全文获取类型
收费全文 | 3125篇 |
免费 | 191篇 |
出版年
2022年 | 11篇 |
2021年 | 24篇 |
2020年 | 9篇 |
2019年 | 19篇 |
2018年 | 34篇 |
2017年 | 40篇 |
2016年 | 43篇 |
2015年 | 86篇 |
2014年 | 91篇 |
2013年 | 230篇 |
2012年 | 161篇 |
2011年 | 183篇 |
2010年 | 108篇 |
2009年 | 97篇 |
2008年 | 157篇 |
2007年 | 183篇 |
2006年 | 163篇 |
2005年 | 142篇 |
2004年 | 162篇 |
2003年 | 166篇 |
2002年 | 166篇 |
2001年 | 61篇 |
2000年 | 67篇 |
1999年 | 81篇 |
1998年 | 45篇 |
1997年 | 43篇 |
1996年 | 30篇 |
1995年 | 31篇 |
1994年 | 29篇 |
1993年 | 39篇 |
1992年 | 61篇 |
1991年 | 38篇 |
1990年 | 43篇 |
1989年 | 50篇 |
1988年 | 30篇 |
1987年 | 43篇 |
1986年 | 31篇 |
1985年 | 38篇 |
1984年 | 34篇 |
1983年 | 25篇 |
1982年 | 16篇 |
1981年 | 26篇 |
1980年 | 21篇 |
1979年 | 16篇 |
1978年 | 15篇 |
1977年 | 19篇 |
1976年 | 17篇 |
1975年 | 12篇 |
1974年 | 15篇 |
1973年 | 16篇 |
排序方式: 共有3316条查询结果,搜索用时 562 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.
4.
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
5.
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
6.
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
7.
Dose-dependent regulation of macrophage differentiation by mos mRNA in a human monocytic cell line. 总被引:4,自引:0,他引:4
下载免费PDF全文
![点击此处可从《The EMBO journal》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The proto-oncogene c-mos was expressed during differentiation of the human monocytic cell line U937 into macrophages. To investigate a possible role of the mos oncogene, we introduced the v-mos gene under an inducible promoter, MT-I, into U937 cells. The v-mos transformed cells expressed mos mRNA at an amount proportional to the concentration of Zn2+ ions. The induction of the v-mos gene caused growth inhibition and macrophage differentiation in these cells. The differentiation of v-mos transformed monocytes into macrophages required continuous expression of the v-mos gene. The extent of expression of phenotypic characteristics of macrophages, such as phagocytosis, cell surface antigens and typical morphology, depends on the amount of mos mRNA present. We were therefore able to demonstrate that the expression of only one oncogene, mos, determines monocyte differentiation into macrophages. 相似文献
8.
VP-16-induced nucleotide pool changes and poly(ADP-ribose) synthesis: the role of VP-16 in interphase death 总被引:2,自引:0,他引:2
A Tanizawa M Kubota H Hashimoto T Shimizu T Takimoto T Kitoh Y Akiyama H Mikawa 《Experimental cell research》1989,185(1):237-246
Exposure of human promyelocytic leukemia cell line (HL-60) to VP-16 resulted in accumulation of DNA strand breaks. Concomitantly, intracellular NAD levels fell at 1 h, followed by declines in ATP at 2 h and in GTP, CTP, and UTP at 3 h. Furthermore, marked morphological changes, such as loss of microvilli or bleb formation, appeared at 4 h and cell death by 8-10 h. The addition of an inhibitor of poly(ADP-ribose) polymerase, 3-aminobenzamide (5 mM), theophylline (2 mM), or thymidine (1 mM), prevented these sequential reductions of nucleotide pools and cell death. In fact, the activation of poly(ADP-ribose) synthesis was detectable within a few hours after treatment with VP-16, although it was smaller than that induced by N-methyl-N'-nitro-N-nitrosoguanidine. These results may suggest the possible role of activation of poly(ADP-ribosyl)ation in VP-16-induced nucleotide pool changes and subsequent interphase death. 相似文献
9.
Biosynthesis, processing and half-life of P-glycoprotein in a human multidrug-resistant KB cell 总被引:1,自引:0,他引:1
A Yoshimura Y Kuwazuru T Sumizawa S Ikeda M Ichikawa T Usagawa S Akiyama 《Biochimica et biophysica acta》1989,992(3):307-314
The biosynthesis, processing, and half-life of the drug efflux pump, P-glycoprotein, were studied in human multidrug-resistant KB (KB-C2) cells selected for resistance to colchicine. An antibody directed against a synthetic oligopeptide corresponding to the amino-acid sequence (Glu-393-Lys-408) of P-glycoprotein from human mdr1 cDNA was prepared in rabbits. With immunoblotting and immunoprecipitation, we detected a 140-170 kDa protein in KB-C2 cells but not in parental sensitive KB cells. KB-C2 cells made a 125 kDa precursor that was slowly processed (t1/2 = 45 min) to the mature form of 140-150 kDa. The processing rate of P-glycoprotein was slower than that of low-density lipoprotein receptor. We detected another 160-180 kDa smear band, which might be a completely denatured form of P-glycoprotein. With immunoblotting, a minor band of high molecular mass (greater than 500 kDa) was also detected and this form increased after the cells were treated with chemical cross-linker, 1,5-difluoro-2,4-dinitrobenzene. The half-life of P-glycoprotein was long; no significant loss of P-glycoprotein was observed within 24 h after synthesis. Cells treated with tunicamycin produced a 120 kDa form of P-glycoprotein which was no longer processed but showed stability similar to that of the mature 140-150 kDa form. Agents that reverse multidrug resistance, phorbol ester and transport substrate did not affect the stability of P-glycoprotein. 相似文献
10.