全文获取类型
收费全文 | 42693篇 |
免费 | 3883篇 |
国内免费 | 28篇 |
出版年
2023年 | 147篇 |
2021年 | 559篇 |
2020年 | 395篇 |
2019年 | 490篇 |
2018年 | 641篇 |
2017年 | 557篇 |
2016年 | 1044篇 |
2015年 | 1758篇 |
2014年 | 1880篇 |
2013年 | 2458篇 |
2012年 | 2982篇 |
2011年 | 3059篇 |
2010年 | 1945篇 |
2009年 | 1660篇 |
2008年 | 2517篇 |
2007年 | 2509篇 |
2006年 | 2272篇 |
2005年 | 2340篇 |
2004年 | 2294篇 |
2003年 | 2181篇 |
2002年 | 2131篇 |
2001年 | 509篇 |
2000年 | 413篇 |
1999年 | 488篇 |
1998年 | 568篇 |
1997年 | 425篇 |
1996年 | 373篇 |
1995年 | 391篇 |
1994年 | 354篇 |
1993年 | 345篇 |
1992年 | 389篇 |
1991年 | 332篇 |
1990年 | 269篇 |
1989年 | 271篇 |
1988年 | 274篇 |
1987年 | 250篇 |
1986年 | 233篇 |
1985年 | 302篇 |
1984年 | 319篇 |
1983年 | 256篇 |
1982年 | 352篇 |
1981年 | 274篇 |
1980年 | 254篇 |
1979年 | 188篇 |
1978年 | 223篇 |
1977年 | 208篇 |
1976年 | 178篇 |
1975年 | 160篇 |
1974年 | 187篇 |
1973年 | 194篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
22.
23.
Katherina Walz Devon Cohen Paul M. Neilsen Joseph Foster II. Francesco Brancati Korcan Demir Richard Fisher Michelle Moffat Nienke E. Verbeek Kathrine Bjørgo Adriana Lo Castro Paolo Curatolo Giuseppe Novelli Clemer Abad Cao Lei Lily Zhang Oscar Diaz-Horta Juan I. Young David F. Callen Mustafa Tekin 《Human genetics》2015,134(2):181-190
24.
Cystine Deprivation Induces Oligodendroglial Death: Rescue by Free Radical Scavengers and by a Diffusible Glial Factor 总被引:4,自引:0,他引:4
Mihoko Yonezawa Stephen A. Back Xiaodong Gan Paul A. Rosenberg Joseph J. Volpe 《Journal of neurochemistry》1996,67(2):566-573
Abstract: In this study we examined the effect on oligodendroglial survival of exogenous cystine deprivation. Oligodendroglia isolated from mixed glial primary cultures derived from brains of 1-day-old rats, and then grown for 3 days, were markedly dependent on extracellular cystine for survival. The EC50 values for cystine for a 24-h exposure ranged from 2 to 65 µ M . After 6 h of cystine deprivation, the cellular glutathione level decreased to 21 ± 13% of the control. Free radical scavengers (α-tocopherol, ascorbate, idebenone, and N-tert -butyl-α-phenylnitrone) were protective against cystine deprivation but had no effect on the glutathione level. An iron chelator, desferrioxamine mesylate, also was protective. These findings suggest that intracellular hydroxyl radicals are important for this toxicity. In contrast to the observations in 3-day-old cultures, the dependence on exogenous cystine for cell viability was not observed consistently in oligodendroglia cultured for 6 days before the onset of cystine deprivation. Several observations suggested that this loss of cystine dependence was due to a diffusible factor. Sensitivity to the toxicity of cystine deprivation in day 6 cultures increased as the volume of medium was increased from 0.3 to 2 ml. Furthermore, preincubation of cystine-depleted medium with astrocyte cultures eliminated the toxicity of the cystine deprivation. HPLC assay of the conditioned cystine-depleted medium showed no significant change in cystine or cysteine concentration. We conclude that oligodendroglia are highly susceptible to cystine deprivation in day 3 cultures and that this susceptibility is due to the accumulation of intracellular free radicals in the setting of glutathione depletion. The resistance of day 6 oligodendroglial cultures is caused at least in part by a diffusible factor. 相似文献
25.
26.
Hypersensitive response of wheat to the Hessian fly 总被引:3,自引:0,他引:3
Paul B. Grover Jr. 《Entomologia Experimentalis et Applicata》1995,74(3):283-294
Hessian flyMayetiola destructor (Say) larvae are able to obtain food from their host plant without inflicting mechanical damage to the plant surface, apparently
by secreting substances which elicit release of nutrients from plant cells surrounding the feeding site. Cells of fully susceptible
plants retain their normal appearances, while in resistant plants extensive areas of cellular collapse occur. These responses
indicate that hypersensitivity is the basis of wheat's resistance to the Hessian fly. The fly's feeding mechanism more closely
resembles that of a pathogen than of a phytophagous insect; correspondingly, both the genetic relationship and resistance
mechanism of the host plant to the parasite are of the sorts commonly associated with bacterial and fungal pathogens. 相似文献
27.
Six brain areas of rats and guinea-pigs, killed by microwave irradiation, were used for the concomitant measurement of the levels and regional distribution of cholinergic, biogenic amine, and amino acid neurotransmitters and metabolites. Acetylcholine (ACh) and choline (Ch) were quantified by chemiluminescence; noradrenaline (NA), dopamine (DA), 5-hydroxytryptamine (5-HT), and their metabolites by HPLC with electrochemical detection (HPLC-EC); and six putative amino acid neurotransmitters by HPLC-EC following derivatisation. The levels and regional distribution of these transmitters and their metabolites in the rat were similar to those reported in previous studies, except that biogenic amine transmitter levels were higher and metabolite concentrations were lower. The guinea-pig showed a similar regional distribution, but the absolute levels of ACh were lower in striatum and higher in hippocampus, midbrain-hypothalamus, and medulla-pons. In all areas, the levels of Ch were higher and those of NA, 5-HT, and taurine were lower than in the rat. The most marked differences between the rat and guinea-pig were in the relative proportion of DA metabolites and 5-HT turnover, as estimated by metabolite/transmitter ratios. This study can be used as a basis for a comprehensive understanding of the central effects of drugs on the major neurotransmitter systems. 相似文献
28.
This overview summarizes the data for how epithelial cells sort and deliver proteins and lipids to the apical and basolateral cell surface domains. The basolateral pathway uses a Rab-SNARE mechanism for docking and fusion, while the apical route employs a different machinery. This latter mechanism is based on lipid microdomains, composed of clusters of sphingolipids and cholesterol, which function as rafts for apical delivery. The sphingolipid-cholesterol raft mechanism seems to be employed generally by mammalian cells to transport raft-associated proteins to their post-Golgi destinations. 相似文献
29.
30.
Paul Van Mele 《Agricultural and Forest Entomology》2008,10(1):13-22
1 Although the weaver ant Oecophylla is the first written record of biological control, dating from 304 ad , there have been fewer than 70 scientific publications on this predator as a biological control agent in Asia, from the early 1970s onwards, and fewer than 25 in Africa. 2 Apart from crop‐specific ecological and perceptual factors, a historical review shows that political and market forces have also determined the extent to which Oecophylla was incorporated into research and development programmes. 3 In Africa, research on weaver ants in biological control concentrated on export crops, such as coconut and cocoa, whereas, in Asia and Australia, research focused on fruit and nut crops, primarily destined for domestic markets. 4 Increased evidence of pesticide inefficiency under tropical smallholder conditions, changing paradigm shifts in participatory research and a growing scientific interest in local knowledge in the early 1990s opened up new avenues for research on conservation biological control. 5 Lobbying and advocacy have been needed to ensure that Oecophylla was recognized as an effective biological control agent. 6 With an increased market demand for organic produce, holistic approaches such as conservation biological control, particularly the use of Oecophylla, are increasing in importance. 7 Multi‐stakeholder strategies for collaborative learning are proposed for a better control of major fruit, nut and timber tree pests in Africa, Asia and Australia. 相似文献