全文获取类型
收费全文 | 26506篇 |
免费 | 1642篇 |
国内免费 | 1966篇 |
出版年
2024年 | 70篇 |
2023年 | 295篇 |
2022年 | 451篇 |
2021年 | 600篇 |
2020年 | 707篇 |
2019年 | 909篇 |
2018年 | 767篇 |
2017年 | 666篇 |
2016年 | 677篇 |
2015年 | 765篇 |
2014年 | 1172篇 |
2013年 | 1456篇 |
2012年 | 842篇 |
2011年 | 1155篇 |
2010年 | 901篇 |
2009年 | 1197篇 |
2008年 | 1250篇 |
2007年 | 1354篇 |
2006年 | 1221篇 |
2005年 | 1156篇 |
2004年 | 987篇 |
2003年 | 926篇 |
2002年 | 872篇 |
2001年 | 729篇 |
2000年 | 716篇 |
1999年 | 671篇 |
1998年 | 661篇 |
1997年 | 572篇 |
1996年 | 624篇 |
1995年 | 531篇 |
1994年 | 488篇 |
1993年 | 540篇 |
1992年 | 457篇 |
1991年 | 455篇 |
1990年 | 370篇 |
1989年 | 312篇 |
1988年 | 312篇 |
1987年 | 273篇 |
1986年 | 227篇 |
1985年 | 281篇 |
1984年 | 291篇 |
1983年 | 177篇 |
1982年 | 211篇 |
1981年 | 184篇 |
1980年 | 156篇 |
1979年 | 116篇 |
1978年 | 113篇 |
1977年 | 67篇 |
1976年 | 60篇 |
1975年 | 27篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
941.
Kendal S. Broadie Michael Bate Nathan J. Tublitz 《Development genes and evolution》1991,199(6):327-334
Summary A complete timetable of embryonic development of the tobacco hawkmoth,Manduca sexta (Lepidoptera: Sphingidae), is presented. Using living embryos, 20 developmental stages from oviposition to hatching are described with respect to their morphological and physiological maturation. This staging series provides a simple method to identify the stage ofManduca development during all phases of embryogenesis. 相似文献
942.
Jan-Kan Chen Ying-Tung Lau Jackson Chu 《In vitro cellular & developmental biology. Animal》1992,28(2):143-145
Summary Rat aortic endothelial cells were found to exhibit clonal variations in response to EGF stimulation in cell growth and prostacyclin
synthesis. EGF-induced growth and prostacyclin synthesis appeared to be regulated in a coordinated manner in that a clone
with a higher response to EGF growth stimulation also exhibited a higher response to EGF-stimulated prostacyclin synthesis.
This observation implys a possible involvement of prostacyclin synthesis in some of the biological effects of EGF on vascular
endothelial cells. 相似文献
943.
ERIC BAILLY RONAN JAMBOU JEAN SAVEL GINETTE JAUREGUIBERRY 《The Journal of eukaryotic microbiology》1992,39(5):593-599
ABSTRACT We investigated the effect of a cysteine proteinase inhibitor (E-64) and an aspartyl proteinase inhibitor (Pepstatin A) on asexual erythrocytic stages of Plasmodium falciparum in culture. These two protease inhibitors showed different patterns of activity. E-64 acted preferentially against trophozoite and schizont stages. After 48 h incubation at high concentrations of E-64 (28, 140, 280 μM), growth was totally abolished and the parasites presented characteristic enlarged food vacuoles. Morphological alterations were also seen after shorter incubation periods (6 h at 28 μM) or 12 h at the inhibitory concentration 50% (12 μM), but an additional culture period (24 h) in inhibitor-free medium allowed normal parasite development, demonstrating a parasitostatic effect. E-64 acts on parasite multiplication; the normal merozoite maturation was altered and the normal reinvasion process partially impaired. Pepstatin A used at the inhibitory concentration 50% (4 μM) killed the parasites before trophozoite development and had a major effect on schizonts maturation. No altered parasite development occurred during an additional culture period without Pepstatin A, demonstrating a parasiticidal effect. E-64 and Pepstatin A used in combination inhibit the parasite growth with a strong synergistic effect. 相似文献
944.
H. J. G. ten Hoopen W. M. van Gulik J. J. Heijnen 《In vitro cellular & developmental biology. Plant》1992,28(3):115-120
Summary Continuous culture is an attractive research tool in physiologic and growth and production kinetics research. However, fulfillment
of the basic assumptions of continuous culture in the experimental set-up may cause problems. The homogeneity of plant cell
cultures and effluent, particularly, may cause problems. This paper presents an experimental set-up which solves these problems
and describes the use of this equipment in a study of the growth kinetics of plant cells. Industrial application of the continuous
culture of plant cells in the production of secondary metabolites seems to be profitable when compared with batch or fed-batch
cultures. However, various problems such as uncoupled product formation and strain instability make fed-batch culture a better
choice.
Presented in the Session-in-Depth Batch Production and Fermentation at the 1991 World Congress on Cell and Tissue Culture,
Anaheim, California, June 16–20, 1991. 相似文献
945.
鲑鱼生长激素cDNA的分子克隆和序列分析 总被引:8,自引:0,他引:8
从太平洋切奴克鲑鱼(Pacific Chinook Salmon,Oncorthychus tschawytscha)垂体poly(A)~+ RNA构建cDNA文库。按照鲑鱼生长激素(sGH)部分氨基酸序列合成两个寡聚脱氧核苷酸探针,它们分别与编码第1—7和第166—172氨基酸序列互补。用探针筛查cDNA文库,得到了完整的sGH cDNA克隆。cDNA序列已测定,包括编码210个氨基酸的编码序列。其中含有22个氨基酸的信号肽序列和188个氨基酸的成熟GH序列。该克隆还包括了5'端和3'端非翻译区,分别为72个和438个碱基对长。与Chum鲑鱼比较表明,核酸序列和氨基酸序列的同源性分别为97%和99%。 相似文献
946.
Protein tyrosine kinases (PTKs) have major roles in signal transduction and growth control. There are several lines of evidence implicating PTKs in the regulation of axon growth, and this has led to the suggestion that they are centrally involved in the transduction of neuronal growth signals. To test this idea, we assayed the effect of the compounds genistein and lavendustin, specific inhibitors of PTKs, on neurite growth. We find that genistein greatly reduces phosphotyrosine in neurons, as expected from its action on other cells. Surprisingly, administration of genistein or lavendustin potentiated substrate-induced neurite growth in at least several different neuronal types. Stimulation of neurite growth by genistein was abolished by vanadate, providing additional evidence that inhibition of PTKs is responsible for this effect. The potentiation of growth is rather general, in that it occurs on several different extracellular matrix substrates and on two different cell adhesion molecules. Both the initiation of neurite growth and the rate of neurite elongation appear to be potentiated. Our results do not provide evidence for models of substrate-induced signal transduction that involve PTKs asa positive and necessary step, but suggest that such kinases play aregulatory role in neurite elongation. © 1992 John Wiley & Sons, Inc. 相似文献
947.
Tyrosine phosphorylation and protein tyrosine kinase (PTK) activity in the growth cone membrane-associated glycoprotein (GCGP) fraction of 1-day-old rat brain were examined. Using immunoblotting and immunoprecipitation techniques, pp60c-src was identified as one of the major PTKs associated with GCGPs. Furthermore, only GCGP-associated src that was also tyrosine phosphorylated was active. Immunoprecipitation experiments using various src antibodies revealed that pp60c-src contributed partially to the PTK activity detected in GCGPs, and that it is associated with several proteins of Mr 140 K, 120 K, 85 K and 50 K. This association of src protein with GCGPs was specific, and another src family member p59fyn, which is also abundant in the brain, did not exhibit such an association. In addition to pp60c-src, the GCGP fraction contained several major phosphotryosine-containing proteins of Mr 140 K, and a 97/90 K doublet that corresponded to the beta subunits of IGF-I/ insulin receptors. These studies show that pp60c-src associated with GCGPs is an active PTK that could be involved in neuronal growth and development, transmembrane signalling, and in recognition and/or adhesive events. © 1992 John Wiley & Sons, Inc. 相似文献
948.
Bovine seminal ribonuclease (BS-RNase), a dimeric homologue of RNase A, cleaves both single- and double-stranded RNA and inhibits the growth of tumor cells. Its catalytic activity against double-stranded RNA, either homopolymeric ([3H]polyA/polyU) or mixed sequence, is enhanced by bovine or human recombinant interferon-γ (IFN-γ). Activation is seen with as little as 4–10 interferon units per assay. Enhancing the degradation of double-stranded RNA, an intermediate in the growth cycle of many viruses, could contribute to IFN-γ's ability to control cell growth and induce an antiviral state. 相似文献
949.
Inhibition of epidermal growth factor-induced DNA synthesis by tyrosine kinase inhibitors 总被引:10,自引:0,他引:10
Kazuo Umezawa Takashi Hori Hirohisa Tajima Masaya Imoto Kunio Isshiki Tomio Takeuchi 《FEBS letters》1990,260(2):201-205
We prepared methyl 2,5-dihydroxycinnamate as a stable analogue of erbstatin, a tyrosine kinase inhibitor. This analogue was about 4 times more stable than erbstatin in calf serum. It inhibited epidermal growth factor receptor-associated tyrosine kinase in vitro with an IC50 of 0.15 μg/ml. It also inhibited in situ autophosphorylation of epidermal growth factor receptor in A431 cells. Methyl 2,5-dihydroxycinnamate was shown to delay the S-phase induction by epidermal growth factor in quiescent normal rat kidney cells, without affecting the total amount ofDNA synthesis. The effect of erbstatin on S-phase induction was smaller, possibly because of its shorter life time. 相似文献
950.
Lessonia trabeculata is one of the major kelps found along the northern coast of Chile. In addition to its ecological and economic importance, L. trabeculata may be severely affected by environmental disturbances such as El Níño, which during 1982–1983 cleared wide areas along the coast of Peru and Chile. The main goal of this work was to mass culture L. trabeculata and to observe the growth of sporophytes obtained in the laboratory and cultured in the sea. Juvenile sporophytes obtained in the laboratory were attached between 1 and 6 m in depth. The linear growth rate, as blade elongation, was recorded weekly for seven months. No significant differences (p < 0.05) were found in sporophyte blade linear growth at different depths. The best elongation growth rate was 7.5 ± 1.6 mm d–1 at 3 m during March. This preliminary work suggests that L. trabeculata follows an annual growth cycle similar to that of other Laminariales with a high rate of blade elongation during the summer and decreasing towards autumn. This species can be considered a potential candidate for aquaculture to increase the availability of raw material and aid in repopulation of overexploited areas. 相似文献