. The bile flow is reduced to about 65% of the control group, whereas total bile acid in 10-min bile samples is similar. Liver histology of 10 week-old rats revealed neither intracellular pigmentation nor architectural abnormalities. 相似文献